Geology of the Sierra Diablo Region Texas

GEOLOGICAL SURVEY PROFESSIONAL PAPER 480

Geology of the Sierra Diablo Region Texas

By PHILIP B. KING

With SPECIAL DETERMINATIVE STUDIES OF PERMIAN FOSSILS By L. G. HENBEST, E. L. YOCHELSON, P. E. CLOUD, JR., HELEN DUNCAN, R. M. FINKS, and I. G. SOHN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 480

Description and interpretation of the varied rocks and structures of a mountain range and its foothills in the Trans-Pecos Region^ with special emphasis on the Lower Permian

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY Thomas B. Nolan, Director

Library of Congress catalog-card No. OS 66-227

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS

Page Stratigraphy Continued Fage Abstract.-_ __-__-__-_-__-__..___-______..______1 Permian______-__-___--_--_____-_-____--_.___. 46 Introduction..______2 Presentation of paleontologic data ______49 Present investigation___--__--___.___--______2 Hueco Limestone____-_-____---_----.----_-_. 49 Acknowledgments______3 Southern part of report area_-______-_. 50 Related investigations..______4 Baylor Mountains.______52 Previous investigations.______4 Central Sierra Diablo______. 54 Annotated bibliography.______5 Apache Canyon area______. 54 Geography ______11 Fossils and correlation______55 Mountain areas ______13 Stratigraphic relations.______57 Lowland areas ______14 Bone Spring Limestone___-_-____----_--__-_. 60 Human geography and history.______16 Sierra Diablo escarpment______61 Stratigraphy ______17 Northern marginal belt______64 Precambrian and Precambrian(?) rocks.______19 Southern marginal belt____-_-_-_------_. 65 Carrizo Mountain Formation______19 Baylor Mountains.______66 Sequence in Carrizo Mountains.______20 Fossils and correlation______66 Metamorphic features.______21 Stratigraphic relations.______72 Stratigraphic relations.______22 Victorio Peak Limestone-____----_---_---__-. 73 Igneous rocks intrusive into Carrizo Mountain Northeastern calcitic facies______73 Formation ______... 22 Southwestern dolomitic fades.______74 Metarhyolite. ______22 Fossils______--___._-_--____. 74 Greenstone ______23 Stratigraphic relations.______74 Veins..______23 Cutoff Shale._.______. 74 Allamoore Formation..______23 Brushy Canyon Formation______78 Limestone ______23 Sandstone tongue of Cherry Canyon Formation. 79 Volcanic rocks..______24 Goat Seep Limestone______79 PhyUite______24 Cretaceous______80 Hazel Formation ______25 Pre-Cretaceous surface.______--__---__-- 81 Conglomerate ______26 Yucca Formation______82 Red sandstone.______26 Bluff Mesa Formation______82 Van Horn Sandstone____-_-__--______-______27 Campagrande Limestone______83 Conglomerate ______28 Sierra Diablo foothills______83 Sandstone ______28 Western Sierra Diablo______. 83 Ordovician______30 Fossils and age______-__------84 Bliss Sandstone______30 Cox Sandstone______84 Main body of formation______30 Southwest of Eagle Flat.______-___. 84 Calcareous division.______30 84 El Paso Limestone______32 Sierra Diablo foothills and Cox Mountain. . Outlying areas______85 Division A______32 Sierra Prieta______85 Division B______32 Fossils and age_____--___-___-______85 Division C______33 Finlay Limestone___.______.___ __. 85 Beds of Middle(?) Ordovician age______34 Local features..-___-_._-______- ____. 86 Montoya Dolomite.______35 Fossils and age______-_-__. 86 Cable Canyon(?) Sandstone Member____ 36 Kiamichi Formation.______87 Upham Member______36 Washita Group______87 Aleman Cherty Member______36 Southwest of Eagle Flat______87 Silurian______38 Sierra Prieta______88 Fusselman Dolomite.______38 Fossils______. 88 Devonian______39 Eagle Ford Formation______88 Beds of Devonian age______39 Igneous rocks______89 Mississippian______41 I _ Marble Canyon-Mine Canyon intrusive complex . 90 Barnett Shale.______41 Marble Canyon stock______-_-___---___- 90 Pennsylvanian______42 Mine Canyon stock______91 Beds of Pennsylvanian age___-____-_-_-_---__ 42 Outlying igneous rocks___-___---__--__---__- 92 in IV CONTENTS

Igneous rocks Continued Page | Descriptions of stratigraphic sections, etc. Continued Page Marble Canyon-Mine Canyon intrusive complex Con. Stratigraphic sections and fossil collections of Ordovi- Metamorphic rocks______92 cian, Silurian, and Devonian rocks Continued Interpretation______94 Sections. Hawkins Tank______130 Sierra Prieta intrusive------.------94 Section 9. Point of mountains.______131 Igneous rocks______-----__-___-_-- 95 Section 10. Apache Spring______132 Metamorphic rocks______-_____--______95 Ordovician and Silurian fossils, not collected Structure-______95 along courses of stratigraphic sections ______133 Regional relations______96 Stratigraphic sections and fossil collections of Intrusive rocks in southern part of report area__.___ 96 Mississippian and Pennsylvanian rocks______133 Basaltic volcanic rocks______-___-______96 Section 11. Mine Canyon______-______133 Unconsolidated deposits of Quaternary age.______96 Section 12. Marble Canyon______._ 134 Landslide deposits____----__-_---_-_-______---- 97 Stratigraphic sections and fossil collections of Permian Deposits of floor of Salt Basin_--______.______97 rocks ______134 Fanglomerate ______98 Section 13. Wylie Mountains______134 Older alluvial deposits__--______--______-_____ 98 Section 14. Bass Canyon______---__--__.___ 136 Younger alluvial deposits______- 98 Section 15. Threemile Mountain______136 Tectonics-.__-______---_-----______99 Other fossil collections from Hueco Limestone Structure of Precambrian and Precambrian(?) rocks_ 100 in Threemile Mountain area. __--______137 Streeruwitz thrust fault ______100 Section 16. Beach Mountain______-______137 Structure of Allamoore and Hazel Formations. _ 101 Section 17. High point of Baylor Mountains. _ 138 Faults with strike-slip displacement-______102 Other fossil collections from Bone Spring Lime­ Fracture zones in Hazel Formation______103 stone near high point of Baylor Mountains. __ 139 Structure of Van Horn Sandstone.______103 Section 18. Northeastern Baylor Mountains_ 139 Structure of the Precambrian surface.______103 Section 19. Northwestern Baylor Mountains 141 Structure of pre-Permian Paleozoic rocks ______104 Section 20. Eagle Flat______141 Structures of Permian and early Mesozoic age______105 Section 21. Streeruwitz Hills______142 Structures of Late Cretacious or early Tertiary age__ 106 Section 22. McAdoo Ranch______.______143 Structures of late Tertiary and Quaternary age_____ 107 Section 23. West of Old Circle Ranch_____ 144 General features_____-__--_---_--______---- 107 Section 24. Old Circle Ranch.______144 Faults bordering the mountains..______107 Section 25. Hazel mine______144 North Diablo fault zone_____-______107 Section 26. Bat Cave______145 East Diablo fault_____-______109 Fossil collections from Hueco Limestone near North Baylor fault.__.___._____. 109 Sheep Peak.______146 East Baylor fault______110 Section 27. Second section south of Victorio Faults on east side of Salt Basin______110 Peak.______.__._._-______146 Faults and related structures within the moun­ Section 28. First section south of Victorio tains______111 Peak______147 Northern part of Sierra Diablo ______111 Collections from Hueco and Bone Spring Lime­ Southern part of Sierra Diablo______112 stones on Victorio flexture west of Victorio Baylor Mountains.-.______113 Canyon______. 148 Beach Mountain and vicinity ______113 Section 29. Victorio Peak______149 Hillside fault and related structures ______114 Section 30. Victorio Canyon______152 Joints._-__---___--_-_--______115 Section 31. North of Victorio Canyon.______153 Regional interpretations and synthesis______117 Section 32. Marble Canyon______155 Fossil collections from Hueco Limestone near Economic geology____-_____--______----______118 Marble Canyon______156 Copper and silver______119 Section 33. Mine Canyon______157 Tungsten and beryllium.______120 Section 34. South of Black John Canyon_____ 158 Talc______-_-.-.______120 Section 35. Black John Canyon ______159 Crushed stone.----.------.------120 Section 36. Apache Peak.______160 Marble and brucite-__---_-____-----__-______120 Fossil collections from Victorio Peak Limestone Nitrate and turquoise___-____-_-----_-______121 in northeastern Sierra Diablo....______160 Ground water______121 Fossil collections from Bone Spring Limestone Oil and gas______..______122 northwest of portal of Apache Canyon.____ 161 Descriptions of stratigraphic sections and fossil collections. 123 Section 37. First section in Apache Canyon.._ 162 Stratigraphic sections and fossil collections of Ordovi- Section 38. Second section in Apache Canyon. 163 cian, Silurian, and Devonian rocks.______123 Section 1. Sixmile Mountain.______T23 Section 39. Third section in Apache Canyon.. 164 Section 2. Yates Ranch______123 Section 40. Fourth section in Apache Canyon. 165 Sections. Dallas mine______124 Section 41. Apache Tank__.______. 166 Section 4. North side of Beach Mountain____ 124 Section 42. Sierra Prieta______166 Section 5. Unconformity locality ______127 Section 43. South Mesa. ______167 Section 6. Southeastern Baylor Mountains___ 128 Fossil collections from Victorio Peak Limestone Section 7. Northeastern Baylor Mountains___ 129 southeast of South Mesa______169 CONTENTS

Descriptions of stratigraphic sections, etc. Continued Page Descriptions of stratigraphic sections, etc. Continued Page Stratigraphic sections and fossil collections of Permian Stratigraphic sections and fossil collections of Creta­ rocks Continued ceous rocks Continued Fossil collections from Goat Seep Limestone Section 51. Roberts Mesa______173 north of South Mesa______169 Section 52. Norton Mesa______173 Section 44. High point of Delaware Mountains. _ 169 Collections from Finlay Limestone and Kiamichi Stratigraphic sections and fossil collections of Creta­ Formation west of Roberts Mesa and Norton ceous rocks_____.______170 Mesa______174 Section 45. Eagle Flat______170 Section 53. Eastern Sierra Prieta______174 Section 46. Streeruwitz Hills______171 Other fossil collections from Washita Group in Section 47. Dome Peak______171 eastern Sierra Prieta_.______176 Section 48. Rock crusher.______172 Section 54. Western Sierra Prieta_ ___ 176 Section 49. Cox Mountain.______172 References cited______-___-______- 177 Section 50. Black Knobs______173 Index_____.______181

ILLUSTRATIONS

(Plates are in separate volume] PLATE 1. Geologic map of Sierra Diablo region, Texas. 2. Panoramic views of Beach Mountain. 3. Stratigraphic sections of Ordovician, Silurian, and Devonian rocks of Sierra Diablo region. 4. Profiles showing stratigraphic features of Permian rocks in Sierra Diablo region. 5-8. Stratigraphic sections of Permian rocks in Sierra Diablo region: 5. Wylie Mountains to Baylor Mountains. 6. Eagle Flat to Victorio Peak. 7. Victorio Peak to Apache Peak. 8. Sierra Prieta to Delaware Mountains. 9. Topographic and index map of Sierra Diablo region. 10. Panoramic views of east-facing escarpment of Sierra Diablo. 11. Panoramic views in Apache Canyon, northern Sierra Diablo. 12. Panoramic views in northern part of Sierra Diablo region. 13. Stratigraphic sections of Cretaceous rocks in Sierra Diablo region and adjacent areas. 14. Geologic map of vicinity of Mine Canyon and Marble Canyon, northeastern Sierra Diablo. 15. Map of Sierra Diablo region showing tectonic features. 16. Geologic structure sections A-A' to J-J' in northern and eastern parts and K-K' to T-T' in southern part of Sierra Diablo region, Texas. Page FIGUKB 1. Map of parts of western Texas and southern New Mexico showing area covered by report on Sierra Diablo region______12 2. Map of Sierra Diablo region showing paleogeology of the surface on which the Hueco Limestone was deposited- 44 3. Map of parts of western Texas and southeastern New Mexico showing provinces of Permian time ____ _ 47 4. Map of Sierra Diablo region showing paleotectonics of Hueco Limestone______51 5. Detailed sections showing unconformities below and above Hueco Limestone in Baylor Mountains.--______53 6. Map of Sierra Diablo region showing paleotectonics of Bone Spring Limestone.______62 7. Map of Sierra Diablo region showing paleotectonics of Victorio Peak Limestone.______75 8. Map of Sierra Diablo region and adjacent areas showing faults and related structural features. ______108

TABLES

Page TABLE 1. Rock formations of Sierra Diablo region, Texas______18 2. Foraminifera identified from Hueco Limestone in central and northern Sierra Diablo.______56 3. Fossils identified from Hueco Limestone of southern calcitic limestone facies.______-__--_-_-___- 58 4. Fossils identified from Hueco Limestone, from marl and calcitic limestone in lower part of northeastern Sierra Diablo (exclusive of Foraminifera)______-----____-_- ___-_ _ __ 59 5. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Foraminifera)- 67 6. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Porifera, Coelenterata, Echinodermata, Bryozoa, and Brachiopoda)______-_-_-_-----_---_--_-_------68 7. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Amphineura, Coniconchia, Lamellibranchiata, Scaphopoda, Gastropoda, Cephalopoda, Annelida, Arthropoda, and Alga) __ 70 VI CONTENTS

Fagc TABLE 8. Fossils identified from Victorio Peak Limestone in central and northern Sierra Diablo_..-______-_----__ 76 9. Fossils identified from Goat Seep Limestone, northern Sierra Diablo ______i'_ _-!______-____ 80 10. Fossils identified from Finlay Limestone, western part of Sierra Diablo region, Texas.___-_____---._-_-----_- 86 11. Fossils identified from Kiamichi Formation, Cox Mountain, Tex______87 12. Fossils identified from beds of Duck Creek age in Washita Group of Sierra Prieta, Tex______-_------_--_-_- 88 13. Fossils identified from beds younger than Duck Creek age in Washita Group of Sierra Prieta, Tex______89 14. Tectonic history of Sierra Diablo region, Texas--___-_-_-______---_____-----_-_------_-_------100 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

By PHILIP B. KING

ABSTRACT directly on Precambrian rocks, erosion having removed the in­ tervening formations. The Sierra Diablo region covers an area 43 miles long and 33 The most extensively exposed rocks in the Sierra Diablo are miles wide in the western part of the State of Texas. The those of Permian age, which consist mostly of the Hueco Lime­ region includes the whole of the Sierra Diablo, a lofty plateau- stone of the Wolfcamp Series and the Bone Spring and Victorio like range whose summits exceed 6,000 feet in altitude. The Peak Limestones of the Leonard Series. These three units, surface of the range slopes gently westward from its crest, but which have an aggregate thickness of about 3,000 feet, lie at to the east, north, and south it breaks off in abrupt escarpments the surface over wide areas on the summits, and are promi­ as much as 2,000 feet high. To the southeast and south the nently exposed on the bordering escarpments. They are tra­ range is flanked by lower foothills, beyond which are the inter- versed by two prominent monoclinal flexures, the Victorio and montane desert basins of the Salt Basin and Eagle Flat. the Babb, one near the middle and the other at the north end In its broader outlines, the Sierra Diablo resembles block of the range. These trend west-northwest and dip north-north­ mountains elsewhere in the Basin and Range province. In east. South of the Victorio flexure only the Hueco Limestone detail, its geologic features are complex, as it is made up of is preserved; to the north the Bone Spring and Victorio Peak rocks of many ages and types, which have been deformed during Limestones overlie it. North of the Babb flexure the Victorio several periods. Peak Limestone is overlain by the Cutoff Shale, also of Leonard The oldest rocks of the region, of Precambrian age, are ex­ age, and by formations of the Guadalupe Series. posed in the foothills south and southeast of the Sierra Diablo. At the base of the Hueco, lying unconformably on the older They include ancient metasedimentary rocks the Oarrlzo rocks, are clastic rocks of the Powwow Member, but the main Mountain Formation, intruded by igneous rocks, and younger body of the formation is an evenly bedded limestone. The unmetamorphosed sedimentary and volcanic rocks the Alla- Bone Spring is more varied; in the northeastern part of the moore and Hazel Formations. The Oarrizo Mountain Forma­ region it is a thin-bedded slope-making black limestone, but tion has been thrust over the younger Precambrian rocks, and southwestward, especially near the flexures, this gives place to for some miles north of the trace of the thrust the younger massive limestone reefs and banks. Near the flexures the Bone rocks have been intensely deformed; farther north they lie Spring is uncomfortable on the Hueco. The Victorio Peak is nearly flat The thickness of the Precambrian rocks cannot be a gray thick-bedded limestone that forms cliffs above the black determined, but it is probably many thousands of feet. limestones of the Bone Spring; its lower part intergrades with Deformation of the Precambrian rocks occurred before depo­ the black limestones, and it is entirely replaced by them in the sition of the Van Horn Sandstone, which lies on their deeply Delaware Mountains, east of the Sierra Diablo. eroded edges. The Van Horn is a coarse red clastic deposit, as The formations of the Guadalupe Series north of the Babb much as 700 feet thick. As it contains no fossils, its age can­ flexure are the sandstone tongue of the Cherry Canyon Forma­ not be proved; but it is probably of late Precambrian age. The tion and the Goat Seep Limestone. The sandstone tongue lies Van Horn was tilted and eroded before the succeeding Bliss on an eroded surface of the Cutoff Shale and is separated from Sandstone was laid down over it. it by a hiatus, as shown by the absence of the Brushy Canyon Pre-Permian Paleozoic rocks crop out in the southeastern and Formation that intervenes between the Cherry Canyon Forma­ northeastern parts of the Sierra Diablo region and form a few tion and the rocks of the Leonard Series in the Delaware inliers elsewhere; their most conspicuous outcrops are on Beach Mountains to the east. Mountain. They include the Bliss Sandstone, El Paso Lime­ Cretaceous rocks overlie the Permian and older rocks on the stone, beds of Middle Ordovician age, and Montoya Dolomite, west slope of the Sierra Diablo and form smaller remnants all of Ordovician age; the Fusselman Dolomite of Silurian age; elsewhere. They are separated from the older rocks by a and chert, limestone, and shale of Devonian age. Total thick­ marked unconformity. In places in the southwestern part of ness of these units it about 2,000 feet. the map area they lie directly on the Precambrian, the inter­ In the northeastern part of the Sierra Diablo, these earlier vening Paleozoic strata having been removed by erosion. The Paleozoic rocks are succeeded by the Barnett Shale of Missis- surface upon which they were deposited was a peneplain, ex­ sippian age and limestone and shale of Pennsylvanian age. humed remnants of which form the summits of other parts of Because of disconnected exposures, the thickness of the Mis- the Sierra Diablo, where all trace of the Cretaceous rocks them­ sissippian and Pennsylvanian rocks cannot be determined; but selves has been removed. they probably do not exceed a few thousand feet. The Cretaceous rocks overlapped northeastward from a geo- The Ordovician, Silurian, Devonian, Mississippian, and syncline. Cretaceous rocks that were deposited along the edge Pennsylvanian rocks were broadly folded and deeply eroded of the geosyncline extend into the southwest corner of the map during Late Pennsylvanian time, so that the succeeding Hueco area, southwest of the Eagle Flat, and include at the base the Limestone of Early Permian age overlies them with marked Yucca and Bluff Mesa Formations, a body of sandstone and angular unconformity. In parts of the region the Hueco lies limestone of Early Cretaceous age that is more than 2,000 feet GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS thick. The Yucca and Bluff Mesa are absent elsewhere in the Formation have been quarried for many years for crushed stone. region, except for a thinned equivalent of their topmost beds The most needed resource in the area is ground water. The in the Campagrande Limestone. best and most abundant supplies have been obtained from wells Elsewhere in the southern half of the Sierra Diablo region, in the Salt Basin near Van Horn; elsewhere, the occurrence, the Cretaceous is represented by the Campagrande Limestone, amount, and quality of ground water vary. 100 feet thick; the Cox Sandstone, 400 to 600 feet thick; and Probably the region contains no important reservoirs of oil the Flnlay Limestone, 50 to 100 feet thick. The Campagrande or gas, as ancient rocks underlie it at relatively shallow depth. is of Trinity age and the Finlay of Fredericksburg age; the The region is of interest to petroleum geologists, however, be­ boundary between the Trinity and Fredericksburg may lie cause the rocks here exposed are about the same age and simi­ within the Cox Sandstone. On Cox Mountain, in the west- lar in character and structure to those which are deeply buried central part of the region, the Finlay is overlain by the Kia­ in the oil fields of the west Texas basin east of the mountain michi Formation, or highest unit of the Fredericksburg Group. region. Farther north, the Cox Sandstone apparently replaces both INTRODUCTION the Finlay and Kiamichi, for in Sierra Prieta, in the northwest corner of the region, it is overlain directly by the Washita PRESENT INVESTIGATION Group. Here, as much as 350 feet of the Washita is preserved, with beds of Duck Creek age at the base and beds possibly as Between 1925 and 1939 the writer, with various col­ young as of Mainstreet age at the top. leagues, made a study of the Paleozoic and associated The sedimentary rocks of the Sierra Diablo are intruded by rocks exposed in the mountains of Trans-Pecos Texas, igneous rocks of probable Tertiary age. These are most abun­ dant near Mine and Marble Canyons in the northeastern part west and southwest of the west Texas Permian basin. of the mountains, where two stocks and numerous dikes and This study was begun under the auspices of the Texas sills lie in the Permian rocks; here, there is a great variety Bureau of Economic Geology and of Peabody Museum of igneous and contact-metamorphosed rocks. Sierra Prieta, of Yale University, but after 1930 it was continued by in the northwestern part of the region, is formed by a thick the U.S. Geological Survey. Most of the results of sill-like body of alkalic composition which intrudes Permian and Cretaceous rocks. Extrusive basalt is preserved a few this study have been published in official reports of the places in the central part of the region. U.S. Geological Survey and the Texas Bureau of Eco­ The Sierra Diablo was given its present form and outlines nomic Geology (King, P. B., 1931; King, E. E., 1931; by disturbances during Cenozoic time. These disturbances King, P. B., 1937; King P. B., and Knight, J. B., 1944; probably occurred during several phases, extending from the King, P. B., and Fountain, H. C., 1944; King, P. B., early Tertiary into the Quaternary. The rocks near the Devil Ridge and Red Hills thrusts in the extreme southwest corner King, E. E., and Knight, J. B., 1945; King, P. B., 1948, of the region were deformed in early Tertiary time, but most 1949; King P. B., and Flawn, P. T., 1953) and in vari­ of the deformation in the Sierra Diabo to the northeast probably ous journal articles (King, P. B., 1934a, b, 1942; and occurred during late Tertiary time. During this time the Sierra others). Diablo was raised nearly to its present height and was broken The present report presents the remaining results of by faults. The faults belong to two systems: a fairly con­ sistent set trending west-northwest and a less regular set trend­ the study that part pertaining to the Sierra Diablo ing generally north. Faults of the latter system follow the region. Field investigations in this region were largely east base of the Sierra Diablo and Baylor Mountains. During completed by 1939, but preparation of a comprehensive Quaternary time faults of this system were displaced again, report was delayed by emergency duties during World and in some places the alluvial fans were faulted. War II and by new Survey projects which began after The lower areas surrounding the Sierra Diablo are exten­ sively covered by unconsolidated deposits of Cenozoic age, the war; thus, only summaries of the results of the work formed during erosion of the uplifted mountain blocks. The in the Sierra Diablo region, or reports on special phases deposits at the surface are all probably of Quaternary age, have appeared hitherto (King, P. B., 1942, p. 556-575, but late Tertiary deposits doubtless underlie them in the deeper 613-634; King, P. B., and Knight, J. B., 1944; King intermontane basins. P. B., and Flawn, P. T., 1953). Because the compre­ The economic products of the region are varied. In some places the rocks are mineralized, and have been extensively hensive report has been prepared more than 20 years prospected. One mineralized area is in the exposed Precam- after completion of the field investigations, it lacks the brian rocks on the south, where copper and silver have been freshness and novelty it might have possessed earlier. produced from the Hazel and Blackshaft mines and from many Nevertheless, many of the geologic observations that smaller workings. Another mineralized area is near Mine and were made before 1939 have not been duplicated subse­ Marble Canyons in the northeastern part of the Sierra Diablo. One of the stocks in that area contains small quantities of tung­ quently, so that a report on the region, based primarily sten and beryllium. Near these stocks, and near the sill at on these observations, is still of value to the public. Sierra Prieta, the metamorphosed, originally dolomitic, Hueco Field investigations in the Sierra Diablo region were Limestone has been altered to a mixture of calcite and brucite, made at intervals by the writer and his colleagues be­ the latter perhaps a source of metallic magnesium. Since 1952 tween 1928 and 1939, as follows: the phyllitic beds in the Allamoore Formation have been ex­ tensively worked for talc. At a locality 8 miles west of Van 1. In the summer of 1928 the writer and E. E. King Horn the metaigneous rocks that intruded the Carrizo Mountain spent 3 weeks in the region, under the auspices of the INTRODUCTION Texas Bureau of Economic Geology and Yale Peabody although a few in outlying areas could not 'be tied into Museum. The objective of this visit was a study of the sections. Permian rocks; various sections were measured and fos­ ACKNOWLEDGMENTS sils were collected. Some reconnaissance mapping was In the investigation of the Sierra Diablo region the also done, and a few incidental observations were made writer's greatest debt is to his field associate and col­ on formations of other ages. laborator, the late J. Brookes Knight, specialist in 2. In the summer of 1931 the writer and J. Brookes Paleozoic gastropods and one of the great paleontolo­ Knight spent 4 weeks in the region for the U.S. Geolog­ gists of our time. Much is due him, not only for his ical Survey. Aguin, chief study was made of the Per­ measurement of sections and collection of fossils, men­ mian stratigraphy and of fossils in the Permian rocks; tioned above, but also for his keen insight into problems but on this visit more attention was given to the associ­ of stratigraphy, paleontology, and paleoecology, which ated rocks, and a start was made on detailed mapping of has contributed in no small measure to the merits of this the region. report. 3. In the summer of 1936, again with J. Brookes During the investigation, geologic features of the Knight, 2 months were spent in the region, continuing region were reviewed with many visitors, among whom the study of the Permian and associated rocks and ex­ the following are noteworthy. tending the mapping. In 1938, the late Samuel G. Lasky, of the U.S. Geo­ 4. In the summer of 1938 the writer and J. Brookes logical Survey, reviewed with the writer the mines, Knight spent 2^ months on a final review of the region, prospects, and mineral deposits of the region, mainly completing the stratigraphic study and most of the map­ in the Precambrian rocks to the south, but also includ­ ping. In the autumn of the same year the writer spent ing those of the Mine Canyon and Marble Canyon area another month mapping the Precambrian and early farther north. In 1941 Lasky made an independent Paleozoic rocks in the southern part of the region. examination of the tungsten deposits of the Mine In addition, shorter visits and field checks were made Canyon area. by the writer during some intervening and subsequent In 1936 Earl Ingerson, at that time with the Geo­ years, as in 1933,1935,1939,1949, and 1951. physical Laboratory of the Carnegie Institution of Mapping during the investigation was done partly Washington, reviewed the intrusive rocks of the Marble on enlargements of the excellent topographic map of Canyon area with Knight. In 1938 Ingerson reviewed the Van Horn 30-minute quadrangle, whose original with the writer the metamorphic rocks in the southern scale was 1:125,000; but in that part of the region to part of the region. the west and north where only inadequate topographic In 1938 the late Josiah Bridge and the late W. H. base maps were available, mapping was done by means Hass, of the U.S. Geological Survey, reviewed with of a net of speedometer and pacing traverses. Kesults Knight and the writer the stratigraphy and paleon­ of these surveys were published in a preliminary map tology of the Ordovician and other early Paleozoic in 1944 (King, P. B., and Knight, J. B., 1944). In 1945 rocks. small-scale air photographs of the region became avail­ Study and identification of rocks and minerals of the able, in 1948 large-scale air photographs. In 1955 a region have been made by many petrographers and geo- topographic map based on photogrammetry was made chemists of the U.S. Geological Survey. Kock and the Army Map Service. In 1951 and 1955 the writer mineral specimens have been identified by C. S. Ross, adjusted his earlier field traverses to the air photo­ Charles Milton, and Donald E. Lee. Chemical analyses graphs and transferred the results to the new have been made by K. J. Murata. In addition, in 1941 topographic base. The resulting geologic map accom­ Milton made an extensive study of specimens from the panying this report (pi. 1) represents the same features Marble Canyon intrusive and its associated contact- as those on the map of 1944, but with some revision and metamorphic rocks. with greater precision of form and location. Study and identification of fossils from the various Stratigraphic studies, measurement of sections, and formations of the region were made by paleontologists collection of fossils were made largely by the author's of the U.S. Geological Survey. Ordovician fossils colleague, the late J. Brookes Knight, at times with the were identified by Josiah Bridge, P. E. Cloud, Jr., assistance of the writer and others. Most of the sec­ Helen Duncan, and Jean Berdan; collections of cono- tions were measured by hand level, and because the donts from the Devonian rocks, by W. H. Hass; Missis- strata of the region are nearly flat lying, no correction sippian and Pennsylvanian fossils, by George H. Girty, for dip was necessary. Many of the fossil collections Mackenzie Gordon, Jr., and E. L. Yochelson; larger were made along the lines of the measured sections, Permian fossils, by P. E. Cloud, Jr., E. L. Yochelson, GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

R. M. Finks, Helen Duncan and I. G. Sohn, fusulinids auspices of the U.S. Geological Survey, Smith and C. C. and other foraminifers, by L. G. Henbest; and Albritton, Jr., expanded this and other surveys into a Cretaceous fossils, by Ralph W. Imlay. comprehensive study of the Sierra Blanca region that Before the studies were made by Survey paleontolo­ adjoins the Sierra Diablo region on the west (Albritton gists, the brachiopods collected from the Permian rocks and Smith, 1965). Geologic features in the southwest in 1928 had been identified by R. E. King, and the fusu­ corner of the map which accompanies the present linids collected in 1928 and 1931 had been identified by report are based on the surveys by Smith. C. O. Dunbar and J. W. Skinner. The memoirs in Between 1949 and 1951 Peter T. Flawn, of the Texas which their results appeared (King, R. E., 1931; Dun- Bureau of Economic Geology, investigated the Pre- bar and Skinner, 1937) are among the earliest of the cambrian rocks of the Carrizo Mountains and outlying modern studies on the Permian fossils of the West areas to the south and also studied the Hazel Mine and Texas Region, and were an invaluable guide in the later the talc deposits which occur in the Precambrian rocks field investigations in the Sierra Diablo region. farther north. He collaborated with the writer in a report on the Precambrian rocks of the Van Horn area BELATED INVESTIGATIONS and their mineral deposits (King, P. B., and Flawn, Besides the field investigation in the Sierra Diablo P. T., 1953). Mapping and other data in the southern region that was made directly by the writer and his as­ part of the present report are are based on this joint sociates, other investigations were made in the region study. during the same period by geologists of the U.S. Geo­ Other studies of special phases of the geology of the logical Survey and Texas Bureau of Economic Geology, region have been made by geologists with other affilia­ some of the results of which are included in this report. tions and have been used in the present report so far The areas covered by some of these investigations are as their published results are available. F. G. Stehli shown in figure 1. studied the Permian rocks and fossils near Victorio Between 1943 and 1946 P. E. Cloud, Jr., and V. E. Peak for a dissertation at Columbia University (Stehli, Barnes, of the U.S. Geological Survey and Texas 1954), and C. O. Dunbar investigated the fusulinids of Bureau of Economic Geology, made a comprehensive the Permian rocks in the same area (Dunbar, 1953). investigation of the Ellenburger Group of central H. J. Howe reviewed the stratigraphy of the Montoya Dolomite in west Texas and southern New Mexico Texas. As part of this study they measured a detailed and made significant observations in the Baylor Moun­ section of the Lower Ordovician rocks on Beach Moun­ tains (Howe, 1959). Hugh Hay-Roe and P. C. Twiss tain and made observations on these rocks elsewhere in studied the Permian and associated rocks in the Wylie the Sierra Diablo region (Cloud and Barnes, 1946, and Van Horn Mountains, southeast and south of the p. 66-71,352-361). present report area, for dissertations at the University In 1944 R. D. Sample and E. E. Gould, of the U.S. of Texas (Hay-Roe, 1957; Twiss, 1959). Some of the Geological Survey, made a detailed examination of the observations by geologists employed by oil companies Hazel, Blackshaft, Sancho Panza, and other mines and have appeared in guidebooks of the West Texas Geo­ mineral deposits of the southern part of the region. logical Society (Adams and others, 1949; De Ford and Between 1944 and 1946 Elliot Gillerman, of the U.S. others, 1951; Haigh and others, 1953). Geological Survey, studied the fluorspar deposits of the Eagle Mountains southwest of the Sierra Diablo and PREVIOUS INVESTIGATIONS mapped the rocks in which they occur (Gillerman, 1953). His geologic map extends a short distance into The Sierra Diablo region was given scant attention the south edge of the Sierra Diablo region, and was by the early geological explores and was not visited by used in compilation of the geologic map which accom­ geologists until the reorganization of the Geological panies the present report. In 1948 and 1949 W. T. Survey of Texas under E. T. Dumble in 1888. Investi­ Holser made a detailed survey of the Cave Peak intru­ gation of the geology of the Trans-Pecos Region for sive in the Mine Canyon area for the U.S. Geological this survey was assigned to W. H. von Streeruwitz, Survey, as part of a study of the nonpegmatitic beryl­ who was in the field with his assistants between the lium resources of the United States (Warner and years 1888 and 1893 (Geiser, 1957). Although most of others, 1959, p. 140-143). their work was done in areas farther south and west, In 1936 and 1937 J. Fred Smith, Jr., mapped the the mines and prospects in the southern foothills of the Devil Ridge area, part of which extends into the ex­ Sierra Diablo were examined, including the Hazel mine, treme southwest corner of the Sierra Diablo region and brief observations were made on the surrounding (Smith, 1940). Between 1947 and 1951, under the rock formations (Streeruwitz, 1890, 1891, 1892, 1893). INTRODUCTION Metamorphic rocks were observed in the Carrizo Moun­ Permian ages. The "Hueco fauna," as understood by tains and the hills north of Eagle Flat, and their nature Girty, however, actually occurs only in one of these was interpreted in a petrographic report by Osairn formations in the Hueco Mountains and elsewhere; the (1893, p. 137-138). Eocks farther north were thought name is now restricted to this part of the original to consist of a red Diabolo Sandstone, assigned to a formation. Devonian age, and an overlying body of limestone, as­ In the Sierra Diablo, the Hueco Limestone as mapped signed to a Carboniferous age on the authority of C. D. by Eichardson is now known to consist of several for­ Walcott, who examined a few fossil collections. Both mations of Early Permian age, the lowest of which is of these supposed units are now known to consist of the restricted Hueco; the angular unconformity recog­ many formations of diverse ages. nized by Eichardson below the Hueco has proved to First systematic geologic work in the Sierra Diablo be basal Permian, rather than basal Pennsylvanian. region was by G. B. Kichardson, under the joint auspices Mississippian and Pennsylvanian elements, which form of the U.S. Geological Survey and the University of large parts of the original Hueco in the Hueco and Texas Mineral Survey. In 1903 Kichardson made a Franklin Mountains, are scantily preserved in the Sierra reconnaissance of the geology and ground-water re­ Diablo region. sources of all the northern Trans-Pecos Eegion in Texas Few geologic observations were made in the Sierra (Eichardson, 1904); later he made more detailed sur­ Diablo region in the decades immediately following veys of the El Paso and Van Horn quadrangles, which the work of Eichardson and Girty. The next period were published as geologic folios (Eichardson, 1909, in which it was studied began in the midtwenties as 1914). an outgrowth of petroleum exploration and develop­ Eichardson's work laid the foundation on which most ment in the West Texas basin to the east. This period of our modern geologic concepts of the Sierra Diablo corresponds to that during which the present investi­ and adjacent regions have been built. He recognized gation was made by the writer and his colleagues; work and defined many of the Paleozoic and Mesozoic forma­ done during that time in the Sierra Diablo region by tions which are still in use and set forth the broader other geologists has already been mentioned. outlines of the geomorphology and structure. However, The following annotated bibliography lists chron­ as only a small amount of time could be spent on these ologically all publications which deal with the geology surveys even those for the geologic folios many de­ of the Sierra Diablo regions. tails have been added later, as may be seen by comparing the present map of the Sierra Diablo region with the ANNOTATED BIBLIOGRAPHY map in the Van Horn folio. Perry, C. C., and others, 1857, Geological reports, in Emory, Older Paleozoic formations the Bliss, El Paso, W. H., Report on the United States and Mexican boundary Montoya, and Fusselman were defined on the basis of survey: U.S. 34th Gong., 1st sess., S. Ex. Doc. 108 (H. Ex. the section in the Franklin Mountains north of El Paso Doc.l35),v.l,pt.2,174 p. (Eichardson, 1908, p. 475-^80), still the standard of Reports (p. 4-5) that west of the igneous rocks of the reference. Presence of the El Paso and Montoya was Limpia (Davis) Mountains are ridges of stratified lime­ also recognized by Eichardson in the Sierra Diablo re­ stone, dipping southwest; on the basis of a few fossils (Terebratula) James Hall assigns the limestone to the gion, and occurrence of the Bliss and Fusselman has Carboniferous (p. 107). Elevated alluvial basins near been proved there subsequently. Eagle Spring are shut off from the Rio Grande by a "vari­ Stratigraphy of the more complex later Paleozoic able mountain range, composed of Carboniferous limestone strata was less clarified, although Eichardson benefited and variously associated igneous rocks." The Sierra Di­ from the advice of G. H. Girty, who was at that time ablo region to the north is not mentioned in this account. working on his classic memoir on the Guadalupian Jenny, W. P., 1874, Notes on the geology of western Texas near fauna (Girty, 1908), based on collections of Permian the thirty-second parallel: Am. Jour. Sci., 3d ser., v. 7, p. fossils from the Guadalupe Mountains and adjacent 25-28. regions. Permian formations, the Delaware Mountain, Discusses the probable Silurian and Carboniferous ages of rocks in the mountains of northern Trans-Pecos Texas, Capitan, and higher units, were recognized east of the mostly north and northwest of the Sierra Diablo region. Salt Basin; but the later Paleozoic rocks to the west were placed in the Hueco Limestone, supposed to be a Cummins, W. F., 1888, Mining districts in El Paso County: Geol. and Sci. Bull. (Texas State Geol. and Sci. Assoc., nearly homogeneous body as much as 5,000 feet thick, Houston, Tex.), v. 1, no. 2. of Pennsylvanian age. As mapped by Eichardson, the Includes a paragraph on the "Diabolo district" that is, the Hueco is now known to include, at one place or another, mineralized area in the southern foothills of the Sierra formations of Mississippian, Pennsylvanian, and Early Diablo. Mentions the nature of the copper and silver ores 6 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS and states that these occur in steeply dipping veins in Dumble, E. T., 1902, The red sandstone of the Diablo Mountains, massive fine-grained red argillaceous sandstone of unknown Texas: Texas Acad. Sci. Trans., v. 4, pt. 2, p. 1-3. age (sandstone of Hazel Formation of present terminology), Discussion of stratigraphy of older rocks of Sierra Diablo which is overlain by Carboniferous limestone. region, based on exposures on west side of Beach Mountain, Streeruwitz, W. H. von, 1889, Mines worked in western Texas: where the red Hazel Sandstone is differentiated from an Geol. and Sci. Bull. (Texas State Geol. and Sci. Assoc., overlying red sandstone (Van Horn Sandstone of present Houston, Tex.), v. 1, no. 12. usage), believed by the author to be of early Paleozoic age. Includes brief description of Hazel mine, its ores, and Phillips, W. B., 1902, Sulphur, oil, and quicksilver in trans-Pecos mining operations then in progress. Texas: Texas Univ. Bull. 9 (Mineral Survey Ser. Bull. 2) 43 p. Hill, R. T., 1890, The Eagle Flats formation and the basins of Contains mineral appraisals and brief notes on geology the trans-Pecos or mountainous region of Texas [abs.]: of various land-survey blocks in El Paso County (including Am. Assoc. Adv. Sci. Proc., v. 38, p. 42. present Culberson and Hudspeth Counties) by B. F* Hill, Quaternary intermontane deposits of Trans-Pecos Texas some of which are in Sierra Diablo region (p. 15, 16, 20, are interpreted to be of lacustrine origin and are named the etc.). Eagle Flats Formation, presumably after Eagle Flat in the Sierra Diablo region, although this is not so stated. Richardson, G. B., 1904, Report of a reconnaissance in trans- Pecos Texas north of the Texas and Pacific Railway: Texas Streeruwitz, W. H. von, 1890, Geology of trans-Pecos Texas: Univ. Bull. 23 (Mineral Survey Ser. Bull. 9), 119 p. Texas Geol. Survey 1st Ann. Kept. (1889), p. 219-235. Report on a survey of an extensive region, of which the Contains general summary of geology and resources of Sierra Diablo region is a part, with special reference to Trans-Pecos Region but includes some notes on geology and ground-water resources but containing the first modern ac­ mineral deposits in Sierra Diablo foothills (p. 221-222, 224). count of the stratigraphy, structure, and geomorphology. 1891, Report on the geology and mineral resources of Girty, G. H., 1908, The Guadalupian fauna: U.S. Geol. Survey trans-Pecos Texas: Texas Geol. Survey 2d Ann. Rept. Prof. Paper 58, 651 p. (1890), p. 665-713. Comprehensive memoir on Permian fossils, mainly from Lengthy description of geology and resources of Trans- Guadalupe Mountains north of Sierra Diablo region. In­ Pecos Texas, including notes on geology and mines in Oar- cludes remarks on some fossils collected from an unknown rizo Mountains and Sierra Diablo foothills (p. 681-684), locality in the Sierra Diablo which also appear to be of accompanied by geologic structure sections (pi. 26). "Guadalupian" character (p. 26); these probably came from Bone Spring Limestone. 1892, Trans-Pecos Texas: Texas Geol. Survey 3d Ann. Rept. (1891), p. 383-389. Richardson, G. B., 1908, Paleozoic formations in trans-Pecos Texas: Am. Jour. Sci., 4th ser., v. 25, p. 474-484. General remarks on Trans-Pecos Region, including notes on geology and mineral deposits of Carrizo Mountains and Contains the first definitions of many of the stratigraphic Sierra Diablo foothills, and a detailed report on Hazel units which occur in the Sierra Diablo and other parts of Mine, with plans and sections (pi. 16). northern trans-Pecos Texas and emendations of definitions of other units that had been proposed by Richardson in re­ 1893, Trans-Pecos Texas: Texas Geol. Survey 4th Ann. port of 1904. Rept. (1892), p. 141-175. Van Hise, C. R., and Leith, C. K., 1909, Pre-Cambrian geology Final summary of the author's 5 yr of observation on the of North America: U.S. Geol. Survey Bull. 360, 939 p. geology and resources of Trans-Pecos Texas; includes strat- igraphic sections and lists of identified fossils from the Includes summary of observations by Richardson and Paleozoic rocks of the Sierra Diablo (p. 167-175). earlier geologists on Precambrian rocks in southern Sierra Diablo region (p. 746-749). Osann, C. A., 1893, Report on the rocks of trans-Pecos Texas: Texas Geol. Survey 4th Ann. Rept. (1892), p. 123-141. Richardson, G. B., 1914, Description of the Van Horn quad­ rangle : U.S. Geol. Survey Geol. Atlas, Folio 194, 9 p. Includes petrographic reports on a diabase from the Sierra Diablo (p. 125-126) and various metamorphic rocks Report on the geology of an area which includes the from the Carrizo Mountains (p. 137-138). eastern half of the Sierra Diablo region, ably presenting the larger features, although many details have been added 1896, Beitrage zur Geologic und Petrographie der Apache by later work. (Davis) Mts., Westtexas: Tschermak's mineralog. petrog. Mitt., v. 15, p. 394-456. Beede, J. W., 1920, Notes on the geology and oil possibilities of the northern Diablo Plateau in Texas: Texas Univ. Bull. Includes description of Precambrian metamorphic rocks 1852, 40 p. [1918]. in Carrizo Mountains and adjacent areas. Deals mainly with region northwest of the Sierra Diablo, Hill, R. T., 1900, Physical geography of the Texas region: U.S. but includes first report of occurrence of strata of "Word" Geol. Survey Topog. Atlas, Folio 3,12 p. (Guadalupe) age at north end of Sierra Diablo (p. 24-26). Includes brief description of topography of Sierra Diablo Baker, C. L., 1927, Exploratory geology of a part of southwest­ region (p. 5) and several photographs (figs. 24, 35). ern trans-Pecos Texas: Texas Univ. Bull. 2745, 70 p. INTRODUCTION

Reconnaissance survey of an extensive area south and Includes an account of Permian stratigraphy of Sierra southwest of Sierra Diablo region, including notes on Pre- Diablo region based on first field season of present investi­ cambrian rocks and Permian (Hueco) limestone in Carrizo gation (p. 14-16) and description of Permian brachiopods, and Wylie Mountains. in part collected in Sierra Diablo region. Many of strati- graphic interpretations have been superseded by later work. Baker, C. L., 1928, Desert range tectonics of trans-Pecos Texas: Pan-Am. Geologist, v. 50, p. 341-373. Girty, G. H., 1931, New Carboniferous invertebrates, pt. 3: Appraisal of evidence for Basin and Range structure in Washington Acad. Sci. Jour., v. 21, p. 390-397. Trans-Pecos Texas and New Mexico, with mention of Sierra Includes description of the brachiopod Schisophoria Diablo region (p. 369-371). peculiaris Girty from Bone Spring Limestone of Sierra Carter, W. T., and others, 1928, Soil survey (reconnaissance) Diablo. of the trans-Pecos area, Texas: U.S. Dept. Agri. ser. 1928, Adkins, W. S., 1933, The Mesozic systems in Texas, in Strati­ no. 35, 66 p. graphy, v. 1 of The geology of Texas: Texas Univ. Bull. General account and map of geography and soils of Trans- 3232, p.239-518. Pecos Region, with some specific notes on Sierra Diablo Description and interpretation of all Mesozoic forma­ region. tions in Texas, with many incidental notes on Cretaceous Baker, C. L., 1929, Overthrusting in trans-Pecos Texas: Pan-Am. rocks in and near the Sierra Diablo region. Geologist, p. 53, p. 23-28. Arick, M. B., 1932, Occurrence of strata of Bend age in Sierra Discussion of folding and thrust-faulting of Cretaceous Diablo, Texas: Am. Assoc. Petroleum Geologists Bull., T. rocks in southern Hudspeth County, including southwestern 16, p. 484-486. corner of report area. At northeastern border of disturbed Reports discovery of fossiliferous strata of Bend age belt, thrust sheets moved toward nearly horizontal strata north of Marble Canyon in the Sierra Diablo ("shale of of Diablo Plateau, the boundary between them being local­ Smithwick age" of Plummer and Scott, 1937, "fossiliferous ized by "shoaling of Cretacic sea" (p. 24). shale of Pennsylvianian age" of present report). Blanchard, W. G., Jr., and Davis, M. J., Jr., 1929, Permian stratigraphy and structure of parts of southeastern New Darton, N. H., 1932, Algonkian strata of Arizona and western Mexico and southwestern Texas: Am. Assoc. Petroleum Texas [abs.]: Geol. Soc. America Bull., v. 43, p. 123. Geologists Bull., v. 13, p. 957-995. Mentions resemblance of the Millican Formation (Alla- Deals mainly with Guadalupe Mountain area, but includes moore and Hazel Formations of present usage) to Grand remarks on Permian rocks of Sierra Diablo and Wylie Canyon Series and Apache Group of Arizona. Mountains (p. 960-962). King, P. B., 1932, Possible Silurian and Devonian strata in Van King, P. B., and King, R. B., 1929, Stratigraphy of outcropping Horn region, Texas: Am. Assoc. Peroleum Geologists Bull., Carboniferous and Permian rocks of trans-Pecos Texas: v. 16, p. 95-97. Am. Assoc. Petroleum Geologists Bull., v. 13, p. 907-926. Reports discovery of Fusselman Limestone and beds of Includes results of first field season of present investi­ Devonian age in Sierra Diablo region during second field gation in Sierra Diablo region on Pennsylvanian and season of present investigation. Permian rocks (p. 911, 922-923), many of which have been King, P. B., 1932, Permian limestone reefs in the Van Horn superseded by later work. region, Texas [abs.]: Washington Acad. Sci. Jour., v. 22, King, R. B., 1929, Mississippian and Pennsylvanian stratigraphy p. 288-289; Geol. Soc. America Bull., v. 43, p. 280-281. of trans-Pecos, Texas [abs.]: Geol. Soc. America Bull., v. 40, Notes on reefs and related deposits in Bone Spring Lime­ p. 190-191. stone of Sierra Diablo region, based on observations during Mentions occurrence of limestone of Strawn age in the second field season of present investigation. Sierra Diablo (the limestone of Pennsylvanian age south of Marble Canyon of present report). Mansfield, G. R., and Boardman, Leona, 1932, Nitrate deposits of the United States: U.S. Geol. Survey Bull. 838, 107 p. Mohr, C. L., 1929, Secondary gypsum in the Delaware Moun­ tain region: Am. Assoc. Petroleum Geologists Bull., v. 13, Includes description of a nitrate prospect ("Potash p. 1395. mine") in Van Horn Sandstone (erroneously ascribed to Cretaceous) in Sierra Diablo foothills (p. 66-68). Presents evidence that the alleged "Dos Alamos gypsum member" in the Guadalupe series of the northern Sierra Sellards, B. H., 1933, Pre-Paleozoic and Paleozoic system in Diablo is not an original part of the stratigraphic sequence. Texas, in Stratigraphy, v. 1 of The geology of Texas: King, P. B., and Leonard, R. J., 1930, Contact metamorphism of Texas Univ. Bull. 3232, p. 15-238. Hueco limestone in trans-Pecos Texas [abs.]: Pam-Am. Brief descriptions of all pre-Paleozoic and Paleozoic for­ Geologist, v. 53, p. 316. mations in Texas, including those in Sierra Diablo region. Note on contact metamorphism adjacent to the Marble Darton, N. H., and King, P. B., 1933, Western Texas and Carls­ Canyon intrusive of northeastern Sierra Diablo. bad Caverns: Internat. Geol. Cong., 16th, United States King, R. B., 1931, Faunal summary and correlation of the 1933, Guidebook 13, 38 p. Permian formations, with description of the Brachiopoda, Contains a summary of geology of Sierra Diablo region pt 2 of Geology of the Glass Mountains: Texas Univ. Bull. (p. 19-27), based on results of first two field seasons of 3042, 245 p. [1930]. present investigation. 8 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Baker, C. L., 1935, Structural features of trans-Pecos Texas, Contains notes on stratigraphy of Sierra Diablo region (p. Pt. 2 in Structural and economic geology, v. 2 of The geol­ 587-590), description of fusulinid species, and lists of fusu­ ogy of Texas: Texas Univ. Bull. 3401, p. 137-214. linids identified from Sierra Diablo region (p. 722-725). Includes brief description of geologic structure of Sierra Plummer, F. B., and Scott, Gayle, 1937, Upper Paleozoic ammoni­ Diablo region and adjacent areas (p. 180-185) and dis­ ties in Texas, in Upper Paleozoic ammonities and fusulinids, cussion of "Texas lineament" (p. 206-214). v. 3 of The geology of Texas: Texas Univ. Bull. 3701, p. 13- King, P. B., 1934, Permian stratigraphy of trans-Pecos Texas: 516. Geol. Soc. America Bull., v. 45, p. 697-798. Includes identifications of ammonites from shale of Smith- Describes Permian stratigraphy of Sierra Diablo region wick age north of Marble Canyon in the Sierra Diablo (p. on basis of results of first two field seasons of present inves­ 25) ("fossiliferous shale of Pennsylvanian age" of present tigation (p. 745-746, 748-763), some of which have been report). superseded by later work. King, R. E., Adams, J. E., and Hills, J. M., 1939, Van Horn King, P. B., 1934, Notes on upper Mississippian rocks in trans- region: West Texas Geol. Soc. Field Trip Guidebook, May Pecos Texas: Am. Assoc. Petroleum Geologists Bull., v. 18, 20-21,1939, 8 p. p. 1537-1543. Road log in southern part of the Sierra Diablo, describing Includes description of Mississippian and adjacent strata localities in Permian and older rocks, based on field results in Sierra Diablo region (p. 1541-1543). of P. B. King. Kirk, Edwin, 1934, The Lower Ordovician El Paso limestone of Bridge, Josiah, 1940, Correlation of early Paleozoic sections in Texas and its correlatives: Am Jour. Sci., 5th ser., v. 28, p. central and western Texas [abs.]: Geol. Soc. America Bull., 443-463. v. 51, p. 1921-1922. Discusses subdivisions and correlation of El Paso Lime­ Includes brief comment on correlation of El Paso Lime­ stone, with special reference to the Franklin Mountains sec­ stone and Bliss Sandstone of Sierra Diablo region. tion but with incidental reference to Sierra Diablo region King, P. B., 1940, Older rocks of Van Horn region, Texas: Am. (p. 451). Subsequent work has added many details to these Assoc. Petroleum Geologists Bull., v. 24, p. 143-156. results, but has not modified the general conclusions. Summary of results of present investigation on Precam­ Sellards, E. H., and others, 1935, Economic geology of Texas, in brian rocks of Sierra Diablo region, which are given in Structural and economic geology, v. 2 of The geology of more detail in King and Flawn (1953) and present report. Texas: Texas Univ. Bull. 3401, p. 215-868. Contains summaries, compiled by C. L. Baker, of copper Miller, A. K., and Furnish, W. M., 1940a, Permian ammonoids deposits (p. 410-411), ground water (p. 373-380), and other of the Guadalupe Mountain region and adjacent areas: resources of Sierra Diablo region. Geol. Soc. America Spec. Paper 26, 242 p. Arick, M. B., 1935, Early Paleozoic unconformities in trans-Pecos Includes description of Propinacoceras Jcnighti Miller and Texas: Texas Univ. Bull. 3501, p. 117-121. Furnish from Bone Spring Limestone of Sierra Diablo Observations on Sierra Diablo region (p. 118-119) include region (p. 42-44). reference to unconformity between Van Horn and Bliss 1940b, Studies of Carboniferous ammonoids, Pts. 5-7: Sandstones and to supposed occurrence of Middle Ordo­ Jour. Paleontology, v. 14, no. 6, p. 521-543. vician rocks in the northeastern Sierra Diablo. Includes description of the ammonoids Diaftoloceras varir Baker, C. L., 1935, Precambrian unconformities in the trans- costatum Miller and Furnish and Pseudoparalegoceras 6eZ- Pecos region: Texas Univ. Bull. 3501, p. 113-114. Ulineatum Miller and Furnish from "Smithwick horizon of Includes interpretation of Precambrian sequence in Sierra Magdalena limestone" in Sierra Diablo (p. 527-532) ("fos­ Diablo region, based on existing publications by Richardson siliferous shale of Pennsylvanian age" of present report). and King. Smith, J. F., Jr., 1940, Stratigraphy and structure of the Devil King, P. B., 1935a, Unconformities in the later Paleozoic of trans- Ridge area, Texas: Geol. Soc. America Bull., v. 51, p. Pecos Texas: Texas Univ. Bull. 3501, p. 131-135. 597-638. Includes remarks on unconformity at base of Hueco Lime­ Geology of deformed Cretaceous rocks in an area south­ stone in Sierra Diablo region and elsewhere and on sup­ west of Sierra Diablo region, part of which forms southwest posed absence of an unconformity at top of Hueco (p. 133- corner of present report area. 134). 1941, Geology of the Eagle Spring area, Eagle Mountains, 1935b, Outline of structural development of trans-Pecos Hudspeth County, Texas: Field and Lab., v. 9, p. 70-79. Texas: Am. Assoc. Petroleum Geologists Bull., v. 19, p. 221- 261. Description of a small area just south of southwestern General account of structure of Trans-Pecos Texas, in­ part of report area. cluding preliminary results of investigation in Sierra Diablo King, P. B., 1942, Permian of west Texas and southeastern region. New Mexico: Am. Assoc. Petroleum Geologists Bull., v. 26, Dunbar, C. O., and Skinner, J. W., 1937, Permian Fusulinidae of p. 535-763. Texas, in Upper Paleozoic ammonities and fusulinids, v. 3 Summarizes final results of present investigation in of The geology of Texas: Texas Univ. Bull. 3701, p. 519- Sierra Diablo region on Permian stratigraphy (p. 556-575) 825. and associated structural features (p. 613-634). INTRODUCTION 9

Wheeler, R. R., 1942, Cambro-Ordovician of southwest [abs.]: Lists nine species of brachiopods from El Paso Limestone Geol. Soc. America Bull., v. 53, p. 1812-1813. of Sierra Diablo region (p. 453) ; descriptions of two of the species (Syntrophina magnet Ulrich and Cooper and Dia- Proposes correlations of El Paso Limestone and Bliss phelasma oJclahomense Ulrich and Cooper) are based in part Sandstone of Franklin Mountains and Sierra Diablo which on specimens collected in Beach Mountain section. have not been substantiated by any other stratigrapher. Evans, G. L., 1943, Progress report on copper investigations: Jackson, A. T., 1948, West Texas caves and shelters, in The Texas Univ. Bur. Econ. Geology Mineral Resources Circ. 24, caves of Texas: Natl. Speleol. Soc. Bull. 10, p. 69-76. . 6 p. Includes notes on Bat Cave and Potash Mine shelter in Brief summary of an extensive investigation of copper Sierra Diablo region (p. 71-72); photographs of Bat Cave mines and prospects in Sierra Diablo region and adjacent on p. 113. areas. King, P. B., 1948, Geology of the southern Guadalupe Moun­ Adams, J. E., 1944, Highest structural point in Texas: Am. tains, Texas: U.S. Geol. Survey Prof. Paper 215, 183 p. Assoc. Petroleum Geologists Bull., v. 28, p. 562-564. D949J Analyzes criteria for recognition of structurally high Detailed description of sequence of Permian rocks of areas and concludes that "Van Horn dome" in southern part Leonard and Guadalupe age in Guadalupe Mountains north of Sierra Diablo region is not the highest structural point of Sierra Diablo region, with incidental reference to rocks in Texas. of Wolfcamp and Leonard age in Sierra Diablo region (p. 12-13). Maps and text also summarize structure and King, P. B., and Knight, J. B., 1944 [Geologic map of the] Sierra geomorphology of Sierra Diablo region (p. 118-120, pis. Diablo region, Hudspeth and Culberson Counties, Texas: 21,23). U.S. Geol. Survey Oil and Gas Inv. Map 2. Map of present report area, based on field surveys of Adams, J. E., and others, 1949, The Permian rocks of the trans- present investigation, but not adjusted to an accurate top­ Pecos region: West Texas Geol. Soc. Field Trip Guidebook, ographic base. Nov. 6-9,1949, 94 p. King, P. B., King, R. E., and Knight, J. B., 1945, Geology of Includes road log in Sierra Diablo region (p. 58-81), Hueco Mountains, El Paso and Hudspeth Counties, Texas: based partly on publications, but including original observa­ U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 36, 2 sheets. tions. Includes comment on possible correlation of Pennsyl- King, P. B., 1949, Regional geologic map of parts of Culberson vanian rocks exposed in Sierra Diablo (sheet 2). and Hudspeth Counties, Texas: U.S. Geol. Survey Oil and Gas Inv. Prelim. Map 90. Miller, A. K., 1945, Permian nautiloids from the Glass Moun­ tains and the Sierra Diablo of west Texas: Jour. Paleon­ Map of a large part of northern Trans-Pecos Texas, in­ tology, v. 19, p. 282-294. cluding Sierra Diablo region, where it is based on results of present investigation. Includes identification and description of nautiloid species from Bone Spring Limestone in the Sierra Diablo. King, P. B., and others, 1949, Pre-Permian rocks of the trans- Sample, R. D., and Gould, E. E., 1945, Geology and ore deposits Pecos area and southern New Mexico: West Texas GeoL of the Allamoore-Van Horn district, Hudspeth and Culber­ Soc. Field Trip Guidebook, Nov. 6-9, 1949, 67 p. son Counties, Texas: U.S. Geol. Survey open-file report, 22 p. Includes a summary of pre-Permian rocks and road log Report on examination of Blackshaft, Hazel, and other in Sierra Diablo region (p. 18-34), mostly compiled from mines and prospects of southern foothills of the Sierra publications. Diablo, and their geological environment. Many of the data in this report are reproduced in King, P. B., and Flawn, Smith, J. F., Jr., and Albritton, C. C., Jr., 1949, Conglomerates P. T. (1953). of western trans-Pecos Texas and their relation to a tec­ tonic boundary [abs.]: Geol. Soc. America Bull., v. 60, Cloud, P. E., Jr., and Barnes, V. E., 1946, The Ellenburger group p. 1921. of central Texas: Texas Univ. Pub. 4621, 473 p. [1948]. Discusses relation of conglomerates in Precambrian, Deals mainly with central Texas, but includes discussion Permian, and Cretaceous rocks in Sierra Diablo region and of subdivisions and correlation of Bliss Sandstone and El west of it to an unstable area toward the southwest. Paso Limestone in Sierra Diablo region and Franklin Mountains (p. 66-74) and detailed section of these forma­ Albritton, C. C., Jr., and Smith, J. F., Jr., 1950, Evidence for tions on Beach Mountain (p. 352-361). aridity in west Texas during Early Cretaceous [abs.]: Geol. Soc. America Bull., v. 61, p. 1440. Miller, A. K., and Youngquist, W. L., 1947, American Permian nautiloids: Geol. Soc. America Mem. 41, 218 p. Interprets chalky limestone and limestone conglomerate at base of Campagrande Limestone as an ancient soil pro­ Deals further with nautiloids from Bone Spring Lime­ file, formed in an arid or semiarid climate. stone in the Sierra Diablo that were reported on by Miller (1945). Broadhurst, W. L., Sundstrom, R. W., and Weaver, D. E., 1951, Public water supplies in western Texas: U.S. Geol. Survey Cloud, P. E., Jr., 1948, Brachiopods from the Lower Ordovician Water-Supply Paper 1106,168 p. of Texas: Harvard Coll. Mus. Comp. Zoology Bull., v. 100, p. 451-472. Gives data on municipal water wells at Van Horn (p. 37). 10 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS DeFord, B. K., and others, 1951, Apache Mountains of trans- Cooper, G. A., and Stehli, F. G., 1955, New genera of Permian Pecos Texas: West Texas Geol. Soc. 1951 Fall Field Trip brachiopods from west Texas: Jour. Paleontology, v. 29, p. Guidebook, Oct. 26-27,1951, 56 p. 469-474. Deals primarily with Apache Mountains east of Sierra Includes description of Spyridophoroa reticulata (King) Diablo region, but includes a note on pre-Permian rocks of from Bone Spring Limestone of the Sierra Diablo (p. 472- the Beach and Baylor Mountains (p. 52-53). 473). Hood, J. "W., and Scalapino, B. A., 1951, Summary of the de­ King, P. B., 1955, Orogeny and epeirogeny through time, in velopment of ground water for irrigation in the Lobo Flats Poldervaart, Arie, ed., The crust of the earth: Geol. Soc. area, Culberson and Jeff Davis Counties, Texas: Texas America Spec. Paper 62, p. 723-740. Board Water Engineers Bull. 5102, 25 p. Mentions the deformational history of Precambrian time Discusses occurrence of ground water in Lobo Flats, a in the Van Horn region as an example of preservation of southern extension of the Salt Basin just south of the re­ the record of orogeny (p. 723-726). port area. Flawn, P. T., 1956, Basement rocks of Texas and southeastern Flawn, P. T., 1952, The Hazel copper-silver mine, Culberson New Mexico: Texas Univ. Pub. 5605,261 p. County, Texas: Texas Univ. Bur. Econ. Geology Bept. Inv. Includes discussion of Van Horn mobile belt, based mainly 9, 23 p. on outcrops in and near Sierra Diablo region, with specula­ Beport on the Hazel mine preliminary to that given in tions as to subsurface extent of the belt (p. 32-36). publication of King and Flawn (1953). Masson, P. B., 1956, Age of igneous rocks at Pump Station Hills, Dunbar, C. O., 1953, A zone of Pseudoschwagerina low in the Hudspeth County, Texas: Am. Assoc. Petroleum Geologists Leonard series in the Sierra Diablo, trans-Pecos Texas: Am. Bull., v. 40, p. 501-518. Jour. Sci., v. 251, p. 798-813. Discussion of petrography and structure of Precambrian Describes a new species of fusulinid from lower part of rocks exposed northwest of Sierra Diablo region, with in­ Bone Spring Limestone and discusses its occurrence, and cidental mention of Precambrian rocks in southern Sierra that of other f usulinids, in the Victorio Peak section in the Diablo and Carrizo Mountains. Sierra Diablo. Moody, J. D., and Hill, M. J., 1956, Wrench-fault tectonics: Gillerman, Elliot, 1953, Fluorspar deposits of the Eagle Moun­ Geol. Soc. America Bull., v. 67, p. 1207-1246. tains, trans-Pecos Texas: U.S. Geol. Survey Bull. 987, 98 p. Interprets Hillside fault of southern part of Sierra Di­ Beport on geology and fluorspar deposits of an area south­ ablo region as having large left-lateral strike-slip displace­ west of Sierra Diablo region, whose extreme north edge ment, and as being a major unit of the "Texas lineament" extends into present report area. (p. 1223-1224). Haigh, B. B., and others, 1953, Sierra Diablo, Guadalupe, and Yochelson, E. L., 1956, Euomphalacea, Trochonematacea, Pseu- Hueco areas of trans-Pecos Texas: West Texas Geol. Soc. dophoracea, Anomphalacea, Craspedostomatacea, and Platy- 1953 Fall Field Trip Guidebook, Nov. 6-7, 1953, 91 p. ceratacea, pt. 1 of Permian Gastropoda of the southwestern Includes road log in Sierra Diablo region (p. 5-37), based United States: Am. Mus. Nat. History Bull., v. 110, p. partly on publications, but including original observations. 179-276. King, P. B., and Flawn, P. T., 1953, Geology and mineral de­ Description of gastropods from Permian rocks in many posits of Precambrian rocks of the Van Horn area, Texas: parts of Texas, New Mexico, and Arizona, including those Texas Univ. Pub. 5301,215 p. from 38 collections from Sierra Diablo region, with an Comprehensive report on Precambrian rocks and associ­ interpretation of the habitat of the groups considered. ated formations of Van Horn area, part of which lies within "Molluscan ledges" of Bone Spring Limestone in Sierra present map area. Chapters by Flawn describe Precambrian Diablo discussed (p. 189-190). rocks of Wylie and Carrizo Mountains (p. 41-44, 51-69) ; a Albritton, C. C., and Smith, J. F., 1957, The Texas lineament: chapter by King describes Precambrian rocks of Sierra Internat. Geol. Gong., 20th, Mexico City 1956, sec. 6, pt. 2, Diablo foothills (p. 71-121). Also includes descriptions of p. 501-518. copper, silver, talc, and other mineral deposits in Sierra Summarizes earlier published accounts of the lineament Diablo foothills, Carrizo Mountains, and elsewhere (p. and new evidence for an against its validity. Proposes 150-173). that the type locality of the lineament be along Eagle Flat, Follett, C. B., 1954, Becords of water-level measurements in in the southern parts of the Sierra Diablo and Sierra Blanca Culberson, Hudspeth, and Jeff Davis Counties, Texas: Texas regions, west Texas. Board Water Engineers Bull. 5415,31 p. Hay-Boe, Hugh, 1957, Geology of Wylie Mountains and vicinity, Includes data on wells in Lobo Flats and Wildhorse Culberson and Jeff Davis Counties, Texas: Texas Univ. Valley districts, just south and east of report area. Bur. Econ. Geology Geol. Quad. Map 21. Stehli, F. G., 1954, Lower Leonardian Brachiopoda of the Sierra Geologic map and text dealing with an area mainly east Diablo: Am. Mus. Nat. History Bull., v. 105, p. 261-358. and south of Sierra Diablo region, but extending into Summarizes stratigraphy of Permian rocks in the Sierra southeast corner of present map area. Diablo, interprets their conditions of deposition, and treats Ramlrez, J. C., and Avecedo, C. F., 1957, Notas sobre le geologla in detail the brachiopods and their ecology in lower part of de Chihuahua: Assoc. Mexicana Geologos Petroleros Bol., Bone Spring Limestone near Victorio Peak. v. 9, p. 583-770. GEOGRAPHY 11

An extensive account of the geology of the State of Chi­ Geologic map and descriptive text, covering the area just huahua, adjoining Trans-Pecos Texas on the southwest, south of the present report area, including data on the with incidental references to formations and structures in Carrizo Moutain Formation and Hueco Limestone. the Sierra Diablo region (p. 605-607, 613-614, 620, 630, etc.). Warner, L. A., Holser, W. T., Wilmarth, V. R., and Cameron, Yochelson, E. L., and Bridge, Josiah, 1957, The Lower Ordo- E. N., 1959, Occurrence of nonpegmatite beryllium in the vician gastropod Ceratopea: U.S. Geol. Survey Prof. Paper United States: U.S. Geol. Survey Prof. Paper 318, 198 p. 294, p. 281-304. Includes description by Holser of Cave Peak intrusive complex (Mine Canyon stock of present report) (p. HO­ Analysis of a gastropod genus which is abundant in some WS), notes on Sierra Prieta intrusive (p. 133), and obser­ Lower Ordovician sequences, including a summary of its vations on related igneous rocks elsewhere in the Trans- occurrence in the El Paso Limestone of the Sierra Diablo Pecos Region (p. 130-135). region and other areas (fig. 103), and a description of Ceratopea unguis Yochelson and Bridge, based on speci­ Finks, R. M., 1960, Late Paleozoic sponge faunas of the Texas mens from Beach Mountain. region; the siliceous sponges: Am. Mus. Nat. History Bull., v. 120, p. 3-160. Batten, R. L., 1958, Pleurotomariacea, Portlockiellidae, Pyma- Includes description of specimens of Permian sponges topleuridae, and Eotomatiidae, pt. 2 of Permian Gastropoda from Sierra Diablo region and a discussion of faunal facies of the southwestern United States: Am. Mus. Nat. History of the sponges, including those of Leonard age in the Sierra Bull., v. 114, p. 159-246. Diablo (p. 28-33). Includes description of gastropod specimens from Sierra Diablo region. Yochelson, E. L., 1960, Bellerophontacea and Patellacea, pt. 3 of Permian Gastropoda of the southwestern United States: DeFord, R. K., and Brand, J. P., 1958, Cretaceous platform and Am. Mus. Nat. History Bull., v. 119, p. 211-293. geosyncline, Culberson and Hudspeth Counties, trans-Pecos Includes description of gastropod specimens from Sierra Texas: Soc. Econ. Paleontologists and Mineralogists, Per­ Diablo region. Bellerophon coquina in lower part of Hueco mian Basin Sec., 1958 Field Trip Guidebook, 90 p. Limestone discussed briefly (p. 216). Description of a traverse across the Cretaceous rocks Martinez, J. D., Statham, E. H., and Howell, L. G., 1960, A just east and south of the report area. Includes two charts review of paleomagnetic studies of some Texas rocks, in of plotted stratigraphic sections of Cretaceous rocks in Aspects of the geology of Texas, a symposium: Texas Sierra Blanca and Sierra Diablo regions (flg. 11, p. 23; Univ. Pub. 6017, p. 15-47. fig. 12, p. 25). Includes paleomagnetic data on red sandstone of Hazel Fillman, Louise, chm., 1958, Lexicon of pre-Pennsylvanian Formation (p. 19). stratigraphic names of west Texas and southeastern New Kepple, H. A., and others, 1962, Leonardian facies of the Sierra Mexico: Midland, Tex., West Texas Geol. Soc., 153 p. Diablo region, west Texas: Guidebook 1962 field trip: Short discussions of all pre-Permian formations of west Permian Basin Section, Soc. Econ. Paleontologists and Texas-southeastern New Mexico region, including those in Mineralogists, Pub. 62-7,148 p. the Sierra Diablo region. Incidental mention is made of Includes road log in Sierra Diablo region, and articles occurrences in the Sierra Diablo and other outcrop areas, on geology by five authors. but main emphasis is on subsurface character and distri­ Underwood, J. R., Jr., 1962, Geologic map of Eagle Mountains bution in West Texas basin. and vicinity, Hudspeth County, Texas: Texas Bur. Econ. Flawn, P. T., 1958, Texas miners boost talc output: Eng. and Geol. Quad. Map 24, scale 1:48,000. Mining Jour., v. 159, p. 104-105; repr., Texas Bur. Econ. Geologic map includes southwestern part of present Geology Rept. Inv. 35. report area and adjacent regions to south and west. Notes on geologic occurrence, mining methods, and pro­ duction of talc from Precambrian rocks in southern foot­ GEOGRAPHY hills of Sierra Diablo. The Sierra Diablo region lies in the Trans-Pecos Pratt, W. E., 1958, Large-scale polygonal jointing: Am. Assoc. province of Texas, or the west-projecting part of the Petroleum Geol. Bull., v. 42, p. 2249-2251. State between the Pecos River and the Rio Grande Unconsolidated deposits of the Salt Basin east of Baylor (fig. 1). Topography, climate, and vegetation of this Mountains are fractured into polygons about 2,000 ft across, as a result of undetermined processes. dry mountainous province are more like those of New Mexico, Arizona, and Chihuahua than those of the rest Howe, H. J., 1959, Montoya group stratigraphy (Ordovician) of Texas. The northern part of the province, in which of trans-Pecos Texas: Am. Assoc. Petroleum Geologists Bull., v. 43, p. 2285-2332. the Sierra Diablo region is situated, has the character­ istic topography of the Basin and Range province of the A regional survey and interpretation of Montoya Lime­ stone, including observations on the formation in the Bay­ States to the west and northwest, with broad, plateau- lor Mountains and a detailed stratigraphic section there like mountain masses that rise in steep escarpments (flg. 29, p. 2328). above intermontane plains or basins. The report area Twiss, P. C., 1959, Geology of Van Horn Mountains, Texas: is dominated by one of the mountain masses, the Sierra Texas Univ. Bur. Econ. Geology Geol. Quad. Map 23. Diablo, which rises steeply on the east above one of the 106 C 105 104 c

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1. Map of parts of western Texas and southern New Mexico, showing area covered by report on Sierra Diablo region, A., and areas covered by recently published reports on adjacent areas: B, Boyd, 1958, El Paso Gap quadrangle; 0, Hayes and Koogle, 1958, Carlsbad Caverns West quadrangle; D, Hayes, 1957, Carlsbad Cavern East quadrangle; E, King, 1947, southern Guadalupe Mountains; F, Albritton and Smith, 1965, Sierra Blanca area; G} Gillerman, 1953, Eagle Mountains fluorspar districts; H, Twiss, 1959, Van Horn Mountains; and I, Hay-Roe, 1957, Wylie Mountains. GEOGRAPHY 13 intermontane plains, the Salt Basin, and slopes gently The escarpments of the Sierra Diablo are outlined by on the west into the less diversified expanse of the faults that have downthrown the rocks on their topo­ Diablo Plateau.1 graphically lower sides on the east by a fault of gen- The climate of the report area is arid to semiarid. eraly northerly trend but with bight-and-cusp pattern, A 20-year record at Van Horn (1939-58) indicates an on the north and south by faults that trend west-north­ annual rainfall that fluctuated between less than 5 inches west. The Bay lor Mountains are likewise a fault block, and more than 27 inches, averaging 9.39 inches. Rain­ implanted in the southern bight of the fault on the east. fall increases with altitude, as shown by a greater den­ The summits of the Bay lor Mountains are even crested sity of vegetation in the Sierra Diablo and other moun­ like those of the Sierra Diablo and, like them, were tains than in the lower country near Van Horn. An probably derived from the pre-Cretaceous peneplain, arid or semiarid climate has existed in the region since but they stand about a thousand feet lower (sections H- the last glacial period and at least intermittently into H' and /-/', pi. 16). The Baylor Mountain block far earlier times. It has thus conditioned not only the forms an intermediate step between the heights of the modern erosional regime and vegetation, but also the Sierra Diablo and the depths of the Salt Basin. soils and landforms that require a longer period for The eastern escarpments of the Sierra Diablo and their creation (Carter and others, 1928, p. 7-11, 25-48). Baylor Mountains were shaped directly by faulting, al­ though they were for the most part modified by subse­ MOUNTAIN AREAS quent erosion. The Baylor Mountains escarpment is The Sierra Diablo, or dominant mountain mass of the now much indented at the mouths of valleys issuing region, is about 25 miles long, and has extensive sum­ from the mountains. The upper part of the Sierra mit areas more than 6,000 feet in altitude; its highest Diablo escarpment has receded a mile or so from the peak (at North Diablo triangulation station) attains trace of the fault along its base; it is also deeply 6,638 feet (pi. 9). West of the crest the summit areas breached by Victorio and Apache Canyons, which ex­ descend 2,000 feet in about 10 miles, and the range tend far headward into the range. These canyons prob­ merges with the lower, less diversified Diablo Plateau. ably originated from major valleys that drained west­ The summit areas, formed of Permian limestone, are ward before they were diverted to their present courses. conspicuously even crested. In most places the even However, uplift of the Sierra Diablo was so prolonged crests are nearly parallel to the strata beneath, but they that the lower part of its escarpment in the segment truncate the abruptly flexed strata near the middle of north of the Baylor Mountains is newer, and is conse­ the range and the limestone units that form the crests quently less eroded. Here, the escarpment ends on an to the north and south belong to different formations. even baseline, bordered on the mountainward side by a The even-crested summit areas were shaped by a pene­ steep rock bench and on the basinward side by a high plain on which Cretaceous rocks were once deposited, extensive alluvial slope, which is itself broken by a low but from which these have now been stripped. Their fault scarp at its north end. westward slope carries the peneplain under Cretaceous The eastern escarpment of the Sierra Diablo is rocks, still preserved in buttes and mesas in the Diablo divided into three topographically contrasting seg­ Plateau in the western part of the report area. Rising ments as a result of intersection of the bordering abruptly nearly a thousand feet above the plateau north­ fault by two west-northwestward-trending monoclinal west of the Sierra Diablo is the dark jagged, rocky flexures, each of which has depressed the strata on the Sierra Prieta, formed by a body of igneous rock that north so far as to preserve a different sequence of was intruded into the Permian and Cretaceous strata. formations. In the southeastern Sierra Diablo, south To the east, north, and south the Sierra Diablo ends of the southern, or Victorio, flexure, the escarpment abruptly in steep escarpments that face toward the in­ consists of smoothly rounded lower slopes, cut on red termontane plains of the Salt Basin and Eagle Flat. sandstone of the Precambrian Hazel Formation, and Its northeastern part rises directly 3,000 feet above the an upper sheer cliff of Hueco Limestone, the lowest floor of the Salt Basin, without intervening foothills, but unit of the Permian sequence (left end of upper view, the lower 500-1,000 feet of the slope is alluvial (sections pi. 10). In the northeastern Sierra Diablo, north of F-F' and G-G'', pi. 16). Farther south the lower Bay- the Victorio flexure, the red sandstone is beneath the lor Mountains and Beach Mountain stand between the surface, and the escarpment is formed entirely of Sierra Diablo and the Salt Basin, and a belt of dis­ Permian limestones. Here it is two-storied, with a continuous foothills stands between it and Eagle Flat. bench of Hueco Limestone below and cliffs of light-gray 1 In some geologic publications the Sierra Diablo has Itself been Victorio Peak Limestone at the top, separated by referred to as the Diablo Plateau, but this usage is erroneous and mis­ leading. For the relative extent of the two features, see figure 1. smoothly rounded slopes cut on the intervening less 14 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS resistant thin-bedded or shaly Bone Spring Limestone is utilized by the line of the Texas and Pacific Railway (left end of lower view, pi. 10). On the northern, or in its course through the mountains (section T-T', Babb, flexure, at the north end of the Sierra Diablo, pi. 16). the Hueco and Bone Spring Limestones in their turn LOWLAND AREAS pass beneath the surface (upper view, pi. 12). In the hills which are a continuation of the Sierra Diablo on Largely because of the long-continued aridity, the the north, the top of the Victorio Peak Limestone forms region has an interior drainage, leading to the Salt a bench at the edge of the Salt Basin which is sur­ Basin on the east and the smaller basin of Eagle Flat mounted by widely spaced mesas, capped by a re­ on the southwest, which have no outlets to the sea. sistant layer in the Guadalupe Series, the Goat Seep South of the region, however, this area of interior Limestone. drainage is being attacked by streams that are cutting By contrast with the escarpment on the east side of headward from the through-flowing Rio Grande. the Sierra Diablo, that on the south side was produced The Salt Basin, or dominant lowland of the report merely by erosion of a terrain that was faulted at a area, lies east of the mountains and extends far north­ remote period. The escarpment is the southernmost ward, past the Texas-New Mexico State line (fig. 1). of several, each formed along faults downthrown to The Salt Basin is 90 miles long, 5 to 15 miles wide, the south, by which both the strata and the topographic and trends north-northwestward parallel to the grain surface step down from the heights of the northern of the mountains and plateaus which border it (King, part of the range (section P-P'', pi. 16). The escarp­ P.B., 1948, pi. 23). Its lowest part, east of the north­ ments were produced, at least in part, by stripping of eastern Sierra Diablo, stands at an altitude a little weak Cretaceous beds off the strong Permian limestone below 3,600 feet. It is a closed depression and the beds; Cretaceous beds are still preserved on the down- focus of a large region of interior drainage. At its thrown sides of some of the faults toward the west. north and south ends it receives drainage from the high Toward the east the escarpments have been further relatively well-watered Sacramento and Davis Moun­ modified by undercutting of weak red sandstone of the tains ; on the west it receives drainage from the Sierra Precambrian Hazel Formation, so that the capping Diablo and Diablo Plateau. Along the Guadalupe and Permian limestone is greatly frayed, and has receded Delaware Mountains on the east the drainage area is irregularly from the original fault traces. smaller, the crests of these mountains being so close Relief in the southern foothills, between the Sierra to the basin that most of their water courses lead east­ Diablo and Eagle Flat, is likewise a product of unequal ward to the Pecos River. erosion of rocks of diverse structures and ages. The Eagle Flat, a less extensive lowland, lies southwest of Streeruwitz, Bean, and Millican Hills to the west are the Sierra Diablo, trending west-northwest across the low and are separated by broad alluvium-covered rock- regional grain for about 25 miles. It receives drainage cut plains, but the Carrizo Mountains and Beach from the southern Sierra Diablo and Diablo Plateau, Mountain to the east are higher and rise steeply above and to a lesser extent from the mountains on the south, the Salt Basin, probably with an intervening fault. most of whose water courses lead southwestward to the Beach Mountain, a rugged mass with an area of about Rio Grande. The eastern part of Eagle Flat drains by a 15 square miles, projects a thousand feet above the roundabout course south of the Carrizo Mountains into lower hills to the west, and is capped by a remnant of the Salt Basin; but the western part is an independent strong Ordovician limestone (pi. 2). The underlying depression whose lowest point is at Grayton Lake, which red massive Van Horn Sandstone, exposed west and has an altitude of a little more than 4,000 feet. southwest of Beach Mountain in the Red Valley and Both the Salt Basin and Eagle Flat are tectonic de­ along Hackberry Creek, has been carved into tables, pressions, produced mainly by downfaulting of their battlements, and towers to produce some of the most floors relative to the mountains that surround them. picturesque scenery in the region. Differential erosion They have been deeply filled by unconsolidated deposits is further demonstrated along the Hillside fault in the of Quaternary and possibly of late Tertiary age washed Carrizo Mountains to the south. The downthrown in from higher lands around them. The unconsolidated northern side of the fault is bordered by a steep obse- deposits have been extensively drilled for water in the quent faultline scarp of Permian limestone and Cre­ Salt Basin, but in few places deeply enough to determine taceous sandstone, whereas the metamorphic rocks of the configuration of their base. A well in the basin the Precambrian Carrizo Mountain Formation on the north of the Sierra Diablo region is reported to have southern upthrown side have been cut into a valley that been sunk 1,620 feet without reaching the base of the GEOGRAPHY 15 deposits. Wells at Van Horn are shallower, as are modification by the wind of the clay hills is indicated those in the irrigation districts of Wildhorse Valley and on air photographs by superposition on the gross fea­ Lobo, to the east and south; but a few of them have pene­ tures of a more delicate grain trending east or east- trated bedrock. Less is known of the depths of the un- southeast. Between the alkali flats and hills of gyp- consolidated deposits in Eagle Flat, but the Southern siferous clay are tracts of level meadowland, underlain Pacific railroad well at Hot Wells was drilled into them by brown clay which supports more grass cover than to a depth of more than 1,000 feet (Baker, 1927, p. 37- that on the gypsif erous clay hills. 40; Broadhurst and others, 1951, p. 57; Hood and Scala- The alluvial slopes, formed by coalescence of the fans pino, 1951, p. 4-5; Follett, 1954, p. 6-15). built by streams which issue from the mountains, are The surface of the southern part of the Salt Basin, as continuous along the entire western border of the Salt far as the north end of the Baylor Mountains, consists Basin at the bases of the Sierra Diablo and other of alluvial slopes extending from the bordering moun­ ranges, except at the northeast corner of the Baylor tains to the axis of the depression along which Wild- Mountains where the rock hills have been partly sub­ horse Creek drains northward. North of the Baylor merged by more distantly derived detritus. The radii Mountains the alluvial slopes on each side do not meet, and gradients of the fans, and the texture of their com­ and between them is a nearly level floor more than 5 ponents, are related to the areas of drainage in the miles wide, formed probably by deposition on the bot­ mountains of the streams which supply them and to the toms of lakes during late Pleistocene time or earlier. recency of faulting along the mountain bases. Large On the alluvial slopes streams are mostly actively trans­ fans of low gradient, composed of relatively fine ma­ porting material away from the mountains, although terial, have been built by Hackberry and Sulphur near their lower ends on the east side the sandy constitu­ Creeks near Van Horn and by Eed Wash, Victorio ents are now being shifted even more vigorously by the Canyon, and Apache Canyon farther north; lesser fans wind. Streams are thus prograding material toward with steeper gradients, composed of coarser material, the basin floor, yet they are not depositing material on have been built by smaller streams in the intervening the floor itself. The floor appears to be virtually stable, segments. The steepest coarsest fans are those along except for minor leveling or deleveling by the wind. As the segment of the Sierra Diablo north of the Baylor the Salt Basin has interior drainage, theoretically its Mountains where relatively recent faulting is most streams should be adjusted to a slowly rising base level; likely. One of the fans in this segment, 1 mile north but the stability of the floor indicates that this condition of Victorio Canyon, has a gradient of 1,000 feet per is not now attained. mile, a radius of six-tenths of a mile, and was built The floor of the Salt Basin is diversified by alkali below a gulch on the escarpment with a drainage area flats (locally called salt lakes) and by hills of gypsifer- of less than half a square mile. On some of the steeper ous clay. One set of alkali flats is east of the northern fans the courses of recent drainage are marked by trains part of the Sierra Diablo, another just north of the end of fresh boulders and gravel, but drainage on fans of of the range. They may be final remnants of more ex­ somewhat larger dimensions is generally incised in the tensive lakes of an earlier period, yet today they contain fan surface, in places as much as 40 feet, the depth de­ water only at long intervals. They are maintained creasing downslope. Most of the drainage on the principally by the wind, which sweeps material from largest fans is fainter and less incised, but Sulphur their surfaces down to ground-water level, an effective Creek forms a wide braided gravel-covered channel limit to downward erosion. The peculiarly fretted out­ nearly to the lower edge of its fan. lines of the alkali flats north of the Sierra Diablo were Most of the streams draining eastward from the probably shaped by this wind work. The hills of gyp- mountains into the Salt Basin have cut downward into siferous clay were also formed by the wind. Over exten­ the rocks of the mountains and have built up alluvial sive areas to the north they have no clearly discernible fans in front; they have done little leveling of the bed­ pattern, but on the east side of the floor opposite the rock by sideward cutting. Chief exceptions are Hack- northern part of the Sierra Diablo they form a remark­ berry Creek, Sulphur Creek, and Red Wash, which able set of closely spaced parallel ridges, trending north- drain the edges of Beach Mountain and the Baylor northwest, which curve westward at the south end of the Mountains and which have cut broad areas of lowland floor, just north of the Baylor Mountains. These, and in rocks that are mainly not calcareous. Recently others like them farther north, probably mark the leveled areas are partly masked by alluvial deposits; shores of the shallow lakes of Pleistocene time, along areas leveled earlier are indicated by terraces a hunded which the clays were raised into low dunes. A later feet or more above modern drainage, which are in part 16 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS capped by older alluvial deposits. Cause of the dissec­ Pecos province to connect the settlements on the Rio tion of the earlier terraces is undetermined, but it may Grande with those farther east. A trail from San be related to continued downfaulting of the Salt Basin Antonio to El Paso, which was subsidized as a mail relative to the adjacent mountain areas. route in 1850, passed south of the Sierra Diablo, through In Eagle Flat, southwest of the Sierra Diablo, ero- Bass Canyon and Eagle Spring. The Butterfield Trail, sional and depositional processes appear to be less active which was subsidized as a mail route in 1857, passed than in the Salt Basin, partly because of its greater north of the Sierra Diablo, through Guadalupe Pass tectonic stability in the recent past, partly because of and Crow Flat. Although American authority over the circuitous drainage connection between it and the the interior of the Trans-Pecos province was virtually main basin. Alluvial slopes thus extend to the axis of relinquished during the Civil War period, a road was Eagle Flat, and extensive rock-cut surfaces have been laid out in 1863 by public subscription from the Rio formed on its north and south sides. Within the flat Grande settlements to the salt deposits of the Salt Basin, itself the fine debris has been raised by the wind into which passed near Sierra Prieta in the northwesterni low sand dunes in extensive areas, as shown on the part of the report area. topographic base map (pis. 1, 9). The last Indian battle in Texas was fought in Janu­ On the north, in the southern foothills of the Sierra ary 1881, when Capt. George W. Baylor, of the Texas Diablo, these rock-cut surfaces, now largely mantled Rangers, defeated an Apache band under the leadership by alluvium, extend between the Streeruwitz, Bean, and of their chief Victorio, in the heights of the Sierra Millican Hills which were carved from the more resist­ Diablo near the peak which now bears his name. With ant conglomerate, limestone, and volcanic units of the the construction of the Southern Pacific and Texas and Hazel and Allarnoore Formations of the Precambrian Pacific railroads a few years later, much of the isolation sequence. In the hills a time of earlier planation is of the region ended, and it was available for occupancy. suggested by accordant levels on their summits. The Sierra Diablo region was originally included in Toward the east, Sulphur and Hackberry Creeks, El Paso County, which at first covered most of the which drain into the Salt Basin, are dissecting the east­ northern Trans-Pecos Texas. In 1911 Culberson ward extensions of the rock-cut surfaces on which the County was established with Van Horn as the county streams draining into Eagle Flat are now flowing. The seat, and in 1917, Hudspeth County, with Sierra Blanca bedrock of red sandstone of the Hazel Formation has as the county seat. The only town in the report area is been scored into a network of valleys and ravines, on Van Horn, with about a thousand people, first located whose crests are gravel deposits that are remnants of a as a station on the Texas and Pacific Railway because surface that once sloped continuously toward Eagle of the availability of excellent well water from the Flat. Westward, the alluvium of the valley bottoms deposits of the Salt Basin. Its growth has been fur­ in the Hackberry and Sulphur Creek drainage areas thered because of its position on the transcontinental rises and merges with the gravel caps, so that the two highway, at the junction of U.S. Highways 80 and 90. sets of deposits cannot be differentiated in the drainage Minor settlements are Allamoore on the Texas and area of Eagle Flat. Pacific Railway and U.S. Highway 80 west of Van Horn, and Hot Wells on the Southern Pacific railroad HUMAN GEOGRAPHY AND HISTORY to the southwest. The valley of the Kio Grande near El Paso, west of Because of the arid climate and forbidding terrain, the Sierra Diablo region, was long a focus of settlement, the Sierra Diablo region has remained sparsely peopled first by agricultural Indians, later by the Spaniards until today a region of extensive landholdings used and Mexicans. Missions were founded as early as the for pasturage of cattle, sheep, and goats. During the 17th century by Franciscan monks, and by the time of last quarter of a century, modern paved highways have establishment of United States sovereignty in 1847 there been built across it U.S. Highways 80 and 90 on the were several towns and farming communities. How­ south and U.S. Highway 62 on the north, which have ever, the interior of the Trans-Pecos province, includ­ brought large numbers of automobile travelers and have ing the Sierra Diablo region, remained empty country, encouraged the development of businesses catering to which was the haunt of roving and marauding bands of them. Also, after the Second World War, extensive Indians. reservoirs of ground water were discovered in the north­ Under the American regime several stage and cara­ ern and southern parts of the Salt Basin, and these van routes were laid out across the interior of the Trans- have been developed by pumping for irrigation. Agri- STRATIGRAPHY 17 cultural areas of 10 square miles or more have thus Mississippian and Pennsylvanian rocks occur only in come into existence at Dell City, Wildhorse Valley, and fragmentary exposures, and their total thickness prob­ Lobo, to the north, east, and south of the Sierra Diablo ably does not exceed 1,000 feet. By contrast, the Per­ region (Scalapino, 1950; Hood and Scalapino, 1951; mian rocks are extensive and attain a thickness of more L. A. Wood, written commun., 1959). than 3,000 feet, although only the lower part of the Existence of copper and silver in mineralized veins system is preserved. in the Precambrian rocks of the southern part of the The Mesozoic is represented by the Cretaceous Sys­ Sierra Diablo region was discovered by some of the tem only. A sequence nearly 5,000 feet thick occurs in earliest American visitors. The vein at the Hazel mine the southwestern part of the report area and extends is reported to have been prospected as early as 1856; from the lower part of the Lower Cretaceous into the practically all the veins which have been mined were lower part of the Upper Cretaceous. In the Sierra mentioned in the reports of Streeruwitz of 1890 and Diablo itself, only the Lower Cretaceous is preserved; 1891 (Streeruwitz, 1891, 1892). The district has pro­ it consists mostly of sandstone with subordinate lime­ duced about 2 million pounds of copper and 4 million stone and marl with a thickness of less than a thousand ounces of silver, but operations have been spasmodic feet. and the possibilities of the district have seemingly not The Tertiary is represented at the surface only by been great enough to attract large-scale capital. Long widely separated intrusive igneous rocks and by small after discovery of the metallic deposits in 1952, talc was remnants of extrusive igneous rocks. Poorly consoli­ found in beds of Precambrian phyllite of the same dated sedimentary rocks of Tertiary age may underlie area; the talc is now being mined at various places the unconsolidated sedimentary rocks of Quaternary by six companies, who by 1957 had produced about age in the lowland areas of the Salt Basin and Eagle 120,000 tons. Flat. Nearly all the sedimentary rocks younger than the STRATIGRAPHY Precambrian and Precambrian (?) contain marine in­ vertebrate fossils. They are especially abundant, Most of the bedrock that crops out in the Sierra varied, and well preserved in the Permian rocks, from Diablo region consists of consolidated sedimentary rocks which large collections were made during the present of Precambrian, Paleozoic, and Mesozoic ages (pi. 1). investigation. Intrusive and extrusive igneous rocks of Precambrian The stratified rocks of the Sierra Diablo region were and Cenozoic ages occupy smaller areas. Within the laid down during progressively changing geographic mountain and foothill areas the bedrock also underlies conditions, which are partly expressed by contrasts be­ the alluvial deposits at shallow depth, but in the low­ tween the successive deposits and faunas and partly by land areas of the Salt Basin and Eagle Flat it is prob­ the many unconformities in the sequence. Some of the ably buried to great depth beneath unconsolidated sedi­ unconformities, such as those which occur between most mentary rocks of Cenozoic age. of the pre-Permian Paleozoic formations, express Precambrian rocks crop out in the foothills south merely gaps in the record, and are not accompanied and southeast of the Sierra Diablo; they are a varied by appreciable tilting or erosion of the underlying beds. sequence of sedimentary rocks many thousands of feet Several of the other unconformities indicate deep or thick, classed as the Carrizo Mountain, Allamoore, and prolonged erosion, deformation of the underlying beds, Hazel Formations. The Carrizo Mountain Formation and even marked orogeny. The Van Horn Sandstone is variably metamorphosed and is intruded by igneous thus lies on the eroded edges of the strongly deformed rocks; the Allamoore Formation contains interbedded and partly metamorphosed earlier Precambrian rocks. volcanic rocks. The Precambrian formations are over­ A lesser angular unconformity separates the Van Horn lain by the Van Horn Sandstone, as much as 700 feet from the Ordovician above. The pre-Permian Paleozoic thick, which is classed as of Precambrian (?) age. rocks were broadly folded, deeply eroded, and in places Paleozoic rocks form the greater part of the mass of removed entirely before the Permian was laid down the Sierra Diablo, as well as some of the adjacent smaller over them. Mild deformation occurred again between mountains, and include all the systems except the Cam­ Permian and Cretaceous time, and the Cretaceous was brian. The Paleozoic rocks are dominantly limestone deposited over a peneplain which bevels all the earlier or dolomite, but there are minor beds or units of shale, rocks. sandstone, conglomerate, and chert. The Ordovician, Table 1 summarizes the formations exposed in the Silurian, and Devonian rocks are about 2,000 feet thick. Sierra Diablo region. 18 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TABLE 1. Rock formations of Sierra Diablo region, Texas

Approximate thick­ System Series Formation Remarks ness (feet)

In mountain areas, alluvium, older gravel deposits, and landslide Quaternary deposits; in Salt Basin, bolson deposits, fanglomerate, and drifted sand. Basalt flows and plugs Tertiary Intrusive igneous rocks

Unconformity

«* < Eagle Ford Formation Preserved only in southwestern part 1,500 3 .ft & 35 of report area. t>UMS o O

Washita Group 350-1, 000 Kiamichi Formation Replaced northward by Cox sand­ 65 stone. Finlay Limestone 60-350 Cretaceous LowerCretaceous Cox Sandstone 500-1, 000 Comanche Campagrande Limestone Lies on pre- Cretaceous rocks, except 25-200 in southwestern part of report area. Bluff Mesa Formation In southwestern part of report area 1, 000-1, 300 only; partly equivalent to Campa­ grande limestone. Yucca Formation In southwestern part of report area 350-1, 500 only

Major unconformity

Goat Seep Limestone >200 Sandstone tongue of Lies on Cutoff shale in Sierra Diablo 150-200 Guadalupe Cherry Canyon For­ mation Brushy Canyon Forma­ In northeastern part of report area tion only

Unconformity

Permian Cutoff Shale 275 Victor! o Peak Limestone Intergrades with Bone Spring Lime­ 900-1, 500 Leonard stone Bone Spring Limestone Wedges out southwestward by inter- 900-1, 300 gradation and overlap

Unconformity

Wolf camp Hueco Limestone Varies in thickness by overlap at 300-1, 500 base and by pre-Leonard erosion at top PRECAMBRIAN AND PRECAMBRIAN (?) ROCKS 19

TABLE 1. Rock formations of Sierra Diablo region, Texas Continued

Approximate thick­ System Series Formation Remarks ness (feet)

Major unconformity

Carbon­ Pennsylvanian Beds of Pennsylvanian Disconnected exposures only Undeter­ iferous age mined Mississippian Barnett Shale Disconnected exposures only >135 Devonian Upper Devonian Beds of Devonian age 125 Silurian Middle Silurian Fusselman Dolomite 300-450 Upper Ordovi­ Montoya Dolomite 230-450 cian Middle (?) Beds of Middle (?) Ordo­ 60-80 Ordovician Ordovician vician age Lower Ordovi­ El Paso Limestone 1150 cian Bliss Sandstone 100-160

Unconformity

Precambrian(?) Van Horn Sandstone As much as 700

Major unconformity

Hazel Formation 5, 000? Allamoore Formation 2, 500?

Sequence broken Precambrian Metarhyolite and green­ Intrusive into Carrizo Mountain stone Formation Carrizo Mountain For­ As much as mation 19, 000

Base concealed

PRECAMBRIAN AND PRECAMBRIAN(?) ROCKS to Victorio Peak and westward along the south side beyond Eagle Flat section house. Near the Texas and Rocks older than the Ordovician are extensively ex­ Pacific Railway this area is separated by a downf aulted posed in the southern part of the Sierra Diablo region block of Paleozoic and Cretaceous rocks from another and for some miles south of it (pi. 1). Three forma­ area of exposure in the Carrizo Mountains. South of tions the Carrizo Mountain, Allamoore, and Hazel the Carrizo Mountains and beyond the Sierra Diablo Formations are classed as of Precambrian age; a region, Precambrian rocks emerge in smaller areas in fourth, the Van Horn Sandstone, is classed as of Pre­ other mountain uplifts on the northeast side of the cambrian (?) age. History of the terminology of these Eagle Mountains, on the west side of the Wylie Moun­ units is indicated in the table below. The Precambrian tains, and in two areas in the Van Horn Mountains. and Precambrian (?) rocks of the Sierra Diablo region (See fig. 8.) and adjoining areas were described in detail in an earlier publication (King, P. B., and Flawn, P. T., CARRIZO MOUNTAIN FORMATION 1953), of which the following account is a summary. The Carrizo Mountain Formation, probably the The largest area of exposure of the Precambrian and oldest Precambrian unit of the Sierra Diablo region, is Precambrian (?) rocks is in the foothills of the Sierra named for exposures in the Carrizo Mountains, south Diablo, extending northward along the east side nearly of the Texas and Pacific Railway at the south edge of 20 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Development of stratigraphic nomenclature of Precambrian rocks of Sierra Diablo region

Streeruwitz ,1891 Dumble, 1902 Richardson, 1914 King, P. B., 1940 King, P. B., and Flawn, P. T., This report 1953

Carboniferous Silurian Ordovician El Paso lime­ El Paso Lime­ El Paso Lime­ El Paso Lime­ stone Ordovician stone Ordovician stone Ordovician stone Bliss Sandstone Bliss Sandstone Bliss Sandstone Potsdam Upper Van Horn Sandstone Cambrian Sandstone Cambrian Van Horn Precambri- Van Horn Precambri- Van Horn Diabolo Sandstone (Cambrian) (?) or Pre­ Sandstone an(?) Sandstone an(?) Sandstone (Devonian?) cambrian Hazel Sand­ Hazel Sand­ Hazel Forma­ Hazel forma­ stone stone tion tion Millican Texan Marble Formation Allamoore Allamoore Allamoore (not classified) (placed above Limestone Formation Formation Hazel Sand­ stone) Algonkian Precambri­ Precambri­ Precambri­ an an an Intrusives in Carrizo Carrizo Schist (not discussed) Carrizo Carrizo Carrizo Mountain Formation Mountain Mountain Formation Schist Group Carrizo Mountain Formation the map area, where it forms the surface in about 25 ably homoclinal. The sedimentary rocks of the se­ square miles (pi. 1). It also crops out at the west base quence are nearly 19,000 feet thick, although this may of the Wylie Mountains in the southeast corner of the exceed their original thickness because of contortion map area (Flawn, in King P. B., and Flawn, P. T., and injection of minor sills. The sequence has been 1953, p. 41-44; Hay-Roe, 1957), as well as in the Eagle distended another 7,000 or 8,000 feet by much thicker and Van Horn Mountains farther south beyond the sills that are separately mapped. map area. The sequence consists of the following units, in de­ The Carrizo Mountain Formation is a thick body of scending stratigraphic order. The sequence is inter­ variously metamorphosed sedimentary rocks, which rupted by intrusive igneous rocks, but these are indi­ have been intruded by large volumes of igneous rocks; cated only where they break the succession completely. the latter are separately described under the succeed­ Titles of the units are those used by Flawn in his ing heading. On the geologic map (pi. 1) the only original description (in King, P. B., and Flawn, P. T., differentiation made in the sedimentary rock is be­ 1953, p. 52-58). tween arkose and quartzite on the one hand, and vari­ ous other rocks, mainly schist, slate, and limestone, on Stratigraphic units of Carrizo Mountain Formation in Carrizo Mountains the other. However, in most areas the formation in­ Approximate thickness cludes distinctive, varied units that could ranks as for­ (feet) mations, were it not for their small areas of exposure. 11. Limestone: Fine-grained hard brown calcare­ In each of the areas these units lie in a stratigraphic ous rock, exposed on one hill at east edge of sequence, partly disrupted by igneous intrusions or mountains. Separated by metarhyolite from obscurred by metamorphism, but correlation between rest of sequence; so relations to other units are uncertain; it may overlie them __ (?) sequences in the different areas has not been established. (Metarhyolite intrusive) SEQUENCE IN CARRIZO MOUNTAINS 10. Feldspathic metaquartzite and meta-arkose: Fine-grained light-gray feldspathic meta­ In the Carrizo Mountains the Carrizo Mountain quartzite and sericitic meta-arkose, exposed Formation, and the igneous rocks which intrude it, in low hills on southeast edge of mountains. project in jagged parallel ridges, mostly trending Foliation is probably parallel to bedding, but northeast, separated by lowlands cut on the less resist­ original bedding planes are not apparent. ant rocks of the formation. The formation dips Contains thin interbedded layers of sericite schist in lower part, lowest of which is gar- steeply southeastward and strikes mostly northeast­ netiferous. Basal contact preserved only in ward (section T-T', pi. 16). Some of the intrusive Bass Canyon, south of map area______2,700 bodies are irregular but most are sill-like, so that they 9. Mixed unit: Fine-grained schist and phyllite, only partly disorder the bedded succession. Where with some layers of schistose quartzite and a sedimentary structures are preserved, mainly in the thin bed of chert conglomerate. Contains arkose and quartzite units, they indicate that tops of numerous small bodies of greenstone, grano- diorite, and metarhyolite, and is much con­ the beds are to the southeast, and as the units of the torted______4,000 formation are not repeated, the whole sequence is prob­ (Thick sills of metarhyolite and greenstone) PRECAMBRIAN AND PRECAMBRIAN(?) ROCKS 21

Stratigrayhic units of Carrizo Mountain Formation in Carrizo Stratigraphic units of Carrizo Mountain Formation in Carrizo Mountains Continued Mountains Continued Approximate Approximate thickness thickness (feet) (feet) 8. Feldspathic metaquartzite and meta-arkose: 1. Meta-arkose: Fine-grained light-gray meta- Light-gray sericitic feldspathic metaquart­ arkose, with thin layers of sericite schist and zite toward northeast, where it forms a phyllite, in small areas in a large greenstone prominent ridge, passing south westward into intrusive south of Mineral Creek. At one lo­ rocks that are more schistose and micaceous. cality the unit dips beneath the chlorite-mica Bedding and crossbedding are visible and schist, indicating that it is the lowest part of indicate that top of beds are to southeast__ 300 the sequence_____ ( ?) Total thickness _____ +18, 700 7. Mixed Unit: Fine-grained sericitic quartzite; fine-grained biotite-sericite schist, and phy- lite; some thin beds of limestone and numer­ METAMORPHIC FEATURES ous thin sills of greenstone. A few hundred The sedimentary rocks of the Carrizo Mountain For­ feet of similar rocks underlie the metarhyo- lite sill near its northeast end, and are prob­ mation in the Carrizo Mountains have been subjected ably part of the same unit, separated by the to at least two periods of metamorphism and have been intrusion______2,000 injected several times by igneous rocks, so that part of (Thick sill of metarhyolite, underlain by a their stratigraphic character has been destroyed. thick sill of greenstone) The quartzite and arkose units preserve many orig­ 6. Phyllite: Blue-gray phyllite or slate, in narrow inal sedimentary structures, such as bedding laminae, lowland between flanking ridges of greenstone crossbedding, and pebbly seams; but the quartz and and meta-arkose. Slaty cleavage may be feldspar are recrystallized, and contain variable parallel to bedding, but bedding is not visible- 600 amounts of chlorite and sericite. The finer grained, 5. Meta-arkose: Mainly gray fine-grained thin- to originally more argillaceous, units mostly contain bio- medium-bedded meta-arkose, containing well- marked bedding laminae, crossbedding, pebble tite, which has been partly converted to chlorite. bands, and a few ripple marks. Sedimentary These units, and to a lesser extent the quartzite and structures indicate that tops of beds are to arkose units, contain a foliation that is closely parallel southeast. Upper 250 ft is hard red-brown to the general homoclinal structure and to the bedding meta-arkose in 2-ft beds. Unit forms a promi­ where this can be observed. The mica, some of the nent ridge on southeast side of Cat Draw, and chlorite, and the foliation are products of an early is well exposed in cuts on U.S. Highway 80 1,700 regional metamorphism whose grade increases progres­ 4. Mixed unit: Fine-grained gray or blue quartzite, sively southeastward to a visible climax in exposures light-gray sericite schist an dark phyllite, dark lustrous slate, thin-bedded blue chert, in the Van Horn Mountains, where some of the rocks and laminated brown and black cherty lime­ are garnetiferous. stone, all of which are interbedded in thin Alteration of biotite to chlorite (and in some areas layers. Contains many thin greenstone sills. garnet to chlorite) indicates a later period of retro­ Forms the broad belt of lowland along Cat gressive and cataclastic metamorphism, whose effects Draw ______1,700 increase perceptibly northwestward across the exposed 3. Meta-arkose and feldspathic metaquartzite: breadth of the Carrizo Mountains. In many of the Fine-grained thin-bedded light-gray felds­ pathic metaquartzite and meta-arkose. Con­ schist and phyllite units the foliation is distorted by tains well-marked bedding and crossbedding crinkles and chevron folds whose axes cross the folia­ which indicate that tops of beds are to south­ tion planes at wide angles. In the Carrizo Mountains east. Forms prominent line of knobs and these structures are most abundant where effects of ret­ ridges on northwest side of Cat Draw___ 1,800-2,000 rogressive metamorphism are greatest, and especially (Thick greenstone sill, underlain by irregular bodies of metarhyolite) where incompetent units abut the competent metarhyo­ lite intrusions. 2. Chlorite-mica schist: Fine-grained lustrous The nature of the different rocks of the sequence in­ dark-colored sericite-chlorite-biotite schist, thin beds of dark slate, and thick beds of fluenced their response to this complex metamorphic coarse pebbly meta-arkose. Forms a low history. Preservation of sedimentary features in the hilly area near Mineral Creek in northwest- quartzite and arkose units resulted from alteration by era part of mountains, nearly surrounded by mass recrystallization. Greater complexity of the intrusive metarhyolite and greenstone, so that relations to adjoining units are preserved in structures in the finer grained units, where original sed­ only a few places______3, 700 imentary features are poorly preserved, probably de- 22 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS veloped because these units absorbed much of the ap­ U.S. Highway 80, 2 to 4 miles southeast of Allamoore, plied stress during progressive and retrogressive and in quarry openings of the Holley Plant of Gifford- metamorphism. Hill Co. northeast of the highway. The earlier progressive regional metamorphism of METARHYOLITE the sedimentary rocks of the Carrizo Mountain Forma­ The metarhyolite superficially has the appearance of tion preceded their intrusion by metarhyolite and an extrusive volcanic rock, as though it were part of the greenstone. These were injected in large part as sills stratigraphic sequence of the Carrizo Mountain Forma­ along the planes of earlier bedding and foliation. The tion. Much of it is layered, some of it contains inter­ intrusive rocks now show strong effects of cataclastic calations of sericite schist and phyllite, and the part and retrogressive metamorphism, evidently related to to the southeast is interbedded in thick units with the the retrogressive metamorphism of the sedimentary sedimentary rocks. However, the layering and schist­ rocks. ose intercalations were produced during metamorphism, STRATIGRAPHIC RELATIONS and the metarhyolite bodies to the southeast are sills, The sequence of sedimentary rocks of the Carrizo which branch or pinch out along the strike and have Mountain Formation exposed in the Carrizo Mountains irregular contacts with the enclosing rocks. preserves neither its top nor base, nor can top or base be The metarhyolite is a hard, blocky or slabby siliceous observed in exposures of the formation elsewhere. The rock of red, pink, brown, buff, or gray color. It is lower part of the sequence is intruded by metarhyolite formed of feldspar and quartz phenocrysts generally and greenstone. Northwest of the Carrizo Mountains, less than 2 mm in diameter, now largely broken, set in in the foothills of the Sierra Diablo, these intrusive an aphanitic groundmass. Texture and appearance of rocks are faulted over other sedimentary rocks of the the rock are similar in all exposures, except for variable Allamoore Formation along a major discontinuity in effects produced by metamorphism. Microscopic study, the Precambrian rocks, the Streeruwitz thrust fault. however, indicates that the feldspar in the southeastern Thus, relations between the Carrizo Mountain and Al­ Carrizo Mountains is microcline, whereas that in the lamoore Formations cannot be determined directly, al­ northwestern Carrizo Mountains and the Sierra Diablo though rather tenuous evidence suggests that the foothills is microcline-microperthite and albite; this Carrizo Mountain is the older formation. difference may have resulted from albitization of an original potassium feldspar in the northwestern areas. IGNEOUS ROCKS INTRUSIVE INTO CARRIZO MOUNTAIN Cataclastic metamorphism has produced a well-de­ FORMATION veloped layering or foliation in much of the metarhy­ Large masses of rhyolite and somewhat smaller olite, on the surfaces of which phenocrysts and mineral masses of greenstone intrude the Carrizo Mountain aggregates have been crushed, streaked, and drawn out Formation. In the Carrizo Mountains they form thin to form a pronounced lineation. In the Carrizo Moun­ to thick sills in the homoclinal sequence of sedimentary tains the foliation generally strikes northeast and dips rocks, as well as a large body at the base of the sequence southeast, broadly parallel to the foliation of the sedi­ to the northwest (section T-T'', pi. 16). The instrusive mentary rocks; in the Sierra Diablo foothills the strike rocks also crop out discontinuously north of the Texas is east or even southeast, parallel to the trace of the and Pacific Railway, along the south edge of the Sierra Streeruwitz thrust. The lineation extends down the Diablo foothills next to the alluvial area of Eagle Flat, dip, mostly southeastward in the Carrizo Mountains, from northeast of Allamoore to northwest of Eagle Flat but in more varied directions in the Sierra Diable foot­ section house (pi. 1). Here, none of the sedimentary hills. In places, thin layers of schist or phyllite are rocks of the Carrizo Mountain Formation are preserved, intercalated in the more massive rhyolite; microscopic and the intrusive rocks are faulted over the Allamoore study indicates that these also are of cataclastic origin, Formation along the Streeruwitz thrust fault. A few as they contain broken remnants of microcline pheno­ bodies of the igneous rocks in the Millican Hills west of crysts. However, much of the potassium feldspar in the Garren Ranch are entirely surrounded by Alla­ the schist and phyllite has been crushed and converted moore Formation; they are probably klippen of the to sericite as a result of intense shearing. The cata­ Streeruwitz thrust sheet (section O-O'', pi. 16). clastic metamorphism is strongest in the northwestern Igneous rocks of the large body in the northwestern bodies of metarhyolite and weakest in the southeastern, Carrizo Mountains, referred to above, consisting of where layering is not conspicuous and lineation and metarhyolite and minor sills of greenstone, are well schistose layers are not common. exposed in low hills southeast of Allamoore and higher In the Sierra Diablo foothills, and to a lesser extent ridges beyond. They are shown in numerous cuts along in the northwestern part of the Carrizo Mountains, part PEECAMBEIAN AND PEECAMBEIAN ( ? ) KOCKS 23 of the nietarhyolite has been converted to a dense sili­ cross the foliation, and some cement the brecciated ceous thinly laminated mylonite, in which the original metarhyolite. The younger cross joints break and offset phenocrysts are nearly destroyed. Ordinarily the my­ the veins; they contain no minerals, except scant coat­ lonite is interlayered with less altered rhyolite in beds ings of specular hematite or chlorite. a few feet thick, which are most abundant close to the sole of the Streeruwitz thrust fault. Al^LAMOORE FORMATION The Allamoore Formation crops out mainly well GREENSTONE south of the Sierra Diablo scarp near Eagle Flat, in a Both the metarhyolite and the sedimentary rocks of belt about 5 miles wide that trends west-northwest the Carrizo Mountain Formation are intruded by green­ (pi. 1). It projects in low barren subparallel ridges. stone, mainly as sills which follow the foliation of the The most prominently exposed parts of the Alla­ host rocks. A few of the sills in the southeastern Car­ moore are its limestone units, but these are interlayered rizo Mountains are as much as 1,800 feet thick; but the with great masses of volcanic rocks, including flows, rest are thinner, and many are only a few feet thick. pyroclastic rocks, and perhaps shallow intrusives. However, even the thicker sills contain numerous septa Thin units of argillaceous rocks, now altered to phyl- of the rhyolitic or sedimentary host rocks. The green­ lite, are also interbedded. stone occurs throughout the exposures of both the Car- As the Allamoore is exposed mainly to the south rizo Mountain Formation and the metarhyolite, in the where deformation of the Precambrian rocks is great­ Carrizo Mountains and the Sierra Diablo foothills, but est, the formation is mostly tilted at high angles and is only the thicker sills are large enough to be shown on complexly folded and faulted (sections K-K', O-O', the map (pi. 1). and P-P', pi. 16). Determination of the stratigraphic The greenstone is a fine- to coarse-grained green to sequence is therefore difficult, and an estimate of its black rock, now largely an amphibolite but probably total thickness is almost impossible. On Tumbledown originally a diorite. The centers of the larger sills are Mountain (sec. 27, Block 66, Twp. 7), where relations hypidiomorphic hornblende diorite, but the walls were are unusually plain, about 1,630 feet of the formation largely changed to amphibolite during shearing and is exposed with neither the top nor base preserved; the retrogressive metamorphism. Andesine was converted sequence is at least partly duplicated by thrust faults to albite or oligoclase, and the epidote and prismatic (King, P. B., and Flawn, P. T., 1953, table 17, p. 80) hornblende grains were reduced to felty masses of acic- (upper view, pi. 2). Any traverse across the strike of ular or fibrous hornblende. The thinner sills are the formation crosses a wide expanse of steeply dipping thoroughly schistose, with schistosity parallel to that beds that can hardly have been produced by repetition of the adjacent metarhyolite and the sedimentary rocks. of a few thin layers, so that the formation is probably Some of the greenstone also contains a lineation which as much as several thousand feet thick. is parallel to that of the enclosing metarhyolite. LIMESTONE VEINS Limestone beds of the Allamoore Formation stand in The Carrizo Mountain Formation, the metarhyolite, jagged ledges and ridges. They are characteristically and the greenstone all contain vein material, generally seamed by bands of chert a quarter to half an inch in narrow stringers and irregular blebs a few inches thick, parallel to the bedding and spaced at intervals thick, but partly in larger bodies. Some veins also of a few inches. Differential weathering of chert and occur in altered limestone of the Allamoore Formation, limestone imparts a ribbed appearance to the ledges. close to the Streeruwitz thrust, and the overriding The chert may be a primary or diagenetic feature; at metarhylite and greenstone. least it antedates the Precambrian orogeny because the The veins are largely milky or vitreous quartz, but chert seams are sliced and broken where the rocks are they also contain small amounts of pink feldspar, mus- strongly deformed, whereas the less brittle intervening covite, specular hematite, and other minerals. In the Carrizo Mountains they contain some tourmaline, as limestone is deformed by flowage. well as iron and copper sulfides. The limestone itself, where least altered, is mainly Structural relations of the veins are complex, and thin bedded and compact, with some more granular or they probably formed at various times late in the igne­ more crystalline layers. Most of the limestone is blue, ous and tectonic history of the enclosing rocks. Many gray, or brown, but some is reddish or purplish. Some veins follow the foliation of the rocks or spread through limestone beds are very thinly and evenly laminated by them irregularly; some are slickensided parallel to the light and dark seams; others as much as 8 feet thick prevailing lineation. Other veins lie on joints that are massive and contain no chert. At a few places the 24 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS limestone is interbedded with intraformational lime­ sandstone with seams of volcanic pebbles and inter­ stone-pebble conglomerate. bedded layers of volcanic conglomerate. Finer grained A specimen of dark gray fine-grained little-altered beds include brown or green siliceous shales, thinly limestone of the Allamoore Formation from Tumble­ laminated pink siliceous rock, and light-green schistose down Mountain was analyzed by K. J. Murata in the laminated rock, all probably derived from different chemical laboratory of the U.S. Geological Survey sorts of tuffs. Interbedded with the volcanic sediments (written commun., 1937), and yielded 83.82 percent are thin beds of reddish limestone that contain igneous CaC03 and 9.32 percent MgC03 ; it also contained 0.05 fragments. percent of organic insolubles, which are apparently like the bituminous material which darkens the Paleozoic PHYLLITE limestones of the region. Another specimen reported Phyllite is almost as widely distributed as the lime­ by Bichardson (1904, p. 25) is more dolomitic, with a stone and volcanic rocks in the Allamoore Formation, higher magnesian content. According to Flawn but it has a smaller volume and generally forms units (written commun., 1959), inclusions of carbonate rock less than a hundred feet thick. These units are grouped in the talc-bearing phyllite layers are also dolomitic. with the limestone on the geologic map (pi. 1). Like The organic matter in the limestone beds of the Alla­ the volcanic rocks, the phyllite is poorly resistant to moore Formation seems to prove existence of life during erosion and is commonly worn down to low ground be­ formation of these ancient rocks, yet searches for fossils tween the limestone ledges. In many places the phyl­ that have so far been made reveal nothing but possible lite and volcanic rocks are interbedded, and a single algal remains. Many of the 'chert-banded or laminated interval between limestone units may consist of phyllite limestone beds have a crinkled wavy or domelike struc­ at one place, of volcanics at another, and of both rocks ture similar to the Cryptozoon or stromatoporiod at others. The phyllite beds were originally shale growths in the earlier Paleozoic rocks; in places these units in the Allamoore Formation; their rather intimate structures project into the beds above as low mounds association with the volcanic units suggests that they or reefs. Other beds resemble the mottled limestones may in part have had a volcanic source. of the earlier Paleozoic, which were perhaps formed The original argillaceous constitutents of the phyllite by organic growth. have been thoroughly altered to foliated, sericitic, or talcose minerals. Most of the rock is gray to dark VOLCANIC ROCKS gray; but parts are black and apparently graphitic, Volcanic rocks probably make up a quarter to a half and others are calcareous. Bedding is indicated by of the total volume of the Allamoore Formation, but alteration of the gray, black, and calcareous varieties, they are less conspicuous than the limestone beds and in part in thin laminae, in part in layers several inches are generally worn down to soil-covered slopes, sags, thick. Bedding is intensely contorted and is crossed and valleys. Their best exposures are in creek banks by strongly marked slaty cleavage nearly parallel to and prospect holes. In a few places more massive parts the axial planes of the folds. The rock weathers white of the volcanic rocks project in rugged black hills. or ashen and splits into flakes, plates, or papery sheets The volcanic rocks are interbedded with the limestone parallel to the cleavage. in units a few feet to hundreds of feet thick, and in Since 1952 talc has been mined from the phyllite places they contain thin limestone beds. units of the Allamoore Formation at various places in Some of the volcanic rocks are very massive and the southern Millican Hills, Bean Hills, and Streeru- weather to brown or black bouldery surfaces; where witz Hills, and these units have been extensively pros­ fresh, these surfaces are dark green or red. Diabasic pected elsewhere (Flawn, 1958). The amount of talc structure is prominent in some of the volcanic rocks, in the phyllite beds varies from place to place. The and in others amygdules are abundant. Most of the dark massive volcanic rocks were probably spread out mineral may have formed from an original fine-grained as subaerial or subaqueous lava flows, but little remains magnesium-bearing tuff. Carbonate rocks adjacent to of primary flow structure, except the rather common the phyllite beds contain little magnesium, and are amygdules. Some of the thicker more massive bodies mainly limestone rather than dolomite, but dolomite may have been shallow sill-like intrusives. forms inclusions in the talc bodies. Large masses of Some of the less massive volcanic rocks are of pyro- pure ceramic-grade foliated to fibrous talc as much as clastic or sedimentary origin, for they contain detrital 150 feet thick occur in places, but in others the talc fragments of igneous rocks and are well stratified. bodies contain layers or irregular masses of chert and Coarser varieties include dark red, brown, or green carbonate rock. PRECAMBRIAN AND PRECAMBRIAN ( ? ) ROCKS 25 ROCK ALTERATION termined; the Carrizo Mountain may represent a down­ Most of the rocks of the Allamoore Formation have ward continuation of the Allamoore, or the two might been more or less changed from their original character, be far apart in age. perhaps mainly by the deformation to which they have The Allamoore Formation is also in contact with the been subjected, but probably with the aid of hydro- Hazel Formation. From structural relations alone it thermal solutions. Alteration is least toward the north, is not possible to determine the original nature of their as on Tumbledown Mountain, and increases southward succession, as either formation overlies the other, de­ to a maximum near outcrops of the metarhyolite that pending on locality. However, the conglomerate of the forms the overriding Streeruwitz thrust sheet. Hazel consists largely of fragments of limestone and The limestone beds are variously altered. The most volcanic rocks derived from erosion of the Allamoore striking alteration is by marmorization, which occurs Formation, which indicates clearly that the Hazel is in small erratically placed areas, perhaps related to in­ younger. tense flowage, squeezing, or hydrothermal activity. The The conglomerate beds show that the Hazel lies un- limestone is recrystallized to marble, mostly white, but conf ormably on the Allamoore, and the great thickness with reddish and bluish streaks that may be inherited and the coarse and angular fragments of the conglom­ from original bedding. Where the limestone was origi­ erates suggest that the Allamoore epoch was closed by nally impure or shaly, it has been made schistose, and an orogeny that probably continued into early Hazel original bedding laminae are thrown into tight isoclinal time. Moreover, some of the limestone fragments in folds. the conglomerate beds are marmorized in the same man­ In a wide band just north of the trace of the Streeru­ ner as parts of the limestone still in place in the Alla­ witz thrust, the limestone of the Allamoore Formation moore. has been extensively silicified to jasperoid. The jas- The nature of the deformation caused by the pre- peroid has lost all traces of bedding and other struc­ Hazel orogeny is obscure, as most of the structure now tures of the original limestone and is traversed by many visible in the Allamoore is shared by the adjacent Hazel quartz veinlets. Its weathered surfaces are brown and and formed during a later, post-Hazel, orogeny. The f elty and are recessed like other carbonate-bearing rocks contact between the two formations is strongly dis­ around quartz veins and siliceous knots. Nevertheless, cordant in most places; but it is generally sheared and the jasperoid probably now contains little carbonate, faulted along a "surface of movement" (pi. 1), so that as it breaks with conchoidal fracture into dark-gray it is difficult to determine their original angular diver­ steel-hard chips. gence, or the irregularity of the surface on which the Where cherty limestone beds have been sheared, the conglomerate was deposited. chert layers are sliced, offset, and broken along innumer­ HAZEL FORMATION able planes of fracture cleavage, and the intervening less brittle limestone has flowed around the chert. The Hazel Formation crops out in many parts of the Where most sheared, the rocks have become a rubble deformed area in the southern part of the Sierra Diablo of angular chert fragments, set in a carbonate matrix. foothills where its rocks are intimately infolded with The more massive diabasic volcanic rocks may have the Allamoore formation (pi. 1). Unlike the Alla­ been much changed mineralogically, but this is little moore, the Hazel is also exposed much farther north in apparent to the eye and even the amygdules are little areas that were less deformed. It crops out around compressed. By contrast, the fine-grained tuffaceous the south and east sides of the scarps of the Sierra volcanics and the phyllite units are highly contorted Diablo where it extends to within a few miles of Vic- and are thoroughly schistose. torio Peak (upper view, pi. 10); it also forms a large inlier in the interior of the range near Sheep Peak. STRATIGBAPHIC EELATIONS The Hazel Formation includes red sandstone which The base of the Allamoore Formation is not exposed. characterizes the upper and northern part, and con­ It is in contact on the south with possibly older meta­ glomerate, which characterizes the lower and southern rhyolite; but this rock has been emplaced along the part. The two rocks are intimately interbedded. Streeruwitz thrust fault, so that it now overlies rather Adjacent to the Allamoore Formation are thick massive than underlies the Allamoore. Farther southeast in layers of conglomerate; but farther from it and higher the Carrizo Mountains, the metarhyolite intrudes the in the sequence conglomerate beds are thinner and more thick sedimentary sequence of the Carrizo Mountain sandy and are separated by increasingly thicker beds Formation. Relations of these sedimentary rocks to of red sandstone, which finally dominate altogether. those of the Allamoore Formation have not been de­ The conglomerate may wedge out northward in the 26 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS sandstone, away from the uplifted masses of Allamoore moore Formation, yet they are surprisingly common at formation from which it was derived; but this is diffi­ hundreds or even thousands of feet above the base. The cult to prove because of the complex structure. fragments are generally poorly rounded and many are The Hazel is a very thick formation, but estimates of angular, thus differing from those in the overlying Van thickness are incomplete. North of the Allamoore for­ Horn Sandstone; their angularity provides a means of mation in the central Streeruwitz Hills is a continuous distinguishing the Hazel fragments from those of the steeply dipping succession which appears to be at least Van Horn. 5,000 feet thick; of this, more than half is conglomerate. The matrix of the conglomerate varies. In the lower On the eastern scarps of the Sierra Diablo near the and southern conglomerate beds, which are most re­ Pecos mine there is more than 2,250 feet of gently dip­ sistant to erosion, it may originally have been calcare­ ping sandstone. ous, but generally it has been silicified and impregnated CONGLOMERATE by iron on weathered surfaces. In the higher and more The conglomerate of the Hazel Formation is one of northern conglomerate beds the matrix includes more the more resistant rock units of the Precambrian suc­ sand and arkose, so that the rock is softer and less cession, and in places forms ridges as high as, or higher coherent. than, those of the limestone of the Allamoore Forma­ Most of the fragments lie helter-skelter in the con­ tion. In the southern belts of outcrop in the Streeru­ glomerate, pieces of all sizes, shapes, and compositions witz and Millican Hills, these ridges are covered by being mingled without sorting. Little or no grain gra­ deep-brown or black-surfaced craggy ledges. Farther dation is visible from base to top of a single layer and north the conglomerate is less consolidated and makes in the more massive phases bedding itself is obscure. fewer ledges, although it forms high hills. In the higher conglomerate beds are scattered gritty The conglomerate is formed almost entirely of frag­ seams or lenses and thin interbedded layers of red sand­ ments derived from the Allamoore Formation and es­ stone. However, rocks transitional from conglomerate pecially of its limestone. All varieties occur in the to sandstone are of small volume. No coarse sandstone fragments, including chert-seamed, laminated, carbo­ or pebbly sandstone of any thickness occurs near the naceous, and marmorized limestone. There are also conglomerate beds, and many of the coarse conglomerate scattered cobbles of bright red jaspery limestone or beds are inserted abruptly between red sandstone that chert. Fragments of the volcanic rocks are common as is as fine and silty as that elsewhere in the area. well, including massive diabasic or amygdaloidal lava The thickness of the conglomeratic part of the Hazel and coarse to fine pyroclastic rocks. The finer pyro- Formation varies from place to place along the out­ clastic rocks in some of the fragments seem to have been crop, but it is uncertain whether the variation results rendered schistose before they were incorporated in the from original differences in amount of conglomerate de­ conglomerate. posited or from structural complication. In the cen­ In a few places the conglomerate also contains cobbles tral Streeruwitz Hills, next to the southern outcrops of or boulders of red granite and coarse rhyolite porphyry. the Allamoore Formation, conglomerate beds are as They are especially abundant between Carrizo Spring much as 3,000 feet thick, of which the lower half is solid and Tumbledown Mountain in the eastern Millican conglomerate and the upper half is interbedded con­ Hills, but a few were observed in the northwestern glomerate and sandstone. Conglomerate with a sim­ Streeruwitz Hills. The granite and porphyry are unlike ilar structure in the southern Millican Hills is about the igneous rocks that intrude the Carrizo Mountain 2,000 feet thick. Formation, but they closely resemble those in boulders Near other belts of the Allamoore Formation farther in the succeeding Van Horn Sandstone. Like those in north, conglomerate beds of the Hazel Formation are the Van Horn, they resemble Precambrian granite and more varied and in places much thinner. Here, the porphyry exposed some distance northwest of the Sierra conglomerate may have been partly removed along the Diablo region. The known distribution of boulders in "surface of movement" between the two formations, the Hazel does not suggest a northwestern source, and but at least a part of the variation is original. they may have been derived from other areas, as yet unknown, where they are now concealed by younger BED SANDSTONE strata. Red sandstone forms the most conspicuous and ex­ Fragments in the conglomerate are of all sizes, from tensive outcrops of the Hazel Formation. It crops out small pebbles to large blocks, mainly limestone, and 6 on smoothly rounded red slopes, only lightly masked by feet or more across. The large blocks are most abun­ vegetation, which extend to considerable heights on the dant in the lower part, near the contact with the Alla­ scarps south and east of the Sierra Diablo, surmounted PRECAMBRIAN AND PRECAMBRIAN (?) ROCKS 27 by light-gray cliffs of the Hueco Limestone. At the surfaces, many of which are coated with a black highly bases of the scarps the slopes flatten into broad pedi­ polished substance a few millimeters thick that also ments, capped in many places by Quaternary gravels extends in ramifying stringers through the rock. Ac­ but mostly carved into an intricate network of hills and cording to Charles Milton (written commun., 1951), valleys, such as those between Beach Mountain and the the substance is a fine-grained aggregate of crystalline Hazel mine. The hills, which are domelike, have tourmaline and hematite dust. rounded crests that descend steeply toward the incising Near some of the large high-angle faults north of streams. the Millican Hills the sandstone has been mashed and The red color of the sandstone is universal, varying reconstituted, so that it loses its flinty conchoidal aspect, from brick red in the northern exposures to a darker and is massive, soft, and earthy. maroon red farther south. Most of the sandstone is Near many faults, joints, and fractures in the north­ very fine grained, verging on, or grading into, siltstone. ern area the sandstone is decolorized. The red rock is It coarsens somewhat southward where it varies more bleached to buff or yellow for several inches or feet in texture from bed to bed; here, some of the coarser away from the fractures. The bleaching is caused by layers form long strike ridges. Part of the sandstone reduction or removal of hematite by percolating solu­ is poorly consolidated, but most is fairly hard and well tions; it is best developed near prospective or produc­ cemented and has a conchoidal fracture. tive veins, and it is considered to be a favorable indica­ Bedding of the sandstone is indicated in most places tion of mineralization by local prospectors. Bleaching by thin closely spaced dark laminae. Much of it is of the red sandstone was also observed beneath the un­ crossbedded on a small scale, and in places it is ripple conformity at the base of the Hueco Limestone in buttes marked on bedding surfaces. The sandstone generally 3 miles south-southeast of the Old Circle Ranch (sec. does not split along bedding planes, as these are 4 Block 67, Twp. 7); this bleaching either occurred thoroughly welded together; instead, it breaks into during pre-Hueco erosion or during later circulation angular blocks along innumerable vertical or inclined of ground water along the unconformity. joints, so that in many places the bedding can be de­ STRATIGRAPHIC RELATIONS termined only by close scrutiny. The thickness of the red sandstone has not been de­ The Hazel Formation is overlain by varied strata of termined, but it is as much as thousands of feet. On much younger age, including those of the Permian and the east-facing escarpment of the Sierra Diablo from Cretaceous systems, but the next younger formation the Pecos mine northward, south-dipping lines of bed­ with which it is in contact is the Van Horn Sandstone. ding are visible on the red sandstone slopes below the Its relations are strongly unconf ormable, even with the cliffs of Hueco Limestone and indicate that more than Van Horn, and the times of formation of the Hazel 2.250 feet is exposed (section P-P', pi. 16). and Van Horn deposits are separated by a major period of orogeny by which the Hazel and Allamoore Forma­ ROCK ALTERATION tions were strongly deformed and by a prolonged period of erosion during which they were deeply trun­ The Hazel Formation is less altered than the Alla- cated. Emplacement of the Carrizo Mountain Forma­ moore Formation, partly because most of it lies farther tion and its intrusive rocks along the Streeruwitz thrust from the belt of strong deformation, and partly because fault probably occurred during this orogeny, as the its sandstone and conglomerate beds are more compe­ conglomerate of the Van Horn is the earliest deposit tent than the Allamoore. which contains fragments of lineated and mylonitized In the strongly deformed belt toward the south, the metarhyolite. The Van Horn Sandstone in the Sierra conglomerate has been sliced in many places along a Diablo foothills lies on both the Hazel and Allamoore multitude of closely spaced shear or cleavage planes. Formations; in the eastern Carrizo Mountains it lies These planes cut through both the matrix and the frag­ on the Carrizo Moutain Formation. ments, but most of the fragments are not flattened. The sandstone is little altered and pressures were VAN HORN SANDSTONE evidently dispersed along innumerable clean-cut ver­ The Van Horn Sandstone is preserved in relatively tical or inclined joints. The sandstone was not sheared small areas in the Sierra Diablo region, the wide dis­ or squeezed in the strongly deformed areas, but was persal and isolation of its outcrops being caused by its sliced and offset by many minor thrust faults. The unconformable relations with various formations that thrusts are especially abundant in the outcrop of sand­ overlie it. The most extensive outcrops are in the Red stone in the Millican Hills that extends east from the Valley, northwest of the town of Van Horn and south­ Garren Ranch, where they are marked by slickensided west of Beach Mountain, which Richardson (1904, p. JT57-108 «S 3 28 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS 28) designated as the type area (pi. 1). It is also ex­ Most are smoothly rounded and some have almost pol­ posed on the northwest corner of Beach Mountain south ished surfaces; a few of obvious local derivation are of the B-Bar Ranch, at several places in the Baylor somewhat less rounded. Many fragments have been Mountains, on the southeast corner of the Sierra Diablo shattered, sheared, and offset by deformation, but some between the Hazel and Pecos mines, on the south-facing were afterwards recemented. The fragments are set in scarp of the Sierra Diablo 4 to 7 miles west of the Old an arkosic sandy matrix, somewhat less consolidated Circle Ranch, and in the eastern Carrizo Mountains than that of the adjacent sandstone beds; in places the south of the Texas and Pacific Railway. fragments are closely packed, but in others they are The Van Horn is characteristically a coarse red ar- widely dispersed in the matrix. Weathering of the kosic sandstone in thick massive beds, mostly friable and poorly consolidated matrix sets free vast quantities of poorly consolidated, crossbedded in many places, and the rounded fragments, which strew the outcrops of the containing scattered pebbles and cobbles. No fossils are formation. known. The sandstone is interbedded with, and under­ The fragments in the conglomerate were derived from lain by, thin to thick beds of conglomerate containing many older rocks, but the dominant fragments, es­ rounded pebbles, cobbles, and boulders made up not pecially in the northern and northwestern exposures, only of the older rocks of the immediate vicinity, but are red granite and red rhyolite porphyry. These dif­ also of granite and rhyolite porphyry unlike any ex­ fer greatly from any igneous rocks exposed in place in posed in the Sierra Diablo region. The greatest the Sierra Diablo region. They are unlike the meta- thickness of the formation preserved at any one place rhyolite intruded in the Carrizo Mountain Formation; is about 800 feet, but it is generally much thinner. moreover, fragments clearly derived from the meta- The red massive clastic rocks of the Van Horn form rhyolite also occur in the Van Horn. The porphyry and some of the most picturesque outcrops in the region granite fragments resemble most the Precambrian ig­ (pi. 2). Its sandstone beds project in great rounded neous rocks exposed some distance to the northwest, as ledges, largely barren of vegetation, which rise on the the red rhyolite porphyry of the Pump Station Hills faces of escarpments into picturesque towers, prows, (King, P. B.. and Flawn, P. T., 1953, p. 123-124; Mas- and battlements. Tables, pedestals, and other fantastic son, 1956) and the coarse red granite at the south end erosion forms are common. The massive ledge-mak­ of the Hueco Mountains (King, P. B., King, R. E., and ing beds are separated by others, less resistant to Knight, J. B., 1945, sheet 1). erosion and generally more conglomeratic, which form Metarhyolite derived from intrusives in the Carrizo intervening shelves. Widely spaced joints, commonly Mountain Formation is a significant but not a dominant set at right angles, are worn into creases or crevices constituent. The fragments have the same lineation that extend across the outcrops and are prominently and cataclastic structure as the rocks of the parent visible from adjacent mountain tops or in air photo­ ledges. The metarhyolite occurs in nearly every out­ graphs. Stream channels cross the shelves in rounded crop of the formation, but is perhaps most abundant swales, but descend from one ledge to the next in nar­ toward the south. row slots that follow the prevailing joints, with many Other fragments are fine- to coarse-grained mafic swirls and potholes. igneous rocks, probably derived from the volcanic rocks CONGLOMERATE and the greenstone intrusives of the Allamoore and The conglomerate beds of the Van Horn are a few Carrizo Mountain Formations; limestone, chert, and feet to several hundred feet thick and are commonly jasper from the Allamoore Formation; red sandstone thickest and coarsest at the base and thinner and finer from the Hazel Formation; and vein quartz. grained higher up. Its basal conglomerate varies. On the Sierra Diablo scarp 4 miles west of the Old Circle SANDSTONE Eanch, the conglomerate is more than 300 feet thick, The sandstone beds of the Van Horn are dominantly but it thins both eastward and westward; eastward up red, but they are generally slightly darker than those of the dip it apparently thins against a buried hill of the the Hazel, being mostly maroon red or purplish red. Allamoore Formation. In other places, as near the The strong colors die out upward, and the highest beds Yates Ranch, basal conglomerate is not well defined, of the formation, where preserved, are orange red or and conglomerate beds and dispersed pebbles are com­ red brown. The sandstone which is coarse, has grains mon throughout the sequence. as much as a millimeter in diameter and scattered larger Fragments in the conglomerate are pebbles, cobbles, grits and small pebbles; it contrasts with the fine silty and boulders, those in the basal beds 4 miles west of the red sandstone of the Hazel. Quartz and feldspar Old Circle Ranch being as much as 3 feet in diameter. grains occur in about equal proportions; much mica is PRECAMBRIAN AND PRECAMBRIAN ( ?) ROCKS 29 found at some localities. In most of the rock, beds are The Van Horn and Bliss were not differentiated by 3-10 feet thick, but some are thicker. Within many the earlier geologists (Dumble, 1902; Richardson, 1904, layers are well-marked crossbeds. Most of these slope p. 28; 1914, p. 4), who interpreted the two units as southward; the others slopes southeastward or south- gradational deposits; but they are actually distinct, and westward but nowhere northward (King, P. B., and the contact between them can be located with confidence Flawn, P. T., 1953, p. 93, fig. 8). These dips are main­ in all exposures. A marked change in sedimentation tained even where the enclosing strata are inclined in an occurred between Van Horn and Bliss time from opposite direction. coarse arkosic continental unfossiliferous deposits in In the higher parts of the formation are some inter- the Van Horn to fine-grained cleanly washed quartzose bedded layers of buff or brown sandstone a foot or two marine fossiliferous deposits in the Bliss. thick, which are more cleanly washed than the rest The Bliss lies unconformably on the Van Horn and and contain more quartz than feldspar. On the south- in nearly all exposures it truncates the tilted beds of the facing scarp of the Sierra Diablo west of the Old Circle underlying formation at a low angle. The sandstone Ranch, one of these layers near the middle of the for­ of the Van Horn for a few feet below the base of the mation extends more than 2 miles. Similar layers are Bliss is commonly bleached from red to yellow by either common south of Threemile Mountain, east of Hillside pre-Bliss weathering or later circulation of ground siding. Near a tank at the summit of the Sierra Diablo water along the contact. escarpment 7 miles west of the Old Circle Ranch (sec. The unconformity between the Bliss and Van Horn 29, Block 52%), the massive arkosic sandstone is inter- is well shown on the north face of Beach Mountain bedded with 5-foot layers of soft flaggy sandstone and east of its northwest corner (sec. 19, Block 66, Twp. 7) greenish clay shale, which are nearly un'consolidated where the angular divergence between their beds is and contain possible f ucoidal markings. 20°, causing more than 200 feet of the Van Horn to be SECTIONS OF VAN HORN SANDSTONE removed within a mile along the scarp. The uncon­ formity is also well marked on Tumbledown Mountain The greatest thickness of Van Horn Sandstone in the (sec. 27, Block 66, Twp. 7) where the Van Horn is region is on the south-facing escarpment of the Sierra dropped against the Allamoore Formation along two Diablo 4 miles west of the Old Circle Ranch (sec. 2, faults, the Dallas and Grapevine, on which there was Block 56), where 759 feet was measured, of which the movement between Van Horn and Bliss time. The lower 335 feet is conglomerate (King, P. B., and Flawn, faulted terrane is truncated by the Bliss Sandstone, P. T., 1953, p. 94, table 19). Here, the Van Horn lies which lies on the Van Horn on the downthrown sides unconformably on the Allamoore Formation and is and on the Allamoore on the upthrown sides in the overlain unconformably by the Hueco Limestone, so angle between the two faults. The Dallas fault has that its original thickness is no longer preserved. not moved since Bliss time, but the Grapevine fault was At the northwest corner of Beach Mountain (sec. 19, displaced in the same direction later. Block 66, Twp. 7) 300 or 400 feet of Van Horn Sand­ stone is exposed on steep slopes below the cliffs of Bliss AGE Sandstone and El Paso Limestone and above red sand­ Dumble (1902, p. 1-3) and Richardson (1914, p. 4) stone of the Hazel Formation. The Bliss truncates the interpreted the Van Horn as being of "Potsdam" or Van Horn, and 1 mile to the east only 75 feet of the "Upper Cambrian(?)" age, a conclusion based partly latter remains. on the marked unconformity between it and the under­ On the west side of Beach Mountain three-quarters of lying Hazel and Allamoore Formations and on the a mile south of the Yates Ranch (sec. 4, Block 66, Twp. occurrence of Scolithus, or worm tubes, in its upper 8), about 325 feet of Van Horn is exposed between the part. With the discovery that this upper part was Hazel Formation west of Hackberry Creek and the equivalent to the Bliss Sandstone and was separated Bliss Sandstone on the face of the mountain to the east. by a marked unconformity from the lower part, a Cam­ Farther south in the Red Valley the formation is prob­ brian age for the Van Horn became less plausible. ably thicker, as it crops out over wide areas and in Moreover, the Van Horn has little resemblance to rocks places dips as steeply as 45°. of known Cambrian age elsewhere. It is therefore now- STRATIGRAPHIC RELATIONS classed as of Precambrian (?) age. In most places the Van Horn Sandstone is overlain Arguments favoring a later age for the Van Horn by the much younger Hueco Limestone of Permian age, are relatively insubstantial. The sandstone lies with but in a few places, as on Beach Mountain, it is overlain marked unconformity on the older formations as a re­ by the Bliss Sandstone of Ordovician age. sult of a time of orogeny and deep erosion, but these 30 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS events need not necessarily mark the end of Precam- sections 1-4, pi. 3, and p. 123-127 2), but it thickens in brian time. It is poorly consolidated, but so also is the the Baylor Mountains from 145 feet in the south (geo­ still earlier Hazel Formation in regions of slight logic section 5) to 160 feet in the northwest (geologic deformation. It is the next formation below the fos- section 8), most of the thickening being caused by siliferous Bliss, but the unconformity between them wedging in of a calcareous division at the top. indicates that there was a hiatus of unknown duration MAIN BODY OF FORMATION between Van Horn and Ordovician time. Arguments favoring an earlier age are stronger. The The Bliss is characteristically a white or light-brown unconformity between the Van Horn and Bliss involved quartzose sandstone, forming beds a few inches to a tilting, faulting, erosion, and changes in sedimentation. foot thick. According to Cloud and Barnes (1946, The Van Horn is unfossiliferous. It was laid down p. 67), most of the layers are perceptibly calcareous; in a continental environment in a region of consider­ but in the field this is apparent only in the upper divi­ able relief, unlike any nearby Cambrian deposits. Its sion, the main body of the formation appearing to be deposits are much more like those of the Hazel than much more quartzitic than the sandstone beds of the those of the Paleozoic, and they seem to imply a repe­ overlying El Paso. Most of the sandstone beds in the tition of some of the conditions under which the earlier Bliss are laminated, crossbedded, and ripple marked, formation was deposited, after an intervening period and many of them, especially in the upper part, contain of orogeny. vertical worm tubes, or Scolitkus. Some of the bed­ ding surfaces are marked by obscure fucoidal struc­ ORDOVICIAN tures. Between the sandstone beds the partings of BLISS SANDSTONE softer, more marly sandstone, which are gray, brown, The Bliss Sandstone was named for Fort Bliss, purple or green. According to C. S. Ross (written northeast of El Paso, Tex., its typical exposures being commun., 1940), the green coloration is caused by an in the southern part of the Franklin Mountains imme­ unidentified iron-bearing clay mineral and not by diately adjacent (Kichardson, 1904, p. 27; 1909, p. 3). glauconite. In the Sierra Diablo region the sandstone here termed The basal few feet of beds of the Bliss, lying uncon- the Bliss was at first grouped with the Van Horn Sand­ formably on the Van Horn Sandstone, is a conglom­ stone (Eichardson, 1904, p. 38; 1914, p. 4) or with the erate of rounded pebbles less than 1 inch to as much as El Paso Limestone (Sellards, 1932, p. 153-156), and 3 inches in diameter, mostly of vein quartz but with was only differentiated later (King, P. B., 1940, p. 153- some of chert, quartzite, and schist. In places, pebbly 156). Its designation as Bliss has been queried in layers are interbedded as high as 60 feet above the base. some reports because of uncertainty of correlation with Some of the matrix of the basal sandstone is red, from the type Bliss, but present knowledge now permits this detritus reworked from the Van Horn Sandstone. correlation to be made with greater assurance. CALCAREOUS DIVISION DISTRIBUTION On the north side of Beach Mountain, Cloud and The Bliss Sandstone crops out only in small areas Barnes (1946, p. 67) observed a 10-inch bed of dolomite in the Sierra Diablo region (pi. 1); elsewhere, it is con­ near the middle of the Bliss. Sections measured by cealed beneath younger Paleozoic formations or re­ J. Brookes Knight and the writer in this vicinity and moved by pre-Hueco erosion. The most extensive ex­ farther north indicate that the upper part of the Bliss posures are on the north, west, and southwest sides of differs somewhat from the main body and consists of Beach Mountain (pi. 2), where it forms a brown band fine-grained slightly calcareous or dolomitic yellowish- on the escarpment, consisting of slopes and thin ledges gray sandstone in beds a foot or so thick, with partings between the red Van Horn Sandstone below and the of marl and with ramifying mottlings on the bedding gray and buff sandstone and limestone ledges of the surfaces. This upper calcareous division of the Bliss El Paso above. The Bliss reappears in small areas is 20-28 feet thick on the north side of Beach Moun­ in the Baylor Mountains to the north, especially in the tain (geologic section 4), but thickens to 43 feet in the southern part (geologic section 5), and in hills near southern Baylor Mountains (geologic section 5) and to Hawkins Tank in the northwestern part (geologic 52 feet farther northwest (geologic section 8). Its sand­ sections). stone beds lack Scolithus tubes, and no other fossils are THICKNESS 3 Stratigraphie sections of rocks of Ordovician to Cretaceous age In Beach Mountain the Bliss Sandstone maintains a which have been measured during the present investigation are de­ scribed at the end of this report and are illustrated graphically on nearly uniform thickness of 105 to 125 feet (geologic plates 3, 5-9. ORDOVICIAN 31 recorded. In the southern Baylor Mountains the top Bliss, are marked by poorly preserved impressions of layer of the division is a crossbedded sandstone. fossil shells, mainly gastropods and linguloid brachi- The sandstone beds of the calcareous division have opods. The most extensive fossil collections have been some features like those of the basal sandy part of the made on the west side of Beach Mountain, up the slope El Paso Limestone, yet they appear to be distinct and from the old Dallas mine (geologic section 3, unit 2). to be more closely allied to the main body of the Bliss. Here, 4^8 feet below the top of the formation, several Occurrence of thin dolomite beds in the typical Bliss on collectors have obtained a fragment of the cephalopod the north side of Beach Mountain suggests that the Clarkoceras, various gastropods including Lytospira, calcareous division fades out into the main body of the OpMleta, and Helicotoma, the trilobite Hystricurus, formation southward. Nevertheless, the northward and archaeostracan crustaceans. At a lower level, 27 thickening of the division, and with it the formation as feet below the top of the formation, the linguloid a whole, suggests that in this direction beds younger brachiopod Lingulepis has been collected in beds which than any on Beach Mountain may wedge in beneath the also contain gastropod cross sections. disconformity at the base of the El Paso Limestone. The higher fauna is clearly of Early Ordovician age, and according to Cloud and Barnes (1946, p. 68), is STRATIGRAPHIC RELATIONS equivalent to that in the Tanyard Formation, or basal The Bliss appears to be disconformable beneath the unit of the Ellenburger Group in central Texas. The El Paso Limestone. On Beach Mountain the contact Lingulepis at a lower level is generally considered to be between them is sharply marked, and the poorly cal­ an index fossil of the Upper Cambrian, but, as remarked careous quartzose sandstone beds of the Bliss are suc­ by Cloud and Barnes (idem) ceeded abruptly by the calcareous sandstone and lime­ the abundance of gastropods in the Bliss Sandstone of the Beach stone beds of the El Paso. In the Baylor Mountains, Mountain sequence, below as well as above Lingulepis, is a fea­ where the calcareous division of the Bliss intervenes, ture unusual in Cambrian strata; and in view of the striking the contrast between the two formations appears to be similarity of the various parts of this sandstone the authors equally striking. Moreover, as observed by Cloud and are inclined to regard it as a single unit * * * of Lower Ordo­ Barnes (1946, p. 68), "commonly as much as 10 inches vician age throughout. of the basal El Paso is a calcareous reworked sand, and REGIONAL RELATIONS locally it contains pebbles and cobbles of quartz and The Bliss Sandstone forms the base of the Paleozoic sandstone." However, the hiatus between the two for­ sequence in the Hueco and Franklin Mountains, west mations is slight, as both are of Early Ordovician age; of the Sierra Diablo in Trans-Pecos Texas, and through­ the Bliss is approximately equivalent to the Tanyard out southern and southwestern New Mexico. Every­ Formation, the basal El Paso to the next younger Gor- where in this region the Bliss Sandstone maintains man Formation of the sequence in the Ellenburger much the same character and thickness and is a single Group of central Texas. rock-stratigraphic unit, although, as indicated below, FOSSILS AND AGE its stratigraphy is probably complex in detail. The most abundant indication of life in the Bliss is The type Bliss of the Franklin Mountains was orig­ the trace fossil Scolithus, probably the tube of a burrow­ inally designated as Upper Cambrian by Walcott (in ing worm, which occurs in every outcrop of the main Richardson, 1909, p. 3) on the basis of Lingulepis and body of the formation, most abundantly in the upper other linguloid brachiopods; but in the Sierra Diablo part but at some localities to within a few feet of the similar brachiopods are associated with gastropods of base. The Scolithus of the Bliss is of the type with Ordovician aspect, and Cloud and Barnes (1946, p. 74) undulating vertical tubes, termed "Sabettarifex" by R. conclude that the Bliss of the Franklin Mountains Richter (Cloud and Barnes, 1946, p. 67). Although should "be considered lowest Ordovician until diag­ Scolithus was cited by Walcott as evidence for the nostic evidence is found." Flower (1958, p. 65) con­ Cambrian (Potsdam) age of the beds containing it curs with this conclusion. (Dumble, 1902), the fossil ranges widely through lower However, in New Mexico to the north and west Paleozoic strata, from Lower Cambrian to Silurian, in Flower (1953, p. 2055; 1958, p. 65-66) has found in the deposits laid down near the shore, and has ecologic Bliss at various levels, from one place to another, fos­ analogues in existing shoal water to intertidal sand- sils of Early Ordovician age and of late and middle flat environments (P. E. Cloud, Jr., written commun., Late Cambrian (Trempealeau and Franconia) ages, and 1954). he suggests the probable existence of corresponding Many of the bedding surfaces of the sandstone, es­ lithologic subdivisions. Still farther west, in south­ pecially in the upper part of the main body of the eastern Arizona, the basal sandy deposit is the Bolsa 32 GEOLOGY OP THE SIERRA DIABLO REGION, TEXAS Quartzite of Middle Cambrian age. This quartzite is 127), where it lies on Bliss Sandstone, is overlain by followed by the Abrigo Limestone of Middle and Late Montoya Dolomite, and is 1,115 feet thick. Elsewhere in Cambrian age, although the Early Ordovician El Paso the region its sequences are not continuous, and only Limestone is also preserved locally. basal, middle, or upper parts are exposed. The Bliss is thus "part of a homotaxic blanket of DIVISION A sediments which began to form in the eastward-expand­ ing Sonoran seaway in southeastern Arizona during Division A, lying on the Bliss Sandstone, is exposed Middle Cambrian time," and which was not laid down mainly in Beach Mountain, but it appears in some places farther east, in New Mexico and west Texas, until Late in the Baylor Mountains and forms the base of the se­ Cambrian and Early Ordovician time (Kelley and Sil­ quence in the inlier near Cox Mountain. On the north ver, 1952, p. 55). This general concept requires modi­ side of Beach Mountain (geological section 4) division fication in detail. The Bolsa and Bliss are probably A is about 250 feet thick. It is separately represented distinct sand wedges (Epis, 1958, p. 2754-2756), and on the geologic map (pi. 1) and structure sections (pi. the Bliss itself may "represent a period of slow and evi­ 16>' dently highly intermittent deposition of sandy ma­ In Beach Mountain and elsewhere division A includes terial" whose base "may be as old as the middle of the two or three sandstone units, which crop out in promi­ Franconia, and its top may extend into the basal Ordo­ nent rounded yellowish or buff ledges. Individual vician" (Flower, 1953, p. 2055). sandstone layers are 5-30 feet thick. The sandstone is medium to fine grained and consists of well-rounded EL PASO LIMESTONE quartz grains and some feldspar grains, mainly with a The El Paso Limestone was named for exposures in dolomitic cement. Many of the layers are crossbedded the southern part of the Franklin Mountains near El and some are glauconitic. Paso, Tex. (Richardson, 1904, p. 29), and was later re­ Between the sandstone layers are units of gray to stricted to the rocks of Early Ordovician age in that yellow limestone, in part dolomitic, some of which are area, the Sierra Diablo, and elsewhere (Richardson, strongly mottled and cherty, between which are part­ 1908, p. 476-479). Kirk (1934, p. 450) suggested a ings and layers of marl and siltstone. Many of the lithologic and faunal subdivision of the El Paso into limestone layers are sandy, some are glauconitic, and well-defined lower and upper units, termed the "Pilo- most of them contain abundant gastropods, cephalopod ceras-Calatkium beds" and the "Taffia beds," and a siphuncles, and other fossils. rather indefinite intervening unit, characterized mainly DIVISION B by Ceratopea. These subdivisions were further refined by Cloud and Barnes (1946, p. 67, 74) and were infor­ Division B of the El Paso Limestone is 813 feet thick mally designated units A, B, and C. This usage is re­ on the north side of Beach Mountain (geologic section tained here. 4). Throughout most of Beach Mountain and the Bay­ lor Mountains the division is a monotonous sequence DISTRIBUTION AND THICKNESS of gray, brownish-gray, or brown dolomite, in beds a In the Sierra Diablo region the El Paso Limestone is few inches to 3 feet thick, which stand in prominent most prominently exposed on Beach Mountain, of which ledges and steep cliffs. The dolomite is mostly fine it forms the main bulk (pi. 2). Farther south and west grained to microgranular, and contains closely to widely it has been removed by pre-Hueco erosion, but to the spaced chert nodules of various sizes, as well as less north it emerges from beneath younger formations in regular siliceous masses. In the lower 100 feet some small areas around the edges of the Baylor Mountains argillaceous and dolomitic limestone is interbedded. (pi. 1). A few of its uppermost beds may be exposed Many of the dolomitic layers contain dispersed sand much farther north, at the base of a fault block in the grains and on the north side of Beach Mountain 60 or salient of the Sierra Diablo northwest of the Figure 70 feet of dolomite near the middle is very sandy. Some Two Ranch (geologic section 9). The El Paso is also dolomite beds at about the same level are perceptibly exposed in the interior of the Sierra Diablo, where it petroliferous. Most of the fossils in the division are forms an inlier north of Cox Mountain, about 7 miles poorly preserved but some are silicified, and large col­ long and 2 miles wide, whose rocks are cut off by the lections have been made in some layers. Especially Cox Mountain fault on the south and overlapped by abundant and characteristic of the upper half of the the Hueco Limestone on the north. division are opercula of the gastropod genus Ceratopea. The only complete section of the El Paso Limestone At the inlier within the Sierra Diablo north of Cox in the Sierra Diablo region is on the north side of Mountain, most of the El Paso Limestone that is ex­ Beach Mountain (geologic section 4, pi. 3 and p. 124- posed belongs to division B, although the upper sand- ORDOVICIAN 33 stone beds of division A emerge toward the east. The various geologists at numerous levels in the formation lower 350 to 400 feet of division B, exposed near the on the north side of Beach Mountain (geologic section two county roads 3 miles east-northeast of Cox Moun­ 4) and in the inlier within the Sierra Diablo northeast tain (western part of sec. 14 and eastern part of sec. 15, of Cox Mountain (X-l and X-2). Fossils identified Block 45%) is largely limestone rather than dolomite from these and other collections, and those which were as farther southeast. The limestone forms beds a few observed in the field, are noted at appropriate places in thick, with some 4-foot ledges. Many beds are mottled the stratigraphic sections and fossil lists (p. 124-131, gray and yellow, and contain ropy brown chert; but a 133). few beds are gray, aphanitic, and abundantly fossilifer- The sequence of fossils as observed on Beach Moun­ ous. A few more dolomitic argillaceous layers are in- tain and elsewhere is capable of zonation and indicates terbedded, some of which contain a green clay mineral, that the El Paso Limestone represents a wide span of and there are several layers of intraformational con­ Early Ordovician time. Cloud and Barnes (1946, p. glomerate. 57-71) have compared the zones of the Sierra Diablo Higher beds of division B, exposed farther northwest region with those in formations of the Ellenburger near the Edwards Ranch and beyond, are drab-gray or Group in central Texas and in formations of the Ozark brown finely crystalline dolomite, more like the bulk of uplift in Missouri, although they indicate that there the division in the Beach Mountain area. is some uncertainty as to their precise equivalents. DIVISION c The 250 feet of beds of division A is abundantly fos- siliferous, except for the lower 70 feet of the Beach At the top of the El Paso are the poorly resistant Mountain section. The division contains the cephalo- strata of division C, which form light-colored slopes pods Piloceras, AUopiloceras^ and Kirkocerasl (mostly and thin ledges between the darker cliffs and ledges of represented only by siphuncles), various gastropods in­ division B below and the Montoya Dolomite above. cluding Opfiileta, Hormotoma, and Lecanospira and the Division C is largely marly, nodular, gray, yellow, or brachiopods Diaphelasma, and Syntrophina. These fos­ buff limestone and dolomite, with some thin layers of sils indicate that the division is broadly equivalent to more compact dolomite. Some of the beds are slightly the Gorman Formation of central Texas and the Roubi- sandy; a few of the more marly ones are greenish, prob­ doux Formation of Missouri. ably from the presence of an iron-bearing clay min­ The 800 feet or more of beds of division B contains eral. On the north side of Beach Mountain (geologic more varied faunas, and has been divided on this basis section 4) division C is 50 feet thick. About the same by Cloud and Barnes into subunits B 1 and B 2. thickness of similar strata occurs beneath the beds of Subunit B 1 (units 10-12, geologic section 4, and all Middle (?) Ordovician age in the Baylor Mountains to the collections of X-l and X-2) is broadly equivalent to the northeast. the Honeycut Formation, or highest unit of the Ellen- STRATIGRAPHIC RELATIONS burger Group of central Texas, and to the Jefferson In the Beach Mountain section the uppermost beds City Formation of Missouri. It is divisible into three of the El Paso Limestone, or division C, are followed zones (P. E. Cloud, Jr., written commun., 1954). A by the Montoya Dolomite. Fossil evidence indicates lower zone is characterized by the gastropods Orospira that the top of the El Paso is of late Early Ordovician and Barnesella, the brachiopod Xenelasma, and the age and the base of the Montoya of early Late Ordovi­ trilobite Jeffersonia. A somewhat higher zone contains cian age, or a little older, so that the two formations are the brachiopod Archaeorthis and Jeffersonia. A still separated by a disconformity. As indicated below, in higher zone contains a probable new species of Helio- the southeastern part of the Baylor Mountains the El cotomaf. In addition, many beds in subunit B 1 con­ Paso Limestone is overlain by a small thickness of beds tain the sponge Calathium. of Middle (?) Ordovician age. These beds are seem­ Subunit B2 (units 2-9, geologic section 4) is probably ingly conformable with division C of the El Paso Lime­ younger than either the Honeycut or Jefferson City stone, and the disconformity at the base of the Montoya Formations of central Texas and Missouri, but older Dolomite must pass above them. than the Black Rock Formation of Arkansas. It is FOSSILS AND AGE characterized especially by opercula of the gastropod Fossils can be observed in the El Paso Limestone in Oeratopea (Yochelson and Bridge, 1957, p. 293), which most exposures. In many places they are poorly pre­ permit division into two main zones. The lower zone served, especially in the middle part, or division B, is characterized by a variety of C. tennesseensis Oder but identifiable material can ordinarily be obtained in and by C. keitlii TJlrich. A higher zone contains C. aff. a few layers. Extensive collections have been made by ankylosa Cullison and Lopfwnemal. 34 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Division C on the north side of Beach Mountain (unit tion in the Franklin Mountains is missing in the Organ 1, geologic section 4) contains a small Maclurites, other Mountains 30 miles to the north. poorly preserved gastropods, the cephalopod Buttso- Rocks of Early Ordovician age emerge again about ceras, and unidentified sponges. Cloud and Barnes 350 miles east of the Sierra Diablo, in the Llano uplift of state (1946, p. 352) central Texas, where they form the Ellenburger Group Small Maclurites is common in high Lower Ordovician strata (Cloud and Barnes, 1946, p. 22-42). Drilling in the at other localities and Buttsoccras is known only from the Oden- intervening West Texas basin indicates that rocks of ville Limestone of Alabama, so it is reasonably probable that this age are continuous beneath the surface, or nearly so, unit C * * * is approximately equivalent to the Odenville between central Texas and the Sierra Diablo (Galley, Limestone of Alabama and correlative with some part of the 1958, p. 401^06; Barnes and others, 1959, p. 25-42). Black Rock Formation of Arkansas * * *. As indicated by paleontologic data (see above), division REGIONAL RELATIONS A and the lower part of division B are broadly equiva­ lent to the Gonnan and Honeycut Formations of the The El Paso Limestone is exposed in the Hueco and Ellenburger Group. The Bliss Sandstone of the Sierra Franklin Mountains west of the Sierra Diablo in Trans- Diablo region is broadly equivalent to the basal forma­ Pecos Texas and also in many of the ranges of southern tion of the group, the Tanyard, but apparently neither and southeastern New Mexico. In the Franklin Moun­ the upper part of division B nor division C of the El tains (Kirk, 1934, p. 447-451; Cloud and Barnes, 1946, Paso Limestone is represented in central Texas. p. 72-75), where the formation is 1,590 feet thick, the same divisions as in the Sierra Diablo region are iden- BEDS OP MU>D:LEOklahoma. character and extent as indicated by later investiga­ The strata of Middle (?) Ordovician age in the south­ tions. eastern part of Beach Mountain are evidently the west­ The Montoya has long been known to contain well- ern featheredge of a unit which is much thicker and marked subdivisions in all its areas of exposure, and in more extensive farther east, and which is missing far­ the Caballo Mountains of New Mexico these sub­ ther west. In the West Texas basin drilling indicates divisions have been termed the Cable Canyon Sand­ the presence between the El Paso and Montoya Forma­ stone, Upham Dolomite, Aleman Formation, and Cut­ tions of as much as 2,000 feet of limestone, shale, and ter Formation (Kelley and Silver, 1952, p. 56-66). sandstone, which is of Middle Ordovician age and is The Upham forms the lower cliff-making part of the equivalent to the Simpson Group of Oklahoma (Fill- Montoya, and the Aleman, the upper slope-making man and others, 1958, p. 122-124; Galley, 1958, p. cherty part; the Cable Canyon is a basal sandy de­ 406-407). Middle Ordovician strata, 235 and 930 feet posit, gradational into the Upham and not everywhere thick, have been reported in two deep wells in the Dela­ developed; and the Cutter is a unit transferred from ware and Apache Mountains, less than 20 miles east of the Fusselman Dolomite, of which it was formerly the nearest outcrops of Ordovician rocks in the Sierra considered to be a lower member (Darton, 1928, p. 14). Diablo region (Maley, 1945, p. 280-281; M. E. Upson, In the Sierra Diablo region the Upham and Aleman are in DeFord and others, 1951, p. 50-52) (Gulf Oil Corp., certainly represented in the Montoya and also possibly 1 M. A. Grisham, sec. 18, Block 99; Humble Oil & Re­ the Cable Canyon, but the Cutter is apparently missing fining Co., B-l Reynolds Cattle Co., sec. 33, Block 62). (Howe, 1958, p. 2328, fig. 29). It is appropriate here to mention another reported In many recent reports the Montoya has been classed occurrence of beds between the El Paso and Montoya as a group and its subdivisions as formations, but this in the Sierra Diablo region (King, P. B., 1934a, p. 1541- is mainly a matter of personal preference. In the pres­ 1542; Arick, 1935, p. 118-119). On the salient of the ent report the subdivisions are classed as members of Sierra Diablo iy2 miles northwest of the Figure Two the Montoya Dolomite. Ranch (center of southern part of sec. 9, Block 66, On Beach Mountain the Montoya Dolomite caps the Twp. 5), the sandstone at the base of the Montoya Dolo­ El Paso Limestone in parts of the summit areas, and mite of geologic section 9 is bordered up to the dip to is also downf aulted along the eastern side (pi. 1 and the northeast by a descending sequence of dark shale, upper view, pi. 2). It crops out at many places along cherty limestone, and finally by light-gray dolomite at the edges of the Baylor Mountains, generally forming the edge of the alluvium. Relations are obscured by the first ledges beneath the Hueco Limestone, although slumping of blocks of the Montoya over strata farther the Fusselman Dolomite intervenes in places. In the down the slope. The questionable beds to the north­ Sierra Diablo farther northwest it forms a small inlier east, however, are like no Ordovician strata in the re­ in Victorio Canyon west of Yictorio Peak, and is ex­ gion; they are like the Mississippian, Devonian, and posed in many of the fault blocks in the salient of the Silurian strata exposed not far away and are here in­ Sierra Diablo between the Figure Two Ranch and terpreted and mapped as a downf aulted block of these Apache Canyon. strata (pi. 1). In a few ravines marly limestone is ex­ The Montoya Dolomite is generally a cliff-making posed in sequence below the Montoya on the upthrown unit. Its lower beds form a wall-like escarpment ris­ side of the fault (unit 1, geologic section 9); although ing above the weaker beds of the upper part of the its age is undetermined, it is tentatively correlated with El Paso, and surmounted by receding ledges of the high­ division C of the El Paso Limestone. er beds. From a distance the formation appears darker colored than the underlying and overlying El Paso and MONTOYA DOLOMITE Fusselman Formations, and its basal sandstone beds, The type area of the Montoya Dolomite is in the where present, form a brown band on the mountain Franklin Mountains north of El Paso, Tex., and the sides. formation is named for Montoya station on the Santa The Montoya Dolomite is 250 to 325 feet thick in the Fe railroad west of the mountains (Richardson, 1908, eastern Baylor Mountains (geologic sections 6, 7, pi. 3 p. 478-479; 1909, p. 4). A more specific type section of and p. 128-130) and is somewhat thinner in the north­ the formation has more recently been designated and eastern salient of the Sierra Diablo (geologic sections 9, measured, and the top redefined (Pray, 1958; Howe, 10). On Beach Mountain (geologic section 4) 416 feet 1959, p. 2321, fig. 24). At the time of the original work, of beds has been assigned to the Montoya, but the upper the Montoya was also recognized in the Sierra Diablo 110 feet might be part of the Fusselman Dolomite. 757-10S--&5 4 36 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

CABLE CANYON(?) SANDSTONE MEMBER forms the greater part of the member in the Hueco and Franklin Mountains farther west. Probably the homo­ In parts of the Sierra Diablo region, sandstone beds geneous fine-grained dolomite facies of the member are prominent at the base of the Montoya, but their developed from the mottled limestone facies by dolo- stratigraphic relations are complex. Most of the sand­ mitization and recrystallization (Howe, 1959, p. 2298, stone beds in the southeastern part of the Bay lor Moun­ tains are probably below the Montoya and are of 2299). Middle(?) Ordovician age, whereas those on Beach ALEMAN CHERTY MEMBER Mountain are gradational with the dolomite of the The Aleman Cherty Member forms a succession of Upham Member and are more certainly part of the cherty ledges above the cliff-making Upham Member, Montoya. Affinities of the sandstone beds in other and is 150 to 240 feet thick in the south (geologic sec­ parts of the region are less clear, and deserve further tions 4, 6, 7) but about 110 feet in the north (geologic appraisal. sections 9,10). The Aleman Member is gray dolomite, On the north side of Beach Mountain (geologic sec­ in beds a few feet thick with interspersed thicker beds. tion 4), a single massive bed lies between division C of Nearly all the beds are cherty, and chert makes up 30 the El Paso Limestone and the dolomite of the Upham or 40 percent of the volume of some of the beds. The Member. It is a ledge-making pinkish sugary sand­ silica content of the member is greater than that of any stone 35 feet thick, dolomitic throughout, and contains other unit in the Paleozoic sequence in the Sierra Diablo a few poorly preserved horn corals a,nd brachiopods. region, with the possible exception of the beds of De­ Farther south on the mountain only the lower 10 feet vonian age. is sandstone; the remainder is sandy dolomite. These In some beds chert forms closely spaced layers a few beds resemble the Cable Canyon Sandstone as described inches thick that taper as long lenses; other beds are in the Caballo Mountains, and like it, appear to be gra­ crowded with spherical chert nodules and irregularly dational with the Upham above, but precise correlation knotted lenses. Brachiopods, corals, and other fossils of such basal sandy deposits between distant areas is not in the dolomite are also commonly silicified, and project assured. on weathered surfaces. Much of the silica in the Aleman In the Baylor Mountains, where several sandstone was probably an original sedimentary constituent, per­ layers occur in the beds of Middle (?) Ordovician age, haps derived from distant areas of volcanism (Howe, sandstone at the base of the Montoya itself is poorly 1959, p. 2306), although the chert itself has been greatly developed, being no more than 10 feet thick in most rearranged during diagenesis of the original sediment, places, and in some, missing altogether. On the salient and later. of the Sierra Diablo V/2 miles northwest of the Figure On the north side of Beach Mountain (geologic sec­ Two Ranch (geologic section 9), the Upham Member is tion 4) the 286 feet of strata preserved above the Upham underlain by 55 feet of sandstone, of which only the Member is notably less cherty than in other sections. lower half forms a strong ledge, the upper half being Two very cherty units, 40 and 25 feet thick, occur in thinner bedded and with interbedded marly layers. the lower part, but the upper 110 feet is a massive cliff- making dolomite without chert. No fossils were ob­ UPHAM MEMBER served in this unit, and although it is tentatively mapped The Upham Member is a prominent cliff-making unit, with the Montoya and does not resemble the Fusselman which is about 100 feet thick toward the south (geologic of nearby areas, it is perhaps an unusual facies of the sections 4, 6) but somewhat thinner farther north latter, or a remnant of the Cutter Member that is other­ (geologic section 9). For the most part it is a homo­ wise missing in the region. geneous light-gray or pinkish-gray fine-grained dolo­ At the inlier in Victorio Canyon in the central Sierra mite, forming massive beds as much as 5 feet thick Diablo, about 100 feet of Montoya is exposed which that weather to dark-gray jagged surfaces. Some of consists of thin to thick beds of gray dolomite, the thin­ the beds contain spherical chert nodules, and in the ner beds crowded with chert layers and lenses. Both southeastern Baylor Mountains there is a very cherty the lithologic features and the rather abundant fossils layer 30 feet below the top. Few fossils are preserved indicate that all these beds are part of the Aleman in the dolomite, although silicified brachiopods and Member. corals occur in places. STRATIGRAPHIC RELATIONS Parts of the member in the northeastern Baylor Moun­ In the Sierra Diablo region the Aleman Cherty Mem­ tains (geologic 'section 7) are of a different facies a ber of the Montoya Dolomite is overlain by the Fussel­ gray limestone mottled by anastomosing yellow dolomite man Dolomite. Where the Fusselman is of massive and containing fairly abundant fossils. This facies dolomite facies, the contact is abrupt; but in the few ORDOVICIAN 37 places where the Fusselman is of limestone facies, the States. According to the original determinations by contact is more obscure. Although paleontological data Ulrich (in "Richardson, 1909, p. 4), the Montoya con­ regarding the age of the Fusselman are rather meager, tains faunas of two ages, one of Trenton (Galena) age fossils of Silurian aspect have been observed here and in the Upham Member and the other of Richmond there, in places not far above its base. (Fernvale) age in the Aleman Member. On the other Farther northwest in Texas and in southern New hand, Kirk (in Richardson, 1914, p. 4; Kirk, 1930, p. Mexico, the Aleman Member is separated from the Fus­ 464, 465) judged that the whole formation was of Late selman Dolomite by the Cutter Member, about 165 feet Ordovician age, although perhaps pre-Richmond. More thick, which contains a fauna of late Late Ordovician recently available evidence has been reviewed by Howe age (Kelley and Silver, 1952, p. 62-64; Howe, 1959, p. (1959, p.2301,2302,2315). 2315-2326). Observations by the writer and by Howe Perhaps the fauna in the Montoya that is most sig­ (1959, p. 2319) indicate that this unit must be missing nificant for correlation with the eastern Ordovician in the Sierra Diablo region. Here, the Aleman Member sequences is the assemblage of brachiopods which occurs of the Montoya Dolomite is apparently separated from in the upper part of the Upham Member and lower part the Fusselman Dolomite by a disconformity, whose of the Aleman Member. This faunal assemblage has hiatus includes the time during which the Cutter Mem­ close affinities with that of the Elgin Limestone Member ber was deposited farther northwest. of the lower part of the Maquoketa Shale of Iowa and may be correlative (Howe, 1959, p. 2301). Correlation FOSSILS AND AGE of the Maquoketa with the type Cincinnatian (Upper Fossils are rather plentiful in the Montoya Dolomite Ordovician) of Ohio is subject to alternative interpre­ of the Sierra Diablo region, especially in the Aleman tations ; it may be entirely of Richmond age, or it may Cherty Member, although most are silicified and poorly include equivalents of the Eden, Maysville, and Rich­ preserved. Collections made during the present inves­ mond. If the former interpretation is correct, both tigation are meager, but more extensive ones, which in­ the Upham and Aleman Members of the Montoya are of dicate a zonation of the sequence, were made by Howe Late Ordovician age; if the latter, the Upham Member (1959, p. 2328, fig. 29) in the Baylor Mountains. includes beds of late Middle Ordovician (Trenton) age. In the Upham Member streptelasmid and halysitid According to Howe, the fauna of the lower part of corals and the brachiopod Lepidocyclus (formerly the Upham Member, including Receptaculites and Rhynchotrema) were observed at various places in the Maclurites, "finds its closest relation with the Red homogeneous fine-grained dolomite facies. More abun­ River formation of southern Manitoba and its wide­ dant fossils occur in the mottled limestone facies in the spread correlatives" (1959, p. 2301), but the age of the northeastern Baylor Mountains (geologic section 7), Red River in terms of the eastern sequences has not been where the sponge Receptaculites, halysitid and f avositid established. The higher brachiopod faunas of the corals, the brachiopod Lepidocyckis, the gastropod Aleman member "possess a strong upper Maquoketa Maclurites, and large orthoceratid cephalopods were aspect" (1959, p. 2315). The fauna of the Cutter Mem­ observed. ber, which overlies the Aleman west of the Sierra Near the top of the Upham Member and in the lower Diablo, is of Late Ordovician and probably Richmond part of the Aleman Member (geologic section 6) Howe age (1959, p. 2326). (1959, p. 2301, 2310-2314) has obtained an extensive For purposes of the present report, it seems best to brachiopod fauna which includes the genera Lepido- classify all the Montoya Dolomite as of Late Ordovician cyclus, Onniella, Thaerodonta, Plaesiomys, Rhyncho- age, but with recognition that at least part of the Up­ tr&ma, Austinella, and Glyptorthis. Higher in the Ale­ ham Member may be somewhat older. man he has observed a distinctive zone characterized by the coral Paleoptiyllum thomi (Hall). REGIONAL RELATIONS From various localities in the Aleman Member the The Montoya Dolomite is exposed in the Hueco and writer and his colleagues have collected the following, Franklin Mountains northwest of the Sierra Diablo in which were identified by P. E. Cloud, Jr., Helen Dun- Texas and in the mountains of southern New Mexico at can, and Jean Berdan: streptelasmatid corals of the least as far north as the Caballo Mountains and as far Streptelasma foerstei and S. prolongatum groups, Foer- west as Silver City. Throughout this area the forma­ stephytluml, PcHeophyllum thomi (Hall), trepostomat- tion and its members are remarkably constant, except ous bryozoans, Dinorthis (Plaesiomys] , "Rafinesquina" for minor regional variations and for the more drastic Platystroptiia, Lepidocyclus, and HypsiptycKwl disappearance of the Cutter Member eastward in the Opinions have varied among paleontologists as to the Sierra Diablo. The regional aspects of the Montoya in age of the Montoya and related units in the Western west Texas and New Mexico have been reviewed by 38 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Kelley and Silver (1952, p. 64-66) and have been the Fusselman between the Montoya and beds of De­ studied in more detail by Howe (1959). vonian age is about 300 feet. At Apache Spring in the The Montoya Dolomite extends eastward beneath the northern Sierra Diablo (geologic section 10), 420 feet surface from its outcrops in the Sierra Diablo and un­ of Fusselman occurs between the Montoya and the derlies that part of the West Texas basin southwest of a Hueco, but the beds of Devonian age and an unknown line between Lubbock and Edwards Counties, Tex. thickness of the upper part of the Fusselman have been (Fillman and others, 1958, p. 90-93; Galley, 1958, p. removed by pre-Hueco erosion. The two sections in­ 407-410). Except for a single small remnant (Barnes, dicate a northward thickening of the Fusselman, which Cloud, and Duncan, 1953), no rocks of Late Ordovician is the reverse of relations in the Montoya. age are preserved in the outcrops of older Paleozoic rocks farther east, in the Llano uplift of central Texas. LITHOLOGY

SILTJEIAN Throughout much of its extent the Fusselman is a monotonous body of massive white or light-gray FTJSSHLMAN DOLOMITE crystalline dolomite, without chert. Dolomitization The Fusselman Dolomite was named for exposures during diagenesis has destroyed or obscured much of near Fusselman Canyon in the Franklin Mountains its original structure. The greater part of the dolo­ north of El Paso, Tex. (Richardson, 1908, p. 479-480; mite is now finely crystalline or sugary, with ghosts of 1909, p. 4). Later, a type section of the Fusselman was fossils here and there, and with patches, vugs, and vein- designated farther north in the Franklin Mountains, lets of coarsely crystalline calcite. Indistinct bedding and the base of the formation was redefined (Pray, planes divide it into layers a few feet to more than 5 1958). Existence of the Fusselman Dolomite in the feet thick, with some partings of thin-bedded hackly Sierra Diablo region was not reported during the earlier dolomite. The dolomite crops out in light-gray ragged investigations (Richardson, 1914) and was only dis­ bouldery surfaces, which contrast with the darker gray covered later (King, P. B., 1932). well-bedded ledges of the Montoya and Hueco Forma­ DISTEIBUTION tions below and above. In the Sierra Diablo region the Fusselman Dolomite At a few places the massive dolomite grades into crops out in more restricted areas than the earlier another facies of darker gray well-bedded limestone Paleozoic formations, as it has been more extensively re­ and dolomitic limestone, containing chert and silicified moved by pre-Hueco erosion. It is exposed discon- fossils in many layers. This facies occurs in the Baylor tinuously beneath the Hueco along the eastern escarp­ Mountains near the eastern portal of Red Tank Canyon ment of the Bay lor Mountains for several miles north (sec. 4, Block 122) and at Apache Spring (northeastern and south of the eastern portal of Red Tank Canyon; part of sec. 7, Block 66, Twp. 5). Near Apache Spring it also occurs in many of the fault blocks in the salient the facies contains irregularly bedded reefy limestone of the Sierra Diablo between the Figure Two Ranch and bodies as much as 30 feet thick, formed largely of Apache Canyon (pi. 1). corals. The well-bedded limestone and dolomitic lime­ stone beds somewhat resemble the upper beds of the THICKNESS Montoya Dolomite on which they lie, and when first The full thickness of the Fusselman Dolomite be­ observed during the present investigation, they were tween the Montoya Dolomite below and the beds of mapped with that formation. They are distinguish­ Devonian age above is preserved in few of its exposures. able from the Montoya because they overlie the full In most places the eroded top of the Fusselman is over­ thickness of its Aleman Member, and because of their lain by Hueco Limestone, and where beds of Devonian gradational relations with the dolomitic facies of the age overlie the Fusselman, its base is concealed. One Fusselman. Both in the Baylor Mountains and at of the most prominent exposures of the Fusselman in Apache Spring some thin to thick layers of light-gray the region is on the point of the mountains 1% miles dolomite are interbedded with the limestone; these lay­ northwest of the Figure Two Ranch (geologic section ers thicken toward the areas of dolomite, so that one 9, pi. 3 and p. 131-132), where it forms a wall-like ridge, facies is replaced entirely by the other within less than a bordered on the northeast by Montoya Dolomite and on mile. the southwest by beds of Devonian and Mississippian The dolomite and limestone facies of the Fusselman age; however, the structure is obscure and the rocks are probably reef and interreef deposits which were laid dip steeply, so that their thickness is uncertain. down contemporaneously on adjacent parts of the sea In the northeastern B,aylor Mountains (geologic sec­ floor. Within the limits of exposure, gradation from tion 7) where the structure is plainer, the thickness of one to the other takes place in varied directions, and DEVONIAN 39 the exposures are not extensive enough to indicate any thickness of about 770 feet in its type area in the Frank­ general pattern. Similar gradations on a smaller scale lin Mountains, and in New Mexico is a few hundred have been observed in the Franklin Mountains (Pray, feet thick or less. 1958, p. 36); they also resemble the gradations which The Fusselman has been assigned a Middle Silurian, have been reported between the Silurian Lone Mountain or Niagaran age (Richardson, 1909, p. 4; Darton, 1928, and Roberts Mountains Formations in Nevada (Win­ p. 14), but recent observations in New Mexico indicate terer and Murphy, 1960). that the formation as originally defined contains strata of more varied ages. In New Mexico two members in STRATIGRAPHIC RELATIONS the Fusselman have long been recognized, but the lower, The Fusselman Dolomite is overlain abruptly by or Cutter Member, is now known to contain fossils of chert, siliceous shale, and thin-bedded limestone of Late Ordovician age, and has been transferred to the Devonian age. No indications of erosion were observed Montoya (see above). In the restricted Fusselman fos­ at the contact, but the two formations are probably dis- sils representing different ages of Middle Silurian and conformable and are separated by a hiatus that repre­ possibly Early Silurian time have been obtained, so that sents considerable parts of Silurian and Devonian time. the formation may include two or more original deposi-

FOSSILS AND AGE tional units, whose identity has been obscured by dolomitization (Flower, 1958, p. 72). Fossils in the dolomitic f acies of the Fusselman are Rocks of Silurian age have been penetrated by drill­ mostly poorly preserved and difficult to identify, because ing in the western part of the West Texas basin east of of the prevailing recrystallization; better preserved the Sierra Diablo, and part of them has been designated fossils occur in the limestone facies, some of which are as Fusselman; but this part, however, interfingers with silicified. other units, and the stratigraphy of the whole is as yet At most localities in both the dolomite and the lime­ uncertain (Fillman and others, 1958, p. 53-57). stone, the common fossils are colonial corals of favositid and halysitid types, and various horn corals, but more DEVONIAN varied assemblages were observed or collected in places. BEDS OF DEVONIAN AGE In dolomite in the upper part of the formation north of Overlying the Fusselman Dolomite in a few places in the mouth of Black John Canyon (center of western the Sierra Diablo region is a thin unit of chert, thin- part of sec. 9, Block 66, Twp. 5), Josiah Bridge and bedded limestone, and shale of Devonian age. As the- J. Brookes Knight observed stromatoporoids, f avositid unit is scantily preserved in the Sierra Diablo, it is in­ corals, crinoid stems, pentamerid brachiopods, and appropriate to give it a new stratigraphic name based trilobite fragments. On the ridge north of Apache on that region; moreover, stratigraphic terminology of Spring (northeastern part of sec. 7, Block 66, Twp. 5) better preserved comparable beds in the Hueco and in the limestone facies, the same geologists collected the Franklin Mountains farther west has not been satis­ trilobite Dalmanites from near the middle of the forma­ factorily resolved. In this report the unit will therefore tion and stromatoporiods, f avositid and halysitid corals, be referred to by the informal title of "beds of Devonian. and brachiopods from higher and lower beds. ajre. Information obtained during the present investiga­ DISTRIBUTION AND THICKNESS tion is insufficient to determine closely the age of the Fusselman Dolomite in the Sierra Diablo region, and Beds of Devonian age are preserved in two areas in- the fossil collections which were made are not now avail­ the Sierra Diablo region (pi. 1). Their main occurrence able for further study. The various corals could not be is near Black John Canyon in the salient of the Sierra differentiated in the field from those in the Montoya Diablo northwest of the Figure Two Ranch (sees. 9 and Dolomite and would require more detailed study than 12, Block 66, Twp. 5), where they form parts of many has been given to them if they were to yield diagnostic of the fault blocks in an area of several square miles. evidence. However, the occurrence in the Fusselman Relations are complex, not only because of the faulting of pentamerid brachiopods and Dalmanites suggests during Cenozoic time, but also because of pre-Hueco> that the formation is partly or wholly of Silurian age. deformation and the unconformity at the base of the Hueco, so that complete sections of the unit are preserved REGIONAL RELATIONS in few places. In the outermost fault block in the salient Like the underlying Paleozoic formations, the Fussel­ of the Sierra Diablo (northeast of base of geologic sec­ man Dolomite extends farther west in Trans-Pecos tion 9), the full thickness of this unit between the Fus­ Texas and also occurs in many of the ranges of southern selman Dolomite on the northeast and the Barnett Shale and southwestern New Mexico. It attains a maximum on the southeast appears to be about 125 feet. Beds of 40 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Devonian age are also preserved in a much, smaller area According to Hass in the Baylor Mountains to the south, on the southeast­ Conodonts in this collection indicate that the rocks from ern spur of the high point of the mountains (unit 14, which they came are early Late Devonian. This age determi­ geologic section 7, pi. 3, sec. 11, Block 122), where 30-50 nation is based chiefly on the presence of Ancyrognathus feet of the lower part of the unit intervenes between the euglyphea and Neoprioniodus alatus. In the western New York section Ancyrognathus euglyphea had been found by me in the underlying Fusselman and the overlying Hueco Lime­ Pipe Creek member of the Hanover shale, and in Chadwick's stone. type Letchworth shale, which Pepper, DeWitt, and Colton place LITHOLOGY in their West Falls formation. All of these formations fall into Beds of Devonian age are characteristically siliceous. G. A. Cooper's Chemung stage of the Upper Devonian. I have also collected A. euglyphea from the basal beds of the Dunkirk In large part they are bedded chert, mainly buff or shale near Hornell, New York. This formation is the basal brown, but partly white, gray, black, or dull green, in member of Pepper and DeWitt's Perrysburg formation. layers less than an inch to several inches thick; near the Neoprioniodus alatus has a somewhat longer range. It appears middle there are also some more massive beds of buff to range from very high in the Middle Devonian into the highest vitreous chert a foot or more thick. Some of the chert, beds of the Upper Devonian Hanover shale. The species is most common in authentic Upper Devonian rocks. The specimens especially in the lower part, is interbedded with dolo- identified as Palmatolepis cf. P. subrecta occur in the collection mitic or argillaceous thin-bedded limestone, which itself as molds. P. subrecta is commonly found associated with contains many irregular chert nodules and lenses. In Ancyrognathus euglyphea in New York and elsewhere through­ the upper part the chert is interbedded with, and grades out the Interior States. Supporting evidence for a Devonian into, siliceous shale, which is platy, black or brown, and age is indicated by other specimens, which belong to the follow­ bituminous. Conodonts, spicules, and spores are visible ing genera: Ancyrodella whose known range is high Middle Devonian-Upper Devonian; Icriodus, Devonian; and Palmato­ under a hand lens in many of the shales. These upper lepis, Upper Devonian. shaly beds are preserved only in the salient of the Sierra Diablo; the remnant in the Baylor Mountains (geologic REGIONAL RELATIONS section 7) consists only of the lower chert and limestone Beds of Devonian age crop out in the Hueco and beds. STRATIGRAPHIC RELATIONS Franklin Mountains farther west in Trans-Pecos Texas and also in many of the ranges of southern and south­ In most places the beds of Devonian age are overlain western New Mexico. with angular unconformity by the Hueco Limestone, but The beds in New Mexico have long been termed the the next higher unit of the normal sequence, the late Percha Shale (Barton, 1928, p. 15-16), but later they Mississippian Barnett Shale, is preserved in the south­ were subdivided into various formations of Middle to eastern part of the salient of the Sierra Diablo. Ex­ Late Devonian age (Stevenson, 1945, p. 220). Other posures there are insufficient to determine its relations geologists (Kelley and Silver, 1952, p. 72-78) have to the beds of Devonian age, but the known ages of the judged that these formations are faunal zones and not two units suggest that they are disconf ormable and are mappable; hence, they have retained the name Percha separated by a large hiatus. for the whole unit. FOSSILS AND AGE In the Franklin Mountains north of El Paso, Tex., beds of Devonian age, lying between the Fusselman Collections were made by W. H. Hass and others in 1938 from the beds of Devonian age in the lower course Dolomite and beds of Mississippian age, are about 175 of Black John Canyon (southeastern part of sec. 9, feet thick, they have been termed the Canutillo Forma­ Block 66, Twp. 5). The material collected is gray and tion (Nelson, 1940, p. 1964; Cooper and others, 1942, brown shale and siltstone, presumably from the upper p. 1749; King, P. B., King, E. E., and Knight, J. B., 1945, section A, sheet 2; Laudon and Bowsher, 1949, p. part of the unit. In this material W. H. Hass (written commun., 1959) has identified the following conodonts: 46). Part of these beds may be equivalent to those in New Mexico; but they are not entirely comparable, Ancyrodella sp. and despite their small thickness their stratigraphy Ancyrognathus euglyphea Stauffer Bryantodus sp. may be complex. The Canutillo of the Franklin Hibbardella sp. Mountains includes an upper shale, a medial fossili- Hindeodella sp. ferous limestone, sandstone, and siltstone, and a lower Icriodus sp. chert. The upper shale has been correlated with, the Ligonodina sp. restricted Percha of New Mexico and the medial unit Neoprioniodus alatus Hinde Paltnatolepis cf. P. subrecta Miller and Youngquist with the Onate Formation of New Mexico (idem); Paltnatolepis sp. hence, these parts are of late Middle and early Late Polygnathus sp. Devonian age. The lower chert has yielded few or no MISSISSIPPIAN 41 fossils and its age is undetermined, except that it is occurrence is on the southwestern or upthrown side of older than the beds of Middle Devonian age and is the complex of fault blocks in the salient, but a small younger than the Silurian Fusselman. A similar, but remnant is also preserved in the northeasternmost fault less fossiliferous, sequence occurs in the Hueco Moun­ block of the salient (south-central part of sec. 9, Block tains (King, P. B., King, R. E., and Knight, J. B., 1945, 66, Twp. 5). Through most of its extent the Barnett sections B to F, sheet 2; Loudon and Bowsher, 1949, is overlain by the Hueco Limestone, and much of its p. 32-34). surface is covered by landslides, talus, and wash de­ In the Sierra Diablo the conodont-bearing beds are rived from that formation. It is thus exposed only probably in the upper part of the unit here discussed. intermittently, where ravines have cut through these According to Hass, these beds are of early late Devo­ surficial deposits. nian age, hence probably equivalent to the middle or upper part of the Canutillo. They may also be equiva­ LITHOLOGY AND THICKNESS lent to part of the Woodford Chert of Late Devonian The Barnett is black, purplish, or dark-gray, carbon­ and Early Mississippian age, which has been identified aceous shale, which contains small phosphatic and py- in the West Texas basin to the east (Fillman and oth­ ritic nodules and lenses and beds of earthy limestone. ers, 1958, p. 144-145) and in a drill hole between the Most of the shale is barren of larger fossils, but lime­ Sierra Diablo and Hueco Mountains to the northwest stone lenses contain cephalopods, fish teeth, and a few (Lloyd, 1949, p. 50). However, the dominantly cherty pelecypods and brachiopods. Fossils in the limestone beds which form the greater part of the unit in the lenses weather free and strew the surface of the Sierra Diablo are probably correlative with the lower outcrops. chert of the Canutillo Formation in the Franklin The Barnett Shale is visible only in small outcrops, Mountains and, like it, belong to some undetermined so that its full thickness cannot be determined. In the earlier part of the Devonian. northeasternmost fault block of the salient about 75 Correlation of the lower cherty beds in the Sierra feet is exposed, lying on beds of Devonian age and cut Diablo and Franklin Mountains with the Caballos off by a fault above. About a mile to the southwest a Nbvaculite of the Marathon region farther southeast large ravine exposes 135 feet of beds beneath the Hueco has been suggested (King, P. B., and King, R. E., Limestone. (See geologic section 11, p. 133-134.) 1929, p. 912; King, P. B., 1932, p. 96); but this correla­ tion has little precise meaning, as the Caballos is prob­ STRATIGRAPHIC RELATIONS ably a composite unit, formed during a relatively long span of Devonian and possibly early Mississippian time Although the Barnett Shale is overlain unconform- (Berry and Neilsen, 1958, p. 2258-2259). ably by the Hueco Limestone in most places, it is bord­ ered on the south by limestone and shale of Pennsyl- MISSISSIPPIA1T vanian age. The contact of the two units is not exposed, BARNETT SHAIKH although small outcrops of each lie closely adjacent; Beds of Mississippian age in the Sierra Diablo region presumably, however, the beds of Pennsylvanian age were previously designated the Helms Formation succeed the Barnett in normal stratigraphic order. As (King, P. B., 1934a, p. 1542-1543; King, P. B., and the Barnett is of Late Mississippian age and the lime­ Knight, J. B., 1944), for a unit whose type area is in stone and shale are of Early Pennsylvania age at their the Hueco Mountains farther northwest in Trans- base, the two stratigraphic units are probably conform­ Pecos Texas. The beds in the Sierra Diablo are of the able or are separated at most by only a small hiatus. same general age as the typical Helms, but, as explained FOSSILS AND AGE below, are of different facies and are more like the Barnett Formation, whose type area is in the Llano The principal occurrence of larger fossils in the uplift of central Texas (Plummer and Moore, 1921, p. Barnett Shale of the Sierra Diablo region is in the ex­ 24); the name Barnett is therefore used in this report. posures described under geologic section 11. In 1931 J. Brookes Knight collected fossils from units 2,3, and 4 DISTBIBUTION of geologic section 11 (USGS 7019), and in 1936 ob­ In the Sierra Diablo region the Barnett Shale is ex­ tained additional material, probably from the same lo­ posed only on the southeast side of the salient of the cality (USGS 14945). From these collections, the fol­ Sierra Diablo northwest of the Figure Two Ranch lowing forms have been identified by Mackenzie Gordon, (mainly in sec. 12, Block 66, Twp. 5; pi. 1). Its main Jr., and E. L. Yochelson, who supplemented earlier 42 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS identifications by G. H. Girty (written comimm.; 1954, p. 414-417). Throughout its extent it is a deposit of 1955): black shale f acies, generally of middle to late Mississip­ pian age, containing brachiopods (LeiorJiynchus) ,

USGS Collec­ various cephalopods, and other fossils characteristic of tion No. that facies. In its type area the Barnett is mainly of

7019 14945 Meramec age and probably does not extend into the Chester (Cloud and Barnes, 1946, p. 59), but in the Coelenterata: West Texas basin Fillman and others (1958, p. 16-17) zaphrentoid coral, gen. undet______X state that similar shale Brachiopoda: varies in age from place to place in the subsurface so that its Composita sp______X age is Kinderhook, Osage, Meramec, and Chester in the south­ Leiorhynchus sp___-______. X X ern part of the Midland and Delaware basins and Central Basin Ambocoelia sp______X platform. Northward the Barnett Shale grades laterally into Cleiothyridinat sp______X limestone which comes into the section from the bottom, so that Lamellibranchiata: its age is progressively younger and younger until in northern Edmondia? sp______X Gaines County it is restricted to the Chester. Posidoniella sp______X Nuculana sp______X X Presumably the shale exposed in the Sierra Diablo lies Cypricardella sp______X near the western edge of this broad sheet of deposit. Gastropoda: Farther northwest in Trans-Pecos Texas, in the Indeterminate specimen ______X Cephalopoda: Hueco Mountains and beyond, equivalent beds of mid­ Bactrites sp______X X dle to late Mississippian age are of different facies, and orthoceratoid nautiloid- ______X constitute the Helms Formation (Beede, 1920, p. 7-8; Girtyoceras sp______X King, P. B., King, K. E. and Knight, J. B., 1945, sheet Neoglyphioceras cloudi (Miller and Young- quist)______-______-___-_---___. X X 2). The Helms consists of 300 to 500 feet of slabby Neoglyphioceras sp______X limestone, gray and cherty below, changing to brown Goniatites choctawensis Shumard______X X and sandy above, where much green shale is inter- Goniatites crenistria Phillips______X bedded. It contains brachiopods, bryozoans, and cri- Pisces: noidal fragments of several faunas, the lower of which Fish teeth and plates______. X X are of Meramec age and the higher of Chester age. Some geologists have restricted the name Helms to the From another collection from the same locality Chester part of the sequence and have named the Mera­ Miller and Furnish have identified the cephalopods mec part the Eancheria Formation (Laudon and Goniatites sp., Girtyoveras sp. cf. G. mesleranum Bowsher, 1949, p. 17-30, 34), but it is doubtful whether (Girty), and Lyrogoniatites sp. cf. L. newsomi (Smith) these subdivisions represent more than faunal zones. (W. M. Furnish, written commun., 1959). The Helms is probably an equivalent on the outcrop of According to Gordon the limestones which interfinger northward with the These collections are Mississippian in age (Meramec-Chester). Barnett in the West Texas basin, as described above. Goniatites choctawensis and NeoglypJiioceras cloudi are also Presumably a similar interfingering between the Bar­ known from the Barnett shale of north-central Texas and rep­ nett and Helms facies occurs between the Sierra Diablo resent a zone that elsewhere crosses the Meramec-Chester and Hueco Mountains, beneath the surface of the Diablo boundary. A wide form of G. crenistria first described from Plateau. British rocks is found in the upper part of the Moorefield For­ mation of Arkansas. G. choctawensis appears higher, in the PENNSYLVANIA^ Ruddell Shale and Batesville Sandstone. The two species of BEDS OF PENNSYLVANTAN AGE Goniatites are not generally found together, G, crenistria being an earlier form. Beds of Pennsylvanian age in the Sierra Diablo were According to Furnish previously termed Bend Formation and Magdalena The lirate goniatitids are one of the indices for P2 or upper Limestone (King, P. B., and Knight, J. B., 1944), the Visean, world-wide. This now means upper Bollandian of first name being derived from central Texas and the northern England and lower Ohesterian of the Midcontinent. second from New Mexico. For the present, however, \ it seems best not to give them formal names. The beds REGIONAL RELATIONS which are exposed in the Sierra Diablo are only frag­ From its type area in central Texas the Barnett ments of a larger sequence, and although they may be Shale extends westward beneath the West Texas Basin, equivalent to parts of the Bend and Magdalena in their where it has been penetrated by drilling (Galley, 1958, typical areas, the latter have much broader strati- PENNSYLVANIAN 43 graphic range. Moreover, relations between the so- of thicker bedded strata than those farther north, it is called Bend and Magdalena within the Sierra Diablo much better exposed. Its tilted ledges beneath the flat- itself, are in doubt as indicated below. lying Hueco are plainly visibly from Texas Highway DISTRIBUTION 54, nearly 2 miles distant to the east (upper view, Beds of Pennsylvanian age are exposed along the pi. 10). lower part of the Sierra Diablo escarpment west and The Pennsylvanian rocks in this area are gray granu­ southwest of the Figure Two Kanch for a distance of lar thick-bedded limestone that stands in prominent about 3 miles, or from north of Mine Canyon to south rounded ledges as much as 25 feet thick separated by of Marble Canyon (pis. 1, 14). However, its outcrops thinner bedded limestone of much the same nature. are interrupted for more than a mile in the middle, Some of the layers contain moderately abundant fossils, between Mine and Marble Canyons, where Hueco Lime­ but none of the limestone is cherty. The beds dip about stone and Tertiary intrusive rocks extend to the base 10° southward, each bed being truncated northward by of the escarpment. Moreover, the Pennsylvanian rocks the unconformity at the base of the Hueco, so that, north of Mine Canyon, like the adjacent Barnett Shale, although less than 100 feet is exposed at any one place, are extensively concealed by landslides and wash from more than 170 feet of beds occurs in a distance of about the Hueco Limestone higher on the slope. half a mile along the scarp. (See geologic section 12.) LOCAL FEATURES STRATIGRAPHIC RELATIONS The strata north of Mine Canyon (western part of The Pennsylvanian rocks, like the other pre-Permian sec. 16, Block 66, Twp. 5) are those previously called formations of the Sierra Diablo region, lie with angular Bend Formation. Both sequence and structure are ob­ unconformity beneath the Hueco Limestone. The scure because of poor exposures, but there is apparently strata are the youngest which are preserved beneath a lower limestone and an upper shale, which dip gener­ this unconformity at any exposure in the region, and ally southward and are truncated northward by the probably lie in the trough of a syncline that was pro­ unconformity at the base of the Hueco Limestone. duced during the pre-Hueco deformation (fig. 2). As The lower limestone is well exposed in several ravines indicated below, the part of the Pennsylvanian sequence near the foot of the escarpment on the downthrown side that is preserved in the Sierra Diablo is no younger than of a fault in the northwestern part of sec. 16, where Middle Pennsylvanian age, and strata of later Pennsyl­ about 35 feet of beds is visible. The limestone is fine vanian age are missing. These beds and the Hueco are grained to aphanitic, dark gray to black, and weathers thus separated by a considerable hiatus. variously buff, yellow brown, or blue gray. The beds FOSSILS AND AGE are a foot or two to less than an inch thick, and some are separated by layers of platy, shaly limestone. The The Pennsylvanian rocks of the Sierra Diablo region limestone is interbedded with units as much as 4 feet are sparingly to abundantly fossiliferous, the most pro­ thick of brown or black bedded chert. It is only lific part being the upper shale beds north of Mine Can­ sparsely fossiliferous, but small collections have been yon, whose fossils have previously been discussed by obtained. Arick (1932, p. 485-486), Plummer and Scott (1937, p. The upper shale is mainly exposed farther south, in 25), and Miller and Furnish (1940b). The fossil col­ the southwestern part of sec. 16, near some f elsite intru- lections from these beds that are here reported on were sives that project as low knobs at the foot of the escarp­ identified by Mackenzie Gordon, Jr., and E. L. Yochel- ment. The shale is best revealed just north of the son, supplementing earlier identifications by G. H. portal of Mine Canyon, but because it is much decom­ Girty (written commun., 1954,1955). posed at the surface, no more than 10 feet of beds is A few fossils were collected by J. Brookes Knight in exposed at any one place. The shale is poorly consoli­ 1931 from the lower limestone north of Mine Canyon, dated, gray to black, carbonaceous, and richly fossilif­ from exposures in the northwestern part of sec. 16, erous. Large areas of its surface are strewn with fossils Block 66, Twp. 5 (USGS 7023). These consist of that were originally pyritized, but which have now Chonetes sp., Cleiothyridina sp., and G-astrioceras weathered to limonite and have been separated from octidentale (Miller and Faber). In addition, gastro­ their matrix. pods were observed in the limestone in the field, but they The beds of Pennsylvanian age south of Marble Can­ are not now represented in the collections. These yon (east edge of sec. 21, Block 66, Twp. 5), like those fossils are too meager to indicate the stratigraphic posi­ north of Mine Canyon, form the basal part of the Sierra tion of the beds containing them, but the Gastrioceras Diablo escarpment and are overlain unconformably by also occurs in the upper shale beds, exposed nearby to the Hueco Limestone. However, as this part is formed the south. 44 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

EXPLANATION MODERN OUTCROP AREAS

Rocks older than Permian

Limestone and shale of Pennsylvanian age

M Mississippian Barnett Shale

DS Devonian and Silurian Beds of Devonian age and Fusselman Dolomite

Oum Upper and Middle (?) Ordovician Montoya Dolomite and beds of Middle(?) Ordovician age 01 Lower Ordovician El Paso Limestone and Bliss Sandstone p v Precambrian(?) Van Horn Sandstone

p Precambrian Hazel, Allamoore, and Carrizo Mountain Formations, and associated igneous rucks

Modern geologic contact

Known or inferred paleogeologic contact

Faults which are known or inferred to have been displaced in pre-Permian time Dotted where concealed by younger pre-Permian deposits

FIGUEB 2. Map of Sierra Diablo region showing paleogeology of the surface on which the Hueco Limestone (basal Permian) was deposited. PENNSYLVANIAN 45 The upper shale beds north of Mine Canyon have In addition to the cephalopods listed above, Miller yielded the following fossils. and Furnish (1940b) have described the species Pseudo­ paralegoceras "bellUineatum. USGS Collection No. The cephalopods of this fauna indicate that it is of

7018 14944 8105 8106 Atoka age. These were correlated by Plummer and Scott (1937, p. 25) with those of their Gastrwceras Coelenterata: listeri zone, which occurs a little below the top of the Chaetetes sp ______X Smithwick Shale of the Llano uplift in central Texas, X or in strata now considered to be late Atoka in age. Zaphrentoid coral, gen. undet ______X However, Gordon (written commun., 1954) states: Bryozoa: "This fauna is correlated with that in the lower part of Stenoporoid bryozoan. ______X X X the Atoka Formation in eastern Oklahoma and western Brachiopoda: Arkansas, particularly because of the occurrence of Composita sp______X Diaboloceras varicostatum Miller and Furnish in both." Productoid brachiopod indet ______X A small collection of fossils was made by J. Brookes Lamellibranchiata : Knight and the writer in 1931 from the limestone beds Nuculana arata (Hall) .______X X X Nuculana n. sp______X X X X south of Marble Canyon, probably mainly from units 5 Nucula cf N. (Nuculopsis) girtyi Schenk. X X and 6 of geologic section 12 (USGS 7010A; field loc. 12). Conocardium n. sp_.______X X X X According to Gordon and Yochelson (written commun., X X 1954) Gastropoda: Euphemites sp. indet_.______X The Pennsylvanian age of the rocks is borne out by the fauna. Knightites (Retispira) bellireticulata Included are such forms as the corals Caninia and Chaetetes ; X X the brachiopods Chonetes, Dictyoclostus, Marginiferal spp., Cindidonema cf. C. texanum Knight- __ X Echinoconchus, Rhipidomella, Girtyettal, Dielasma, Spirifer cf. Platyzona sp______X S. rockymontanus Marcou, Punctospirifer, Phricodothyris per- X X X X plexa (McOhesney), Crurithyris, Cleiothyridina, and Composita Slraparollus aff. S. savagei Knight- __ _ X X X subtilita (Hall) ; and several pelecypods and gastropods. Spirioscala sp ______X Gastropod n. gen ______X X X ---- Besides these fossils, Garner L. Wilde reports the oc­ Gastropods indet ______X currence in the rocks south of Marble Canyon of Fusu- Cephalopoda: lina^ Wedekindellina, and Fusulinella, which indicate an Bactrites sp ______X Dolorthoceras 3 spp ______X X X early Des Moines age (Kepple and others, 1962, p. 20). Cydoceras sp______X The corals and brachiopods of this fauna are not diag­ X X X nostic of any particular zone in the Pennsylvanian, but Adnatoceras sp ______v some of them are more characteristic of the lower part Lirocerast sp ______X than the upper part of the Pennsylvanian in nearby re­ Stenopronorites ?p______X Boesites scotti Miller and Faber______X gions. Chaetetes and Spirifer rockymontanus are thus Gastrioceras occidentale (Miller and common in the lower division of the Pennsylvanian Faber) ______X X X X in the Hueco Mountains farther northwest in Trans- Diaboloceras varicostatum Miller and Pecos Texas (King, P. B., King, R. E., and Knight, Furnish______X X X X Pseudoparalegoceras lenticulare (Plum­ J. B., 1945, sheet 2, sections G, H). The fusulinids re­ mer and Scott)______.______X X X X ported by Wilde confirm this correlation. Glaphrites raymondi Plummer and REGIONAL RELATIONS Scott ______X X X X Proshumardites primus (Plummer and Pennsylvanian rocks are exposed in many mountain Scott ______X ranges northwest of the Sierra Diablo region in Trans- Pisces: Pecos Texas and in New Mexico; they have also been Fish teeth ______X penetrated by numerous wells in the West Texas basin 7018 (field loc. 12). Shale hills north of portal of Mine Canyon and west of felsite to the northeast and east (Galley, 1958, p. 419-423). In intrusive, in southwestern part of sec. 16, Block 66, Twp. 5. Collected by J. most places the Pennsylvanian sequence is thicker and Brookes Knight, July 1931. 14944 (field label Pbs-1). Approximately the same locality as that of 7018. Collected more complete than in the Sierra Diablo, and much is J. Brookes Knight, 1936. known of its stratigraphy (see, for example, Thompson, 8105. Approximately the same locality as that of 7018. Collected by M. B. Arick for Humble Oil Co., February 1931. 1942, p. 27; Lloyd, 1949, p. 34H.O). Because of the 8106. About a quarter of a mile north of the locality of the preceding collections, fragmentary representation of the Pennsylvanian rocks north of felsite intrusive. Collected by M.B. Arick for Humble Oil Co., February 1931. in the Sierra Diablo, it is inappropriate to summarize 46 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS the regional stratigraphy of the Pennsylvanian in this bearing shales of the lower part of the Pennsylvanian report, but it is appropriate to speculate regarding the System in the west Texas-New Mexico region do not relation of this fragmentary sequence to the more com­ form persistent time-stratigraphic units of wide extent, plete sequences known elsewhere. but are f acies that occur in different stratigraphic order In the Sierra Diablo the sequence and relations of the from one mountain area to another. different parts of the Pennsylvanian strata are un­ PERMIAN certain, not only because of disconnected exposures, Rocks of the Permian System occupy the largest sur­ but because the rocks and fossils of the parts north face area of any in the Sierra Diablo region. They are of Mine Canyon and south of Marble Canyon are prominently exposed on the escarpments on the east, so different that few comparisons between them are north, and south sides of the Sierra Diablo and form possible. However, the strata in all exposures dip to many square miles of its summits. They also occur in the south, and those north of Mine Canyon are adjacent the adjacent Baylor Mountains, Beach Mountain, and to exposures of the Mississippian Barnett Shale, so the Carrizo Mountains, as well as in the Delaware and that they would seem to form the base of the unit and Wylie Mountains, across the Salt Basin in the northeast to lie beneath the strata south of Marble Canyon. and southeast corners of the report area (pi. 1). Comparison with the more complete section of the Because of the variability of the subdivisions of the Magdalena Group in the Hueco Mountains farther Permian System in the Sierra Diablo region, it is diffi­ northwest in Trans-Pecos Texas suggests another pos­ cult to ascribe a total thickness to the part preserved sible interpretation (King, P. B., King, K. E., and there. Several thousand feet is exposed nearly every­ Knight, J. B., 1945, sheet 2). In that area the Mag­ where along the escarpments in the northeastern Sierra dalena Group, which is about 1,300 feet thick, forms Diablo (pis. 4-8), the maximum being 2,128 feet on three lithologic divisions which can be correlated on the Victorio Peak. At the north end of the range near basis of fusulinids and other contained fossils with South Mesa, 2,140 feet is exposed, which includes strata the subdivisions of the standard Pennsylvanian section higher than those on Victorio Peak. Smaller thick­ of the midcontinent region. The lower division, 500 nesses of the lower part of the Permian are preserved in feet thick, is thick-bedded coralline limestone and the southern Sierra Diablo, the Baylor Mountains, is approximately of Morrow and early Atoka age. The Beach Mountain, and the Carrizo Mountains. In the middle division, 300 feet thick, is marl, marly limestone, Wylie Mountains to the southeast the Permian sequence and shale and is approximately of late Atoka and early is 4,473 feet thick, but most of it is exposed only east of Des Moines age. The upper division, of variable thick­ the report area. Permian strata exposed in the Dela­ ness because of the unconformity at the top, is lime­ ware Mountains within the report area are 1,783 feet stone and interbedded marl and is approximately of thick, but they are only part of the much thicker se­ late Des Moines, Missouri, and early Virgil ages. quence of the Delaware and Guadalupe Mountains. Lithologically, the lower limestone of the Magdalena The Permian rocks of the Sierra Diablo region are Group in the Hueco Mountains closely resembles the largely limestone, dolomitic limestone, and dolomite but beds south of Marble Canyon in the Sierra Diablo, and there are subordinate layers of shale, sandstone, and like them contains Chaetetes and Spirifer rockymon- conglomerate. Their stratigraphy is the most complex tanus. This lower limestone lies directly on the Missis­ of the rocks of any system in the region. They vary sippian Helms Formation, with no intervening shale greatly, not only in thickness, but also in lithology and or thin-bedded cherty limestone like the beds north faunas. In some areas the whole Permian is a monot­ of Mine Canyon in the Sierra Diablo. The first onous sequence of poorly fossiliferous dolomitic lime­ shale in the Hueco Mountains section is that in the stone, yet only a few miles away it may be interbedded lower part of the middle division. Like the shale north richly fossiliferous massive limestone, thin-bedded lime­ of Mine Canyon in the Sierra Diablo, this is of Atoka stone, and shale (pi. 4). Many of these variations are age. The two shales might be equivalent, although that visible in three dimensions because the rocks are ex­ in the Hueco Mountains lacks the prolific cephalopods posed not only on the escarpment faces, but in canyons of the Sierra Diablo, and contains mainly a brachiopod behind the escarpments and in outlying mountains in fauna. If the two are equivalent, the true sequence of front of them. the Pennsylvanian limestone strata in the Sierra Di­ The complex variable stratigraphy of the Permian ablo is the reverse of the sequence indicated by the rocks was created by unequally subsiding tectonic units field relations. in the depositional area the Delaware basin on the A possible alternative is that the thick-bedded coral­ northeast and the Diablo platform on the southwest line limestones and the cephalopod- or brachiopod- (fig. 3). Because of unequal subsidence, the basin gen- PERMIAN 47 107' 106 = 105' 104° 103' 102' 101' 100°

29

EXPLANATION

Outcrops of Wolf camp, Leon­ Boundaries of provinces of Basin areas Deformed pre-Wolfcamp Area covered by ard, Guadalupe, and Ochoa Permian time Paleozoic rocks of Mara­ this report Series (Permian), and their thon folded belt equivalents

FIGURE 3. Map of parts of western Texas and southeastern New Mexico stowing provinces of Permian time. 48 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS erally stood at greater depth than the platform; thus, Permian section in the Guadalupe Mountains and ex­ the basin received mainly shaly and sandy deposits, tends the sequence to the base of the system. the platform mainly stratified carbonate deposits; on Stratigraphic terminology of the Permian rocks in the intervening basin margin grew extensive limestone the Sierra Diablo region has varied with the work of reefs and banks which were the home of varied marine successive geologists and has evolved with increasing life. Because of unequal subsidence, many of the units knowledge. Because of the long span of the present on the platform are also separated by unconformities, investigation, the Stratigraphic terminology used by the along which the underlying strata have been eroded, author and his colleagues is not the same in their suc­ and the overlying strata wedge out by overlap. cessive publications. The following table compares The Permian rocks of the Sierra Diablo region belong the classification used in the present report with that largely to the Wolfcamp and Leonard Series, the suc­ in earlier reports. ceeding Guadalupe Series being represented merely by The Permian rocks were investigated primarily by small remnants at the north end of the range. This means of description and measurement of Stratigraphic situation contrasts with that in the Guadalupe Moun­ sections, mostly the work of J. Brookes Knight. The tains, across the Salt Basin to the north, where only the greater part of the fossils collected were on the lines of upper part of the Leonard Series emerges from beneath these Stratigraphic sections. Details of the nature of a thick sequence of the Guadalupe Series, the latter be­ the Permian rocks may be found in the descriptions of ing followed by part of the Ochoa Series (King, P. B., the sections at the end of the report. The sections are 1948, p. 7-100). The Permian section in the Sierra also illustrated on plates 5-8. Variations in the Per­ Diablo thus usefully supplements the more famous mian rocks between the sections were observed during

Stratigraphic classification of Permian rocks in Sierra Diablo region

Richardson, 1914 Beede, 1920 King, P. B., and King, E. E., King, P. B., 1934b King, P. B., 1942; King, P. B., This report 1929; King, B. E., 1931 and Knight, J. B., 1944

Goat Seep Goat Seep Limestone Limestone

Word Delaware Mountain Delaware Mountain Sandstone tongue Sandstone tongue Not Formation Formation of Cherry Canyon of Cherry Canyon observed Formation Formation

Cutoff Shaly Cutoff Shale Member

Victorio Peak SpringLimestoneBone FormationLeonard Victorio Peak Massive Victorio Peak Victorio Peak Member Member Gray Member Limestone (zone D)

Leonard LimestoneBoneSpring Bone Canyon (zone C) Hueco Member Black Limestone limestone, Bone Spring etc. Limestone (zone B)

Hess FormationGym Formation (zone A) Limestone rt Main body LimestoneHueco -2 of formation d) Manzano Fi i-3 Upper Basal clastic g Powwow Wolfcamp Basal beds member g Member HH Formation HH PERMIAN 49 field mapping, as shown on the geologic map (pi. 1) ing the present investigation and do not include those and in views of the escarpment faces and canyon walls, yielded from other investigations. In each table the which are illustrated in the panoramas (pis. 10,11, and fossils are shown according to the formations in which upper 12) and in geologic sections V-V to Z-Z' (pi. 4). they occur, and in the order in which they are given in The text which follows is a summary of these data. the stratigraphic sections and fossil lists (p. 134-170). It has not proved feasible to introduce any further re­ PRESENTATION OF PAUBONTOLOGIC DATA finements in zonation. However, the fossils of the Fossils were collected from the Permian rocks of the Hueco Limestone occur in several well-marked f acies, Sierra Diablo region during successive field seasons of shown separately in tables 3-5 the calcitic limestone of the present investigation, and have been identified at the southern and southwestern part of the Sierra Diablo different times by various paleontologists. Brachio- region, the marl and calcitic limestone of the northeast­ pods of the earlier collections were identified by E. E. ern part, and the main body of the formation of the King (1931, p. 14-15), and fusulinids by C. O. Dunbar northeastern part, containing only foraminifers. The and J. W. Skinner (1937, p. 587-590). Later collec­ fauna of the Bone Spring Limestone, although not di­ tions were identified by P. E. Cloud, Jr., E. L. Yochel- visible into zones or facies, is so extensive that it has son, and L. G. Henbest (written commun., 1954,1955); been subdivided according to taxonomic groups into additional identifications were made by E. M. Finks, tables 5-7. The faunas of the Victorio Peak and Goat A. E. Palmer, and I. G. Sohn. Fossils collected by Seep Limestones are shown in tables 8 and 9, respec­ other geologists from the Permian rocks of the region tively. have been identified and described by G. H. Girty (1931), A. K. Miller and W. M. Furnish (Miller and HUECO LIMESTONE Furnish, 1940a; Miller, 1945), C. O. Dunbar (1953), The lowest Permian formation of the Sierra Diablo F. G. Stehli and G. A. Cooper (Stehli, 1954; Cooper region is the Hueco Limestone, whose type area is in the and Stehli, 1955), E. L. Yodielson (1956, 1960), and Hueco Mountains farther northwest in Trans-Pecos others. Texas. As indicated above, the Hueco as now defined Identifications of Permian fossils collected during includes only part of the beds originally so named by both earlier and later phases of the investigation are Eichardson (1904, p. 32-38; 1908, p. 480-482), or the listed on pages 134-170, in the texts of the stratigraphic part which contains the Hueco fauna as understood by sections, or in appropriate geographic order where not Girty. This part is a carbonate facies of the Wolf camp collected in measured sections. Stratigraphic position Series, which is extensive in northwestern Trans-Pecos of most of the collections is indicated on the plotted Texas and adjacent areas. In both the Hueco Moun­ stratigraphic sections (pis. 5-8) and their geographic tains and the Sierra Diablo, the Hueco lies uncon- position on the index map of the region (pi. 9). formably on Pennsylvanian and earlier rocks. In the Because many revisions of the fossil terminology and Hueco Mountains its top is poorly defined, because of taxonomy have been made between the times of the uncertainty as to what strata, if any, are preserved above earlier and later investigations, the names used for the it; in the Sierra Diablo the Hueco is overlain by the same fossils are likely to vary from one collection to Bone Spring Limestone of the Leonard Series, at least another. Although it has not been feasible to revise the in part unconformably. earlier identifications to agree with the later, the earlier identifications are of historical interest; some of the OUTCBOP earlier collections, for example, contain type specimens The Hueco Limestone is extensively exposed in the of genera or species. All collections marked "KEK" southern half of the report area (pi. 1). It forms most and "D & S" on pages 134-170 are therefore listed in the of the surface of the Sierra Diablo south of the Victorio form in which they were originally presented, with flexure and stands in ledges or cliffs at the edges of the the understanding that they would require review to bordering escarpments. It also forms much of the bulk harmonize them with the collections marked "USGS" of the Baylor and Wylie Mountains to the east and or "F." southeast, and is preserved in smaller outliers in Beach To provide a sampling of the whole fauna of the dif­ Mountain, the Carrizo Mountains, and the Streeruwitz ferent Permian formations in the Sierra Diablo region, Hills. North of the Victorio flexure in the Sierra based on a single taxonomic standard, the later fossil Diablo, the Hueco stands at a lower level than farther identifications have also been assembled in a set of tables south, and is extensively covered by younger Permian (tables 3-9). formations. Here it projects as a bench on the lower The fossils listed in these tables represent only part part of the escarpment between Victorio Peak and of those which have been collected and identified dur­ Apache Canyon; within the range it emerges only in 50 GEOLOGY OF THE SIEKRA DIABLO REGION, TEXAS Victorio and Apache Canyons and in the uplift on the wedge out by overlap. The Powwow Member of the south side of the Sierra Prieta intrusive. The Hueco Sierra Diablo region is formed of varicolored coarse to Limestone doubtless extends northwestward beneath fine clastic rocks, which become coarser downward and the surface from the Sierra Diablo and joins the type southward, and pass upward and northward into marl Hueco in the Hueco Mountains. and thin beds of limestone that are conformable with the main body of the formation. All the Powwow THICKNESS strata are poorly resistant to erosion and form slopes The thickness of the Hueco Limestone varies re­ between the ledges above and below, on which exposures markably. The gross pattern of the variations is not are likely to occur only in ravines; in places the Pow­ entirely clear, as in many places the full thickness of wow has been mapped principally by its topographic the formation is not preserved; where preserved, it ap­ expression. As in other transgressive deposits, fossils pears to be greatest in the platform area to the south occur only in the more marly or limy beds above the and southwest and thinnest near the edge of the base; these fossils are like those in the main body of basin area to the northeast. the formation which succeeds it, and their facies vary The Hueco is about 1,400 feet thick in the Wylie in the same manner as those of the fossils of the over­ Mountains (geologic section 13) and 1,100 feet or more lying strata. thick in the head of Apache Canyon (geologic sections The main body of the Hueco Limestone is not divisi­ 37-40). At the lower end of Apache Canyon it thins ble into units except in local areas, but its lithology and to a few hundred feet (geologic sections 36, 37). Along faunas vary significantly from place to place (fig. 4). the Sierra Diablo escarpment between Apache Canyon Toward the south and southwest it is a thin- to thick- and Victorio Peak, the thickness averages 500 feet, but bedded gray calcitic limestone with a well-defined but it is thicker than 900 feet in places and thinner than rather restricted invertebrate assemblage. Farther 400 feet in others (geologic sections 27-34). At several northeast, as in the Baylor Mountains and the central places in the northern Bay lor Mountains it wedges out and northern Sierra Diablo, much of the main body is a entirely, so that the succeeding Bone Spring Limestone thin-beded dolomitic limestone, containing few fossils directly overlies the earlier rocks. other than fusulinids. However, in the same area the Many of the variations in thickness of the Hueco are basal Powwow member contains invertebrate fossils caused by overlap of the formation against its uncon- much more varied than those farther southwest. This formable basal surface and by truncation of its top be­ fossil assemblage extends in places into the main body fore the Bone Spring was deposited over it. These and occupies all of it near Victorio Peak; here it occurs relations, or combinations of both, are well displayed in thin- to thick-bedded calcitic limestone, unlike the in Apache Canyon and parts of the Baylor Mountains. prevailing dolomitic limestone of the vicinity. There is also a possibility, difficult to assess, that differ­ The calcitic southern and southwestern facies was ent thicknesses of Hueco Limestone were deposited deposited on the platform of Hueco time. The other from place to place. two facies to the northeast were deposited nearer the LITHOLOGY AND SUBDIVISIONS basin of Hueco time. However, the facies of the Hueco seem to be little related to the Victorio flexure, which In the Sierra Diablo region the Hueco Limestone in­ markedly influenced the distribution of facies in the cludes a thick main body of bedded calcitic and dolo- succeeding Bone Spring deposits. mitic limestone and thinner basal beds, the Powwow SOUTHERN PAET OF REPORT AREA Member. The type Powwow Member is in the Hueco Moun­ In the southern part of the report area the Powwow tains, where it forms a basal lens of conglomerate and Member is thick and coarsely clastic at most places; the red beds a few miles long (King, P. B., and King, R. E., main body of the formation is of the calcitic southern 1929, p. 911; King, P. B., King, E. E., and Knight, and southwestern facies. The full sequence of the J. B., 1945). The beds termed Powwow Member in the Hueco is exposed in the Wylie Mountains (geologic sec­ Sierra Diablo region (King, P. B., and Flawn, P. T., tion 13, pi. '5), but only partial sections of the lower part 1953, p. 34-36; 98-99; Hay-Roe, 1957; Twiss, 1959) 3 are preserved farther west where, in places, the eroded are more extensive and varied. They everywhere under­ top of the formation is overlain by Cretaceous strata. lie the main body of the formation except at a few places Among the better exposed sections to the west are those on the higher parts of the pre-Hueco surface where they on Threemile Mountain northwest of Van Horn (geo­ logic sec. 15, pi. 5) and on the butte northwest of Eagle 8 Hay-Roe and Twiss class the Powwow as a formation separate from Flat section house at the south end of the Streeruwitz the Hueco Limestone, which they restrict to the main body of the formation of present terminology. Hills (geologic section 20, pi. 6). PERMIAN 51

EXPLANATION

OUTCROP AREAS

Rocks older and younger than Permian

OTHER SYMBOLS

Thickness of Hueco Limestone in feet, where determined

Edge of hills or escarpments which were partly or wholly overlapped by Hueco Limestone

Trend of linear features in Hueco Limestone Alined fusulinid tests or echinmd spines

Boundary between calcitic limestone on southwest and thin-bedded fusulinid-bearing dolomitic lime- 95 stone on northeast

Approximate western limit of marl and calcitic limestone in lower part of formation which contains varied fossils

FIGURE 4. Map of Sierra Diablo region showing paleotectonics of Hueco Limestone. 52 GEOLOGY OF THE SIEKKA DIABLO REGION, TEXAS In the southern part of the report area the Powwow echinoid spines and plates, and a few brachiopods. The Member lies mainly on various Precambrian and Pre- marly layers contain mollusks, particularly poorly pre­ cambrian(?) formations, although on Beach Mountain served bellerophontoid gastropods. Fusulinids are it extends onto Ordovician rocks. Its basal surface was lacking in most places, although a few stray forms have moderately irregular, as shown by large variations in been discovered. They are abundant about 500 feet thickness of the member within short distances and by above the base in the Wylie Mountains, at a level higher variations in the character and volume of the coarser than any strata preserved farther west, as at Threemile clastic constituents. In the Wylie and Carrizo Moun­ Mountain and Eagle Flat. tains these variations indicate a basal topography with Farther north this calcitic limestone changes into a relief of several hundred feet (Flawn, in King, P. B., more dolomitic fusulinid-bearing limestone. In ex­ and Flawn, P. T., 1953, p. 34-35, 43; Hay-Roe, 195T; posures on the east side of Beach Mountain (geologic Twiss, 1959). In the Carrizo Mountains, Powwow section 16), both the main body of the Hueco and the deposits were laid against a north-facing scarp along Powwow Member are dolomitic, but the same fossil the Hillside fault. North of the fault the Powwow is assemblage occurs as farther south, here nearly de­ as much as 250 feet thick and overlies the Van Horn stroyed by dolomitization. Along the south-facing Sandstone, but it contains abundant angular fragments escarpment of the Sierra Diablo, dolomitic layers come of the metarhyolite that intrudes the Carrizo Mountain in gradually eastward, by interbedding and inter- Formation south of the fault. These fragments de­ tonguing, and fusulinids increase correspondingly. On crease in abundance and coarseness northward, where the escarpment above the Hazel mine (geologic section they are intermingled with fragments from other 25, pi. 6) the main body of the Hueco is largely thin- sources (King, in King, P. B., and Flawn, P. T., 1953, bedded dolomitic limestone, which is different from the p. 99). The Ordovician carbonate rocks of Beach limestone farther south and west and contains many Mountain must have projected as an erosion remnant on fusulinids. The boundary between the calcitic and dolo­ the pre-Hueco surface. At Threemile Mountain the mitic facies of the main body of the Hueco is traceable basal 70 feet of the Powwow is a lenticular mass of northwestward from the Old Circle Ranch (geologic limestone pebbles and cobbles of the El Paso Limestone, section 24, pi. 6) across low exposures in the southern evidently derived from talus of an ancestral Beach part of the Sierra Diablo.

Mountain, not far to the north. BAYLOR MOUNTAINS Aside from the breccia and conglomerate derived In the Baylor Mountains the Hueco Limestone lies from earlier rocks, much of the Powwow in the southern with angular and erosional unconformity on older area is bedded coarse sandstone, partly arkosic, of ver­ Paleozoic rocks, mainly the El Paso, Montoya, and milion-red, purple, brown, or yellow hues. Some of this Fusselman Formations, and is separated from the Bone sandstone was assigned to the Van Horn by earlier Spring Limestone above by a less evident unconformity geologists (Richardson, 1914, p. 4; Baker, 1927, p. 9), (fig. 5). The Hueco varies greatly in thickness in but its true age is indicated not only by its more varied different parts of the mountains, by overlap along the nature, but by its unconformable relations below and unconformity at the base and by truncation along the conformable relations above. unconformity at the top. The coarsely clastic and varicolored parts of the Striking features of the basal unconformity are hills Powwow are succeeded at most places by more cal­ of older Paleozoic rocks, against and over which the careous strata, mainly gray or yellow calcareous shale Hueco was deposited (fig. 4). The pre-Hueco hills or marl, but they include thin intercalated limestone seem to be most extensive in the northern part of the beds. These strata are fossiliferous the fossils mountains, near the Victorio flexure, but the west edge weathering free on the surface in places and they have of another hill is well exposed at the "unconformity yielded large collections at Threemile Mountain and in locality" in the southern part (sec. 3, Block 65, Twp. the Streeruwitz Hills. 7) (fig. 5A) . The edges of some of the hills were steep The overlying main body of the formation is strati­ scarps as much as 200 feet high, near which the basal fied limestone in thin to thick beds, mainly gray and Hueco contains breccia lenses formed of coarse frag­ calcitic, but with some more dolomitic layers, and with ments of the adjacent older rocks. The Hueco was many poorly resistant marly partings; a few of the beds draped over the hills of older rocks, and its strata slope contain small chert concretions. The main body char­ away from them with initial dips, some as steep as 15°. acteristically forms ledges and slopes. The limestone Draping of the Hueco over the hills of older rocks beds contain an abundant but restricted invertebrate may account for some of the truncation of its upper fauna that includes minute staffellid foramiiiifers, surface. At the beginning of Bone Spring time the PERMIAN 53

WEST EAST Ei Paso Limestone

^prTT.\» .:..*I».*."-r : v»; ' : ' - * ; Van Horn Sandstone % « - «Y;l'V'»'*V.^r

NORTH SOUTH Bone Spring Limestone

B

WEST EAST Bone Spring Limestone 3

APPROXIMATE SCALE 500 1000 1500 2000 FEET

FIGURE 5. Detailed sections showing unconformities below and above Hueco Limestone in Baylor Mountains. A, South end of mountains ("unconformity locality," northwestern part of sec. 23, Block 65, Twp. 7) showing unconformity at base of Hueco and one between Van Horn sandstone (Precambrian?) and Bliss Sandstone (Ordovieian). B, Northwestern part of mountains (southwestern part of sec. 43. Block 65, Twp. 6) showing unconformities below and above Hueco. 0, Outlying hill northwest of mountains, west of Texas Highway 54 (center of sec. 9, Block 66, Twp. 6) showing unconformity at top of Hueco. higher standing parts of the Hueco, over the buried even here does not exceed 100 feet. Where the Pow­ hills, were eroded more than the lower. The most wow occurs, it is red, bun3, and yellow marl and shale prominent exposure of an angular unconformity be­ interbedded with conglomerate layers containing tween the Hueco and Bone Spring is on a hill in the pebbles of the older Paleozoic carbonate rocks. northwestern Baylor Mountains west of Texas High­ The main body of the Hueco Limestone in the Baylor way 54 (summit 4410, sec. 9, Block 66, Twp. 6) (fig. Mountains is largely thin-bedded aphanitic dolomitic 50) , where the Bone Spring overlies Hueco strata that limestone, containing few fossils other than molds of dip 1° west or southwest; inclination of the Hueco was small fusulinids. Although few of the limestone beds probably a primary slope off a hill of El Paso Lime­ are thick or massive, the whole unit stands in steep stone that is exposed east of the highway. slopes or cliffs. The main body is as much as 700 feet The Powwow Member is thin in the Baylor Moun­ thick along Red Tank Canyon and elsewhere in the tains and is missing entirely near the buried hills in southern part of the mountains, but farther north both the northern part. It is thickest to the southeast, but it and the underlying Powwow thin out. In the north- 54 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS ern part of the mountains the Hueco is a dolomitic lime­ Canyons (geologic sections 32 and 33, pi. 7), however, stone no more than a few hundred feet thick (geologic the lower 120-150 feet is thick-bedded blue-gray calcitic sections 18 and 19, pi. 5), and at a few places it is limestone, with some intervening thinner beds, which missing entirely on tops of the hills of the underlying contain fusulinids and other fossils similar to those in rocks (fig. 5B ; section Z-Z', pi. 4). the Powwow Member beneath. At the east base of Vic­ torio Peak (geologic section 29, pis. 6, 7), where the CENTRAL SIERRA DIABLO main body is exceptionally thin, it is fossiliferous On the east-facing escarpment of the Sierra Diablo, throughout and is all calcitic limestone in thin to thick the Hueco forms a bench or line of cliffs which is at the beds. The thin beds are dark gray to black, with wavy top to the south of the Victorio flexure, but which de­ bedding surfaces, irregular chert nodules, and partings scends to the base to the north (pi. 10). The Hueco is of marl. The thick beds are light gray and cherty and also exposed behind the escarpment in Victorio Canyon. are lenticular or moundlike; some are brecciated. At In the central Sierra Diablo the uncomf orable base the top is an especially thick lens or reef body (the of the Hueco emerges only toward the south and north. "KHz lens" of Dunbar, 1953, p. 802), a quarter of a mile South of the Victorio flexure the Hueco lies on red across and 115 feet thick at the apex. It is mostly mas­ sandstone of the Precambrian Hazel Formation, but sive gray limestone containing sponges, corals, massive it overlies a hill of steeply dipping Montoya Dolomite bryozoans, and a few other fossils, but it is brecciated in Victorio Canyon (section X-X', pi. 4). Where the at its edges. The succeeding Bone Spring beds overlap base is exposed again from Marble Canyon northward, the lens. the Hueco lies on higher Paleozoic formations, includ­ APACHE CANYON AREA ing rocks of Peimsylvanian age. At the lower end of Apache Canyon the Powwow The Powwow Member at the base is generally some­ Member is thin or missing, and the overlying main body what more than a hundred feet thick, but it is as much of the formation is less than 200 feet thick (geologic as 250 feet thick at a locality south of Victorio Peak section 36, pi. 8). The Hueco dips south westward at an (geologic section 27, pi. 6) and another three-quarters angle of a few degrees up the canyon, but its top, over­ of a mile south of Marble Canyon, both probably in lain unconformably by Bone Spring Limestone, rises local valleys on the pre-Hueco surface. At the east a thousand feet in the same direction (pi. 11; section foot of Victorio Peak (geologic section 29, pis. 6, 7), V-U1', pi. 4). The Hueco thus forms as much as the 134 feet is exposed, but the base is not visible. The lower half of the walls and the canyon in its middle lower part of the Powwow is clastic, varicolored, and and upper course, but the beds exposed are younger and conglomeratic. Conglomerate fragments were derived higher than those at the lower end. The whole of the from the Hazel Formation, the Van Horn Sandstone, formation is not exposed-in the upper part of the can­ and various older Paleozoic formations. The associated yon, but matching of units in different sections suggests sandstone and shale beds are arkosic and red, yellow, that it is more than 1,100 feet thick. or gray. The upper part is yellow or gray marl and Three subdivisions of the Hueco Limestone are recog­ shale interbedded with thin layers of limestone, and in nizable in the canyon, designated as divisions A, B, and places is abundantly f ossilif erous. Large collections of C in geologic sections 37,38,39, and 40 (pi. 8). Division invertebrate fossils have been obtained from this part A at the base is about 400 feet thick; it is thick-bedded of the Powwow Member near the portals of Victorio, dolomitic limestone, weathering brown and craggy, and Marble, and Mine Canyons. contains some interbedded thinner layers. Division B, The overlying main body of the Hueco is more than about 250 feet thick, is light-gray to dark-gray calcitic 600 feet thick at Bat Cave south of the Victorio flexure limestone, resembling the southwestern f acies of the for­ (geologic section 26, pi. 6), where the top is not pre­ mation, which forms ledges that are lighter gray and served, and about 800 feet thick south of Black John less massive than those of the divisions below and above. Canyon (geologic section 34, pi. 7), but it is much thin­ Division C is preserved only in the headwaters of the ner at nearby localities. At Marble Canyon (geologic canyon, where it is about 400 feet thick; it is thick- section 32, pi. 7) it is 357 feet thick, and at the east base bedded dolomitic limestone like division A. In places it of Victorio Peak (geologic section 29, pis. 6, 7), about contains thin interbedded layers of porcelaneous dolo­ 200 feet. mite that weather white and splintery. All the divi­ Most of the main body, and especially its upper part, sions contain abundant fusulinids, but other fossils are is thin-bedded dark-gray aphanitic dolomitic limestone scarce. The three subdivisions are local units that have containing few fossils other than fusulinids, most of no counterparts elsewhere in the Sierra Diablo region; which are preserved as molds. Near Marble and Mine they have probably been produced by intertonguing of PERMIAN 55 the northeastern and southwestern facies of the forma­ but it is scantily represented in the collections. Diel- tion. asma is abundant at a few localities, but rare elsewhere. Northwest of the head of Apache Canyon the Hueco Mollusca, especially gastropods and pelecypods, are is exposed in an uplift on the south side of the Sierra numerically as abundant as the brachiopods, but are Prieta, over an area of a few square miles. About 550 equally restricted as to kind. The most widely dis­ feet of beds emerge, whose base is cut off by the igneous tributed gastropods are bellerophontaceans, mainly pre­ rock (geologic section 42, pi. 8). Most of the limestone served as steinkerns (Yochelson, 1960, p. 216). Less is dolomitic and resembles the upper part of the Hueco abundant are species of Omplmlotrochus^ Straparollus in the head of Apache Canyon. (Euomphalus) , and Meekospira. The pelecypods in­ clude species of AUorisma, Aviculipinna, and Septim- FOSSILS AND CORRELATION yalina. Fragments of the scaphopod Plagioglypta oc­ Smaller foraminifers occur in nearly all parts of the cur at many localities. Of the remaining fossil groups Hueco Limestone, but the larger f oraminifers, the f usu- perhaps the most abundant are echinoids, but these are linids, are vastly more abundant in the northeastern preserved only as detached spines and plates that are part of the region (table 2). In the marl and calcitic probably specifically indeterminate by modern stand­ limestone of the lower part in the northeastern sections, ards. The only other fossils of interest are dasyclada- fusulinids are associated with varied fossil of other cean algae, which occur at a locality on the south- phyla, but in the dolomitic limestone of the upper part facing escarpment of the Sierra Diablo southwest of they crowd the layers, almost to the exclusion of other the former McAdoo Ranch (geologic section 22, pi. 6) ; fossils. In the calcitic limestone of the southern and these probably lived in an environment of very shallow southwestern area, fusulinids are strangely rare, except tropical to subtropical waters (P. E. Cloud, written for a zone about 500 feet above the base in the Wylie commun., 1954). Mountains and small staffellids which are common in Fossils in the marl and calcitic limestone of the lower many layers. part of the Hueco in the northeastern part of the region The fusulinid fauna of the Hueco Limestone in the show a much greater diversity, especially among the Sierra Diablo region is notable for the abundance of brachiopods (table 4). Dictyoclostus wolfcampensis small species (Dunbar and Skinner, 1937, p. 589), es­ (King) and species of Composita occur here as farther pecially Parafusulma linearis (Dunbar and Skinner), southwest, but they are overshadowed by other genera Pseudofusulina emaciata (Beede), P. powwowensis and species, including Dictyoclostus (Ghaoiella) aff. D. (Dunbar and Skinner), Schubertella kingi Dunbar and boliviensis (d'Orbigny), Buxtonia (Kochiproductus] Skinner, and Schwagerina beUula Dunbar and Skinner. victorioensis King, species of Linoproductus, "Margini- This assemblage furnishes a ready field criterion for fera" (Kozlowskia) capaci (d'Orbigny), "Marginifera" distinguishing the Hueco from the overlying Bone aff. uM.n lasallensi-s (Worthen), "Marginifera" (Koz­ Spring, with its perceptibly larger forms of fusulinids. lowskia) cf. "M" wabasliensis (Norwood and Pratten), In some layers of the Hueco the small species are asso­ and a fine-spined species of Waagenoconcha. Mollusks ciated with species of the larger, more robust genus Pseudoschwagerina. The characteristic fusulinids of are numerically and taxonomically less abundant, and the Hueco seem to range throughout the formation and include much the same assemblage as in the south­ have been observed low in some sections, high in others western area, with the addition of a few orthoceratid (table 2); no zonation within the formation is appar­ cephalopods. Corals occur at many localities, and ent from the available data. bryozoans are abundant at a few, especially in the Pow­ The remaining fossil groups, as noted in the strati- wow Member near the mouths of Marble and Mine graphic descriptions, are markedly differentiated into Canyons. southwestern and northeastern f acies that correspond REGIONAL RELATIONS OF FAUNA to lithologic differences between the strata in the two areas. All the fusulinid species of the Hueco Limestone oc­ The fauna of the southwestern facies is well-defined cur in beds of Wolf camp age throughout a wide region but little varied, and is remarkably alike at all localities in the Southwestern States. However, according to L. (table 3). The most abundant brachiopods are the G. Henbest (written commun., 1955), most of them productoids Dictyoclostus wolfcampensis (King), D. characterize more particularly bed 14 and higher parts (n. subgen.) cf. D. hessensis (King), and the non- of the Wolf camp at its type section in the Glass Moun­ productid Composita, particularly C. subtUita (Hall). tains, and he suggests that the highest fusulinid-bear- Hustedia was observed at many places in the field, ing layers in the Hueco Limestone of the Sierra Diablo 56 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TABLE 2. Foraminifera identified from Hueco [Identifications by L. G. Henbest. Explanation of symbols: X, genus or species present; var, variety of species present; cfr, specimen

Distribution of fossils in stratigraphic section,

tionofsouth Second27sec­ VictorioPeak 26 Bat Cave Sheep Peak area Victorio flexure

*t TO

Foraminifera: X X X X X X 1 1 X X X X X X X Millerellidsp.. __ .. .._ . .-

1 1 1 var var cfr 1 aff X X 1 X X

X 1 aff aff cfr 1 1 1 X 1 X X X

1 1 X X 1 1 1 X X X 1 1 X X 1

sp .- -_ . .-_ . . __ . . . X 1 1 X X X X Staffetta lacunosa Dunbar and Skinner. ... ______X X X Tetrataxis sp . ______X X X X X X Textulariidae ______. __ . _ __ . ______X Trepeilopsis sp ______Tritidtes subventricosus Dunbar and Skinner ______aff X aff

spp . ..

1 Osagia is a consortium or an alternative association of incrusting algae and tubiform, sedentary foraminifers of the subfamily Cornuspirinae. region may be younger than any beds preserved in 14) has noted the identity of many brachiopod species the type Wolf camp. of the northeastern facies to those in the type Wolf- Differentiation of the Hueco faunas into a northeast­ camp, but some of the brachiopods of this facies, such ern and southwestern facies may represent a transition as Buxtonia (Kochiproductus) victorioensis King and from a fauna like that of the type Wolfcamp into one Dictyoclostus (Ghaoiella) aff. D. boliviensis (d'Or- like that of the type Hueco, although available collec­ bigny), also occur in the lower part of the Hueco near tions from the Sierra Diablo region are not so varied Powwow Canyon in the Hueco Mountains. as those from either of these units in their type areas. Many of the brachiopods and gastropods of the Hueco Presumably the differentiation expresses a change from fauna are very similar to, or specifically identical with, a depositional environment of shale, marl, and limestone those in the upper part of the Cisco Group and in the in the basin area to one of dominant limestone in the Wichita Group of central Texas. Brachiopods in the platform area. However, the differences are mainly in Camp Creek Shale Member of the Pueblo Formation relative abundance of species and groups rather than are like those in the Hueco, and Dictyoclostus (OJiaoi- in the gross assemblages. Thus, E. E. King (1931, p. ella) aff. D. boliviensis (d'Orbigny) is abundant there. PERMIAN 57 Limestone in central and northern Sierra Diablo compared with the species Usted; afl, specimen related to species but probably different; ?, specunen doubtfully assigned to genus or species] locality, and collection number indicated

37section First 39 Third ApacheTank41 SierraPrieta42 30 31 North of inApache section in 29b Victorio Peak Victorio Victorio Canyon Marble32 38 Second section in Apache Canyon Canyon Canyon Apache Canyon Canyon

1O r~ BF2718 ta

X XXXX X X X X X X X X X X X X

? X X X var X var X X var X X var var X ? X ? Xvar X X ? ? X X afl X ? cfr X X X X X X X ? X X X X X X X var X X ? ? ? ? ? ? ? ? afl ? X ? X X X ? ? X ? ? ? X X X X X

off ? f X X

On the other hand, the Hueco gastropods resemble those throughout the Sierra Diablo region (fig. 2). During at somewhat higher levels in the central Texas section. the latter part of Pennsylvanian tune these rocks were The Hueco species of Straparollus (Euomphalus) and broadly folded, locally faulted, and greatly eroded. Naticopsis occur in the Grape Creek Limestone Member Erosion penetrated deepest in the more uplifted area of the Clyde Formation, and those of Omphalotrochus to the south and southwest, where the Hueco was de­ extend as high as the Lueders Limestone. posited on the Precambrian and Precambrian (?) for­ Faunas like those in the Hueco also extend well to mations. Earlier Paleozoic formations (the El Paso, the west of Texas; for example, Williams (in Gilluly Montoya, and Fusselman Formations) were preserved and others, 1954, p. 39-41) has compared the Hueco from pre-Hueco erosion in synclinal areas in Beach fauna with that of the Colina Limestone of the Naco Mountain and the Baylor Mountains. Later Paleozoic Group in southern Arizona. formations (the Barnett Shale and Pennsylvanian rocks) were similarly preserved in a deeper synclinal STEATIGRAPHIC RELATIONS area in the northeastern Sierra Diablo. In many places As indicated above, the Hueco Limestone lies uncon- erosion progressed so far that the Hueco was deposited formably on all the earlier rocks of the sequence on a nearly level surface, but in others it was laid 58 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS TABLE 3. Fossils identified from Hueco Limestone of southern calcitic limestone fades [Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, L. G. Henbest, and E. L. Yochelson. Explanation of symbols. Under Foraminifera: X, species or genus present; ?, specimen doubtfully assigned to genus or species. Under other biological groups: A, abundant; C, common; X, present; R, rare] Distribution of fossils in stratigraphic section, locality, and collection number indicator

13 Wylie 15 Threemile Near Threemile 22 Mc- Near Mountains Mountain Mountain 20 Eagle Flat 20 Streerawitz Hills Adoo Sheep Ranch Peak

6937 7003 7013 7005 7005x 14430 14437 14438 14426 7028 7008 7003a 7003b 14432 7013a 14424 F 2718c F9813 14431 F9809 7013b F9812 F9808

Foraminifera: ? ? X X ? X X X X X X X X X Porifera: X A X Coelenterata: X c R X Echinodermata: R c X R A R Bryozoa: FtZTlGStcUd SD X R X X X R R X X X X R Bryozoans indet., encrusting, massive, and fenestrate X R R Brachiopoda: X C R X A X R C A A R X R A R C R X C A A A X R A X R A C X X X A R C R C X X X Lamellibranchiata: X X X X X X X X R C X R X X Gastropoda: X R R A C A C C X X A R X X X R X X X X X A R C X X X X R R X C X X sp . X X R X R X X C C A C A X A A X A Sublitidindet. -I ' __ . ____ .' ____ .'...... X X R Scaphopoda: X C C X C Cephalopoda: Nautiloid indet- ______X Arthropoda: X Plants: X X X PERMIAN 59 TABLE 4. Fossils identified from Hueco Limestone, from marl and calcitic limestone m lower part, in northeastern Sierra Diablo (exclusive of Foraminifera) [Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, and E. L. Yochelson. Explanation of symbols: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphie section, locality, and collection number indicated

27 31 34 Second 30 North South section Victorio 29 Victorio Peak Victorio of 32 Marble 33 Mine Canyon of south flexure Can­ Victorio Canyon Black of yon Can­ John Number Victorio yon Can­ Peak yon

8550 7001a 14452 14429 8553 8554 8555 8556 8557 8558 8551 7050 7004 7004a 7001 7056 8552

Porifera: X X Coelenterata: C X X X R R C X X X X C Echinodermata: R X X A c X X C R X Bryozoa: X C X R C R X X C C X C C C C X A R R R A R Brachiopoda: X C X X A C X X C X X X A A R R X R R X A C R X X C C X X X Dtetyoclo&tus (ChaoieUa) aft. D. bolioiensis A C C C R X R A C C R R R R c C X g R X C X X X C X X R C A R X X A C X X X "Marginifera" (Kozlowskia) capad (d'Orbigny). X C X X cf. "M." wabashensis (Norwood and Prat- ten)...... A C A X X X R R X X X X X X A X R R R R X C X X X C C X A Lamellibranchiata: R X R X X X X X X X Myalinid indet ______.. X X X X Sevtimualinat so.. . - ... X

757-108 65 5 60 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

TABLE 4. Fossils indentified from Hucco Limestone, from marl and caldtic limestone in lower part, in northeastern Sierra Diablo (exclusive of Foraminifera) Continued pdentiflcations by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, and E. L. Yochelson. Explanation of symbols: A, abundant; C, common; X, present; R, rare] Distribution of fossils in stratigraphic section, locality, and collection number indicated

27 31 34 Second 30 North South section Victorio 29 Victorio Peak Victorio of 32 Marble 33 Mine Canyon of south flexure Can­ Victorio Canyon Black of yon Can­ John Number Victorio yon Can- Peak yon

8550 7001a 14452 14429 8553 8554 8555 8556 8557 8558 8551 7050 7004 7004a 7001 7056 8552

Gastropoda: R R R X R X X X X X X X X X X OT\ X X X X X X X X Cephalopoda: X X Annelida: C Arthropoda: Trilobite indet.. ______X X over hills and valleys with a relief of several hundred are angularly truncated. Here also, as described below, feet. the Bone Spring overlaps the Hueco surface and passes Similar pre-Permian deformation and erosion oc­ into marginal reefs, banks, and pebble beds, the latter curred in the Hueco Mountains farther northwest containing fusulinids reworked from the Hueco. Field (King, P. B.5 King, K. E., and Knight, J. B., 1945), evidence is less conclusive for an unconformity between and it may correspond approximately to the climax of the Hueco and Bone Spring elsewhere, as in the seg­ deformation in the Ouachita fold belt of the Marathon ment of the Sierra Diablo scarp between Victorio Peak area to the southeast (King, P. B., 1937, p. 134-136). and Apache Canyon; but the large variations in thick­ However, in many of the ranges of southern New Mex­ ness of the Hueco in this segment may have been caused ico the sequence is nearly complete from the Pennsyl- partly by erosion of its top. Very likely the uncon­ vanian into the Permian, and any unconformity be­ formity at the top of the Hueco fades out into the basin tween them is slight or local. Conformable relations area, like the one at the base, but its disappearance may between Pennsylvanian and Permian strata are also in­ be northeast of any outcrops in the Sierra Diablo dicated by drilling in the West Texas basin to the east. region. In the part of Texas and New Mexico northwest of the BONE SPRING LIMESTONE Ouachita fold belt, pre-Permian deformation and ero­ The second formation of the Permian System in the sion was probably greatest in the positive areas and was Sierra Diablo region is the Bone Spring Limestone, slight or lacking in the negative areas. named for exposures in Bone Canyon below Bone The top of the Hueco, where preserved, is likewise an Spring, in the Guadalupe Mountains north of the unconformity. In the southwestern part of the Sierra Sierra Diablo (Blanchard and Da vis, 1929, p. 961). Diablo region, the Hueco is overlain by Cretaceous The type Bone Spring, and that farther south in the rocks, and has been variably truncated by pre-Cretace- ous erosion. Farther north the Bone Spring Limestone Guadalupe and Delaware Mountains, is "black lime­ is preserved, and also lies unconfonnably on the stone" (the "basal black limestone" of Girty, 1908, p. Hueco certainly in many places, and perhaps every­ 10), but in previous reports the term Bone Spring has where. The unconformity is most evident along the been applied also to rocks of other sorts, laid down in edges of the basin of Bone Spring time, in Apache Can­ different environments, the gray Victorio Peak Lime­ yon, on the Victorio flexure south of Victorio Peak, and stone (King, P. B., and King, K. E., 1929, p. 922) and in the northern Baylor Mountains, where Hueco strata the Cutoff Shale (King, P. B., 1942, p. 569-570); it has PERMIAN 61 thus been used for all strata of Leonard age in the regularly, especially near the marginal areas. Irregu­ northern Trans-Pecos Region. larly dipping layers are extensive and well exposed in However, the term Leonard Series is adequate to ex­ the Guadalupe Mountains (King, P. B., 1948, p. 15-16; press time-stratigraphic relations in northern Trans- Newell and others, 1953, p. 86-88), and occur also in Pecos Texas. Moreover, the Victorio Peak Limestone the Sierra Diablo region. and Cutoff Shale are thick persistent units with their In the Delaware Mountains in the northeastern part own special characters in the shelf and platform areas. of the report area, well out in the basin of Bone Spring It is therefore appropriate to restrict the Bone Spring time, the exposed part of the formation is all black lime­ to deposits primarily of basin facies like those at the stone; but the lower part of the black limestone in the type locality and to class the Victorio Peak Limestone Sierra Diablo is interbedded with various lighter gray, and Cutoff Shale as other formations of the Leonard more clastic or more dolomitic layers, which are mainly Series. In the Delaware basin area, represented by tongues of the marginal deposits. exposures in the Delaware Mountains in the northeast In the Sierra Diablo region black limestone deposits corner of the report area, the Bone Spring occupies the of the basin area are bordered by marginal deposits to­ whole of the Leonard interval; but in the Sierra Diablo ward the southwest, whose position coincides with the it occupies only the lower part and is succeeded by the Babb and Victorio flexures that cross the northern and Victorio Peak and Cutoff, of later Leonard age. The central parts of the range (fig. 6). Both flexures are Bone Spring Limestone of the Sierra Diablo region has downbent northeastward toward the basin and were its own assemblage of marginal deposits, different from probably in process of growth during Bone Spring those of the units above. deposition, although they were much accentuated later. OUTCROP One marginal belt extends east-southeastward across Apache Canyon to the front of the mountains near Mine The Bone Spring Limestone, as thus restricted, crops and Marble Canyons and parallels the upper end of the out at midheight on the east-facing escarpment of the Babb flexure. Along it, the black limestone deposits Sierra Diablo from near Victorio Peak northward past pass abruptly into limestone reefs which overlap and Apache Canyon, where it is a little less than a thousand wedge out against the sloping surface of the Hueco feet thick (pi. 1). Most of it is black limestone that limestone. At the southeast end of the belt the reefs characteristically forms a smoothly rounded slope be­ either terminate or bend southwestward beneath a cover tween the bench of Hueco Limestone below and the cliff of Victorio Peak Limestone to join the marginal de­ of Victorio Peak Limestone above, but the slope is in­ posits along the Victorio flexure. The marginal belt terrupted by ledges in the lower part (pi. 10). Similar along the Victorio flexure is exposed across the central rocks are preserved hi a large outlier in the northern Sierra Diablo, east-southeastward to the front of the Baylor Mountains, and form the lower part of the west- mountains south of Victorio Peak, and reappears in the facing escarpment of the Delaware Mountains, as in the northern Baylor Mountains. Along it, black limestone northeast corner of the report area. Marginal deposits interfmgers up the dip with thickening limestone banks, of the Bone Spring, mainly thinner and including ledge- which are truncated by erosion at their upper ends and making limestone reefs and banks, are exposed on the do not wedge out against the older rocks of the flexure. Sierra Diablo escarpment near Mine and Marble On the platform at the upper end of the northern Canyons and south of Victorio Peak, as well as in the marginal belt, at the head of Apache Canyon, the Vic­ central Baylor Mountains, but they are best shown in torio Peak Limestone is separated from the Hueco Lime­ cross section on the walls of Apache and Victorio stone by only a thin wedge of strata, and the area re­ Canyons behind the escarpment. ceived no deposits during most of Bone Spring time. LITHOLOGY AND FACIES On the platform at the upper end of the southern The dominant rock of the Bone Spring is "black lime­ marginal belt, in the southern Sierra Diablo and the stone" which, in the type area in the Guadalupe Moun­ central Baylor Mountains, Bone Spring Limestone ex­ tains, is a fine-grained impure limestone in beds a few tends over the Hueco a mile or so south of the Victorio inches thick, colored dark gray or black by bituminous flexure. The Bone Spring must have wedged out material (King, P. B., 1948, p. 14-15). Elsewhere in eventually farther south, because in the Wylie Moun­ the Delaware Mountains, the Sierra Diablo, and the tains the Victorio Peak Limestone lies directly on the Baylor Mountains the facies called black limestone is Hueco. more varied, as it includes both thinner and thicker SIERRA DIABLO ESCARPMENT black limestone beds and thinly fissile black or brown Bone Spring Limestone is exposed along the north­ siliceous shale. Layers of the black limestone dip ir­ eastern segment of the Sierra Diablo escarpment from 62 GEOLOGY OF THE SIEERA DIABLO REGION, TEXAS

EXPLANATION

OUTCROP AREAS

Bone Spring Limestone Light shading indicates black limestone and associated deposits; dark shading indicates marginal deposits, principally massive limestone reefs and banks

Older and younger Permian rocks

Rocks older and younger than Permian

OTHER SYMBOLS

1270 Thickness of Bone Spring Limestone, in feet, where determined

Trend of linear features in Bone Spring Limestone Alined fusulitrid tests

Gradational boundary between black limestone on northeast and mar­ ginal deposits on southeast

Inferred southwestern margin of Bone Spring Limestone Formation absent farther southwest b\f overlap on Hueco Limestone and by intergradation with Victoria Peak Limestone

10 MILE?

FIGURE 6. Map of Sierra Diablo region showing paleotectonics of Bone Spring Limestone. PERMIAN 63 south of Victorio Peak nearly to Babb Canyon, where Many are tongues of the reefs and banks of the mar­ it passes beneath the surface. In this segment the Bone ginal belts, and increase toward them in number and Spring is mainly black limestone, except for the margi­ thickness. At Victorio Peak and Marble Canyon nal deposits on the Victorio flexure at the south end and (geologic sections 29 and 32, pi. 7) they extend as high for an interruption of several miles by the reef body as 400 feet above the base of the Bone Spring; but near Mine and Marble Canyons. Stehli (1954, p. 273) farther away from the marginal belts, as near Victorio proposed that the black limestone north of the reef body Canyon (geologic sections 36 ancf 37, pi. 8), they oc­ was deposited in an open basin and that to the south in a cupy a smaller interval. In places a hundred feet or deep lagoon behind the reef, but the rocks of the two so of ledge-making beds succeeds the ledge-making areas are identical lithologically and faunally and are Hueco Limestone, with few partings of black limestone, not likely to have been deposited in different environ­ so that the boundary between the Bone Spring and ments. Hueco is topographically indistinct. However, the Most of the Bone Spring in this segment is dark- rocks above and below the boundary differ in both tex­ gray or black dense thin-bedded limestone, which ture and fossils. weathers platy, light gray, buff, or brown, and is carved Individual ledge-making beds are a few feet to more into rounded slopes. Much of it is siliceous or argil­ than 150 feet thick. Some are well bedded and persist laceous; analysis of one specimen indicates 23.65 per­ for miles along the outcrop, others pinch or swell cent organic insoluble material (King, P. B., 1948, p. within short distances, changing from bedded to mas­ 14, specimen 3). Most of the beds are a few inches sive, and a few are lenses of small extent. The ledge- thick, but some are thicker, others paper thin; parts are making beds are partly calcitic but mostly dolomitic, are featureless within the beds, others very thinly lami­ fine to coarse grained, and in places brecciated. Many nated. Some beds contain chert in long thin layers beds are crowded with brachiopod and mollusk shells, or lenses. Interbedded with the limestone, in places some of which are silicified, but others contain little in thick units, is brown platy or papery siliceous shale, else than fusulinids and crinoid columns. which grades locally into stony shale or bedded chert. Most of the ledge-making beds are bioclastic and are These limestone and shale beds are nearly unfossilif- formed of fossil shells and fragments. Part of the erous, but some contain spicules, brachiopod shells, and organic material accumulated in place, in patcli reefs more obscure organic markings. Further details of the or more extensive layers; in these Stehli (1954, p. 278) nature of the black limestone have been given by Stehli has observed shells still in position of growth. Part (1954, p. 278). was redeposited from growth areas elsewhere, mainly in In many places bedding in the black limestone dips shallower water, and was spread over the black lime­ irregularly, at a steeper angle than that of the forma­ stone deposits in broad sheets, or as local banks or wind­ tions above or below. Irregular bedding on a small rows. Two special kinds of bioclastic deposits deserve scale in the lower part was observed in ravines between Victorio and Marble Canyons, where channels in lime­ notice. stones are filled by limestone of slightly different char­ A little above the base of the Bone Spring in Black acter, and where some beds are contorted, broken by John Canyon (section 35; USGS 6938, 7055), north­ minor thrusts, and truncated by beds above. Irregular west of the portal of Apache Canyon (USGS 14439), bedding on a larger scale occurs near the marginal belts. and in the Baylor Mountains as described below, are In Apache Canyon (geologic sections, 36, 37, and 38, "molluscan ledges," which are very local lenses packed pi. 8) black limestone beds dip away from marginal with molluscan shells. Gastropods dominate, but there reefs at angles of 12° to 25° northeastward; at the head are also pelecypods and cephalopods, as well as a few of Marble Canyon (geologic section 32, pi. 7) they dip scaphopods, pteropods, and chitons. P. E. Cloud, Jr., at a lower angle southward. Exposures are generally and E. L. Yochelson (written commun., 1954) state insufficient to determine the gross pattern or origin of Fossils from these beds were silicified and have been prepared these structures. In part at least they resulted from for study by etching with hydrochloric acid. The residues con­ primary deposition on the slopes of the higher-stand­ tain great quantities of shell fragments compared to the com­ ing reefs and other marginal deposits; some were prob­ plete specimens recovered. The rock resembles the present-day ably acentuated by slumping or sliding of the newly coquinas in concentration of shell fragments. deposited sediments. These shells are not in position of growth, and were Interbedded with the black limestone, especially in probably removed from their growth areas by waves the lower part of the Bone Spring, are layers of lighter and currents, which redeposited them in banks on the gray thicker bedded limestone, which project as ledges. sea floor (compare Yochelson, 1956, p. 190). 64 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Fusulinids collected at many localities within a hun­ NORTHERN MARGINAL BELT dred feet of the base of the Bone Spring are either Wolf- The northern marginal belt of the Bone Spring Lime­ camp (Hueco) species, or a mixture of Wolfcamp with stone emerges from younger Permian rocks on the west Leonard (Bone Spring) species, whereas the associated wall of Apache Canyon, and is exposed thence east- larger fossils are of Leonard affinity. Collections of this southeastward for 5 miles to the front of the Sierra kind were made at Victorio Peak (geologic section 29b, Diablo near Mine Canyon. Marginal deposits of the F 2716), Victorio Canyon (geologic section 30, F 2723), belt were laid on an eroded surface of the Hueco Lime­ and northwest of the portal of Apache Canyon (F 9815, stone, which is low and flat along the mountain front, 9816, 9817). (See p. 151-153,161-162.) Petrographic but which rises southwestward nearly a thousand feet study of specimens from these and other localities by in Apache Canyon. Henbest demonstrates that the anomalous association of The marginal belt is well exposed in cross section on Wolfcamp and Leonard fusulinids results from redepo- the northwest wall of Apache Canyon (pi. 11; section sition of the Wolfcamp f usulinids in younger sediments. F-F', pi. 4). Here the Bone Spring Limestone thins Typical is the following report on specimens from about southwestward from 880 feet (geologic sections 37 and 70 feet above the base of the Bone Spring on Victorio 38, pi. 8) to a few hundred feet (geologic sections 40, Peak (geologic section 29b, unit 16, F 2716) by L. G. 41, pi. 8), mainly by overlap on the rising surface of Henbest (written commun., 1955). the Hueco but partly by intergradation of the upper These specimens include two kinds of f usulinid-bearing lime­ beds with the Victorio Peak Limestone. The thick body stone, which will for convenience be termed types 1 and 2. of Bone Spring in the northeastern part of the canyon Type 1 is a calcarenite that consists of well-sorted subspheri- cal grains 0.15 to 0.45 mm in diameter. The grains are highly is mainly black limestone, but it passes southwestward rounded fragments of lithified fusulinids, echinoderm ossicles, into marginal deposits. No more than a few hundred and very fine grained limestone. Each grain is coated with a feet of marginal deposits occur at any locality, although layer of clear calcite 15 to 20 microns thick. This clear coating they have a vertical range as great as the slope of the has no oolitic structure, and contrasts with the well-graded underlying Hueco. matrix, which consists of calcareous fine silt. In the sample the grains are as closely packed as they can lie. At about midpoint in the canyon (geologic section Most of the grains are fusulinid fossils. The high degree of 39, pi. 8) the Bone Spring includes a massive unit of rounding indicates that these were either: (a) filled with sedi­ saccharoidal dolomitic limestone that stands in mas­ ment and lithified before they were eroded, rounded, and re- sive dark ledges and a thinner underlying unit of cherty deposited, or (b) impregnated and lithified during abrasion. The and marly limestone. The massive unit contains little latter is indicated because the chamber filling is silt and detritus, whereas before breakage the interior volutions of fusulinid shells else than fusulinids, but fossils are more varied in the are ordinarily inaccessible to silt and are generally filled with unit below and many are silicified. Tongues of the crystalline calcite. Further support to this alternative is given massive unit extend with primary dip into the lower by the weathered, corroded conditions of the shells, and the pres­ part of the black limestone farther northeast. The ence of a coating of chemically precipitated or nonoolitic type. black limestone itself has steep primary dips, and in­ The fusulinid detritus consists of species of Schwagerina, Pseudofusulina, and perhaps other genera of Schwagerininae. cludes many lenses or lumps of massive gray limestone, These appear to be Hueco fusulinids. No Bone Spring species some of which are crowded with sponges, bryozoans, were recognized, but the preservation is so fragmentary that and other fossils. Probably these lenses were patch certain Bone Spring species could occur without recognizing reefs that grew along the edge of the overlapping Bone them as such. Spring deposits. In this part of the canyon the uncon- Type 2 consists of unsorted partly silicified angular to rounded detritus, containing an extraordinary variety of well-preserved formable basal surface is generally overlain by 25 feet shells of fusulinids and other foraminifers. Indistinct particles or so of ledge-making dolomitic limestone, which is not of limestone of a different facies are also present, as well as a obviously conglomeratic but which may have been re­ few coated sand grains like those of type 1 lithology. worked in part from the Hueco beneath. In places it In this f aunal aggregate part of the species are typical of the contains not only indigenous fusulinids but f usulinids upper part of the Hueco Limestone in the Sierra Diablo, and of Wolfcamp type that were redeposited from the to some extent of the uppermost beds of the type section at Wolfcamp, notably: Pseudoschwagerina gerontica, P. teatana Hueco. var. or Pseudofusulina huecoensis var., Parafusulina linearis, In the southwestern part of the canyon, where the top Bchubertella kingl, and part of the smaller foraminifers. On of the Hueco stands high, it is separated from the Vic­ the contrary, Parafusulina schucherti, P. diabloensis, other torio Peak Limestone by thin-bedded slope-making parafusulinid species, and Schwagerina gumbeli are character­ dolomitic limestone, generally a few hundred feet thick istic of the Bone Spring. The exact range of none of these but thinning to less than 50 feet in the westernmost forms can be stated with finality, but the evidence is clear lithologically and biologically that this fauna is a depositional exposure (sec. 15, Block 32). This unit is mapped as aggregate, in which Hueco fossils have been redeposited with Bone Spring, although it is equivalent to only a little early Bone Spring fossils. of the upper part of the formation in the northeastern PERMIAN 65 sections. At Apache Tank (geologic section 41, pi. 8) and T-T'j pi. 4); exposures farther west are less in­ the limestone of the unit, which is interbedded with formative as the relief is lower. pink and yellow marl, overlies a conglomerate of lime­ In the southern marginal belt, as in the northern, both stone pebbles and cobbles that was probably derived the surface of the Hueco Limestone and the strata of from the Hueco. the Bone Spring slope northeastward, the former de­ Southeast of Apache Canyon the marginal deposits scending more than a thousand feet and the latter dip­ form an escarpment nearly a thousand feet high, from ping 5° to 20°. Part of this slope is primary, as in the which the strata in front have mostly been eroded (sec­ northern belt, but the slope was much accentuated by tion F-F', pi. 4). The rocks of the escarpment are a later movements on the Victorio flexure. The surface reef of dolomitic limestone, parts of which are very of the Hueco Limestone was much eroded before the massive, parts thick bedded with a primary dip to the Bone Spring was laid over it, as indicated by variations northeast. Within the reef, much of the original or­ in thickness of the formation, by angular discordance ganic structure has been destroyed by dolomitization between it and the Bone Spring, and by pebble beds in and recrystallization, but in places obscure traces of the Bone Spring; Bone Spring strata, however, do not crinoid columns, bryozoans, sponges, and algae are overlap the Hueco as they do in Apache Canyon. visible, as well as better layered streaks or lenses of The Bone Spring Limestone on Victorio Peak (geo­ bioclastic debris. logic section 29a, pi. 6) north of the flexure is 970 feet The intertonguing of the reef mass with the black thick, but at midpoint on the flexure (geologic section limestone is preserved at a few places, as on the spur 28, pi. 6) it has thickened to 1,050 feet, despite loss of that extends north to Apache Peak. Here, outer ends much of its upper part by intergradation with the Vic­ of the reef tongues and isolated patch reefs embedded torio Peak Limestone. At the top of the flexure (geo­ in the black limestone are not so dolomitized as the logic section 27, pi. 6) 850 feet of the formation is main reef and preserve better their original nature. preserved, although the Victorio Peak is missing. Many contain a profusion of sponges, massive bryo­ Southward thickening of the Bone Spring is caused by zoans, crinoid columns, thick-shelled productids and swelling of each layer as it changes into marginal f acies, other brachiopods, as well as cobbles and pebbles that so that the thick sequence in the south is equivalent only are at least partly of algal origin. to the lower part of the thinner sequence in the north. Near Mine Canyon the reef extends to the edge of the These relations are well shown in cross section south Sierra Diablo escarpment, and any further extension of Victorio Peak and in Victorio Canyon (sections to the southeast has been downfaulted. Probably it X-X' and F-F', pi. 4). On the east slope of Vic­ did not continue much farther in this direction, because torio Peak and in the lower course of Victorio Canyon, dips in the reef and associated black limestone change a 100-foot bed of gray limestone forms a prominent from northeast near Black John Canyon, to east near ledge about 300 feet above the base of the formation. Cave Peak, to south at the head of Marble Canyon This bed is traceable to the upper end of the flexure, (section W-W, pi. 4). By coincidence, this change in where its thickness and its distance above the base of dip is near the large igneous stocks at Cave Peak and the Bone Spring have doubled. To the north, beds Marble Canyon, but the stocks disturbed the strata very below and above the ledge are mainly black limestone, little during their intrusion. The dips were not pro­ but to the south, thick units of cliff-making dolomitic duced by the intrusions, but are primary features of the limestone wedge in. These have been interpreted as reef. On the escarpment face at the head of Marble reefs (King, P. B., 1962, p. 630), but "although the de­ Canyon, intertonguing of the reef front southward with posits are largely made up of organic debris, there is black limestone is well exposed, and presumably the little evidence for more than occasional wave-resistant reef continued thence southwestward under a cover of structures" (Stehli, 1954, p. 274). Between the wedges younger Victorio Peak Limestone (fig. 6). the black limestone changes into green clay shale and yellow nodular limestone, both containing many fossils, SOUTHERN MARGINAL BELT some of which weather free. Some beds are formed of The southern marginal belt of the Bone Spring Lime­ closely packed fusulinid shells, which in places include stone extends east-southeastward like the northern and both indigenous species and species reworked from the is exposed for 8 miles along the Victorio flexure, emerg­ Hueco. ing from alluvium on the west and projecting to the In the southernmost exposures many beds between the Sierra Diablo escarpment on the east. Best exposures lower wedges are conglomerate, derived in part from are on the escarpment south of Victorio Peak and in erosion of the Hueco Limestone farther south. The Victorio Canyon (upper view, pi. 10; sections X-X' conglomerate is formed of well-rounded limestone peb- 66 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS bles of various colors and textures, % inch to 1 inch in near the high point of the mountains (BM 5568), which diameter, which lie in a matrix of dolomitic or marly slope northward with primary dip into the black lime­ limestone. Both matrix and pebbles contain fusulinids stone. Some of them are dolomitic, others calcitic; and other fossils. some are fine grained, others coarse and bioclastic with One wedge of massive dolomitic limestone directly abundant silicified fossils. overlies the Hueco and thickens southward like the rest, FOSSILS AND CORRELATION extending a mile or two beyond succeeding parts of the Bone Spring and the upper end of the Victorio flexure Fossils are preserved in varying abundance in the to form remnants on the crest of the Sierra Diablo. different kinds of rocks of the Bone Spring Limestone, This basal dolomitic limestone is more massive than the but all its fossils make a varied assemblage (tables 5-7). Hueco Limestone on which it rests, and it weathers more Fossils are scarce in most of the black limestone, prob­ jagged. Unlike the Hueco, it contains large fusulinids ably because of an original poverty of life; they are and other fossil shells in places, some of which are poorly preserved in the reefs and banks, because of sub­ silicified. sequent dolomitization and recrystallization. They are BAYLOR MOUNTAINS most abundant and best preserved in the ledge-making beds and lenses of gray limestone that are interbedded The Bone Spring Limestone forms most of the north­ in the lower part of the black limestone. Fusulinids ern part of the Baylor Mountains and resembles that in and other f oraminif ers occur here in varied associations. the Sierra Diablo. The downfaulted eastern extension On the other hand, the kinds of larger invertebrates of the Victorio flexure crosses the northeast corner of the vary greatly in proportion from bed to bed and place mountains, where Bone Spring strata dip 10° to 30° to place, owing to either environmental differences in north-northeastward with the Victorio Peak Limestone the growth areas or sorting of the shells during trans­ at the top, but both flexure and earlier structures are portation and redeposition. Variations from these obscured by closely spaced northwest-trending faults of causes overshadow any faunal zonation within the for­ Cenozoic age (section Z-Z', pi. 4). The full sequence mation, if such exists. of the Bone Spring is exposed only toward the north­ east, where it is probably about a thousand feet thick, FATJNAL ASSEMBLAGES but only the lower part could be measured (geologic Fusulinids of the Bone Spring Limestone include section 18, pi. 5). such characteristic species as Parafusulina diabloensis Most of the formation in the northeastern part of the Dunbar and Skinner, P. imlayi Dunbar, and P. schu- mountains is black limestone, which includes the usual cherti Dunbar and Skinner. Earlier collections from thin-bedded dark-gray or black limestone and platy the Sierra Diablo did not yield Scfiwagerina hessensis siliceous shale. However, the uppermost 500 feet forms Dunbar and Skinner, S. gumbeli Dunbar and Skinner, beds as much as several feet thick and contains many or S. crassitectoria Dunbar and Skinner, which are chert nodules. Southward, as on the Victorio flexure characteristic of the lower part of the Leonard Series in the Sierra Diablo, part of the black limestone gives of the Glass Mountains, and it was thought that the place to shale, calcareous marl, and earthy limestone. lower Leonard might be missing here (Dunbar and These rocks contain abundant fossils, many of which Skinner, 1937, p. 589). However, all these species have weather free. been discovered later in the Sierra Diablo (Dunbar, The black limestone contains layers of lighter gray 1953, p. 804-809; L. G. Henbest, written commun., thick-bedded or massive limestone, but most of them are 19.55), and the supposed hiatus must not exist. Simi­ very lenticular. One group of lenticular layers 300 or larly, Parafusulina fountaini Dunbar and Skinner and 400 feet above the base of the Bone Spring is more per­ Pseudofusulina setum (Dunbar and Skinner), which sistent than the rest, although the layers wedge out and were supposed to characterize the younger Victorio nearly disappear in places, and in others coalesce into Peak Limestone, are now known to occur more spar­ a prominent ledge several hundred feet thick. Not far ingly in the Bone Spring. above these layers at one locality (geologic section 18 ; At many places, mostly within a hundred feet of the USGS 6983,14475) is a "molluscan ledge" like those in base of the Bone Spring Limestone, fusulinids of Wolf- the northeastern Sierra Diablo. camp (Hueco) type are mingled with those of Leonard Southward in the Baylor Mountains, as farther west (Bone Spring) type but, as stated above, studies by on the Victorio flexure, a massive dolomitic limestone Henbest (written commun., 1955) indicate that the wedges in at the base of the Bone Spring and caps the Wolf camp fusulinids have been redeposited from earlier Hueco over much of the central part of the mountains strata. All the specimens of PseudoscJiwagerina which (section Z-Z*', pi. 4). Higher wedges are preserved have been identified from the lower part of the Bone PERMIAN 67 TABLE 5. Fossils identified, from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Foraminifera) [identifications by L. G. Henbest. Explanation of symbols: X, genus or species present; var, variety of species present; aff, specimen related to species but probably differ­ ent; 1, specimen doubtfully assigned to genus or species] Distribution of fossils in stratigraphic section, locality, and collection number indicated

19 27 Second 31 37 39 North­ section 30 North First 38 Second Third western south of Victorio 29b Victorio Victorio of Northwest of section section in section Baylor Victorio flexure Peak Canyon Victorio Apache Canyon in Apache Canyon in Mts. Peak Canyon Apache Apache Canyon Canyon

51" 5 |3 So2 IsS II § PH Ei [z, Jt ll f**>L f^-~^!? s! £1 £! Zl fe (Z)^-- %i ^ ZA h ^ Foraminifera: Indigenous and probably indigenous genera and species: aft 1 X X X X X X X X X X X X X X X X ? X X ? X ParafusiMna attenuata Dunbar and ? X aff X X X X ? Parafusulina diabloensis Dunbar X Parafusulina fountaini Dunbar and var X X var X var ? var aff schucherti Dnnbar and Skinner. . X ? X X X X X ? X X X ? ? ? ? X X Pseudofusulina setum (Dunbar and X X ? X Schwagerina^ franklinensis Dunbar X Schwagerina gumbeli Dunbar and X X ISchwagerina gumbeli Dunbar and X X pseudoregularis Dunbar and X X X X ? X X X ? X ? X ? X X X X X X X X Genera and species redeposited from Hueco limestone: IParafusvMna gracUUatis (Dunbar X Parafusvlina linearist (Dunbar and X var Xvar X X Pseudofusulina, powwowensis (Dun- ? X X X Pseudoschwagerina gerontica Dunbar var Pseudosehwagerinat laxixsima (Dun- ? Pseudoschwagerina texana Dunbar ? ? X X X Schubertdla kingi Dunbar and X ...... X var Schwagerina beUula Dunbar and aff var aff

Spring are probably of this origin, except the oddly the lower part of the Bone Spring in the Victorio Peak shaped Pseudoschwagerina stanislavi Dunbar, which is area, is summarized as follows by Stehli (1954, p. 280): indigenous to the Bone Spring and is seemingly a late An interesting feature of this and other collecting localities is variant of the genus (Dunbar, 1953, p. 809-812). the complete imbalance of the organic assemblage. There are The remaining groups of invertebrates of the Bone ten times as many brachiopod individuals as all others com­ Spring Limestone form two contrasting assemblages, bined. Second in importance are the bryozoans, which occur in large numbers and include both stony forms and delicate with few forms in common. The most widely distrib­ fenestellids. Pelecypods are next in variety but are very low uted assemblage is dominated by brachiopods, the other in numbers of individuals. Crinoid debris is abundant. Corals occurs in the "molluscan ledges." are present in moderate numbers. Gastropods are of limited A typical collection dominated by brachiopods, from variety, but there are moderate numbers of individuals. Cephal- 757-108 05 6 TABLE 6. Fossils identified from Bone Spring Limestone, Baylor Mountains, and northeastern Sierra Diablo (Porifera, Coelenterata, Echinodermata, Bryosoa, and Brachiopoda) [Identifications by P. E. Cloud, Jr., Helen Duncan, and R. M. Finks. Explanation of symbols: X, present; C, common; A, abundant; R, rare] og Distribution of fossils in stratigraphic section, locality, and collection number indicated H 17 27 Sec­ o High ond sec­ 31 35 North­ point of Near High point 18 Northeastern Baylor 19 Northwest­ tion 29b Victorio 30 North 32 Black west of Baylor of Baylor Mountains ern Baylor south Victorio flexure Peak Victorio of Marble John Apache Moun­ Mountains Mountains of Canyon Victorio Canyon Canyon Canyon tains Victorio Canyon Peak

6983- 7055- 14439 14475 6938 Mol- 7048 7053 7009 7000a 7000 Mol- 7002a 7002b 14454 8544 8543 8542 8562 8561 8539 8540 7010 Mol- luscan luscan luscan ledge P ledge ledge w Porifera: Qirtyocoelia dunbari R. H. King- _ _ __ X X X X X X X X X X X X X X X A X Coelenterata: X X R X g c A X X X R C C X X X X A X R X Echinodermata: X X X X X X Bryozoa: X C X X C R X R R X c X C R X A C X R R C c A X A R X R X R X X X R X X C StTiatovora sp. . X X X X X R PERMIAN 69

X X X

X X X

X 0 o X X XO o

X tf X X Xtf

XX X p* X X v/

X X XX

O - tf <{ P4 P5 «X

X o P5X p» P5

o X x X X

X o X - />/

1 0 0 W 1*^ X X x XXX «

o « X Xo o «

ox o X O 0 0 P5 P5 X

o o o

O X

X \/ X

o o X o o X X X

XX X X XX X X X X

iSgjiarnMiari Leptodussip ____-. (Cancrinella)Linoproductus spp..____._.__ "M." affcapaci"Marginifera"(Kozlowskia) Productidsindet.. . g » c >» > 1 t 1 t c 1 -^ c a c t . M'Orhifmv*_. 1 j ' £ '4 > C 1 indetOrthotetacean £ i 1 i 1> c I I I > g 'c c 1 a >a « V. 1 4 >i1V. _ s '5 K , G '.I g g ^g 3 h l c ^ 1 1* I ? 1 spp- 1 >s \ 1 1 1 *- ««.; c 1 J 1 1 g-j i'! c) y ! "» t gj ^ '* i1 / 1 3 J'1 1 !£ £ i i 1i 11 CQ TABLE 7. Fossils identified from Bone Spring Limestone, Baylor Mountains and northeastern Sierra Diablo (Amphineura Conoonchia, Lamellibranchiata, Scaphopoda, Gastropoda, Cephalopoda, Annelida, Arthropoda and Alga) [Identifications by W. M. Furnish, A. K. Miller, I. G. Sohn, and E. L. Yochelson. Explanation of symbols: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphic section, locality, and collection number indicated

17 27 Sec­ North­ High Near high 19 North­ ond 31 32 35 west point of point of 18 Northeastern western section 29b Victorio 30 North Marble Black of Baylor Baylor Baylor Mountains Baylor south Victorio flexure Peak Victorio of Canyon John Apache Moun­ Mountains Mountains of Canyon Victorio Canyon Canyon tains Victorio Canyon Peak

6983- 7055- 14439 14475 6938 Mollus- 7048 7053 7009 700a 7000 Mollus- 7002a 7002b 14454 8544 8543 8542 8562 8561 8539 8540 7010 Mollus- can can can ledge ledge ledge

Amphineura: R C Coniconchia(?): Hyoltthessp...... ______X Lamellibranchiata: X X X X X A c X R C Myalinid indet ______R X C A X X C X Nuculana spp______. X A C X R c X X C C Pectenoid indet. ______X X X Permophorus sp... ______.. X X R X X Pterial sp. ______X c X R Schizodussp...... c X Streblopteriasp...... ______c X Pelecypods indet. ______R Seaphopoda: X " Laevidentalium" sp ______.. __ _ R X R R R C Gastropoda: X X X R R Apachetta sp ______X X X X X X X X X X R X X X R X X C Bellerophontid indet. ______C X Cinclidonema sp. _ -.._ . ... ______X Discotropis girtyi Yochelson ______X Donaldinat sp. ______. . __ - _____ X R X Euconospira pulchra Batten. .--_-. ... ______X X Euphemites cf. E. imperator Yochelson ___ _ X X cf. E. kingi Yochelson. __ _. ._ __ _ X X SP_____ - X X X R Glabrocingulumsp.-.-...... ______X X X R Glyptospira sp ______.. _ X X Knightttes (Retispira) sp. _ _ - _ -- - _ _ __ X c X X iMmellospira conica Batten. _.--_---.- ______X cf. Lozonemasj)...... ______X R Murchisonid indet- ______X Naticopsis sp ______X X R Orthonema sp ______X R Peruvispira sp. ______X X Pharkidonotus sp______.. X Platyceras sp .. _. ______X X X Pleurotomarian indet--- ______-_ _ _ X X X X X Pseudozygopleuran indet _____ ._. _____ X X X X X X X R Straparottus (Euomphalus) glabribasis Yochel-

X R X Sublitid indet ______X X X X X R R Cephalopoda: X X spp X X X C X R R R A C Annelida:

Arthropoda: R R

R

Alga: 72 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS opods are very rare. Sponges and arthropods are represented and the straight-shelled genus Pseudorthoceras (Miller by rare fragmentary material. Fusulinids are abundant. and Furnish, 1940a, p. 42-44; Miller, 1945). Distinctive brachiopods of the assemblage are Dic- The fauna of the "molluscan ledge" in the northeast- tyoclostus (Chaoiella) guadalupensis (Girty), Bux- era part of the Baylor Mountains (USGS 6983,14475) tonia (Kochiproductus) victorioensis King, Chonetes is transitional between the molluscan and brachiopod (Chonetinella) victoria/mis Girty, species of Enteletes, assemblages. Although it includes abundant pelecy­ Wellerella, and Stenocisma, and a small species of pods, these are associated with Meekella, Enteletes, Pro- Avonia. Many layers also contain Meekella, Leptodus, ricJithofenia, and other brachiopods, as well as massive and ProrwJithofenia,) adapted to life on a firm sub­ bryozoans. A collection from near the high point of stratum, probably in a reef environment. Collections the Baylor Mountains (USGS 7009) is of similar tran­ from some beds contain many productids, whereas sitional character, as it contains nearly equal numbers others are dominated by Enteletes and other non- of brachiopods and mollusks. productids; but these differences are not stratigraph- ically significant. Many of the brachiopod species of CORBELATION the assemblage have been described by R. E. King Bone Spring faunas differ from those of the under­ (1931), some by Stehli (1954, p. 289-357). lying Hueco, and have many affinities with the higher Bryozoans are varied, but most of the genera at any faunas of the Guadalupe Series. They include locality are represented by only a few specimens, except the earliest of the large fusulinids which characterize for fistuliporoids, which form abundant large masses in the zone of Parafusulina, as well as the peculiarly some layers. Sponges are abundant in places, most of adapted brachiopods Leptodus and Prorichthofenia. the identifiable ones being Heliospongia or Defordia- These and other distinctive features of the Bone Spring like forms. Spicules have been recovered in many in- fauna characterize the Leonard Series in the West soluable residues and indicate a greater abundance of Texas Region. sponges than would be inferred from the larger speci­ From the stratigraphic position of the Bone Spring mens that have been collected. Horn corals of lons- Limestone in the Sierra Diablo, between the Hueco daleoid type and colonial corals occur here and there. Limestone and Victorio Peak Limestone, it would seem In the brachiopod-dominated assemblage mollusks are to be equivalent to the lower part of the type Leonard notable mainly for their paucity of number and variety, Series of the Glass Mountains, and there is some con­ in contrast to the assemblage in the "molluscan ledges." firmation of this in the fossils. Thus, a group of The assemblage in the "molluscan ledges" is domi­ schwagerinid species by which Dunbar and Skinner nated by mollusks, almost to the exclusion of other (1937, p. 586) characterized the lower part of the type phyla. Brachiopods are represented by only a few Leonard occurs also in the Bone Spring. R. E. King specimens; sponges, corals, bryozoans, and crinoid (1931, p. 14) found that most of the brachiopod species debris are uncommon. The mollusks are mainly gastro­ in his collections from the Bone Spring occur in the type pods and pelecypods, the first dominating the ledge Leonard. Also, most of his collections ascribed to the "Hess limestone" were from basal ledges of the Bone northwest of Apache Canyon (USGS 14439), the sec­ Spring as now defined; he found that many brachiopod ond, the ledge at Black John Canyon (USGS 7055, species from it occur in the Hess Limestone of the Glass 6938); cephalopods, scaphopods and chitons are less Mountains, now known to be a facies of the lower Leon­ abundant. According to Yochelson (1956, p. 189) ard. According to Stehli (1954, p. 276 ) Pelecypods are abundant, comprising well over half of the fossils recovered at the locality [at Black John Canyon]. Of It must be noted that in the Sierra Diablo the lower Bone these, Nucula, Nuculana, and Astartella are the commonest Spring contains a few forms which in the Glass Mountains are types, and parallelodontids are fourth in abundance. Most of seemingly restricted to the Wolfcamp, and a possibility exists the other pelecypod genera are represented by only a few that these rocks are somewhat older than the Leonardian in specimens. the Glass Mountains. Gastropods are varied, being represented by nearly 20 genera. STRATIGRAPHIC RELATIONS High-spired forms of several unrelated genera are somewhat more common than gastropods of other shapes; however, there Throughout the Sierra Diablo region the varied de­ is no striking difference in numbers of individuals among the posits of the Bone Spring Limestone are overlain con­ several genera. No large gastropods occur, and few of medium formably by the light-gray thick-bedded Victorio Peak size are present. Limestone. Cephalopods from the ledge northwest of Apache The Victorio Peak Limestone also intergrades ex­ Canyon include the ammonite Propinacoceras knighti tensively with the upper part of the black limestone Miller and Furnish, four genera of coiled nautiloids, of the Bone Spring, both by intertonguing and by PERMIAN 73 abrupt passage from light-gray into black strata in units the south slope of Victorio Peak it is nearly 1,500 feet several hundred feet thick. Intergradation of the two thick, but the lower half intergrades with black lime­ formations is prominently exposed on the south slope stone in the northern part of the mountain. Even of Victorio Peak, on the escarpment just north of Vic- allowing for erosion after Permian time, the formation torio Canyon, and in Apache Canyon (sections U~U', thus varies much in thickness from place to place, F-F', W-W, and Y-Y', pi. 4). At all such places probably mainly by intertonguing with the Bone Spring gray limestone changes to black northeastward, toward Limestone beneath. the basin area. Well out in the basin area, in the Dela­ ware Mountains in the northeast corner of the report NORTHEASTERN CALCIIIC FACIES area, black limestone extends to the top of the Leonard Along the east-facing escarpment of the Sierra Di­ interval and probably includes equivalents of the Vic­ ablo, the Victorio Peak is a light-gray thick-bedded torio Peak (fig. 7). limestone, mainly calcitic but slightly dolomitic in part, However, the Victorio Peak Limestone does not re­ which stands in sheer cliffs that in places are remark­ place the whole Bone Spring Limestone away from the ably fluted and pinnacled. Beds are a few feet or tens basin area. In the marginal belts it overlies thick- of feet thick, and in places are irregularly inclined at bedded gray limestone layers of different character, low angles in different directions. Near Apache Peak which were laid down as reefs or banks during Bone and Apache Canyon, where the gray limestone ex­ Spring time. In the platform areas these lower strata tensively intergrades northeastward with the black wedge out, and the Victorio Peak lies with hiatus on limestone of the Bone Spring, long tongues of gray the Hueco Limestone. limestone extend into the black and descend several hundred feet from the main body toward their outer VICTORIO PEAK LIMESTONE ends (section U-U', pi. 4). The calcitic limestone of The Victorio Peak Limestone is named for Victorio the Victorio Peak is probably mainly a bank deposit Peak (King, P. B., and King, E. E., 1929, p. 922), the (King, P. B., 1948, p. 27), although it may contain prominent detached summit about midway along the some small reef masses along its northeastern margin. east-facing escarpment of the Sierra Diablo (upper In places the Victorio Peak Limestone is separable view, pi. 10). The Victorio Peak is a formation of later into lithologically distinct subdivisions, but these are of Leonard age which is thick and extensive around the local extent. Between Victorio Canyon and Mine Can­ margins of the basin area in the Guadalupe Mountains, yon the lower 250 feet is massive gray limestone, with the Sierra Diablo, and the Wylie Mountains. indistinct bedding planes, that stands in a prominent The Victorio Peak Limestone forms the summits of cliff. Above is thinner-bedded gray limestone, with the Sierra Diablo north of the Victorio flexure (pi. 14), much interbedded buff marl, sandy and cherty lime­ breaking off on the east-facing escarpment into promi­ stone, and platy siliceous limestone. Many of these nent light-gray cliffs that surmount slopes carved from upper beds are fossiliferous, and contain productids, the Bone Spring Limestone (lower view, pi. 10). North other brachiopods, sponges, and crinoid stems, some of of the Babb flexure it descends to the edge of the Salt which are silicified. Basin, where it forms a low bench capped by younger On the Babb flexure (geologic section 43, pi. 8) the formations that extends northward beyond the report Victorio Peak is separable into three divisions. The area (upper view, pi. 12; section B-Bf, pi. 16). A thick lower division is gray thick-bedded dolomitic small remnant of the Victorio Peak is preserved at the limestone, in part cherty, which weathers gray brown northeast corner of the Baylor Mountains, and a large and splits along closely spaced joints. About halfway outlier forms the eastern slope of the Wylie Mountains up is a thin layer of fine-grained sandstone. The middle (geologic section 13; Hay-Koe, 1957). division, 100 feet thick, is thin-bedded dolomitic lime­ The Victorio Peak Limestone is overlain by higher stone, which weathers white and porcelaneous and forms Permian formations at the north end of the Sierra Diablo and in the Wylie Mountains. On the Babb flex­ a persistent light-colored slope. The upper division, ure at the north end of the Sierra Diablo its full thick­ 50-65 feet thick, is dark-gray calcitic fossiliferous lime­ ness is 975 feet; in the Wylie Mountains it is about stone, which is overlain by the Cutoff shale. The three 1,600 feet but includes undifferentiated beds of Guada­ divisions of this area are significant, because they are lupe age at the top. Elsewhere in the Sierra Diablo, nearly identical with divisions of the Victorio Peak the Victorio Peak Limestone is the highest Permian Limestone in the Guadalupe Mountains to the north formation and its full sequence is undetermined; here (King, P. B., 1948, p. 17), and assist in correlation of 500 to 1,000 feet of beds are commonly preserved. On the formation between the two areas. 74 GEOLOGY OF THE SIERKA DIABLO REGION, TEXAS SOUTHWESTERN DOLOMITIC FACIES Dunbar and Skinner occur also, although they are more West of the front of the Sierra Diablo the dominantly characteristic of the Bone Spring beneath. calcitic thick-bedded f ossilif erous limestone of the Vic- Sponges which occur at many places are mostly torio Peak changes to dolomitic thin-bedded poorly fos- Defordia-like forms and are probably a significant fea­ siliferous limestone. One facies gives place to the other ture of the whole fauna in bulk (Finks, 1960, p. 28-32). in about a mile along a well-defined boundary that ex­ Corals are less common. Dasycladacean algae, mostly tends north-northwest across the mountains from Vic- Macroporella, are abundant at one locality, and indi­ torio Canyon to a little east of Sierra Prieta (fig. 7). cate an environment of shallow tropical to subtropical The dolomitic limestone includes white 6-inch to 1- water. foot layers with crinkled laminae that weather to jagged The fauna is dominated by brachiopods, and espe­ surfaces and dull-gray thicker layers. Analysis of a cially by productids, such as Buxtonia (KocJiiproduc- typical specimen from near the Slaughter Ranch by tus) victorioensis King.4 Of the nonproductids, per­ K. J. Murata (written commun., 1940) indicates a con­ haps the most abundant genera are Enteletes and Neo- tent of 50.25 percent CaCO3, 38.75 percent MgCO3, and spirifer. Bryozoans are mostly rare, but massive fis- 1.34 percent insoluable material; the carbonate fraction tuliporoids occur here and there, and at one place num­ is close to the composition of the mineral dolomite. erous Batostomella. Mollusks are likewise uncommon Most of the dolomitic limestone beds are probably un- and are mostly moderate- to large-sized gastropods. fossiliferous, but some contain ghosts of fusulinids, STKATIGRAPHIC RELATIONS crinoid stems, and bellerophontids. The top of the Victorio Peak Limestone is not pre­ The Victorio Peak Limestone of the small remnant served in most of the Sierra Diablo region, but north in the Baylor Mountains and the larger body in the of the Babb flexure it is followed by the Cutoff Shale. Wylie Mountains is of the same dolomitic f acies as that Over the wide area in which the contact between the in the western Sierra Diablo. two units is exposed, thick-bedded calcitic limestone of The thin-bedded dolomitic limestone of this facies of the Victorio Peak is overlain by thin-bedded shaly the Victorio Peak somewhat resembles the dolomitic limestone of the Cutoff, and although the two rocks limestone beds of the underlying Hueco in the north­ are not interbedded, they appear to be conformable. eastern Sierra Diablo; it closely resembles Permian lime­ In the Wylie Mountains southeast of the report area stones of other ages elsewhere in the West Texas region the Cutoff Shale is not recognizable, and beds mapped that have been interpreted as back-reef or lagoonal de­ as Victorio Peak are succeeded by the Seven Rivers posits the Hess Limestone Member of the Leonard For­ Limestone of Guadalupe age (Hay-Roe, 1957). The mation and Gilliam Limestone of the Glass Mountains equivalent of the top of the Victorio Peak Limestone and the Carlsbad Limestone of former usage of the of other areas however, must lie within the dolomitic Guadalupe Mountains. The dolomitic limestone of the limestone beds beneath, as parafusulinids of Guadalupe Victorio Peak was laid down on platform areas, which type are reported from their upper part. were probably separated from the basin area by low banks of the calcitic limestone facies. CUTOFF SHALE FOSSILS The Cutoff Shale is named for Cutoff Mountain (King, P. B., 1942, p. 569-570), in the Guadalupe Nearly all the fossils that have been collected from Mountains near the Texas-New Mexico boundary. Like the Victorio Peak Limestone are from the calcitic facies, the Victorio Peak Limestone, the unit is characteristic on the rim of the Sierra Diablo escarpment or near the Babb flexure (table 8). The fauna indicated by these 4 Earlier identifications by R. B. King in the Sierra Diablo and by G. H. Girty in the Guadalupe Mountains suggested that a common collections is less extensive than that of the Bone Spring brachiopod species of the Victorio Peak Limestone is Dictyodostus Limestone, but it is less known because of poorer pres­ (called "Productus") ivesi. However, according to P. E. Cloud, Jr., (written commun., 1960) : ervation and the relative inaccessibility of the outcrops. "The brachiopod that R. E. King figured as Productus ivesi in his For these reasons the faunal makeup also differs much Glass Mountains memoir (and of which I have the figured specimens before me) is a Leonard species that somewhat resembles Dictyoclostus from one collection to another, but probably no collec­ bassi of the Kaibab Limestone, but which is not present in any Sierra tion approaches the whole biota of its locality. Diablo collection examined by me. "I have also studied Newberry's three cotype specimens of Productus Fusulinids are dominated by large parafusulinids ivesi, which are presumably also from the Kaibab, and regard them as and pseudofusulinids, such as Pamfusulina fountaini unidentifiable productids. Possibly they are small specimens of Dictyo­ dostus has si and perhaps they are the same as D. hessensis, but there Dunbar and Skinner and Pseudofusulina setum (Dun- is no way to tell, and D. ivesi, unhappily, must be relegated to the bar and Skinner). The somewhat smaller Parafusu- limbo. I can only guess that the Sierra Diablo specimens identified by R. E. King as D. ivesi represent the same species I have referred to D. lina diabloensis Dunbar and Skinner and P. scfiucherti cf. hessensis." PERMIAN 75

EXPLANATION

OUTCROP AREAS

Black limestone of Bone Spring

Contains equivalents of Victorio Peak

Older and younger Permian rocks

Rocks older and younger than Permian rocks

OTHER SYMBOLS

600 + 975 Thickness of Victorio Peak Lime­ stone, in feet, where measured Most determinations an partial, due to erosion of top; thickness of the only com­ plete sequence is underscored

Observed intertonguing between gray Victorio Peak Limestone and black Bone Spring Limestone Arrow points toward black limestone fades

Observed boundary between thin- bedded dolomitic limestone on southwest and thick-bedded cal- citic limestone on northeast

Inferred boundary between gray Victorio Peak Limestone on south­ west and black Bone Spring Lime­ stone on northeast

FIGURE 7. Map of Sierra Diablo region showing paleotectonics of Victorio Peak Limestone. 76 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS TAELE 8. Fossils identified from Victoria Peak Limestone in central and northern Sierra Diablo {Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, L. G. Henbest, and E. L. Yochelson. Explanation of symbols. Under Foraminifera: X. species or genus present; var, variety of species present; afl, specimen related to species but probably different; ?, specimen doubtfully assigned to genus or species. Under other biological groups: A, abundant; C, common; X, present; R, rare]

Distribution of fossils in stratigraphic section, locality, and collection number indicated

31 37 38 39 29a North 32 First Second Third Victorio of Marble Northeastern Sierra Diablo section section section 40 South Mesa Southeast of South Mesa Peak Victorio Canyon in to in Canyon Apache Apache Apache Canyon Canyon Canyon

F9820 8545 8546 7011 7006 14470 14445 14448 14461 F9836 F9825 8534 8535 8536 8537 8541 8547 14444 F9837 F9818 F9821 F2691 F2698 F2709 14449

Foraminifera: X X X X X X X ? Parafusulina bakeri D unbar and ? var Parafusulina? bosei var. attenuata aff Parafusulina diabloensis Dunbar and X cfr. diabloensis Dunbar and Skin- X X IParafumlina fountaini Dunbar and var Parafusulina linearis (Dunbar and Skinner). ___ . ___ ...... var X X X X Pseudofusulina setum (Dunbar and ? ? X Schubertella kingi Dunbar and X var X X X Porifera: X X X X X X X Coelenterata: - X X R X R Echinodermata: C C X X Bryozoa: C C X X X A X X X R X Brachiopoda: Avonia sp. ("Avonia" sp., Avonia X X R X Buxtonia (Kochiproductus) victorio- C C C R C C X R X X C R C X X X Dictt/oclostus (Chaoidla) guadalupensis (Girty) ...... C X "Dictyoclostus" afl. D. semistriatus (Meek)...... X X Enteletes dumblei Girty ...... C X R C X X R R X X X A R X C ------X X R X Neospirifer cf. N. pseudocameratus (Girty)...- .-... __. . _.. C R X C C X X X C X X C X X X Rhynchopora sp...... ______... X PERMIAN 77

TABLE 8. Fossils indentified from Victoria Peak Limestone in central and northern Sierra Diablo Continued Distribution of fossils in stratigraphic section, locality, and collection number indicated

31 0>7__ 38 39 29a North 32 First Second Third Victorio of Marble Northeastern Sierra Diablo section section section 40-South Mesa Southeast of South Mesa Peak Victorio Canyon in in to Canyon Apache Apache Apache Canyon Canyon Canyon

F9820 8545 8546 7011 7006 14470 14445 14448 14461 F9836 F9825 8534 8535 8536 8537 8541 8547 14444 F9837 F9818 F 9821 F2691 F2698 F2709 14449

Brachnpoda Continued X X X X X C X Welleretta of. W.degans (Qirty) ___ R R Lamellibranchiata: X Parallelodontid indet ______X Gastropoda: X X X C X X X X X X X R X X Scaphopoda: X X Cephalopoda: X Arthropoda: X Vertebrata:

Alga (dasycladacean): A of the platform areas where it was probably once ex­ beds of black limestone occur near the middle, and north tensive, although it is now exposed only in the western of North Mesa the top bed is a granular dolomitic lime­ part of the Guadalupe Mountains (King, P. B., 1948, stone containing crinoid stems and small limestone peb­ p. 18; Boyd, 1958, p. 13-14) and north of the Sierra bles. The Cutoff contains very few fossils. It much Diablo. Its equivalents in the basin area are uncertain; resembles the black limestone f acies of the Bone Spring- the beds there that were once tentatively assigned to Limestone and probably formed during a brief incur­ the Cutoff (King, P. B., 1948, p. 16) are here classed as sion of basin deposits over the platform, area (Stehli, a member of the Brushy Canyon Formation. 1954, p. 275). North of South Mesa, shale and limestone beds of the 1ITHOLOGIC FEATURES Cutoff are separated by thin layers of earthy gypsum In the report area the Cutoff Shale is preserved only in which coarser crystals are embedded. The shale and north of the Babb flexure and northeast of Sierra limestone beds are turned up and broken, suggesting Prieta, from whence it extends northward for about 12 growth of the gypsum between them. The gypsum oc­ miles, (pi. 1). Here it surmounts the ledges of Victorio curs only in the Cutoff Shale and not in formations be­ Peak Limestone and forms rolling hills, or lower slopes low or above it; but it forms no definite layers so that of mesas that are capped by Goat Seep Limestone. The the term "Dos Alamos gypsum member" that was once Cutoff of this area is 250-275 feet thick, or somewhat applied to it (King, P. B., and King, R. E., 1929, p. 922) thicker than in the Guadalupe Mountains. is unwarranted. Mohr (1929) believed that the gyp­ The Cutoff of the Sierra Diablo region is interbedded sum was introduced by circulating ground water from thin-bedded or platy gray to black limestone, brown the gypsiferous deposits of the Salt Basin, but the gyp­ siliceous or sandy shale, and thin-bedded fine-grained sum is more likely an original constituent of the Cutoff sandstone. The limestone layers weather into light- that has been reconstituted and disordered by modern gray or buff hackly fragments. At South Mesa thicker processes of weathering. 78 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS FOSSILS age. Elsewhere in that area it is overlain by the sand­ The Cutoff Shale is very meageiiy fossiliferous, and stone tongue of the Cherry Canyon Formation of mid­ it has yielded no well-defined fauna. Most of the layers dle Guadalupe age. Although there is little indi­ contain only a few brachiopods or other shells; where cation of erosion at the contact, there was apparently shells are abundant, they are apt to be of a single genus. a hiatus. North of the Sierra Diablo the upper sur­ During field investigations in the Sierra Diablo and the face of the Cutoff is eroded and is overlain by the sand­ Guadalupe Mountains, the writer and his colleagues ob­ stone tongue of the Cherry Canyon Formation. served or collected the brachiopods Squamularia, Correlation of the Cutoff Shale with the sequence in Chonetes, and Composita, and poorly preserved mol- the basin area is uncertain. It was originally suggested lusks. A somewhat larger collection of brachiopods (King, P. B., 1948, p. 16) that its equivalent is in shaly was made near Bone Spring in the Guadalupe Moun­ strata between the black limestone of the Bone Spring tains from strata of Cutoff type (King, P. B., 1948, p. and the sandstone of the Brushy Canyon (the Pipeline 24); but these strata are not physically connected with Shale Member of the Brushy Canyon Formation of this the type Cutoff, and their precise relations to it are report), but this correlation now appears less likely. unknown. Alternatively, Newell and others (1953, p. 23, fig. 10) A similar meager fossil assemblage has been observed proposed that the Cutoff is equivalent to shaly beds by Boyd (1958, p. 59-60) in the Cutoff Shale of the cen­ below the uppermost black limestone of the Bone Spring tral Guadalupe Mountains in New Mexico. Here, in the Delaware Mountains (geologic section 44, unit Chonetes and several genera of gastropods are the most 10), and they imply that this uppermost black limestone common shells, but one locality yielded nautiloids and is younger than the Cutoff. Their proposal, although the ammonites Pseudogastrioceras sp. and Perrinites interesting, involves tracing of beds across the very con­ hilli ( Smith). From the same area paraf usulinids have fused rocks of the Bone Spring flexure, where tracing been collected at several localities and have been identi­ by the writer (King, P. B., 1948, p. 17) has yielded dif­ fied as of Guadalupe type (Warren, 1955, p. 12; Boyd, ferent results. Correlation of the Cutoff with the 1958, p. 60-61). A possible similar occurrence is a col­ Brushy Canyon Formation or higher units of the Gua­ lection of Dunbar and Skinner (1937, p. 725, loc. 140) dalupe Series (Warren, 1955, p. 12) has little basis in near Dos Alamos north of the Sierra Diablo, from known field relations. "cherty beds in basal part of Delaware Mountain sand­ In summary, faunal evidence as to the classification stone a few feet above the Bone Spring [Victorio of the Cutoff Shale is equivocal; physical evidence, Peak(?)] Formation," which contains Parafusulina however, indicates that it is more likely a part of the rothi Dunbar and Skinner. Leonard Series than the Guadalupe Series, although its precise equivalent in the Leonard sequence of the basin AGE area is undetermined.

The Cutoff Shale has been interpreted as a unit of STRATIGRAPHIC RELATIONS late Leonard age (King, P. B., 1948, p. 18; Newell and In the Sierra Diablo region the Cutoff Shale is over­ others, 1953, p. 22-23; Boyd, 1958, p. 60-61), but some lain unconformably by the sandstone tongue of the geologists (Warren, 1955, p. 12) have suggested that it Cherry Canyon Formation. On South Mesa a medium- is of Guadalupe age. grained sandstone bed of variable thickness at the base Most of the scanty fauna of the Cutoff is not a diag­ of the sandstone tongue lies on an eroded surface of the nostic of either series; although the ammonite Perrinites Cutoff. On North Mesa the sandstone tongue nearly or suggests a Leonard age, and the fusuliiiids are reported completely wedges out on the unconformity. This un­ to suggest a Guadalupe age. This situation should be conformity is probably the boundary between the expected in beds lying near a boundary between series Leonard and Guadalupe Series; it also may express a which contain similar and gradational faunas. Thus, hiatus during which the Brushy Canyon Formation was much of the basis for judging the proper classification deposited in the basin area to the east during early of the Cutoff must be in physical evidence, and es­ Guadalupe time. pecially in correlation of the sequence in the platform area with that in the basin, where the Leonard and BRUSHY CANYON FORMATION Guadalupe Series are more clearly differentiated. The Brushy Canyon Formation is missing in the One reason for the original assignment of the Cutoff Sierra Diablo and the area north of it, but it occurs in Shale to the Leonard Series was that its southern edge the Delaware Mountains to the east, as in the northeast in the Guadalupe Mountains is eroded and is overlain corner of the report area (pi. 1) (geologic section 44, pi. by the Brushy Canyon Formation of early Guadalupe 8). The Brushy Canyon, a formation of the basin area, PERMIAN 79 overlaps the edges of the basin (King, 1948, p. 28-32). As shown by outcrops in the southern Guadalupe It is the basal formation of the Guadalupe Series. Mountains (King, P. B., 1948, p. 38), the sandstone The most prominently exposed parts of .the Brushy tongue is equivalent to the lowest part of the typical Canyon Formation are thick beds of relatively coarse Cherry Canyon Formation of the Delaware Mountains, sandstone, which are separated by units of thinner bed­ and represents an extension of its sandy beds from the ded finer grained sandstone and sandy shale. The for­ Delaware basin across the marginal areas; in the mar­ mation is about 1,000 feet thick, but its top is not ex­ ginal areas, the place of higher parts of the Cherry posed within the report area in the Delaware Mountains Canyon Formation is taken by the Goat Seep Limestone. and is only preserved farther east. Typical Cherry Canyon Formation is apparently ex­ At the base of the Brushy Canyon Formation in the posed at the foot of the Delaware Mountains in the Delaware Mountains is a persistent unit, 30-150 feet northeastern part of the report area (pi. 1), but these thick (geologic section 44, unit 12), of black platy shale exposures were not visted during the present investiga­ and shaly sandstone, interbedded with layers of lime­ tion. In the northern part of the report area the sand­ stone and sandstone. This unit lies with abrupt con­ stone tongue of the Cherry Canyon Formation is over­ tact on black limestone of the Bone Spring and is over­ lain conformably by the Goat Seep Limestone. In lain with gradational contact by the Brushy Canyon. It places, layers of the Goat Seep seemingly intertongue was tentatively correlated with the Cutoff Shale of the with the sandstone. platform area (King, P. B., 1948, p. 16), but although GOAT SEEP LIMESTONE it lies in the same general stratigraphic position, it now The Goat Seep Limestone is named for Goat Seep seems unlikely that the two units could be equivalent. on the west side of the Guadalupe Mountains (King, A rather abundant brachiopod fauna in parts of the P. B., 1942, p. 588), where it is a succession of massive shaly unit has affinities with both Leonard and Guada­ limestone banks and reefs that are equivalent to the mid­ lupe faunas (King, P. B., 1948, p. 24). The unit also dle and upper parts of the Cherry Canyon Formation contains large species of Pa/rafusulina and species of the of the basin area. Northward on the west side of the ammonites Waagenoceras and Medlicottia (Newell and Guadalupe Mountains, the Goat Seep loses its massive others, 1953, p. 23), which are more clearly of Guadalupe character and passes into back-reef or platform deposits, affinity. which are thick-bedded dolomitic limestone with many Both physical relations and fossils indicate that the thin-bedded or sandy partings. These back-reef de­ shaly unit is more closely related to the Brushy Canyon posits extend into the central Guadalupe Mountains of Formation above than to the Bone Spring Limestone New Mexico, where they have been termed the "Gray- beneath. It is therefore termed the Pipeline Shale burg-Queen sequence" (Boyd, 1958, p. 15-16), after Member, following Warren (1955, p. 11), and is classed formations whose type areas are in the northern Guada­ as a basal member of the Brushy Canyon Formation. lupe Mountains. The equivalent of the Goat Seep Limestone in the SANDSTONE TONGUE OF CHEBBY CANYON FOBMATION northern part of the Sierra Diablo region resembles the The Cutoff Shale of the northern part of the report back-reef beds of the Guadalupe Mountains, and forma­ area is followed by the sandstone tongue of the Cherry tion names of the northern Guadalupe Mountains might Canyon Formation (King, P. B., 1942, p. 588), which be applied to it, as was done by Stehli (1954, p. 275). forms the upper part of the slope of South Mesa, and However, it is somewhat more convenient to retain the other summits farther north that are capped by Goat term Goat Seep for it in the same manner as has been Seep Limestone (pi. 1). done for back-reef beds in the southern Guadalupe On South Mesa the unit is 150-190 feet thick, and Mountains (King, P. B., 1948, p. 40). most of it is buff fine-grained thin-bedded sandstone. LITHOLOGIC FEATURES At the base, however, is a more massive layer of brown In the report area the Goat Seep Limestone is pre­ medium-grained sandstone that contains poorly pre­ served only north of the Babb flexure, where it forms served fusulinids, as well as shale and limestone pebbles the resistant caps of South Mesa and Middle Mesa (pi. derived from the underlying Cutoff. The layer rests on 1 and upper view pi. 12). Other outliers occur farther a channeled surface of the Cutoff Shale, and its thick­ north, on North Mesa and the hills west of Dos Alamos. ness varies within short distances from 5 to 40 feet. On On South Mesa the Goat Seep is about 200 feet thick North Mesa, north of the report area, the sandstone (geologic section 43b, unit 24), but its top is not pre­ tongue is not exposed; it is either missing by overlap served, either here or elsewhere in the region. on the Cutoff, or is very thin and covered by talus from On South Mesa the Goat Seep is mainly light-gray the Goat Seep Limestone above. or pink dolomitic limestone in beds a few feet thick 80 GEOLOGY OF THE SIERRA DIABLO REGION", TEXAS containing irregular knotted small to large chert masses brachiopods, but adequate collections are difficult to and poorly preserved fossils. Most of the fossils are obtain because of poor preservation of the fossils. silicified, and many form voids lined by crystalline cal- Available collections include 15 genera of brachi­ cite. opods, of which Composite, Stenocisma, Neospirifer, Thicker layers of gray-brown dolomitic limestone and Leptodus, and "Marginifera," are most significant. medium-grained dolomitic sandstone are interbedded They also contain a few sponges, corals, bryozoans, and whose surfaces weather dark gray and pitted. Some mollusks. Fusulinids are abundant in many layers and of the more sandy layers are crossbedded. Bedding in are probably mainly large forms of Parafusulina, al­ the Goat Seep is very irregular, in places chaotic, in though specific ^identification can be made of only a few others inclined in a consistent direction, the beds extend­ specimens. ing with primary dip to the base of the formation where Physical matching of sections and tracing of beds in they seemingly intergrade with the upper part of the the Guadalupe Mountains indicate that the Goat Seep sandstone tongue of the Cherry Canyon Formation. Limestone is equivalent to part of the Cherry Canyon On North Mesa, beds like those on South Mesa are Formation of middle Guadalupe age. This fact is con­ overlain by a unit of thicker bedded dolomitic limestone firmed by what is known of its fauna. The large containing many fusulinids, which forms prominent parafusulinids are characteristic of beds of early and dark jagged ledges. middle Guadalupe age, and according to R. E. King (1931, p. 15), most of the brachiopods are like those of FOSSILS AND AGE the Word Formation of the Glass Mountains, which is The Goat Seep Limestone of the Sierra Diablo region of early and middle Guadalupe age. contains a rather abundant fauna (table 9), mainly of STRATIGRAPHIC RELATIONS TABLE 9. Fossils identified from Goat Seep Limestone, northern Sierra Diablo In the Sierra Diablo region the Goat Seep Limestone {Identifications by P. E. Cloud, Jr., Helen Duncan, R. M. Finks, L. G. Henbest, and is the highest Permian formation preserved, and it is E. L. Yochelson. Explanation of symbols: X, species or genus present; C, com­ mon; A, abundant; R, rare] unknown whether higher strata of the system were ever Distribution of fossils in stratigraphic section, locality, and collection number laid down there. Any such strata have long since been indicated removed by erosion, because the Permian of the region 43- is overlain unconformably by rocks of the Cretaceous South North Dos Mesa Mesa Alamos System. The Goat Seep Limestone itself is not in con­ 8548- 8549 2697 F2688 tact with Cretaceous rocks, but its upper surface on South, Middle, and North Mesa is accordant with a sur­ Foraminifera: X face elsewhere in the region on which Cretaceous rocks X were deposited and later removed. This accordant sur­ Porifera: X face extends westward from South Mesa, across the X X Goat Seep Limestone onto the Victorio Peak Limestone, Coelenterata: which is overlain by Cretaceous rocks at Sierra Prieta. X Bryozoa: CRETACEOUS c X Rocks of the Cretaceous System in the Sierra Diablo Brachiopoda: X region are mainly preserved in the western part of the A X Dictyodostus (Chaoiella) cf, D. guadalupensis (Girty).. X X report area. They border the Sierra Diablo on the west, X R down the dip from the Paleozoic and Precambrian rocks, C C although they are preserved in a few small outliers X Marginifera aft. M. lasallensisl (Norwood and Pratten) . X farther east (pi. 1). They also form the whole of the "Marginifera" aft. "M." occidental!* Sehwellwein of C bedrock in the southwest corner of the report area south­ X R west of Eagle Flat, along the southeastward extension C X of Devil Ridge and in the foothills of the Eagle Moun­ X R tains. The Cretaceous rocks of the Sierra Diablo are C R R the fringe of a much more extensive body to the west, Wellerella sp ______X southwest, and south, in the Finlay, Quitman, Eagle, Lamellibranchiata: X Van Horn, and other mountain ranges. Gastropoda: X The Cretaceous formations of northern Trans-Pecos Texas were first defined and described by Richardson CRETACEOUS 81 (1904, p. 46-50), but modern conceptions of their stra­ Limestone, the Edwards. The Washita Group shows tigraphy are based largely on work done here and else­ the same northward change from dominant limestone in where in the State by Adkins (1933, p. 272-400). Cre­ the south into shale, marl, and sandstone to the north. taceous rocks west and southwest of the Sierra Diablo In the Sierra Diablo region, however, the surface of region have been reported on for the U.S. Geological overlap is more steeply canted; variations which occur Survey by Albritton and Smith (1964) and by Giller- along the outcrop in distances of several hundred miles man (1953, p. 15-33); those to the south are currently in central and north-central Texas are compressed here under study by DeFord and associates (Brand and to within a few scores of miles (pi. 13). DeFord, 1958; DeFord and Brand, 1958; Twiss, 1959). Not far southwest of the Sierra Diablo region, geo- The description given in this report of the Cretaceous synclinal conditions prevailed during Cretaceous time, rocks southwest of Eagle Flat is based on publications and a great thickness of Early Cretaceous sediments of Smith (1940), Gillerman (1953), and Albritton and was deposited, in places following on the latest Jurassic. Smith (1965). The Yucca and Bluff Mesa Formations of the south­ Cretaceous rocks of the Sierra Diablo region belong western part of the report area were deposited along the mainly to the Comanche, or Lower Cretaceous Series. margins of this geosyncline. Cretaceous rocks farther Bocks of the Gulf, or Upper Cretaceous Series, are pre­ north, along the west edge of the Sierra Diablo, were served only southwest of Eagle Flat, although they may deposited on a shelf area that bordered the geosyncline once have extended over the region farther north. The toward the northeast. formations recognized in the region are listed in the Overlap relations in the shelf area along the west edge table below. of the Sierra Diablo are not completely preserved, be­ Cretaceous formations of the Sierra Diablo region cause of fragmentation of the Cretaceous rocks by ero­ sion. It is clear, however, that the Yucca Formation is Southwest of Western Sierra Sierra Prieta missing by overlap, and that the Bluff Mesa has passed Diablo Eagle Flat into a thinned equivalent, the Campagrande Limestone. Gulf Eagle Ford 0 (') The overlying Cox Sandstone, a thick extensive sheet of Series Formation quartzose sands, must replace the Finlay Limestone and Kiamichi Formation northward, for at Sierra Prieta, Washita (0 Washita sandstone like the Cox is overlain directly by basal Group Group strata of the Washita Group, of Duck Creek age. A Kiamichi Kiamichi further extension of the same overlap north of the re­ Formation a Formation port area is indicated in the Cornudas Mountains, near the Texas-New Mexico boundary, where Adkins (1932, Finlay Finlay Cox p. 354) observed Duck Creek fossils in sandstone less Limestone Limestone Sandstone Comanche than 30 feet above the base of the Cretaceous sequence. Series Cox Cox PRE-CRETACEOUS SURFACE Sandstone Sandstone Cretaceous rocks of the Sierra Diablo region were Bluff Mesa Campagrande Campagrande deposited on a surface that evenly bevels the rocks be­ Formation Limestone Limestone neath. For the most part the Cretaceous lies on Permian rocks, although in an area in the Sierra Diablo foothills (*) (3) Yucca northeast of Eagle Flat it lies directly on the Precam- Formation brian Hazel and Allamoore Formations. This area was the locus of greatest uplift during pre-Permian defor­ ' Not preserved. * Not exposed. mation, where the pre-Permian Paleozoic formations * Absent. had been removed by erosion, and where the Permian Lower Cretaceous rocks of the Sierra Diablo region itself was deposited in a smaller thickness than else­ resemble those of the classic area of the Comanche where. Rather oddly, the Cretaceous rocks have no­ Series in central and north-central Texas, and like them, where been observed in contact with any of the Paleozoic record an overlap of Cretaceous deposits on an eroded formations which elsewhere intervene between the Pre- surface of the Paleozoic rocks the Wichita paleoplain cambrian and Permian. of Hill (1901, p. 363). Thus, the Yucca Formation re­ South of the Victorio flexure the Cretaceous lies on sembles the Travis Peak of central Texas; the Bluff the Hueco Limestone, and in places on Precambrian Mesa Formation and Campagrande Limestone, the Glen rocks (section K-K'', pi. 16); north of the flexure it lies Rose; the Cox Sandstone, the Paluxy; and the Finlay on the higher Victorio Peak Limestone (section A-A', 82 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS pi. 16). North of the Babb flexure the Cretaceous was terial in a semiarid or arid climate." They suggest probably deposited on younger Permian formations of (Albritton and Smith, 1965) that the features observed the Guadalupe Series, but it is not now preserved above on the summit areas in the Sierra Diablo are not com­ them. In contrast with the earlier unconformable sur­ patible with those in the Finlay Mountains, and prob­ faces in the Sierra Diablo region (as at the base of the ably were formed by weathering under more humid Van Horn Sandstone and at the base of the Hueco Lime­ conditions. Clearly, knowledge regarding pre-Cre­ stone) , the surface at the base of the Cretaceous is re­ taceous conditions of weathering remains elusive, and markably even. Except in the area where it lies on further evidence must be awaited. Precambrian rocks in the Sierra Diablo foothills, no hills or hollows occur. The surface of the pre-Creta­ YUCCA FORMATION ceous rocks was reduced to a peneplain, formed in part The Yucca Formation, or oldest Cretaceous unit in by prolonged subaerial erosion during early Mesozoic the Sierra Diablo region, occurs only southwest of time, and afterwards perfected by marine erosion of the Eagle Flat (pi. 1), where its exposures are segments of advancing Cretaceous seas. two belts of outcrop that are extensive beyond the re­ Over wide areas in the Sierra Diablo, Cretaceous port area. The Yucca in Love Hogback and the Red rocks are no longer preserved, but its topographic sum­ Hills lies above the Devil Eidge thrust and is exposed mits are an accordant surface which is probably the thence northwestward along Devil Eidge (Smith, 1940, peneplain upon which the Cretaceous was once depos­ p. 604). The Yucca farther east, north of Eagle ited and later removed by erosion. Some remnants of Spring, lies beneath the Devil Eidge thrust and is at Cretaceous rocks are perched on this surface, as on the the end of a belt of outcrop which extends southward west rim of Victorio Canyon and at Black Knobs, and along the foothills of the Eagle Mountains (Gillerman, it seemingly extends beneath the larger bodies of Cre­ 1953, p. 15). taceous farther west. The summits of the downfaulted The Yucca Formation consists of interbedded lime­ Baylor Mountains to the east are probably parts of the stone, conglomeratic sandstone, and shale, all of red, same surface, for a few remnants of Cretaceous sand­ brown, or gray colors. The sequence above the Devil stone are preserved there in downfaulted blocks. Eidge thrust is more than 1,600 feet thick, but the The pre-Cretaceous peneplain in the Sierra Diablo is base is not exposed (geologic section A, pi. 13). The preserved on accordant divides, some at altitudes greater full sequence below the Devil Eidge thrust near Eagle than 6,000 feet. These divides were not produced by Spring is 330 feet thick (geologic section B, pi. 13), stripping of the bedding planes of the underlying but farther south the formation wedges out entirely in Permian rocks as they truncate the bedding at a low places by overlap on the Hueco Limestone. angle in most places, but more steeply on the Victorio The Yucca Formation contains few fossils, but it is and Babb flexures. The peneplain is preserved most clearly of early Comanche age, and is perhaps approxi­ extensively on the Victorio Peak Limestone in the north­ mately equivalent to the Travis Peak Formation of cen­ eastern part of the Sierra Diablo, between Victorio and tral Texas. Southwest of the report area it may include Apache Canyons, where many of the valleys are sepa­ strata of earliest Cretaceous age, or older than the base rated by nearly level summits as much as half a square of the Comanche Series in its type area. mile in area. On these summits, the underlying lime­ stone is thinly covered by red-brown residual clay, BLUFF MESA FORMATION through which limestone pinnacles project, and in The Bluff Mesa Formation, which overlies the Yucca, which large quantities of residual chert are embedded, is also differentiated only southwest of Eagle Flat (pi. different from the sparser chert that occurs in the lime­ 1); but strata equivalent to its upper part extends stone is the adjacent valleys. The residual clay and farther north, where they are termed the Campagrande chert were surely formed at a time earlier than that Limestone. Like the Yucca, the Bluff Mesa is exposed during which the adjacent valleys were cut, and they above the Devil Eidge thrust in the southwest corner may have been produced by weathering before the of the report area and below the Devil Eidge thrust near Cretaceous deposits were laid over the region. Eagle Spring farther east. Albritton and Smith (1950, p. 1440) have described The Bluff Mesa consists of massive limestone beds, features on the basal Cretaceous surface in the Finlay with some marl partings and minor units of sandstone Mountains which they believe are "part of an ancient and shale. Above the Devil Eidge thrust near the re­ soil profile, probably reworked and similar in origin to port area it is about 1,000 feet thick (geologic section lime-enriched zones of the southwestern United States, A, pi. 13), but it thickens northwestward to as much as and developed by weathering of calcareous parent ma­ 1,600 feet at the type locality on Bluff Mesa south of CRETACEOUS 83 Sierra Blanca. Below the Devil Ridge thrust near are lumpy and perhaps contain algal balls, but no other Eagle Spring, the Bluff Mesa is no more than 250 feet fossils were observed. Analysis of a specimen from thick, and the limestone is interbedded with much shale, the Bean Hills indicates 93.66 percent CaCO3,1.18 per­ sandstone, and conglomerate (geologic section C, pi. 13). cent MgCOs, and 5.50 percent insoluble material (K. J. The Bluff Mesa is rather abundantly fossiliferous Murata, written commun., 1940). In most of the Bean throughout, and contains a fauna like that of the Glen and Streeruwitz Hills the "cap ledge" is the highest bed Rose Formation in central Texas. Exogyra quitmanen- preserved. The upper ledge maker, informally termed sis Cragin is common in the lower part, and Orbitolina the "IsTodosaria bed," is a darker gray, more distinctly texana (Roemer) occurs from base to top. bedded, more fossiliferous limestone 15-25 feet thick. CAMPAGRANDE LIMESTONE At a few places its weathered surfaces are studded with shells of the medium-sized foraminifer Haplostwhe The Campagrande Limestone is the basal Cretaceous ("Nodosaria"), and in many places it contains oyster unit in the Sierra Diablo and farther west in the Diablo and echmoid fragments. Plateau, although it is equivalent to strata well above Between and above the two ledge-making beds are the base of the Cretaceous in the area southwest of shale, marl, and nodular limestone, parts of which are Eagle Flat, that is, to the upper part of the Bluff Mesa bioclastic and contain oyster fragments and traces of Formation. rudistids. The Campagrande Limestone is named for the feature WESTERN SIERRA DIABLO shown on modern maps as Campo Grande Arroyo In the plateau country west of the Sierra Diablo the (Richardson, 1904, p. 47), in the Finlay Mountains basal Cretaceous is a set of calcareous strata, no more about 25 miles west of the report area. At its type than 25 feet thick in most places, but thickening to 50 locality it is 630 feet thick, but it varies from 375 to 800 feet at Black Knobs and to 80 feet on the east side of feet elsewhere in the Finlay Mountains (Albritton and Sierra Prieta. These strata are not easily recognized Smith, 1965.) In the foothills south of the Sierra on first view: in some places they resemble the under­ Diablo it is as much as 200 feet thick in places (geologic lying Permian and in others, modern caliche and lime­ sections 45, 46, p. 174-175) but is generally less. stone gravel. Their nature as a basal Cretaceous de­ Farther north it is mostly less than 50 feet thick, al­ posit is made clear in favorable exposures. though it attains 80 feet on the east side of Sierra Prieta These calcareous strata are classed with the Cam­ (geologic section 53, pl.13 and p. 170-171). pagrande Limestone, because field relations suggest that SIERRA DIABLO FOOTHILLS they were once physically joined to the Campagrande farther south. However, they are not only thinner The Campagrande Limestone forms a nearly con­ tinuous band of outcrop south of the south-facing than the Campagrande in its more typical exposures, escarpment of the Sierra Diablo, where it is overlain but they lack its regular stratigraphy, are nearly with­ out fossils, and may be partly of younger age. They toward the west by Cox Sandstone (pi. 1). It is also much resemble the Yearwood Formation of the Apache preserved in smaller outliers in the Bean and Streeru- witz Hills farther south. Toward the north and west Mountains east of the report area, as described by Brand and DeFord (1958, p. 373-376), which is also the Campagrande lies on the Hueco Limestone, but in most of the foothills it bevels the Hueco and lies di­ a thin basal Cretaceous unit, mainly limestone, with a basal conglomerate. rectly on the Precambrian Hazel and Allamoore Forma­ tions. Near Cox Mountain (geologic section 49, pi. 13) the Campagrande is limestone, partly nodular and marly, Basal beds of the Campagrande are conglomerate containing limestone and chert pebbles in its lower part; with a limestone matrix, containing numerous pebbles in places it has a strong ledge at the top. Most of the of Hueco Limestone, minor pebbles of chert, and toward limestone is light gray or white, but it is commonly the base, fragments of Precambrian rocks. In places mottled yellow or red, so that it has a "burnt" appear­ the conglomerate is as much as 80 feet thick; but it ance. On the east side of Sierra Prieta (geologic sec­ varies abruptly in thickness within short distances by tion 53, pi. 13), where the formation is somewhat thick­ overlap on irregularities of the pre-Cretaceous surface, er, limestone of the sort described forms ledges several and in places is missing entirely. feet thick, separated by white or buff marl and clay. The overlying part of the formation, about 100 feet Poorly preserved oysters and gastropods occur at vari­ thick, has a more regular stratigraphy, and includes ous levels, and nodules or lumps in the marly layers may two beds of ledge-making limestone. The lower ledge be of algal origin. maker, informally termed the "cap ledge," is a massive Relations of these basal Cretaceous strata in the west­ bed of light-gray limestone 25-50 feet thick. Parts ern Sierra Diablo are puzzling. At Cox Mountain and 84 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS farther south they are overlain by many hundreds of SIEBBA DIABLO FOOTHILLS AND COX MOUNTAIN feet of Cox Sandstone, Finlay Limestone, and Kiamichi The most extensive exposures of the Cox Sandstone Formation; whereas at Sierra Prieta to the north they are along the base of the south-facing escarpment of are overlain by less than 200 feet of sandstone, part or the Sierra Diablo in its western half (pi. 1). Small to all of which is of Finlay and Kiamichi age. Either the large outliers occur farther east, near the Gifford-Hill calcareous strata are a transgressive deposit which be­ rock crusher in the northwestern Carrizo Mountains, comes younger toward the north, or they are separated and to the north in the plateau country, in the area near from the overlying sandstones by a disconformity, the Cox Mountain. The top of the formation is preserved magnitude of whose hiatus increases northward. A dis­ only on Cox Mountain (geologic section 49, pi. 13), conformity is reported between the calcareous Year- where it is overlain by Finlay Limestone; but the part wood Formation and the overlying Cox Sandstone in of the formation which is preserved on Dome Peak the Apache Mountains (Brand and De Ford, 1958, p. (geologic section 47, pi. 13) and in the northwestern 376-377). Carrizo Mountains (geologic section 48, p. 171) is as FOSSILS AND AGE thick or thicker. The Campagrande Limestone in the Sierra Diablo The most conspicuous parts of the formation are foothills is fossiliferous, but no significant collections massive sandstone beds, forming units 15 to more than were obtained during the present investigation. In the 100 feet thick. The sandstone beds weather brown and type area in the Finlay Mountains it contains many break out in great rectangular or cubical blocks that foraminifers and various megafossils, including Poro- strew the slopes below. These blocks tend to overwhelm cystis globularis (Giebel), corals, pelecypods, various and obscure any interbedded less resistant units, which rudistids, and gastropods, such as Turritella (Albrit- actually form a considerable part of the formation to­ ton and Smith, 1965). This fauna, like that of the Bluff ward the south, although they are probably less impor­ Mesa Formation, is of Glen Rose or late Trinity age. tant near Cox Mountain. The massive sandstone beds, which are formed of COX SANDSTONE medium- to coarse-grained quartz sand, have great vari­ The Cox Sandstone is named for Cox Mountain ations in texture and structure from layer to layer. (Richardson, 1904, p. 47), west of the Sierra Diablo Many parts are crossbedded, in part on a large scale, within the report area; but a better reference locality and some bedding surfaces are ripple marked. Much is perhaps in the Finlay Mountains beyond the report of the sandstone contains dispersed well-rounded quartz area, where it lies in sequence between the type Cam­ and chert pebbles as much as an inch in diameter; in pagrande Limestone and type Finlay Limestone. places these pebbles are concentrated in streaks or lenses, Toward the north the Cox is a nearly continuous or in beds of conglomerate. The sandstone is charac­ body of sandstone, which is a little more than 400 feet teristically dotted with small brown ferruginous spots thick on Cox Mountain and 540-675 feet thick in the or nodules, which are especially conspicuous on weath­ Finlay Mountains. The Cox Sandstone thickens south­ ered surfaces and which may have originated from ward, attaining more than a thousand feet southwest pyritic segregations in the original rock. of Eagle Flat; as it thickens, it becomes finer grained In the Sierra Diablo foothills less resistant inter­ and acquires many interbedded layers of limestone and bedded units 10 to 25 feet thick occur throughout the shale. The Cox is one of the most prominently exposed formation, but they are thicker and more prominent in parts of the Cretaceous sequence, projecting in buttes, the lower few hundred feet. In the upper part most mesas, and hogbacks, on which its sandstone beds form of the interbedded units are thinner bedded finer massive ledges. grained lighter brown sandstone; but lower down they SOUTHWEST OF EAGLE FLAT include red and purple silty shale and marl and scattered beds of nodular gray limestone or dense brown to red The Cox Sandstone is 1,066 feet thick in a measured section a little west of the edge of the report area (geo­ limestone. Within the report area none of the limestone logic section A, pi. 13), and is as thick or thicker in the beds are fossiliferous, but near Sierra Blanca farther belt of outcrop farther east near Eagle Spring (geo­ west they contain the thick-shelled gastropod Actaeo- logic section C, pi. 13). It consists of brown sandstone netta and various oysters (geologic section P, pi. 13). that is finer grained and more quartzitic than farther On Cox Mountain the interbedded units are apparently north, with fewer crossbeds and ripple marks, and with thinner, but some beds of purplish shale were observed; much interbedded shale, siltstone, and fossiliferous lime­ 15 feet of nodular limestone has been reported 225 feet stone (Smith, 1940, p. 612). below the top (DeFord and Brand, 1958, p. 23, pi. 7). CRETACEOUS 85 OUTLYING AREAS 120 feet below the top where Exogym teseana Roemer, East of the exposures described, smaller outliers of Alectryonia carinata (Lamarck), and various pelecy- the Cox are preserved in places atop the dominant ter­ pods and gastropods of Fredericksburg type are re­ rain of Permian carbonate rocks (pi. 1). A small patch ported (Adkins, 1932, p. 354). of sandstone no more than 10 feet thick overlies the Presumably part or all of the sandstone on Sierra tilted Bone Spring Limestone of the Victorio flexure on Prieta is equivalent to the Finlay Limestone and Kia­ the west rim of Victorio Canyon (northwestern part michi Formation elsewhere in the Diablo Plateau, al­ of sec. 14, block 43) (section X-X', pi. 4) and is capped though it might include equivalents of the typical Cox by a remnant of Tertiary vesicular basalt. Farther west Sandstone in its lower part. Disappearance of the in the same vincinity sandstone patches are scattered Finlay toward Sierra Prieta seems abrupt on first view, over the upland. Some of these patches may be layers as mesas capped by its limestone beds occur within 6 in the Bone Spring Limestone, but some are certainly miles to the southwest, and at only slightly greater dis­ outliers of the Cretaceous. Cretaceous fossils have been tances to the south and west. However, these limestone collected in this area by the local ranchmen, but none beds are no more than a few feet thick, and most of the were observed during the present investigation. Finlay on the mesas is marl and sandy marl, with sev­ Similar outliers of the Cretaceous occur in the Baylor eral conspicuous sandstone beds. The Kiamichi (?) Mountains, in Red Tank Canyon a mile east of Red Formation which overlies the Finlay in an outlier 9 Tank (west-central part of sec. 8, Block 66), where miles southwest of Sierra Prieta (Block 35, west of re­ steeply dipping sandstone overlies the Hueco Limestone port area) is all sandstone. and is downfaulted against it on the south. FOSSILS AND AGE In all these outlying areas sandstone lies directly on No fossils were observed in the Cox Sandstone in the the Permian rocks, and the Campagrande Limestone report area, except for those in beds probably younger that intervenes on the western slopes of the Sierra than the typical Cox on Sierra Prieta. To the west, Diablo is missing. near Sierra Blanca and in the Finlay Mountains, gas­ SIERRA PRIETA tropods and pelecypods of marine origin occur in lime­ At Sierra Prieta, 18 miles north of Cox Mountain, stone and marl that is interbedded with the massive the lower part of the Cretaceous includes a unit of mas­ sandstone of the upper half, whereas the silty shale sive sandstone which is mapped with the Cox (pi. 1), units of the lower half contain charophytes, ostracodes, although its relations are somewhat different from those and silicified wood, probably of littoral origin (Albrit- of the Cox farther south. The sandstone is underlain ton and Smith, 1965). The thick-shelled gastropod by Campagrande Limestone, but it is overlain directly Actaeonella is the most abundant marine invertebrate by the Washita Group. The Finlay Limestone and fossil. Kiamichi Formation which should intervene are not The poorly fossiliferous Cox Sandstone intervenes represented as such. Physical connection of the sand­ between fossiliferous beds of Trinity age (Bluff Mesa stone on Sierra Prieta with the typical Cox is and Campagrande) and of Fredericksburg age (Fin- not demonstrated, as a wide alluvial-covered area in­ lay) , indicating that it lies near the boundary between tervenes ; nevertheless, the two sandstones are probably these two groups. Evidence is insufficient to prove parts of the same transgressive body. whether the Cox is of Trinity age, of Fredericksburg In the eastern part of Sierra Prieta the sandstone is age, or includes beds of both ages. 135 feet thick (geologic section 53, pi. 13), but in the FINLAY LJMESTONB western part it is as much as 190 feet (geologic section The Finlay Limestone is named for the Finlay Moun­ 54, pi. 13). The upper part includes 50 or 60 feet of tains (Richardson, 1904, p. 47-48), about 25 miles west massive brown medium- to coarse-grained sandstone, of the report area, where it overlies the Cox Sandstone in part crossbedded and pebbly like the Cox. Above it with the top not preserved; elsewhere, as near Sierra is a smaller thickness of lighter brown finer grained thin­ Blanca and on Cox Mountain, it is followed by the ner bedded sandstone; below it is a greater thickness Kiamichi Formation. The Finlay characteristically of friable buff sandstone, marly sandstone, and gray, includes ledge-making beds of rudistid-bearing lime­ buff, or purple shaly sandstone. stone, but these beds vary greatly in number and thick­ Many of the sandstone beds contain fragments of ness; they form most of the unit southwest of Eagle silicified wood, and some of their bedding surface show Flat, but are interbedded northward with increasing fucoidal markings. In the western part of Sierra Pri­ thicknesses of nodular limestone, marl, and sandstone. eta invertebrate shells occur in the upper half of the Like the underlying Cretaceous formations, the Finlay sandstone, and are especialy abundant in massive beds thins northeastward. It is more than 350 feet thick 86 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS southwest of Eagle Flat and as much as 200 feet thick and gastropods; and the sandstone beds, fragments of in the Finlay Mountains; the full thickness north of silicified wood. Sierra Blanca, however, is 150 feet and on Cox Moun­ FOSSILS AND AGE tain, 60 feet. In the Finlay Mountains the Finlay Limestone con­ The Finlay Limestone is only scantily preserved in tains a varied invertebrate fauna, including the f orami- the report area (pi. 1), and its outcrops are mainly ex­ nifer Dictyoconus ("Orbitolina") walnutensis Carseyj tensions of larger ones farther west those southwest Exogyra, Gryphaea, rudistids, and other pelecypods; of Eagle Flat of the outcrops in Devil Ridge, and those the ammonite Engonoceras; gastropods; and echinoids. west of the Sierra Diablo of the outcrops in the Diablo (Albritton, and Smith 1965). Collections from the Plateau (Albritton and Smith, 1965). A small isolated report area, largely from the marl beds, are more re­ outlier surmounts the Cox Sandstone on Cox Mountain. stricted, consisting of pelecypods, gastropods, and a few echinoids; rudistids are common in the ledge- LOCAL FEATURES making beds but are poorly preserved. The fauna of Southwest of Eagle Flat, the Finlay above the Devil the Finlay Limestone is of Fredericksburg age, and the Eidge thrust is a nearly continuous sequence of limestone formation is equivalent to part or all of the Edwards beds a few feet to more than 5 feet thick with only a few Limestone farther east in Texas. marly partings; fossils are abundant but poorly pre­ Table 10 indicates the fossils of the Finlay Limestone- served. About 350 feet of Finlay overlies the Cox on which have been identified from collections made west Devil Ridge just west of the report area, but the top is of the Sierra Diablo, in or near the report area. All missing (geologic section A, pi. 13). The Finlay is but the first lot were identified by R. W. Imlay (written more extensively exposed on the pediment northeast of commun., 1940,1950). the Devil Ridge thrust; however, outcrops are low and TABLE 10. Fossils identified from Finlay Limestone, western obscure, and little is known of the sequence. part of Sierra Diablo region, Texas On Cox Mountain (geologic section 49, pi. 13) where [Identifications by E. W. Imlay] the full thickness of the Finlay is 60 feet, it includes two ledge-making beds of gray limestone, one at the top and Locality and fossil collection number another near the middle, with slope-making nodular North­ Cox South­ eastern limestone, sandy limestone, and marl between and below. Moun­ west of Rob­ Nor­ part of tain Rob­ erts ton Triple The ledge-making beds contain rudistids, the slope-mak­ (De erts Mesa Mesa Hill Ford Ranch (USGS (USGS quad. ing beds contain oysters and gastropods. and (USGS 17844, 17281, (Albrit­ Brand, 17844, 17843) 17900) ton and Northwest of Cox Mountain the Finlay Limestone 1958) 17843) Smith, forms Roberts Mesa (Block 39) and Norton Mesa 1965) (Block 34), each several square miles in area, which are Lamellibranchiata: X outliers of more extensive tablelands farther west (pi. X X X X X 1). Only about 80 feet of the formation is exposed Pecten (Neithea) occidental}* Con- X (geologic sections 51,52, p. 173-174), the base being con­ X Modidus concentrice-castellatus cealed by alluvium and the top being a stripped surface X X of the limestone caprock. This caprock is probably near X X the top of the formation, for it is overlain by sandstone X X of the Kiamichi( ?) Formation west of the report area X X (Block 35). X X X X X Near Roberts and Norton Mesas the only strong lime­ X X stone bed is the caprock at the top, which is no more Gastropoda: than 6 feet thick. Below is marl and calcareous sand­ X ori X stone, with several beds of brown massive sandstone, the Nation1! cf. N.I pedernalis Roemer. X X most conspicuous of which is 8 or 10 feet thick and has X X X X X X been separately mapped (pi. 1). The sandstone is Turrttella seriatim-granulata X medium grained, crossbedded, and ripple marked, the X Cerithiumt cf. C.I pecosense Stan- ripples commonly trending northwestward. Tracing of X X X the sandstone beds from mesa to mesa along the west X edge of the report area indicates that they wedge out X Echinoidea: southward. The limestone caprock contains poorly pre­ X served rudistids; the marl beneath, abundant pelecypods X CRETACEOUS 87 KIAMICHI FORMATION TABLE 11. Fossils identified from KiamicM Formation, Cox The KiamicM Formation is named for the Kiamichi Mountain, Tens. River in southeastern Oklahoma, from whence it ex­ [Identifications by E. W. Imlay, except in last two columns] tends southward into north-central Texas as far as the Fossil collection number DeFord Adkins and Brazos Eiver. Adkins (1932, p. 351-355) has demon­ 1932, Brand, USGS USGS USGS USGS p. 353 1958 strated the wide extent of the same unit in Trans-Pecos 17838 17837 17836 17280 Texas. Coelenterata: Within the report area the Kiamichi Formation is Parasmilia sp., and other X preserved only on Cox Mountain (geologic section 49, X pi. 13), where 65 feet of fossiliferous marly limestone, Lamellibranchiata: X X X X marl, and thin-bedded sandstone overlie the Finlay cf. O. corrugata Gabb _ X X Exogyra texana Eoemer __ X X limestone and are followed unconformably by Tertiary X Trigonia emoryi Conrad X X X basalt. Similar strata with the same fauna, 100 feet Of) X Pecten (Neithea) subalplnus thick, occur farther west near Flat Mesa north of Sierra X X (Neithea) irregularis Blanca (geologic section D, pi. 13), and are capped by Bose X X X sandstone with a Duck Creek fauna (Adkins, 1932, p. X X 352). X The Kiamichi evidently passes northward into sand­ Gastropoda: X X stone, because at Sierra Prieta the Washita Group is X X X X underlain directly by sandstone whose upper part con­ X tains a Fredericksburg fauna (see under "Cox Sand­ X X Cephalopoda: stone") . In the area between Cox Mountain and Sierra Oxytropidoceras acwticarina- X Prieta, a little west of the report area (Block 35), 34 X cf. O. supani (Lass- feet of fossiliferous sandstone, probably the Kiamichi X X X Formation, is preserved in an outlier on the Finlay X Limestone (Albritton and Smith, 1965). Echinoidea: Enallaster texanus (Eoemer). X The Kiamichi Formation is not exposed southwest of Eagle Flat within the report area, its position being facies of limestone, marl, and shale; and the reef lime­ occupied by an alluvial-covered swale (section 19, Block stone facies but they are compressed within a shorter 69, Twp. 8; pi. 1). However, it probably exists in this distance than in central and north-central Texas. On area, as Gillerman (1953, p. 25) observed the formation, Sierra Prieta the group consists largely of the marginal with its characteristic fossils, farther southeast in the facies; southwest of Eagle Flat, the neritic facies; and same outcrop belt in the foothills of the Eagle Moun­ farther to the south, the reef facies. tains (geologic section C, pi. 13). Various formations of the Washita Group have been On Cox Mountain the Kiamichi Formation contains differentiated in adjoining areas to the south and east a varied fauna of pelecypods, gastropods, and cephalo- (Gillerman, 1953, p. 25-31; Brand and DeFord, 1958,5 pods, and minor corals and echinoids. The most char­ p. 379-386; Twiss, 1959). In the report area varied acteristic fossils are various species of the cephalopod ages of different parts of the group are indicated by the Ossytropidoceras and the oyster G-ryphaea navia Hall, fossil collections, but it has not been feasible to sub­ the first indicating broadly a late Fredericksburg age, divide the group on any other than a zonal basis. and the second more specifically a Kiamichi age. Table 11 lists fossils that have been identified from SOUTHWEST OF EAGLE FLAT the collections made in the Kiamichi Formation on Cox The Washita Group occurs below the Devil Ridge Mountain. The first four lots were identified by E. W. thrust southwest of Eagle Flat, where it crops out in Imlay (written commun., 1940). low parallel ridges and forms a band of outcrop several WASHITA GROUP miles wide (pi. 1). About a thousand feet of strata lies Within the report area the Wasliita Group, or high­ beneath the Eagle Ford Formation, but although the est unit of the Comanche Series, is preserved only south­ Finlay Limestone underlies them on the northeast, the west of Eagle Flat and on Sierra Prieta (pi. 1), intervening Kiamichi Formation and the basal beds of the Washita Group are concealed. although outcrops are more extensive in the surround­ ing region. Within the region all three facies of the 6 Brand and DeFord (1958, p. 378) have proposed a "Sixshooter group that were distinguished by Adkins (1932, p. 361) Group" to encompass the Finlay Limestone of Fredericksburg age and the overlying formations of Washita age, but justification for supplant­ occur the marginal sandy facies; the normal neritic ing the long-established Washita Group in this region is not apparent. 88 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Here the Washita Group is chiefly thin-bedded lime­ TABLE 12. Fossils identified from "beds of Duck Creek age stone, in part marly and sandy (geologic section B, pi. Washita Group of Sierra Prieta, Tex. 13). The lower 680 feet is limestone and marly lime­ [Identifications by R. W. Imlay, except In last column] stone; the middle 150 feet, sandstone, calcareous sand­ Fossil collection number stone, and shale; and the upper 200 feet, limestone and 17904 17905 17915 17801- Adkins, sandy limestone (Albritton and Smith, 1965). Fossils 18091 1932 are abundant in marly beds of the lower unit 480 to 580 Lamellibranchiata: X feet below the top of the group and include such diag­ Inoceramus cf. I. comancheanus Cragin ______X nostic species as Alectryonia quadriplicata (Shumard), X Alectryonia aff. A. carinata Lamarck. X X Turrilites brazoensis Roemer, and Mortoniceras wintoni X X X (Adkins) (Smith, 1940, p. 616-617), which occur in X X Pecten (Neithea) subalpinus Bose. ... X X X north-central Texas at levels between the Weno and (Neithea.) sp. ______X X Mainstreet Formations. The three units southwest of X X X Eagle Flat may correspond approximately to the Pholadomya cf. P. shattwki Bose ..... X X Homomya cf. H. ligeriensis (d'Or- Georgetown Limestone, Grayson Formation, and Buda X X X Limestone as differentiated by Gillerman (1953, p. 25- Tapfs? cf. T.I chihuahuensis Bose .... X 31) in the foothills of the Eagle Mountains a few miles X Gastropoda: to the southeast (geologic section C, pi. 13), but this X correlation has not been verified. X Cephalopoda: Cymatoceras texanum (Shumard) .... X X SIERRA PRIETA C.?sp... __ ...... X X Idiohamites cf. L.fremonti (Marcou).. X On Sierra Prieta the Washita Group overlies the cf. 7. comancheanus (Adkins and Winton) ...... X sandstone mapped as Cox, and is variably truncated X Eopachydiscus brazoense (Shumard)-. X X X X above by the thick sill of igneous rock which caps the Eopachydiscus? cf. E.I laevicanicula- X mountain (pi. 1; section A-A', pi. 16). As the beds sp. juv X Mortoniceras cf. M. leonensis (Con­ are poorly resistant to erosion, they are extensively rad).... __ . __ ...... ___ .. X X X Pervinqueria cf. P. kiliani (Lasswitz). X X X masked by landslides and float from the igneous rock X X X and are exposed mainly in ravines (upper view, pi. 12). sp...... X X X However, fairly complete sections can be measured in Echinoidea: X several places. At the east end of Sierra Prieta (geo­ Pkymosa cf. P. maxicanum Bose ..... X X X logic section 53, pi. 13) 350 feet of Washita beds is X X X X preserved below the sill, and at the west end (geologic Pliotaxaster whUei (Clark) .._ ..... X X section 54, pi. 13), 175 feet. Brarhiopoda: Kingenal cf. K3 leontnsis (Conrad).. X X X Most of the group is marl, nodular limestone, sandy X X shale, and thin-bedded sandstone. No very distinctive lithologic subdivisions are apparent, although a consid­ sequence at the west end of the mountain with the erable range in age is indicated by the fossils, which are Weno. abundant throughout. At all localities the basal 40 or FOSSILS 50 feet of beds is of Duck Creek age; these beds con­ Tables 12 and 13 indicate fossils which have been tain abundant Eopachydiscus, Mortoniceras, Pervin- identified from collections made in the Washita Group queria, and other ammonites, some of which must have on Sierra Prieta. Table 12 shows the fossils from the been of exceptional size, for preserved fragments are Duck Creek horizon; table 13 shows those from higher several feet across. Higher in the section, layers of strata that are known to include faunas of several hori­ oyster shell coquina are interbedded at various levels, zons, probably ranging from Fort Worth to Mainstreet. composed mainly of G-ryphaea washitaensis Hill. The All the identifications are by R. W. Imlay (written age of the strata above the Duck Creek horizon can be commun., 1940), except those by W. S. Adkins in the determined only approximately. Imlay (written com- last column. mun., 1940) suggests correlation of successive collec­ EAGUB FORD FORMATION tions in the thick sequence at the east end of the moun­ The Eagle Ford Formation, the only unit of the Gulf tain with the "Denton or Weno," and the "Fort Worth Series in the report area, is preserved southwest of or Denton," and states that the highest collection is Eagle Flat, where it forms a belt of outcrop about a "not younger than Mainstreet." Adkins (1932, p. 354) mile wide between the Washita Group and the Devil tentatively correlated the highest beds in the thinner Ridge thrust, which truncates its top (pi. 1). About IGNEOUS ROCKS 89 TABLE 13. Fossils identified from beds younger than Duck Creek age in Washita Group of Sierra Prieta, Test. [Identifications by R. W. Imlay, except in last column] Fossil collection number Adkins 17907 17908 17909 17910 17911 17912 17913 17914 17902 1932

Lameilibrancbiata: X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X SD X X X Gastropoda: X X X X X X X X Cephalopoda: X X X X X X X X Ecbinoidea: X X X X X X X X X Pseudopyrina clarki (B5se). ______X cf. P. inaudUa (Bbse). ______X X X X X X X X X X Brachiopoda: X X X

1,400 feet of strata is preserved, which is black fissile Cretaceous ages, are probably of Tertiary age. They are bituminous shale that passes upward into buff sand­ outliers of much more extensive Tertiary intrusive and stone, in part quartzitic, interbedded with some shale extrusive igneous rocks to the west and south (Albritton and chalky limestone. Fossils are not abundant, but and Smith, 1965, Gillerman, 1953, p. 34-49; Twiss, 1959; various foraminifers, Inoceramus, Ostrea, and other Hay-Roe, 1957). pelecypods, and a few genera of gastropods have been The largest bodies of intrusive rocks are near Marble reported (Smith, 1940, p. 618). and Mine Canyons in the northeastern Sierra Diablo and at Sierra Prieta northwest of the Sierra Diablo; IGNEOUS ROCKS smaller bodies occur farther south (pi. 1). The only In the Sierra Diablo region igneous rocks occupy extrusive rock is basalt, which is preserved in a few much smaller areas than the sedimentary rocks, but they small outliers in the western Sierra Diablo. Composi­ are varied and widely distributed (pi. 1). Some lie in tions and relations of the various intrusive and extru­ the Precambrian sedimentary and metamorphic rocks sive rocks differ so much that they were probably formed arid are themselves of Precambrian age; these rocks during widely separated parts of Tertiary time, and at have been described above (p. 22-23,24). Others, which least one body, that at Mine Canyon, may include ig­ intrude or lie on rocks as young as of Permian and neous rocks of several different ages. 90 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS MAEBLE CANYON-MINE CANYON INTRUSIVE rounded knobs and boulders. It is cut by several sets COMPLEX of joints, spaced tens of feet apart, of which the most The most varied assemblage of intrusive rocks is in prominent in the southern part trend east-west. Speci­ the northeastern part of the Sierra Diablo west of the mens of the syenite which were examined in thin section Figure Two Eanch, on the lower slope of the escarp­ by Ingerson and Milton are dominantly potassium feld­ ment near Marble Canyon and Mine Canyon (pi. 14). spar and sodic plagioclase (oligoclase), the proportions Here, the Permian rocks are invaded by two stocks, each varying from specimen to specimen. Quartz is minor, about half a mile in diameter, and by various outlying comprising less than 6 percent of the rock, and mainly dikes and sills. One of the stocks, at the head of Marble forms graphic intergrowths with the potassium feld­ Canyon, is composed of coarse plutonic rocks of granitic spar. Mafic minerals include brown biotite, brownish- texture, and has been eroded into a basin. The other green hornblende, and gray-violet diopsidic pyroxene. stock, south of the portal of Mine Canyon, is composed Some specimens contain minor amounts of calcite, in largely of finer grained porphyries and breccias, and crystals as much as 0.5 mm in diameter, which extin­ projects in Cave Peak, a conical summit prominently in guish uniformly. Ingerson suggests that the calcite is not an alteration product, but was dissolved in the view from Texas Highway 54 (lower view, pi. 10). magma and crystallized during the orthomagmatic At their present levels of erosion both stocks invade stage. mainly the dolomitic strata of the Hueco Limestone; Between syenite and country rock is a band of darker in places however, their contacts extend as low as the gabbroic igneous rock of granitic texture like the sye­ basal clastic Powwow Member of the Hueco, and in nite, although somewhat finer grained. Specimens that others as high as the siliceous black limestone beds of have been studied in thin section by Ingerson and Mil­ the Bone Spring Limestone. Neither stock has notably ton are dominantly intermediate plagioclase (andesine); deformed the country rock beyond a few feet from its potassium feldspar is subordinate. Mafic minerals in­ contact. Nevertheless, the country rock has been meta­ clude brown biotite, diopsidic pyroxene, and olivine and morphosed for distances as much as 400 feet from the minor quantities of magnetite, ilmenite, and spliene. igneous rocks the main body of the Hueco Limestone The dark gabbroic rock is somewhat more resistant to varieties of marble, and the rocks below and above it to erosion than the syenite, and in places projects as a to various complex lime and magnesian silicate horn- low wall between it and the country rock. The outcrop felses. of the gabbroic rock in the northern and southern parts The intrusive complex near Marble and Mine Can­ of the stock is as much as 400 feet wide; elsewhere, it yons was studied by the writer at various times during is narrower, and at several places on the east and west the present investigation. It was also studied for the sides is missing altogether. Throughout its extent it U.S. Geological Survey, in the field or laboratory, by maintains its entity as a distinct rock unit, and no gra- W. T. Holser (in Warner and others, 1959, p. 140-143, dational phases between it and the syenite were ob­ pi. 5), Earl Ingerson (written commun., 1937), S. J. served. The contact between them is nowhere exposed, Lasky (oral commun., 1938; written commun., 1940), but in a few float boulders a syenitic rock was observed and Charles Milton (written commun., 1940). Chemi­ to intrude gabbroic rock. Apparently the gabbroic cal analyses of some of the rocks were made by K. J. rock is an early phase of the intrusion of the stock and is Murata (written commun., 1937, 1940). The present not merely a border phase of the syenite produced by account is compiled from these various observations. assimilation of the adjacent country rock. MARBLE CANYON STOCK On the east side of the stock, for 8 to 10 inches from the country rock, the dark gabbroic rock is finer grained The Marble Canyon stock is oval in plan, about three- than the remainder, indicating a chilled contact. Within quarters of a mile long and a quarter of a mile wide, 15 feet of the contact at the same locality it contains and is elongated north-south (pi. 14). Where the con­ several aplite and pegmatite dikes, as well as inclusions tact of the stock with the country rock is exposed, it of a dark hornfels of different composition from the is nearly vertical. The core of the stock, comprising adjacent country rock, which was probably brought up most of its volume, is a quartz-bearing syenite of coarse from a lower level. On the north side of the stock the granitic texture. The syenite is bordered by a discon­ dark gabbroic rock (or the syenite where this is miss­ tinuous band of darker gabbroic rock; both are tra­ ing) is separated from the country rock by a zone 10 versed by many dikes of aplite and pegmatite, some of or 20 feet wide, which is a confused mass of stringers of which extend short distances into the country rock on coarse igneous rock, aplite and pegmatite, and hornfels. the west. Both the syenite and the dark gabbroic rock are tra­ The syenite has been eroded into a basin, partly versed by widely spaced dikes a few inches to as much as covered by arkosic sand and soil, from which project 8 inches across, mainly of fine-grained aplite but includ- IGNEOUS ROCKS 91 ing some coarse pegmatite. Specimens from the dikes, diameter. Microscopic examination by Milton indi­ according to Ingerson and Milton, consist mostly of po­ cates that the feldspar is slightly albitized orthoclase, tassium feldspar and a little quartz, plagioclase feldspar and that the groundmass is formed of interlocking being nearly or wholly lacking. However, one of the feldspar and quartz, many small euhedral plates and dikes in the dark gabbroic rock on the east side of the patches of biotite, and minor sphene. The porphyry stock contains abundant nepheline, its only occurrence grades irregularly into a breccia of the same material in the complex; it is associated with potassium feldspar, whose fragments are as much as 1 inch across. In a band about 10 feet wide next to the central core of partly replaced by "chessboard" albite. porphyritic granite, the porphyry has been silicified and MINE CANYON STOCK traversed by quartz veinlets, producing a rock that re­ The Mine Canyon stock is three-quarters of a mile sembles an aplite. northeast of the Marble Canyon stock and superficially The core of the Mine Canyon stock is prophyritic resembles it, as it lies in Permian carbonate rocks and granite which forms a cylindrical mass about 500 feet has a diameter of about three-quarters of a mile (pi. 14). in diameter, exposed on the north slope of Cave Peak. Nevertheless, its internal character is almost wholly dif­ The porphyritic granite is medium grained and is com­ ferent, as it includes few rocks of granitic texture, and posed of quartz and orthoclase phenocrysts in a finer is formed mainly of units of fine-grained porphyry and grained groundmass. Microscopic examination by breccia. Observed contacts with the country rock are Milton indicates that the orthoclase phenocrysts are nearly vertical, like those in the Marble Canyon stock, somewhat albitized, and that the groundmass is an inter­ but the light rhyolite breccia of the stock projects in locking aggregate of quartz and feldspar, with a few several bosses on the slope of Marble Canyon to the epidotized skeletons of biotite. south, suggesting a low dip of the contact away from Light rhyolite breccia forms the greatest surface area, the main stock. However, the light rhyolite breccia and probably the greatest volume, of any of the intru­ is a late component of the stock and probably invaded sive units in the Mine Canyon stock. Cave Peak is the country rock more irregularly than the earlier formed of it, and its weathered blocks are the principal components. constituents of the out wash from the stock. The breccia The components of the Mine Canyon stock are dis­ occupies a wide band around the periphery of the stock; crete units of light rhyolite porphyry, dark rhyolite nevertheless it intrudes and crosscuts all the igneous porphyry, porphyritic granite, and light rhyolite brec­ units previously described and it must have the struc­ cia, which are ringed concentrically around a center on ture of a ring dike. On the east side of the stock the the slope north of Cave Peak. Not all the units are breccia lies within concentric bands of light rhyolite progressively younger from the periphery inward, as porphyry and metamorphosed country rock. On the one might assume. The dominant rock of the stock, or west side it crosses these bands and invades little-altered light rhyolite breccia, occurs mainly toward the periph­ country rock; here, light rhyolite porphyry and meta­ ery, yet it is the youngest major igneous unit in the morphosed country rock remain only as inclusions in complex. the breccia. The light rhyolite breccia was evidently Light rhyolite porphyry forms irregular masses as intruded after the climax of the contact metamorphism. much as 400 feet wide against the country rock on the The light rhyolite breccia is an aphanitic light-gray south and east sides of the stock; it is also preserved as or white igenous rock which contains closely to widely inclusions in the light rhyolite breccia farther west. spaced angular fragments an inch to several feet across. Much of the porphyry is poorly exposed and is covered Many of the fragments are like the matrix, others are extensively by float from the adjacent light rhyolite rhyolite porphyry with conspicous flow structure, and breccia. Most of it is aphanitic, greenish gray where a few are metamorphosed limestone and other country fresh, and weathers light gray or buff. In places it con­ rocks. Inclusions of other rocks of the stock 10 feet or tains phenocrysts of feldspar and quartz as much as more across occur in places, especially on the west side 3 mm in diameter, but elsewhere these are smaller or and near the summit of Cave Peak. Microscopic exami­ lacking altogether. According to Milton, the ground- nation by Ingerson of speciments from an outlying boss mass is an aggregate of randomly oriented feldspar of the breccia on the north slope of Marble Canyon indi­ laths, strewn with brown biotite and opaque minerals. cates that the matrix is mainly quartz and potassium Dark rhyolite porphyry crops out in a band about 500 feldspar, partly forming small phenocrysts, but chiefly feet wide on the north slope of Cave Peak, encircling the a groundmass which also includes much secondary core of porphyritic granite. The porphyry is dense, calcite. dark gray to black, and breaks along joints into The light rhyolite breccia has been somewhat min­ straight-sided blocks. It contains abundant pheno­ eralized throughout, as indicated by extensive iron oxide crysts of feldspar, and a few of quartz, about 2 mm in staining of weathered surfaces. Most of the introduced 7.57-105 92 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS minerals form threads or narrow veinlets which trend adjacent host rocks, mainly the Hueco Limestone. Most westward, northwestward, or northward. Mineraliza­ of the contact metamorphism is related to the emplace­ tion is most extensive on the east side near the contact ment of the coarse-grained intrusive rocks and is less with the dark rhyolite porphyry and on the west side related to the finer grained porphyries and breccias. near the contact with light rhyolite porphyry inclu­ Effects of the metamorphism vary not only with dis­ sions. The dominant mineral is pyrite, but there is also tance from the stocks, but also with the compositions of chalcopyrite, fluorite, and huebnerite (iron-manganese the rocks in the stratigraphic sequence. Most of the tungstate). According to Holser, some of the veinlets country rock that has been metamorphosed is dolomite contain minor amounts of beryllium (less than 0.1 per­ and limestone of the main body of the Hueco Lime­ cent BeO). stone ; in some places, however, the clastic rocks of the Rocks of the Mine Canyon stock are cut by widely Powwow Member are involved, in others the siliceous spaced vertical dikes, some as much as 4 feet wide. A black limestone of the Bone Spring Limestone. specimen from one of the dikes on the east side of the Close to the stocks the metamorphic rocks are varie­ stock is described by Milton as a dull light-gray fine­ ties of hornfels. grained rock, composed of interlocking particles of al­ A dark heavy hornfels forms large inclusions in the kali feldspar with sparing phenocrysts of the same dark gabbroic rock on the east side of the Marble Can­ feldspar and a few embayed phenocrysts of quartz, yon stock. Its sedimentary origin is shown by varying and apparently without mafic minerals. mineral compositions of its bedding laminae. Accord­

OUTLYING IGNEOUS ROCKS ing to microscopic determinations by Milton and In- gerson, it is composed of tiny grains of diopside and a East and north of the Marble Canyon and Mine little calcite, quartz, and sphene, which are poikilitically Canyon stocks are numerous smaller bodies of intru­ enclosed in a groundmass of andesine feldspar. This sive rocks, mainly dikes and sills (pi. 14). Except for hornfels differs so much from the adjacent country rock minor aplite dikes, none seem to be related to the Marble that it has either been carried up from a lower strati- Canyon stock. Most of them probably originated dur­ graphic level, or has absorbed much material from the ing later phases of the intrusion of the Mine Canyon igneous rock in which it lies. stock. Nearby on the east side of the Marble Canyon stock, On the north slope of Marble Canyon, a boss of light the country rock close to the intrusive has been altered rhyolite breccia, which is an offshoot of the main brec­ to a white or light-gray hornfels that is difficult to cia intrusion, projects into the Hueco Limestone. Not distinguish from the more extensive marble adjacent to far away the marl and thin limestone beds of the Hueco it. Microscopic examination by Milton indicates that are traversed by sills less than a foot thick of light- this hornfels is a mosaic of equidimensional quartz gray aphanitic igneous rock, whose affinity to the main grains crowded with tiny diopside crystals and with breccia mass is suggested by their content of breccia veinlets and irregular areas of zeolite. fragments. South of Marble Canyon aphanitic igne­ A more complex hornfels has been formed from the ous rock forms a dike that follows a northwest-trend­ marl and marly limestone of the Powwow Member of ing fault. the Hueco Limestone within a few feet of the intrusive Outlying intrusions are extensive from Mine Canyon contact of the Mine Canyon stock on its east side. northward for 4 miles, nearly to Apache Canyon (pi. Chemical composition of this rock is as follows: 1). Most of them are sills which follow the relatively weak strata of the Powwow Member of the Hueco Chemical analyses, in percent, of hornfels from Powwow Member of Hueco Limestone on east border of Mine Canyon stock Limestone, but two plugs invade the fossiliferous shale {Analyst, K. J. Murata, 1940] of Pennsylvanian age just north of Mine Canyon. In 797 A 797B (white (gray the segment between Mine Canyon and Apache Canyon phase) phase) the strata have been displaced by block faulting and Insoluble____.______5.56 ______6.28 SiO2______-__-_--_--_- 25.38 ______-_--_ 24.56 the sills have been similarly displaced, indicating that CaO___-_-______55.00 _-______----_ 54.04 the igneous rocks were intruded before the faulting. MgO------_------3.93 ______3.06 Most of the igneous rocks of the outlying masses are R2O3_-_------_------1.62 ______2.80 light-gray aphanitic much-jointed felsite. The felsite CO______-_-- - 5.95 ______7.00 has been greatly kaolinized and iron stained by weather­ H2O + _.______--_- 2.03 ______2.09 ing, so that no fresh specimens could be collected that H_O-______.29 ______.09 would be suitable for petrographic study. Total______99.76 99.92 METAMORPHIC ROCKS SiO2 in insoluble______3.60 ______----_. 1.00 Intrusion of both the Marble Canyon and Mine Can­ F______-__-___._-_- .21 ______.05 yon stocks produced much contact metamorphism in the SO3______.14 ______None IGNEOUS ROCKS 93 An intensive study of this hornf els was made by Mil­ stock 200-400 feet wide. The marble band is somewhat ton. Most of it is very fine grained, consisting for the narrower around the Mine Canyon stock, and is trun­ most part of sharply defined areas that vary from white cated in the western part of its periphery by the younger to shades of green or gray, each variation indicating intrusive mass of light rhyolite breccia. a different mineral composition. Much of the horn- The following analyses indicate the nature of the fels is spurrite (CaCO3 -2Ca2SiO4) and merwinite marble surrounding the Marble Canyon stock. The (Ca3Mg(SiO4) 2), but some assemblages contain vari­ first group of analyses is of marble from various places able amounts of calcite (CaCO3 ), periclase (MgO), around the periphery. The second group illustrates vesuvianite (Ca6[Al(OH,F)]Al2 (SiO4) 5), wollastonite variations in the composition of altered and unaltered (CaSiOs), and grossularite (3CaO A12O3 3SiO2 ). The rocks at about the same stratigraphic level, eastward spurrite and merwinite are replaced by radiophyllite along Marble Canyon from the stock. (CaSiOS 'H2O), and there are minute veinlets of thau- Chemical analyses, in percent, of white marble around the masite (CaSiO3 -CaCO3 -CaSO4 -15H_O). Some speci­ periphery of the Marble Canyon stock mens include breccia fragments of diopside and quartz, [Analyst, K.J. Murata, 1937, 1940] probably altered from chert. The principal assemblages belong to the sanidine facies of metamorphism, which 788 772 783 784 785 786 according to Turner (in Fyfe, Turner, and Verhoogen, Inorganic insoluble. 0.42 0.60 0.50 0.18 0.29 0.73 Soluble R2O3 __ .. 0) .60 (') 0) 0) 0) 1958, p. 213-215), is conditioned by very high tempera­ 61.14 64.89 64.73 85.25 61.80 63.98 MgCOs-. _ ... .. 12.79 2.67 14.02 6.02 5.49 ture (600°-1000° C) and very low pressure (pH2O gen­ Mg(OH)j.._ ..... 25.57 33.21 31.88 31.92 29.82 erally less than a few hundred bars). Alteration of the Total. __ ... 99.92 99.30 99.78 99.45 100.03 100.02 assemblages to the hydrous minerals radiophyllite and thaumasite represents a retrogression from the intense 1 Not determined. 788. White marble, southeast side of stock, high on slope and 50 ft below top of Hueco initial metamorphism. Limestone. 772. White marble, east side of stock not far from contact, lower part of Hueco Lime­ Another variant of the hornfels occurs on the south stone. 783. White marble, north side of stock, 2-10 ft from contact, upper part of Hueco side of the Marble Canyon stock, where black limestone Limestone. 784. White marble, northwest side of stock, 15-30 ft from contact, Hueco Limestone extends into the zone of metamorphism. Original bed­ or basal Bone Spring Limestone. 785. White marble, west side of stock, not far from contact, upper part of Hueco ding, which is still preserved, is indicated by alternating Limestone or basal Bone Spring Limestone. 786. White marble, west side of stock south of preceding locality, not far from con­ thin white and gray layers. Chemical composition of tact, upper part of Hueco Limestone or basal Bone Spring Limestone. this rock is as follows: Chemical analyses, in percent, of marble and unaltered limestone on east side of Marble Canyon stock along Marble Canyon Chemical analyses, in percent, of hornfels from Bone Spring [Analyst, K. J. Murata, 1937J

[Analyst, K. J. Murata, 1940 772 773 774 A 774 B 787 A 787 B 1.28 1.26 SiO2 ___ .__...._-..-... 44.20 ______36.90 0.60 0.27 £t\j . Oo .10 CaO....__. ______45.00 .._-__.-_.__-. 48.01 Soluble R2O3 ------/»rv 27 12 oc MgO__---______6.29 ______12.25 CaCO3 ------64.89 68.56 86.88 55.49 T> r\ i on o AQ MgCOs. __ ------None 30.07 11.69 44.01 Mg(OH)2 . ______33.21 None None None CO2__---__-_--__------_- 2.06 ._._._.__-___. .43 H.O + .77 ______.26 Total ______QQ qrj inn 4.4. 100. 01 100. 12 H2O ______.34 ______.08 CaO_____---____---_- 36.35 38.42 46.68 31.09 Total ______100.56 ... ______100.41 MgO_ ___---_----._- 22.95 14.38 5.59 21.05

772. White marble, east side of stock not far from contact, lower part of Hueco Lime­ This hornfels is largely akermanite (Ca2MgSi2O7) stone. 773. Black "baked" limestone at gateway in Marble Canyon, east of intrusive. and merwinite (Ca3Mg(SiO4) 2), proportions of which 774 A. Unaltered Hueco Limestone from about same horizon as specimen 773, north slope of Marble Canyon several hundred yards east of gateway; from vary from one specimen to another, and minor calcite. lower beds of calcitic limestone. Part of the merwinite forms large crystals which poiki- 774 B. Same locality as preceding: from upper beds of dolomitic limestone. litically enclose the smaller grains of akermanite. One The marble is uniformly white and fine grained. specimen contains thick light-gray veins of wollaston­ Chemical analyses of five of the specimens tabulated ite. above show a content of 61-66 percent calcite (CaCO3 ) Beyond the hornfels zone around the Marble Canyon and 21-33 percent brucite (Mg(OH) 2). Much of the and Mine Canyon stocks a much larger volume of the marble probably has a similar composition, as it was country rock has been altered to white marble. The derived from original dolomitic limestone beds of the white marble forms a band around the Marble Canyon Hueco and Bone Spring. However, one specimen con- 94 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS tains no brucite and much more calcite, and was prob­ for assimilation of the country rock is inconclusive, but ably derived from a calcitic limestone bed. According not much assimilation is likely to have occurred in such to Ingerson, the brucite was derived from serpentine, shallow intrusives. The dark gabbroic rock around the which formed from hydrothermal alteration of olivine, Mable Canyon stock is not a contaminated border f acies the olivine having developed by action of siliceous of the central syenite but a somewhat earlier intrusive. vapors on the original magnesian limestone. Much of There is no indication of stoping, as the stocks contain the brucite still retains the serpentine structure, and few or no inclusions of country rock; but possibly blocks many of the brucite patches enclose remnants of olivine of country rock were pushed upward ahead of the in­ in the serpentine mesh. trusives. Just beyond the band of white marble is a somewhat During the initial intrusive epoch the magma of the narrower band of finely crystalline black limestone with Marble Canyon stock solidified as a coarse-grained a "baked" or calcined appearance, which is less altered granitic rock, and the stock has had no subsequent than the marble although thoroughly recrystallized. igneous history. By contrast, the Mine Canyon stock This is prominently exposed on the slopes of Marble became a conduit that was utilized by later ascending Canyon east of the Marble Canyon stock, but is less magmas, producing a complex of later porphyries and conspicuous elsewhere. Its black color is caused by an breccias. At least the latest of these, the light rhyolite enrichment of organic matter, now carbonized, as shown breccia, was emplaced under conditions of much lower by the 0.26 percent of organic insoluble in the analyzed temperature and pressure than the initial intrusions, as specimen (773), as compared with none in the marble it crosscuts the earlier metamorphic 'aureole and in and 0.06-0.10 percent in the unaltered limestone. The places is in contact with little-altered limestone. organic matter was probably expelled from the original The brecciated nature of both the light rhyolite limestone of the marble zone during metamorphism. breccia and the earlier dark rhyolite breccia suggests The black limestone contains traces of original bedding, that the Mine Canyon stock was open to the surf ace dur­ chert concretions, and fossils. The boundary between ing their emplacement, and formed a volcanic conduit. it and the marble is abrupt, but it fades gradually into Perhaps by this time the surface had been stripped of unaltered limestone and extends farther away from the its cover of poorly resistant Cretaceous strata, down to stocks in some strata than in others. the top of the resistant Permian carbonate rocks whose top is little more than 1,500 feet above the present ex­ INTERPRETATION posures of the stock. Two epochs of later intrusion and The Marble Canyon and Mine Canyon stocks were possible volcanism are indicated. The first marked the emplaced before the block faulting of the Sierra Diablo. time of emplacement of the dark rhyolite porphyry and Outlying sills are faulted, and the proximity of the breccia and ended with solidification of the core of stocks themselves to the fault scarp at the edge of the porphyritic 'granite. During the second, the light range is incompatible with their relatively deep-seated rhyolite breccia invaded the periphery of the earlier core origin. During intrusion of the stocks they were proba­ as a ring dike and irregularly invaded the country rock. bly at least covered by the Permian carbonate rocks of Perhaps at about the same time the surrounding country the Sierra Diablo which now extend 1,500 feet or more rocks were intruded by f elsite dikes and sills, some as above the present outcrops of the stocks. During part much as 2 or 3 miles north of the Mine Canyon stock. of the intrusive epoch the Permian rocks themselves were probably covered by several thousand feet of sandy SIERRA PRIETA INTRUSIVE and shaly Cretaceous strata. In the Diablo Plateau northwest of the Sierra Diablo The Marble Canyon and Mine Canyon stocks must is the Sierra Prieta, a crescentic mass of intrusive rock have been formed initially during a single intrusive about 4 miles long, which projects 500-1,000 feet above epoch, but they have had different subsequent histories. its surroundings (pi. 1). The igneous rock of Sierra The zones of contact metamorphism around these stocks were formed during the initial epoch, at a time of max­ Prieta forms a thick sill of complex structure, which imum burial. The postulated maximum depth of cover dips beneath Hueco Limestone of Permian age on the is compatible with the spurrite and other minerals of south side and overlies shale, marl, and sandstone of the metamorphic suite, which indicate recrystallization the Washita Group of Cretaceous age on the north and under conditions of high temperature and low pressure. east sides (section A-A', pi. 16). In places the in­ The stocks were emplaced without deforming the coun­ trusive rock crops out in cliffs and ragged ledges; but try rock more than a few feet from their contacts. Their in many others it has broken down into blocks and mode of intrusion has not been determined. Evidence boulders, some of which are nearly in place, others of IGNEOUS ROCKS 95 which have moved varying distances from their original Analyses of marble and altered limestone from Hueco Limestone on positions. On the north and east sides of the mountain south side of Sierra Prieta intrusive are extensive masses of disordered, land-slipped blocks [Analyst, K. J. Murata, 1940] of igneous rock, now in process of dissection, produced 809 810 811 by undercutting of the weak strata of the Washita Group beneath the sill. Some of these land-slipped Insoluble.- ______1.16 1.66 0.19 R2O3---- _ _.._ _ . ______1.16 .16 n. det. masses are as much as a mile from the present outcrops CaCO. ______67.23 96.30 64.03 of igneous rock on the mountain and were probably de­ MgCOs--.. - --______None 2.82 None 29.72 None 35.15 rived from greater extensions of the sill during an Mg(OH) 2______earlier time. Total. ______qq 27 100. 94 99.37

IGNEOUS HOCKS 809. Marble from just above Igneous contact, three-quarters of a mile northwest of Black Mountain Tank (center of sec. 17, block N). 810. Black "baked" limestone, 30 ft above contact, same locality as preceding. The igneous rock of the Sierra Prieta is an alkalic 811. Marble, forming a dikelike mass in limestone, half a mile east of preceding porphyry, whose main body is conspicuously spotted by locality. phenocrysts of dark-green mafic minerals that lie in a The Cretaceous rocks which underlie the intrusive gray finely crystalline felsic groundmass. In the cen­ are little altered, except for slight induration of the tral part of the intrusive the spots are half an inch shale of the Washita Group close to the contact. The across, but they are smaller toward the margins. The Cox Sandstone, where it is in contact with the intrusive rock splits into plates and flags whose surfaces have a on the west side of the southeastern prong of the moun­ lustrous schistose appearance. A specimen examined tain, contains cavities coated by concentric growths of a under the microscope by C. S. Ross (written commun., blue mineral which C. S. Ross has determined to be 1938) consists of fluorite. a coarsely felted groundmass of sodic plagioclase, with >a few STRUCTURE phenocrysts of nepheline. Ferromagnesian minerals are The igneous rock of the Sierra Prieta forms a thick aegerite-augite and an amphibole resembling riebeckite. The latter commonly forms a reaction rim around the nepheline south-dipping sill that is broadly accordant with the grains, or even occurs within them. An'alcite and another strata adjacent to it (section A-A', pi. 16). However, zeolite are associated with the nepheline. the sill overlies the Washita Group of Cretaceous age At the margins of the intrusive the coarse spotted on its north side and underlies the Hueco Limestone of igneous rock gives place to a uniformly fine-textured Permian age on its south side. The intrusive must, rock 25 feet or more thick, which in places forms mas­ therefore, have zigzagged through the strata during sive ledges. According to D. E. Lee (written commun., its ascent, partly following the bedding, partly break­ 1959) ing across it. An estimated 80 percent of the rock is made up of a finely felted These inferred general relations are illustrated by out­ groundmass of feldspar blades. An X-ray diffraction pattern crops in the eastern prong of the mountain. In much of crushed material indicates that this groundmass is mostly of the prong the intrusive is a sill that overlies strata sodic plagioclase but includes perhaps as much as 25 percent near the top of the Washita Group. Farther west, orthoclase. The rock also contains smaller amounts of analcite however, the base of the intrusive descends abruptly and a mineral that may be chabazite. Tiny grains of unidenti­ fied pyroxene are scattered throughout the rock. across the edges of the Washita Group and all the under­ lying formations down to the Hueco Limestone (lower METAMORPHIC BOCKS view, pi. 12). The abruptly descending contact is bor­ The Hueco Limestone that overlies the igneous rock dered by a ledge 25 feet or more thick of the fine­ on the south side has been metamorphosed to marble for grained phase of the intrusive, which is broken by 3-25 feet from the contact, beyond which it is blackened joints normal to the contact. and "baked" for as much as 50 feet farther. In places A tabular inclusion of Hueco Limestone 300 feet long marble also extends beyond the main body as dikelike and 75 feet thick was observed near the center of the masses, probably adjacent to joints or fractures. Inliers intrusive (center of sec. 25, block N); this inclusion of altered limestone are exposed in valleys south of the may be a part of a septum connected with the main body intrusive contact, indicating a low dip of the igneous of the Hueco farther south. Other inclusions of Hueco rock beneath the limestone. The following analyses may exist in the intrusive, but if so, they are covered by indicate that the marble consists of variable amounts of the extensive surface debris of the igneous rock. calcite and brucite, so that the Hueco Limestone has The igneous rock is broken by many vertical joints, been altered in much the same manner as it has been spaced 10 or 15 feet apart, and by flat or gently dipping near the Marble Canyon and Mine Canyon stocks. joints a few feet apart. These joints outline the 96 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS weathered blocks which strew the surface. Many of Eemnants of a flow of vesicular basalt form the sum­ the vertical joints trend west or west-northwest, and mit of Cox Mountain (sees. 19 and 20, Block 45^), and some faults of the same trend drop the igneous rocks a remnant of another flow is preserved on the west rim and the Cretaceous strata northward. Possibly these of Victorio Canyon (sec. 14, Block 43). The flows at faults are not fundamental displacements, and instead, both places lie on an eroded surface of the Cretaceous resulted from superficial settling of joint-bounded rocks at Cox Mountain on the Kiamichi Formation blocks of the massive sill over the weaker underlying with a few feet of intervening limestone gravel and at strata of the Washita Group. Victorio Canyon on a small thickness of Cox Sand­ REGIONAL RELATIONS stone. Regarding the rock at Cox Mountain, D. E. Lee reports (written commun., 1960) The Sierra Prieta intrusive is part of an extensive group of alkalic intrusive of Tertiary age in Trans- The rock is a porphyritic olivine basalt. The phenocrysts are olivine and calcic plagioclase as much as 2 mm across. Most Pecos Texas (Warner and others, 1959, p. 131). It is crystals in the groundrnass are less than 0.2 mm in size, and some the southeasternmost of a chain of sills, laccoliths, and are as small as 0.03 mm. The dominant molecule in the olivine stocks which extend 40 miles northwestward across the phenocrysts must be forsterite. Most of these phenocrysts are Diablo Plateau beyond the report area and include those in process of alteration to a bowlingitelike- mineral. In part of Antelope Hill, Sierra Tinaj a Pinta, Cerro Diablo, this alteration is complete; elsewhere the altered material forms a rim around the olivine. The groundmass, in estimated order and the Cornudas Mountains (King, P. B., 1949). Be­ of abundance, consists of calcic plagioclase, magnetite-ilmenite, yond this chain are similar intrusives of alkalic igneous clinopyroxene, olivine, and carbonate. Some of the carbonate rocks in the Hueco Mountains (King, P. B., King, R. is concentrated in ill-defined patches including other minerals. E., and Knight, J. B., 1945, sheet 1), and a small plug in Apatite is also present. the southern part of the report area (see below). In the Sierra Diablo foothills farther south are sev­ eral basalt plugs, one northeast of England Tank in the INTRUSIVE BOCKS OF SOUTHERN PART OF REPORT AREA Cox Sandstone (northwestern part of sec. 24, Block 51), two others northwest of the Keen Ranch in the Small bodies of intrusive rocks of probable Tertiary Campagrande Limestone (sec. 6, Block 56). The latter age occur at widely separated places in the southern were examined by Flawn (in King, P. B., and Flawn, part of the report area (pi. 1). P. T., 1953, p. 100), who reports that the plugs consist On the east side of the Carrizo Mountains (sec. 5, of black aphanitic basalt that contains small phenocrysts Block 6, Twp. 9) are several small dikes and sills of of black glassy augite and spinel. Associated with the diabase, the largest of which follows the unconform- plugs are basalt sills less than 5 feet thick which con­ able contact between the Carrizo Mountain Formation tain numerous phenocrysts of olivine, spinel, and augite and Van Horn Sandstone (Flawn, in King, P. B., and as much as 1-2 cm in diameter and a few augite pheno­ Flawn, P. T., 1953, p. 67). crysts with the surprising dimensions of 4-5 cm. How­ At the southwest end of the Streeruwitz Hills 2i/£ ever, some of this basaltic rock is vesicular, indicating miles west-northwest of Eagle Flat section house (cen­ that it was intruded near the surface. ter of east line of sec. 3, Block 69, Twp. 8) a small plug of massive unsheared spotted igneous rock lies in UNCONSOLIDATED DEPOSITS OF QUATERNARY AGE metarhyolite of Precambrian age (King, P. B., in King, R. E., and Flawn, P. T., 1953, p. 100). Although the Unconsolidated deposits of Quaternary age cover rock was not examined microscopically, it much re­ about a third of the report area; they are separated into sembles the alkalic intrusive rocks of Sierra Prieta and a number of units on the geologic map (pi. 1) based elsewhere in the Diablo Plateau. more on differences in character, surface form, and Southwest of Eagle Flat, small sills of rhyolite origin than on chronological sequence. The uncon- porphyry intrude the Washita Group and Eagle Ford solidated deposits were mapped partly by cursory field Formation (sec. 20, Block 67^; sec. 3, Block 69, Twp. study and partly from air photographs. 9; Smith, 1940, p. 619-620). They are probably re­ The environment and origin of the unconsolidated lated to the more extensive igneous masses of the Eagle deposits has already been discussed in this report (see Mountains adjacent to the south. section on "Geography"), and the similar unconsoli­ dated deposits in the nearby southern Guadalupe Moun­ BASALTIC VOLCANIC ROCKS tains were treated at length in an earlier publication Small bodies of basalt of surface or near-surface (King, P. B., 1948, p. 127-160). Here, the unconsoli­ origin occur at widely separated places in the western dated deposits in the Sierra Diablo region are described part of the report area (pi. 1). briefly as map units. UNCONSOLIDATED DEPOSITS OF QUATERNARY AGE 97 The unconsolidated deposits that lie at the surface in Mountains and Apache Mountains, drilled 1,150 feet the Sierra Diablo region are all of Quaternary age. in the deposits before reaching Permian bedrock. Most Some of these, on the alluvial fans at the edges of the of the wells drilled near Van Horn and in the Wild- mountains and on the valley bottoms and pediment sur­ horse Valley irrigation district to the east are less than faces within the mountains, are of Recent age and are 600 feet deep and fail to reach the base of the deposits in process of formation today. Others, which have (Richardson, 1914, p. 9; Follett, 1954, p. 6-9), but two been dissected by modern drainage or buried beneath wells about 950 feet deep that were drilled 8 miles east- the surface deposits, are of earlier and probable Pleisto­ northeast of Van Horn (sec. 19, Block 63) are reported cene age. In the intermontane areas of the Salt Basin to have entered limestone bedrock (Leonard A. Wood, and Eagle Flat, where the unconsolidated deposits are written commun., 1959). The age of the deeper uncon- known from well drilling to be hundreds or thousands solicated deposits of the Salt Basin is undetermined, but of feet thick, the older and deeper deposits may be of those at the surface are of Pleistocene and Recent age. late Tertiary age. However, no unconsolidated deposits The surface of the lowest part of the Salt Basin, north of late Tertiary age are exposed in the region, and no of the Baylor Mountains, is a nearly level floor more means are at present available to distinguish possible than 5 miles wide, formed of clay, silt, and sand which buried unconsolidated deposits at this age from those of are shown as a unit on the map (pi. 1). The clay, silt, Quaternary age. and sand were probably deposited on the bottom of a lake or succession of lakes during Pleistocene time LANDSLIDE DEPOSITS (King, P. B., 1948, p. 137, 156-157). Their nearly level Among the oldest unconsolidated deposits in the re­ surface may be a relatively old feature, inherited from gion are landslides on the slopes of the intrusive igneous the lake bottom and modified only by minor shifting of body of Sierra Prieta, in the northwestern part of the material by the wind. No material derived from the map area. They are disordered bouldery masses of adjacent mountains seems to be in process of deposition igneous rock derived from the intrusive, and occur on on the floor today. its west, north, and southeast sides. Those on the north The floor of the Salt Basin is diversified by alkali side are especially extensive, and conceal the bedrock flats, hills of gypsiferous clay, and areas of drifted over an area of several square miles. All the landslides quartz sand which are differentiated on the map (pi. 1), occur where the intrusive lies as a sill on shale and other all of which have been partly or wholly shaped by the weak beds of the Washita Group of Cretaceous age; wind. they were formed by undermining of the massive One set of alkali flats (locally called "salt lakes") is igneous rock by erosion of the weak beds. Talus and east of the northern part of the Sierra Diablo, another small landslides of igneous rock are forming today on is just north of the end of the range. Grayton Lake, outcrops of the Washita Group by such undermining, an alkali flat of similar character, forms the lowest part but the main landslides are much older, are much dis­ of the closed depression of Eagle Flat in the southwest­ sected, and in part are preserved as detached erosion ern part of the map area. The alkali flats may be the remnants. Moreover, some of the landslide masses final remnants of more extensive lakes of an earlier pe­ north of Sierra Prieta are as much as a mile from pres­ riod, yet today they contain water only at long intervals; ent outcrops of the igneous sill on the mountain, and they are maintained principally by the wind, which probably formed when it was more extensive than now. sweeps material from their surfaces down to ground- All the main landslides appear to be of the same general water level, an effective limit to downward erosion. age, and they may have formed at a time when the The hills of gypsiferous clay have no clearly discern­ erosional and climatic regime differed considerably ible pattern over extensive areas toward the north; but from that of today. on the east side of the floor opposite the northern part of DEPOSITS OP PLOOB OP SALT BASIN the Sierra Diablo, they form a remarkable set of closely spaced parallel ridges, trending north-northwestward, The Salt Basin, the large intermontane area along the which curve westward just north of the Baylor Moun­ east side of the Sierra Diablo region, is deeply filled by tains. These ridges, and others like them farther north, unconsolidated deposits washed in from the higher lands probably mark the shores of one of the latest shallow around it. A well in the basin north of the Sierra lakes of Pleistocene time (King, P. B., 1948, p. 156-157, Diablo region is reported to have been drilled in the pi. 23), along which the clays were raised into low deposits to a depth of 1,620 feet without reaching their dunes. Later modifications of the clay hills by the wind base (Baker, 1927, p. 40). The West & Armour, I is indicated by superposition on the gross features of a Davis Investment et al. oil test, between the Baylor more delicate grain trending eastward or east-southeast- 98 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS ward. Between the alkali flats and hills of gypsiferous the segment of the Sierra Diablo north of the Baylor clay, the floor of the basin is a level meadowland, under­ Mountains, where relatively recent faulting has created lain by brown clay. a regime of active erosion and deposition. The areas of drifted quartz sand occur only in the OLDER ALLUVIAL DEPOSITS northeastern part of the map area, at the lower ends of alluvial fans extending out from the Delaware Moun­ Within the mountains small thicknesses of alluvial tains east of the Salt Basin. The sand was probably deposits have been spread over the bottoms of valleys or derived ultimately from erosion of sandstones of the over more extensive rock-cut plains and pediments. Delaware Mountain Group which form a conspicuous Most of these deposits are near the levels of modern part of these mountains; the absence of sand adjacent to drainage and are of relatively young age, but earlier the Sierra Diablo and other mountains west of the Salt periods of alluviation are indicated by gravel-capped Basin is due to these mountains being composed largely remnants as much as a hundred feet above modern of carbonate rocks. Within the report area the drifted drainage. sands form a relatively featureless expanse without dune These remnants are most extensive in the foothills forms, although conspicuous dunes of the same material south and southeast of the southeastern angle of the occur farther north (King. P. B., 1948, p. 138). Sierra Diablo, where they overlie former pediments that were cut on red sandstone of the Hazel and Van FANGLOMERATE Horn Formations. For the most part the pediments Along the edges of the Salt Basin are deposits of and gravel deposits were formed by tributaries of fanglomerate which are built into alluvial fans that Sulphur and Hackberry Creeks which drain eastward slope toward the basin from the adjacent mountains. into the Salt Basin; but the western ones, north of the The fans have coalesced into an alluvial slope less than Millican Hills, were formed by streams draining into 1 mile to more than 5 miles wide that is nearly con­ the east end of Eagle Flat. Toward the west the older tinuous along the edges of the Sierra Diablo and other gravel deposits merge with the younger alluvial cover mountains west of the Salt Basin. East of Beach of Eagle Flat, so that the two sets of deposits cannot be Mountain and the Baylor Mountains the alluvial slopes differentiated. Dissection of the older gravel deposits extend from the mountains on either side of the Salt southeast of the Sierra Diablo may be related to renewed Basin to its axis, where Wildhorse Creek drains north­ downfaulting of the Salt Basin, which revived erosion ward. Farther north the alluvial slopes on the two sides in the mountain areas. do not meet, because they are separated by the basin Within the Sierra Diablo the bottoms of many floor, discussed above. canyons and valleys have been filled by alluvial deposits, The fanglomerate, which has been in process of for­ which were later dissected to depths of 50 or 100 feet mation since the mountains assumed their present form, and partly removed. In many of the valleys that drain probably has a wide range in age. The older fanglom­ westward from the mountains, dissection has no more erate, now buried, is probably of Pleistocene or even than trenched the alluvium; but in most of those which earlier age; but part of the fanglomerate at the surface drain eastward into the Salt Basin, the older alluvial is in process of accumulation today, the moderately deposits have been reduced to terrace remnants. Most dissected remainder being only a little older. The fan- of these older deposits are not recorded on the map (pi. glomerate at the surface must be younger than the bulk 1), being either omitted or not differentiated from the of the deposits on the floor of the Salt Basin, as the younger alluvial deposits, but they are sufficiently ex­ alluvial fans are being prograded toward the floor. tensive and prominent to be shown separately in Apache The fanglomerate varies in composition, depending Canyon. Causes of the canyon filling and subsequent on the bedrock of the source areas in the mountains from dissection indicated by these deposits are undetermined. which it was derived, and in texture, depending on the They may be related to a time of tectonic stability, fol­ sizes and gradients of the streams which supplied it. lowed by one of renewed downfaulting; in the Salt The fanglomerate of large fans of low gradient, com­ Basin, or they may be related to climatic fluctuations posed of relatively fine material, is differentiated on the during Pleistocene time. map (pi. 1) from that of fanglomerate of lesser fans with steeper gradients built by smaller streams, com­ YOUNGER ALLUVIAL DEPOSITS posed of coarser materials. Large fans have been built Most of the unconsolidated deposits within the Sierra by Hackberry and Sulphur Creeks near Van Horn and Diablo and west of it, as well as in Eagle Flat, are by Ked "Wash farther north. Lesser fans with the steep­ mapped as an undifferentiated unit of younger alluvial est gradients and the coarsest fanglomerate are along deposits (pi. 1). Deposits included in the unit are un- TECTONICS 99 doubtedly complex, but data obtained from field in­ er tectonic stability of Eagle Flat in the recent past. vestigation and study of air photographs are insufficient The central part of Eagle Flat is doubtless a tectonic to provide a meaningful separation. Most of the depression like the Salt Basin; but because of its pres­ alluvial deposits at the surface that are included in the ent stability, its unconsolidated deposits are not capable unit must be relatively young, as they lie at or near the of an obvious subdivision like that in the main basin. levels of modern drainage and are partly in process of They are therefore mapped as undifferentiated young­ formation today; some that are moderately dissected er alluvial deposits (pi. 1). Along the northern and are slightly older. The younger alluvial deposits in southwestern margins of the flat, the alluvial deposits some areas probably overlie deposits of Pleistocene age, cover broad rock-cut plains or pediments that extend and in Eagle Flat perhaps still older deposits. between and through low hills of deformed Precam- The younger alluvial deposits accumulated in three brian and Cretaceous rocks. Within the flat itself the drainage areas, one on the east side of the Sierra Diablo alluvial slopes extend from either side of the axis. Al- and adjacent ranges leading directly into the Salt Basin, luviation has cut off the western part of the flat from another on the west slope of the Sierra Diablo in the the remainder to form a closed depression surrounding northwestern part of the map area leading northwest­ the alkali flat of Grayton Lake. The sandy surface ward by circuitous route into the Salt Basin, and a third materials in many parts of the flat have been raised by in the southwestern part of the map area leading into the wind into low dunes, shown by a stippled pattern on Eagle Flat. the topographic base (pis. 1,9). The younger alluvial deposits in the drainage area on Like the Salt Basin, the tectonic depression of Eagle the east side of the Sierra Diablo are mostly of small Flat, within its encircling pediments, must be thickly extent and fill the bottoms of valleys that indent the filled by unconsolidated deposits of Pleistocene or even escarpments. Their composition and texture is like that earlier age. At Hot Wells these deposits have been of the fanglomerate in the fans down the slope, beyond penetrated to a depth of 1,000 feet without reaching the edges of the mountains, but they are differentiated their base (Baker, 1927, p. 40), but little other data are because they are relatively thin and were deposited on available as to their thickness, nature, or extent. eroded bedrock. The most extensive alluvial deposits in this drainage area lie between the Baylor Mountains TECTONICS on the east and the higher escarpments of the Sierra The Sierra Diablo region lies within the Basin and Diablo on the west, where the bedrock is mainly sand­ Range province. Present topographic features have stone rather than carbonate rocks. Here, tributaries of largely been shaped by block faulting that originated Sulphur Creek and Red Wash have cut extensive pedi­ during Cenozoic time, which produced mountains and ments which were subsequently covered by a small thick­ plateaus in places, and intermontane lowlands in oth­ ness of sand and gravel. ers that are now for the most part filled by erosional On the west slope of the Sierra Diablo, narrow strips debris. of alluvium extend up the valleys in places nearly to Nevertheless, the Sierra Diablo region had a consid­ the mountain crest and expand down the slope west erable prior tectonic history, so that the geologic struc­ of the mountains into broad alluvial plains separated ture varies, not only from one place to another, but by widely dispersed rock hills and mesas. The bedrock between rock systems of different ages. Successive times in parts of this western area has been folded and faulted, of disturbance are indicated by the several angular but so long ago as not to have shaped the present topog­ unconformities that interrupt the rock sequence be­ raphy. The plains are thus erosional rather than tec­ tween the formations of Precambrian age and the Van tonic depressions, and their alluvial cover, although ex­ Horn Sandstone of Precambrian (?) age, between the tensive, is probably rather thin. The alluvial deposits Van Horn Sandstone and the Bliss Sandstone of Ordo- toward the south have nearly featureless gently sloping viciaii age, between the rocks of Pennsylvanian age and surfaces, but north of the Victorio flexure they are dis­ the Hueco Limestone of Permian age, and between sected to depths as great as 50 feet. Along some of the formations of Permian age and those of Cretaceous larger drainage courses are alluvial flats lower than the asre.o At least two of these unconformities that be- tops of the dissected deposits, so that there have been neath the Van Horn Sandstone and that beneath the several cycles of cutting and filling. Hueco Limestone record times of major orogeny. In the drainage area of Eagle Flat modern erosional By Permian time the Sierra Diablo region had evolved depositional processes are less active than in the Salt into a positive area, the Diablo platform, which sub­ Basin, partly because of the circuitous drainage con­ sided less than the Delaware basin to the northeast, nection between them, and partly because of the great- and perhaps other basins to the southwest. Once ere- 7571-108 65 8 100 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS ated, this positive area persisted into later times, so that The block-faulted structure produced during later Cretaceous deposits overlapped it from the southwest Cenozoic time was thus not newly born, but had its and were later strongly deformed on the southwest side; antecedents in the complex events of earlier times. whereas the rocks of the Sierra Diablo region itself The tectonic history of the Sierra Diablo region is remained little disturbed until later in Cenozoic time. summarized in table 14. TABLE 14. Tectonic history of Sierra Diablo region, Texas Age Record in the rock sequence Kind of structure

Late Tertiary to Pleisto­ Bolson deposits. Block faulting along north-trending and west-north­ cene. west-trending faults; uplift of mountain areas and depression of Salt Basin and Eagle Flat. Early Tertiary Unconformity between Cretaceous sedi­ Folding and thrusting of Cretaceous rocks southwest of mentary rocks and Tertiary volcanic Eagle Flat. rocks south of the report area. Early Mesozoic Angular unconformity between Cretaceous Mild regional deformation and local flexing. and Permian rocks. Permian Fdcies variations in Permian rocks Greater subsidence of Delaware basin than Diablo plat­ form; local flexing. Late Pennsylvanian Angular unconformity between Hueco Lime­ Deformation of pre-Permian rocks into broad anticlines stone and older rocks. and synclines; local displacement along west-north­ west-trending faults and flexures. Between Ordovician and Unconformity between Bliss Sandstone and Tilting and local faulting. Precambrian(?) Van Horn Sandstone. Between Precambrian(?) Angular unconformity between Van Horn Faulting of west-northwest trend with strike-slip dis­ and Precambrian Sandstone and older rocks. placement. Intense folding and faulting of Allamoore and Hazel Formations; emplacement of Streeruwitz thrust sheet. Later Precambrian Probable unconformity between Hazel and Probable deformation. Allamoore Formations; coarse conglom­ erate in Hazel Formation. Earlier Precambrian Deformation of Carrizo Mountain Formation, progres­ sive and retrogressive metamorphism, injection of rhyolite and greenstone into sedimentary rocks.

Structural features of the Sierra Diablo region are Mountains is the Streeruwitz thrust fault (King, P. B., illustrated in horizontal dimensions by the tectonic map in King P. B., and Flawn, P. T., 1953, p. 102-103), (pi. 15), which shows the same items of structure as on which forms a boundary between the much-metamor­ the geologic map (pi. 1), except for omission of those phosed Carrizo Mountain Formation and its associated in the Precambrian Hazel, Allamoore, and Carrizo intrusive rocks on the south and the disturbed but little- Mountain Formations that formed before Van Horn metamorphosed Allamoore and Hazel Formations on time. In addition, the tectonic map shows known or in­ the north (pi. 1). The fault is exposed discontinuously ferred structure contours on the top of Precambrian along the south edge of the Sierra Diablo foothills from and Precambrian (?) rocks and data on the nature and the Streeruwitz Hills eastward to a locality 2 miles trends of joints. Structural features are also illus­ northeast of Allamoore (sec. 16, Block 67, Twp. 8), trated in vertical dimension by 10 structure sections and it reappears in a small area near the Texas and extending generally eastward across the northern Pacific Railway in the northern Carrizo Mountains and eastern parts of the region (pi. 16) and by 10 struc­ (sec. 17, Block 66, Twp. 8), thus having a known strike ture sections extending generally northward across the length of about 15 miles. Besides, several small patches southern part of the region (pi. 16). of metarhyolite lie amidst the Allamoore Formation in the Millican Hills more than iy2 miles north of the STRUCTURE OP PRECAMBRIAN AND PRECAMBRIAKX?) ROCKS trace of the Streeruwitz fault (sec. 5, Block 67, Twp. 8), and are probably klippen of its thrust sheet (section STREERUWITZ THRUST FAULT <9-<9',pl.l6). The major structural feature of the Precambrian At all places the overriding rocks along the Streeru­ rocks of the Sierra Diablo foothills and the Carrizo witz fault are metarhyolite, which is cataclastically TECTONICS 101 altered, with strongly developed lineation and streaks namic and hydrothermal processes; but little of the of mylonite. Lineation trends generally southward, original sedimentary structure has been lost, and there is normal to the trace of the thrust, and is probably paral­ no trace of the cataclastic metamorphism that is promi­ lel to the a fabric axis. In the Carrizo Mountains" nent in the metarhyolite south of the thrust. Further this metarhyolite intrudes the base of the Carrizo north the disturbance decreases, and the Hazel Forma­ Mountain Formation, a metasedimentaiy sequence some tion along the eastern and southern escarpments of the 19,000 feet thick (section T-T', pi. 16). The Carrizo Sierra Diablo dips at low angles. Mountain Formation probably forms most of the over­ The coarse thick conglomerate of the lower part of riding block of the thrust, although it is nowhere known the Hazel Formation attests that the Allamoore Forma­ to be in contact with it. The steeply dipping homo- tion was deformed just before and during the early part clinal beds of the formation strike northeastward (pi. of Hazel time. Part of the complex structure now visi­ 1), whereas the Streeruwitz fault strikes west-north­ ble in the Allamoore Formation must have been pro­ ward. Presumably the northeast-striking homocline is duced by this deformation; but this cannot be unraveled truncated by the fault. from the dominant structure, shared by both the Alla­ The Streeruwitz fault overrides the Allamoore For­ moore and Hazel, which is of post-Hazel and pre-Van mation, which is extensively silicified and marmorized Horn age. near it, and for a greater distance away from it is in­ The exposed contact between the Allamoore and tensely deformed by folds with a west-northwest strike Hazel Formations is of complex origin. In places the parallel to the fault trace. The Hazel Formation is original unconformable upper surface of the Allamoore nowhere in contact with the fault but is preserved a may be preserved, but in most places there has been short distance to the north where it is as much deformed movement between the two formations of undetermined as the Allamoore (sections K-K', 0-0', P-P', and magnitude, caused mainly by differences in competency others, pi. 16). Emplacement of the Streeruwitz thrust of their rocks. In some places the Allamoore Formation sheet must have occurred after Hazel time. even overlies parts of the Hazel Formation well above Actual contacts between the overriding metarhyolite its base, and the two are separated by a low-angle thrust and the overriden Allamoore Formation are exposed in fault of large displacement. These conditions vary from many ravines or hillsides in the Sierra Diablo foothills, place to place along the contact in a manner that can­ but there is no sharply marked cleancut surface. Near not easily be differentiated. Rather than introduce pos­ the contact the metarhyolite is lineated and mylonitized, sibly unjustified interpretations on the geologic map the Allamoore is schistose and marmorized, and both (pi. 1) and structure sections (pi. 16), the contact be­ units are strongly silicified; but in many places the con­ tween the Allamoore and Hazel is therefore indicated tact is masked by schistose amphibolite or by quartz as a "surface of movement." veins. Aberrant dips of foliation and trends of linea­ Just north of the Streeruwitz thrust fault in the tion in the metarhyolite near the contact attest further Sierra Diablo foothills is a belt of Allamoore Formation movement after the creation of the cataclastic structure. a mile or more wide (pi. 1). In this belt the Allamoore The Streeruwitz fault is clearly older than the Hueco is strongly folded and faulted in a manner that has not Limestone of Permian age, as the Hueco lies unconf orm- been completely worked out. In the Millican and Bean ably on the fault trace in the Streeruwitz Hills (section Hills some downfolds preserve bodies of conglomerate K-Kf, pi. 16). The fault must also be older than the of the Hazel Formation, and in the Millican Hills other Van Horn Sandstone of Precambrian (?) age, as the Van downfolds preserve bodies of metarhyolite which are Horn lies unconf ormably on Hazel, Allamoore, and Car­ klippen of the Streeruwitz thrust sheet. Toward the rizo Mountain Formations that were deformed during east, between Buck Spring and Carrizo Spring, the the thrusting, and as it contains fragments of metarhyo­ structures plunge eastward and the Allamoore and lite that was lineated and mylonitized during these Hazel Formations are folded together into several movements. steeply dipping anticlines. The southern belt of Allamoore Formation is bor­ STRUCTURE OF ALLAMOORE AND HAZEL FORMATIONS dered on the north by the Hazel Formation. In both The Allamoore and Hazel Formations for 3 miles the Millican Hills and Streeruwitz Hills the adjacent north of the trace of the Streeruwitz fault are intensely Hazel is a massive coarse conglomerate as much as 2,000 folded and faulted as a result of forces directed from feet thick, which is probably a basal deposit. In the the south; presumably the disturbance in this belt is Streeruwitz Hills successive units of limestone, phyllite, related to emplacement of the Streeruwitz thrust sheet. and volcanics are cut off against the conglomerate (pi. Rocks of the disturbed belt have been altered by dy­ 1), due either to an angular unconformity or to thrust- 102 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS ing. In other places, notably in the Bean Hills, Alla- ment of the Sierra Diablo 3 to 6 miles west of the Old moore Formation lies against red sandstone of the Hazel Circle Kanch (sections L-L' and M-M'', pi. 16), but the without conglomerate, and the contact is more clearly a body of greatest interest is near the Sancho Panza, St. thrust fault. Elmo, and Blackshaft mines (sec. 16, Block 67, Twp. Thrusting of Allamoore over Hazel at the north edge 7; pi. 1) where a thin layer of Allamoore is tectonically of the southern belt is most convincingly displayed west intercalated in the Hazel. Toward the southeast this of the Garren Kanch in the Millican Hills (sec. 4, Block layer dips steeply or is overturned, but to the northwest 67, Twp. 8) where a "subsidiary nappe," or recumbent it dips at low angles eastward or northeastward. The fold of Allamoore Formation, overrides the Hazel For­ layer is not more than 10 feet thick and is highly sheared mation across a breadth of about a mile (section 0-0', and sporadically mineralized. As shown in mine work­ pi. 16). The carapace of the nappe is limestone which ings, the under surface is marked by grooves or steps is traceable, with a few interruptions, from its lower to parallel to the strike, and includes horses of the under­ its upper limb. The core of the nappe is volcanic rock lying sandstone. The upper surface is a strong firm and phyllite. The nappe is enclosed by conglomerate sandstone, which may itself have been sheared over the of the Hazel Formation, which is discordant below and Allamoore beneath. accordant above. The discordant conglomerate beds North of the main northern outliers of the Allamoore beneath the nappe contain numerous tourmalinized Formation, the Hazel Formation stands steeply in slickensided surfaces. places, as along Hackberry Creek, where vertical beds North of the southern belt of Allamoore Formation of red sandstone and interbedded conglomerate are well is a belt of Hazel Formation, whose south edge in the exposed. Farther north the structure flattens abruptly, Millican and Streeruwitz Hills includes the thick bodies forming the "north edge of the steep-dip zone" of the of coarse conglomerate already mentioned. In most geologic map (pi. 1). Near the Hazel mine (sec. 14, places the Hazel dips homoclinally northward, with Block 66, T. 7) the red sandstone layers are nearly gradually flattening dips, but greater complexity than horizontal, but from there northward toward Victorio would otherwise be inferred is indicated by reappear­ Peak they dip at angles of 30° or less toward the south ance of bodies of Allamoore Formation north of the (section P-P', pi. 16). Similar low dips of the red belt. sandstone are visible at various places farther west, Most of these northern bodies of Allamoore Forma­ even where the sandstone is overlain by displaced masses tion have a synclinal structure and overlie the Hazel of Allamoore Formation (section M-M', pi. 16). Formation adjacent to them. This feature is well dis­ played in an area of high relief near Tumbledown FAULTS WITH STRIKE-SLIP DISPLACEMENT Mountain (sec. 27, Block 66, Twp. 7; section R-R, The Sierra Diablo foothills are crossed by west- pi. 16; upper view, pi. 10), where about 2,000 feet of northwestward-trending faults, most of the longer of Allamoore is synclinally dowiifolded in the Hazel and which displace Van Horn and Paleozoic formations, is repeated by a thrust in its lower part. A much but some of the shorter of which occur only in the Alla­ larger body of Allamoore Formation with similar struc­ moore and Hazel Formations. The obvious larger dis­ ture is preserved in the Bean Hills (section Z-Z/, pi. placements on these faults are of Cenozoic age, although 16). In the Millican Hills a northern body of Alla­ some have moved earlier, between Cretaceous and Van moore Formation likewise has a synclinal structure Horn time. Displacement during these Cenozoic and (section P-P1', pi. 16), but is still tenuously connected earlier times was dominantly dip slip. with the southern belt by a narrow band of limestone, However, some of these faults may have had still indicating that this body is the inverted forward edge of a recumbent fold. In an exceptional area near the earlier strike-slip displacements. Such earlier strike- Garren Kanch (northwestern part of sec. 3, Block 67, slip displacements are indicated most convincingly along Twp. 8) Allamoore of the northern body dips 20° W. the Grapevine fault, where there is a left-lateral offset in normal order beneath conglomerate of the Hazel of the "north edge of the steep-dip zone" in the Hazel Formation, but tracing of the contact indicates that Formation by about half a mile (pi. 1). Elsewhere in these strata have been rotated nearly 360° from their the area of outcrop of Hazel and Allamoore Formations original position. are shorter faults of the same trend which do not extend Some of the northern bodies of the Allamoore Forma­ into younger rocks, and which displace nearly vertical tion lie far to the north, over gently dipping red sand­ Allamore and Hazel Formations in the same sense. stone that is probably high in the Hazel sequence. Sev­ Perhaps these were displaced during the same epoch eral of them occur at the foot of the south-facing escarp­ of strike-slip movement. TECTONICS 103 The left-lateral strike-slip displacements along the faults. The Van Horn itself was tilted and faulted faults of west-northwestward trend do not seem to be before Early Ordovician (Bliss) time, as shown where related to dip-slip displacements on these and similar the contact is exposed in Beach Mountain and the Bay- faults seen in the Van Horn and younger formations. lor Mountains. Discordance between the Van Horn A period of strike-slip faulting is thus suggested, at and Bliss is generally only a few degrees, but it is as some time after deformation of the Allamore and Hazel much as 20° on the north face of Beach Mountain. Formations and before deposition of the Van Horn Faulting before Bliss time is shown on Tumbledown Sandstone. Strike-slip displacement of the west-north­ Mountain where the Van Horn was dislocated by the westward-trending faults may have established a Dallas and Grapevine faults. The Dallas fault and "grain" in the region which was utilized during later the Van Horn and Allamoore Formations that were times of deformation by differently directed forces. displaced by it are truncated by the Bliss Sandstone and no later movement occurred along the fault. The FRACTURE ZONES IN HAZEL FORMATION Grapevine fault was downthrown to the south both be­ In the gently dipping red sandstone of the Hazel For­ fore and after Bliss time, so that the Van Horn is pre­ mation just south and east of the southeast corner of the served only on its south side, whereas the displaced Bliss Sierra Diablo are the Hazel and Pecos fracture zones. occurs on both sides. Along the Carrizo Spring fault The Hazel fracture zone is a set of en echelon fractures to the south, tilted Van Horn is truncated by Bliss, sug­ 31/2 miles in length, trending nearly eastward from the gesting that it likewise was displaced before Bliss time. Mohawk mine. The Pecos fracture zone extends 2 Throughout most of its extent the Van Horn is over­ miles north-northeastward, past the Pecos mine and lain unconformably by the Hueco Limestone of Eureka prospect. Permian age. The Hueco truncates the several widely The fractures are vertical mineralized fissures on dispersed basinlike areas in which the Van Horn is now which the ore bodies of the Hazel mine and other mines preserved. These basinlike areas conform broadly to and prospects are located. Within the zones, the frac­ the structure of the succeeding pre-Permian formations, tures lie parallel or en echelon, or diverge at acute suggesting that they were formed at least partly during angles. Outcrops of the fractures are commonly indi­ the late Paleozoic pre-Hueco deformation. cated by bleaching of the red sandstone immediately The Van Horn Sandstone is tilted and broadly adjacent. In vertical section the fractures are zones a warped, so that it dips commonly at angles of 5° or 10°, few feet to 40 feet wide of bleached, brecciated, and although in places it lies nearly horizontal, and in parts sliced country rock, interlaced with a gangue of barite, of the Eed Valley it dips as steeply as 45°. In the Red calcite, and quartz, which contains sulfides of copper, Valley there appear to be several broad folds or east­ silver, and other metals. ward-plunging noses. To the north near Carrizo The relative ages of these fracture zones and the high- Spring, dips are northeastward or eastward; near angle faults and joints of adjacent areas are uncertain. Threemile Mountain they are generally southeastward; The fracture zones extend across the dominant west- south of Threemile Mountain they are again northward. northwestward-trending faults and joints, apparently without offsetting them or being offset by them, yet STRUCTURE OF THE PRECAMBRIAN SURFACE the west-northwestward-trending faults seem to have been displaced intermittently from late Precambrian to The known or inferred configuration of the upper late Tertiary time. Moreover, emplacement of the surface of the Precambrian and Precambrian (?) rocks metallic-mineral deposits may have occurred much later in the Sierra Diablo region is illustrated by structure than the time of formation of the fractures themselves, contours on plate 15. The regional configuration of the in zones of weakness already created. It has been sug­ surface in northern Trans-Pecos Texas was presented gested (King, P. T., and Flawn, P. T., 1953, p. 151) that earlier (King, P. B., and Flawn, P. T., 1953, pi. 19B; the metallic mineral deposits were emplaced in Tertiary Flawn, 1956, pi. 1; DeFord and Brand, 1958, p. 38). time, but the fractures themselves might have been The surface chosen for contouring is the top of the created at any time following the deposition and defor­ Carrizo Mountain, Allamoore, Hazel, and Van Horn mation of the Hazel Formation. Formations. For the most part this is not the surface of a "basement," as most of the rocks which form the STRUCTURE OF VAN HORN SANDSTONE surface are sedimentary and toward the north are little The Van Horn Sandstone of Precambrian (?) age altered or deformed; moreover, one unit, the Van Horn does not share the structure of the Carrizo Mountain, Sandstone, is unconformable on the remainder. The Allamoore, and Hazel Formations, but lies on their Van Horn Sandstone must be included with the forma­ deeply eroded surfaces and truncates their folds and tions contoured because its erratic thickness is unpre- 104 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS dictable away from areas of outcrop. Information on regional feature in the State, although Precambrian the configuration of the surface is reliable in the south­ rocks project higher in the much narrower more local­ ern half of the Sierra Diablo region, where the top of ized uplift of the Franklin Mountains farther west the Precambrian and Precambrian (?) rocks is exposed (Adams, 1944). Northeast of the high-standing area in many places. The configuration farther north can the Precambrian surface probably descends below sea only be inferred, and the contours there are extrapo­ level beneath a thick body of Paleozoic rocks in the lated from higher formations. Such extrapolation is Delaware basin; southwest of the high-standing area it fairly accurate where pre-Permian formations are probably descends to as great a depth beneath a thick exposed, as these have nearly constant thicknesses body of geosynclinal Mesozoic rocks. throughout the region. It is much less accurate where The area of high-standing Precambrian rocks is only Permian or younger formations are exposed, be­ domical only in the broadest sense, as it now consists of cause of their variable thicknesses and the one or more a number of distinct but closely adjacent mountain up­ angular unconformities beneath them. lifts, separated by downf aulted areas; it may have been Contours on the upper surface of the Precambrian a more continuous feature before block faulting of later and Precambrian(?) rocks of the report area (pi. 15) Cenozoic time. It probably originated mainly during show that it stands high throughout the southern half the pre-Hueco deformation of later Paleozoic time. of the Sierra Diablo, as well as in the foothills to the The pre-Permian Paleozoic sequence of the region is like south and the Carrizo Mountains beyond. The surface that elsewhere in northern Trans-Pecos Texas and south­ culminates at an altitude of somewhat more than 6,000 ern New Mexico, and provides no indication of any feet near the southeastern angle of the Sierra Diablo nearby positive area. Moreover, the high-standing area and lies at more than 5,000 feet over extensive areas does not appear to be related to any special part of the nearby. In the northern half of the Sierra Diablo and Precambrian complex, as it crosscuts diverse Precam­ in the Baylor Mountains, the surface is generally much brian rocks and structures. The positive area, once lower, in the former area standing at altitudes between created, manifested itself in various guises during later 1,000 and 2,000 feet, and perhaps descending to sea level times during Permian and Mesozoic times when it re­ near the north end of the range. The border between ceived smaller thicknesses of sediments than surround­ the high-standing and low-standing parts of the surface ing areas, during Late Cretaceous and early Tertiary in the southern and northern parts of the Sierra Diablo time when it was less deformed than the area to the is seemingly near the Victorio flexure in the exposed southwest, and in late Tertiary and Quaternary time rocks, where the surface may have been abruptly flexed when it was raised by block faulting. During these or faulted. times its role was perhaps relatively passive or even Configuration of the surface of the Precambrian and accidental. For example, uplift was probably greater Precambrian (?) rocks is a product of all the deforma­ during the late Cenozoic block faulting in the Guadalupe tions to which it was subsequently subjected. Many of Mountains than in the area of high-standing Precam­ its complexities in the map area are an obvious result brian rocks, yet the uplift there was insufficient to raise of the block faulting of later Cenozoic time, yet most the Precambrian rocks as high because of the much of its gross features were produced by the pre-Hueco thicker overburden of Paleozoic strata. deformation of later Paleozoic time, during which the rocks of earlier Paleozoic, Precambrian(?), and Pre­ STRUCTURE OF PRE-PERMIAN PALEOZOIC ROCKS cambrian age were uplifted and deeply eroded before Much of the complexity of the map pattern of the the Permian was deposited over them (fig. 2). pre-Permian Paleozoic rocks in the Sierra Diablo re­ Features of the Precambrian surface within the map gion results from the unconformity at the base of the area are part of a larger pattern of positive and nega­ Hueco Limestone, which causes the Hueco, at one place tive areas in northern Trans-Pecos Texas which were or another, to lie on all the older rocks of the sequence also produced by successive deformations during Paleo­ (pi. 1). This unconformity resulted from folding, zoic and later times. Precambrian rocks are exposed faulting, and deep erosion of the underlying rocks not only in the southern part of the Sierra Diablo, but events that were of Late Pennsylvanian age, as rocks of in several mountain areas adjacent to it on the south Early Pennsylvanian age lie unconf ormably beneath the (fig. 8), where their upper surface rises to an altitude Hueco in the northern Sierra Diablo. of more than 5,000 feet. This high-standing area has The pre-Hueco deformation is strikingly illustrated been called the "Van Horn dome" by Baker (1927, p. by the distribution of the Ordovician rocks in the south­ 41; 1934a, p. 182), who interpreted it as "the highest eastern foothills of the Sierra Diablo (pi. 1). On Beach uplift in Texas." Certainly it is the highest-standing Mountain they overlie the Van Horn Sandstone and TECTONICS 105 comprise the Bliss Sandstone, El Paso Limestone, and south it lies on Hazel and Allamoore Formations. The Montoya Dolomite, a mass nearly 2,000 feet thick. pre-Hueco structure thus indicated had much the same Three miles to the northwest, at the southeast corner of position as the later South Diablo fault, although it may the Sierra Diablo, the Hueco Limestone lies on red sand­ have been no more than a broad flexure. stone of the Hazel Formation; all the Ordovician rocks Other faults or abrupt flexures were probably dis­ and the Van Horn Sandstone are missing. A paleogeo- placed at this time, some of which are indicated hypo- logic map of the surface on which the Hueco was de­ thetically on the paleogeologic map (fig. 2) and the posited (fig. 2) indicates that Beach Mountain lay near structure sections (pi. 16). A fault along the Victorio the southwest end of a broad syncline that plunged flexure is likely, because on the escarpment south of northeastward, whereas the southeast corner of the Victorio Peak, Hueco Limestone is known to lie on Sierra Diablo lay on the crest of the next broad anticline Precambrian Hazel Formation at least part of the dis­ to the northwest. tance across the flexure (section Y-Y', pi. 4), whereas 2 Another syncline is indicated farther north, in the miles to the west in Victorio Canyon the Hueco on the northeastern part of the Sierra Diablo where Barnett flexure lies on steeply tilted Upper Ordovician Montoya Shale of Mississippian age and limestone and shale of Dolomite (section K-X', pi. 4). This tilting may be Pennsylvanian age are preserved beneath the Hueco related to a fault of pre-Hueco age, downthrown to the Limestone. In most of this syncline the angular di­ north (section N-N', pi. 16). A fault or flexure nearly vergence between the Hueco and older rocks is only a coinciding with the present Cox Mountain fault is also few degrees; but on the south flank, at an inlier in Vic- possible (sections K-K', L-L'', and M-M', pi. 16). torio Canyon (sec. 13, Block 43), the Montoya Dolomite North of the fault, Hueco Limestone lies on Lower Or­ dips 75° N., whereas the overlying Hueco dips only dovician El Paso Limestone, whereas in the nearest ex­ gently in the same direction. On the north flank the posures to the south it lies on Precambrian (?) Van Fusselman Dolomite and beds of Devonian age diverge Horn Sandstone or Precambrian Hazel Formation. at only slight angles from the Hueco, except at a local­ All these faults or abrupt flexures, known or in­ ity l^j miles northwest of the Figure Two Ranch (sec. ferred, are downthrown northward, toward the dom- 12, Block 66, Twp. 5) where the Fusselman is nearly inantly negative area that resulted from the pre-Hueco vertical, and is either faulted or sheared against the deformation, whereas in Cenozoic time the displace­ Montoya and Devonian beds on either side. ment on most of the faults was southward. Abrupt truncation of pre-Hueco formations near some of the west-northwestward-trending faults of the STRUCTURES OF PERMIAN" AND EARLY MESOZOIC AGE region suggests that these faults were dislocated during the pre-Hueco deformation. This is most strikingly Cretaceous formations of the Sierra Diablo region shown along the Hillside fault (section Q-Q'', pi. 16). lie unconformably on the older rocks in the same man­ On the northern or downthrown side of the fault, the ner as the Hueco Limestone at the base of the Permian. Powwow Member of the Hueco Limestone lies on the Where the Cretaceous is no longer preserved, an exten­ Van Horn Sandstone, but contains coarse angular frag­ sion of its basal unconformity is indicated by wide areas ments of Precambrian metarhyolite; these fragments of even-crested summits from which an original Cre­ were obviously derived from south of the fault and de­ taceous cover has been removed by erosion. The pre­ crease in abundance away from it. Presumably the served base of the Cretaceous and its exhumed surface metarhyolite projected as a scarp along the Hillside show that truncation of rocks beneath is less than at the fault during deposition of the Powwow Member. base of the Permian. In most of the Sierra Diablo Where the Sulphur Creek fault crosses the Sierra Di­ region the Cretaceous was deposited on Permian ablo escarpment 1 mile north of the Hazel mine, the rocks on Guadalupe Series in the north, on Leonard Hueco Limestone of the northern or upthrown side Series in the middle, and on Wolfcamp Series in the overlies 750 feet of Van Horn Sandstone, whereas on the south. The only exception is in the western part of the southern or downthrown side it lies on red sandstone Sierra Diablo foothills where the Cretaceous lies on of the Hazel Formation (section Q-Q', pi. 16). The Precambrian rocks (pi. 1). Curiously, the Cretaceous Van Horn is folded into a syncline whose correspond­ at no place lies directly on earlier Paleozoic formations ence with the fault may be partly coincidental, as the which intervene elsewhere in the region between the syncline seemingly diverges from the fault farther east. Permian and the Precambrian. On the South Diablo fault west of the Old Circle Ranch, In most places the angular discordance between the the Hueco Limestone again lies on the Van Horn Sand­ Cretaceous and older rocks is slight, but it is greater on stone on the upthrown side, whereas some miles to the several monoclinal flexures that extend west-northwest- 106 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS ward across the region, on which Permian strata are remnant of Cretaceous sandstone overlies the tilted downbent north-northeastward (pis. 1,15; fig. 8). Permian rocks (section N-N', pi. 16; section X-X', The northernmost, or Babb flexure, is at the north pi. 4). end of the Sierra Diablo and is named for the old Babb Nevertheless, the flexures are an accentuation of fea­ Ranch, west of which it is prominently exposed (up­ tures existing in the region during Permian time, which per view, pi. 12). It has been traced thence west-north­ were themselves inherited from the pre-Hueco deforma­ west into the Diablo Plateau for more than 10 miles, tion. Pre-Hueco deformation caused the southern part past the north side of Sierra Prieta. It may also ex­ of the Sierra Diablo region to become a positive area and tend east-southeastward for nearly the same distance the part to the north a negative area (fig. 2). During to the mouth of Apache Canyon, but here its course Permian time the positive area, or Diablo platform, re­ is obscured by the North Diablo fault zone of Cenozoic ceived relatively shallow-water deposits, mainly car­ age. The Victorio flexure is about 12 miles farther bonates ; whereas the negative area, or Delaware basin, south and is named for Victorio Peak, south of which received relatively deep-water deposits, including black it is exposed on the Sierra Diablo escarpment (upper limestone and siliceous shale during Leonard time (figs. view, pi. 10). It has been traced tftence west-northwest 6,7) and fine-grained sandstone during Guadalupe time. into the Sierra Diablo and east-southeast into the Bay- During Leonard time limestone reefs and banks formed lor Mountains for a distance of 21 miles. along the boundary between the platform and basin Both the Babb and Victorio flexures are a mile or (sections Z7-Z7', X-X', and Y-Y', pi. 4). The Hueco two wide. On the flexures Permian rocks dip mostly Limestone extends with little change across these flex­ 10° northward, but they dip less in places and more ures, as well as the flexure near the South Diablo fault than 15° in others. Structure on the flexures is ob­ zone. Initial flexing must have occurred immediately scured by irregular bedding of many units involved, but after Hueco time, as there is a prominent unconformity some evenly bedded units cross them, such as 'the Hueco at the top of the formation on the Babb and Victorio Limestone on the Victorio flexure and the Victorio Peak flexures. Inequalities of relief produced by this uncon­ Limestone on the Babb flexure (sections B-B', N-N', formity probably influenced location of reefs and banks and P-P', pi. 16; sections X-X' and T-Tf, pi. 4). Dis­ during Leonard time, although flexing may have con­ placement on the flexures, as determined by differences tinued during deposition of the Leonard Series itself. in height of the evenly bedded units at the upper and STBUCTUBES OF LATE CBETACEOUS OB EABLY lower ends, is 1,700 feet on the Victorio flexure and 1,000 TEBTIABY AGE feet on the Babb flexure. A third flexure that was truncated by the uncon­ Southwest of Eagle Flat, in the southwest corner of formity at the base of the Cretaceous is indicated far­ the map area, Cretaceous rocks are strongly deformed, ther south, along the South Diablo fault, where the as first observed by Baker (1927, p. 5). These rocks possibility of pre-Hueco flexing has already been noted. and structures are a small segment of the northeastern At a place S1/^ miles west of the Old Circle Ranch (sec. front of the Chihuahua tectonic belt (DeFord and 2, Block 56) about 900 feet of Van Horn Sandstone and Brand, 1958, p. 72), which was deformed after the Cre­ taceous rocks were deposited, and mainly before vol­ Hueco Limestone form an escarpment north of the fault, canic rocks of probable Tertiary age were spread over whereas Campagrande Limestone lies directly on red them. The front of the Chihuahua tectonic belt extends sandstone of the Hazel Formation to the south (section M-M', pi. 16). This must have been caused by north­ northwestward beyond the report area through Devil ward downflexing in pre-Cretaceous time, in the same Ridge, the Quitman Mountains, and Malone Mountain direction as on the Babb and Victorio flexures, but (Albritton and Smith, 1965) (figs. 3, 8), and south­ opposite from the downthrow on the later South Diablo eastward through the Eagle Mountains and Indio fault. The flexure evidently diverged westward from Mountains (Gillerman, 1953, p. 39-40; DeFord and the fault, as in this direction the Van Horn and Hueco Brand, 1958, p. 72-85). The area of deformed rocks in extend a short distance south of it (section Z-Z', pi. 16). the United States is only a small part of the Chihuahua The flexures and other features just described de­ tectonic belt, most of which lies in Mexico. veloped at some time after deposition of the Permian Two major faults break the rocks southwest of Eagle rocks now preserved in the Sierra Diablo region and be­ Flat the Devil Ridge thrust and the Red Hills thrust, fore deposition of the Cretaceous rocks. Tilted Permi­ about 2 miles farther southwest (Smith, 1940, p. 630- an rocks on the Babb and Victorio flexures are trun­ 631) (pis. 1, 15.) These faults are exposed in few cated by the pre-Cretaceous surface, and on the Victorio places; but the Devil Ridge thrust at one place dips flexure west of the rim of Victorio Canyon a small 54° SW., and the Red Hills thrust at another dips 22° TECTONIC& 107 SW. Smith estimates that the minimum displacement to the dominant north-northwestward-trending faults of the Devil Eidge thrust is about 4% miles and that of the area. of the Eed Hills thrust about 3 miles. In the southern part of the region another fault sys­ The Devil Eidge thrust carries Yucca and Bluff tem trending west-northwestward crosses the northerly Mesa Formations over Washita Group and Eagle Ford system. Its faults are most abundant in the Sierra Formation. The Washita and Eagle Ford are thrown Diablo, but some occur in the Apache Mountains and into complex minor folds for a mile or two northeast southern Delaware Mountains east of the Salt Basin of the fault trace, beyond which the underlying Creta- (fig. 8). Like the northward-trending faults, they ceaus rocks are less deformed. The Yucca, Bluff Mesa, moved in late Tertiary time; but they are generally in Cox, and Finlay Formations above the Devil Kidge the interiors of the ranges rather than along their thrust dip homoclinally southwestward, mainly at borders, and they do not share the latest movements of angles of 15°-30°, but in places an overturned syncline the northerly faults. Some of them have had a con­ is preserved next to the Eed Hills thrust. siderable pre-Cenozoic history, as discussed above. In In the Sierra Diablo region northeast of the Chi­ the Sierra Diablo the dominant joint set is parallel to huahua tectonic belt neither the Cretaceous nor the un­ the west-northwesterly faults, rather than to the north­ derlying Paleozoic rocks contain structures like those erly faults that border the range (pi. 15). The west- southwest of Eagle Flat, and this region probably re­ northwesterly faults seemingly follow lines of weak­ mained little disturbed until later in Tertiary time. ness in the crust more ancient than those followed by the northerly faults. STRUCTURES OP LATE TERTIARY AND QUATERNARY AGE FAULTS BORDERING THE MOUNTAINS GENERAL. FEATURES The Sierra Diablo and adjacent mountains and foot­ The Sierra Diablo is one of a group of ranges in hills are probably bordered continuously by faults along northern Trans-Pecos Texas in which the surface fea­ the edge of the Salt Basin, although these are generally tures have been shaped largely by tectonic movements concealed by Quaternary deposits and are exposed at during late Tertiary and Quaternary time as else­ only a few places. The longest segments, on the East where in the Basin and Eange province of which the Diablo and East Baylor faults, are parts of the north­ region is a part. On the east is the upheaved block of erly fault system; but these segments are separated by the Guadalupe, Delaware, and Apache Mountains; next others on the North Diablo and North Baylor faults be­ to the west is the depressed block of the Salt Basin; be­ longing to the west-northwesterly fault system, whose yond is the upheaved block of the Sierra Diablo (fig. 8). positions nearly coincide with the Babb and Victorio flexures. Small segments of the faulted margins of the Faults are the dominant structural features of the Delaware and Wylie Mountains along the east side of boundaries between the mountains, or areas of upheaval, the Salt Basin also extend into the report area. and the Salt Basin, or area of depression. Most of the steep escarpments that face the basin have been NORTH DIABLO FAULT ZONE outlined by such faults, which have dropped the strata The North Diablo fault zone extends east-southeast­ thousands of feet toward the basin. It places between ward for 8 miles from near the old Babb Eanch to the the mountains and basin are foothills of downdropped salient of the Sierra Diablo near Apache Peak. The strata, such as the Patterson Hills west of the Guada­ zone consists of subparallel interlacing faults that en­ lupe Mountains, and Beach Mountain and the Baylor close narrow wedges, mainly of Victorio Peak Lime­ Mountains east of the Sierra Diablo. stone, dropped 1,000-1,500 feet below equivalent strata The general trend of the faults along the edges of the on the main escarpment to the south (upper view, pi. basin is northerly, although there are offsets along faults 12), which are intermediate in structural height be­ that trend in other directions. Faults of the northerly tween the bedrock of the escarpment and that beneath system on the east side of the Sierra Diablo trend the Salt Basin. The principal faults are downthrown toward the Salt Basin; but complications are produced irregularly in various directions east and west of north by minor faults downthrown toward the escarpment (fig. 8). Many faults of the northerly system moved and by steep tilting or folding of the rocks in some of several times during late Tertiary and Quaternary time. the fault blocks, so that black limestone of the Bone The last movements were of late Pleistocene age and o Spring Formation emerges in places (section C-C', pi. produced low scarps that still persist in the older 16). alluvial deposits and the adjacent bedrock. In the The surface of the large fault at the foot of the Sierra Guadalupe Mountains the dominant joint set is parallel Diablo escarpment is exposed 1% miles west of the 108 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

105° 104*

31

EXPLANATION

Igneous, metamorphic, Sedimentary rocks of Volcanic rocks of early Intrusive igneous rocks Bolson deposits and and sedimentary Paleozoic and Meso- Tertiary age of Tertiary age thick alluvial fill of rocks of Precambri- zoic age late Tertiary and an age . .Quaternary age

Low-angle thrust faults High-angle faults, Monoclinal flexures of Anticlinal axis and of early Tertiary age mainly of late Terti- Permian and early domes Dotted where concealed by ary and Quaternary Mesozoic age younger deposits age In part followed by reef Dotted where concealed by zones of Permian age bolson deposits; major faults in heavy thick lines

FIGDEB 8. Map of Sierra Diablo region and adjacent areas showing faults and related structural features. Faults and flexures of west-northwesterly trend extend across the width of the map, and are crossed by other faults of diverse trend. TECTONICS 109 portal of Apache Canyon, and dips 70°-80° toward the but the bench of Hueco Limestone at the base ends on an downthrow, with flat-lying black limestone of the Bone even line along the fault and is little dented by the heads Spring on the upthrown side and gently tilted Victorio of alluvial fans. In the southern bight the Hueco Lime­ Peak Limestone on the downthrown side. stone, which forms the rim of the escarpment, has At the west and east ends of the North Diablo fault receded a mile or two from the fault; the slopes below zone, the displacement at the border of the mountains it, which are formed of poorly resistant red standstone continues along northward-trending faults to the west of the Hazel Formation, have been carved into a con­ along a fault which extends northward at the bases of cave surface, with pediments at the base. South, Middle, and North Mesas and to the east along Landforms of the Sierra Diablo escarpment suggest the East Diablo fault which extends southward. The that the East Diablo fault along its base moved rather western prolongation of the North Diablo fault zone late in geologic time the even base line of the outer itself coincides with the Babb flexure, which is broken bench, the actively growing alluvial fans in front, and in places by small faults of the same trend (section the small length of most of the canyons behind. Late B-B', pi. -6). The fault zone was probably formed by movements are further indicated by low fault scarps a renewed movement along one segment of the flexure in short distance east of the main fault (pis. 1,15). One late Tertiary and Quaternary time. The steep tilting crosses the alluvial fans northeast of Apache Peak, and folding of the Permian rocks in parts of the fault somewhat north of the end of the East Diablo fault. zone may antedate the faulting and be related to the It extends for 3 miles with a trend slightly west of north earlier flexing. and is about 15 feet high. Another scarp of about the EAST DIABLO FAULT same height occurs in the southern bight east of the Pecos mine, in alluvium overlying Ordovician rocks of The East Diablo fault borders the Sierra Diablo on the Baylor Mountains block. the east for 25 miles. It has a bight and cusp pattern, The surface of the East Diablo fault, or of rocks with three cusps or salients near the Hazel Mine, Vic­ closely adjacent to this surface, is exposed between torio Peak, and Apache Peak separated by two curved Marble and Victorio Canyons in the northern bight, bights, each about 10 miles across. adjacent to the outcrops of downfaulted bedrock. The East of the southern bight the Sierra Diablo is sep­ Hueco Limestone of the upthrown block extends hori­ arated from the Salt Basin by the intermediate block zontally to the fault and is not internally disturbed ex­ of the Baylor Mountains, whose summits stand a thou­ sand feet or more below those of the Sierra Diablo. cept for north-trending vertical joints, some veined by Opposite the Baylor Mountains the East Diablo fault calcite, which are nearly parallel to the main fault. is bordered by pediments and bedrock hills, rather than By contrast, the downthrown strata are steeply dragged, by thick alluvial deposits. greatly jointed, shattered, and silicified. Best exposures In the central and northern salients and the inter­ of the fault surface are three-quarters of a mile north vening northern bight, the East Diablo fault borders on of the portal of Victorio Canyon (opposite elevation the Salt Basin, and its displacement is greater than in point 4550, sec. 3, Block 66, Twp. 6), where it is followed the southern bight. In most places bedrock on the by a breccia zone 25-50 feet wide, of angular fragments of black limestone derived from the downthrown block. downthrown side is concealed by a series of coalesced alluvial fans, many of which are still in process of The fault surface is nearly vertical, or dips eastward growth. At a few places between Victorio Canyon and at a steep angle. Marble Canyon, however, small patches of steeply Rocks near the East Diablo fault are exposed in the dragged bedrock emerge on the downthrown side of the southern bight 1% miles northwest of Red Tank (sec. fault (section G-G', pi. 16). Some contain Victorio 21, Block 54%), where the fault is adjoined on the Peak Limestone, whose base is 1,200 feet lower than at downthrown side by low hills of El Paso Limestone. the nearest point on the escarpment to the west. Total Close to the fault the limestone is much brecciated and displacement in the zone of the East Diablo fault is is traversed by north-trending vertical joints and wide probably much greater, the remainder being accounted calcite veins that are probably nearly parallel to the main fault. for by drag of the downthrown beds and displacement NORTH BAYLOR FAULT on probable faults to the east, which are concealed by the Quaternary deposits. The Baylor Mountains project northeastward into The East Diablo fault follows the base of the east- the Salt Basin as an acute-angled salient, on the north facing escarpment of the Sierra Diablo, 2,000 feet or side of which are much eroded hills that extend west­ more high (pi. 10). In the northern bight the crest of ward with a nearly straight front for 9 miles to the the escarpment has receded a mile or so from the fault, East Baylor fault. These hills are probably bordered 110 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS on the north, beneath the adjacent alluvium, by the Some of the bedrock exposed at the foot of the Baylor North Baylor fault, which separates the Baylor Moun­ Mountains, mostly El Paso Limestone, is probably close tains block from the deeply depressed part of the Salt to the East Baylor fault. Northeast of the high point Basin beyond. of the mountains (BM 5568) the limestone is stained The North Baylor fault produces an easterly offset red and yellow, is sliced by closely spaced joints, dips of the mountain front similar to that on the North steeply and erratically, and in places is much brec- Diablo fault zone, and like it, nearly coincides with a ciated. South of Eed Tank Canyon the El Paso near major structure in the Permian rocks, the Victorio the mountain base dips steeply northwestward, perhaps flexure. The flexure is prominently exposed on the mainly as a result of pre-Hueco deformation. It is Sierra Diablo escarpment just west of the terminus cut by closely spaced northeastward-trending joints, of the North Baylor fault; its easterly extension is indi­ some nearly vertical, others dipping 50°-60° SE., and cated in the Permian rocks of the northeastern Baylor is offset by minor faults downthrown toward the Salt Mountains, where there are depositional features and Basin, probably related to the main fault at the edge northward-tilted beds similar to those on the flexure of the mountains. farther west. The inferred trace of the North Baylor FAULTS ON EAST SIDE OF SALT BASIN fault would lie within the prolongation of the flexure, although it seemingly trends eastward and the flexure Short segments of faults which border the mountains east-southeastward. along the east side of the Salt Basin extend into the map area in places, one along the Delaware Mountains EAST BAYLOR FAULT in the northeast corner, another along the Wylie Moun­ The East Baylor fault, like the East Diablo fault, tains in the southeast corner (pis. 1, 15). forms a boundary between bedrock of the mountains The part of the Delaware Mountains in the northeast and unconsolidated deposits of the Salt Basin. It fol­ corner of the map area is a prominent salient that lows the east side of the Baylor Mountains, Beach projects westward into the Salt Basin at about mid- Mountain, Threemile Mountain, and the Carrizo length in the range (fig. 8). Bedrock ends toward the Mountains for a distance of about 20 miles, probably basin along a remarkably even baseline, strikingly terminating a few miles south of the edge of the map shown on air photographs, different parts of which area near the line of the Southern Pacific railroad. trend northward, northeastward, and west-northwest­ Unlike the East Diablo fault, its course is nearly ward. Behind the base line the mountains rise 1,500 straight in a north-northeasterly direction (pis. 1, 15), feet, and are formed nearly to their tops by poorly although minor irregularities are suggested by recesses resistant thin-bedded black limestone of the Bone in the base line of the adjoining mountains. Spring Formation. The salient was probably upf aulted The East Baylor fault is nowhere exposed, but its relatively late in geologic time. presence is indicated by the steep faces of the adjoining In a canyon about a mile south of the north end of mountains; the Baylor Mountains rise nearly as high the salient (sec. 9, Block 65, Twp. 4), where the faulted above the Salt Basin, and with nearly as even a base contact between the black limestone of the mountains line, as the Sierra Diablo along the East Diablo fault. and the f anglomerate of the basin is well exposed, the Moreover, some miles out in the basin southeast of the fault surface is nearly vertical and is followed by a zone Baylor Mountains (sec. 25, Block 65, Twp. 7) is an iso­ of calcite 5 feet wide, containing angular fragments of lated flat-topped hill, composed of Hueco Limestone black limestone. Stratification in the adjacent bedrock that stands at least 1,200 feet lower than in the moun­ is nearly horizontal and shows little indication of in­ tains (pis. 1, 15; section /-/', pi. 16). Although the ternal disturbance. rock spurs along the fault terminate on an even line, South of the salient, downfaulted bedrock forms low they are variously indented by the heads of alluvial hills at the foot of the high scarp and is tilted toward fans, and there are large reentrants where Sulphur the Salt Basin, although it may be faulted beneath the Creek and Hackberry Creek enter the Salt Basin. alluvium farther out. Nevertheless, some late faulting may have occurred in The Wylie Mountains, part of which form the south­ places. In the northeastern Baylor Mountains narrow east corner of the map area (pis. 1, 15), are bordered pediments at the base of the scarp are slightly higher on the west by the West Wylie fault, which has been than adjacent alluvial deposits on the east; farther discussed by Baker (192T, p. 42; 1928, p. 370-371), south the wide pediment cut on Van Horn Sandstone Hay-Eoe (1957), and others. East of the fault is an near Hackberry Creek terminates in a scarp about 25 escarpment about 1,200 feet high, at whose base the feet high along the edge of the Salt Basin. Precambrian Carrizo Mountain Formation emerges TECTONICS 111 from beneath the Hueco Limestone. West of the fault, thrown northward, and major west-northwesterly toward a southern arm of the Salt Basin drained by faults in the southern part are downthrown southward, Wildhorse Creek, are hills of downfaulted west-tilted perhaps on opposite flanks of the area of maximum up­ Hueco Limestone, partly separated by alluvium. Hay- heaval during the main period of block faulting. By Roe (1957) estimates that displacement of the Hueco contrast, all the earlier faults and flexures along the Limestone on the West Wylie fault is about 480 feet. same trend were downthrown northward, away from a The north side of the Wylie Mountains, facing the positive area on the south. main part of the Salt Basin, forms a moderately Toward the east in the Baylor Mountains and Beach straight front, much frayed by erosion and indented by Mountain, the west-northwesterly faults give place to alluvial valleys. It may be bordered beneath the adja­ faults trending northeastward and northwestward, cent alluvium by a fault of nearly east-west trend, as which variously offset or intersect each other. These suggested on figure 8. However, the throw of this pre­ trends are also reflected in the joint pattern (pi. 15). sumed fault cannot be great, as limestone was pene­ Evidently this expresses a fundamental change in the trated above a depth of 950 feet in two wells drilled fracture pattern from that in the Sierra Diablo, as about 4 miles north of the mountains and 8 miles east- many of the west-northwesterly faults of that area northeast of Van Horn (sec. 19, Block 63) (Leonard A. curve eastward into northeasterly or northwesterly Wood, written commun., 1959). faults.

FAULTS AND RELATED STRUCTURES WITHIN THE NORTHERN PART OF SIERRA DIABLO MOUNTAINS The northern half of the Sierra Diablo, north of the Many parts of the interiors of the mountains are Victorio flexure, is formed of a thick mass of Permian faulted. Faulting is greatest in the mountain salients, carbonate rocks, with the Victorio Peak Limestone at especially in the northeast corners of the Sierra Diablo the top. Even-crested ridge summits on this limestone and Baylor Mountains, where the rocks are split into are remnants of an exhumed surface on which Creta­ narrow parallel fault blocks. Elsewhere near the ceous rocks were once deposited, from which can be mountain borders in the Baylor Mountains and Beach reconstructed a half dome that was produced by warp­ Mountain, the rocks are broken into rectangular blocks, ing after Cretaceous time. The summits rise from an bounded by faults trending in various directions. The altitude of 5,000 feet on the west and southwest to southern part of the Sierra Diablo is broken into blocks 6,638 feet at the apex near the North Diablo triangu- several miles wide along parallel faults which die out lation station in the northeastern part of the mountains. westward, but the northern part is less broken. The remainder of the dome beyond, if it ever existed, is The faults in the interiors of the mountains had less now broken off along the North Diablo and East Diablo direct influence on shaping the topography than the faults. Permian rocks of the half dome are warped in faults along the borders. Many of the interior faults the same manner as the summits, and the warping prob­ are followed by scarps on their upthrown sides, but ably influenced the configuration of the top of the Pre- these scarps are resequent fault-line scarps formed of cambrian. (See structure contours, pi. 15). Creta­ resistant limestones and caused by removal of weak ceous rocks form widely spaced outcrops down the slope beds from the downthrown sides by differential erosion. of the half dome on the west, and may underlie the Moreover, along a few faults where rocks on the up- alluvium-covered trough which separates it from the thrown sides are weaker, obsequent fault-line scarps Victorio flexure on the southwest. have formed on resistant rocks on the downthrown sides. Most of the half dome is little broken, but it is crossed Probably the faults in the interiors of the mountains by widely spaced faults of small displacement (section participated in the main epoch of faulting in late Ter­ F-F', pi. 16), trending west-northwestward and down- tiary time, but they were largely inactive later, when thrown to the north, and by prominent joints trending there was further displacement on the faults along the west-northwestward and north-northeastward (pi. 15). mountain borders. Some of the faults are prominently exposed on the walls Most of the faults in the interior of the Sierra Diablo of Apache Canyon (pi. 11), where they stand nearly trend west-northwestward. Indications of earlier vertical; but elsewhere they are expressed by faint movements on the west-northwesterly faults, discussed scarps or alined topographic sags and are less easy to above, and the prominence of joints of the same trend trace on-the ground than on air photographs. The suggest that these faults formed by reactivation of a longest fault zone extends 12 miles east-southeastward long-persistent grain. Minor west-northwesterly faults across the mountains to the north rim of Victorio Oan- in the northern part of the Sierra Diablo are down- yon, where it fades out before reaching the edge of the 112 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS mountains in an area of pervasive jointing (pis. 1, 15). by the exhumed pre-Cretaceous surface, on which a few Weathering along the joints causes a remarkable flut­ outliers of Cretaceous rocks are preserved. Toward the ing in the cliffs of Victorio Peak Limestone north of west, however, broad flexures and folds in the Creta­ Viotorio Canyon. ceous rocks follow the same trend (pis. 1, 15) and con­ A small tract in the salient of the Sierra Diablo east tinue beyond the map area (fig. 8). of Apache Peak has a much more complex structure The faults of the southern part of the Sierra Diablo than the rest of the northern part of the Sierra Diablo. involve mainly the Hueco Limestone, which forms ma­ Here, Permian and earlier Paleozoic rocks are broken turely dissected scarps on their upthrown sides, the by as many as six faults in a breadth of a mile or less, height of some of which nearly equals the fault dis­ most of which trend northwestward but with a few ait placement. Along a few of the faults Cretaceous rocks right angles. They are downthrown alternately north­ are preserved on the downthrown sides. These may eastward and southwestward to create narrow inter­ have covered much of the Sierra Diablo region at the vening horsts and grabens (section E-E'', pi. 16). The time of the faulting, but were afterwards largely re­ faulted tract is bordered on the northeast and east by moved by erosion to produce resequent fault-line scarps the North Diablo and East Diablo faults, at the edge in the limestone. Dissection of the scarps is enhanced of the Salt Basin, and is separated from the main part where formations beneath the Hueco emerge especially of the Sierra Diablo on the southwest by a large north­ the poorly resistant red sandstone of the Hazel Forma­ westward-trending fault along which the rocks are tion. Where the red sandstone is exposed, the scarps downthrown as much as 500 feet northeastward. are irregularly frayed and in places have retreated a Location of the tract in a salient between the North mile or more from the faults. Diablo and East Diablo faults suggests that it was The faults are named, from north to south, the Bat broken during displacement of these faults, perhaps Cave fault, Cox Mountain fault, Sulphur Creek fault, rather late in geologic time. The only direct indication Sheep Peak fault, Circle Ranch fault zone, and South of late displacements in the tract is the offsetting of Diablo fault. Each fault originates near the eastern f elsite sills which lie at the same stratigraphic position border of the mountain block and dies out westward in in adjacent fault blocks. The sills are probably of plateau country beyond the mountains (pis. 1, 15). Tertiary age and were injected late in the history of The Cox Mountain and South Diablo faults extend 20 the adjacent Marble Canyon-Mine Canyon intrusive miles across the map area and the latter continues at complex. (See section, "Igneous rocks," p. 92.) least 10 miles farther west, but the other faults are

SOUTHERN PART OF SIERRA DIABLO shorter. The Cox Mountain, Sheep Peak, and South Diablo faults are displaced more than a thousand feet In the southern half of the Sierra Diablo, south of in places, but most of the others were displaced a few the Victorio flexure, Hueco Limestone at the base of the hundred feet or less (pi. 16). Permian sequence forms the country rock over extensive Long segments of the faults have nearly straight or areas and Precambrian and Precambrian (?) rocks, gently curved traces, but the Sheep Peak and Sulphur mainly sandstones of the Hazel and Van Horn Forma­ Creek faults branch eastward. The Circle Ranch fault tions, lie near the surface. Structurally the southern zone is not a continuous line of displacement, but con­ half of the Sierra Diablo differs much from the north­ sists of many minor faults, lying partly parallel, partly ern, being a succession of north-tilted blocks several en echelon or branched, which separate two blocks that miles broad trending west-northwest and downthrown are less disturbed. The South Diablo fault, although a to the south (pis. 1,15,16). zone of continuous major displacement, consists of many On the Victorio flexure between the two halves of the segments of slightly different trend from which minor Sierra Diablo, Permian rocks are tilted northward. The faults branch eastward on each side. flexed Permian rocks may overlie a larger fault or flex­ Toward the east the faults pass from the Hueco Lime­ ure beneath (fig. 2; section N-N', pi. 16), which sepa­ stone into the homogeneous red sandstone of the Hazel rates an area of high-standing Precambrian rocks on Formation, where their courses are difficult to trace on the south from one of low-standing Precambrian rocks the ground. The Bat Cave and Cox Mountain faults on the north. (See structure contours, pi. 15.) Unlike may abut the East Diablo fault at the edge of the moun­ the other structures of the southern half of the Sierra tain block at nearly right angles, but the junctions are Diablo, the flexure is largely a pre-Cretaceous feature. covered by alluvium. The Sulphur Creek fault is read­ (See p. 105-106.) Although it trends in the same direc­ ily traceable on air photographs through the red sand­ tion as the faults farther south, it is not faulted. stone to an acute-angled junction with the south end of Toward the east its tilted Permian rocks are truncated the East Diablo fault between Beach Mountain and the TECTONICS 113 Baylor Mountains. The Sheep Peak, Circle Ranch, and more steeply northward, probably along an eastward South Diablo faults appear from air photographs to extension of the Victorio flexure. die out in the red sandstone within short distances east The rocks of the interior of the Baylor Mountains are of the scarps of Hueco Limestone, but other faults of greatly faulted on the northeastern and southeastern similar trend, lying en echelon, continue into Beach sides, where many narrow blocks have been down- Mountain (pis. 1,15). dropped away from a less disturbed nucleus in the west- Westward, all the faults except the South Diablo fault central part. As in the greatly faulted northeastern lose displacement and die out within the map area, but salient of the Sierra Diablo, these blocks seemingly the disturbance on some is extended a short distance broke away from the more stable mountain area during farther by flexures or folds. An abrupt flexure con­ displacement of the major faults on the northern and tinues 2 miles beyond the end of the Sheep Peak fault, eastern sides of the mountains. and a broad anticline occurs at the end of the Cox Moun­ The internal faults are of two systems, one in the tain fault. northeastern part which trends northwest, the other in The planes of all the faults dip steeply, where visible. the southeastern part which trends northeast. Those in A steep dip toward the downthrow was observed on the the northeastern part are a quarter of a mile to a mile Sheep Peak fault south of Sheep Peak and on the South apart, but branch or interlace. Most are downthrown Diablo fault north of the Keen Eanch. Similar steep toward the northeast, dropping the intervening blocks dips may be inferred where the Bat Cave, Cox Moun­ toward the salient of the mountains (section $-/S", pi. tain, and Sulphur Creek faults cross the cliffs of Hueco 16). The traces of the faults across steep hills indicate Limestone on the east-facing escarpment of the Sierra that they stand nearly vertical. One of the longer Diablo. However, a fault on the^xtension of the Sheep faults near the center of the mountains extends north­ Peak fault, where exposed in a Hueco Limestone cliff westward to the East Diablo fault, where it apparently ly^ miles west of the Hazel mine, dips 60° N. toward matches a fault of west-northwest trend on the Sierra the upthrown block. In a few places, as on the Cox Diablo escarpment to the west. Exposures are insuffi­ Mountain fault west of the Pecos mine and the Sheep cient to determine the exact relations of the two faults Peak fault west of Sheep Peak, calcite veins occur in to each other, or to the East Diablo fault. The faults the Hueco Limestone at or near the fault planes. The in the southeastern part are fewer. One pair, with a veins contain limonite and hematite, perhaps weathered curvature convex toward the southeast, bounds a narrow from original sulfide minerals. Where the faults in­ outlying block of Montoya Dolomite, and another set volve Hueco Limestone and Cretaceous formations, these extends discontinuously along Eed Tank Canyon. On rocks are dragged steeply on the downthrown sides, one of the faults in Eed Tank Canyon a small remnant whereas the rocks on the upthrown sides are little dis­ of Cretaceous sandstone is preserved on the downthrown turbed. In some places, as on faults of the Circle side. The faults of the two trends intersect near Eed Eanch zone southeast of the Circle Eanch, displacement Tank Canyon on the eastern side of the mountains, by drag is greater than on the fault itself. where many of the northwest-trending faults abut the northeast-trending faults. BAYLOR MOUNTAINS BEACH MOUNTAIN AND VICINITY The Baylor Mountains form an irregular quadrilat­ Beach Mountain, which borders the Salt Basin south eral block 9 miles long and 7 miles wide, implanted in of the Baylor Mountains, is a smaller mass which pro­ the southern bight of the East Diablo fault. Their jects as high as or higher than the latter (pi. 2). Un­ summits are about a thousand feet lower than those of like the Baylor Mountains it is formed largely of Ordo- the Sierra Diablo on the west and about a thousand feet vician carbonate rocks. It is an erosion remnant rather higher than the floor of the Salt Basin on the east and than a fault block and is not structurally separated from north. The mountains are bordered on all sides by the main block of the Sierra Diablo on the west. Like faults the East Diablo, North Baylor, and East Bay­ the Baylor Mountains it is much broken internally by lor faults and are a block that stands at an inter­ two systems of faults trending nearly at right angles mediate level between the heights of the Sierra Diablo (pis. 1,15). and the depths of the Salt Basin. They consist of a One system includes the Grapevine and Carrizo plate of Permian rocks, whose foundation of earlier Spring faults (sections R-R' and S-Sf, pi. 16). Faults Paleozoic rocks crops out around the edges (pi. 1). of the system originate in the Precambrian rocks west The Permian rocks are flat lying or gently tilted, except of Beach Mountain, where they trend west-northwest at the northeast corner of the mountains where they dip or west, but in the mountain they curve into east-north- 114 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS eastward or northeastward courses. The traces of the Carrizo Mountain Formation and associated igneous faults across the steep western face of the mountain indi­ rocks on the southern upthrown side. The valley which cate that they stand nearly vertical. In Beach Moun­ has been eroded south of the scarp is followed by the tain the faults involve Ordovician formations and Hueco line of the Texas and Pacific Railway in its course Limestone and were probably displaced during late through the Carrizo Mountains from the Salt Basin to Tertiary time, but the Grapevine fault and perhaps the Eagle Flat. A major displacement on the fault oc­ Carrizo Spring fault had a considerable prior history. curred after Cretaceous time, perhaps during the late (See p. 103.) On the Grapevine fault deformed Hazel Tertiary, but erosional features along it indicate that Formation was offset with left-lateral strike-slip dis­ it has been inactive since. placement, probably during late Precambrian time, and An earlier movement on the Hillside fault is indi­ the Van Horn Sandstone was downthrown to the south cated by the Powwow Member at the base of the Hueco before Bliss time. Limestone north of the fault, in which fragments of The faults of the second system, like those of the first, metarhyolite derived from south of the fault increase seemingly originate toward the west in the west-north­ in size and abundance toward it. Presumably newly up- westerly system of the Sierra Diablo, but in Beach faulted metarhyolite projected as a scarp along the fault Mountain they curve into northwestward or north- at the time of deposition of the Powwow Member (fig. northwestward courses. This is shown most clearly by 2). These relations show further that no significant a branch of the Sulphur Creek fault which curves south- strike-slip displacement could have occurred along the wUrd into the northern part of Beach Mountain, where fault during or since Hueco time, for the fragments in a thick sequence of El Paso and Montoya Formations the Powwow Member on the northern side match rocks is preserved on its downthrown eastern side (lower in place on the immediately adjacent southern side. view, pi. 2). Like faults of the first system, some of The Hillside fault forms the southern boundary of those of the second were displaced before late Tertiary the thick bodies of Van Horn Sandstone in the Sierra time. The Van Horn Sandstone was downthrown to Diablo region (pi. 1), and to the south the Powwow the east along the Dallas fault before Bliss time and the Member of the Hueco Limestone generally lies on the fault was not displaced again later (see p. 102-103), yet Carrizo Mountain Formation and associated igneous it is parallel to others of the same trend which displace rocks. The boundary is not absolute, however, as a few Ordovician formations and the Hueco Limestone. thin remnants of Van Horn are preserved south of the The two fault systems meet complexly in the east- fault along the eastern side of the Carrizo Mountains. central part of Beach Mountain (pis. 1, 15). Faults Toward the western end of the Hillside fault near trending north-northwest terminate against the Grape­ the Gifford-Hill rock crusher (sec. 28, Block 67, Twp. vine fault, but the Carrizo Spring fault terminates east­ 8), Cretaceous formations are downthrown northward ward against a fault of north-northwest trend. The against metarhyolite, and the displacement probably Hueco Limestone at the east end of the mountain (sec­ much exceeds 1,000 feet (section T-T1', pi. 16). Equal­ tion J-J', pi. 16) is preserved in a block that is bounded ly great displacement must have occurred several miles on the west and north by faults of the two intersecting farther east (sec. 16, Block 66, Twp. 9) where Hueco systems. Limestone, lying on Van Horn Sandstone and topped HILLSIDE FAULT AND RELATED STRUCTURES by a Cretaceous outlier, forms a high scarp north of The Hillside fault forms a major line of discontinuity the fault (section Q-Q'', pi. 16). Flawn (in King, P. in the southern part of the map area, between the Car­ B., and Flawn, P. T., 1953, p. 115) reports that on the rizo Mountain Formation and associated igneous rocks south side of the fault a mile east of the rock crusher, on the south and the Van Horn Sandstone, Hueco Lime­ a small patch of Powwow Member of the Hueco Lime­ stone, and Cretaceous formations on the north. It ex­ stone lies on metarhyolite, indicating not only that part tends west-northwest along the northern side of the of the displacement occured before Hueco time, but Carrizo Mountains for a known distance of 8 miles, ter­ that the post-Hueco displacement is less than at nearby minating eastward against the East Baylor fault near localities; however, the patch of Powwow may lie in Van Horn and disappearing westward beneath the allu­ a wedge that was displaced less than the main fault vium of Eagle Flat near Allamoore (pis. 1, 15). block to the south. Through most of its course the Hillside fault is fol­ The surface of the Hillside fault, or rocks close to it, lowed on its northern downthrown side by a prominent is exposed at several places in the segment extending escarpment of Hueco Limestone and Cretaceous forma­ 2 miles east from the rock crusher. In the easternmost tions as much as 500 feet high. This is an obsequent exposure, metarhyolite is separated from the Van Horn fault-line scarp, formed by more rapid erosion of the Sandstone by a nearly vertical zone of brecciated quartz TECTONICS 115 along the fault plane, the Van Horn to the north being during or since Hueco time. There is no indication of bleached and closely jointed. Farther west the metar- an extension of the Hillside fault zone west of the hyolite close to the fault contains several steeply dip­ Streemwitz Hills or east of Wylie Mountains. Neither ping zones of breccia, which crop out in wall-like ridges. in the gap between Sierra Blanca and the Quitman One zone dips 70° S., but may follow the foliation Mountains on the west; nor between the Apache Moun­ planes of the metarhyolite, rather than the fault plane. tains and Davis Mountains on the east does the struc­ In this vicinity fragments in the Powwow Member ture permit the existence of a throughgoing strike-slip north of the fault have been shattered by later de­ fault. The folds and faults in the Mesozoic rocks south formation. of Sierra Blanca are part of the Chihuahua tectonic North of the Hillside fault in the eastern half of its belt, a regional feature that extends far south westward trace, the Hueco Limestone and adjacent Van Horn and southeastward from the Hillside fault. Left-lat­ Sandstone are broken by four or five minor eral strike-slip displacements have been observed on faults trending north-northwest, the western group of minor faults in the Precambrian rocks north of the which extends nearly across the Ked Valley to the Car- Hillside fault (see p. 102-103), but there is no indica­ rizo Spring fault. In an exposure of one of the west­ tion that these faults were displaced in this manner ern minor faults, its surface dips 80° E., toward the after Precambrian time. downthrow. The minor faults reflect a pervasive frac­ JOINTS turing of the block north of the fault along the same The writer made systematic observations on the joints trend, as shown by abundant joints in the Hueco Lime­ in the Sierra Diablo region, similar to those made ear­ stone and Van Horn Sandstone which also trend north- lier in the southern Guadalupe Mountains (King, P. B., northwest (pi. 15). 1948, p. 114-117, pi. 20). Summaries of the joints iii The Hillside fault may be part of a zone of faulting the Sierra Diablo region have been published previ­ which extends somewhat farther east and west. It is ously (King, P. B., and Knight, J. B., 1944, structure nearly in line with the north side of the Wylie Moun­ map; King, P. B,., and Flawii, P. T., 1953 pi. 10), but tains across the Salt Basin to the east, which may be further details are given here (pi. 15). bordered beneath the alluvium by a minor fault, like­ All the rocks of the Sierra Diablo region are cut by wise downthrown to the north (fig. 8). About 10 miles many joints. Those in the greatly deformed Precam­ west of the known terminus of the Hillside fault, along brian formations trend in diverse directions, dip at all the southern edge of the Streemwitz Hills, are ridges angles from horizontal to vertical, and are so complex and knobs of Hueco Limestone, tilted southward, that it was not considered worth the effort to record or which may lie in a fault zone between the hills and the analyze them. Those in the younger gently dipping tectonic depression of Eagle Flat (sections K-K', pi. stratified rocks the Van Horn Sandstone, the Paleo'- 16). This fault zone may continue farther east and zoic formations, and the Cretaceous formations dip west, but relations are concealed beneath the alluvial steeply and are arranged in systematic patterns that are plains along the north side of the flat. The inferred susceptible of measurement and study. Steeply dip­ fault zone has about the same trend as the Hillside ping joints also occur in the gently tilted parts of the fault, but is downthrown southward, in the opposite Hazel Formation, along with other joints inclined at direction. lower angles, and some of these are recorded 011 the The Hillside fault lias been ascribed an inordinate map (pi. 15). role in the tectonics of the region by Moody and Hill Most of the steeply dipping joints in all the strati­ (1956, p. 1223-1224), who interpret it as a major ele­ fied formations are straight and smooth, even where ment in the "Texas lineament" (Kaiisome, 1915, p. 295; they cut through irregularly bedded rocks or alterna­ Baker, 1935a, p. 211-214; Albritton and Smith, 1957), tions of hard and soft strata. At the surface some extending westward through the gap between Sierra Blanca and the Quitman Mountains (fig. 1), and per­ of the joints are open fissures, but these probably were haps past the south end of the Franklin Mountains near enlarged by weathering, and most of them narrow and El Paso. They believe that it "represents a large-scale tighten at depth. Single joints commonly extend across left-lateral wrench fault" and that the structures in the the entire breadth of any exposure, and where several Mesozoic rocks south of Sierra Blanca are "second- sets occur, most of them, cross one another without de­ order drag folds relative to this wrench." flection. Spacing of the joints depends on the nature This interpretation is not supported by local geologic of the rock; they are widely spaced in massive rocks, relations. The composition of the Powwow Member such as the Van Horn and Cox Sandstones, and are north of the Hillside fault indicates that no significant closely spaced in thin-bedded brittle rocks, such as the strike-slip movement could have occurred on the fault Ordovician and Permian limestones and dolomites. 116 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Nearly all the joints dip steeply or stand nearly ver­ averages. Each figure used in plotting the rosettes is tical. During the field investigation, conspicuous de­ thus the average of the original percentage for the viations of the joints from the vertical were recorded, direction shown, and the percentage of the two direc­ but it was found that such deviations were so slight tions lying 5° on each side of it. To indicate the amount that they could be ignored. The most significant fea­ of information available for each unit summarized, the tures of the joints appear to be their trends in hori­ number of stations and number of observations used zontal plan, and the largest number of observations are marked by the different rosettes. were made on these trends. On the map (pi. 15) the Observations on the trends of the joints are of inter­ trends of joints are summarized by two methods: est, for they amplify and fill in the fracture pattern of 1. Joints at individual stations are shown by lines of the rocks which is otherwise only partly suggested by various lengths, radiating from the point of observa­ the fault pattern. tion. Records made at the stations commonly consisted In the fault block formed by the Sierra Diablo and of measurements at two or more points in the immediate its foothills to the north and south, the dominant joints vicinity, at each of which all joints were recorded, and trend west-northwest, parallel to the west-northwest- notations were made of the dip and prominence of each; trending faults and flexures of the same area. These observations at a station may include as many as 20 joints dominate, not only near the faults and flexures, individual measurements. It is impossible to represent but also where the rocks are otherwise little disturbed. all these measurements on the map (pi. 15); joints at The next most abundant joints, in places of nearly equal each station are accordingly summarized, the most abun­ magnitude, trend nearly at right angles to the north- dant four or five joint sets being plotted, with lengths northeast. Ordinarily, these joints are not followed by of lines indicating their relative prominence. Besides any faults, suggesting some fundamental difference in the joints which were measured on the ground, joints their nature. The remaining joints trend in all direc­ which are prominent in air photographs are also indi­ tions between those of the dominant sets, but in many of cated. the units summarized two maxima are indicated on the 2. Joints are further summarized statistically by rosettes that are about midway between the trends of rosettes, which are overprinted at various places on the the two dominant sets. A striking feature in the Sierra map (pi. 15). For purposes of summary the observa­ Diablo block is the subordination of joints trending tions are grouped according to tectonic units of differ­ northward parallel to the faults of northerly trend ent ages and according to locality. Separate statis­ which border the range. As shown on the map (pi. 15), tical summaries were made for joints of the Van Horn some north-trending joints are recorded close to the East Sandstone, the Ordovician to Pennsylvanian rocks, the Diablo fault, but their number is insufficient to influence Permian rocks, and the Cretaceous rocks, each rock significantly the form of the rosettes. group representing a tectonic unit separated from the Eastward in the Baylor Mountains and Beach Moun­ others by a significant structural unconformity. Oc­ tain, the joint pattern changes significantly in the same currence of joints in the different tectonic units was manner as the fault pattern. Here, two joint sets of further segregated into structurally significant units nearly equal magnitude trend northeast and northwest, of area, whose boundaries are shown in an inset map in the same directions as the faults. In the Red Valley accompanying plate 15. north of the Hillside fault, where minor faults trend Each rosette shows the relative abundance and prom­ north to north-northwest, a prominent joint set in the inence of the joints of various trends that were meas­ same direction is recorded by the rosettes (pi. 15). ured in each stratigraphic and areal unit. A tally was Subdivision of the recorded joints according to tec­ made of the number of joints in each 5° of arc, and tonic units was made primarily to test the possibility each tally was converted into a percentage of the total of significant differences between jointing in rocks of number recorded. As a check, a tally was also made of different ages, but the results are inconclusive. Al­ the prominence of the different joint sets observed. though there are differences in the patterns of rosettes This tally was found to agree closely with the number in rocks of various ages in the same units of area, these of joints of each set which were observed, indicating seem less likely to be caused by differences in age than that the most abundant joints also tend to be the most by differences in amounts of data, or by differences in prominent joints. As originally worked out, wide vari­ susceptibility to jointing of the rocks themselves. In ations were found between percentages at some of the many areas, for example, the rosette for the Permian adjacent points on the arcs, probably because of a per­ rocks shows many joints in all directions with poorly sonal equation in making the observations. The per­ defined maxima, whereas rosettes for the Van Horn centages were therefore evened by means of moving Sandstone and the Cretaceous rocks show much better TECTONICS 117 defined maxima. This is partly because more observa­ adjoin it, such as the Sierra Diablo. Along the edges tions were made on the extensively exposed Permian of the Salt Basin the latest faults of Pleistocene age are rocks, partly because the Permian carbonate rocks frac­ of northerly trend. In the Guadalupe and Delaware tured more diversely than the dominant sandstones of Mountains the principal northward-trending structure the other two units. The dominant joint trends in rocks is an arch, fractured along its crest by longitudinal of different ages in the same unit areas thus appear to faults and joints (King, P. B., 1948, p. 109), but in the bo nearly alike. Sierra Diablo and adjacent mountains, the principal This suggests that the dominant joint pattern in all structures are fault blocks which have been little arched the rocks might be less closely related to the earlier or flexed. The northward-trending structures of orogenies than it is to the upheaval of the mountain Trans-Pecos Texas and New Mexico are seemingly blocks in late Tertiary and Quaternary time. It seems products of a regional tension, whose axis of least stress unlikely, however, that rocks which have been in proc­ was oriented approximately east and west. ess of accumulation and deformation since Precambrian Along the edges of the Sierra Diablo the northward- time could have remained without fractures until such trending structures break across the west-northwest- a late period. Moreover, evidence so far presented indi­ ward-trending structures, as though these largely cates that faulting and flexing along a west-northwest originated earlier. Within the range the dominant trend has recurred many times in the history of the area. faults and joints trend west-northwest, and northward- It would thus appear that joints related to this trend, trending structures are scantily represented, if at all and perhaps others, formed long before the latest up­ (pi. 15). Nevertheless, west-northwestward-trending heaval, and were renewed in successively younger rocks structures significantly truncate or offset northward- that were laid down unconformably over the older. trending structures in other places, especially in the Apache Mountains east of the Sierra Diablo. Also, the BEGIONAL INTEBPBETATIOET AND SYNTHESIS Salt Basin is peculiarly segmented, apparently by west- The structure of the Sierra Diablo and surrounding northwestward-trending faults that extend short dis­ regions is dominated by a network of faults (pi. 15, tances into the ranges which border it (fig. 8). Each fig. 8) that formed in later Cenozoic time. The faults segment is offset left laterally from the ones on either are a product of the stress pattern which existed at the side, suggesting a possible strike-slip displacement time, and would seem to be capable of mechanical along the west-northwestward-trending faults which analysis on that basis. Such an analysis is made diffi­ bound them. Nevertheless, no such displacements can cult, however, by the extensive prior tectonic history of be observed where these faults enter the adjoining the region. At least part of the faulting resulted from ranges. It seems more likely that the northward-trend­ reactivation of earlier faults and flexures, which were ing structures, during their formation, reactivated an created by forces different from those which prevailed earlier west-northwestward-trending grain, and were during later Cenozoic time. Once created, these earlier modified by it. faults and flexures became zones of weakness which Evidence has been presented (p. 102-103, 105-106, could be utilized afterwards by new forces with new 111-115) that the west-northwestward-trending struc­ orientations. tures were intermittently displaced between late Pre­ The fault network of the region consists principally cambrian and late Cenozoic time. Faults of this trend of two sets of faults and related features, one trending that are of late Precambrian age can be proved with northward, the other west-northwestward, which cross certainty at only a few places, yet the fact that they or intersect in a complex manner (fig. 8). The north­ exist at all suggests that a grain of this trend originated ward-trending set dominates, and may be most closely in the Precambrian basement early in the history of the related to the stresses existing during later Cenozoic region and controlled the structures formed during later time; the west-northwestward-trending set is mainly tectonic episodes, in strata of younger ages laid down subordinate, and may have formed principally by re­ over the basement. Many of the faults of west-north­ activation of earlier zones of weakness. westerly trend that are of late Precambrian age have The northward-trending structures extend far north­ left-lateral strike-slip displacements of a mile or less; westward beyond the Sierra Diablo into New Mexico, but no strike-slip displacement can be proved on faults and perhaps westward into Chihuahua, but they die out of similar trend in the younger rocks, and on some of the southward in Trans-Pecos Texas. Throughout their faults there is evidence against such a displacement. extent they largely control the modern topography, The conglomerate of the Powwow Member of the Hueco attesting the relative recency of their formation. They Limestone on the north side of the Hillside fault was thus outline the Salt Basin and the mountains which derived from a source just south of the fault, and dem- 118 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS onstrates that no strike-slip displacement occurred along left-lateral strike-slip displacement. Albritton and it during Permian time or later. Smith (1957, p. 515) conclude that "after more than Seemingly, then, the forces which caused the subse­ half a century, the idea of the Texas lineament remains quent flexing and faulting of the west-northwestward- in the class of plausible hypothesis." trending structures were of a different kind and orien­ The substance of these proposals seems to be that the tation from those of late Precambrian time, and were alleged lineament forms a zone between more stable and merely guided by the lines of weakness already estab­ less stable parts of the continental crust between a lished. Some of the structures, as those formed during mainly cratonic area on the north, as in the Colorado the pre-Hueco deformation of later Pennsylvanian time, Plateau, and a mobile area on the south, in the southern were products of a mild compressional folding. Suc­ part of the Basin and Range province and the ranges ceeding structures may have been dominantly tensional of Mexico. In places, as in the Transverse Ranges of and the incidental products of dominantly vertical California, the zone contains faults with left-lateral movements that created major positive and negative strike-slip displacement. In others, as in Arizona and areas. During Permian time such vertical movements Trans-Pecos Texas, the zone marks the passage from a differentiated the positive area of the Diablo platform dominantly thrust-faulted terrain on the south to a from the negative area of the Delaware basin on the dominantly block-faulted terrain on the north. More­ northeast; during Cretaceous time similar movements over, the Transverse Ranges of California are alined differentiated the positive area from a geosynclinal area with the lengthy Murray f racture zone of the Pacific on the southwest. Ocean basin on the west, which probably involves a The discussion so far indicates the local causes for the strike-slip displacement of the oceanic crust (Menard, west-northwestward-trending structures. Are they 1955, p. 1164-1167). also a product of more fundamental regional causes, Whether any persistent throughgoing structures exist and are they merely a segment of a large regional fea­ along the lineament in the continental crust is doubtful. ture? Some geologists (Hill, 1902, p. 173; Ransome, Even conceding transverse faults in gaps between the 1915, p. 295; Baker, 1935a, p. 211-214; Moody and Hill, ranges of the southern part of the Basin and Range 1956, p. 1223-1224; Albritton and Smith, 195T) ascribe province, which would now be concealed from detection them to the "Texas lineament," a supposed major struc­ by unconsolidated deposits, no lengthy structures, due ture that is believed to extend across south-centra] to more than local causes, can be proved. No rift fea­ North America from the Pacific to the Gulf Coast. tures comparable to those along active faults with The original definition of this structure by Ransome strike-slip displacement occur east of California. (op. cit.) is of interest: It would therefore appear that the Texas lineament [It] coincides in general with the southwest boundary of the marks rather vaguely a boundary between parts of the Colorado Plateaus and with the valley of the Rio Grande. It is continental crust of North America that have possessed along this general line that the uplifted masses of Paleozoic different degrees of mobility through geologic time, rocks of the Colorado Plateau province, as in the Franklin Mountains near El Paso, look out to the south over the Creta­ that these differences in mobility have influenced the ceous terrain of the Mexican Plateau. Mr. R. T. Hill has called development of varied local structures, such as those of attention to this feature in several of his papers and points out west-northwest trend in the Sierra Diablo region, but that in the Trans-Pecos Region it coincides with a zone of fault­ that the differentiation has not been of sufficient mag­ ing which is older than the north-south faults to which the nitude to produce any throughgoing structures com­ bolder topographic features are due. The entire, rather vaguely defined and perhaps in part imaginary, zone from the Pacific parable to the great faults of California or the fracture to the Gulf of Mexico may be called the Texas lineament. zones of the Pacific Ocean basin.

Subsequent proponents of the Texas lineament do ECONOMIC GEOLOGY not mention Ransome's filial unflattering, but probably just, characterization of this feature. Metallic and nonmetallic mineral deposits of the Baker (1935a, p. 212) extends the Texas lineament Sierra Diablo region are varied. Some of these deposits as described by Ransome "from Point Conception on have yielded or continue to yield profitable production, the Pacific coast of southern California to Cape San and others may be capable of later exploitation; but Roque, the easternmost point of South America, the many are too small or of too low a grade to be of eco­ zone determining the northeastern coast line of South nomic interest. The region has also been extensively America and passing through the island of Cuba"; he drilled with varying success for water, and in a few proposes that it be renamed the "Hill intercontinental places unsuccessfully for oil and gas. Most of these re­ lineament." Moody and Hill (1956, fig. 11) believe sources have been described in various earlier publica­ that the lineament is a zone of "wrench faults" with tions, and are merely summarized here. ECONOMIC GEOLOGY 119 COPPER AND SILVER 6 have been worked in the Blackshaft, St. Elmo, and Vein deposits containing metallic sulfide minerals Sancho Panza mines (pi. 1). Deposits of Blackshaft occur in a number of places in the Precambrian rocks in type are in crushed, sheared, and silicified limestone, the eastern part of the foothills of the Sierra Diablo, phyllite, and igneous rock of the Allamoore Formation, and to a lesser extent in the Carrizo Mountains. Ore has and in associated fault gouge, which together form a been produced intermittently from several mines since bed a few feet thick along a low-angle thrust fault, en­ 1880, and the veins in other places have been explored closed by the Hazel Formation. The bed is folded into by many prospects. The principal metals of the de­ an irregular east-plunging syncline, so that it dips posits are copper and silver, but some deposits also con­ steeply in the southeastern part and very gently in the tain zinc and lead. Some rich pockets of ore were dis­ northwestern part, where it crops out over a wide area covered during the early days of mining, but most of and is susceptible to opencut mining. The crushed and the ores of the district are of low grade, averaging about sheared rock of the Allamoore Formation has been 21^3 to 3 percent of copper. veined and replaced by gangue minerals and metallic The most prolific mine in the district is the Hazel, sulfides, principally of copper, although there are scat­ which lies near the foot of the Sierra Diablo 10 miles tered rich silver-bearing pockets. northwest of Van Horn (sec. 14, Block 66, Twp. 7). It 3. Other deposits have been prospected in the Alla­ is one of the oldest mines in Texas, and the largest pro- moore Formation of the Millican Hills and the Carrizo ucer of copper in the State. Moderate amounts of ore Mountain Formation of the Carrizo Mountains. In the have also been produced from the Blackshaft and workings of all these prospects mineralization seems to Sancho Panza mines a few miles to the southwest, but have taken place in narrow unsystematic veins and vein- production from the remaining mines and prospects has lets, with little replacement of limestone or other host been much less. Total production of the district is dif­ rocks. Prospecting so far has failed to yield any ficult to estimate because records are fragmentary, and sizable ore bodies, and no ore is known to have been are generally lacking for the period before 1900. A produced from the deposits. possible 'approximation is 140,000 tons of ore, yielding 4. Another type of deposit occurs only at the Dallas 2,700,000 pounds of copper and 4,000,000 ounces of mine on the west side of Beach Mountain (pi. 1). Here, silver. a fault of pre-Ordovician (pre-Bliss) age has thrown The copper and silver deposits occur in four principal the Van Horn Sandstone down against the Allamoore associations, of which only two have yielded production: Formation, and the limestone of the Allamoore adjacent 1. Deposits of Hazel type lie in the northern part of to the fault has been veined and mineralized. No ore the district, near the foot of the scarps of the south­ is known to have been produced from this deposit. eastern angle of the Sierra Diablo. These deposits are Although these deposits occur in varied structural in vertical fissure veins or mineralized fractures, lying situations, the deposits themselves are of such a similar in gently dipping compact red sandstone of the Hazel makeup as to suggest that they all formed from a com­ Formation. The veins are commonly indicated in sur­ mon cause at the same time. The deposits are domi- face outcrops by bleaching of the red sandstones im­ nantly in Precambrian rocks, and similar deposits are mediately adjacent. They consist of zones a few feet only scantily developed in the adjacent Paleozoic and to 40 feet wide of bleached, brecciated, and sliced coun­ Cretaceous rocks. In all the deposits, narrow previ­ try rock, interlaced with a gangue of barite and other ously formed zones of weakness in the country rock minerals, which contain sulfides of copper, silver, and were later veined and replaced by gangue and metallic other metals. The deposits of Hazel type are not hap­ minerals brought in by hydrothermal solutions. The hazardly located, but occur along two fracture zones. zones of weakness in the Blackshaft type of deposits The Hazel fracture zone, about &y2 miles in length, were formed during Precambrian time; those of the trends nearly east and west and contains deposits of the Dallas mine originated between Precambrian (?) and Hazel mine, Marvin-Judson prospect, and Mohawk Ordovician time; the age of the zones of weakness of mine (pis. 1, 15). The Pecos fracture zone, about 2 the Hazel type of deposits is unknown. miles in length, trends north-northeast and contains the Regional considerations suggest that the metallic ore deposits of the Pecos mine and Eureka prospect. deposits of the district were emplaced hi the zones of 2. Deposits of Blackshaft type occur in a belt about weakness during Tertiary time. Paleozoic and Cre­ iy2 miles long just north of the Millican Hills, and taceous rocks contain mineral deposits in the Eagle and Quitman Mountains not far to the southwest in Trans- "See King, P. B., and Flawn, P. T. (1953, p. 149-168), which con­ Pecos Texas, and similar deposits are widely distributed tains detailed descriptions of the mines and prospects and references to earlier publications. in adjacent parts of Chihuahua and New Mexico. 120 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Tertiary intrusive and volcanic rocks are also common Flawn, P. T., 1953, pis. 2, 3). The phyllite units are throughout the region. The ore deposits in the district generally less than 100 feet thick, but are as much, as may be principally in the Precambrian rocks, not be­ 300 feet thick in places; individual units vary in thick­ cause the deposits are old, but because the Precambrian ness along the strike as a result of crumpling and flow- rocks were lower and nearer the source of hydrothermal age of the incompetent rock. The amount of talc in solutions, and because the Precambrian rocks have been the units varies from place to place. The mineral may much more deformed and fractured than the Paleozoic have formed from an original fine-grained magnesium- and later rocks which overlie them. bearing tuff or marl. Carbonate rocks adjacent to the phyllite units contain little magnesium, and are mainly TUNGSTEN AND BERYLLIUM limestone rather than dolomite, but dolomite forms in­ The Mine Canyon stock in the northeastern part of clusions in the talc bodies. Large masses of pure the Sierra Diablo (sec. 20, Block 66, Twp. 5) has been ceramic-grade foliated to fibrous talc as much as 150 sporadically prospected for many years for tungsten feet thick occur in places, but in others the talc bodies and other metals. The most extensive work was done contain layers or irregular masses of chert and carbon­ in 1940 and 1941, by William Eossman of Pecos, Tex., ate rock. who put more than a thousand feet of adits and shafts Six companies are operating in the district, and into the slopes of Cave Peak. through 1958 these had produced a total of 120,000 tons The light rhyolite breccia of the stock has been some­ of talc; in 1960 they produced 60,000 tons. In 1960 a what mineralized throughout, as indicated by extensive processing mill was installed at Allamoore. About 90 iron staining of weathered surfaces. Most of the intro­ percent of the talc produced in the district is sold for duced minerals occur in narrow veinlets which trend ceramic purposes and is used for manufacture of wall westward, northwestward, and northward; the veinlets tile, the remainder being marketed as an insecticide are 3 inches or less thick, and fray out into joints within carrier. 50 or 100 feet along the strike. According to S. G. CRUSHED STONE 8 Lasky (written commun., 1941), the dominant mineral Crushed stone is produced by Gifford-Hill Co. of is pyrite, but there is also chalcopyrite, fluorite, and Dallas, Texas, at its Holley plant 2^ miles east of Alla­ huebnerite (iron-manganese tungstate); in addition, moore (sec. 27, Block 67, Twp. 8). The plant and work­ Richardson (1914, p. 9) reports the presence of wolf- ings are in the northwestern part of the Carrizo Moun­ framite. None of the outcrops or workings on Cave tains just southwest of the Texas and Pacific Eailway, Peak show sufficient quantities of tungsten minerals to between the railroad and U.S. Highway 80. The plant make the deposit of economic interest. was opened in 1926, and has been in nearly continuous In 1948 the outcrops and workings on Cave Peak operation since that date. were sampled for beryllium by W. T. Holser, as part The stone used for crushing is the metarhyolite that of an investigation of nonpegmatitic occurrences of this intrudes the Carrizo Mountain Formation. In the metal in the United States (Warner and others, 1959, workings this is pink or reddish, siliceous, and consid­ p. 140-143). Analyses of samples indicate that the erably more massive and blocky than elsewhere in the veinlets and rocks adjoining them in places contain as area. As elsewhere, it contains broken and elongated much as 0.1 percent BeO, but mostly much less, and phenocrysts of quartz and feldspar, and some layering, that none occurs in the other rocks of the area. defined by different colors and varying composition, but TALC ^ the rock does not split readily along the layering. Large reserves of metarhyolite remain in the neighbor­ Talc was discovered in the Allamoore Formation hood, although most of it is more foliated, and hence south of the Sierra Diablo in 1952, and has since been more slabby and less massive than that which is now mined and prospected in the Streeruwitz, Bean, and quarried. Millican Hills and on Tumbledown Mountain, for a The crushed metarhyolite has been used to ballast the distance along the strike of 17 miles. line of the Texas and Pacific Eailway between Dallas The talc occurs in phyllite units that are interbedded and Sierra Blanca, and has also been used to a more with the limestone and volcanic units of the formation. limited extent in highway construction. On the geologic map (pi. 1) the phyllite units are grouped with the limestone units, but they were shown MARBLE AND BRUCITE separately in an earlier publication (King, P. B., and In the Sierra Diablo region, marble occurs sporadi­ cally in limestone units of the Precambrian Allamoore 7 See King, P. B., and Flawn, P. T., (1953, p. 170-172) and Flawn (1958, p.104-105). See King, P. B., and Flawn, P. T., (1963, p. 172-173). ECONOMIC GEOLOGY 121 Formation, but its main occurrence is in the Permian tion of ground water in the region have been summarized Hueco Limestone in contact metamorphic zones adja­ by Eichardson (1914, p. 9). Eichardson (1914; 1904, cent to igneous intrusives of Tertiary age. A zone of p. 89-95) and Baker (1935b, p. 373-380) have reported marble in the Hueco, 200-400 feet wide, encircles the on the earlier results of drilling for water. Later re­ Marble Canyon stock, and a slightly narrower zone ex­ sults of drilling have been investigated by the Texas tends part of the way around the periphery of the Mine Board of Water Engineers, in cooperation with the U.S. Canyon stock; a zone 3-25 feet thick overlies the sill of Geological Survey, and have been reported on in part Sierra Prieta on its south side. (Broadhurst and others, 1951, p. 37, 97; Hood and Marbles derived from the Hueco Limestone are white, Scalapino, 1951; Follett, 1954, p. 6-15). uniformally crystalline and massive, seldom retaining The principal source of ground water in the region any relic bedding structures, although they are ob­ is the unconsolidated deposits of Cenozoic age in the scurely jointed. Analyses indicate that they vary in intermontane basins, especially in the Salt Basin and to composition from nearly pure CaCO3 to mixtures of a lesser extent in Eagle Flat. Water in the Salt Basin CaCO3 with MgCO3 and Mg(OH) 2. The latter forms varies widely in quality, as illustrated by two analyses the mineral brucite, and in some specimens amounts to published by Eichardson (1914, p. 9), one from Van as much as 30 percent of the rock. The magnesium- Horn, the other from the Figure Two Eanch which con­ bearing marbles were obviously derived from the more tain, respectively, 425 and 2,366 parts per million of dolomitic layers of the original limestone. dissolved solids. The marbles of the Sierra Diablo region have been The analysis of water from Van Horn is representa­ little developed until recently. A "marble quarry" was tive of that in the southern part of the Salt Basin, where shown on the east side of the Marble Canyon stock on alluvial slopes extend out from the mountains on either the topographic map of the Van Horn quadrangle, side to a central axis, along which Wildhorse Creek which was surveyed in 1904 and 1905, but only a little drains northward. Water was discovered at Van Horn surface stripping was done during this period, and very shortly after construction of the Texas and Pacific Eail- little marble was taken out (Richardson, 1914, p. 9). way, and has proved to be of the best quality of any In the winter and spring of 1961 and 1962 this deposit along the line west of the Pecos Eiver. It is obtained was being reopened and prospected by the Texas Con­ from unconsolidated deposits at a depth of about 600 struction Materials Co. of Houston, Tex., with plans for feet in several wells drilled by the railroad and by the production of dimension stone and for use of broken town of Van Horn; the municipal wells yield 100,000 material in terrazzo tile. The brucite which occurs in gallons per day (Broadhurst and others, 1951, p. 37). many of the marbles is a possible source of metallic Since World War II, ground water in the southern magnesium, but it is intermixed with the carbonate part of the Salt Basin has been further exploited by minerals of the marble. drilling in the Lobo Flats district about 12 miles south NITRATE AND TURQUOISE of Van Horn and in the Wildhorse Valley district about A few very minor mineral deposits have been recorded 8 miles northeast of Van Horn (each a little beyond the in the Sierra Diablo region. Nitrate has been pros­ edge of the map area, pi. 1). In both districts a dozen pected on an overhanging cliff of Van Horn Sandstone, or more wells supply sufficient water to irrigate areas of 7 miles northwest of Van Horn (sec. 24, Block 67, Twp. more than 10 square miles (Hood and Scalapino, 1951; 8), but it is a superficial coating produced from dis­ Leonard A. Wood, written commun., 1959); a few integration of bat guano (Mansfield and Boardman, square miles are also irrigated by wells on the east side 1932, p. 66-68). Thin films of turquoise were reported of the Salt Basin 5 miles northeast of the northeast by Eichardson (1914, p. 9) in some of the copper pros­ corner of the Baylor Mountains. Wells in the Wild- pects in the Carrizo Mountain Formation of the Carrizo horse Valley district yield 800 to 1,200 gallons per min­ Mountains west of Van Horn, but probably in very ute from unconsolidated deposits at depths of 200 to small amounts, as none was observed there during the 600 feet. The most productive areas are seemingly present investigation. nearest Wildhorse Creek, and wells several miles on each side of it have yielded insufficient water for practi­ GROUND WATER cal irrigation. Two wells in the southern part of the In the Sierra Diablo region, ground water has been district (sec. 19, Block 63) were drilled into limestone explored by drilling from the time of the first American bedrock when they failed to obtain water in the uncon­ settlements to the present, but with results which have solidated deposits; one of these is reported to have varied according to the geologic conditions at different yielded 350 gallons per minute at 1,000 feet and 400 gal­ localities. Geologic conditions which govern accumula­ lons per minute at 1,500 feet. 122 GEOLOGY OF THE SIEKRA DIABLO REGION, TEXAS Ground water at Van Horn, in the Lobo Flats dis­ are formed largely of various formations of carbonate trict, in the Wildhorse Valley district, and elsewhere in rock, which are less likely to contain accumulations of the southern part of the Salt Basin is evidently derived ground water than the surrounding unconsolidated de­ from water moving northward through the unconsoli- posits. A few successful wells have been drilled, main­ dated deposits in a manner comparable to the surface ly in the alluvium of the valleys, but many others have drainage of Wlldhorse Creek and its tributaries. These proved to be dry. One of the deeper unsuccessful wells, streams drain extensive areas in the high relatively well drilled at the Slaughter Ranch in the northern part watered Davis Mountains (fig. 1). These mountains of the Sierra Diablo, is reported to have been sunk to evidently provide a large recharge area, so that ground a depth of more than a thousand feet in Permian car­ water in the southern part of the Salt Basin is probably bonate rocks. In the Sierra Diablo and the other moun­ capable of continued exploitation. tain areas the chief supplies of water will probably con­ The analysis of water from the Figure Two Ranch, tinue to be from artificial surface reservoirs (locally mentioned above, is representative of that in the main termed "tanks"), many of which have been constructed, part of the Salt Basin, where alluvial slopes extend only as shown on the topographic base map (pis. 1, 9). a few miles out from the mountains on each side, with a nearly level alkaline floor 5 miles or more wide between OIL AND GAS them. On the floor, ground water is reached at a depth Possibilities for accumulations of oil or gas in the of 30 feet of less, and is taken out by ranch wells for Sierra Diablo region appear to be remote. watering stock. As indicated by the analysis, it is of Possibilities are least likely in the southern half of poor quality, all of it being so saline or gypseous that it the region, south of the Victorio flexure. Here, Pre- would be valueless for irrigation purposes. It is un­ cambrian and Precambrian (?) rocks lie either at the likely that water of better quality could be discovered in surface or within a thousand feet of the surface (pis. 15, the unconsolidatecl deposits at any depth in the main 16). Moreover, in much of this part of the region part of the Salt Basin, for this has been an area of con­ Permian Hueco Limestone rests directly on Precam­ centration of mineral salts throughout the history of brian and Precambrian (?) rocks, with the earlier the basin as a topographic feature. Paleozoic sequence removed by pre-Hueco erosion. The unconsolidated deposits of Eagle Flat, the in- Possibilities are somewhat greater north of the Vic­ termontane basin south of the Sierra Diatlo} have been torio flexure, as the Precambrian and Precambrian (?) less extensively drilled for water than the Salt Basin. rocks lie at greater depth beneath the surface, and as Besides scattered ranch wells, wells about 1,000 feet both the Permian and pre-Permian Paleozoic sequences deep have obtained water at Hot Wells and Torbert on are more completely preserved (pis. 15,16). Two wells the line of the Southern Pacific railroad in the southern have been drilled in this structural situation about 10 part of the report area (pi. 1), and at the town of Sierra miles north of the northwest corner of the report area Blanca west of the report area (Baker, 1935b, p. 374- to depths of 4,518 and 4,794 feet (A. R. Jones, 1 E. W. 375). The wells at Sierra Blanca yield 36,000 gallons Mowry in sec. 36, Block 70, Twp. 2; General Crude Oil, of water per day which contains 1,655 ppm of dissolved 1 Merrill & Voyles in sec. 8, Block 69, Twp. 2) (Haigh solids (Broadhurst and others, 1951, p. 97); hence, the and others, 1953, p. 78-81), both of which passed yield is smaller and of poorer quality than at Van Horn. through a complete sequence of Paleozoic formations As noted by Baker (op. cit.) ground water at Hot Wells beneath the Permian, but apparently without showings and Torbert stands less than 100 feet higher than at Van of oil or gas. Horn, suggesting that the ground water, like the surface Possibilities are greatest northeast and east of the water, drains from Eagle Flat into the Salt Basin. Re­ Sierra Diablo region, within the former Delaware basin serves of water in Eagle Flat are probably much less area, where both Permian and Pennsylvanian strata at­ than those in the Salt Basin, as the drainage area tribu­ tain great thickness, as shown by both surface exposures tary to it is smaller and is largely country with scanty and drill records (King, P. B., 1948, p. 12-13). In the rainfall. Along the northern border of Eagle Flat, in Apache Mountains east of the Sierra Diablo, several the southern foothills of the Sierra Diablo, where Pre- wells have drilled through these strata into lower cambrian rocks lie near the surface, ranch wells obtain Paleozoic formations, including the Middle Ordovician small supplies of water from the overlying unconsoli­ Simpson Group (Maley, 1945; M. E. Upson, in DeFord dated deposits; some of the earlier of these wells were and others, 1951, p. 50-52). This group is productive noted by Richardson (1914r, p. 9). of oil in the West Texas basin farther east, but is The mountain areas, including the large Sierra Diablo missing in most parts of the Sierra Diablo region on and the smaller Baylor Mountains and Beach Mountain, the west. In the Salt Basin, between the Apache Moun- STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 123 tains and the Baylor Mountains (sec. 5, Block 86) the Disconformity. West & Armour, 1 Davis Investment et al. test was com­ Bliss Sandstone: Feet 8. Sandstone, brown; in 1- to 3-in. beds; with part­ pleted in 1960 at a depth of 8,201 feet, but reports are ings of sandy marl or marly shale, the upper conflicting as to the rocks penetrated whether the well of which are greenish. Sandstone beds con­ entered "Ellenburger( ?)," that is, El Paso Limestone, tain Scolithus; an open-coiled euomphalid gas­ at total depth (Horak and others, 1961, p. 834), or tropod and various trails observed on bedding whether it failed to reach the base of the Permian. It surfaces______. 55 7. Sandstone, fine-grained to gritty; in 6-in. beds; is not known whether showings of oil or gas were found parts crossbedded, other parts containing Sco­ in this well. lithus; forms ledges _ _ 7 6. Sandstone, brown, marly______1 DESCRIPTIONS OF STRATIGRAPHIC SECTIONS AND 5. Sandstone, fine-grained to gritty; in 1- to 2-ft FOSSIL COLLECTIONS beds; thinly laminated to thinly crossbedded, STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS with abundant Scolithus in upper part; forms OF ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS ledges______16 4. Sandstone, gray to brown, coarse-grained to con­ SECTION 1. SIXMILE MOUNTAIN glomeratic; contains quartz pebbles______2 The following is a section of the basal part of the El 3. Covered______.______7 Paso Limestone and of the Bliss Sandstone, at the south 2. Sandstone, gritty, laminated to crossbedded; with end of Beach Mountain, on the west side of Sixmile thin seams of quartz pebbles; mainly gray but partly pink, due to content of red detritus de­ Mountain (with BM 5315 at top), near SW cor. sec. rived from Van Horn sandstone______26 10, Block 66, Twp. 8. The section was measured by P. 1. Conglomerate, gray; composed of rounded quartz B. King and J. Brookes Knight in 1931; fossils were and chert pebbles in a coarse poorly sorted observed in the field but were not collected. sand matrix______. 5 Angular unconformity. Top of mountain; no higher beds exposed. Van Horn Sandstone at base of section. El Paso Limestone: Summary of section 1 Division B : Feet 19. Limestone, granular; possibly slightly El Paso Limestone: sandy, but not mottled ; in 1- to 4-in. beds; Part of division B exposed______324 contains small chert masses. Forms a Division A____.______206 great cliff, the full height of which was not ascended. Estimated thickness 250 Part of El Paso Limestone exposed______530 18. Limestone, buff, sandy, thin-bedded; thinly Bliss Sandstone______114. 5 laminated in some beds; gastropod im­ prints observed ______28 SECTION 2. YATES RANCH 17. Sandstone, buff, friable______1 The following is a section of the basal part of the El 16. Limestone, buff, sandy; in 6-in to 1-ft beds; Paso Limestone and of the Bliss Sandstone on the west contains lenses of nonsandy limestone_ 45 Division A: side of Beach Mountain, on a spur half a mile east of 15. Sandstone, coarse-grained, calcareous, Yates Ranch, near SW cor. sec. 3, Block 66, Twp. 8. white; weathers gray; forms massive The section was measured by J. Brookes Knight and ledge______21 Josiah Bridge in 1938; fossils were observed in the 14. Sandstone, calcareous, thin-bedded; forms field but not collected. a slope______32 13. Limestone, brown, sandy______26 Summit of spur; higher beds not measured. 12. Sandstone, fine-grained, calcareous, buff to El Paso Limestone: white; top bed glauconitic. Cystid stems Division B: peet abundant in lower part. Mostly forms 34. Dolomite______._____ 15 thin ledges, but locally projects in a cliff 31 33. Limestone, dolomitic; contains poorly pre­ 11. Limestone, brown, sandy; in 1-ft beds, served fossils ; forms a ledge______4 weathers pitted- _ __ _ 24 32. Limestone, dolomitic, thin-bedded; forms a 10. Sandstone, fine-grained, white; in 6-in to slope______.______23 3-f t beds; mostly thinly laminated, but Division A: crossbedded in part. Forms prominent 31. Sandstone, dolomitic; forms a massive ledge_ 7 rounded ledges______36 30. Marl, sandy, yellow; forms a slope______5 9. Sandstone, somewhat calcareous, brown; 29. Sandstone, dolomitic; forms a massive ledge_ 27 with widely spaced laminae. Five feet 28. Dolomite, yellow; contains poorly preserved above base of unit is a layer of brown gastropods and cephalopoda; forms ledges- 27 sandy thin-bedded limestone, partly nod­ 27. Limestone, dolomitic, yellow; contains silici- ular and mottled, whose base is crowded fied gastropods; forms a ledge______4 with gastropod casts______36 26. Limestone, mottled, dolomitic, yellow___ . _ 7 757-108 65 9 124 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS El Paso Limestone Continued P. E. Cloud, Jr., and Josiah Bridge (written commun., Division A Continued Feet 1954). (See also Cloud and Barnes, 1948, p. 67-68.) 25. Limestone, mottled gray; forms thin ledges. Bedding surfaces covered with brown dolo- El Paso Limestone: mitic fucoidal markings; contains gastro­ Division A: Feet pods and cephalopods 45 6. Dolomite; forms ledges; continues up the slope 24. Limestone, marly, dolomitic; forms a slope 7 of mountain____ _ (?) 23. Sandstone, calcareous; forms a ledge 2 5. Sandstone, coarse, pinkish, somewhat dolo­ 22. Sandstone, marly; forms a slope 4 mitic; in part crossbedded. Contains faint 21. Sandstone, dolomitic, light-gray, massive; markings on bedding surfaces 36 forms a prominent ledge. Fucoidal mark­ 4. Limestone, brownish, slightly sandy, dolo­ ings abundant near base and faint Scolithusl mitic; in 1- to 2-ft beds; interbedded with tubes occur near top 45 marl______.______75 20. Limestone, sandy, marly, dolomitic; forms 3. Sandstone, pink, dolomitic; forms a massive a slope______12 ledge. Piloceras observed at top, and else­ 19. Limestone, sandy, dolomitic; forms a ledge_ 3 where worm borings and fucoidal mark­ 18. Sandstone, marly__ _ 10 ings______18 17. Sandstone; contains Lytospira; forms a Disconformity. ledge_ 3 Bliss Sandstone: 16. Marl; forms a slope_ _ 7 2. Sandstone, light-brown to red-purple; in 3-in. to 15. Sandstone, dolomitic; forms a ledge _ 2 2-ft beds; with thin shaly partings, contain­ 14. Sandstone, dolomitic, marly; forms a slope 12 ing abundant Scolithus and obscure fucoidal 13. Sandstone; contains poorly preserved fossils; markings. A fragment of ClarJcoceras, Lyto­ forms a ledge_ 1 spira sp., Ophileta sp., Helicotoma cf. H. uni- 12. Mainly covered on slope; a few ledges and angulata (Hall), gastropod cross sections, and much float of coarse brownish-red sand­ archaeostracan crustaceans were collected 5-8 stone______- 14 ft below top (TF 437; Oe 4, USGS 2751; X 3, Disconformity. TJSGS 3589) ; Hystricursus"! sp. and Lytospira Bliss Sandstone: gyrocera from same general level (B 173); 11. Sandstone, coarse, reddish, thin-bedded; con­ Lingulepis sp. and gastropod cross sections 27 ft tains rare Scolithus, as well as Lytospira below top (TF 438)______88 and linguloid brachiopods near top_____ 31 1. Sandstone, quartzitic, with rare Scolithus. Some 10. Sandstone, coarse, reddish; contains abund­ beds are red, because of content of detritus ant Scolithus; forms prominent ledges___ 15 derived from Van Horn__ _ _ 17 9. Sandstone, with many conglomerate layers_ 15 Angular unconformity. 8. Sandstone______.______3 Van Horn Sandstone at base of section. A short dis­ 7. Conglomerate______20 tance to the southwest the Bliss overlaps the Dallas 6. Sandstone______.______20 fault and lies on Allamoore Formation beyond it. 5. Conglomerate______1 Summary of section 3 4. Sandstone, thin-bedded; contains rare El Paso Limestone: Scolithus ___. ______, 11 Part of division A exposed______129 3. Conglomerate____.______2 Bliss Sandstone______105 2. Sandstone, thin-bedded; contains rare Scolithus______.______12 SECTION 4. NORTH SIDE OF BEACH MOUNTAIN 1. Conglomerate, coarser than any rocks above_ 1 The following is a section of Montoya Dolomite, El Angular unconformity. Van Horn Sandstone at base of section. Paso Limestone, and Bliss Sandstone on the north side Summary of section 2 of Beach Mountain, on a blunt spur projecting north- El Paso Limestone: northwest from elevation point 5,590, in the east half Part of division B exposed______42 of sec. 22, Block 66, Twp. 7. This section was origi­ Division A______244 nally measured by King in 1931. It was measured Part of El Paso Limestone exposed______286 again in 1936 by Knight, who revisited it with Josiah Bliss Sandstone______113 Bridge in 1938, when further collections and observa­ SECTION 3. DALLAS MINE tions were made. The section of El Paso Limestone The following is a section of the basal part of the El and Bliss Sandstone was remeasured in great detail Paso Limestone and of the Bliss Sandstone, on the by P. E. Cloud, Jr., and V. E. Barnes in 1944 and 1945 northwest side of Beach Mountain, on the slope east of (Cloud and Barnes, 1946, p. 352-361). Tumbledown Mountain above the abandoned Dallas In the text given here, description of the Montoya mine, near the center of the western part of section 28, Dolomite is from Knight's section, and descriptions of Block 66, Twp. 7. The section was measured in 1936 the El Paso Limestone and Bliss Sandstone are by J. Brookes Knight and reviewed in 1938 in com­ abridged from the published section of Cloud and pany with Josiah Bridge. Fossil identifications are by Barnes; however, lists of fossils collected by Knight, STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 125 Bridge, and others are added at the appropriate places. El Paso Limestone Continued Unit numbers for the El Paso and Bliss are the same Division B: Feet as those in the published section of Cloud and Barnes, 2. Dolomite, fine-grained, brown to grayish- brown; in 1-in to 3-ft beds; some inter- which were given in descending order, or the reverse bedded shaly dolomite; mostly forms steep of the usual arrangement. The Bliss Sandstone is fur­ slopes and ledges; some small chert nod­ ther illustrated by section 4a, by Knight, measured at ules in lower part, and minor chert and nearly the same place as the main section, and by sec­ siliceous masses elsewhere. Ceratopea sp., tion 4b, by King, measured about half a mile to the Hormotoma sp., and large gastropods col­ lected 45 ft above base (TF 441) ; Lopho- southwest, in the southwestern part of sec. 22, on nema sp. and longicone siphuncles 85 ft the opposite, or upthrown side of a fault. Fossil iden­ above base (Oe 12, USGS 2758) ; Cera­ tifications are by P. E. Cloud, Jr., but they include topea anJcylosa Cullison 142-144 ft above some earlier determinations by Josiah Bridge (written base (TF 326) ; Lophonema? sp., Hor­ comnmn., 1954). motoma spp., Ceratopea aff. C. anklosa Cullison, and C. spp.? near top (Oe 13). Top of mountain; no higher beds exposed. Ceratopea and Hormotoma observed else­ Montoya Dolomite: where______.___ 160 Aleman(?) Oherty Member or Fusselman(?) 3. Covered on bench; probably argillaceous Dolomite: Feet dolomite_____ 20 8. Dolomite, light-gray, unfossiliferous; without 4. Dolomite, fine-grained, grayish-brown to chert; forms upper cliff on mountain. This brown; well bedded, but forming thick unit might be Fusselman Dolomite rather ledges; a thin intraformational conglomer­ than Montoya, but until fossil evidence for ate 51 ft above base, a few layers of chert such an assignment is available, it is re­ nodules. Dolomite is markedly sandy tained in the Montoya______110 in lower 48 ft. Two genera of high-spired Aleman Cherty Member: gastropods collected 48 ft above base (TF 7. Dolomite, thin-bedded, purplish-pink to light- 439). Ceratopea observed 85 ft above gray ; without chert; forms a slope between base______-______101 cliffs above and below. DinortMs (Plaesi- 5. Dolomite; similar to overlying beds, but omys) large n. sp. collected (Om 1, USGS with sand only in a thin layer 12 ft above 2761) ______28 base. Contains some chert nodules. 6. Limestone, dolomitic, hackly, light-gray to Hormotoma and other small gastropods pink; without chert______25 observed___ 24 5. Limestone, dolomitic, massive, pinkish-gray; 6. Dolomite; coarser grained than beds above with chert bands______25 or below; light-pink to brownish____ 2.5 4. Limestone, dolomitic, massive, pinkish-gray; 7. Dolomite; like beds above, except in lower without chert. Poorly preserved corals and 8 ft, which is fine grained, grayish brachiopods observed______58 brown; yields a weak petroliferous odor 3. Limestone, dolomitic, gray to slightly pink, when broken. Some beds contain chert, very cherty; parts very thin bedded____ 40 in part oolitic; others contain scattered Upham Member: sand grains. A siphuncle of a probable 2. Limestone, dolomitic, light-gray to slightly Mcqueenoceras observed 12 ft above pink; forms massive 3- to 7-ft beds that base; Hormotoma, sp. and another si­ stand in a cliff. Contains a few dolomit- phuncle 37 ft above base______184.5 ized poorly preserved brachiopods, includ­ 8. Dolomite, very fine grained, grayish- ing Lepidocyclus______95 brown; irregularly bedded in layers as Cable Canyon (?) Sandstone Member: much as 3 ft thick; forms lower part of a 1. Sandstone, massive, pinkish, saccharoidal, prominent bluff. Chert lenses in lower dolomitic. Forms a cliff and breaks off in part and minor chert elsewhere. Dolo­ huge blocks. A few poorly preserved cup mite contains abundant sand grains in corals observed______35 lower 3 ft-______53 Disconformity. 9. Dolomite, mostly very fine grained, gray to El Paso Limestone: brownish-gray; irregularly bedded in Division C: layers as much as 3 ft thick; consider­ 1. Dolomite and limestone, earthy, nodular, ably less cherty than beds beneath. brownish-gray; with interbedded 4- to Ceratopea tennesseensis Oder and pilo- 14-in. layers of compact dolomite; forms ceratid siphuncles collected 80 ft above a gently sloping bench between the ledges base (TF 436) ; Ceratopea cf. C. tennes­ and cliffs above and below. Small Mac- seensis Oder and C. cf. C. keitM Ulrich lurites, poorly preserved high-spired gas­ 95 ft above base (TF 324) ; C. cf. C. ten­ tropods, sponges, and a probable Buttso- nesseensis Oder, C., sp., and an endocer- ceras collected 7-12 ft above base (TF atid siphuncle 118 ft above base (TF 327; Oe 14, USGS 2760)______50 325) ; and from several beds in about the 126 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

El Paso Limestone Continued El Paso Limestone Continued Division B Continued Feet Division A Continued Feet same part of the section Ceratopea aff. 16. Sandstone, dolomitic, yellowish to pinkish, 0. tennesseensis Oder and C. jenJcinensis medium- to fine-grained, crossbedded; in Cullison, and C. spp. (Oe 11, USGS 2757) _ 120 beds as much as 5 ft thick; forms a promi­ 10. Dolomite, very fine grained to dense, gray nent persistent ledge. Some feldspar to brownish-gray; irregularly bedded in grains______29 layers as much as 3 ft thick. Chert forms 17. Siltstone, dolomitic; interbedded with fine to abundant nodules and masses in lower half, coarse sandstone; yellowish to pinkish; and some beds higher up. A siphuncle of in beds as much as 4.5 ft thick; forms a Mcqueenoceras type and a large Ceratopea ledge. Some glauconite at base______21 observed 9 ft above base; Calathium, Cera­ topea, sp., a Mcqueenoceras siphuncle, and 18. Dolomite, silty and sandy, fine-grained, yel­ another endoceratid siphuncle collected 18 lowish- to brownish-gray; weathers earthy_ 15 ft above base (TF 322) ; Callathium sp., 19. Dolomite, partly calcitic, very fine grained, Helicotomal sp., a small gastropod, Mc­ yellowish- to brownish-gray ; in 1-in. to 4-ft queenoceras sp., and a piloceratid? beds; forms a prominent ledge in lower siphuncle from same general level (Oe 10, part. Some glauconite in middle. Cystid USGS 2756) ; Calathium, a Ceratopea, gas­ plates and columnals observed 29 ft above tropods, and a fragment of a cephalopod base______40 from chert at top (TF 323) ______85 20. Limestone, dolomitic, fine-grained, gray to 11. Dolomite, fine-grained, brownish, yellowish, yellowish-gray; in 1-in to 1-ft beds. Con­ or pinkish, thin-bedded; in 1- to 20-in. tains abundant chert in lower 3 ft. A beds; interbedded with dolomitic and ar­ sponge like Archaeoscyphia, Diaphelasma, gillaceous limestone in upper 18 ft; forms Allopiloceras sp., and a trilobite were col­ benches. Some chert lenses in lower part lected 12 ft above base (TF 318)_____ 17 and a thin bed of cherty sandstone near 21. Limestone, fine-grained, gray, nodular; inter­ middle. ArchaeO'Scyphia cf. A. annulata bedded with calcareous shale__ _ 6 Cullison, and a fragment of a probable 22. Limestone, medium- to fine-grained, gray; Pynoceras collected 18-20 ft above base with dolomitic streaks; weathers to thin (TF 320) ; Archaeorthfe costellata Ulrich beds; abundant glauconite in lower part. and Cooper and cystid plates at top (TF Piloceratid siphuncles abundant in lower 321; Oe 9, USGS 2755). Hormotoma, 3 ft. Lytospira, "Euconia," Ophileta Ceratopea, siphuncles of brevicone cephalo- (OzarTcispira) cf. 0. rotuliformis (Meek), pods, ArchaeortMs, Firikelnburgia,, and Ca­ Diaphelasma cf. D. OJclahomense Ulrich lathium were observed at various other and Cooper, and other brachiopods col­ levels______50 lected 2 ft above base (TF 315; Oe 7, part; 12. Dolomite, fine- to medium-grained, vuggy; B 39, USGS 3590) ; Ophileta (Ozarlcispira) calcitic in upper part; yellowish gray to rotuliformis Meek, Lytospira! Hormotoma light gray; in 1- to 30-in. beds; some scat­ small sp., Bucanella sp., Euconia sp., Pela- tered sand grains in lower part. Xenelasma giellal sp., Holopea-like gastropod, a syntrophiodes Ulrich and Cooper, a sponge, raphistomoid gastropod. Endocycloceras Hormotoma sp., and Polhemia"! collected sp., and Hystricurus sp. from 9 ft above 4-6 ft above base (TF 319) ; Calathium base (Oe 7, USGS 2753; C 39, USGS 3591) ; sp., Hormotoma sp., Ceratopea sp., and Diaphelasma oTtlahomense Ulrich and Mcqueenoceras sp. at about the same level Cooper, Syntrophina sp., Ophileta (OzarJc- (Oe 8, USGS 2754). Orospiral and Hor­ ispira) cf. O. rotuliformis (Meek), motoma, were also observed______13 Ophileta sp., Hormotoma sp., a raphis­ Division A: tomoid gastropod, and a small cyrtendo- 13. Sandstone, dolomitic, fine- to medium- ceratid cephalopod from higher up (TF grained ; quartz grains well-rounded, some 317) ______-______16 feldspar grains______4 23. Dolomite, fine-grained, brownish-gray; in 14. Dolomite, moderately sandy, very fine beds a few inches thick; interbedded with grained, gray; in 1-in. to 2-ft beds; quartz gray limestone. Clarkella sp., Syntrophina grains well rounded and frosted. Polhe­ sp., Ophileta (Ozarkispira) cf. 0. rotuli­ mia, small brevicone cephalopods, and syn- formis (Meek), and Homotoma sp. were trophioid brachiopods like Diaphelasma collected 9-11 ft above base (TF 433), and observed 3 ft above base______8 poorly preserved Rhomtiellal and Lecano- 15. Dolomite, sandy and shaly; dolomitic sand­ spiral were observed at the same level. stone; yellowish to brownish gray, with a Cystid plates, Tetralo^ula sp., OzarJcispira greenish shaly layer at top. Gastropods sp., Lytosplral Piloceras sp., Allopiloceras suggesting Euconia and Polhemia observed sp., and Kirkocerast were collected 15-17 near middle______11 ft above base (TF 434) ______26 STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 127

El Paso Limestone Continued El Paso Limestone: Division A Continued Feet Division A: Feet 24. Sandstone, dolomitic, medium- to coarse­ 7. Sandstone, friable; with partings of greenish grained, crossbedded, yellowish-gray to marly shale; becomes calcareous 10-15 ft , pink; forms a prominent ledge_____ 9 above base ______30 25. Siltstone, and very fine grained dolomitic Disconformity. sandstone______12 26. Dolomite, silty and sandy; interbedded with Bliss Sandstone: siltstone, sandstone, and green shale; forms Calcareous division: a light-colored slope. At base is a 4- to 10- 6. Sandstone, quartzitic, brown, thinly lami­ in. bed of reddish sandy dolomite, contain­ nated; forms a ledge______2 ing rounded pebbles and cobbles of sand­ 5. Sandstone, friable, buff; in 1-ft beds; full of stone, the largest 10 in. in diameter. Lies calcareous tubular structures______13 with abrupt contact on Bliss Sandstone 38 4. Limestone, buff, sandy______5 Disconformity. Main body of formation: 3. Sandstone, gray, friable; in 1- to 3-in. beds; Bliss Sandstone: all contain Scolithus______37 27. Sandstone, fine- to coarse-grained; contains 2. Sandstone, less resistant than beds above pebbly layers in lower half; pinkish or yel­ or below______26 lowish ; friable to quartzitic, slightly cal­ 1. Sandstone gritty, quartzitic; weathers brown; careous throughout; in 1-in. to 2-ft beds. brown; crossbedded on a small scale. Con­ Is interbedded with argillaceous sandstone tains seams of rounded quartz pebbles as and shale, the latter of greenish or purplish much as half an inch in diameter_____ 10 color. The well-indurated sandstone layers contain vertical Scolithus tubes. Angular unconformity. Lingulepis, Lingulella, a possible Lytospira, Van Horn Sandstone at base of section. and archaeostracan crustaceans were col- Summary of section 4 collected 98-105 ft above base (TF 432) ; Montoya Dolomite: many beds show impressions or molds of Aleman(?) Cherty Member or Fusselman various unidentified gastropods______125 limestone (?) ______.______110 Angular unconformity. Aleman Cherty Member______177 Van Horn Sandstone at base of section. TJpham Member______95 Cable Canyon (?) Sandstone Member__ 35 Section 4a [Section of Bliss Sandstone measured at approximately the same place as lower part of preceding, by J. Brookes Knight, 1936] Total Montoya Dolomite-______417 El Paso Limestone: El Paso Limestone: Division A: Division C______50 4. Sandstone, fine-grained, friable, dolomitic; Division B______813 with obscure winding tubules on bedding; Division A_ 252 forms a ledge______10 Total El Paso Limestone 1,115 Disconformity. Bliss Sandstone: Bliss Sandstone: Main section __ 125 Calcareous division: Section 4a______125 3. Sandstone; a little more massive and dolomitic Section 4b______93 than beds below, with finer grained sand; gray to yellow; no Scolithus______28 SECTION 5. UNCONFORMITY LOCAUTY Main body of formation: 2. Sandstone; forms ledges on slope. Some lay­ The following is a section of the basal part of the El ers, which are more quartzitic than remain­ der, contain Scolithus; others are cross- Paso Limestone and of the Bliss Sandstone in the south­ bedded. Between the sandstone layers are ern part of Baylor Mountains, on a prominent bluff that partings of soft marly sandstone. Sand­ faces into a reentrant valley north of Sulphur Creek, stones and marls are light gray, brown, and near the middle of the south line of sec. 22, Block 65, purplish red; some marls are green_____ 72 1. Sandstone, pebbly and gritty, gray to reddish- Twp. 7. This bluff is prominently in view from Texas brown, crossbedded. At base is a quartz- Highway 54 to the south and is illustrated in figure 5A. pebble conglomerate which lies with sharp The bluff of El Paso and Bliss is overlapped on the west contact on Van Horn Sandstone______22 by the Hueco Limestone, whose base stands several Angular unconformity. Van Horn Sandstone at base of section. hundred feet lower, and which contains talus blocks de­ Section 4b rived from unit 8 and other resistant beds of the Ordo- [Section of Bliss Sandstone measured about half a mile southwest of vician sequence; the place was hence referred to during preceding section on opposite, or upthrown side, of a fault, by P. B. King, 1931] the field investigation as the "unconformity locality," 128 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS and that title is retained here. The section was mea­ Bliss Sandstone Continued sured by J. Brookes Knight in 1936; fossil identifica­ Main body of formation Continued Feet beds contain rounded cobbles 3 in. across, tions are by P. E. Cloud, Jr., (written commun., 1954). mostly of vein quartz, but a few of schist Top of section; higher beds of El Paso Limestone occur and quartzite 17 to northeast, but the whole Ordovician sequence is Angular unconformity. overlapped on the west by Hueco Limestone. Van Horn Sandstone at base of section. El Paso Limestone: Summary of section 5 Division A: Feet El Paso Limestone: 14. Limestone, dolomitic______(?) Part of division A exposed 120. 5 13. Sandstone, crossbedded, light-brown to pink, Bliss Sandstone: dolomitic; forms a ledge______12.5 Calcareous division 43 12. Limestone, marly and sandy, mottled, light- Main body of formation- 102 gray __ 25 11. Limestone, dolomitic; interbedded with Total Bliss Sandstone 145 marly layers; contains poorly preserved SECTION 6. SOUTHEASTERN BAYL.OR MOUNTAINS gastropods______22 10. Not exposed in line of section; to east is The following is a section of Fusselman Dolomite, yellow sandy limestone, slightly mottled, Montoya Dolomite, beds of Middle (?) Ordovician age, containing poorly preserved Ophileta, and the upper part of the El Paso Limestone on the with interbedded marl layers______25 southeast face of Baylor Mountains 1 mile south- 9. Limestone, dolomitic, slightly sandy; in 1-ft beds; contains Piloceras______16 southwest of the portal of Eed Tank Canyon in the 8. Limestone, dolomitic, slightly sandy, thin- northwestern part of sec. 6, Block 122. A generalized bedded, dark-gray; weathers brown. section was measured in this vicinity by P. B. King Piloceras and other cephalopods collected and E. E. King in 1928, but the sequence was studied (Oe 2). Forms top of a projecting prom­ in more detail later by H. J. Howe (1959, p. 2312-2313, ontory that overlooks valley to the south. 20 Disconformity. 2328), when two sections were measured about half a Bliss Sandstone: mile apart, termed "B-l and B-2." The descriptions Calcareous division: of the Montoya and Fusselman Dolomites given here 7. Sandstone, coarse, crossbedded; interbedded are from Howe's section B-l (1959, fig. 29, p. 2328); with finely sandy dolomitic limestone, and that of the beds of Middle(?) Ordovician age is from marl______15 6. Limestone, dolomitic, finely sandy, yellowish- his section B-2 (written commun., 1959); some obser­ gray; in part with ramifying mottlings; vations by P. B. King and E. E. King have been added. interbedded with marl______28 Fossil identifications are by H. J. Howe. Main body of formation: 5. Sandstone, quartzitic; in 6-in to 1-ft beds; Hueco Limestone at top of section. interbedded with softer more argillaceous Angular unconformity. sandstone and blue-green shaly sandstone. Fusselman Dolomite: Feet Many of the sandstone layers are cross- 10. Dolomite, very fine grained, very light gray; bedded and ripple marked, and the quartz- weathers brownish orange and sugary. Massive, ose layers contain ScolitJius. Lingulepis n. except for basal few feet, which is faintly lam­ sp. and Lytospira! collected from near base inated______._ _ 70 (Oe 1, TJSGS 2748; Oe 5, USGS 2765; Oe Disconformity (?). 6, USGS 2752) ______30 Montoya Dolomite: 4. Sandstone, shaly, brown, white, and green; Aleman Cherty Member: forms a slope. One thin bed contains 9. Dolomite, microgranular, faintly thinly lami­ Scolithus______10 nated, brownish-gray; weathers light olive 3. Sandstone, quartzitic, brown; in 1-ft beds; gray. About 40 percent of unit consists of contains Scolithus______20 elongated irregular white chert nodules that 2. Sandstone, quartzitic, red-brown, purplish, weather light brown______18 and white; forms somewhat thinner layers 8. Dolomite, very fine grained, thick-bedded to than beds above; interbedded with white very thick bedded, light-gray; weathers and green marly sandstone. The quartzitic brownish orange. Near top, contains Hyp- sandstone layers are crossbedded in part, siptycha, Streptelasma, and favositids; Pa- contain Scolithus, and have fucoidal mark­ leophyllum thomi (Hall) zone is well devel­ ings on bedding______25 oped lower down; near base, contains Thaero- 1. Sandstone, coarse, crossbedded, reddish to donta and Lepidosyclus______24 white; contains quartz pebbles in lower 3 7. Dolomite, very fine grained, light-gray. About ft. Scolithus occurs 4 ft above base, and 15-20 percent of unit consists of chert nodules, in a few beds higher up. To east, basal elongated parallel to bedding______15 STRATIGEAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 129

Montoya Dolomite Continued Summary of section 6 Continued Aleman Cherty Member Continued Feet Montoya Dolomite Continued Feet 6. Dolomite, very fine grained, thick-bedded to Upham Member______101 very thick bedded, light-gray; weathers Cable Cany on (?) Sandstone Member_ 2 brownish orange; contains sparse chert nod­ ules. Horn corals are scattered throughout Total Montoya Dolomite ___ 250 and Lepidocyclus was observed near top__ 40 5. Dolomite, microgranular, homogeneous to Beds of Middle(?) Ordovician age______66 faintly laminated, light-gray; about 30 per­ Part of El Paso Limestone exposed- ____ _ 240 cent of unit consists of light-gray elongated chert nodules______20 SECTION 7. NORTHEASTERN BAYLOR MOUNTAINS 4. Dolomite, microgranular, light-gray. "Key The following is a section of beds of Devonian age, chert" horizon occurs at top; remaining Fusselman Dolomite, Montoya Dolomite, and beds of part of unit consists of about 10 per­ cent elongated chert nodules. "Key chert" Middle (?) Ordovician age on the southeast spur of the contains Lepidocyclus manniensis (Foerste), high point of Baylor Mountains (BM 5568), a mile L. laddi Wang, L. capax (Conrad), L. sp., northeast of the portal of Red Tank Canyon, in the Onniella sp.,Thaerodonta sp., Plaesiomys bel- northwestern part of sec. 9, Block 65, Twp. 7. The sec­ listriatus Wang., Rhynchotrema sp., Austin- tion was measured by J. Brookes Knight in 1938, but ella sp., Glyptorthis sp., and fragments of other fossils______30 notes made by Knight and the writer during earlier Upham Member: years have been incorporated. Fossils were not col­ 3. Dolomite, like unit 1; contains very common lected, but were observed during measurement of section. fossil fragments, and Onniella sp., TUaero- Section 7a illustrates further features of the beds of donta sp., Lepidocyclus sp., and Glyptorthis Middle(?) Ordovician age and the upper part of the sp ______29 El Paso Limestone at a locality half a mile to the north­ 2. "Key chert," containing 15-20 percent small irregular chert nodules, arranged in closely east, near the center of sec. 2, Block 65, Twp. 7; it was spaced layers______6 furnished through the courtesy of C. C. Branson (writ­ 1. Dolomite, fine-grained to very fine grained, ten commun. 1950), who measured it in 1947. Fossils thick-bedded to very thick bedded, light- noted in the section were identified by G. A. Cooper. gray; weathers brownish orange. Con­ tains Receptaculites and Halysites, nearly Hueco Limestone at top of section. obliterated by dolomitization______66 Angular unconformity. Cable Cany on (?) Sandstone Member: Beds of Devonian age: Feet h. Dolomite, sandy______2 14. Limstone, dolomitic, gray-brown, buff, or pink, thin-bedded or nodular; contains very abund­ Disconformity. ant irregular nodules and lenses of black or Beds of Middle (?) Ordovician age: brown chert; preserved beneath Hueco Lime­ g. Sandstone, fine-grained, brown; forms a ledge_ 10 stone only on southwestern of two spurs of f. Shale and argillaceous dolomite______17 the mountain______30-50 e. Sandstone, dolomitic______3 Disconformity ( ?). d. Shale and argillaceous dolomite______26 Fusselman Dolomite: c. Sandstone, fine-grained, brown; forms a ledge_ 10 13. Beds like those below, occurring on southwest­ El Paso Limestone: ern of two spurs of mountain; not preserved on northeastern spur where main part of Division C: section was measured. Approximate thick­ b. Shale and argillaceous dolomite, probably equiv­ ness_____ 25 alent to division C of geologic section 4___ 40 12. Dolomite, fine-grained light-gray; weathers sal­ Division B: mon gray and pitted; forms massive ledges a. Limestone, dolomitic, finely crystalline; wea­ several feet thick. A few beds are indistinct­ thers light gray and contains a few irregular ly mottled, and some in upper part are thin chert masses; in beds a few feet thick; forms bedded and hackly. No chert or fossils ob­ conspicuous ledges. Contains Ceratopea near served _ 275 top _. ______200 Disconformity (?). Similar strata below base of section, forming less con­ Montoya Dolomite: spicuous ledges, dipping more steeply and cut by close­ Aleman Cherty Member: ly spaced joints; one or more faults downthrown to­ 11. Limestone, dolomitic, light-gray; contains ward the southeast probably duplicate the sequence. thick chert lenses_____ 20 10. Limestone, dolomitic, light-gray, thin- Summary of section 6 bedded; contains sparse chert nodules Fusselman Dolomite______70 and lenses. Poorly preserved Lepidocy­ Montoya Dolomite: clus, "OrtMs," and other brachiopods ob­ Aleman Cherty Member______147 served . 75 130 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Montoya Dolomite Continued El Paso Limestone Continued Aleman Cherty Member Continued Division B: Feet 9. Limestone, dolomitic, gray, thin-bedded; 1. Dolomite, dense, slightly cherty and sandy, contains abundant ramifying chert gray to pink; contains scattered frosted masses______._ _ 28 sand grains______50 8. Limestone, dolomitic, gray; contains moder­ Base of section covered by alluvium. ately abundant chert nodules and lenses. Summary of section 7 Poorly preserved brachipods observed 55 Beds of Devonian age______30-50 7. Limestone, dolomitic, light-gray; in 6- to 18- Pusselman Dolomite___ __ 300 in. beds; contains many silicifled Lepido- Montoya Dolomite: cyclus, "Orthis," other brachiopods, and Aleman Cherty Member___ _ 238 cup corals ______50 Upham Member___ _ 61 6. Limestone, dolomitic, very cherty______10 Cable Cany on (?) Sandstone Member- __ 7-25 Upham Member: Total Montoya Dolomite______306-324 5. Limestone, dolomitic, gray; thinner bedded Beds of Middle (?) Ordovician age (in section 7a) 86 than below______18 El Paso Limestone (in section 7a) : 4. Limestone, dolomitic, very cherty; forms a Division C______59 ledge. Probably the same as lower "key Part of division B exposed-_ _ 50 chert" interval, unit 2 of section 6_ _ 3 3. Limestone, dolomitic, gray; in 3- to 5-ft Part of El Paso Limestone exposed. 109 beds; mottled, with mottlings projecting in relief on weathered surfaces. Haclur- SECTION 8. HAWKINS TANK ites, Lepidocyclus, Favosites, halysitid The following is a section of the basal part of the El corals, cup corals, and Receptaculites ob­ Paso Limestone, and of the Bliss Sandstone and Van served. Base concealed on spur, but ex­ posed in ravine to north______40 Horn Sandstone, in a group of hills between the north­ Cable Canyon ( ?) Sandstone Member: west corner of the Bay lor Mountains and Sierra Diablo 2. Sandstone, brown, crossbedded______7-25 scarp, west of Texas Highway 54. The section was Disconformity. measured on a conical butte half a mile southwest of Beds of Middle (?) Ordovician age: Hawkins Tank, near the center of the north line of sec. 1. Limestone, earthy, yellow, pink, and brown; 10, Block 54%, but some observations made on adjacent without sandstone beds; exposed in ravine hills have been added. The section was measured by north of spur______(?) P. B. King in 1936 ; fossils were noted in field, but have Base of section covered by alluvium. not been formally identified. Section 7a Top of butte ; higher beds exposed in gome of hills farther [Section of beds of Middle(?) Ordovician age and upper part of east, probably including parts of division B of El Paso El Paso Limestone measured half a mile northeast of preceding Limestone, but could not be placed in sequence ; many section; by C. C. Branson, 1947] of hills are capped by Hueco Limestone, which over­ Montoya Dolomite at top of section, with a 2-ft bed of steps all the earlier strata down to the Hazel For­ sandstone at base. mation. Disconformity. El Paso Limestone : Beds of Middle (?) Ordovician age: Division A : 9. Dolomite, yellow, very sandy; contains frosted 21. Limestone, sandy, marly, brown __ _ 7 sand grains, with a green shale parting a 20. Limestone, gray ; forms ledges ______4 little above base______8 19. Limestone, marly, brown ; forms a slope. _ 5 8. Shale, green, with thin layers of buff fucoidal 18. Limestone ; forms thin ledges, with marl sandstone______4 partings _____ .______12 7. Siltstone, fine-grained, buff, well-bedded; con­ 17. Limestone, evenly layered, gray; in 6-in. tains frosted sand grains______5 beds ; contains abundant silicified fossils, 6. Sandstone, saccharoidal, crossbedded; white, including Piloceras, Ophileta, Lytospira, with greenish areas______7 Hormotoma, and possible sponges (Oe3)_ 4 5. Sandstone, dolomitic, silty, yellow______18 16. Limestone, nodular, marly; forms a slope _ 13 4. Limestone, shaly and silty, platy, yellow_____ 26 15. Limestone, forming a slope below and pass­ 3. Sandstone, calcareous, nodular; contains frosted ing into prominent ledges above ; lower part sandy, brown or gray-brown, thin sand grains, also Desmorthis ? and cystid plates- 18 bedded; upper part gray, in 1-ft beds, El Paso Limestone: mottled or lumpy, containing spongy light- Division C: brown chert that forms networks of tu­ 2. Dolomite, calcitic, sandy, knotty, buff to yel­ bules on bedding, and nodules of compact low, sparsely fossilferous, poorly exposed_ 59 bluish chert ______28 STRATIGRAPHIC SECTIONS, ORDOVICIAN, SILURIAN, AND DEVONIAN ROCKS 131

El Paso Limestone Continued Summary of section 8 Continued Division A Continued Feet Bliss Sandstone: Feet 14. Sandstone, fine-grained, calcareous, brown Calcareous division 52 or buff; in 6-in to 1-ft beds; in part lami­ Main body of formation 103 nated, in part crossbedded; forms massive ledges______.______17 Total Bliss Sandstone- 159 Disconformity. Van Horn Sandstone______>150 Bliss Sandstone: Calcareous division: SECTION 9. POINT OF MOUNTAINS 13. Sandstone, finer grained than below; slight­ ly calcareous, buff or brown; forms ledges The following is a section of the Montoya Dolomite, a foot thick, separated by slopes______40 and parts of the overlying Fusselman Dolomite and 12. Sandstone, coarse, quartzose, slightly calcar­ underlying El Paso Limestone, on a projecting salient eous 'and glauconitic; weathers brown; in of the Sierra Diablo escarpment 1% miles northwest of massive ledge______3 Figure Two Ranch, on a ridge projecting northeast 11. Sandstone, thin-bedded, soft, buff______6 10. Sandstone, coarse, quartzose, calcareous; from a flat-topped butte capped by Hueco Limestone, weathers brown______3 near the center of the southern part of sec. 9, Block 66, Main body of formation : Twp. 5. The section was measured by P. B. King in 9. Sandstone, quartzitic, noncalcareous, gray; 1931; fossils were noted in the field, but have not been forms ledges______4 formally identified. 8. Sandstone, thin-bedded, friable, buff_____ 13 7. Sandstone, quartzitic; in part crossbedded; Hueco Limestone at top of section. weathers brown; in 1- to 3-ft beds with Angular unconformity (Barnett Shale and beds of marly partings; forms ledges______10 Devonian age are preserved beneath the unconform­ 6. Sandstone, thin-bedded, quartzose, apparent­ ity at nearby localities). ly glauconitic______16 Fusselman Dolomite: Feet 5. Sandstone, quartzitic, gray; weathers red 11. Dolomite, white to light-gray, finely crystal­ brown ; forms two groups of ledges; in part line ; with veins, patches, and vugs of crys­ crossbedded and in part containing Scoli- talline calcite. A poorly preserved favosite thus______10 coral noted. Forms obscure massive beds, 4. Sandstone, medium-grained, quartose, white which dip steeply and stand in a wall-like or buff; mostly in beds a few inches thick, ridge. Approximate preserved thickness 100-200 but with some 1-f t beds near middle. Beds Disconformity (?). contain dark laminae and many contain Montoya Dolomite: Scolithus ______50 Angular unconformity. Aleman Cherty Member: Van Horn Sandstone: 10. Limestone, dolomitic; in 3- to 4-ft beds; 3. Sandstone, coarse, arkosic, red-purple to maroon- weathers to drab gray jagged surfaces. red ; in massive rounded 5- to 10-ft ledges, with Contains abundant nodules, knotted scattered pebbles, and interbedded conglomer­ lenses, and long beds of light-gray to ate layers made up of closely packed well- brown chert, weathering rusty. Brach- rounded pebbles and cobbles as much as 6 in. iopods observed- 38 in diameter, of same composition as those in 9. Limestone, dolomitic; thinner bedded than unit 1. Toward top, sandstone is irregularly below and above 30 decolorized to brown adjacent to joints. Thick­ 8. Limestone, dolomitic; in 2- to 3-ft beds; ness exposed, to base of slope______100 weathers to dark gray jagged surfaces. 2. Poorly exposed across flat, toward hill to north­ Toward top, nodular layers of brown west; dip changes from less than 5° in unit chert several inches thick are inter­ above to 20° in unit below, and several faults bedded. Contains abundant brachio- may occur, but interval is probably small___ (?) pods______. 21 1. Conglomerate, coarse; interbedded with friable 7. Limestone, dolomitic; in 1- to 2-ft beds; coarse maroon-red sandstone. Conglomerate weathers to dark gray jagged surfaces, consists of closely packed well-rounded pebbles with a few chert nodules. Contains and cobbles of vein quartz, mafic volcanic rocks, abundant brachiopods, in part silicified, chert, limestone, massive red rhyolite, and including Lepidocyclus and "Orthis"__ 21 schistose lineated metarhyolite______50 Upham Member: Angular unconformity. 6. Limestone, dolomitic, finely crystalline, Hazel formation, fine-grained red sandstone at base of dark-gray; in 2- to 3-ft beds contain­ section. ing knotted nodules and lenses of brown Summary of section 8 chert______20 El Paso Limestone: 5. Limestone, dolomitic; weathers jagged and Part of division A exposed______90 pitted; forms a slope. Contains brachio­ Part of El Paso Limestone exposed_____ 90 pods and corals 11 757-108 65 10 132 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Montoya Dolomite Continued Fusselman Dolomite Continued Feet Upham Member Continued Feet 9. Limestone, in part cherty; contains Favosites and 4. Limestone, dolomitic, finely crystalline, cup corals (X 8)______37 dark-gray; weathers to drab-gray pitted 8. Limestone, dolomitic ; without chert-_-_ 37 surfaces. Forms massive beds and prom­ 7. Limestone, somewhat dolomitic, medium-bedded; inent ledges, cut by vertical joints. in part brecciatecl, with numerous chert masses. Contains abundant corals, especially in Contains brachiopods and the trilobite Dalma- upper part, including Streptelasma and nites (X 7)______38 halysitid corals______37 6. Limestone, massive; forms a coral reef. Corals Cable Canyon (?) Sandstone Member: include several species of Favosites, Halysites, 3. Sandstone, marly, thin-bedded, buff; and cup corals (X 6) _ _ 37 bedded with thin quartzitic layers 30 5. Limestone, dolomitic; contains brecciated chert, 2. Sandstone, saccharoidal, pale-brown; also Favosites, Halysites, and cup corals (X 5) 18 weathers dark brown; in thick beds 4. Dolomite, without chert_ _ 8 breaking out in large blocks______25 3. Limestone, dolomitic, very cherty; contains Haly­ Disconformity. sites and other corals (X 4)______25 El Paso Limestone: 2. Dolomite, white; forms ledges______50 1. Dolomite, white; weathers light buff; without chert Division C: or fossils; forms prominent ledge in ravine at 1. Limestone, marly, mottled, yellow; ob­ northeast base of spur______21 scured in part by sandstone blocks from Base of section concealed by alluvium. above. Exposed thickness about_ 10-15 Base of section cut off by fault; rocks of Devonian and Section lOa Mississippian age on downthrown side to northeast. Top of spur; higher beds not measured. Fusselman Dolomite: Summary of section 9 k. Dolomite; weathers to pitted surfaces; silici­ Part of Fusselinan Dolomite exposed______100-200 fied along joints 6 Montoya Dolomite: j. Dolomite; not so massive as bed below. Walk­ Aleman Cherty Member______110 ing of beds between sections lOb and lOa indi­ Upham Member______68 cates that cherty units 3 and 5 of the former Cable Canyon (?) Sandstone Member__ 55 should lie in this unit about 30 ft above base ______100 Total Montoya Dolomite______233 i. Dolomite, finely crystalline massive, light-gray; Part of El Paso Limestone exposed______10-15 weathers to light-buff pitted surfaces____ 38 Disconformity (?). SECTION 10. APACHE SPRING Montoya Dolomite: Aleman Cherty Member : The following is a section of the Fusselman Dolomite h. Covered______6 and the upper part of the Montoya Dolomite on the g. Limestone, dolomitic; with abundant chert ridges north of Apache Spring. The section is in two layers; forms ledges______14 parts. Section lOa, of the Montoya Dolomite and the f. Limestone, dolomitic; contains rounded chert lower part of the Fusselman Dolomite, was measured nodules 2-3 in. in diameter; forms a slope 4 e. Limestone, dolomitic, very cherty; forms prom­ on the ridge half a mile north of the spring, in the inent ledges______-_ 22 southeastern part of sec. 4, Block 66, Twp. 5. It is im­ d. Limestone, dolomitic ; with sparse chert layers. perfectly tied by a cherty unit in the Fusselman Dolo­ At top, contains a branching colonial coral, mite with the lower part of section lOb, which was Lepidocyclus, "Orthis," and other brachi­ measured on the ridge just northwest of the spring, in opods______20 c. Limestone, dolomitic; silicified Streptelasma the northeastern part of sec. 7, Block 66, Twp. 5. The at base______21 section was measured by J". Brookes Knight and Josiah b. Limestone, dolomitic, gray; without chert; Bridge in 1938; fossils were collected and identified in forms ledges; contains poorly preserved the field, but are not now available for reexamination. silicified brachiopods______21 Upham Member: Section lOb a. Limestone, dolomitic; contains some chert Hueco Limestone at top of section. bands and nodules; forms a massive cliff at base of exposure______32 Angular unconformity. Base of section concealed by alluvium. Fusselman Dolomite: Feet Summary of section 10 11. Dolomite, massive, without chert. Stromatopora Fusselman Dolomite: observed near base______85 In section lOb______416 10. Limestone, forming ledges and cliffs. Contains In section lOa______144 silicified fossils near top, including Favosites, several species of cup corals, and Stromatopora Approximate total Fusselman Dolomite in over­ (X 9) ______60 lapping sections______420 STRATIGRAPHIC SECTIONS OF MISSISSIPPIAN AND PENNSYLVANIAN ROCKS 133

Summary of section 10 Continued X 10 (USGS 3598). Montoya Dolomite, probably Aleman Montoya Dolomite: Feet Cherty Member. Inlier of steeply dipping strata projecting Aleman Cherty Member______108 amidst outcrops of Hueco Limestone, in Victorio Canyon 2 miles Part of Upham Member exposed______32 west-southwest of summit of Victorio Peak, near eastern center of sec. 14, block 43. Collected by J. B. Knight, 1938; identified Part of Montoya Dolomite exposed______140 by P. E. Cloud, Jr., Jean Berdan, and Helen Dunean (written commun., 1954). OKDOVICIAN AND SILURIAN FOSSILS, NOT COLLECTED Streptelasmatid corals, one specimen probably related to ALONG COURSES OF STBATIGBAPHIC SECTIONS 8. foerstei group; "Rafinesquina" sp.; Hypsiptycha sp.; Lepidocyclus sp.; dinorthid brachiopods gen. and sp. ? The following fossils were collected from Ordovician Om 2 (USGS 2762). Montoya Dolomite, Aleman Cherty and Silurian rocks but not in any measured section: Member. West slope low ridge on west side of Baylor Moun­ X 1 and X 2 (USGS 3594, S595, 3596, and 3597). El Paso tains, a quarter of a mile east of Texas Highway 54, near center Limestone, lower part of division B. Inlier within the Sierra of sec. 6, Block 66, Twp. 8. Collected by P. B. King and J. Diablo northeast of Cox Mountain; low hills between the two Brookes Knight, 1936; identified by Helen Dunean and Jean county roads, in northwestern part of sec. 14 and northeastern Berdan (written commun., 1954). part of sec. 15, Block 54%. A sequence 340-400 ft thick is Streptelasmatid corals, in part probably related to S. foerstei exposed, between sandstone beds at or near the top of division group. A on the southeast, and unconformably overlying Hueco Lime­ OmS (USGS 2763). Montoya Dolomite, Aleman Cherty stone on the northwest (Cloud and Barnes, 1946, p. 71), but the Member. East slope of Baylor Mountains a quarter of a mile nature of the exposures are such that no section could be south of eastern portal of Bed Tank Canyon, in east-central measured. Two sets of collections are available: The first set part of sec. 4, Block 122. Collected by J. B. Knight, 1936; (X 1 and X 2) consists of a lot from the lower beds and another identified by P. E. Cloud, Jr., Jean Berdan, and Helen Dunean lot from the higher, made by J. Brookes Knight in 1938. The (written commu., 1954). second set X2a-X2e) consists of five lots from the same succes­ Palaeophyllum thomii (Hall) ; FoerstepJiylluml sp. undet.; sion of beds, made by Josiah Bridge, J. Brookes Knight, and Streptelasmatid corals, in part probably related to S. others, later in the same field season. In addition, collections prolongatum group; PlatystropMa sp.; DinortMs (Aus- TF 329 to TF 335 were made in 1944 by Cloud and Barnes tinella) sp.; HypsiptycMa sp.; Lepidocyclus sp., tre- (1946, p. 71), but the fossils identified from them are not repro­ postomatous bryozoans. duced here. Identifications are by P. E. Cloud, Jr. (written Om 4 (USGS 2764). Fusselman(?) Dolomite; light-gray commun., 1954). Each set of collections is given in descending bedded limestone, several hundred feet higher stratigraphically stratigraphic order. than Om 3, in same sequence. Originally mapped as upper part X 2. Higher beds to northwest, near saddle. CalatMum sp., of Montoya Dolomite, but later interpreted as a calcitic facies Orospira sp., Bamesella"!, Hormotoma sp., bellerophontid? of Fusselman. Southeast slope of Bed Tank Canyon, a quarter sp., other gastropods, endoceratid cephalopods, Xenelas- of a mile above its eastern portal, in west-central part of sec. ma? sp., TritoecMa"! 4, Block 122. Collected by J. B Knight, 1936; identified by X 1. Lower beds, between saddle and county road. Cala­ Helen Dunean, and Jean Berdan (written commun., 1954). tMum sp., Ceratopea n. sp., C. sp.?, Hormotoma sp., Streptelasmatid coral gen. and sp. ? Orospira cf. 0. elegantula Cullison, gastropod gen. and sp.? orthoid brachiopods gen. and sp.?, trilobite gen. and STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS sp.? OF MISSISSIPPIAN AND PENNSYLVANIAN ROCKS X 2 e. Near saddle, at top of sequence from which collec­ tions were made. Brachiopod gen. and sp. ? SECTION 11. MINE CANYON X 2 d. Gastropod unident.; Mcqueenoceras siphuncle; coiled nautiloid aff. Curtoceras, Tarphyceras, and Eurystomites; The following is a section of part of the Barnett Hystericurusl, Jeffersonia sp., archaeostracan crustacean? Shale exposed in a ravine about half a mile north of gen. and sp.? the portal of Mine Canyon, in the southwestern part X 2 c. CalatMum, Bamesella sp. aff. B. lecanospiroides of sec. 12, Block 66, Twp. 5. The section was measured Bridge and Cloud, Bolbocephalus"! sp., Jeffersonia sp. aff. J. missouriensis Cullison. by J. Brookes Knight in 1931. Fossils collected from X 2 b. Pelmatozoan columnal, Orospiral sp., Diparelasmal units 2, 3, and 4 have been identified by Mackenzie sp. Gordon, Jr., and E. L. Yochelson, and are discussed X 2 a. Near county road, not far above sandstone exposure. on pages 41-42. Ceratopea n. sp., Orospira sp., gastropod gen. and sp.? orthoid gen. and sp. ? Hueco Limestone at top of section. X 15 (USGS 3599). El Paso Limestone, upper part of divi­ Unconformity. sion B, which is here overlain unconformably by Hueco Lime­ Barnett Shale: Feet stone. Northeastern Baylor Mountains, half a mile northeast 9. Limestone, white, impure 5 of stratigraphic section 7a, on northeast side of next ridge. 8. Shale, green 10 Collected by J. B. Knight in 1938; identified by P. E. Cloud, Jr. 7. Shale, purplish-brown; interbedded with shaly (written commun., 1954). limestone- 10 Ceratopea cf. C. ankylosa Cullison, Hormotoma sp., Raphi- 6. Limestone, buff, shaly, friable; contains poorly stoma sp. preserved fossils 10 134 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Barnett Shale Continued Feet here because they are of some descriptive and historical 5. Shale, purplish, carbonaceous; interbedded with interest. thin limestone beds that contain poorly pre­ served fossils______20 From collections made during the earlier phases of 4. Shale like that above, but containing limestone the investigation, brachiopods were identified by R. E. lenses and concretions as much as 3 ft in di­ King (1931) and fusulinids by Dunbar and Skinner ameter; these and similar limestone lenses be­ (1937). Collection numbers are preceded by REK for neath contain well-preserved fossils 10 the brachiopods so identified and by D & S for the 3. Shale, dark-gray; contains pyrite and selenite, also phosphatic nodules; lenticular limestone beds fusulinids so identified. These collections are deposited near top__ _ 20 at Peabody Museum, Yale University. 2. Shale, purplish, carbonaceous; limestone concre­ Fossils in collections made during the later phases of tions and lenses at top and 20 ft below top 50 the investigation were identified by paleontologists of 1. Shale, black, massive, to base of exposure (?) Base concealed by alluvium. the U.S. Geological Survey (P. E. Cloud, Jr., and E. L. Part of Barnett Shale exposed______135-f- Yochelson, written commun., 1954; L. G. Henbest, writ­ ten commun., 1955). They are indicated by accession SECTION 12. MARBLE CANYON numbers prefixed by USGS, and the Foraminifera by The following is a section of part of the beds of additional accession numbers prefixed by "F." In addi­ Pennsylvanian age exposed along the base of the Sierra tion, the field labels of J. Brookes Knight and the Diablo escarpment south of Marble Canyon, along the writer are also generally indicated. These collections east edge of sec. 21, Block 66, Twp. 5. The section was are deposited with the U.S. Geological Survey. measured by P. B. King and E. E. King in 1928, and SECTION 13. WYUCB MOUNTAINS fossils were collected from units 5 and 6 by J. Brookes Knight and P. B. King in 1931. Identification of these The following is a section of the Hueco and Victorio fossils by Mackenzie Gordon, Jr., and E. L. Yochelson Peak Limestones in the Wylie Mountains, beginning in is given on page 45. the southeast corner of the report area, and proceeding Hueco Limestone at top of section. eastward across the mountains about 10 miles. Sec­ Angular unconformity. tions of the Hueco Limestone on the west face of the Beds of Pennsylvanian age: Feet Wylie Mountains were measured by P. B. King and 10. Limestone, gray, thin-bedded; forms a slope _ 22 E. E. King in 1928, and by P. B. King and J. Brookes 9. Limestone, light-gray, granular; forms a ledge 22 8. Limestone, light-gray, thin-bedded; forms a slope. 24 Knight in 1931, at which time scattered observations 7. Limestone, light-gray, granular; forms a ledge 25 were also made on higher strata farther east. Sub­ 6. Slope on which bedrock is concealed; Spirifer, sequently, the whole mountain area has been mapped cup corals, and other fossils on surface___ 5 and described by Hay-Eoe (1957). Fossils collected in 5. Limestone; forms a ledge; contains bellerophon- 1928 were identified by E. E. King (1931) and Dunbar tids and cup corals______3 4. Covered ______11 and Skinner (1937); those collected in 1931 were identi­ 3. Limestone, light-gray, granular; contains crinoid fied by E. L. Yochelson (written commun., 1959); those columnals______22 collected by Hay-Eoe were identified by E. V. Hollings- 2. Covered______6 worth and D. A. Drake (Hay-Eoe, 1957). Some col­ 1. Limestone, light-gray, granular; forms a ledge__ 30 lections from the same area were made earlier by G. B. Base concealed by alluvium. Part of beds of Pennsylvanian age exposed______170 Eichardson and identified by G. H. Girty (Eichardson, 1914, p. 5). STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS The section given here is compiled from these sources. OF PERMIAN BOCKS Data on the Powwow Member of the Hueco Limestone The sections and fossil lists which follow describe combine observations by King and his associates and fossils which were collected and identified during both by Hay-Roe. Units 3-7 of the main body of the Hueco the earlier and later phases of this investigation. As Limestone are generalized from the sections by P. B. many revisions of fossil terminology and taxonomy King and E. E. King and by P. B. King and J. Brookes have been made between the times of the earlier and Knight, which were measured on the slope west of eleva­ later investigations, the names for the same fossils are tion point 5039 (sec. 3, Block 64). The section of likely to vary from one collection to another. It has Victorio Peak Limestone is from Hay-Eoe, with the not been feasible to revise the earlier identifications to addition of some observations by P. B. King and J. agree with the later, but the earlier listings are given Brookes Knight. STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 135

Seven Rivers Formation in eastern foothills of Hueco Limestone Continued Wylie Mountains, and farther east. Main body of formation Continued Feet Conformity (?). chert nodules and lenses. Spicules, Victorio Peak Limestone: fusulinids, productids, gastropods, Dolomite member: Feet and echinoid spines observed in 12. Dolomite, granular; with calcite various layers. Forms summit of vugs; pale brownish gray; weath­ west face of Wylie Mountains south ers deeply pitted; in thick massive of elevation point 5039______173 beds. Contains abundant species of 6. Limestone. In upper part thinner Parafusulina (identified by R. V. bedded and darker gray than beds Hollingsworth), which are said to above and below, forming thin be of Leonard type in lower part ledges on slope; in lower part, and of Guadalupe type in the upper some thicker, lighter gray ledges. part. Most of these weather to A few beds in upper part contain cavities, but part are silicifled. small chert nodules. Fossils are Forms eastern third of Wylie abundant in many beds, but are Mountains______..____ 1,100 mostly visible in cross section, Marl member: and are partly destroyed by dolomiti- 11. Marl, dolomitic; poorly exposed be­ zation. From collections of 1928 cause of slumping of overlying have been identified Staffella sp., beds; wedges out along strike south Pseudoschwagerina texana Dunbar of mountains______15 and Skinner, Productus incal Limestone member: d'Orbigny, and Productus invest 10. Limestone and dolomite, yellowish- to Newberry (D & S 141, 142; REK brownish-gray; weathers to light- 508). Collection of 1931 contains gray pitted surfaces; in 4- to 6-in. Polypora sp., Composita sp., and beds; contains rare poorly pre­ Omphalotrochus sp. (USGS 7005x) ; served fossils. In 1931, bellero- echinoid spines, a pinnid pelecypod, phontid gastropods as much as 3 in. and bellerophontid gastropods also in diameter were collected in basal observed______211 beds, and in higher beds a large coarsely ribbed spiriferoid (USGS 5. Limestone, dolomitic, fine-grained to dense, gray to dark-gray; in 1- to 7052) ______4 TO 4-ft beds; forms ledges and cliffs. Basal member: Some beds are laminated and a few 9. Marl, dolomitic, thin-bedded, yellow- are brecciated. Some poorly pre­ gray to pale-brown; with thin served echinoid spines and bellero­ ledge-making dolomite layers, in- phontid gastropods observed______terbedded with red silty shale and 196 crossbedded limestone-pebble con­ 4. Limestone, partly dolomitic, gray to glomerate. Forms a light-colored pink; weathers gray; in 1- to 3-ft slope-making band between the beds; forms ledges and slopes, with ledges that extends southward a covered interval at base______75 across the mountains______30-60 3. Limestone, gray to gray-brown; mainly Unconformity. in 6-in. to 1-ft beds; forms slopes Hueco Limestone: and thin ledges below, where there Main body of formation: are many marl partings, but pass­ 8. Limestone, similar to that below, ing into a strong ledge at top, which forming summits of western third is prominent at about midheight on of Wylie Mountains. Thickness in­ west face of mountains. A few beds determinate on outcrop because of contain chert nodules and lenses. numerous closely spaced faults of Fossils are abundant, but are mostly small displacement. Amount given poorly preserved and fragmented. is obtained by subtracting measured Productus hessensis King and thickness of lower beds from total Composita subtilita (Hall) have been thickness of main body of forma­ been identified from collection of tion (1,240 ft) in Cosden Petro 1928 (REK 507). Collection of 1931 leum Oockrell 1 well at east edge includes echinoid spines; the bra- of mountains (sec. 7, Block 80)__ 450 7. Limestone, dense, dark-gray to gray- chiopods Composita cf. C. sultilita brown; in 6-in to 2-ft beds; forms (Hall), and Dictyoclostus (n. sub- ledges 5-30 ft thick, separated by gen.) cf. D. hessensis (King), D. slopes, in which platy limestone wolfcampensis (King) ; the gastro­ and shale are interbedded. Many pods Omphalotrochusl sp. and a bel­ of the limestone beds contain short lerophontid ; and the pelecypod Avi- 136 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone Continued Hueco Limestone Continued Main body of formation Continued Feet Main body of formation Continued Feet culopecten sp. (USGS 7005) ; staffel- 5. Limestone, poorly exposed______13 lid foraminifers also observed______139 Powwow Member: Powwow Member: 4. Sandstone, calcareous, micaceous, fissile 5 2. Marl and nodular limestone, buff, 3. Sandstone, irregularly banded red and gray 20 poorly consolidated. Abundant staf- 2. Sandstone, coarse, conglomeratic, gray; lying fellid foraminifers, Composita, pro- unevenly on unit below- ______8 ductid brachiopods, euomphalid gas­ 1. Sandstone and conglomerate, micaceous, dark- tropods, pectenoid pelecypods, and purplish-red, containing angular fragments echinoid spines and plates observed. of quartz and schist. (This unit was as­ Also contains the ostracodes Ellip- signed by Baker to the Van Horn sandstone; sellal distenda Kellett, Healdia! sp., observations by King, confirmed by Flawn, ParaparcMtes humerosus Ulrich and indicate that it is part of the Powwow mem­ Bassler, and P. magnus Kellett, and ber, although Flawn has found true Van the foraminifer Globovalvulina sp. Horn sandstone below the Hueco a mile or (identified by D. A. Drake)______20 two to the northeast.) -______250 1. Sandstone, siltstone, and shale, arkosic Angular unconformity. and conglomeratic, poorly consoli­ Carrizo Mountain Formation at base of section. dated, dark-red-brown to orange. Summary of section 14 Thickness varies abruptly within Hueco Limestone: short distances, as a result of deposi­ Part of main body of formation exposed 438 tion on an irregularly eroded surface Powwow Member _ 283 of underlying rocks______20-150 Angular unconformity. Part of Hueco Limestone exposed ____ 721 Metamorphic rocks of Carrizo Mountain Forma­ tion at base of section. SECTION 15. THREEMUJEJ MOUNTAIN Summary of section 13 Victorio Peak Limestone______1, 615-1, 645 The following is a section of Hueco Limestone on Hueco limestone: Threemile Mountain, at the east end of the high ridge Main body of formation______1, 244 northwest of Van Horn, in the southeastern part of sec. Powwow Member______40-170 13, Block 66, Twp. 8. The main part of the section Total Hueco Limestone______1,284-1,414 (units 1-14) was measured up the east face of the mountain to the top of a spur, the higher beds being SECTION 14. BASS CANYON added from the summit of the mountain, 750 ft to the The following is a section of the Hueco Limestone in northwest, which is separated from the spur by minor the southern Carrizo Mountains, on the south slope of faults, downthrown to the west. The section was meas­ Bass Canyon, about 1^ miles south of the south edge ured by J. Brookes Knight in 1931, and some additional of the report area (sec. 18, Block 66, Twp. 9). A sec­ notes and fossil collections were made in 1938. Larger tion at this locality is given by Baker (1927, p. 9), and fossils were identified by P. E. Cloud, Jr., and E. L. a section of the main body of the formation was meas­ Yochelson; foraminifers were identified by L. G. Hen- ured by P. B. King and R. E. King in 1928; the area best (written commun., 1954,1955). Besides the fossil was later mapped by Flawn (in King, P. B., and Flawn, collections from Threemile Mountain listed here, others P. T., 1953, p. 67 and pi. 1). In the section given here, were made by G. B. Eichardson in 1907, which were the description of the Powwow Member is by Baker identified by G. H. Girty (USGS 7184; field loc. 37), and that of the main body of the formation by P. B. and by J. W. Beede and others for the Texas Bureau of King and R. E. King. Fossils were identified by E. E. Economic Geology, which were identified by E. E. King King (1931). (1931, REK Te). Top of ridge; no higher beds preserved. Hueco Limestone: Top of mountain; no higher beds preserved. Main body of formation: Feet Hueco Limestone: 8. Limestone, dark-gray; in 1-ft beds; inter- Main body of formation: Feet bedded with thin-bedded yellow-brown lime­ 19. Limestone, thinner bedded and darker than stone______255 below; near top, cross sections of pelecypods 7. Limestone, dark-gray, thin-bedded______70 observed- 38 6. Limestone, dark-gray, thick-bedded; forms 18. Limestone, massive, gray; weathers pitted_ 12 prominent ledges. Contains Productus Jies- 17. Limestone, thin-bedded, light-gray; a few beds sensis King and Composita subtilita (Hall) 2-3 ft thick______38 (REK 510) ; staffellid foraminifers, echinoid 16. Limestone, dark-gray; contains some chert and spines, and gastropods also observed____ 100 fossils 17 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 137

Hueco Limestone Continued Hueco Limestone Continued Main body of formation Continued Feet Powwow Member Continued Feet 15. Limestone, dark-gray; forms a slope; con­ dens (Morton) ; the gastropods Straparol­ tains chert and a few echinoid spines, and lus (Euomphalus) cornudanus (Shumard), near base, large bellerophontids____ 23 Omphalotrochus obtusispira (Shumard), 14. Limestone, thin-bedded; forms top of south­ and a large bellerophontid; and the eastern spur______10 scaphopod Plagioglyptal sp. (USGS 14430; 13. Limestone, massive, gray; contains chert and field label C 7) ______22 bellerophontids______55 3. Sandstone, arkosic, conglomeratic, yellow; 12. Limestone, thin-bedded; weathers yellowish; mostly forms a slope, but with ledges to­ succeeding unit. Contains echinoid spines ward the top______77 and other fossils______25 2. Sandstone, arkosic, red; contains scattered 11. Limestone, forming a ledge; contains bryo- chert pebbles near base and a layer of lime­ zoans______18 stone-pebble conglomerate in a red arkosic 10. Limestone, forming slopes and ledges; con­ matrix at top______37 tains bryozoans and large echinoid spines_ 11 1. Conglomerate, gray; formed of limestone 9. Limestone, gray, massive; with thin marl pebbles and cobbles, probably derived from partings near base and bands of chert nod­ El Paso Limestone to north. This unit is ules near top. This and adjacent beds con­ a very local deposit, and thins rapidly tain Wewokella (Talpaspongia) clavata (R. westward______..______70 H. King), other sponges and their spicules, Angular unconformity. Syringopora sp. and other compound corals; Van Horn Sandstone in massive red ledges at base of echinoid spines and plates; Fenestella sp., section. Fistulipora sp., Polypora sp., and other Summary of section 15 bryozoans; the brachiopods Composita cf. C. Hueco Limestone: subtilita (Hall), Crurithyrisl sp., Dictyo- Part of main body of formation exposed_____ 357 clostus wolfcampensis (King), various die- Powwow Member______206 lasmids including Dielasma aff. D. bovidens (Morton), Hustedia mormoni (Macrou), Part of Hueco Limestone exposed 563 and Meekellal sp.; the pelecypods Alloris mal sp., Aviculopecten sp., Aviculopinna sp., OTHER FOSSIL COUUECTIONS FROM HUECO LIMESTONE Pseudomonotis sp., and Septimyalina sp.; IN THREEMIUE3 MOUNTAIN AREA the gastropods Betterophon parvicristatus The following fossils were collected by P. B. King Yochelson and other bellerophontids, Euconispira cf. E. missouriensis (Swallow), and J. Brookes Knight from the Hueco Limestone in a loxonematacean, Meekospira sp., Nati- the Threemile Mountain area, but not in any measured copsis sp., Omphalotrochus obtusispira section: (Shumard), Stegocoelia! sp., Straparollus USaS 14438, F 9813 (field label C 15). About 4 miles west (Euomphalus) cornudanus (Shumard), and of Threemile Mountain, on south side of ridge, south of eleva­ a subulitid; the scaphopod Plagioglyptat tion point 5083 (southwestern part of sec. 16, Block 66, Twp. 8). sp.; and ostracodes (USGS 6937,14437; field Lower part of main body of Hueco Limestone contains unde­ labels 11, C 14). The beds also contain termined bryozoans; the brachiopods Dictyoclostus wolfcam­ the foraminifers Stafella sp., and Ozawai- pensis (King), D. (n. subgen.) huecoensis (King), and Com- nella sp. (F. 2718c, 9812), and Dunbar and posital sp.; and the gastropods Omphalotrochus"! sp., Stegoco- Skinner report the presence of Schivagerina elia"! sp., Straparollus (Euomphalus) cornudanus (Shumard) ; bellula Dunbar and Skinner (D & S 90)__ 30 large bellerophontids, and a subulitid. The limestone is 8. Limestone, marly; forms a slope; poorly ex­ crowded with small foraminifers of the Spandelina group and posed except in ravines. Contains bellero­ Staffella sp. and with juvenaria of fusulinids, probably includ­ phontids______35 ing Schubertella. 7. Limestone, gray; forms a ledge______6 USGS 14426 (field label C S). About 3% miles west-north­ 6. Marl and marly limestone ; containing bellero­ west of Threemile Mountain, on an outlier whose summit is phontids______19 elevation point 5079 (near center of sec. 9, Block 66, Twp. 8). 5. Limestone, thick-bedded, gray to light-gray; Limestone and interbedded marls of main body of Hueco 25-50 with marl partings; forms a ledge. Con­ ft above Powwow Member contain echinoid spines, the tains bellerophontids______20 brachiopods Dictyoclostus wolfcampensis (King) and Com­ Powwow Member: posita cf. C. subtilita (Hall) ; and the gastrophod Omphalo- 4. Limestone, marly; forms a slope; poorly ex­ trochus obtusispira (Shumard). Staffellid foraminifers and posed except in ravines. Fossils occur in productid gastropods were observed in the field, but are not the marls and are scattered on the slope, represented in the collection. derived from this bed and those just above. They include fenestrate and branching SECTION 16. BEACH MOUNTAIN bryozoans; the brachiopods Dictyoclostus wolfcampensis (King), Composita cf. C. The following are two sections of the Hueco Lime­ subtilita (Hall), and Dielasma cf. D. bovi- stone on the eastern flank of Beach Mountain. Section 138 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS 16a was measured at the east end of a mesalike outlier Section 16b Continued whose summit is elevation point 5021 (near center of Hueco Limestone Continued Main body of formation Continued Feet south line of sec. 6, block G). Section 16b was measured 5. Limestone, dolomitic; gray, in 3- to 5-ft beds; about three-quarters of a mile farther east, in a block forms receding ledges. A euomphalid gastro­ downfaulted farther than rocks of the preceding, and pod observed near top; irregular siliceous extends south westward from outcrops of Montoya Dolo­ masses lower down may in part be much mite to the crest of the ridge (southwestern part of sec. altered fossils______- _ 50 4. Limestone, dolomitic, splintery; forms thin 6, Block 65, Twp. 8). The sections were measured by ledges on slope, with a 2-f t ledge near middle J. Brookes Knight in 1931. Fossils were observed in the that contains poorly preserved bellerophontid field, but none were collected. Small collections, which gastropods______35 were made in the same area by G. B. Richardson in 3. Slope, with a thin ledge of splintery yellow- 1907, have been identified by G. H. Girty (USGS 7182, gray dolomitic limestone at top__ __ 10 Powwow Member: 7l82a; field Iocs. 25, 27). 2. Slope, poorly exposed. Some outcrops of red Section 16a marl at top, but most of surface is covered by limestone pebbles and reddish wash__ 30 Top of outlier; no higher beds preserved. 1. Conglomerate, sandy, yellow, composed of lime­ Hueco Limestone: stone pebbles derived from underlying Ordo­ Main body of formation : Feet vician rocks______3 10. Limestone, dolomitic, blue-gray, thin-bedded; Angular unconformity. forms 1- to 3-ft ledges; contains minute Monotoya Dolomite at base of section, on northeast. mollusks______70 Summary of section 16 9. Limestone, dolomitic, yellow-gray, splintery; forms 5- to 15-ft ledges; contains poorly pre­ Hueco Limestone: served silicified fossils, including bellero- Section 16a: phontids__ _.______105 Part of main body of formation exposed__ 269 8. Limestone, dolomitic, yellow-gray; in 1- to 2-f t Powwow Member______52 beds; interbedded with dolomitic marl; forms a slope______100 Part of Hueco limestone exposed______348 7. Limestone, dolomitic, yellow-gray; forms Section 16b: a ledge; contains staffellid foraminifers and Part of main body of formation exposed__ 235 Powwow Member______33 large productids______3 6. Slope, with a thin ledge of dolomitic lime­ Part of Hueco Limestone exposed______268 stone near middle; probably mostly marl__ 15 5. Limestone, dark blue-gray, mottled; forms a SECTION 17. HIGH POINT OF BAYL.OR MOUNTAINS ledge; cross sections of small gastropods observed______3 The following section of the Hueco and Bone Powwow Member: Spring Limestones was measured on the eastern face of 4. Marl, sandy, poorly consolidated; yellow, be­ Baylor Mountains, up a southeast-trending spur, whose low nearly white at top______8 summit is the high point of the mountains, at BM 5568 3. Sandstone, fine-grained, marly, red; contains (northeastern part of sec. 1, Block 122, and southern pebbles near base______25 part of sec. 3, Block 65, Twp. 7). A section was meas­ 2. Slope without exposures; pebbles on surface_ 17 ured here by P. B. King and R. E. King in 1928, and 1. Conglomerate, made up of limestone pebbles again by J. Brookes Knight in 1931. The section derived from underlying Ordovician rocks_ 2 Angular unconformity. given is that of Knight, but some notes made in 1938 Montoya Dolomite at base of section. have been added, and the fossils collected in 1928 are placed in their approximate positions in the section. Section 16b Fossils collected in 1928 were identified by R. E. King Top of ridge; no higher beds exposed. (1931), and those collected in 1931 by P. E. Cloud, Jr., Hueco Limestone: and E. L. Yochelson (written commun., 1954). Main body of formation: Top of mountain ; no higher beds exposed. 6. Limestone, dolomitic, gray; in 3- to 5-ft beds, Bone Spring Limestone: Feet becoming thinner bedded, darker, and less 17. Limestone, dolomitic, light-gray, massive; has an dolomitic upward. In the thinner darker original dip to north, and forms great cliffs north beds cross sections of small mollusks are of summit BM 5568______200 visible; the topmost Tedge contains poorly 16. Limestone, fine-grained, light-gray, thin-bedded; preserved gastropods, including Euconispira, contains fossil fragments. Forms a cliff whose euomphalids, and bellerophontids, as well as summit is BM 5568; wedges out northward be­ Composita, cup corals, and echinoid spines- 140 neath, and partly intergrates with unit above_ 110 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 139

Bone Spring Limestone Continued Feet Bone Spring Limestone Continued Feet 15. Shale, calcareous or marly, yellow to pink; with 4. Limestone, dolomitic, light- to dark-gray; in 1- to some ledges of dark-gray limestone a foot or two 4-ft beds; weathers jagged in part; forms a slope. 'thick, in part fossilferous______55 Some beds contain molds of fusulinids that are 14. Limestone, dark-gray, thin-bedded, cherty, very fos- larger than those below_ 110 siliferous. From a collection made in 1928 at Unconformity ( ?). about this level, R. E. King identified the brachi- Hueco Limestone: opods Rhipidomella mesoplatys baylorensis King Main body of formation : (type), Streptorhynchus pyramidalel King, Pro- 3. Limestone, dolomitic, light-gray, thinly and ductus ivesi Newberry, Productus schucherti evenly bedded, splintery; forms cliffs in King, Linoproductus cora angustus King, Mar­ upper part. Most beds contain molds of ginifera sublaevis King, Aulostegas triagonalis small fusulinids, and a bed 25 ft above base King, Spirifer (Neospirifer) pseudocameratus contains nodules of probable algal origin 308 Girty, Hustedia meekana (Shumard), and Com- 2. Limestone, dolomitic, light gray-brown; in 2- posita mira (Girty) (REK 503)______10 to 5-ft beds; weathers somewhat pitted; 13. Limestone, dolomitic, irregularly bedded; with sili- forms a ledge; contains vugs, cavities, and teeous bands that contain fossils______45 fusulinid molds _ _ 10 12. Limestone, dolomitic, gray, massive; contains Powwow (?) Member: sponges at base ______10 1. Poorly exposed on slope; in ravines are out­ 11. Limestone, granular, light-gray, thick-bedded, crops of limestone-pebble conglomerate in cherty; contains many gilicified brachiopods_ 15 gray-brown dolomitic matrix 35 10. Limestone, light-gray, thin-bedded and laminated; Angular unconformity. interbedded with siliceous shale. Many cherty Beds of Devonian age, and Fusselman Dolomite at base of bands are fossiliferous and contain hexactinellid section (see section 7). sponge spicules; the bryozoans Fistuliopora sp., Summary of section 17 Acanthocladia sp., and Polypora sp.; the brachio­ Part of Bone Spring Limestone exposed __ _ 995 pods Buxtonia (Kochiproductus) victorioensis Hueco Limestone: King, Chonetes sp., Composita sp., Dictyoclostus Main body of formation____ 318 (Chaoiella) guadalupensis (Girty), Hustedia Powwow (?) Member-_ 35 sp., Linoproductus (Cancrinella) sp., "Margini- fera" sp., "Martinia" sp., Meekella sp., orthoteta- Total Hueco Limestone______353 cean indet., "Spirifer" sp., and Stenocisma sp.; OTHER FOSSIL COLLECTIONS FROM BONE SPRING a nuculoid pelecypod; the gastropods Apachella LIMESTONE NEAR HIGH POINT OF BAYLOR MOUN­ sp., Babylonites sp., Euphemites cf. E. imperator TAINS Yochelson, E. sp., and Knightites (Retispira) sp.; the scaphopod Plagioglypta sp.; and the tril- The following fossils were collected from the Bone obite Delarial sp. (USGS 7048 ; field label 24 A). Spring Limestone by P. B. King in 1931, on the ridge From a collection made in 1928 at about the same west of the high point of the Baylor Mountains; the level, R. E. King identified the brachipods collections are not in the measured section, but their Rhipidomella mesoplatys baylorensis King, Meek­ ella difflcilis Girty, Marginifera manzanica Girty, stratigraphic positions can be approximated. Prorichthofenia likharewi King, Camarophoria USGS 1053. Ridge west of high point of Baylor Mountains, venusta Girty, Hustedia meekana (Shumard), near elevation point 5535 (northeastern part of sec. 2, Block and Composita subtillta (Hall) (REK 502)__ 50 122), from black limestone above middle reef beds (approx. 9. Limestone, dolomitic; contains abundant molds of unit 15 of section 17). Contains the coral Lophophyllum sp.; fusulinids in parallel orientation ; weathers very the bryozoan Fistulipora sp.; the brachiopods Chonetes sp., Lino­ jagged; forms ledges that alternate with 2- to productus (Cancrinella) sp., "Marginifera" spp., Dictyoclostus 3-ft layers of marl. To north, the dolomitic (Chaoiella) guadalupensis (Girty), productids indet., Steno- layers wedge out into light-gray platy fossilifer­ cismal sp., Neospirifer sp., and Rhipidomella sp.; the pelecypods ous limestone ______110 Astartella sp. and a pectenoid; and a bellerophontid gastropod. 8. Limestone, dolomitic, thin-bedded; contains poorly USGS 7009. North end of ridge west of high point of Baylor preserved large fusulinids, crinoid columnals, Mountains (southeastern part of sec. 4, Block 65, Twp. 7), from and cup corals; weathers very jagged; some in­ top of middle reef beds (approx. unit 14 of section 17, or at terbedded marl near top______55 about same level as collection REK 503). Contains the bryo­ 7. Limestone, dolomitic, massive; in part brecciated; zoans Fistulipora sp. and Striatopora sp.; the brachiopods weathers very jagged; forms a lens; contains Leptodus sp., Rhipidomella sp., and a productid; the pelecy­ poorly preserved large fusulinids and other fos­ pods Astartella sp., "Cypricardinia" sp., a nuculoid, and sils______20 Pteria! sp.; and the gastropods Apachella sp., Euphemites sp., Glabrocingulum sp., and a pleurotomarian. 6. Limestone, dolomitic; resembles beds below, but forms receding ledges______40 SECTION 18. NORTHEASTERN BAYLOR MOUNTAINS 5. Limestone, dolomitic, light-gray, thick-bedded; weathers jagged; forms cliffs; contains poorly The following section of the Hueco and Bone Spring preserved crinoid columnals near top______165 Limestones was measured in the northeastern part of the 140 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Baylor Mountains northwestward up the first ridge Bone Spring Limestone Continued Feet southwest of elevation point 4888 (north-central part of 14. Limestone, granular, gray, thick-bedded; contains a large Enteletes and other fossils 14 sec. 48, Block 65, Twp. 6), with higher beds on elevation 13. Limestone, dolomitic, gray, massive. Contains point 4888 added (south-central part of sec. 37, Block the bryozoan Fistulipora sp.; the brachiopods 65, Twp. 6), which are downfaulted with respect to the MeeJcella sp., Prorichthofenia sp., and Weller- main section. The section was measured by J. Brookes ella sp. (large) ; a pseudozygopleuran and a Knight in 1931, but some additional observations were pleurotomarian gastropod, and an indetermi­ nate nautiloid (USGS 7000; field label 25 B). made in 1938. Fossils were identified by P. E. Cloud, Sponges were observed near base- 45 Jr., and E. L. Yochelson (written commun., 1954). 12. Limestone, black, thin-bedded; with an irregular upper contact_____-_____-__-_ _ 5 Top of ridge; no higher beds exposed. 11. Limestone, dolomitic, light-gray, massive; con­ Bone Spring Limestone: Feet tains large fusulinids______35 18. Limestone, dark-gray, fine-grained to dense; chert 10. Limestone, granular, light-gray, thin-bedded, fos- nodules in 6-in to 2-ft beds; weathers to siliferous; mostly forms float on a slope___ 20 smooth gray surfaces and forms cliffs. Re­ 9. Limestone, dolomitic, massive, in part brecciated; sembles limestone at high point of Baylor forms a reefy mass; contains rare fossils- _ 35 Mountains (unit 16, section 17). Thickness 8. Limestone, slabby, black; forms a slope_____ 25 given is approximately that on elevation point 7. Limestone, dolomitic; brecciated below, massive 4888; on ridges at northeast, near northeast end above; forms a reefy mass. Contains many of mountains, these limestones are several silicified fossils, and near base, large fusulinids- 40 times thicker______100 6. Limestone, platy to thin-bedded; light-gray below 17. Limestone, thin-bedded, black; forms a slope. and black above; forms a slope; several 2-ft On southeast slope of summit 4888, about 150 ft beds of granular limestone interbedded near stratigraphically above unit 14, a thin lens of bioclastic limestone (or "molluscan ledge") con­ base ______110 tains a prolific dominantly molluscan fauna 5. Limestone, dolomitic, light-gray, thin-bedded to (USGS 6983, USGS 14475; field labels 27, C platy; with a 10-f t ledge of granular fossilif er­ 33). This includes the corala Amplexus sp., ous limestone interbedded 17 ft above base. Cladochonus sp., and Lophophyllum sp.; the This contains the brachiopods Prorichthofenia bryozoans Acanthocladia sp., Cystodictya sp., >sp. and "Marginifera" sp., the gastropod War- Fenestella sp., Fistulipora sp., MeeJcopora sp., thia waageni Yochelson, and the scaphopod Polypora sp., Rhom'bopora sp., Septopora sp., Plagioglypta sp. (USGS 7000a; field label 25 Stenopora sp., and Striatopora sp.; the brachi- AA). At about the same level, large indeter­ opods Avonia sp., Buxtonia (KocMproductus) minate fusulinids were collected (F 9822; field victorioensis King, CJionetes sp., (large), Com- label C 24 B)______66 posita sp., Enteletes cf. E. dumblei Girty, 4. Limestone, dolomitic, siliceous, gray, thin-bedded Hustedia mormoni (Marcou), Leptodus sp., and laminated; forms a slope______15 Heekella difflcilia Girty, orthotetacean indet., 3. Limestone, dolomitic, granular, light-gray; forms Rhipidomella sp., Squamularia sp., and Well- a ledge, with a slope beneath______8 erella sp.; and the trilobite Delaria"! sp. The Erosional unconformity. mollusks include the pelecypods Acanthopecten Hueco Limestone: sp., Astartella nasuta Girty, Aviculopecten sp., 2. Limestone, dolomitic, bedded, in part brecciated; Edmondia sp., Myalinid indet., Nucula sp., forms massive ledges. Some 1-ft beds of light- Nuculana spp., Paleoneilo sp., Parallelodon sp., gray compact limestone are interbedded about PermopJiorus sp., Pseudomonotis sp., Pterial 15-ft below top. The dolomitic beds contain sp., Schizodus sp., Solenoyma sp., and Stre'blop- numerous small or slender fusulinids, mostly teria sp.; the gastropods Anomphalus sp., preserved as molds and partly filled by quartz, Babylonites sp., Bellerophon deflectus Chronic, which are indeterminate in the laboratory Glyptospira sp., Knightites (Retispira) sp., cf. (F 3908; field label C 24 A). The unit varies Loxonema sp., Naticopsis sp., Orthonema sp., in thickness, due to the unconformities at the top pleurotomarian indet., StegocoeUat sp., "Stro- and base of the Hueco; a thickness of 100 ft was leus" sp., sublitid indet, Trachydomia sp., "T." measured nearby to the east in 1938, but the unit sp., and "Worthenia" sp.; the chiton "Grypho- pinches out entirely between the Bone Spring chiton" sp.; the scaphopod Plagioglypta sp.; and El Paso a short distance to the south____ 80 and an orthoceratid cephalopod and an am­ 1. Conglomerate, dolomitic; contains angular pebbles monite______.._-______200 of limestone, dolomite, and chert, derived from 16. Limestone, granular, dark-gray, evenly bedded; underlying Ordovician formations-___ __ 15 contains some poorly preserved fossils. Forms Angular unconformity. top of ridge southwest of summit 4888_____ 20 El Paso Limestone (division A) at base of section. 15. Limestone, platy and siliceous, gray and black; Summary of section 18: forms a slope. Some 1-ft beds of gray granular Part of Bone Spring Limestone exposed___ _ 823 limestone interbedded in lower part______85 Total Hueco Limestone_ 95 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 141

SECTION 19. NORTHWESTERN BAYIX)R MOUNTAINS Bone Spring Limestone Continued Feet The following is a section of the Hueco and Bone Donaldinal sp., Platyceras sp., pseudozygo- Spring Limestones on a northwestern hill of the Baylor pleuran indet., Stegocoelia! sp., Straparollus Mountains, whose summit is elevation point 4364, lying (Euomphalus) cf. S. (E). Jcaibabensis Chronic, about half a mile east of Texas Highway 54 (southeast­ Trachydomia sp., and "T." sp.; the scaphopod ern part of sec. 42, Block 65, Twp. 6). The section is Dentalium sp.; and an ammonite (USGS 7002b; field label 26). Ledges near the base of based on observations by P. B. King and J. Brookes the slope contain indeterminate fusulinids; Knight in 1931 and 1936. The units are incompletely the sponges Fissispongia n. sp., n. gen. aff. F., described, and their thicknesses are estimated; the sec­ and Girtyocoelia dunbari R. H. King; the tion is included mainly to indicate the relative positions bryozoan Fistulipora sp.; the brachipods Com- of the fossil collections. Larger fossils were identified posita sp., Enteletes sp., Neospirifer sp., pro- ductid indet, ProricMhofenia sp., Squamu- by P. E. Cloud, Jr., and E. L. Yochelson, and f oraminif- laria sp., and Wellerella sp.; the pelecypods ers by L. G. Henbest (written commun., 1954, 1955). Parallelodon sp., pectenoid indet, and Pseu- Top of hill; no higher beds preserved. domonotis sp.; and the gastropods Bellerophon Bone Spring Limestone: Feet sp. and Euphemites sp. (USGS 7002a) 175 6. Limestone, dolomitic; weathers brown and Unconformity (angular and erosional at nearby locali­ jagged; similar to unit beneath, but somewhat ties). thinner bedded. Contains algae, crinoid Hueco Limestone: stems, and abundant large fusulinids, rather 3. Limestone, dolomitic, massive; interbedded with poorly preserved as a result of dolomitization. thin-bedded limestone and bedded chert; forms Fossils are better preserved at this level a mile ledges. In lower part contains the brachio­ to the southeast, where the rock is a calciru- pods Meekellal sp., "Productus" sp., Leptodus dite in which many of the fusulinid shells are sp., and Hustedia hessensis King (USGS completely preserved, although most show the 7002) ______100 effects of attrition. Rounded pellets of lime­ 3. Limestone, dolomitic, gray-brown; weathers stone are abundant, some of which contain fos­ pitted______.______50 sils that belong to a different facies from that represented by the matrix. This rock prob­ 1. Limestone, dolomitic, thin-bedded; crumpled in ably is a lithified beach sand, derived from places; contains some small fusulinids. This nearby reefs. It contains the foraminifers unit wedges out entirely against the El Paso Climacammina sp., Tetrataxis sp., Staffella Limestone at the south end of the ridge, where sp., Pseudofusulina setum (Dunbar and Skin­ unit 2 lies on the El Paso; a mile to the south­ ner), Parafusulina imlayi Dunbar var., fusu­ west, units 2 and 3 are also missing, so that linids of the P. attenuata-P. bakeri series, P. unit 4 lies on the El Paso. Thickness to base schucherti Dunbar and Skinner, and P.I sp. of slope in northern part of hill______100 (F 2720; field label Pb 16)______50 Angular unconformity. 5. Limestone, dolomitic; weathers brown and El Paso Limestone at base of section; exposed only at jagged; thick bedded to massive, with some south end of hill. marl partings. Poorly preserved sponges, Summary of section 19 Geyerella, Leptodus, and productids ob­ Part of Bone Spring Limestone exposed 325 served, and some thin layers contain fusu- Total Hueco Limestone______150-250 linids-______100 4. Slope-making beds, mainly covered by blocks that SECTION 20. EAGLE FLAT have slumped from above. Appears to be mostly thin-bedded cherty fossiliferous lime­ The following is a section of the Hueco Limestone stone, but shale and marl are exposed in places at the east end of the high ridge north of Texas and near base. A fossiliferous limestone near top locally yields an extensive fauna, which in­ Pacific Railway, about a mile northwest of Eagle Flat cludes indeterminate fusulinids; the corals section house (center of south line of sec. 1, Block 69, Gladochonus sp. and Lophophyllum sp.; the Twp. 8). The Powwow Member was measured on the bryozoans Batostomella sp., Fistulipora sp., slope at the eastern end, where it is exposed in a gully; and Striatopora sp.; echinoid plates; the the main body of the formation was measured about brachiopods Chonetes (Chonetinella) victori- anus (Girty), Crurithyris sp., Dielasma spp., half a mile to the northwest on the north side of the Enteletes cf. E. dumblei Girty, Hemiptychina ridge, beginning about 500 feet east of an abandoned sp., Hustedia mormoni (Marcou), Leptodus prospect pit, the higher beds (units 22-24) being added sp., Meekella sp., Neospirifer sp., orthoteta- from a ridge top to the west. The section was meas­ cean indet., Rhipidomella sp., and Wellerella ured by J. Brookes Knight in 1931. Fossils were identi­ sp.; the pelecypods Acanthopecten sp. and Par- allelodon sp.; the gastropods Anomphaltis sp., fied by P. E. Cloud, Jr., and E. L. Yochelson (written Babylonites sp., Bellerophon deflectus Chronic, commun., 1954). 142 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Top of ridge; no higher beds exposed. Hueco Limestone Continued Hueco Limestone: Powwow Member Continued Feet Main body of formation: Feet 7. Shale, sandy, yellow; mostly covered 18 24. Limestone, dark-gray, thin-bedded; contains 6. Conglomerate, red _ 2 small gastropods 8 5. Shale, red, sandy _ 6 23. Limestone, forming a ledge__ _ 3 4. Conglomerate, gray; formed of schist and 22. Limestone, thin-bedded, splintery; weathers chert pebbles___ 7 gray; contains echinoid spines and a few 3. Shale, red, sandy 6 other fossils______-______- 25 2. Conglomerate, yellow; formed mainly of lime­ 21. Limestone, thin-bedded to slabby, gray to light- stone from Allamoore Formation, but in­ gray ; weathers yellow; mostly forms a cluding a few pebbles of schist and green­ slope, but with 2-f t ledges at intervals. Con­ stone_ ____- _ 16 tains a few echinoid spines in upper part- 71 1. Conglomerate, arkosic, red; formed of peb­ 20. Limestone, moderately thin-bedded; forms bles of schist and greenstone 13 cliffs; 2 or 3 cherty beds; contains mol- Angular unconformity. lusks like those in unit 18______16 Metarhyolite of Precambrian age at base of section. 19. Limestone, gray; forms a slope, with a few Summary of section 20 ledges toward top______22 Hueco Limestone: 18. Limestone, dark-gray, cherty; forms a cliff, Part of main body of formation exposed____ 245 containing abundant mollusks in upper part, Powwow Member _ 125 including bellerophontids______20 17. Limestone, thin-bedded; forms a slope____ 18 Part of Hueco Limestone exposed _____ 370 16. Limestone, dark-gray, cherty, massive; forms a cliff; contains echinoid spines and a few SECTION 21. STREERUWITZ HILLS other silicified fossils______18 The following sections of the Hueco Limestone are in 15. Limestone, dark-gray, thin-bedded; forms a slope; contains abundant echinoid spines 8 the Streeruwitz Hills, on closely adjacent mesas, lying ft above base- ______16 21/2 to 31^3 miles northwest of the Eagle Flat section 14. Limestone, dense, dark-gray; weathers mouse house. They were measured by J. Brookes Knight gray; forms a massive cliff; contains abun­ in 1931, but additional fossils were collected from each dant ramifying chert nodules and silicified section in 1938. Section 21a is at the southeastern end fossils. The latter include echinoid spines, the brachiopods Composite cf. C. subtilita of the eastern mesa (center of sec. 26, Block 57), and (Hall) and Dictyoclostus wolfcampensis section 21b is about three-quarters of a mile to the King; and the gastropods bellerophontid northwest, at the west end of the western mesa (east- indet., KnigJitites (Retispira) sp., Naticopsis central part of sec. 27, Block 57). Larger fossils were sp., Omphalotrochus sp., and Straparollus identified by P. E. Cloud, Jr., and E. L. Yochelson, and (Euomphalus) cornudanus (S h u m a r d) USGS 7008; field label 1 A)______28 foraminifers by L. G. Henbest (written commun., 1954, Powwow Member: 1955). 13. Limestone, forming a slope______8 Section 21a 12. Limestone, forming a ledge; contains large Top of mesa; no higher beds exposed. chert nodules______3 Hueco Limestone: 11. Marl, forming a slope; interbedded with thin Main body of formation: Feet limestone layers -______14 8. Limestone, massive; forms ledge at top of 10. Limestone, containing large bellerophontids- 3 mesa_ __ 10 9. Limestone, gray; interbedded with marl, con­ 7. Limestone, thin-bedded; forms a slope___ 15 taining abundant fossils, which include the 6. Limestone, dark-gray, massive; forms cliff 20 bryozoans Fenestella sp., Polypora sp., and Powwow Member: Rhombopora sp.; the brachiopods CleiotJiy- 5. Limestone, dense, splintery, light-gray, thin- ridina sp., Composita sp., Dictyoclostus bedded; contains much chert and is inter­ wolfcampensis (King), and dielasmids in­ bedded with shale. Upper beds form thin cluding Dielasma aff. D. Kovidens (Morton) ; ledges on slope. The limestones contain the myalinid and pseudomonotid pelecypods; the foraminifers Bradyinal sp., a spandelinid, gastropods Bellerophon parvicristatus Yoch- Schubertella Tcingil Dunbar and Skinner, Tri~ elson, and other abundant but poorly pre­ ticites or Pseudofusulina sp., and Schwager- served bellerophontids, Euconispira cf. E. ina Jcnighti Dunbar and Skinner; cup corals; missouriensis (Swallow), Knightites the bryozoan Septopora sp.; echinoid spines; (Knightites) sp., a loxonematacean, Nati­ the brachiopods Composita cf. 0. subtilita copsis sp., and Straparollus (Euomphalus) (Hall), Dictyoclostus cf. D. wolfcampensis cornudanus (Shumard) ; and the scapho- (King), "Dielasma" sp., and Hustedia sp.; pod Plagioglyptal sp., (USGS 7028; field the pelecypods Allorisma sp. and Pseudomo- label 5)______27 notis sp.; the gastropods OmphalotrocJius 8. Limestone, sandy, yellow, fossiliferous____ 2 ol)tusispira (Shumard), KnigJitites (Retis- STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 143

Section 2 la Continued Summary of section 21 Hueco Limestone Continued Hueco Limestone: Powwow Member Continued Feet Section 21a: Feet pira) sp., and large 'bellerophontids; the sca- Part of main body of formation exposed___. 45 phopod Plagioglyptal sp.; and plant frag­ Powwow Member______. 103 ments (USGS 7003, 7003a, 14431, F 9808; field labels 2 B, C 8) ______47 Part of Hueco Limestone exposed _ 148 4. Shale, marly; with a thin ledge of splintery Section 21b: limestone near middle, containing quartz Part of main body of formation exposed- 28 geodes. Contains small fusulinids; the bry- Powwow Member _ 133 ozoans Fistulipora sp., Polypora sp., Septo- pora sp., and Streblotrypa sp.; echinoid Part of Hueco Limestone exposed 161 spines; the brachiopods Cleiothyridina sp.; SUCTION 22. McADOO RANCH Composita cf. C. subtilita (Hall), Cruritny- risl sp., Dictyoclostus wolfcampensis (King), The following is a section of the Hueco Limestone "Dielasma" sp., and Wellerella sp.; the pele- near the west end of the south-facing escarpment of the cypods Nucula sp. and a myalinid; the gas­ Sierra Diablo, on the east side of a gap in the ridge, tropods Bellerophon huecoensis (Yochelson) 2 miles southwest of the Gordon (formerly McAdoo) and other bellerophontids, Euconispira cf. E. missouriensis (Swallow), Naticopsis sp., Ranch (center of north line of sec. 29, Block 52^). and Straparollus (Euomphalus) cornudanus The section was measured by J. Brookes Knight in 1931. (Schumard) ; a nautiloid; and the scaphopod Many fossils were observed in the field but not col­ Plaffiofflypta'i sp. (USGS 7003b; field label lected ; the small collections which were made were iden­ 2D) ______30 tified by P. E. Cloud, Jr. (written commun., 1954). 3. Limestone, shaly, splintery, red______10 2. Shale, calcareous, red______8 Top of ridge; no higher beds exposed. 1. Conglomerate, arkosic, massive; formed of peb­ Hueco Limestone: bles of limestone, greenstone, and schist, de­ Main body of formation: feet rived from Precambrian formations_____ 8 12. Limestone, gray, slabby; contains chert and Angular unconformity. calcite vugs; marly partings in lower part. Greenstone of Precambrian age at base of section. Contains a bellerophontid and Straparollus (Euomphalus) cornudanus (Shumard) Section 21b (USGS 701Sb; field label 8 C)______45 Top of mesa ; no higher beds exposed. 11. Limestone, forming a ledge; bellerophontids Hueco Limestone: and other fossils observed- _ 5 Main body of formation : 10. Limestone, gray; weathers pitted; in 4-ft beds, 6. Limestone, alternating beds of which are gray, alternating with thinner beds ; in part forms coarse-grained, and slabby, and pink to cliffs, in part ledges and slopes. Some beds yellow, dense, and splintery. Both types contain chert nodules and small quartz contain echinoid spines and other fossils 20 geodes; a bed about 25 ft above base con­ 5. Limestone, pink-weather ing, buff, fossiliferous_ 8 tains large masses of white chert. Fossils rare; echinoid spines observed______110 Powwow Member: Powwow Member: 4. Limestone, gray; cherty toward top; inter- 9. Limestone, slabby, gray to pinkish-gray. Con­ bedded with marl. Contains the forminifers tains a dasycladacean alga, probably Mizzia Bradyinat sp., Ozawainella sp., Staffella sp., (USGS 7013a; field label 8 B). Staffellid and spandelinids; the sponge Wewokella foraminifers observed______10 (Talpaspongia) clavata (R. H. King) and 8. Limestone, slabby, pink; with a thin bed of spicules; echinoid spines; the brachiopods arkosic sandstone in middle; minute fossils Composita cf. G. subtilita (Hall) and Dictyo­ observed_ . _ - 11 clostus wolfcampensis (King) ; and the gas­ 7. Limestone, pinkish-gray; in 4-ft ledges; sepa­ tropod Straparollus (Euomphalus) cornu­ rated by arkosic sandstone_ _ 22 danus (Shumard), and others (USGS 14432, F 9809; field label C 9)______60 6. Limestone, dense, pink; weathers yellow; in 1-ft ledges, separated by greater thicknesses 3. Limestone, dense, pinkish; weathers yellow of slabby arkosic sandstone. A limestone brown; interbedded with marl; forms ledges bed near middle contains a dasycladacean and slopes; fossiliferous at top______66 alga (USGS 7013; field label 8 A); mi­ 2. Limestone, shaly, pink; with a bed of splintery nute gastropods and staffellid foraminifers limestone at top______4 observed_ ____ 14 1. Conglomerate, calcareous; formed of pebbles 5. Sandstone, arkosic, pinkish-gray, poorly con­ of limestone of Allamoore Formation____ 3 solidated; mostly forms a slope 20 Angular unconformity. 4. Covered by talus; probably like adjoining Allamoore Formation at base of section. units______. . 20 144 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Hueco Limestone Continued ured by J. Brookes Knight in 1931. Fusulinids were Powwow Member Continued Feet collected, and were examined by Dunbar and Skinner 3. Sandstone, arkosic, pinkish-gray, conglom­ eratic; forms a ledge______7 (193T), but they were identified only in part. 2. Covered by talus; probably like adjoining Top of escarpment; no higher beds exposed. units______25 Hueco Limestone: 1. Sandstone, arkosic, coarse, yellowish-gray, Main body of formation: Feet poorly consolidated ______5 11. Limestone, light-gray, thin-bedded; forms Angular unconformity. ledges; a few beds contain fusulinids (D & Van Horn Sandstone at base of section. S 98; field label 10 D)______50 Summary of section 22 10. Limestone, containing large calcite vugs and Hueco Limestone: some chert; forms upper part of massive Part of main body of formation exposed____ 160 cliff. Contains fusulinids at top (D & S Powwow Member______134 97; field label 10 C), and large echinoid Part of Hueco Limestone exposed______294 spines______. 35 9. Limestone, light-gray; forms lower part of SECTION 23. WEST OF OLD CIRCLE RANCH massive cliff. Contains Schivagerina linearis Dunbar and Skinner (D & S 96; field label The following is a section of the Hueco Limestone on 10 B), poorly preserved productids, and at the south-facing escarpment of the Sierra Diablo, on top, large echinoid spines and a euom- the east side of a wide gap in the ridge, 3%miles west of phalid______.__ 25 the Old Circle Ranch (northeastern part of sec. 2, 8. Limestone, partly covered; forms a slope; float contains abundant fusulinids 20 Block 56). The section was measured by J. Brookes 7. Limestone, light-gray; forms a massive ledge__ 16 Knight in 1931. Fusulinids were collected, and were 6. Limestone, compact, light-gray to pink ; forms examined by Dmibar and Skinner (1937), but they a massive cliff in lower half. Fusulinids were not identified. abundant in lower part, including Schwage- rina linearis Dunbar and Skinner, and 8. Top of ridge; no higher beds exposed. emaciata (Beede) (D & S 95; field label Hueco Limestone: 10 A) ______52 Main body of formation: Feet 6. Limestone, gray, massive; contains euompha- 5. Limestone, compact, gray; with some chert lid gastropods and large echinoid spines_ 5 nodules___ _ _ .._____ 15 5. Limestone, gray; with indistinct bedding; 4. Limestone, poorly exposed; forms a slope 10 forms a cliff. Fusulinids collected at top 3. Limestone, compact, massive, gray; contains and base (D & S 92, 93; field labels 9 B, 9 chert nodules___ _ 11 C) ; other fossils rare or obscure____ 35 Powwow member: 4. Limestone, gray; in 2- to 5-ft beds; contains 2. Shale, arkosic, light-yellow-gray; with thin abundant fusulinids (D & S 91; field label ledges of conglomerate in lower half__ 31 9 A)______35 1. Conglomerate, arkosic, yellow__ 5 3. Limestone, gray; forms a massive ledge__ 10 Angular unconformity. Powwow Member: Red sandstone of Hazel Formation at base of section. 2. Limestone, sandy, pink; contains calcite vugs_ 8 Summary of section 24 1. Marl, arkosic; mostly yellow, becoming red Hueco Limestone: below, with thin beds of yellow limestone and Part of main body of formation exposed_____ 234 conglomeratic limestone, and with beds of Powwow Member______36 arkosic conglomerate in lower part, whose pebbles have been reworked from those in Part of Hueco Limestone exposed______270 the Van Horn Sandstone-______80 Angular unconformity. SECTION 25. HAZEL MINE Van Horn Sandstone at base of section. Summary of section 23 The following is a section of the Hueco Limestone on Hueco Limestone: the southeastern angle of the Sierra Diablo escarpment, Part of main body of formation exposed______85 half a mile north-northeast of the Hazel mine (south­ Powwow Member______88 eastern part of sec. 41, Block I). The Powwow Mem­ Part of Hueco Limestone exposed______173 ber was measured on the southeastward-projecting ridge below the upper cliffs, the higher beds up the SECTION 24. OLD CIRCLE RANCH northeast side of the ridge through a cleft in the cliffs, The following is a section of the Hueco Limestone on thence westward to the ridge summit. The section was the escarpment overlooking Deer Creek from the west, measured by J. Brookes Knight and P. B. King in 1931. half a mile northwest of Old Circle Ranch (southwest No fossils were collected, although they were observed corner of sec. 23, Block 531/£). The section was meas­ in the field. STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 145

Top of ridge; no higher beds exposed. Hueco Limestone Continued Hueco Limestone: Main body of formation Continued Feet Main body of formation: Feet part. Poorly preserved fusulinids observed 10. Limestone, dolomitic; somewhat thinner in lower part. A bed 100 ft above base con­ bedded and lighter gray than beds below; tains better preserved foraminifers, including forms ledges and slopes above the main Staffella sp., Schubertella Mngi Dunbar and cliffs______.______130 Skinner, PseudofusuUna? sp., and Schwag- 9. Limestone, dolomitic, dark-gray; in even beds erina bellula Dunbar and Skinner (F 2703; 3-5 ft thick; contains fusulinid molds; forms field label Ph 18). Near the top occur cliffs. Basal part is pinkish-gray and con­ Climacammina sp., Schubertella Mngi Dunbar tains some chert______150 and Skinner, Triticites aff. T. subventricosus 8. Limestone, dolomitic, light-gray; contains Dunbar and Skinner, and Schwagerina sp. abundant fusulinid molds______5 (F 2719; field label Ph 19) ; with these were 7. Limestone, dolomitic, light-gray; forms cliffs; observed poorly preserved Omphalotrochus- 165 contains poorly preserved fossils______31 6. Limestone, dolomitic, gray, thin-bedded; con­ 6. Limestone, light-gray; with many calcite vugs; tains fusulinid molds______150 contains poorly preserved bellerophontids, 5. Limestone, dolomitic, gray, thick-bedded ; forms and in upper foot, staffellid foraminifers_ 12 lower part of a slope; contains unidentifiable 5. Limestone, dense, light-gray; weathers yellow; small fusulinids (F 2696; field label Ph 12) __ 75 contains fossil fragments______3 Powwow Member: 4. Limestone; calcitic below, dolomitic toward top; gray, thin-bedded; forms a great cliff. 4. Sandstone, arkosic, calcareous, yellow, poorly Fusulinids abundant in lower part and exposed on slope______5 3. Limestone, sandy, yellow ______3 scarcer toward top. At base contains the fusulinids and other foraminifers Schuber- 2. Conglomerate, yellow; interbedded with gray sandy marl in upper part. Conglomerate at tella kingi"? Dunbar and Skinner, Pseudo base consists of closely packed coarse peb­ -fmulina powwowensist (Dunbar and Skin­ bles and cobbles of limestone and of red ner), Parafusulina linearis (Dunbar and sandstone from Hazel formation. Conglom­ Skinner) var., and Schwagerina bellulal erate above consists of smaller pebbles of Dunbar and Skinner (F 2693; field label red sandstone and resistant foreign rocks, Ph 15). Near middle contains Geinitzina with scattered seams of limestone pebbles, sp., Schubertella kingil Dunbar and Skinner, set in an arkosic sandstone matrix_____ 85 Parafusulina, linearis (Dunbar and Skinner) 1. Conglomerate, red, arkosic; made up of peb­ var., and Pseudoschwagerina texana Dunbar bles of red sandstone, quartzite, and igneous and Skinner (F 2714; field label Ph 16)___ 195 rocks _.______5 3. Limestone, marly, gray ; forms ledges; contains Angular unconformity. abundant fusulinids in lower half. Contains Red sandstone of Hazel Formation at base of section. the fusulinids and other foraminifers Osagia Summary of section 25 incrustata Twenhofel (algal-foraminiferal Hueco Limestone: colonies), a tolypamminid, Trepeilopsis sp., Part of main body of formation exposed_____ 331 textulariids, Spandelina sp., Endothyra sp., Powwow Member______98 Tetrataxis sp., a millerellid, Staffella sp., Osawainella! sp., PseudofusuUna pow- Part of Hueco Limestone exposed______429 wowensis (Dunbar and Skinner, tSchwager- ina Ttellula Dunbar and Skinner, Parafusulina SECTION 26. BAT CAVE linearis (Dunbar and Skinner), and Pseudo- schwagerina beedei Dunbar and Skinner (F The following is a section of the Hueco Limestone on 2690; field label Ph 14)___ 20 the escarpment of the Sierra Diablo at Bat Cave, on the Powwow Member: south side of an eastward offset of the escarpment 1% 2. Limestone, dolomitic, sandy, massive; contains miles north-northeast of the Pecos Mine (northeastern quartz pebbles in lower part. Upper part part of sec. 13, Block 54%). The section was measured contains many small unidentifiable fusulinids (F 2711; field label Ph 13) ______90 by J. Brookes Knight in 1936. Fusulinids and other 1. Conglomerate, yellow; made up of limestone foraminifers were identified by L. G. Henbest (written pebbles, with a dolomitic matrix toward top__ 48 commun., 1955); other fossils were observed in the field, Angular unconformity. but were not collected. Bed sandstone of Hazel Formation at base of section. Top of escarpment; no higher beds exposed. Summary of section 26 Hueco Limestone: Hueco Limestone: Main body of formation: Part of main body of formation exposed_____ 605 7. Limestone, dolomitic, gray, thin-bedded; with Powwow Member______138 some interbedded very light gray layers and much interbedded calcitic limestone in upper Part of Hueco Limestone exposed______743 146 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

FOSSIL COLLECTIONS FROM HUECO LIMESTONE NEAR Straparollus (Euomphalus) cornudanus (Shumard), and SHEEP PEAK Worthenia sp.

No stratigraphic sections were measured on Sheep SECTION 27. SECOND SECTION SOUTH OE1 VICTORIO Peak, or near it, but the fossils listed below were col­ PEAK lected from the Hueco Limestone on the peak, and in surrounding areas. Collections were made by J. The following is a section of the Hueco and Bone Brookes Knight in 1936 and 1938; fusulinids and other Spring Limestones on the escarpment of the Sierra foraminifers were identified by L. G. Henbest and Diablo at the upper end of the Victorio flexure 2^4 larger fossils by P. E. Cloud, Jr., and E. L. Yochelson miles south of Victorio Peak (southwestern part of sec. (written commun., 1955, 1954:). 19, Block 43). The section was measured by J. Brookes Knight in 1938. Larger fossils were identified by P. E. USGS 8560, F 2112 (field, label Ph. 25). Hueco Limestone, Cloud, Jr., and E. L. Yochelson and fusulinids and lower part of main body of formation, north slope of Sheep Peak (northeastern part of sec. 18, Block 53%). Contains the other foraminifers by L. G. Henbest (written commun., fusulinids ISchwagerina bellula Dunbar and Skinner, Para- 1954,1955). fusulina cfr. P. linearis (Dunbar and Skinner), and IPseudo- scJiwagerina beedei Dunbar and Skinner; the brachiopods Top of ridge above escarpment; no higher beds exposed. Meekella sp. and Linoproductus sp.; and the gastropod Straparol- Bone Spring Limestone: &eet lus (Euomphalus) sp. indet. 19. Limestone, dolomitic; forms a cliff; approximate USGS 8559 (field label Ph 24). Hueco Limestone, basal part thickness______-______200 of main body of formation, lying directly on red sandstone of 18. Shale, yellow; interbedded with limestone and Hazel Formation, the Powwow Member being missing at the limestone-pebble conglomerate, both very fos- locality. Knoll 1% miles north-northwest of Sheep Peak (north­ siliferous. Unit dips steeply northward and western part of sec. 13, Block 53%). Contains the brachiopod thins abruptly, being little more than 75 ft thick Linoproductus sp. a quarter of a mile to the north. Contains the USaS 8560a, F 2701 (field label Ph 28). Hueco Limestone sponge Heliospongia vokesi E. H. King; colonial, main body of formation. Three miles east-northeast of Sheep semicolonial, and cup corals; the brachiopods Peak on south side of valley of Deer Creek, south of Cox Moun­ Buxtonia (Kochiproductus) victorioenste King, tain fault, in bed of a dry creek (center of sec. 15, Block 54%). Dictyoclostus (Chaoiella) guadalupensis (Gir- Contains the fusulinids and other foraminifers Geinitzina sp., ty), Enteletes sp., "Marginifera" cf. "M." wal- Spandelinoides sp., Schubertella sp., Triticites subventricosus eottiana (Girty), and Stenocisma cf. S. inequalis Dunbar and Skinner, Pseudofusulinat sp., and Pseudoschwa- (Girty) ; and the gastropod Bellerophon de- gerina beedei Dunbar and Skinner. flectus Chronic. Fusulinids and other foramini­ USGS 8560a, F 2695 (field label Ph. 29). Hueco Limestone, fers include textulariids, Spandelina sp., Geinit­ main body of formation. Four miles east-northeast of Sheep zina sp., Textrataais spp., Staffella sp., Pseudo- Peak on ridge north of valley of Deer Creek, north of Cox schwagerina uddeni (Beede and Knicker), Para- Mountain fault (center of sec. 14, Block 54%). Contains the fusulina schuchertil Dunbar and Skinner, P. fusulinids and other foraminifers Climcammina sp., Geinitzira attenuata'i Dunbar and Skinner, and P. spp. sp., Spandelina sp., Tetrataxis sp., Schubertella Jcingi Dunbar (USGS 14454, F 9827; field label C 25 C). The and Skinner, Schwagerina bellula Dunbar and Skinner, Triti­ fusulinids are exceedingly abundant, but tlieir cites spp., Parafusulina linearisl (Dunbar and Skinner), and tests are commonly abraded or broken, after Pseudoscliwagerina, texana Dunbar and Skinner var. lithification but before incorporation in the sedi­ VSGS 8560a, F 2704 (field label Ph 27). Hueco Limestone, ment. Hueco and Bone Spring fusulinids have main body of formation. Four and a quarter miles east of been mixed by redoposition, the specis of Pseu- Sheep Peak and 1% miles south of Bat Cave, on rim of Sierra doschwagerina representing the former, and the Diablo escarpment, in upfaulted block south of Cox Mountain two species of Parafusulina representing the fault (center of east line of sec. 17, Block 54%). Contains the latter______. 215 fusulinids and other foraminifers Endothyra! sp., Schubertella 17. Limestone, dolomitic, massive 45 Jcingil Dunbar and Skinner, Triticites aff. T. subventricosus 16. Slope, with limestone float blocks that contain Dunbar and Skinner, and Schwagerina sp. Leptodus and other fossils of Bone Spring aspect 50 VSGS 14474 (field label C 32). Hueco Limestone, main body 15. Limestone, dolomitic; forms slopes and ledges; of formation. Four miles west-northwest of Sheep Peak at contains poorly preserved fusulinids as well as north end of low ridge, south of Sheep Peak fault (center of larger fossils ______150 west line of sec. 13, Block 52%). Contains the gastropod 14. Limestone, dolomitic, massive; forms a cliff 30 Stegocoelia n. subgen. n. sp. 13. Limestone, dolomitic, gray; forms ledges on slope; USGS 14424 (field label C 1). Hueco Limestone, main body contains silicified fossils of Bone Spring aspect- 30 of formation. Three miles west-northwest of Sheep Peak at 12. Slope ; no exposure_ 45 crest of ridge, north of Sheep Peak fault (northeastern part of sec. 13, Block 52%). Contains the brachiopod Composita cf. 11. Limestone, massive, lenticular, reefy; in part brec- C. subtilita. (Hall) ; a parallelodontid pelecypod; and the gas­ ciated ; contains a few silicified fossils_ 20 tropods Bellerophon parvicristatus Yochelson, Meekospira sp., 10. Limestone, thin-bedded; contains nodules of gray a murchisonid, Naticopsis sp., Peruvispira sp., Stegocoelia'j sp., chert______.. 5 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 147

Bone Spring Limestone Continued Feet Hueco Limestone Continued 9. Limestone, conglomeratic or bioclastic, gray, thin- Powwow Member Continued Feet bedded ; forms ledges. Contains cup corals and 1. Conglomerate, sandy; forms ledges at base and a few silicified brachiopods of Bone Spring as­ top. Contains angular to rounded pebbles pect, including Enteletes. Fusulinids and other and cobbles, consisting of red sandstone foraminifers include textulariids, Geinitsina sp., from Hazel Formation, but including dolo­ Spandelina sp., Spandelinoides sp., Tetrataxis mitic and calcitic limestone, quartz, quartzite, spp., Staff ellal sp., ISchubertella Jcingi Dunbar and rhyolite____ 68 and Skinner, Pseudoschwagerina laxissimal Angular unconformity. (Dunbar and Skinner), Paraschwagerina sp., Red sandstone of Hazel Formation at base of section. Pseudoschwagerina uddeni (Beede and Knick- Summary of section 27 er), and ISchwagerina c omp act a (White) Part of Bone Spring Limestone exposed 855 (USGS 14453, F 3806; field label C 25 B). Most Hueco Limestone: of the identified species of fusulinids are charac­ Main body of formation___ 393 teristic of the Hueco, rather than of the Bone Powwow Member _ 248 Spring, but the bioclastic nature of the rocks Total Hueco Limestone______- 641 suggests possible redeposition______65 Unconformity (?). SECTION 28. FIKST SECTION SOUTH OF VICTORIO PEAK Hueco Limestone: The following is a section of the Hueco, Bone Spring, Main body of formation : 8. Limestone, dolomitic, granular, gray-buff, very and Victorio Peak Limestones, about V/2 miles south of massive; contains molds of very small Victorio Peak (from the southeastern to northwestern fusulinids______100 parts of sec. 19, Block 43). The section begins on the 7. Limestone, dolomitic, gray-buff, massive; southeast near the northernmost outcrop of red sand­ weathers to fairly smooth surfaces; forms stone of the Hazel Formation and extends northwest­ cliffs. Contains molds of very small fusu­ linids in upper half______140 ward across successive ledges and slopes to the summit 6. Limestone, marly, and marl; interbedded of the peak marked by elevation point 6353. The sec­ with ledge-making layers of slightly dolomitic tion was measured by P. B. King and R. E. King in limestone. Lower part of unit contains a 1928. Brachiopods in the collections made were identi­ small cup coral cf. Caninia sp.; the annelid fied by R. E. King (1931) and fusulinids by Dunbar Spirorbis sp.; and the brachiopods Dictyo- clostus (n. subgen.) cf. D. hessensis (King), and Skinner (1937). D. wolfcampensis (King), Aulostegesl, Top of peak 6353; no higher beds exposed. Waagenoconcha n. sp., Linoproductus sp., Victorio Peak Limestone: Feet "Marginifera" n. sp. aff. "If." lasallensis 25. Limestone, light-gray, massive; forms a cliff. (Worthen), Composita sp., and Neospirifer The unit is approximately equivalent to the spp. The same strata contain the fusulinids lower part of the Victorio Peak Limestone on and other foraminifers Climacammina sp., nearby Victorio Peak, although its lower part Spandelina sp., Geinitsina or Spandelina sp., appears to interfinger in that direction with Endothyral sp., Tetrataxis sp., Schubertella shale and marl of Bone Spring Limestone__ 130 kingil Dunbar and Skinner, Pseudofusulina Intergradation. uddeni? (Dunbar and Skinner), Pseudofusu­ Bone Spring Limestone: lina sp. confr. P. uddeni (Dunbar and 24. Limestone, gray; forms two thick cliff-making Skinner) and Parafusulina aff. P. Unearis units and some minor ledges, separated by (Dunbar and Skinner) (USGS 14452, F 9823; thinner beds of buff sandy marl. The lime­ field label C 25 A). The last species occurs stone units wedge out northward into marl not in a limestone very different litholigically far north of peak 6353. Marls north of the from that containing the other species; field peak contain the brachiopods Enteletes dum- relations between the two rock types are 'blei Girty, Chonetes permianus Shumard, Pro- unknown______. 135 ductus ivesi Newberry, P. schucherti King, 5. Limestone, thin-bedded; contains many fusu­ Harginifera cristobalensis Girty, M. manzani- linids, productid brachiopotls, and bellero- ca Girty, Aulosteges magnicostatus Girty, Lyt- phontid gastropods______18 tonia nobilis americanus (Girty), Camaro- Powwow Member: phoria venusta Girty, Spirifer (Neospirifer) 4. Sandstone; marly in upper part; some layers pseudocameratus Girty, and Composita mira fine grained and red, others coarse grained (Girty) (REK 484)______170 and yellow; forms a slope______70 23. Limestone, finely crystalline, gray; weathers 3. Sandstone, red, fine-grained; with a few ledges white; in 1-ft beds______16 of coarse conglomeratic yellow sandstone_ 40 22. Marl, buff, sandy______50 2. Sandstone, coarse to conglomeratic, yellow; 21. Limestone, dolomitic, finely crystalline, gray; in mostly poorly exposed on slope, which is 1- to 2-ft beds; contains irregular chert nod­ covered by pebbles weathered from con­ ules. Weathers to light-gray smooth surfaces glomerate______70 and forms a receding slope__ 303 148 GEOLOGY OF THE SIE.RRA DIABLO REGION, TEXAS

Bone Spring Limestone Continued Feet Hueco Limestone Continued 20. Limestone, black, thin-bedded______20 Main body of formation Continued Feet 19. Limestone, dolomitic, finely crystalline; in 1- to ular chert masses. Composita and other 2-ft beds. Weathers to gray-brown granular silicified fossils observed 74 surfaces and forms massive ledges ___ 63 8. Limestone, dense, thin-bedded, gray, cherty; 18. Limestone, black, platy; weathers gray; inter- contains many fusulinids 17 bedded with drab shale above. A conglomer­ 7. Limestone, finely crystalline, dark gray; atic layer in lower part contains Productus weathers buff; in 1-ft beds; contains the ivesi Newberry (REK 489)______175 fusulinid Sch^vagerina linearis Dunbar 17. Limestone, dolomitic, finely crystalline, gray; and Skinner, and the brachiopods Produc­ with faint bedding planes, moderately closely tus dartoni King (type), Productus semi- spaced; weathers drab gray. Thickens north­ stratus Meek, Linoproductus cor a (d'Or- ward along outcrop to as much as 150 ft____ 45 bigny), and Composita mira (Girty) 16. Shale, drab; weathers buff; with thin seams of (REK 460, D & S 99)____ 27 shaly sandstone and some beds of fossiliferous Powwow Member: limestone ______.______54 6. Shale; drab to gray, passing into red below; 15. Limestone, finely crystalline; contains siliceous much concealed by talus 48 masses and poorly preserved slicified fossils_ 1 5. Shale, sandy, maroon-red 27 14. Shale, drab; weathers buff; some interbedded 4. Sandstone, coarse to conglomeratic, brown- 17 thin limestone layers. Fossils in the lime­ 3. Shale, sandy, maroon-red___ 27 stone layers, and weathered from the shale, in­ 2. Shale, sandy, brown; interbedded with thin clude the fusulinids Parafusulina schucherti sandstone layers 4 Dunbar and Skinner and Parafusulina sp., and 1. Sandstone, coarse, conglomeratic, brown; the brachiopods Rhipidomella mesoplatys ~bay- contains subangular to rounded pebbles, lorensis King, Enteletes dumblei Girty, Derbya mostly limestone and chert, but with a few nasuta Girty, Chonetes Mplicatus King, Mar- of quartz, rhyolite, and schist; no pebbles ginifera sublaevis King, H.l whitei King, Pro- of red sandstone from rock beneath 2 richthofenia uddeni (Bose), Spirifer marcoui Angular unconformity. infraplicata King, Squamularia guadalupensis Red sandstone of Hazel Formation at base of section. (Shumard), and Spirifernia laaeal Girty Summary of section 28 (REK 485, D & S 127)______17 Part of Victorio Peak Limestone exposed 130 13. Limestone, dolomitic, drab to orange-brown; Bone Spring Limestone 1, 064 crowded with fusulinids in upper part____ 75 Hueco Limestone: 12. Limestone, dense to granular, gray; weathers Main body of formation 388 gray brown; in 2-ft beds, separated by beds of Powwow Member______125 shale The limestone beds are crowded with fossils, which are silicified on the surface. Total Hueco Limestone- 513 Collections from several beds include the COLLECTIONS FROM HTTECO AND BONE SPRING LIME­ brachiopods Rhipidomella hessensis King, STONES ON VICTORIO FLEXURE WEST OF VICTORIO Enteletes dumblei Girty, E. liumbonis King, CANYON Streptorhynchus pygmaeum Girty, HeeJcella No stratigraphio sections were measured of the attenuata Girty, Chonetes spinoliratus di- abloensis King, Productus dartoni King, P. Permian rocks on the Yictorio flexure west of sections ivesi Newberry, Marginifera sublaevis King, 27 and 28, or west of the front of the Sierra Diablo, but Mf whitei King, Strophalosia hystericula fossils were collected at various localities in the Hueco Girty, Prorichthofenia UJcharewi King, P. Limestone and lower part of the Bone Spring Lime­ teguliferoides King (types), Lyttonia noMlis stone, which are listed below. The collections were americanus (Girty), Pugnoides elegans (Girty), Spiriferina angulata King (type), made in 1936 and 1938, mainly by J. B. Knight, but in Hustedia hessensis King, and Composita suT)- part by P. B. King; fusulinids and other foraminifers tilita (Hall) (REK 47 8,419) ______75 were identified by L. G. Henbest, and larger fossils by Unconformity (?). P. E. Cloud, Jr., and E. L. Yochelson (written com- Hueco Limestone: mun., 1954,1955). Main body of formation: U8GS 8544 (field laTtel Pb IS). Bone Spring Limestone, 11. Limestone: dolomitic in part; finely granu­ limestone layers above unit of limestone-pebble conglomerate. lar; gray-brown; faintly bedded; forms East side of Victorio Canyon, on end of spur a quarter of a 10- to 20-ft ledges; contains irregular mile northwest of BM 6148 (north-central part of sec. 18, Block chert masses______243 43). Contains the brachiopods Avonia spp., Buxtonia (Kochir 10. Limestone, dolomitic, dense, faintly bedded; productus) victorioensis King, Chonetes large sp., Enteletes sp., weathers to a rough surface, containing ir­ Leptodus sp., orthotetacean indet., Rhipidomella sp., and regular chert masses______27 Stenocisma sp.; the pelecypod Acanthopecten sp.; and the gas­ 9. Limestone, dense, thin-bedded, gray; weath­ tropods Anomphalus sp., Babylonites sp., and a pleurotamarian. ers light gray; contains spherical to lentic- A shark's tooth was observed in the field. STEATIGEAPHIC SECTIONS OF PERMIAN ROCKS 149

USGS 8543, F 2692 (field label Pb 12). Bone Spring Lime­ and all the identified species are of Hueco type. Contains the stone, limestone layers interbedded with unit of limestone- fusulinids and other foraminifers Climacammina sp., Staffella pebble conglomerate. West of Victorio Canyon on south side of sp., ScJiubertella Jcingi Dunbar and Skinner, Parafusulina ridge, and three-quarters of a mile north-northeast of Estes linearis (Dunbar and skinner), Pseudofusulina^ sp., Schwag­ Place (west-central part of sec. 14, Block 43). Contains the erina bellulal Dunbar and Skinner, and S.I sp. fusulinids and other foraminifers Climacammina sp., Spandel- USGS 8560a, F 2118 (field label Ph 26). -Hueco Limestone, inoides sp., Pseudofusulina setum (Dunbar and Skinner) var., three-quarters of a mile southwest of Estes Place (southwestern Parafusulina schucherti Dunber and Skinner, P. imlayi Dunber, part of sec. 16, Block 43). Contains the fusulinids and other and P. spp.; the sponges Fissispongia n. sp., Girtyocoelia dun- foraminifers Geinitzina sp., Tetrataxis sp., Staffella sp., a bari R. H. King, Heliospongia voJcesi R. H. King, and Stereo- millerellid, Ozawainellal sp., Pseudofusulina aff. P. pow­ dictyum orthoplectum Finks; the coral Lophophyllum sp.; the wowensis (Dunbar and Skinner), P. sp., and Schwagerinal sp. bryozoan Fistulipora sp.; a crinoid calyx; the brachiopods USGS 14428, F 9806 (field label C 5) . Hueco Limestone, tilted Aulostegesl sp., Enteletes cf. E. dumblei Girty, Hustedia sp., on Victorio flexure. Strike ridge 6 miles west-northwest of Isogramma sp., productid indet, Scacchinella sp., and Wellerella Estes Place and 2^ miles east of Dagger Tank (northwestern sp.; a pelecypod with revolving lirae; and the gastropods part of sec. 3, Block 44). Contains the fusulinids and other Glabrocingulum sp., "Trachydomia" sp., and "Worthenia" sp. foraminifers Climacammina sp., a spandelinid, Tetrataxis sp., USGS 8542, F 2713 (field label Pb 11). Bone Spring Lime­ Schubertella"! sp., Pseudofusulina cfr. P. powwowensis (Dunbar stone, from limestone beds interbedded near top of lowest unit and Skinner), and P. sp. of thin-bedded dolomite. West of Victorio Canyon on south side of ridge a mile east of Estes Place (center of sec. 17, Block 43). SECTION 29. VICTORIO PEAK Contains the fusulinids and other foraminifers Geinitzina sp., Spandelinoides sp., Endothyra sp., a millerellid, Parafusulina The following sections are of the Hueco, Bone Spring, diabloensis Dunbar and Skinner, and P. imlayi Dunbar var.; and Victorio Peak Limestones on the east slope of the corals Cladochonus sp. and Triplophyllum sp.; the bryozoan Victorio Peak west of the West-Pyle Cattle Co. head­ Gystodictya sp.; and the brachiopods Derbyia sp., Entelets cf. quarters, or Corn Ranch (west-central part of sec. 6, E. dumblei Girty, Leptodus sp., MeeJcella difficilis Girty, Neo- spirifer sp., productids indet., "Spiriferina" sp., Streptorhynchus Block 66, Twp. 6, into the southeastern part of sec. sp., and Wellerella sp. 10, Block 43). Two sections were measured here dur­ USGS 14435, F 9810 (field label C12) . Hueco Limestone, near ing the investigation, both of which are given, because base, on slope above inlier of Montoya Dolomite. Northwest each contains important collections of identified fos­ side of Victorio Canyon 1% miles northest of Estes Place (north­ sils, and because the two sections have different scopes eastern part of sec. 14, Block 43). Fusulinids and other and were measured at somewhat different places, thus foraminifers occur in a detrital conglomeratic limestone, in both the matrix and the pebbles, all the free fusulinid shells in illustrating the varying stratigraphic features of the the matrix being abraded. Field relations indicate that the locality. These and other sections which have been meas­ strata are of Hueco age, and this is confirmed by the fusulinid ured here were discussed by Dunbar (1953, p. 802-809). species, but their manner of occurrence indicates that they have Section 29a (same as section C of Dunbar, 1953, fig. been redeposited in their present position. The foraminifers include Geinitsina sp., Spandelina sp., Endothyra sp., a bradyinid, 2 and pi. 1A) was measured by P. B. King and R. E. Tetrataxis sp., Staffella sp., Schubertella Tcingil Dunbar and King in 1928, and begins nearly due west of the ranch, Skinner, Parafusulina linearis (Dunbar and Skinner), Pseudo­ at the foot of the Sierra Diablo escarpment, on the north fusulina emaciata (Beede), and Pseudoschwagerina beedei Dun- side of a reentrant valley, passes south of a prominent bar and Skinner. limestone lens ("Kfiz lens") at the top of the lower USGS 14429, F 9807 (field label C 6) . Hueco Limestone, upper part. In Victorio Canyon, a few feet above channel, near junc­ cliffs, and extends up an eastern spur of Victorio Peak tion of a side canyon from southeast, 2 miles east-southeast of nearly to its summit, or as far as the cliffs of the Estes Place (southwestern part of sec. 16, Block 43). Contains Victorio Peak Limestone could be scaled. Brachiopods the fusulinids and other foraminifers Tetrataxis sp., spanelinids, collected in this section were identified by R. E. King Osawainella! sp., Sohubertella Mngi Dunbar and Skinner, Pseu­ (1931) -and fusulinids by Dunbar and Skinner (1937). dofusulina aff. P. powwowensis (Dunbar and Skinner), P. sp., Schwagerina sp., ParafusuUnal sp.; the sponge Heliospongia Section 29b (same as section B of Dunbar, 1953, fig. voJcesi R. H. King; cup corals; rhomboporoid bryozoans; crinoid 2 and pi. 1A) was measured by J. Brookes Knight in columns and echinoid plates; the brachiopods Chonetes sp., 1931, and begins about half a mile north of the first sec­ Dictyoclostus (n. subgen.) cf. D. hessensis (King), Glossothyris tion in the next reentrant valley at the foot of the Sierra sp., and Punctospirifer sp.; and the gastropods "Anomphalus" sp., S trap ar ollus (Euomphalus) sp., a bellerophontid, a Diablo escarpment, but converges upward with the first murchisonid, and a pleurotomarian. section, passing north of the prominent limestone lens USGS 14436, F 9811 (field label C IS). Hueco Limestone, and ending near the middle of the Bone Spring Lime­ upper part, about a quarter of a mile southwest of and up­ stone, or above its highest abundantly fossiliferous lay­ stream from locality C 6, 1% miles southeast of the Estes Place ers. Larger fossils collected in this section were iden­ (southwest cor. sec. 18, Block 43). All the fusulinid shells in tified by P. E. Cloud, Jr., and E. L. Yochelson and this collection are maturely rounded, but are not fragmented, and have clearly been transported and redeposited. Field rela­ fusulinids and other foraminifers by L. G. Henbest tions indicate that the strata containing them are of Hueco age, (written commun., 1955,1954). 150 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Section 29a Bone Spring Limestone Continued Feet 22. Limestone, fine-grained, white; with indistinct bed­ Top of Victorio Peak; no higher beds exposed. ding; forms a cliff that rims the outer spurs of Victorio Peak Limestone (type section) : Feet Victorio Peak______100 31. Rocks similar to unit 30, extending to top of peak, 21. Covered, except for a few ledges of fossiliferous forming an unscalable cliff; thickness estimated- 200 limestone like those beneath 50 30. Limestone, medium-crystalline, light-gray; con­ 20. Limestone, fine-grained, gray; forms a ledge; con­ tains subspherical chert nodules as much as 4 tains abundant silicified fossils. These include in. in diameter. Bedding planes are a foot or the fusulinid Parafusulina diabloensis Dunbar two apart, but the rock is coherent and weathers and Skinner, and the brachiopods Enteletes massive, forming remarkably fluted cliffs. Upper dumblei Girty, Meekella attenuata Girty, 200 ft is more dolomitic than remainder, and Derbya nasuta Girty, Glionetes Mplicatus King, weathers buff and pitted. Strata 100 ft above C. spinoliratus diabloensis King, Productus ivesi base contain the fusulinid ScJiwagerina setum Newberry, Marginifera sutlaevis King, M.I Dunbar and Skinner, and the brachiopods wliitei King, Prorichtliofenia teguliferoides King, Waagenoconcha montpelierensis (Girty), Pro­ Lyttonia noMlis americanus (Girty), Spiriferina ductus ivesi Newberry, Spirifer marcoui infra- angulata King, and Hustedia hessensis King plicata King, and Spirifer (Neospirifer) pseu- (REK 476, D & S 130) ; massive bryozoans docameratus Girty (REK 496, REK 500; D & also observed 5 S 132)______450 19. Limestone, black, siliceous, thin-bedded to platy; with some interbedded 6-in to 2-ft layers of gray 29. Limestone, medium-crystalline, light-gray, cherty; granular fossiliferous limestone. These contain thin bedded but coherent; forms massive out­ fusulinids; massive bryozoans; crinoid stems, crops and a bench at top. Contains the brachio­ the brachiopods Marginifera, Pugnax, and vari­ pods Heekella difflcilis Girty, Chonetes subli- ous productids; and the gastropod Platyceras___ 66 ratus Girty, Productus ivesi Newberry, Lyttonia nobilis americanus (Girty), Spirifer marcoui in- 18. Limestone; in 1-ft ledges; separated by platy fraplicata King, Hustedia meekana (Shumard), black siliceous limestone; forms slopes. The and Composita mexicana (Hall) (REK 499). ledges contain the fusulinids Parafusulina In 1936 a collection was made from approxi­ diabloensis Dunbar and Skinner and a slender mately this unit, from cliff falls on the southeast species of Parafusulina; and the brachiopods side of Victorio Peak; according to Cloud and Prorichthofenia teguliferoides King, and Pug- Yochelson it contains a cup coral; rhomboporoid, noides elegans (Girty) (REK 475, D & S 129) 67 fistuliporoid, and other bryozoans; the brachio­ 17. Limestone, fine-grained; in 2- to 6-ft beds; gray, pods Avonia sp., Buxtonia (Kochiproductus) weathering light gray and to a rough surface. victorioensis King, Chonetes sp., "Marginifera" Contains silicifled fossils, including, fusulinids, spp., productid indet, Prorichthofenia sp., RMpi- cup corals, and Hustedia-_____ 22 domella sp., and Wellerella cf. W. elegans 16. Limestone, black, siliceous, thin-bedded. Contains (Girty) ; and the pelecypod Streblopteria sp. Hustedia Jiessensis King and Composita subti- (USGS 8545; field label Pb 14)______150 lita (Hall) (REK 474) ; productids also ob­ served_ 73 Intergradation. Unconformity ( ?). Bone Spring Limestone: Hueco Limestone: 28. Limestone, dark-gray to black; in 6-in to 1-f t beds; Main body of formation : contains small chert nodules______33 15. Limestone lens or reef (termed "Kfiz lens" 27. Limestone, fine-grained, gray; in 1- to 2-ft beds; by Dunbar, 1953, p. 802, and "Huecoan bio- contains small subspherical chert nodules and a herm" by Stehli, 1954, p. 282), which forms few fossils______55 prominent cliff about a quarter of a mile in 26. Limestone, black, dense, platy; in moderately length, at top of lower bench of eastern spur thick beds; contains thin wavy laminae; forms of Victorio Peak. Section crosses south edge steep slope below Victorio Peak______247 of lens, which tapers southward, and thick­ 25. Limestone, black, dense; platy to papery, fissile; ens northward to more than 150 ft, the over­ weathers buff or brown. Top of unit forms sum­ lying beds through unit 18 wedging out mit of an outer spur of Victorio Peak______154 against it. Consists of dense faintly bedded limestone, weathering to light-gray rough 24. Limestone, black, dense, platy; weathers buff; in surfaces, containing some small chert 10- to 20-ft units; interbedded with chert in 1- masses. Abundant cup corals, massive to 3-ft beds; and gray fossiliferous limestone_ 71 bryozoans, Hustedia, and a large Omplial- 23. Limestone, gray; contains abundant silicified fos­ otrochus observed-- 115 sils, mostly massive bryozo>ans although some 14. Limestone, dense, gray, thin-bedded; with beds are crowded with fusulinids. Contains the shaly partings; bedding surfaces somewhat fusilinids Parafusulina schucherti Dunbar and wavy; some layers contain much chert. Skinner, and Parafitsulina sp., and the brachio- Contains the fusulinids Triticites victor­ pod Productus ivesi Newberry (REK 477, D & S ioensis Dunbar and Skinner and Schwa- 131) ______.______25 gerina laxissima Dunbar and Skinner; and STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 151

Section 29a Continued Bone Spring Limestone Continued Feet Hueco Limestone Continued etna (Girty), "H." (KoslowsUa) aff. "If." (K.) Main body of formation Continued Feet wabashensis (Norwood and Pratten), "H." sp., the brachiopods Productus ivesi Newberry MeeJcella sp., productids indet., Rhipidomella Buxtonia peruviana (d'Orbigny), and sp., ScaccJiinella sp., Spiriferina sp., and Wetter- Avonia loulei (Kozlowski) (REK 472, D & ella sp.; the pelecypod Acanthopecten sp.; and S 100) ______44 the gastropods Apachella sp., Euconispira pul- 13. Limestone, dense, light-gray; in 1- to 3-ft cJira Batten, Grlabrocingulum sp., Platyceras sp., beds; contains small subspherical chert nod­ and Shewdagoniat sp. (USGS 8561, F 2710; field ules ; forms a massive cliff. Contains slen­ label Pb 7)______115 der fusulinids as much as half an inch in 17. Limestone, dark-gray; in 1- to 2-ft beds; inter- length, and the brachiopods Chonetes sub- bedded with thin-bedded siliceous black lime­ liratus Girty, Productus ivesi Newberry, and stone______35 Linoproductus cora (d'Orbiguy) (REK 16. Limestone, gray, massive; forms a ledge; con­ 471)______50 tains silicified fossils. The limestone is bio- 12. Limestone, thin-bedded to platy, dark-gray; clastic, consisting of fragments of calcareous weathers pale buff ___ 4 fossil debris of sand to pebble size, with some 11. Limestone, finely crystalline, gray nodular; larger angular limestone cobbles, all variably contains numerous fossils that appear in silicified. Contains the fusulinids and other cross section ; a Chonetes observed in float 25 foraminifers Climaeammina sp., Oeinitsina sp., Powwow Member: Spandelina sp., Tetrataxis spp., Ozawainella sp., 10. Sandstone, shaly, poorly consolidated, buff; *Schubertella kingi Dunbar and Skinner, Boul- partly covered by wash from above___ 16 tonia aff. B. rawi Lee, "iSch-wagerina pseudoreg- 9. Sandstone, calcareous, medium-grained; in ularis Dunbar and Skinner, ?$. gumblei Dunbar part cross bedded; contains rounded lime­ and Skinner, *Pseudoschwagerina gerontica stone pebbles; forms two ledges. Imprints Dunbar and Skinner var., *P. texanal Duubar of long, slender fusulinids observed on bed­ Skinner, Parafusulina diabloensis Dunbar and ding surfaces._ _ 22 Skinner, *P. linearis Dunbar and Skinner, and 8. Shale, reddish, sandy, poorly exposed _ 33 var., P. schucherti Dunbar and Skinner and P. 7. Conglomerate, red to buff; formed of peb­ spp. (F 2716; field label Pb 6). The fusulinids bles of red sandstone, limestone, and chert, are preserved partly as whole shells, partly as in a coarse sandstone matrix; grades up­ ward into coarse red sandstone____ 17 fragments and detritus with varying degrees of 6. Shale, sandy, maroon-red, poorly exposed- 13 rounding. They represent a depositional aggre­ 5. Limestone, dense, splintery, brown_____ 1 gate in which forms characteristic of the Hueco 4. Covered ______6 (marked by asterisk) have been reworked and 3. Limestone, dense, splintery, brown 2 mixed with those characteristic of the Bone 2. Covered______7 Spring. Unit 16 also contains the sponge Helio- 1. Sandstone, gray, quartzitic__ _ 5 spongia voJcesi R. H. King; the corals Cladocho- Base of exposure at edge of alluvial fan; probably near nus sp., Lonsdaleial sp., and Triplophyllum sp.; base of Hueco Limestone and Powwow Member. the bryozoans Chainodictyat sp., Cystodictya sp., Domoporal sp., Fistulipora sp., Septopora sp., Section 29b and Striatopora sp.; the brachiopods Chonetes (Chonetinella) victorianus (Girty), Enteletes Bone Spring Limestone: cf. E. dumblei Girty, Hustedia mormoni (Mar­ 19. Limestone, black, uufossiliferous; extends up cou), "Marginifera" cf. "If." sublaevis King in spur to base of Victorio Peak Limestone; not part, and "H." (KosloivsMa) cf. "H." capaci measured. (See section 29a)______(?) (d'Orbigny) ; the gastropods Babylonites sp. 18. Limestone, black, siliceous, thin-bedded; with in- and Straparollus (Euomphalus) glabribasis terbedded 1-ft ledges of dark-gray bioclastic fos- Yochelson; an annelidlike Spirorbis; and solen- siliferous limestone. These contain the fusu­ oporoid and other algae (USGS 8562, field label linids Ozawainella sp., Staff'ella! sp., Parafusu- lina imlayi Dunbar, P. aff P. bosei Dunbar and Pb 6)______15 Skinner, and Parafusulinal sp.; the sponges 15. Limestone, gray; in 1- to 2-ft beds; contains silici­ Fissipongia n. sp., Lyssacina incertae sedis, and fied fossils; interbedded with thin-bedded black spicules; a cup coral; the bryozoans Fenestella limestone and cherty shale______30 sp., Fistulipora sp., Septopora sp., and Striat- 14. Limestone, massive, gray, bioclastic; with a few opora sp.; the brachiopods Avonia sp., Buxtonia embedded angular limestone cobbles; contains (Kochiprodiictus) victorioensis King, Chonetes silicified fossils of Bone Spring aspect_____ 15 consanguineus Girty, C. (Chonetinella) victor- 13. Limestone, gray, fossiliferous; in very irregular 1- ianus (Girty), Crtirithyris sp., Derbyia sp., En- to 2-ft beds, interbedded with thin-bedded black teletes sp., Hustedia mormoni (Marcou), H. sp., limestone and cherty shale ___ 18 Leptodus sp., "Marginifera" cf. "H." walcotti- Unconformity (?). 152 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone: Hueco Limestone Continued Main body of formation: Feet Main body of formation Continued Feet 12. Northern edge of limestone lens or reef (unit (Dunbar and Skinner), P. sp., Pseudosch­ 15 of section 29a) ; massive limestone with wagerina'i laxissima (Dunbar and Skinner), embedded angular fragments of fossiliferous P. beedei Dunbar and Skinner, Schwagerina limestone. Contains abraded and rounded "bellulal Dunbar and Skinner, ?/8. Ttellula fragments of fusulinid shells, probably in­ Dunbar and Skinner, S. knighti Dunbar and cluding Parafusulina linearis Dunbar and Skinner, Spandelina sp., and Tetrataxis sp. Skinner, Pseudofusulina powwowensis Dun- (F. 2707; field label Ph 6)______33 bar and Skinner, tSchwagerina Kellula Dun- 7. Limestone, dark-gray, massive, cherty; forms bar and Skinner, and Pseudoschwagerina sp. a strong ledge. Contains the foraminifers (F 2706, filed label Ph 10)______7 Geinitzina sp., juvenaria of fusulinids, and 11. Limestone, fine-grained, dark-gray; contains a fragment of a larger fusulinid; a lons- black chert nodules; in 1-ft beds; with marl daleoid coral cf. Waagenophyllum texanum partings. Contains the fusulinids and other Heritsch; and the gastropod Omphalo- foraminifers Geinitzina sp., Schubertella trochus sp. (USGS 8554, F 2689; field label kingi Dunbar and Skinner, Parafusulina, Ph 5)______-___ __ 30 linearis (Dunbar and Skinner) var., Pseudo­ Powwow Member: fusulina franklinensis (Dunbar and Skin­ 6. Limestone, marly, black; interbedded with ner), and var.; the cup coral Lophophyllum shale. This unit, and the one next beneath, sp.; an orthoceratid cephalopod; the gastro­ contain Parafusulina ("Schwagerina") lin­ pod Omphalotrochus sp.; and the brachio- earis (Dunbar and Skinner) (F 2700; field pods Avonia (n. subgen.) cf. A. boulei label Ph 4; identified by C. O. Dunbar, 1953, (Kozlowski), Chonetes sp., Dictyoclosfus (n. p. 804) ; the coral Syringopora sp.; the pel- subgen.) cf. D. hessensis (King), "Margini- ecypod Edmondia sp; and the brachiopods fera" sp,. a productid, Neospirifer sp., and Chonetes n. sp.?, and Linoproductus cf. L. Rhipidomella sp. (USGS 8556, F. 2721; field cora (d'Orbigny) (USGS 8553; field label label Ph 9)______37 Ph 4)______15 10. Limestone, dolomitic, cherty, light-gray; forms 5. Sandstone, calcareous, yellow, fossiliferous; a massive ledge. Near top, contains the with interbedded marl; forms a ledge_____ 15 fusulinids Schubertella kingi Dunbar and 4. Sandstone, yellow; forms a ledge _ ___ 6 Skinner, Pseudoschwagerina'? laxissima 3. Marl, gray, and interbedded yellow sandstone; (Dunbar and Skinner), and Schwagerina unfossiliferous______35 belluto Dunbar and Skinner (F 2687; field 2. Sandstone and siltstone, poorly consolidated_ 55 label Ph 8; identified by C. O. Dunbar, 1953, 1. Conglomerate, yellow; contains limestone peb­ p. 804)______32 bles ; forms a ledge______8 9. Limestone, very dark gray, cherty; in 2- to 3-f t Base of exposure at edge of alluvial fan; probably near beds, with marl partings. Contains the base of Hueco Limestone and Powwow Member. fusulinids Triticites victorioen$is Dunbar Summary of section 29 and Skinner, Pseudoschwagerinal laxissima Section 29a: (Dunbar and Skinner), Pseudofusulina Part of Victorio Peak Limestone exposed______800 franklinensis (Dunbar and Skinner), and P. Bone Spring Limestone______968 texana Dunbar and Skinner (F 2715; field Hueco Limestone: label Ph 7; identified by C. O. Dunbar, 1953, Main body of fonnation______238 p. 804) ; the coral Lophophyllum sp.; the Part of Powwow Member exposed______122 bryozoans Cystodictya sp. and Goniocladia sp.; the pelecypods Aviculopecten1! sp., Avi- Part of Hueco Limestone exposed ___ 360 culopinnal sp., and Oonocardium sp.; and Section 29b: the brachiopods Buxtonia (Kochiproductus) Part of Bone Spring Limestone measured _____ 228 victorioensis King, Chonetes cf. O. consan- Hueco Limestone: guineus Girty, Composita sp., Derbyia sp., Main body of formation______169 Dictyoclostus (Chaoiella) aff. D. oolimensis Part of Powwow Member exposed______134 (d'Orbigny), Enteletes aff. E. wordensis King, Hustedia sp., Linoproductus large n. Part of Hueco Limestone exposed- 303 sp., "Marginifera" cf. "M" wabashensis (Norwood and Pratten, "M." sp., Neospirifer SECTION 30. VICTORIO CANYON sp., Rhipidomella sp., Spirifer sp., "Spiri- ferina" sp., and Waagenoconcha sp. (USGS The following is a section of the Hueco and Bone 8555; field label Ph 7)______30 Spring Limestones at the portal of Victorio Canyon, be­ 8. Limestone, very dark gray, cherty; in 2- to ginning at its channel and proceeding south, up a spur 3-ft beds. Contains few larger fossils, but of Victorio Peak to top of outer bench, beyond which fusulinids and other foraminifers are abund­ ant, including Climacammina sp., Endothyra beds were not measured (south-central part of sec. 3, sp., Geinitzina sp., Parafusulina linearis Block 66, Twp. 6, into northeastern part of sec. 1, Block STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 153 43). The section was measured by J. Brookes Knight Main body of formation Continued Feet in 1936. Larger fossils were identified by P. E. Cloud, Hueco Limestone Continued linearis (Dunbar and Skinner), and Para­ Jr., and E. L. Yochelson and fusulinids and other fusulina slender sp. (F. 2717; field label foraminifers by L. G. Henbest (written commun., 1954, Ph 12)______5 1955). Earlier collections from the same locality have 3. Limestone, slightly dolomitic, dark-gray, been identified by E. E. King (1931), and Dunbar and cherty, massive; forms cliffs; some beds Skinner (1937) (EEK 459, 470; D & S 101, 102, 103), brecciated. Contains larger fossils like those in unit beneath, such as productids and but their lists are not reproduced here. bellerophontids, but few or no fusulinids 130 Top of outer bench on north spur of Victorio Peak; higher Powwow Member: beds, mainly black limestone, not measured. 2. Limestone, sandy and marly, black; inter- Bone Spring Limestone: Feet bedded with shale; both very fossiliferous. 7. Limestone, dolomitic; in 3- to 4-ft ledges, with a Contains the fusulinids and other foramini­ pebbly layer 10 ft below top. Contains poorly fers Spandelinoidest sp., Osawainella spp., preserved fossils resembling those beneath. Long, Schu'bertella sp., Schioagerina bellulal Dun- slender fusuilinids abundant at top______85 bar and Skinner, Pseudofusulina powwowen- 6. Limestone, slightly dolomitic, light-gray; in 2-ft sis (Dunbar and Skinner), and Parafusulina beds. The rock is abundantly fossiliferous, bio- linearis (Dunbar and Skinner) var.; the clastic, and in part contains limestone pebbles. bryozoan Stenopora sp.; the brachiopods The pebbles contain a staffellid, abundant Schu- Avonia (n. subgen.) cf. A. boulei (Kozlow- 'bertella, Jcingi Dunbar and Skinner, Parafusulina ski), A. sp., Buxtonia (KooMproductus) vic- or Pseudofusulina sp., and Pseudofusulina pow- torioensis King, Ghonetes n. sp., Gomposita wowensis"! (Dunbar and Skinner) var., which are sp., Grurithyris sp., Derbyia sp., Dictyoclos- fusulinids of Hueco type. The matrix contains tus wolfcampensis (King), Linoproductus the fusulinids and other foraminifers Qeinitzina cf. L. oora (d'Orbigny), "Marginifera" aff. sp., Tetrataxis sp., Quinquelooulinal sp., Oza- "M." lasallensis (Worthen), and Squamu- ivainellal sp., Staffella sp., *Schwagerina aff. S. laria sp.; the pelecypods Allorisma sp., Avi- bellula Dunbar and Skinner, *Pseudofusulina'i culopectenl sp., Aviculopinna sp., a mya- laxissima (Dunbar and Skinner) or P. powwow- linid, "Nucula" sp., a parallelodontid, and ensis (Dunbar and Skinner) var., ISchwagerina Pseudomonotis sp.; and the gastropods bel- gumblei Dunbar and Skinner, IParafmulina lerophontid indet., "Donaldina" gp., Euconi­ diabloensis Dunbar and Skinner, and P. schu- spira cf. E. missouriensis (Shumard), a oherti Dunbar and Skinner; the fusulinids are murchisonid, Naticopsis sp., and a pseudo- largely of Bone Spring type, with the exception zygopleuroid (USGS 8557, F 2694; field label of those marked by an asterisk, which are of Ph 11)______45 Hueco type (F 2723; field label Pb 8). Rework­ 1. Sandstone, red and brown; with seams of con­ ing and mixing of fusulinids and other foramini­ glomerate in upper part; unfossiliferous _ 30 fers from different stratigraphic levels is indi­ Base of exposure at level of channel of Victorio Canyon; cated. Larger fossils include Lonsdaleiat sp., and probably near base of Hueco Limestone and Powwow other cup corals; the bryozoans Fenestella sp., Member. Fistulipora sp., Polypora sp., and Rhombopora Summary of section 30 sp.; crinoid stems; the brachiopods Ghonetes Part of Bone Spring Limestone measured _ __ 112 (ChonetineUa) victorianus Girty, C. large sp., Hueco Limestone: Enteletes sp., Hustedia hessensis King, "Margi- Main body of formation -______207 nifera" (KozlowsJcia) cf. "M" capaci (d'Orbigny), Part of Powwow Member exposed______75 MeeJcella sp., and Streptorhynchus sp.; and the gastropods Apachella sp., Euconispira pulchra Part of Hueco Limestone exposed______282 Batten, and Straparollus (Euomphalus) glabri- basis Yochelson (USGS 8539; field label Pb 8)_ 27 SECTION 31. NORTH OF VICTORIO CANYON Unconformity (?). Hueco Limestone: The following is a section of the Hueco, Bone Spring, Main body of formation: and Victorio Peak Limestones, beginning at the foot 5. Limestone, slightly dolomitic, dark-gray, of the Sierra Diablo escarpment 2 miles north of the massive; forms cliffs. Fossils scarce and portal of Victorio Canyon, and extending westward to poorly preserved______72 a promontory of the Victorio Peak Limestone at the 4. Limestone, cherty; forms a slope. Contains the fusuilinids and other foraminifers Glima- top of the escarpment (northwest cor. sec. 2, Block 66, cammina sp., Geinitzina sp., Spandelinoides1! Twp. 6, across the northern part of sec. 22, Block 42). isp., Endothyra sp., Staffella sp., Ozawainella The section was measured in 1936, the lower part sp., Schubertella Jcingi Dunbar and Skinner, (through unit 11) being hand leveled and described in Triticitesl spp., Pseudoschwagerina texana Dunbar and Skinner, Pseudofusulina hueco- detail by J. Brookes Knight, and the higher strata ensis Dunbar and Skinner, Parafusulina covered in less detail by observations of P. B. King, 154 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS with thicknesses estimated. Larger fossils were iden­ Bone Spring Limestone Continued Feet tified by P. E. Cloud, Jr., and E. L. Yochelsoii and Skinner var., and P. ? spp.; the coral Lons- daleia"i sp.; the bryozoan Fistulipora sp.; a fusulinids and other foraminifers by L. G. Henbest platycerid gastropod; and the brachiopods (written commun., 1954, 1955). Heekella sp., Avonia sp., Prorichthofenia sp., a Crest of Sierra Diablo escarpment; no higher beds ex­ productid, Hustedia sp., and Enteletes cf. E. posed. dumWei Girty (USGS 8540, F 2705; field label Victorio Peak Limestone: Feet Pb 9) ______1^2 IS. Limestone, fine-grained; oolitic in part; light- to 10. Slope, with a reefy ledge of brecciated limestone dark-gray; thin- to medium-bedded, with some at top, containing silicified fossils of Bone thicker beds at top. Some interbedded layers Spring type, including large fusulinids 33 are marly or slightly sandy, very cherty, and Conformity (?). weather buff. Fossils moderately abundant in Hueco Limestone: some layers. A mile to the south of end of Main body of formation: section were collected a sponge; the bryozoan 9. Limestone, dolomitic, gray, massive; with Phyllopora sp.; the echinoderm "Echinocrinus" irregular wavy bedding in lower half; sp.; the brachiopod Buxtonia (Kochiproductus) forms a cliff. Contains a few silicified sp.; the gastropods bellerophontid indet., Cal- fossils______25 listomarial sp., Meekospira sp., loxonematid in­ 8. Limestone, dolomitic, fine-grained, gray, thin- det., Stegocoelia"? sp., and Warthia cf. W. waa- bedded ; contains black chert nodules 10 geni Yochel&on; an ammonite; and the scapho- 7. Limestone, dolomitic, gray, massive; almost pod Plagioglypta sp. (USGS 8546; field label without bedding; forms a cliff. Contains Pb 15)______250 poorly preserved silicified fossils- 28 17. Limestone, gray, massive; with widely spaced 6. Limestone, dolomitic, thin-bedded, cherty. faint bedding planes, with low original dip. Contains the fusulinids and other foram­ The unit forms sheer unscalable walls, recessed inifers Climacammina spp., Tetrataxis sp., into embayments, shelters, and caves, and in Schubertella kingi Dunbar and Skinner, places with pinnacles standing in front, sepa­ Pseudofusulina powwowensisl (Dunbar and rated from the rest by weathering along joints__ 250 Skinner), Pseudoschwagerina beedei Dun- 16. Limestone, medium-grained, gray; in 1- to 2-ft bar and Skinner, and ScJiwagerina sp. (F beds, some crowded with fusulinids; forms 2702; field label Ph 23)______10 slopes and small ledges. Unit is transitional 5. Limestone, dolomitic, thin-bedded, cherty; both vertically and laterally, from gray lime­ forms a slope______10 stone facies of Victorio Peak into black lime­ 4. Limestone, dolomitic, very cherty; forms a stone fades of Bone Spring; both it and units ledge______10 14 and 15 beneath merge into typical cliff-mak­ 3. Limestone, partly dolomitic, partly calcitic, ing Victorio Peak Limestone on first spur north gray; in 1- to 2-ft beds, with marl partings; of Victorio Canyon______100 forms a slope. Contains the fusulinids Intergradation. ScJmbertella kingi Dunbar and Skinner, Bone Spring Limestone: PseudoscJiwaperinal laxissima (Dunbar and 15. Limestone, black; in 6- to 18-in. beds______340 Skinner), P. sp., Pseudofusulina sp., Para­ 14. Limestone, gray, granular; contains silicified fos­ fusulina linearis (Dunbar and Skinner) (F sils ; forms a ledge. Merges with basal part of 2708; field label Ph 22) ; corals, Composite/,, Victorio Peak Limestone to the south, but and small productids observed______48 wedges out to north______10 2. Limestone, dolomitic; forms upper part of 13. Limestone, black. In lower three-quarters is very lower cliff. The rock is bioclastic, frag- thin bedded or platy, with closely spaced light mental, and contains many silicified fossils. and dark laminae. In upper quarter the beds Fusulinids are preserved as abraded to en­ are thicker, weather light gray, and contain tire shells. These and other foraminifers much chert. Bedding slopes irregularly at low include a bradyinid, Staffella sp., Triticites angles, probably due to original dip of deposit_ 395 aff. T. subventricosus Dunbar and Skinner, 12. Irregular cliff; on line of section formed of thin- Pseudofusulina powwoicensisl (Dunbar and bedded black limestone, with some thicker beds Skinner), ScJiwagerina bellula'i Dunbar and near top; farther south includes massive reefy Skinner, SI Jiessensis (Dunbar and Skin­ limestone beds ______50 ner), and Parafusulina linearis (Dunbar 11. Limestone, black to dark-gray, fine grained; in 1- and Skinner) var. (F 2722; field label Ph to 2-ft beds; contains silicified fossils and bands 21) ; crinoid columns and corals observed_ 20 and lenses of brown chert; interbedded toward 1. Limestone, calcitic, fine-grained, nearly black; top with thinner bedded black limestone. This with marly partings. Contains the bryozoan unit, and that next beneath, contains the Stenopora sp.; and the brachipods Chonetes fusulinids Schubertella kingi Dunbar and Skin­ sp., Buaetonia (KocMproductus) victorloen- ner var., Psetidofusulina setum (Dunbar and sis King, Linoproductus cf. L. cora (d'Orbig- Skinner), Parafusulina fountaini Dunbar and ny), and a productid; fusulinids were not STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 155

Hueco Limestone Continued Feet Victorio Peak Limestone Continued Feet Main body of formation Continued rim of the escarpment northwest of upper end seen in place, but a float block contains of section, near head of Marble Canyon, were Schubertella! sp., and Parafmulina, linearis collected the sponges Actinocoelia meandrina (Dunbar and Skinner) USGS 8558, F 2699; Finks, Defordia densa Finks and Strioderma field label Ph 20)______25 coscinum Finks; crinoid stems; the braehio- Base of section at edge of alluvial fan; no lower beds pods Buxtonia (Kochiproductus) victorioensis exposed. King, Neospirifer sp., and a large productid Summary of section 31 (USGS 7011, 14444; field label C 19)_____ 250 Part of Victorio Peak Limestone exposed______600 49. Limestone, light-gray to white, granular or cry­ Bone Spring Limestone______950 stalline; in thick beds, with some thinner Part of Hueco Limestone exposed______186 beds; forms a sheer unscalable cliff that rims the Sierra Diablo escarpment. Contains sparse SECTION 32. MARBLE CANYON brown chert nodules. In 1928, at head of ridge south of Marble Canyon, was collected the The following is a section of the Hueco, Bone Spring, brachiopod Buxtonia victorioensus King and Victorio Peak Limestones on the ridge south of (type) (REK 498)______250 Marble Canyon, beginning near the base of the Sierra Intergradation. Diablo escarpment half a mile south of portal of the Bone Spring Limestone: canyon and 3 miles southwest of old Figure Two Ranch 48. Limestone, black; in 2- to 8-in. beds; irregularly headquarters, and ending on a projecting angle of the bedded, with partings of shale and chert; crest of the escarpment half a mile east of Chambers tri­ forms a cliff ______1T5 angular station (across the northern part of sec. 21, 47. Limestone, black, thinly laminated, platy; inter- bedded below with siliceous brown shale. Block 66, Twp. 5). A section was measured here by Forms a long slope between upper cliffs and P. B. King and R E. King in 1928, but few significant lower bench of Sierra Diablo escarpment. fossil collections were made. The lower part of the sec­ Thickness measured on ridge south of Marble tion was again measured by J. Brookes Knight in 1931, Canyon intrusive, where there is a low original from the base of the escarpment to the top of the outer dip toward south, away from reef masses north of Marble Canyon _ 695 bench (through unit 46). The section given here is that 46. Limestone, dolomitic, gray; without bedding; of Knight, but the higher part has been added from the lenticular; passes laterally into thinner bedded section of King and King, and from observations which black limestone. Parts are brecciated, the were made along the crest of the escarpment, in 1938 fragments including not only gray limestone, and earlier. Larger fossils were identified by P. E. but black limestone and chert. Forms crest of outer bench of escarpment. Abundantly Cloud, Jr., and E. L. Yochelson (written commun., fossiliferous; contains large Parafusulina sp.; 1954), and fusulmids were identified by C. O. Dunbar sponge spicules; the bryozoan Fistulipora sp.; and J.W. Skinner (1937). the brachiopods Meekella sp., Leptodus sp., A suite of fossil collections from nearby, on the ridge Prorichthofenia sp., a productid, Hustedia mormoni (Marcou), Squamularia sp., Ente- north of Marble Canyon, was made by G. B. Richard­ letes sp., and Dielasma sp.; and a triolobite son and G. H. Girty in 1907, and identifications by (USGS 7010, D & S 134; field label 21 K)__ 27 Girty were partly reported in the Van Horn folio 45. Limestone, black, platy, shaly; with thin chert (Richardson, 1914, p. 5; USGS 7165, 7l65a, 7168a to beds; weathers yellow brown and forms a 7168h; field locality 85). However, the ridge north of slope______55 the canyon lies in a dolomitic reef f acies of the Permi­ 44. Limestone, dolomitic, coarsely crystalline, gray; an rocks and yielded few fossils except in the Hueco forms ledges on slope. Partly silicified and poorly preserved fusulinids, crinoid columns, Limestone near the base and the Victorio Peak Lime­ and echinoid spines observed______25 stone near the top; Girty observed a resemblance be­ 43. Limestone, black, thin-bedded, shaly______3 tween the facies of the latter and that of the much 42. Limestone, dolomitic, coarsely to finely crystal­ younger Capitan Limestone. line, gray; in 2-ft beds. Contains irregularly Top of escarpment; no higher beds exposed. silicified areas; poorly preserved fusulinids Victorio Peak Limestone: and crinoid columns observed ______50. Limestone, gray; in beds a few feet thick, parts 41. Limestone, dark-gray to black, thin-bedded; with of which have low original dips; forms ledges chert bands; weathers brown to light gray; and slopes at top of escarpment. Some inter- forms a slope ______45 bedded marl; platy, siliceous brown limestone; 40. Limestone, dolomitic, crystalline, light-gray; and slightly sandy cherty buff limestone. Fos­ weathers deeply pitted; forms ledges on slope. sils are moderately abundant in places and are Abundant fusulinid molds observed, some filled partly silicified. From several places along the by calcite______._ 45 757-108 «5 11 156 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Bone Spring Limestone Continued Feet Hueco Limestone Continued Feet 39. Limestone, dolomitic, gray; forms a ledge; top Main body of formation Continued and base is massive, but middle is thinly 21. Limestone, dark-gray, irregularly bedded. bedded. Contains poorly preserved fusulinids Contains the fusulinids Schubertella (D & S 133; field label 21 J) ______10 kingi Dunbar and Skinner, Schwagerina, 38. Limestone, black, thin-bedded, poorly exposed; emaciata (Beede), and Triticities pow- forms a slope, with a few ledges of gray wowensis (Dunbar and Skinner) (D & S cherty limestone______27 106; field label 21 D)______37. Limestone, dolomitic, massive, brecciated, silic- 20. Limestone, dark-gray, massive; contains 'a ified; forms a rounded ledge. Contains poorly few fusulinids ______preserved fusulinids (D & S 111; field label 19. Limestone, gray, irregularly bedded; con­ 21 I) ; a sponge, crinoid columns, and a large tains many fusulinids- ______16 spiriferoid brachiopod observed 30 18. Slope; underlying beds concealed . 6 36. Limestone, coarsely crystalline, light-gray; in 17. Limestone, light-gray, irregularly bedded; 2- to 3-f t ledges; contains chert lenses ; inter- contains a few silicified fossils______4 bedded with thinner bedded more compact 16. Slope; underlying beds concealed _ 18 limestone. Contains poorly preserved, silici- 15. Limestone, granular, gray; contains silici­ fied fusulinids (D & S 110; field label 21 H) ; fied fossil fragments______crinoid columns observed_____ 66 Powwow Member: 35. Limestone, dolomitic; forms a slope 5 14. Limestone, marly, irregularly bedded; forms a slope. Contains the fusulinids 34. Limestone, dolomitic, light-gray, massive; forms Schubertella Tcingi Dunbar and Skinner a ledge_ _ 18 and Schwagerina emaciata (Beede) (D 33. Slope; underlying beds concealed 8 & S 105; field label 21 B) ; other poorly 32. Limestone, dolomitic, light-gray_ _ 3 preserved fossils observed _ 5 31. Limestone, dolomitic, dark-gray, thin-bedded; 13. Marl: poorly exposed _ _ 14 contains small chert nodules and a few fossils- 25 12. Limestone, granular, gray. Fusulinids not Conformity (?). observed, but contains fragments of other fossils ..______Hueco Limestone: 11. Limestone, marly, nodular. Contains the Main body of formation: fusulinids Staffella sp. and Schwagerina 30. Limestone, dolomitic, thinly and evenly emaciata (Beede) (D & S 104; field bedded; lower part dark gray, upper part label 21 A)______3 light gray to pinkish; contains large chert 10. Slope; underlying beds concealed-______8 nodules in lower part, and some fusulinid 9. Limestone, pinkish-gray, unfossiliferous__ 3 molds. Forms sheer massive cliffs_ 175 8. Sandstone, arkosic, yellow; poorly ex­ 29. Limestone, dolomitic, thin-bedded; forms a posed______12 slope; contains scattered large chert nod­ 7. Conglomerate, arkosic, red; contains peb­ ules, and near the middle a few calcitized bles of igneous rocks______5 fusulinids______. _ 40 6 Slope; underlying beds concealed-______10 28. Limestone, dolomitic, light-gray, massive. 5. Conglomerate, arkosic, red _ 10 At top, contains the fusulinids Schubert- 4. Sandstone, arkosic, poorly consolidated, ella kingi Dunbar and Skinner and red______10 Schwagerina emaciata (Beede) (D & S 3. Slope; underlying beds concealed______5 109; field label 21 G) ______15 2. Conglomerate, arkosic _ ___ _ 5 27. Limestone, dolomitic, thin-bedded; contains 1. Covered; at nearby localities base of Pow­ a few chert nodules______10 wow Member is a conglomerate, contain­ 26. Limestone, dolomitic, massive; forms a cliff, ing pebbles of chert and red sandstone_ containing chert nodules in lower half_ 35 Angular unconformity. Pennsylvanian rocks at base of section. (See section 25. Limestone, calcitic, thin-bedded. Contains 12.) the fusulinids Schubertella Jcingi Dunbar Summary of section 32 and Skinner and Schwagerina emaciata Part of Victorio Peake Limestone exposed-______(Beede) (D & S 108; field label 21 F). A 500 later collection at about the same level Bone Spring Limestone _ 1,270 Hueco Limestone: contains the brachiopods Derftyia sp. and Linoproductus sp. (USGS 8551; field label Main body of formation______357 Powwow Member______100 Ph 2)______3 24. Limestone, massive______4 Total Hueco Limestone ______457 23. Limestone, marly. Contains the fusulinids Bchubertella kingi Dunbar and Skinner FOSSIL COLLECTIONS FROM HUECO LIMESTONE NEAR and Schwagerina emaciata (Beede) (D & MARBLE CANYON S 107; field label 21 E) ______4 An outcrop of marl and marly limestone forms a con­ 22. Limestone, dolomitic, massive______10 spicuous bluff just above the channel on the north side of STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 157 the portal of Marble Canyon (approx. units 11 to 14 of Hueco Limestone: Feet section 32) (east-central part of sec. 20, Block 66, Twp. Main body of formation: 21. Limestone, dolomitic, light-gray, thinly and 5). Collections have been made here by various geolo­ and evenly bedded; contains abundant fusu- gists at different times, including G. B. Richardson and linid molds; forms almost unscalable cliffs; G. H. Girty, E. E. King, J. W. Skinner, and J. Brookes thickness estimated _ 200 Knight. The following fossils have been identified: 20. Limestone, dolomitic, light-gray; contains small calcitized fusulinids; forms a massive REK 456, D & S 113, 114. Collected by B. E. King and J. bench______.______38 W. Skinner, and identified by B. E. King (1931) and by Dunbar 19. Limestone, dolomitic, dark-gray to black; con­ and Skinner (1937) : The fusulinids Schubertella kingi Dunbar tains large spherical chert nodules; forms and Skinner, PseudoscJiwagerina uddeni (Beede and Knicker), a slope below cliffs. Contains the fusu­ P. texana Dunbar and Skinner, Schwagerina huecoensis Dunbar linids Schubertella Jcingi Dunbar and Skin­ and Skinner, and $. knighti Dunbar and Skinner; and the ner, Triticites powwowensis Dunbar and brachiopods Orthotichia Joozlowskii King, Chonetes permianus"! Skinner, Pseudoschwagerina beedei Dunbar Shumard, Isogramma millepunctata (Meek and Worthen), and Skinner, and Schwagerina emaciata Productus semistriatus Meek, P. wolfcamp ensis King, Lino- (Beede) (D & S 121; field label 13 F) ___ 46 productus cora (d'Orbigny), Marginifera dugoutensis"! King, 18. Limestone, dolomitic, massive-_ 50 and Composita subtilita angusta King. 17. Limestone, dolomitic, light-gray, massive. USaS 7050, 8550, F 27181) (field labels 22, Ph 1) . Collected Contains the fusulinids Schubertella Jcingi by J. Brookes Knight in 1931 and 1936; identified by L. G. Hen- Dunbar and Skinner, Schwagerina emaciata best, P. E. Cloud, Jr., and E. L. Yochelson (written commun., (Beede), and S. huecoensis Dunbar and 1955, 1954) : The fusulinids and other foraminifers Climacam- Skinner (D & S 120; field label 13 B) ; other mina sp., textulariids, Geinitzina sp., Endothyra sp., a bradyinid, silicified fossils observed______55 Staffella lacunosal Dunbar and Skinner, Ozawainella huecoen­ 16. Limestone, thin-bedded; forms a slope. Con­ sis'! Dunbar and Skinner, Schubertella Jcingi Dunbar and Skin­ ner, Pseudofusulina huecoensis Dunbar and Skinner, and var., tains the fusulinids Schubertella Jcingi Dun- P. powwowensis (Dunbar and Skinner), Schwagerina knighti bar and Skinner, Schwagerina emaciata Dunbar and Skinner, Paraschwagerina gigantea (White), Pseu- (Beede), and Pseudoschwagerina sp. (D. & doschwagerina uddeni (Beede and Knicker), and P. teaana var. S 119; field label 13 D) ______25 ultima Dunbar and Skinner; the coral Lophophyllum sp.; the 15. Limestone, gray, massive; forms lowest ledge, bryozoans Fenestella spp., Fistulipora sp., and Septopora sp., irregularly bedded in lower part; contains ecinoid plates and a crinoid calyx; the brachiopods Chonetes large round chert nodules and silicified fos­ sp., Cleiothyridina sp,,, Composita sp., Crurithyris sp., Dictyo- sil fragments- 43 clostus (Chaoiella) aff. D. boliviensis (d'Orbigny), D. (n. sub- 14. Limestone, fine-grained; gray below and black gen.) cf. D. hessensis (King), D. wolfcampensis (King), Iso­ toward top; contains many large chert nod­ gramma sp., "Marginifera" (Kozlowskia) capaci (d'Orbigny), ules. Contains unidentifiable fusulinids; Schizophoria sp., and Squamularia sp.; the pelecypods Aviculo- the coral Chaetetes sp.; echinoid spines; and pecten? sp. and Septimyalina sp.; the gastropods Amphiscapha the brachiopods Dictyoclostus (Chaoiella) cf. A. muricata (Knight), a bellerophontid, Naticopsis sp., Om- phalotrochus obtusispira (Shumard), and Pharkidonotus sp.; aff. D. boliviensis (d'Orbigny), D. cf. D. an orthoceratid cephalopod; and a trilobite. hessensis (King), productid indet., Neospiri- fer sp., and Hustedia sp. (USGS 7001, SECTION 88. MINE CANYON D & S 118; field label 13 C) ; bryozoans ob­ served______33 The following is a section of the Hueco Limestone 13. Limestone, coarse-grained, gray; with many on the north side of the portal of Mine Canyon, begin­ chert nodules. Contains unidentifiable ning about 1% miles west-southwest of old Figure Two fusulinids; sponge spicules; the corals Clisio- Ranch headquarters, above outcrops of lower fossilif- phyllum sp. and Lophophyllum sp.; the bryo­ erous shale of Pennsylvanian age and proceeding to the zoans Anisotrypa sp., Cystidictya sp., Fistu­ top of the outer bench of Sierra Diablo escarpment lipora sp., Polypora sp., Septopora sp., and (southeastern part of sec. 15, Block 66, Twp. 5). The Stenopora sp.; echinoid spines and crinoid section was measured by J. Brookes Knight in 1931, columns; the brachiopods Cleiothyridina but some additional fossil collections were made in 1936. cf. D. hessensis (King), D. (Chaoiella) aff. cf. D. wolfcampensis (King), D. (n. subgen.) Fusulinids were identified by C. O. Dunbar and J. W. cf. D. hessensis (King), D. (Chaoiella) aff. Skinner (1937) and larger fossils by P. E. Cloud, Jr., D. boliviensis (d'Orbigny), Dielasma sp., and E. L. Yochelson (written commun., 1954). Hustedia sp., "Marginifera" (Kozlowskia) cf. "M. (K.) wabashensis (Norwood and Bone Spring Limestone: Feet Pratten), Rhipidomella sp., and Squamu­ 22. Dolomitic facies overlying top of section, not tra­ laria sp., the pelecypod Cypricardina sp.; versed (?) and the gastropod Platyceras sp. (USGS Conformity (?). D & S 117; field label 13 B) __ 17 158 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Hueco Limestone Continued main outer bench of Sierra Diablo escarpment, northeast Powwow Member: Feet of which rocks are downfaulted (east-central part of 12. Limestone, marly; poorly exposed on slope; sec. 13, Block 66, Twp. 5). The section given here is contains abundant large bryozoans_____ 22 11. Limestone, granular, gray. Contains the f usu- based on detailed measurement of the lower beds linids Schubertella kingi Dunbar and Skin­ (through unit 11) by J. Brookes Knight in 1931, with ner, Schwagerina huecoensis Dunbar and higher beds added from a more generalized section by Skinner, and S. emaciata (Beede) ; the P. B. King and K. E. King in 1928. Fusulinids col­ sponge Stereodictyum orthoplectum Finks; the coral Campophyllum sp.; the bryozoans lected by Knight were identified by Dunbar and Skinner Anisotrypa sp., Cystidictya sp., Fistulipora (1937) and a small lot of brachiopods by P. E. Cloud, sp., Meekopora sp., Septopora sp., and Bteno- Jr., and E. L. Yochelson (written commun., 1954). pora sp.; echinoid spines and plates, crinoid Section 34a is included to illustrate variation in thick­ columns and a calyx; the brachiopods Bux- ness of Hueco Limestone. It was measured in 1928 by tonia (Kochiproductus) victorioensis (King), C omposita sp., Dictyoclostus P. B. King and E. E. King on a flat-topped outlier in the (Chaoiella) aff. D. boliviensis (d'Orbigny), downfaulted area, about half a mile northeast of the D. cf. D. Jiessensis (King), D. cf. D. wolf- main section (north-central part of sec. 12, Block 66, campensis (King), D. sp., Enteletes aff. E. Twp. 5). wordensis King, Hustedia sp., Linoproductus sp., "Harginifera" (Kozlowskia) cf. "If." Bone Spring Limestone: Feet (K.) wabashensis (Norwood and Pratten), 13. Shale, siliceous, brown; interbedded with granular productid indet., Rhipidomelfa sp., Rhyncho- light-gray dolomitic limestone; forms top of pora sp., Schizophoria sp., and Squamularia outer bench. These and higher beds were not sp.; the pelecypod Aviculopectenl sp.; the measured, as they form edge of a reef mass gastropods Omphalotrochus obtu&ispira with original dips toward northeast, which ex­ (Shumard), Naticopsis sp., and a loxone- tends up to Victorio Peak Limestone_ __ (?) matacean; and a trilobite (USGS 7001a, Conformity (?). 7004, 8552, D & S 116 field labels 13 A, Hueco Limestone: Ph 3)______3 Main body of formation: 10. Limestone, marly, thin-bedded, poorly ex­ 12. Limestone, dolomitic, finely crystalline, gray; posed. Contains the fusulinids Schubertella weathers dirty gray and pitted; in 6-in to kingi Dunbar and Skinner, Schwagerina 1-ft beds, but forms massive cliffs. Contains huecoensis Dunbar and Skinner, 8. emaciata some subspherical chert nodules. Thick­ (Beede), S. nelsoni Dunbar and Skinner, ness estimated______750 and Pseudoschwagerina Tteedei Dunbar and 11. Limestone, light-gray; contains small fusu­ Skinner (D & S 115; field label 13 AA)__ 45 linids______8 9. Shale and sandstone, arkosic, red______3 10. Limestone, thin-bedded______12 8. Sandstone, arkosic, brown___ _ _ 10 9. Limestone, marly; forms a slope between cliffs. 7. Slope; beds concealed-______15 Contains the fusulinids Pseudoschwagerina 6. Sandstone, arkosic; contains small pebbles_ 3 uddeni (Beede and Knicker), P. texana 5. Shale, arkosic, red______20 Dunbar and Skinner, and Schwagerina 4. Conglomerate, arkosic, red; contains small huecoensis Dunbar and Skinner (D & S 122; limestone pebbles______13 field label 16 A)______3 3. Shale, sandy; gray at base; poorly exposed_ 25 8. Limestone, dolomitic; forms a cliff______17 2. Sandstone, arkosic, red; conglomeratic at 7. Limestone, dolomitic, gray, massive; contains base______25 unidentified fusulinids (D & S 123; field 1. Conglomerate, arkosic, massive; composed of label 16 B) ______18 pebbles of limestone and igneous rocks___ 4 Powwow Member: Angular unconformity. 6. Limestone, thin-bedded. Contains unidenti­ Shale of Pennsylvanian age at base of section, poorly ex­ fied fusulinids and the brachiopods Lino- posed in upper part. productus"! (cf. Cancrinella) sp., L. sp., and Summary of section 33 Composita sp. (USGS 7056, D & S 124; field Hueco Limestone: label 16 C) : bellerophontid gastropods Main body of formation______507 observed______15 Powwow Member______188 5. Limestone, forming scattered ledges on slope, with fossils in float-______20 Total Hueco Limestone ______695 4. Slope, covered by talus______50 (Trachyte sill about 10 ft thick) SECTION 34. SOUTH OF BLACK JOHN CANYON 3. Slope, covered by talus______70 2. Conglomerate, arkosic _ _ _ _ 20 The following is a section of the Hueco Limestone 1. Conglomerate; composed of limestone pebbles- 10 half a mile south of Black John Canyon, on the divide Angular unconformity. between the canyon and drainage to the southeast, up the Beds of Devonian age at base of section. STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 159

Section 34a Bone Spring Limestone Continued Feet Top of outlier; no higher beds exposed. (USGS 7055a; field label 20 A) ; bryozoans, and Bone Spring Limestone: Feet productid, spiriferoid, and rhynchonellid 4. Shale, siliceous, brown; capped by a 4-ft bed of ^brachiopods observed. _ _ _ 20 dolomitic limestone, containing bryozoans____ 44 9. Limestone, black, thin-bedded to platy; with Conformity (?). interbedded thin layers of granular fossilifer- Hueco Limestone: ous limestone______25 Main body of formation: 8. Molluscan ledge. Limestone, dark-gray, coarse­ 3. Limestone, dolomitic; forms a slope______80 grained, bioclastic; contains a rich fauna domi­ 2. Limestone, dolomitic, finely crystalline, light- nated by mollusks, partly silicified. Forms a gray ; weathers dirty gray or pitted; forms lens several hundred feet long which tapers into ledges and cliffs. Contains some small sub- black platy limestone. Contains the fusulinid spherical chert nodules as much as 10 in. in Parafusulina dlabloensis Dunbar 'and Skinner; diameter, and fusulinid molds; near middle the sponges Anthracosycon uniforme Finks and was collected Composita mexicana (Hall) Stioderma coscinum Finks; cup and tabulate (REK 462). About 125 ft below top is a thin corals including Aulopora sp., Cladochonus sp. trachyte sill______355 and Lonsdaleial sp. ; echinoid spines and Powwow Member: crinoid columns; the bryozoans Acanthocladia 1. Slope; underlying beds concealed______55 sp., Septopora sp., and Striatopora sp.; the Angular unconformity. brachiopods Chonetes sp., Leptodus sp., and Fusselman and Montoya Dolomites at base of section. various productids; the pelecypods Anthra- (See section 9.) coneilo sp., Astartella nasuta Girty, A sp., Summary of section 34 "Cypricardinia" sp., Nucula sp., nuculoid Main section: indet., Nuculana sp., Parallelodon spp., Pleuro- Hueco Limestone: phorus sp., Pterial sp., and Streblopteria sp.; Main body of formation______808 the gastropods Anomphalus sp., Apachella sp., Powwow Member______180 Babylonites sp., Bellerophon deflectus Chronic, B. sp., bellerophontid indet., Cinclidonema sp., Total Hueco Limestone______993 Discotropis girtyi Yochelson, Donaldina"! sp., Section 34a: JHuphemites sp., Glabrocingulum sp., Glypto- Hueco Limestone: spira sp., Knightites (Restispira) sp., cf. Loxo- Main body of formation______435 nema sp., Naticopsis sp., Orthonema sp., Powwow Member______55 Peruvispira sp., pleurotomarian indet., pseudo- zygopleuran indet., Shewdagonial sp., sublitid Total Hueco Limestone______490 indet., Warthia waageni Yochelson, and "Wor- thenia" sp.; orthoceratid and nautiloid cepha- SECTION 33. Bia.CK JOHN CANYON lopods; the scaphopods "Laevidentalium" sp., and Plagioglypta sp.; the chiton "Gryphochi- The following is a section of parts of the Hueco and ton" sp.; the pteropod Hyolithes sp.; the ostra­ Bone Spring Limestones on the west side of the south codes Bairdia sp., Bairdiocypris"! sp., Healdia fork of Black John Canyon, about a mile south of sp., Hollinella sp. or spp., Kellettina sp., and Apache Spring (center of east line of sec. 14, Block 66, RoundyeHa"! sp.; and the trilobite Anisopyge Twp. 5); a pair of minor faults displaces the Hueco and sp. (USGS 6938, 7055, D & S 135; field label 20)_ 5 7. Limestone, black; wtih some thin beds of granu­ Bone Spring immediately to the northeast. The sec­ lar limestone _ __ 10 tion combines observations and measurements by J. 6. Limestone, granular, gray, massive; wedges out Brookes Knight and P. B. King in 1931. A fusulinid northeastward- _ 25 from the collections was identified by C. O. Dunbar and 5. Limestone, black, platy; weathers gray brown; J. W. Skinner (1937) and the ostracodes by I. G. Sohn forms a slope 50 (written commun., 1960). The rest of the fossils were 4. Limestone, bioclastic; partly silicified on surface; contains abundant crinoid columns, a few fusu­ identified by P. E. Cloud, Jr., and E. L. Yochelson linids, and limestone pebbles of possible organic (written commun., 1954). origin; forms ledges; interbedded with black Higher beds on slope not measured. platy limestone ___ 75 Bone Spring Limestone: Feet 3. Limestone, black, thin-bedded to platy; interbed­ 11. Limestone, black, thin-bedded; forms a slope. ded wtih siliceous shale______10 The brachiopods Chonetes and Marginifera, 2. Limestone, dolomitic, bioclastic; of irregular tex­ pelecypods, and possible algae observed___ 50 ture ; contains abundant crinoid columns and 10. Limestone, dark-gray, granular; partly silicified a few fusulinids. Forms thick beds and ledges 10 on surface; contains layers of subangular lime­ Conformity(?). stone cobbles of different texture from matrix. Hueco Limestone: Forms several ledges, but is lenticular, wedging 1. Limestone, dolomitic, thinly and regularly bedded; out into black limestone northeastward. Con­ contains fusulinids. Forms steep cliffs, extend­ tains fusulinids, a sponge, and crinoid stems ing to canyon bottom. Thickness estimated 500 160 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Base of section, no lower beds exposed. Bone Spring Limestone Continued Feet Summary of section 35 Feet 12. Limestone, dolomitic, thin-bedded; contains many limestone pebbles and a few poorly preserved Part of Bone Spring Limestone measured__ _ 280 fossils. Contains a 3-ft igneous sill in upper Part of Hueco Limestone exposed _ _ 500 part______50 SECTION 36. APACHE PEAK 11. Slope; underlying beds concealed 13 The following is a section of the Hueco, Bone Spring, 10. Limestone, gray, granular, fossiliferous 2 9. Marl, forming a slope _ 8 and Victorio Peak Limestones on the north spur of 8. Limestone, dolomitic; in 2- to 3-ft beds; weathers Apache Peak, beginning on the south side of portal of drab gray and jagged. Contains numerous Apache Canyon and extending to summit of peak silicified crinoid columns, and other fossils 16 (southeastern part of sec. 5, Block 66, Twp. 5, into 7. Shale, siliceous, brown; and platy black lime­ northeastern part of sec. 1, Block 42). A section was stone 33 measured on the spur by P. B. King and K. E. King Unconformity (?). in 1928, and was remeasured along the same course by Hueco Limestone: Main body of formation: P. B. King in 1931. The section given here is that of 6. Limestone, dolomitic, thin-bedded; in part very 1931, but some data have been added from the earlier cherty 37 section, including the fossil collection of unit 18, whose 5. Limestone, dolomitic, thick-bedded; forms brachiopods were identified by K. E. King (1931). ledges ______26 Thickness of the Bone Spring Limestone represents 4. Limestone dolomitic, thin-bedded; forms ledges separated by slopes_ 20 vertical distances obtained by hand leveling, and is not 3. Limestone, dolomitic, massive; weathers drab corrected for an original dip to northeast, off a reef mass gray and to a rough surface; forms promi­ to the southwest. nent ledges______32 Top of peak; no higher beds exposed. 2. Limestone, dolomitic, gray; forms thin ledges 32 Victorio Peak Limestone: Feet Powwow Member: 25. Limestone, light-gray, thick-bedded; contains chert 1. Conglomerate, bluff; formed of limestone peb­ bles in a marl matrix; poorly exposed in lenses. Some granular layers on this peak and on the outlier to south, contain large productids, most places- 48 Leptodus, Marginifera, and gastropods. Lime­ Angular unconformity. stone of Apache Peak stands about 300 ft lower Fusselman Dolomite at base of section. than main body of Victorio Peak Limestone on Summary of section 36 crest of escarpment 1% miles to south, but inter­ Part of Victorio Peak Limestone exposed 50 vening outliers demonstrate its continuity and Bone Spring Limestone______853 indicate an original dip to northeast______50 Hueco Limestone: Intergradation. Main body of formation______147 Bone Spring Limestone: Powwow Member-_ _ 48 24. Limestone, black, thin-bedded; forms a slope__ 60 23. Limestone, black; contains long lenses of black Total Hueco Limestone______195 and brown chert, and some beds of dark-gray granular limestone; forms a ledge______50 FOSSIL. COLJjECTTONS FROM VICTORIO PEAK IJCMB- 22. Limestone, black, slabby; weathers white_____ 50 STONE IN NORTHEASTERN SIERRA DIABIX> 21. Limestone, dark-gray, granular, fossiliferous; in Fossils were collected from the Victorio Peak Lime­ 6-in. beds______6 20. Shale, siliceous; interbedded with platy black stone in the northeastern Sierra Diablo, near the rim of limestone; weathers gray or yellow. Has an the escarpment, at various localities between Victorio original dip of about 5° northeastward_____ 372 and Apache Canyons, or near the upper ends of sections 19. Shale, siliceous, platy or stony, brown______75 31, 32, and 36, some of which have been listed in the 18. Limestone, dark-gray, granular; contains silicified sections. All collections are from the upper beds of fossils. At about this level were collected the brachiopods Chonetes permianus Shumard and the Victorio Peak Limestone exposed at their locality, Composita subtilita (Hall), and various gastro­ 500 feet or more above the base of the formation, but are pods (REK 483) ______3 not necessarily near the stratigraphic top of the forma­ 17. Shale, siliceous; with interbedded platy black tion. Collections 7006 and 7011 were made by P. B. limestone______10 King in 1931; collection 8546 (Pb 15) was made by 16. Limestone, dark-gray, granular, cherty; in 1-ft P. B. King and J. Brookes Knight in 1936; the rest beds; weathers light gray or white. ___ 37 15. Shale, siliceous; interbedded with dense platy were made by Knight in 1938. Fusulinids and other 13. Shale, siliceous______10 foraminifers were identified by L. G. Henbest, and tains abundant silicified fossils______10 larger fossils by P. E. Cloud, Jr., and E. L. Yochelson 14. Limestone, dark-gray, granular; in 2-ft beds; con- black limestone; weathers yellow _____ 48 (written commun., 1955,1954). STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 161

USGS 8546 (field label PI 15) . Crest of Sierra Diablo escarp­ Jr., and E. L. Yochelson (written commun., 1955,1954). ment north of portal of Victorio Canyon. (See unit 18, section Some cephalopods have been identified by A. K. Miller 31. p. 154.) and W. M. Furnish (Miller and Furnish, 1940a; Miller, USGS 7011, 14444 (field label C 19). Crest of Sierra Diablo escarpment near head of Marble Canyon. (See unit 50, section 19-15). 32. p. 155.) USGS 144489, F 9814 (field label C 16). Molluscan ledge in USGS 7006. Crest of Sierra Diablo escarpment at head of lower part of Bone Spring Limestone, about 100 ft above base. Black John Canyon, from half a mile north of North Diablo Fossils occur in a lens of bioclastic limestone, lying in platy triangulation station, for half a mile northwestward (northern black limestone, or in much the same association as those of the part of sec. 5, Block 42). Contains undetermined fusulinids molluscan ledge in Black John Canyon (unit 8, section 35), and and sponges; crinoid stems; the bryozoans Fistulipora sp., show a similar diversity. Rhombopora sp., and Septopora sp.; the brachiopods Avonia sp., Includes poorly preserved fusulinids; several genera of Chonetes sp., Derbyia sp., Enteletes sp., Hustedia sp., Leptodus sponges; the bryozoan Septopora sp.; echinoid spines; the sp., Heekella sp., Neospirifer sp., productid indet., Rhipidomella brachiopods Composita small sp., Isogramma sp., and productids sp., "Spirifer" sp., and Stenocisma cf. S. inequalis (Girty) ; the indet.; the pelecypods Astartella sp., myalinids indet., nuculoid the pelecypods Acanthopecten sp., parallelodontid iudet., and indet., Nuculana spp., Paleoneilo sp., Parallelodon sp., pectenoid Streblopteria sp.; and a tooth of Helodus or Orodus type. indet., Permophorus sp., Pteriat sp., and others; the gastropods U8G8 14470, F 98S7 (field label C 29) . Crest of Sierra Diablo Anomphalus sp., Apachella sp., Bellerophon sp., Donaldina"! sp., escarpment, near preceding and farther northwest, about a mile Euphemites cf. E. imperator Yochelson, E. sp., Enightites (Re- north of North Diablo triangulation station (northwest cor. tispira) sp., murchisonid indet., Naticopsis sp., Peruvispira sp., Sec. 5, Block 42). Contains much abraded shells of at least Pharkidonotus sp., pseudozygopleuran indet., Stegocoeliaf sp., two species of Parafusulina; the sponges Actinocoelia mean- "Strobeus" sp., sublitid indet., "Trachydomia" sp., Warthia drina Finks and Defordia densa Finks; cup coralsi and crinoid waageni Yochelson, and "Worthenia" sp.; the nautiloids Hichel- stems; fenestrate and fistuliporoid bryozoans; the brachiopods inoceras spp., Mooreoceras sp., Pseudorthoceras sp., Metacoceras Avonia sp., Buxtonia (Eochiproductus) sp., Chonetes sp., Com- mammiferum Miller, M. megapora Miller, If. spp., and Coopero- posita sp., Dictyoclostiis (Chaoiella) quadalupensis (Girty), cerasl sp. (Miller, 1945, p. 282-283) ; the ammonite Propinaco- Dielasma sp., Enteletes dumblei Girty, Hustedia mormoni (Mar- ceras knighti Miller and Furnish (holotype) (Miller and Fur­ cou), Leptodus sp., "Marginifera" spp., Meeketta? or Geyerellal nish, 1940a, p. 42-44) ; the scaphopod Plagioglypta sp.; and the sp., Noespirifer sp., Rhipidomella sp., Rhynchopora sp., Steno­ trilobite Anisopyge sp. cisma cf. S. inequalis (Girty), Streptorhynchus sp., and Weller- USGS 14443, F 9817 (field label C 18 a). Bone Spring Lime­ ella cf. W. elegans (Girty) ; gastroix>ds, including Babylonites; stone, 50 ft above base. Except for a single brachiopod, Rhipi- and the trilobite Anisopyge? sp. domella sp., collection consists of fusulinids and other foramini­ USGS 14445, F 9818 (field label C 20). South rim of Apache fers, which include Climacammina sp., Geinitzina sp., Endothyra Canyon 3 miles west of North Diablo triangulation station and sp., Tetrataxis sp., *Parafusulina linearis"! (Dunbar and Skin­ 2 miles northeast of Slaughter Ranch (center of sec. 20, Block ner) and var., *?P. gracilitatis (Dunbar and Skinner), *Pseudo- 32). Contains the dasycladacean green alga Macroporella sp.; fusulina powwowensis (Dunbar and Skinner), *Pseudoschwag- poorly preserved fusulinids or bryozoans; and the brachiopods erina teseanal Dunbar and Skinner, *Schwagerina bellula Dun- "Spirifer" sp., and Enteletes sp. bar and Skinner var., and Parafusulina? spp. Of the fusulinids USGS 14448, F 9820 (field label C 22), and USGS 14449, F in this collection, only the last are of Bone Spring type, the 9821 (field label C 28). Two collections about half a mile apart, remainder, marked by asterisks, being of Hueco type. The two on north slope of first valley south of Apache Canyon, 2 miles types have a different lithic appearance, and the association west-southwest of North Diablo triangulation station and 2 miles suggests redeposition of fusulinids from several stratigraphic northeast of Slaughter Ranch (central part of sec. 8, Block 42). levels. Contains the fusulinids and other foraminifers Climacammina USGS 14442, F 9816 (field label C 18 B) Bone Spring Lime­ sp., Gemitsina sp., Spandelinoides sp., *Tetrataxis sp., Endoth- stone, near base. Dolomite, crowded with poorly preserved yra sp., *Schubertella Jcingi Dunbar and Skinner var., *Parafusu- fusulinids, which include Parafusulina linearis? (Dunbar and linal aff. P. bosei var. attenuata Dunbar and Skinner, P. schu- Skinner), Pseudofusulina powwowensis (Dunbar and Skinner), oherti Dunbar and Skinner, P. diabloensis Dunbar and Skinner, and Pseudoschwagerina texana Dunbar and Skinner. These and Pseudofusulina setuml (Dunbar and Skinner). (Asterisks are all of Hueco type, and there is no evidence in the sample indicate forms which occur in both collections.) for or against the possibility of their redeposition in Bone Spring beds. FOSSIL COLLECTIONS FROM BONE SPRING LIMESTONE U8G814441, F 9815 (field label C 18 A) . Basal Bone Spring NORTHWEST OF PORTAL OF APACHE CANYON Limestone or topmost Hueco Limestone, apparently somewhat Fossils were collected in the lower part of the Bone lower stratigraphically than preceding. Sample is a fragment of limestone crowded with fusulinids and other foraminifers, Spring Limestone at several levels a mile west-north­ which show two different associations. west of the portal of Apache Canyon, above the outer One group occurs in pebbles in the limestone and includes bench of the Sierra Diablo escarpment (northeastern Gemitsina sp., Spandelinal sp., Schubertella kingi Dunbar and part of sec. 6, Block 66, Twp. 5). No section was meas­ Skinner, Parafusulina linearis? (Dunbar and Skinner), Pseudo­ ured, but the collections are listed below in stratigraphic fusulina powwowensis (Dunbar and Skinner), and Schwagerina aff. S. bellula Dunbar and Skinner. All these fusulinids are of order. The collections were made by J. Brookes Knight Hueco type. in 1936; fusulinids and other foraminifers were identi­ The matrix contains Parafusulina diabloensis Dunbar and fied by L. G. Henbest, and larger fossils by P. E. Cloud, Skinner and a very slender species of Parafusulina?. The first 162 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS is definitely of Bone Spring type, but the affinities of the second Bone Spring Limestone Continued Feet are uncertain. 20. Limestone, gray, oolitic; contains siliceous The occurrence of Parafusulina diabloensis in the matrix masses; forms a massive reeflike, lenticular suggests strongly that the rock containing it is part of the Bone ledge. Large fusulinids observed 5 Spring Limestone, and that the fusulinids of Hueco type in the 19. Limestone, dark-gray, siliceous, platy; weath­ pebbles have been redeposited. ers brown and forms a slope. Poorly pre­ served bellerophontid gastropods observed- 50 SECTION 37. FIRST SECTION IN APACHE CANYON 18. Limestone, shaly, buff; splits into paper-thin The following is the northeasternmost of five sections sheets; passes upward into dark-gray platy siliceous limestone, with some interbedded of the Hueco, Bone Spring, and Yictorio Peak Lime­ layers of granular limestone. Unit has ir­ stones in the Apache Canyon. The section is on the regular dips. A ledge near middle contains northwest wall of the canyon, on a spur extending east- the brachiopod Lissochonetes sp. (USGS southeast from the peak marked by elevation point 5741, 14460; field label C 27 B) ; sponge spicules beginning at the channel of the canyon and proceeding and euomphalid gastropods observed 40 to the summit of the peak (across southern part of sec. 6, 17. Limestone, dark-gray, siliceous, platy 25 16. Limestone, dark-gray, siliceous, platy; weath­ Block 66, Twp. 5). The section was measured by J. ers yellow; a thin bed of gray granular Brookes Knight in 1938; fusulinids and other foramini- limestone at top, contains silicified fossils 27 fers were identified by L. G. Henbest, and larger fossils 15. Limestone, gray, granular; forms ledges and by P. E. Cloud, Jr., and E. L. Yochelson (written contains silicified fossils of Bone Spring commun., 1955,1954). type; interbedded with dark-gray siliceous thin-bedded limestone; weathers yellow 8 Top of peak; no higher beds exposed. 14. Limestone, dolomitic, finely conglomeratic; Victorio Peak Limestone: Feet forms a ledge. Contains the brachiopod 28. Limestone, granular, light-gray; in 1-ft. beds; Marginiferat sp., and the fusulinids and contains some chert. Contains the sponge other foraminifers Geinitsina sp., Schwag- Jereina cylindrica Finks; a cup coral; the erinal franMinensis Dunbar and Skinner, braehiopods Dictyoclostus (Chaoiella) 8. gumWei Dunbar and Skinner, Parafusu­ guadalupensis (Girty), Enteletes sp., "Mar- lina aff. P. lineata Dunbar and Skinner, P. ffinifera" sp., and Rhipidomella sp; and the sohucherti Dunbar and Skinner, and P. spp. gastropods Discotropis cf. D. girtyi Yochel­ (USGS 14447, F 9819; field label C 21 A)__ 3 son, Euphemites exquisitus Yochelson, and 13. Limestone, dolomitic; weathers craggy and Knightites (Retispira) sp. (USGS 14461; and forms a slope. Silicified crinoid col­ field label C 27 D)______100 umns observed 8 27. Limestone, granular, gray; in 1- to 2-ft beds; Unconformity. upper half forms a cliff and lower half a Hueco Limestone: slope; poorly preserved fossils observed. Division B: Base lies at about same altitude as base of 12. Limestone, dolomitic, light-gray; forms a main body of Victorio Peak Limestone half ledge . 3 a mile to southwest, but is stratigraphically 11. Limestone, dolomitic; weathers craggy higher, the lower beds of Victorio Peak and forms a slope_ 12 Limestone wedging out into black limestone 10. Limestone, calcitic or only slightly dolo­ facies of Bone Spring northeastward, with mitic, gray, thin-bedded; weathers original dip ______110 light gray and to a smooth surface; Intergradation. forms upper part of lower bench in Bone Spring Limestone: canyon. Contains abundant molds of 26. Limestone, black to dark-gray, platy_____ 160 small fusulinids; a collection 30 ft below 25. Limestone, gray, granular; forms a ledge___ 3 the top includes Schubertella kingi Dun- 24. Limestone, dark-gray, siliceous, platy; with a bar and Skinner, Schwagerina bellula"! few 6-in. to 1-ft. beds. Beds have an orig­ Dunbar and Skinner, and Pseudofusu- inal dip northeastward, in places as steep as lina sp. (F 9826; field label C 27 "special 25°______370 collection")______.______142 23. Limestone, dark-gray, shaly, very thin bedded, Division A: yellow; with original dips as steep as 25°_ 50 9. Limestone, dolomitic, massive; weathers 22. Limestone, gray, granular, bioclastic, brecci- craggy; contains abundant molds of ated; forms a reef like lenticular ledge. small fusulinids______205 Abundantly fossiliferous; contains corals, 8. Limestone, dolomitic, thick-bedded; con­ massive bryozoans, and the brachiopods tains much chert in topmost ledge; forms Avonia and Dictyoclostus______5 a slope______38 21. Limestone, dark-gray, siliceous, platy; a few 7. Limestone, dolomitic, massive; weathers ledges of gray granular limestone in lower craggy; contains small cherty masses. part, in one of which a well-preserved gas­ Contains abundant molds of small fusu­ tropod was observed______55 linids and some crinoid columns _ __ 25 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 163 Hueco Limestone Continued Bone Spring Limestone Continued Feet Division A Continued Feet Skinner, and other parafusulinids of Bone Spring 6. Limestone, dolomitic, thick-bedded to mas­ type (F 9835; field label C 28 H)______50 sive ; forms ledges; does not weather so 30. Limestone, gray, fine-grained to compact; in 1- craggy as adjacent units; chert absent to 2-ft beds; contains many silicified fossils of in this and units beneath______48 Bone Spring aspect______100 5. Limestone, dolomitic, thin-bedded; forms 29. Limestone, dark-gray to black; in 6-in to 1-ft beds_ 55 aslope ______40 28. Limestone, dark-gray to black; interbedded with 4. Limestone, dolomitic, massive; weathers layers of gray granular limestone that contains craggy ______15 silicified fossils______100 3. Limestone, dolomitic, gray-brown; does not 27. Limestone, dark-gray to black; in 1- to 2-ft beds; weather so craggy as adjacent units____ 10 some lenses of granular limestone near base, 2. Limestone, dolomitic, massive; weathers which contain bryozoans_ __ 85 craggy; forms ledges. Contains molds 26. Limestone, dark-gray to black, thinly laminated; of small fusulinids; extends down to in 6-in to 1-ft beds; weathers buff and forms a channel of Apache Canyon______30 slope. Contains a well-preserved sponge (USGS 1. Strata not exposed on line of section; 14467; field label C 28 G). This unit, and next thickness to base of Hueco Limestone two above, have an original dip of 12° to the probably______20-50 northeast______95 Angular unconformity. 25. Limestone, gray, granular, reefy; contains abund­ Fusselman Dolomite, exposed beneath Hueco Lime­ ant bryozoans, sponges, and other fossils 35 stone a quarter of a mile to northeast. 24. Limestone, gray to light-gray; weathers buff or Summary of section 37 brown; platy or thinly laminated, in 6-in to 1- Part of Victorio Peak Limestone exposed______210 ft beds. Near middle is a 6-ft bed of more gran­ Bone Spring Limestone______809 ular limestone. Beds of unit have irregular Hueco Limestone: original dips______110 Division B______157 23. Limestone, black, thinly laminated, thin-bedded 15 Division A______431-i61 22. Limestone, light-gray, weathers buff; siliceous, platy. Has steep irregular original dips __ 25 Total Hueco Limestone______588-618 21. Limestone, granular, massive, lenticular and reefy; contains sponges _ _ _ 15 SECTION 38. SECOND SECTION IN APACHE CANYON 20. Limestone, gray to dark-gray, siliceous, platy; The following is a section of the Hueco, Bone Spring, forms a slope______12 and Victorio Peak Limestones on the northwest wall of 19. Limestone, granular, massive, reefy and lenticular- & 18. Limestone, dark-gray, thin-bedded_ 7 Apache Canyon, three-quarters of a mile southwest of 17. Limestone, light-gray; brecciated in part; very section 37, from the channel of the canyon, up a spur massive, but reefy and lenticular; contains silici­ to the rim at a point half a mile southwest of Elusive fied fossils______60 triangulation station (west-central part of sec. 2, 16. Limestone, marly; forms slopes with interbedded Block 42, to center of sec. 1, Block 32). The section ledge-making dark-gray limestone. Contains abundant silicified fossils of Bone Spring type, was measured by J. Brookes Knight in 1938; fusulinids including the brachiopod Hustedia sp., as well and other foraminifers were identified by L. G. Hen- as the fusulinids and other foraminifers Geinit- best ; a few larger fossils were identified by P. E. Cloud, sina sp., Endothyra sp., Quinqueloculina sp., Oza- Jr., and E. L. Yochelson (written commun., 1955, wainella sp., Staffellal sp., Schwagerina gumbeli 1954). Dunbar and Skinner, Parafusulina diabloensis Dunbar and Skinner, P. fountains Dunbar and Rim of canyon; no higher beds exposed. Skinner, and P. imUyil Dunbar (USGS 14466, F Victorio Peak Limestone: Feet 9834; field label C 28 F)______30 33. Limestone, light-gray, granular, thick-bedded to 15. Limestone, dolomitic; contains the fusulinids and massive; forms ledges and cliffs. Strata dip other foraminifers Tetrataseis sp., Parafusulina northeastward and lower part intertongues with scJiucherti Dunbar and Skinner, and P. fountaini black limestone beds of Bone Spring. Contains Dunbar and Skinner (F 9833; field label C 28 three species of Pseudofusulina or Parafusulina, E) ; echinoderm fragments observed _ 7 or both, apparently of Bone Spring type (F 9836; 14. Limestone, dolomitic; weathers craggy; contains field label O 28 I)______150 poorly preserved large fusulinids- 10 Intergradation. Unconformity. Bone Spring Limestone: Hueco Limestone: 32. Limestone, dark-gray, compact; in 1- to 2-ft beds; Division C: forms a slope and contains some chert and a 13. Limestone, dolomitic, dark-gray (weathers few fossils______60 brown and craggy), very massive. Contains 31. Limestone, gray, compact; forms a cliff. Contains abundant molds of small fusulinids and abraded and broken fusulinid shells, which in­ poorly preserved Omphalotrochus. Uncon- clude IParafusulina diabloensis Dunbar and formable surface at top of unit slopes north- 757-108 65 12 164 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Hueco Limestone Continued Summary of section 38 Continued Division C Continued Feet Hueco Limestone: Feet eastward and cuts out this unit on next Division C______- 40 ridge to northeast______40 Division B______- 217 Division B: Part of division A exposed-_ 172 12. Limestone, light-gray; in 2-ft beds; interbed- ded with thinner layers of white dolomitic Part of Hueco Limestone exposed 429 limestone. Near top it contains the fusu- SECTION 39. THIRD SECTION IN APACHE CANYON linids Parafusulina linearis (Dunbar and Skinner), and Pseudoschwagerinal lawis- The following is a section of the Hueco, Bone Spring, sima (Dunbar and Skinner), and P. sp. (F and Victorio Peak Limestones on the northwest wall of 9832; field label C 28 D) ______45 Apache Canyon, a mile southwest of section 38, from the 11. Limestone, light-gray, finely granular, channel of the canyon to the rim at a point 1% miles massive. Contains many fusulinids and other foraminifers, whose shells are vari­ south of Elusive triangulation station (across south­ ably abraded; these include Climacammina western part of sec. 10, Block 32). The section was sp., Staffella sp., Schiibertella Mngi Dunbar measured by J. Brookes Knight in 1938; fusulinids and and Skinner, Pseudofusulina emaciatal other foraminifers were identified by L. G. Henbest (Beede), P. gracilitatisl (Dunbar and Skin­ (written common. 1955). ner) var., P. powwowensis (Dunbar and Skinner), and Parafusulina linearis (Dun- Rim of canyon ; no higher beds exposed. bar and Skinner) var. (F 9831; field label Vietorio Peak Limestone: Feet C 28 C)______10 31. Limestone, dolomitie, fine-grained, light-gray; 10. Dolomite, white, porcelaneous, splintery___ 5 weathers yellow; in massive beds, containing 9. Limestone, light-gray, massive; contains many fusulinid molds as much as three-quarters of an fusulinids, and other fossils, poorly pre­ inch in length______20 served______30 30. Limestone, dolomitic, light-brown; in massive 8. Limestone, dolomitic, gray ______5 beds, containing molds of large fusulinids___ 105 7. Limestone, light-gray; in 2-ft beds; contains 29. Limestone, somewhat dolomitic, crystalline, light- the fusulinids and other foraminifers gray ; forms a massive cliff. Contains the fusu­ Qeinitsina sp., Schubertella Mngi Dunbar linids and other foraminifers Climacammina sp., and Skinner var., Parafusulina linearis Geinitswa sp., Schubertella Mngi Dunbar and (Dunbar and Skinner), and Pseudoschwa- Skinner var., Parafusulina linearis (Dunbar and gerina teacana Dunbar and Skinner (F. Skinner) var., P. cfr. P. dialloensis Dunbar and 9830; field label C 28 B) ; other fossils are Skinner or Pseudofusulina, and IP. fountaini poorly preserved ______25 Dunbar and Skinner var. (F 9825; field label C 6. Limestone, light-gray; in 2-ft beds ____ 32 26 C) ; cross sections of brachiopods observed_ 105 5. Limestone, light-gray; interbedded with white 28. Limestone, dolomitic, light-gray; forms ledges; dolomitic limestone that contains fusulinid interbedded with marl. Molds of fusulinids and molds ____. ______35 a fenestellid bryozoan observed______25 4. Limestone, gray; contains at the base the fusu­ 27. Limestone, dolomitic, fine-grained, light-gray; linids and other foraminifers Spandelinoides forms a massive ledge______15 sp., Endothyra sp., Scliubertella Mngi Dun- Conformity. bar and Skinner, Triticites ventricosust Bone Spring Limestone: (Meek and Hayden) var., T. sp., and Pheu- 26. Limestone, dolomitic, saccharoidal, brown; weath­ dofusulina"! sp. (F 3805; field label C 28 ers dark gray; contains small fusulinid molds. A) ______..______30 Forms a set of very massive dark ledges, as Division A: viewed from a distance, which contrast with the 3. Limestone, slightly dolomitic, light-gray; in 8- lighter colored ledges above______168 to 18-in. beds; interbedded with thin-bedded 25. Dolomite, white, porcelaneous______1 white dolomitic limestone______35 24. Limestone, dolomitic, fine-grained; in 3-ft beds; 2. Limestone, dolomitic, dark-gray, thin-bedded; contains poorly preserved silicified fossils____ 20 contains fusulinid molds in part______17 23. Limestone, dolomitic, cherty, marly; weathers yel­ 1. Limestone, dolomitic, dark gray; weathers low ; contains large fusulinid molds___,___ 25 brown ; in 4- to 6-ft beds; contains many molds 22. Limestone, dolomitic, light-gray; contains large of small fusulinids______120 fusulinids. Weathers craggy and forms mas­ Alluvium of floor of Apache Canyon at base of section; sive ledges______30 lower beds concealed. In the field it was estimated that 21. Limestone, somewhat dolomitic, light-gray, com­ the lowest exposed beds are 300-400 ft above base of pact; interbedded with pink chert. Contains Hueco, as exposed in northeastern part of canyon. the fusulinids and other foraminifers Bradyinal sp., Geinitzinal sp., and Parafusulina linearis Summary of section 38 (Dunbar and Skinner) var. (F 9824; field label Part of Victorio Peak Limestone exposed______150 C 26 B) ; a cup coral, crinoid columns, and a Bone Spring Limestone______879 Hustedia observed 27 STEATIGRAPHIC SECTIONS OF PERMIAN ROCKS 165

Unconformity. Summary of section 39 Continued Hueco Limestone: Hueco Limestone: Feet Division C: Feet Division C______399 20. Limestone, dolomitic, thin-bedded; forms con­ Division B______327 spicuous light-gray outcrops; contains molds Part of division A exposed- _ 28 of small fusulinids______45 19. Limestone, dolomitic, dark-gray, thick-bed­ Part of Hueco Limestone exposed- ___ 754 ded; a few layers full of small fusulinid molds ______.______85 SECTION 40. FOURTH SUCTION IN APACHE CANYON 18. Limestone, dolomitic; forms ledges that are conspicuously light gray, with a few layers The following is a section of the Hueco, Bone Spring, full of small fusulinid molds______37 and Victorio Peak Limestones on the south wall of 17. Limestone, dolomitic, dark-gray, thin-bedded; Apache Canyon 2 miles southwest of section 39, from weathers to a rough surface; a few layers the floor of the canyon to the elevation point 5841 on the full of fusulinid molds _____ 65 16. Dolomite, white, porcelaneous _ 3 rim (north half of east line of sec. 18, Block 32). The 15. Limestone, dolomitic, dark-gray; weathers section was measured by J. Brookes Knight in 1931; no craggy; contains small fusulinid molds___ 10 fossils were collected, although they were observed and 14. Dolomite, white, porcelaneous ______1 recorded in the field. 13. Limestone, dolomitic, light-gray; weathers craggy; contains some small fusulinid Rim of canyon; no higher beds exposed. molds; forms top of a bench______90 Victorio Peak Limestone: Feet 12. Limestone, dolomitic, dark-gray; forms mas­ 10. Limestone, dolomitic; forms thinner ledges than sive ledges ______30 below which alternate with slopes to top 100 11. Limestone, dolomite, light-gray; in 1- to 4-ft 9. Limestone, dolomitic, evenly bedded; forms a beds, some of which contain molds of small cliff ______- 60 fusulinids____.______30 Conformity. 10. Limestone, dolomitic; contains fusulinid Bone Spring Limestone: molds and forms a slope______3 8. Limestone, dolomitic, thin- to thick-bedded; forms Division B: ledges ______200 9. Limestone, in alternating thin and thick beds_ 22 Unconformity. 8. Limestone,, dark-gray. Contains the fusulinids Hueco Limestone: and other foraminifers Climacammlna, sp., Division C: Spandelina sp., Geintzina sp., a bradyinid, 7. Limestone, dolomitic, gray; forms ledges on Tetratatvis sp., Schu'bertella kingil Dunbar slope, but passes into a massive cliff on next and Skinner, Pseudofusulina emaciata spur to west 50 (Beede), and Pseudoschwagerina cf. P. 6. Limestone, dolomitic, light-gray; in 1 to 5-ft leedei Dunbar and Skinner (F 9828; field ledges; contains traces of fossils 80 label O 26 A)______5 5. Limestone, dolomitic, gray, massive; forms 7. Limestone,, gray; in beds as much as 6 ft thick. cliffs; contains a few fossils, including large Forms top of a bench______130 productid brachiopods and a large euompha- 6. Limestone, light- to dark-gray; mostly in 1-ft lid gastropod- _ 75 beds, with some 3-ft beds. In lower 50 ft Division B: are some interbedded 5-ft beds of dolomitic 4. Limestone, light-gray, thin- to thick-bedded 78 limestone that contains the fusulinids and 3. Limestone, light-gray; forms a massive ledge; other foraminifers Spandelina sp., Geinitzina contains a large Meekella, productid brachio­ sp., Tetrataaeis sp., textulariids, Schubertella pods, and a large euomphalid gastropod- 5 kingi Dunbar and Skinner, and Triticites 2. Limestone, light-gray, thin- to thick-bedded. spp. (F 9829; field label C 26 AA). These dolomitic beds are probably equivalent to Fusulinids observed in float_ - 205 upper part of division A farther northeast 1. Limestone, light-gray, thin- to thick-bedded. in Apache Canyon ______170 Many silicified shells of Composita observed Division A: on weathered surfaces 25 5. Limestone, dark-gray; forms a ledge_____ 2 Alluvium of floor of Apache Canyon at base of section; 4. Slope; underlying beds concealed______3 no lower beds exposed. 3. Limestone, dolomitic, light-gray, massive; con­ Summary of section 40 tains molds of small fusulinids______8 2. Slope; underlying beds concealed______10 Part of Victorio Peak Limestone exposed_ 160 1. Limestone, dark-gray; in massive ledge___ 5 Bone Spring Limestone 200 Base of section in channel of Apache Canyon; no lower Hueco Limestone: beds exposed. Division C______205 Summary of section 39 Part of division B exposed______313 Part of Victorio Peak Limestone exposed______270 Bone Spring Limestone______271 Part of Hueco Limestone exposed __ 518 166 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

SECTION 41. APACHE TANK Summary of section 41 Feet Part of Victorio Peak Limestone exposed 170 The following is a section of the Hueco, Bone Spring, Bone Spring Limestone 259 and Victorio Peak Limestones on the southwest wall of Part of Hueco Limestone (division C) exposed 228 Apache Canyon above Apache Tank, up to summit SECTION 42. SIERRA PRIETA marked by elevation point 5690, iy2 miles northwest of The following is a section of the Hueco and Victorio section 40 (northeastern part of sec. 14, Block 32). The Peak Limestones exposed on the south side of Sierra section was measured by J. Brookes Knight in 1931, but Prieta, which form the roof rocks of the Sierra Prieta additional observations and collections were made in intrusive. The Hueco Limestone was measured from 1938. Fusulinids were identified by L. G. Henbest, and the intrusive contact three-quarters of a mile north­ larger fossils by P. E. Cloud, Jr., and E. L. Yo'chelson west of Black Mountain Tank, across a high conical (written commun., 1955,1954). hill and lower hills to the south, to the alluvial valley Rim of canyon; no higher beds exposed. near the tank (eastern part of sec. 47, block N). The Victorio Peak Limestone: Feet Victorio Peak Limestone was measured on the low scarp 11. Limestone, dolomitic, in 2- to 3-ft ledges; forms south of the alluvial valley (northeastern part of sec. a slope. A large euomphalid gastropod ob­ 50, block N). The section was measured by J. Brookes served- _ 110 Knight in 1938; fusulinids and other foraminifers were 10. Limestone, dolomitic, light-gray; with ramifying identified by L. G. Henbest (written commun. 1955); siliceous masses in top beds. Forms a mas­ other fossils were observed in the field, but were not sive cliff______60 Conformity. collected. Bone Spring Limestone: Top of scarp; no higher beds exposed. 9. Limestone, dolomitic; in 1- to 8-f t beds; thicker beds Victorio Peak Limestone: Feet are granular and weather jagged, thinner ones 22. Limestone, dark-gray, dolomitic; weathers dense. Contains a myalinid pelecypod (USGS craggy; interbedded with white or light-gray 7007a; field label 29 B) ; poorly preserved large porcelaneous dolomite- 50 euomphalid gastropod observed 165 21. Limestone, dolomitic, light-gray, massive- _ 10 8. Limestone, dolomitic, light-gray, splintery; lower 20. Limestone, dolomitic, light-gray; weathers brown beds porcelaneous, higher ones granular and and craggy; interbedded with compact buff weather jagged______18 thin-bedded dolomitic limestone; a poorly pre­ 7. Limestone, gray and yellow; interbedded with served bellerophontid gastropod observed _ 20 marl ______22 19. Slope on north face of scarp; underlying beds con­ 6. Marl, gray, yellow, and pink _ _ _ 18 cealed; probably thin-bedded dolomitic lime­ 5. Conglomerate, formed of limestone pebbles and stone ______-_____-_ _ _- 35 cobbles, standing in massive ledges, with inter­ 18. Alluvial valley 900 ft broad; underlying beds vening slopes ______36 concealed; probably thin-bedded or marly dolo­ mitic limestone______- 150 Unconformity. Hueco Limestone: Unconformity. Division C: Hueco Limestone: 17. Limestone, dolomitic, dark blue-gray; weathers 4. Limestone, dolomitic, thin-bedded; poorly ex­ craggy 10 posed on slope______52 16. Limestone, dolomitic, white or light-gray, porce­ 3. Limestone, dolomitic, thin-bedded. In 1931, laneous ; some dark-gray craggy dolomitic lime­ about 30 ft from base, was collected the fusu- stone ; mostly poorly exposed, but forms ledges linid Triticites (=Pseudofusulina) pow- in part______45 wowensis Dunbar and Skinner (D and S 15. Swale; underlying beds concealed______15 125; field label 29 A). In 1938, from same 14. Limestone, dolomitic, light-gray splintery; inter­ general level, were collected Scliubertellal bedded darker craggy-surfaced dolomitic lime­ sp., Pseudofusulina aff. P. uddeni (Dunbar stone, with a few 1-ft beds of white porce­ and Skinner), and Schwagerina hessensisl laneous dolomitic limestone. Both light-gray Dunbar and Skinner (F 9805; field label and dark-gray dolomitic limestone beds con­ C 4) ______105 tains numerous molds of small fusulinids-__ 30 2. Limestone, dolomitic, poorly bedded, massive. 13. Limestone, dolomitic, dark-gray______5 Contains fusulinids; the corals Syringopora 12. Limestone, dolomitic light-gray; with a 1-ft bed sp., and Lonsdaleia sp.; the brachiopods Dic- of white porcelaneous dolomitic at base___ 15 tyoclostus sp. and Composita sp.; and the 11. Limes-tone, dolomitic, lightrgray, partly splintery, gastropod Omphalotrochus obtusispira (Shu- partly craggy ______100 mard) (USGS 7007; field label 29 AA)__ 60 10. Limestone, dolomitic, light-gray, splintery____ 40 1. Limestone, dolomitic, dark-gray; forms 9. Limestone, dolomitic, dark-gray; weathers to ledges ______H smooth light-gray surfaces; forms 1- to 2-ft Base of section in stream channel; no lower beds exposed. beds ______25 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 167

Hueco Limestone Continued Feet The section extends up the east face of South Mesa at 8. Limestone, dolomitic; in alternating dark-gray about midlength, or nearly due west of the old Babb and light-gray layers; weathers craggy. Top Kanch (along eastern half of center line of sec. 18, bed contains large pseudoschwagerinids which were unidentifiable in the laboratory (F 9839; Block 67, Twp. 4). Sections were measured here by P. field label 0 31 B)______15 B. King and K. E. King in 1928, and by J. Brookes 7. Limestone, dolomitic, dark-gray to black; weath­ Knight in 1936. Fusulinids collected in 1928 were iden­ ers craggy and forms a conspicuous ledge 17 tified by C. O. Dunbar and J. W. Skinner (1937), and 6. Limestone, dolomitic, dark-gray; weathers the brachiopods by R. E. King (1931). Fusulinids and craggy; interbedded with light-gray dolomitic limestone. Contains many molds of small other foraminifers collected in 1936 were identified by fusulinids ______13 L. G. Henbest, and larger fossils by P. E. Cloud, Jr., 5. Limestone, dolomitic, dark-gray; forms a massive and E. L. Yochelson (written commun., 1955, 1954). ledge. Contains Climacammina 2 sp., G-einit- The section given below combines the field observa­ zina sp., Spandelina sp., and Schwagerina aff. tions of 1928 and 1936 and includes both sets of fossil 8. hawJcinsi Dunbar and Skinner (F 9838; field label C 31 A)______12 identifications. 4. Limestone, dolomitic, dark-gray; forms a massive Section 43b ledge ______8 3. Limestone, dolomitic, dark blue-gray; parts more Top of South Mesa; no higher beds exposed calcitic than others. Beds near middle form Goat Seep Limestone: Feet a hogback ridge. A bellerophontid observed 50 24. Limestone, dolomitic, light-gray to pink; 2. Limestone, dolomitic, dark blue-gray; weathers weathers brown and to rough surface; in blue; probably slightly altered by intrusive; in thin to thick irregular beds. Contains 1- to 2-ft beds. Poorly preserved staffellid fo- rounded chert nodules, geodes, and silici­ raminifers and an Omphalotrochus observed_ 100 fied fossils. The latter include poorly pre­ 1. Contact rocks next to intrusive: Limestone, dolo­ served fusulinids; the sponges Actinocoelia mitic, gray or brown, mannorized and bleached; meandrina Finks, A. ? sp., and Stioderma co- weathers yellow; alternating with bluish thin- scinum Finks; a cup coral; the bryozoan bedded baked and silicified limestone, probably "Acanthocladia" sp.; the pelecypod "Avicu- originally argillaceous. Crinoid columns ob­ lopecten" sp. indet.; the gastropod Platy- served in top layer ______47 ceras sp. indet.; and the brachiopods Cho- netes (Chonetinella) sp., "Harpinifera" sp. Intrusive contact at base of section; igneous rock of Sierra Prieta intrusive beneath. aff. M. occidentalis Schwellwein or M. wal- cottiana (Girty), "M." sp., Dictyoclostus Summary of section 42 (Chaoiella) cf. D. guadalupensis (Girty), Part of Victorio Peak Limestone exposed______265 Leptodus cf. L. americanus Girty, Composita Part of Hueco Limestone exposed______547 sp., Neospirifer sp., Stenocisma n. sp., Hus- SECTION 43. SOUTH MESA tedia cf. H. mormoni (Marcou), Wellerella cf. W. elegwns (Girty), Enteletes spp., Rhyn- The following is a section of the Bone Spring Lime­ choporal sp., Dielasma sp., and a phricodo- stone, Victorio Peak Limestone, Cutoff Shale, sandstone thyrinid (USGS 8548, F 2688; field label tongue of Cherry Canyon Formation, and Goat Seep Pd 1) ______200 Conformity. Limestone, at the north end of the Sierra Diablo, from Sandstone tongue of Cherry Canyon Formation: south of Babb Canyon and the Babb flexure, to the top 23. Sandstone, fine-grained to silty, buff; weath­ of South Mesa. The section is in two parts: ers brown; mostly thin bedded, but with Section 43a was measured by P. B. King and R. E. thicker layers toward base- ______150 22. Sandstone, medium-grained, dolomitic; weath­ King in 1928, and covers the Bone Spring Limestone ers brown; forms a massive bed. Contains and Victorio Peak Limestone, which are exposed at the poorly preserved fusulinids. Thickness var­ east end of the cuesta that borders Babb Canyon on iable ; lies with irregular contact on under­ the south, beginning in a reentrant valley a mile south lying shale and limestone, of which it con­ of the portal of the canyon (mainly in western part of tains chips and pebbles _ ____ 5-40 Unconformity. sec. 29 Block 67, Twp. 4). A small collection made in Cutoff Shale: 1936 has been inserted at its appropriate position; iden­ 21. Shale, fine-grained, sandy______22 tifications were made by P. E. Cloud, Jr., and E. L. 20. Limestone, laminated, sandy______5 Yochelson (written commun., 1954). 19. Limestone, gray to black, fine-grained, platy to Section 43b covers the upper part of the Victorio medium-bedded; some platy fine-grained sandstone. A Squamularia observed. Forms Peak Limestone, and the higher formations, and is tied a bench______139 to section 43a by the occurrence in both of the distinc­ 18. Shale, siliceous and sandy, buff______11 tive middle division of the Victorio Peak Limestone. 17. Limestone, dense, platy, buff and gray____ 8 168 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Cutoff Shale Continued Feet Victorio Peak Limestone Continued Feet 16. Slope; underlying beds concealed______11 Middle division Continued 15. Limestone, gray, dense, platy______18 4. Limestone, dolomitic, dense, white or light- 14. Shale, siliceous; interbedded with platy gray gray ; in 1- to 2-ft beds. Contains irregu­ limestone ______33 lar specks of crystalline calcite. Forms 13. Limestone, dense, gray, -thinly laminated. a slope with thin ledges 45 Contains Composita mira (Girty) (REK Lower division: 506) ; poorly preserved brachiopods and a 3. Limestone, dolomitic, dark-gray; forms possible ammonite observed______15 ledges_____ . 23 12. Limestone, thin-bedded, dark-gray, and sili­ 2. Limestone, dolomitic, light-gray; weathers ceous shale, poorly exposed______13 pitted; forms a massive ledge; contains Conformity. small crinoid columns 8 Victorio Peak Limestone: 1. Limestone, medium-bedded; poorly ex­ Upper division: posed at base of slope- _ 33 Base of section covered by alluvium; no lower beds ex­ 11. Limestone, dolomitic, dark-gray; forms posed. massive ledges; interbedded with Section 43a thinner bedded limestone. Collection Top of cuesta; higher beds exposed north of Babb can­ of 1928 contains the fusulinid yon (see section 43b). Schwagerina setuml Dunbar and Skin­ ner, and the brachiopods Productus dar- Victorio Peak Limestone: toni sullivanensis King, Productus ivesi Upper division: Newberry, Lyttonia nobilte americamis 7. Limestone, dark-gray, thick-bedded; forms (Girty), Spirifer (Neospirifer) pseudo- dip slope of cuesta 50 cameratus Girty, and Squamularia Middle division: quadalupensis (Shumard) (D&S 6. Limestone, dolomitic, light-gray, thin-bed­ 137, REK 493). In 1936 collections ded; with partings of marly sandstone. were made near top of unit (USGS Weathers white and forms a conspicuous 8535, F 2698; field label Pb 2) and near light-colored band on hillsides_.____ 34 middle of unit (USGS 8534, F 2691; Lower division: field label Pb 1). These contain the 5. Limestone, gray, thick-bedded; interbedded fusulinids and other foraminifers Gei- with layers of light-gray dolomitic lime­ nitzina sp., Endathyra sp., a schuber- stone in upper part; includes lower part tellid or millerellid, Parafusulina of middle division as distinguished in baJceri Dunbar and Skinner var., P. section 42b______260 fountaini Dunbar and Skinner, and 4. Limestone, dolomitic, gray; weathers drab Pseudofusulina setum (Dunbar and gray or gray brown; in 1- to 2-ft beds; Skinner) ; lophophyllid corals; the bry- forms thick ledges and cliffs-______300 ozoans "Batostomella," sp., a fistuli- 3. Sandstone, fine-grained, brown______12 poroid, and "Stenopora" sp.; the gastro­ 2. Limestone, finely crystalline, dark-gray; pod Edbylonites sp.; and the brachio­ weathers light gray; in 1- to 10-ft beds; pods Buxtonia (Kochiprodttctus) cf. B. forms ledges and cliffs. Contains irregu­ victorioensis King, Chonetes (Choneti- lar chert nodules______250 nella) spp., Composita sp., "Dictyoclos- Break in section. (Across reentrant valley a mile south tus" aff. D. semistriatus (Meek), Hus- of portal of Babb Canyon; a fault of small displace­ tedia sp., Leptodus sp., "Marginifera" ment follows the valley, and some of lower part of spp., Neospirifer cf. N. pseudocameratus Victorio Peak Limestone may be cut out along it; (Girty), Rhipidomella sp., "Spirifer" basal Victorio Peak overlies the Bone Spring Lime­ sp., and Squamularia sp 65 stone south of the valley.) Middle division: Bone Spring Limestone: 10. Limestone, dolomitic, white or light-gray; 1. Limestone, black to dark-gray, weathers drab forms a slope_ ___ 15 gray; fine grained; in 3- to 6-in. beds; in 9. Limestone, dolomitic, dark-gray; forms a part with brown chert bands, and with marl massive ledge _ 5 partings. Some beds contain silicified fos­ 8. Limestone, dolomitic, white or light-gray; sils. In 1936 were collected the brachiopods forms a slope__ ___ 10 Chonetes sp., Avonia sp., Busetonial cf. B. 7. Limestone, dark-gray; forms a massive (Kochiproductus) sp., and the gastropod ledge______3 Anomphalus"! sp. (USGS 8538; field label 6. Limestone, dolomitic, white or light-gray; Pb5). Thickness about______500 forms a slope; slender fusulinids ob­ Base of section covered by alluvium. served______38 Summary of section 43 5. Limestone, dolomitic, dark-gray; con­ Part of Goat Seep Limestone exposed______200 tains calcite vugs; forms a prominent Sandstone tongue of Cherry Canyon Formation___ 155-190 ledge ______3 Cutoff Shale______275 STRATIGRAPHIC SECTIONS OF PERMIAN ROCKS 169 Summary of section 43 Continued Mesa, beyond the map area. (See King, P. B., 1949.) Victorio Peak Limestone: Feet Collections were made in these outliers by R. E. King Upper division (in section 43b)______65 in 1928, and by J. Brookes Knight in 1936. Brachio­ Middle division (in section 43b)______119 pods in the 1928 collections were identified by R. E. Lower division (approx., in section 43a) __ 822 King (1931); fusulinids and other foraminifers in the Total Victorio Peak Limestone- 1,006 1936 collections were identified by L. G. Henbest, and Part of Bone Spring Limestone exposed. 500 larger fossils by P. E. Cloud, Jr., and E. L. Yochelson (written commun., 1955,1954). FOSSIL COLLECTIONS FROM VICTORIO PEAK STONE SOUTHEAST OF SOUTH MESA REK 504, D & S 139. Goat Seep Limestone at east end of North Mesa (north of present map area, western part of sec. Southeast of South Mesa, foothills fringing the 40, Block 67, Twp. 3). Includes unidentified fusulinids and northeast-facing escarpment of the Sierra Diablo con­ the brachiopods Enteletes wordensis King, Meekella skenoides sist of Victorio Peak Limestone that has been down- Girty, Linoproductus waagenianus (Girty), Avonia signata faulted and tilted. Collections were made from it by (Girty), Marginifera opima (Girty), Aulosteges guadalupensis R. E. King in 1928, and by J. Brookes Knight in 1936. Shumard, A. tuberculatus King, Lyttonia nobilis americanus (Girty), Camarophoria venusta Girty, Spirifer (Neospirifer) Brachiopods in the first collections were identified by pseudocameratus Girty, Hustedia meekana (Shumard), and R. E. King (1931). Fusulinids and other foraminifers Composita emarginata afflnis Girty. in the second were identified by L. G. Henbest, and USGS 8549 (field label Pd 2). Goat Seep Limestone, near larger fossils by P. E. Cloud, Jr., and E. L. Yochelson base. Same locality as REK 504. Contains a polyporoid bryo- (written commun., 1955,1954). zoan and the brachiopods Linoproductus'} sp., Marginifera aff. USGS 8536 (field label PI 3). Victorio Peak Limestone. M. lasallensis? (Meek and Worthen), if.? sp., "Pustula" sp., Hogback ridge at foot of Sierra Diablo escarpment, 3 miles Dictyoclostus (Chaoiella) cf. D. guadalupensis (Girty), Steno- southeast of South Mesa, southwest side near west end (north­ cisma sp., Composita sp., and Wellerella sp.; fusulinids observed eastern part of sec. 5 Block 31). Contains the brachiopods in field, but not reported on. Meekella sp., ProricMofenia sp., Buxtonial cf. (Kochiproductus) F 2697 (field label Pd 3). Goat Seep Limestone, from float sp., and "Spirifer" sp. near Dos Alamos Hills (sec. 17, Block 67, Twp. 3). A porous USGS 8537, F 2709 (field label Pb 4). Victorio Peak Lime­ coquina, crowded with large very slender fusulinids that are stone. Near foot of northeast slope of hogback ridge, about probably Parafusulina maleyl var. referta Dunbar and Skinner. half a mile east of its western end (northeastern part of sec. 4, Block 31). Contains the fusulinids and other foraminifers SECTION 44. HIGH POINT OF DELAWARE MOUNTAINS Geinitzinal sp., Pseudofusulina setum (Dunbar and Skinner) and Pseudofusulina or Parafusulina sp.; the brachiopods The following is a section of the Bone Spring Lime­ Chonetes sp., Buxtonia (Kochiproductus) ? sp., "Marginifera" stone and Brushy Canyon Formation on a promontory sp., Avonia small sp., Enteletest sp. and Rhipidomella sp.; the of Delaware Mountains near the northeast corner of pelecypod lAstartella sp.; Meekospira sp. and other gastropods; the map area. The section begins at the fault at the and the scaphopod Plagioglypta sp. west base of the mountains, on a salient 3 miles north- USGS 8541 (field label Pb 10). Victorio Peak Limestone, float on alluvial fan below and north of locality Pb. 4. Contains northwest of Cone triangulation station, and proceeds Buxtonia (Kochiproductus) cf. B. victorioensis King. eastward to the summit of a mesalike outlier at the crest REK 494- Victorio Peak Limestone, at approximately the (center of sec. 4 to center of sec. 3, Block 65, Twp. 4). same locality as Pb 4. Contains the brachiopods Productus The section was measured by R. E. King in 1928; fusu­ schucherti King, Marginifera manzanica Girty, M. reticulata linids were identified by C. O. Dunbar and J. W. Skin­ angusta King, Martinia rhomboidalis Girty, and Composita subtilita (Hall). ner (1937), and brachiopods by R. E. King (1931). REK 495. Victorio Peak Limestone at east end of hogback This section is the same as section 49 of King (1948, pi. ridge, about half a mile east of locality Pb 4 and REK 494 8). (northwestern part of sec. 3, Block 31). Contains the brachio­ Summit of outlier; no higher beds exposed. pods Chonetes permianus Shumard and Productus ivesi New- Brushy Canyon Formation: berry. Main body of formation: feet USGS 8547 (field label Pb 17). -Victorio Peak Limestone. 13. Sandstone, coarse, light-buff; in thick beds, Ridge of downfaulted rocks 1% miles northwest of portal of interbedded with thinner bedded finer Apache Canyon, and about 4 miles southeast of preceding lo­ grained sandstone; some bedding surfaces calities (southeast part of sec. 43, Block 66, Twp. 4). Contains show molds of large parafusulinids__ 205 Enteletes cf. E. dumblei Girty. Pipeline shale member: 12. Shale, sandy, dark-gray, thinly laminated_ 33 FOSSIL COLLECTIONS FROM GOAT SEEP LIMESTONE Conformity (?). NORTH OF SOUTH MESA Bone Spring Limestone: 11. Limestone, black, dense; in 2- to 6-in. beds; The Goat Seep Limestone is preserved in a series of forms a prominent cliff. A few poorly pre­ mesalike outliers for about 10 miles north of South served fossils observed______264 170 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS Bone Spring Limestone Continued Feet other geologists and are described in their publications. 10. Shale, sandy, thinly laminated, gray; weathers The locations of these four sections are as follows: yellow brown. The shale contains concretions of black granular limestone a foot or two broad (A) Devil Ridge above Devil Ridge thrust. Section of Yucca and a foot thick, also some interbedded 3- to Formation, Bluff Mesa Formation, Cox Sandstone, and Finlay 6-in. layers of black limestone______82 Limestone, measured by J. Fred Smith, Jr. (1940, p. 625-628, 9. Limestone, black, dense, thinly laminated; sec. 3). Measured south westward across Front Ridge and forms a cliff; contains spherical concretions Devil Ridge at a locality about Sy2 miles west of the edge of 3-in. to 1-ft across______115 the present report area and 5 miles south of town of Sierra 8. Limestone, black, dense; sandy in part; thin- Blanca, in northwestern part of Block 69%. bedded to papery ______126 (B) Southwest of Eagle Flat below Devil Ridge thrust. 7. Limestone, black, sandy; in 8-in. to 1-ft beds_ 18 Section of Washita Group measured by J. Fred Smith, Jr. 6. Limestone, black, unevenly bedded; contains (1940, p. 628-629, sec. 5). Measured south westward across low irregular masses of chert and siliceous lime­ ridges south of Bola siding, in southwestern part of present stone. Some beds very fossiliferous_____ 93 report area, in sec. 46, Block 69, Twp. 8, and sec. 3, Block 69, 5. Limestone, black; very thinly and evenly Twp. 9. A section of the overlying Eagle Ford Formation is bedded, with a few thicker bedded fossilif­ given in the original publication, but is not plotted on plate 13. erous layers. Forms a well-defined ledge. (C) Spar Valley, below Devil Ridge thrust. Section of Yucca Contains the fusulinid Parafusulina sp., and Formation, Bluff Mesa Formation, Cox Sandstone, Finlay Lime­ the brachiopods Meekella attenuata Girty, stone, and Washita Group, measured by Elliot Gillerman (1953, Productus leonardensis King, Productus occi- p. 19-29, sees. 2, 4, 5, and 6). As plotted on plate 13, the sec­ dentalis Newberry, Productus sp., Striatifera tion combines various partial sections measured in the vicinity pinnaformis (Girty), Prorichthofenia likha- of Spar Valley on the east side of the Eagle Mountains about rewi King, Pugnoides bidentatus (Girty), 5 miles south of southern edge of present report area. To com­ Pugnoides texanusl (Shumard), Spirifer plete the sequence, the basal Cretaceous beds exposed near Eagle (Neospirifer) mexicanus latus King, Amboco­ Spring just south of the present report area have been plotted elia guadalupensis Girty, and Hustedia meek- from descriptions by Gillerman. ana (Shumard) (REK 491 D & S 153)____ 77 (D) Flat Mesa, north of Sierra Blanca. Section of Cox Sand­ 4. Limestone, black, platy or papery; with some stone, Finlay Limestone, Kiamichi Formation, and basal part layers of granular chert______132 of Washita Group, described by W.S. Adkins (1932, p. 352) and 3. Limestone, black; in 1- to 6-in. beds; contains measured by P. B. King (unpub. field notes, 1930). Measured many thick chert layers and granular siliceous across north end of Flat Mesa about 6 miles north-northwest of layers ______72 town of Sierra Blanca, near the center of the east line of Block 2. Limestone, black; in beds half an inch to 5 in. 71, Twp. 7. thick, but somewhat irregularly bedded, with interbedded chert layers as much as 3 in. SECTION 45. EAGUS F!LAT thick, and lenses of fossil breccia that contain whole shells of brachiopods. These include The following is a section of parts of the Campa- Meekella attenuata Girty, Chonetes permi- grande Limestone and Cox Sandstone on a mesa 1% anus Shumard, lAnoproductus waagenianus miles east of Eagle Flat section house (sec. 8, Block 68 (Girty), and Ambocoelia guadalupensis Girty Twp. 8). The section was measured by P. B. King and (REK 490)______258 1. Limestone, black; in even beds half an inch to J. Brookes Knight in 1931. Fossils were observed in an inch thick, with a few chert bands_____ 308 the field, and a few were collected in 1938, which proved Base of section at fault at foot of escarpment; no lower to be unidentifiable. beds exposed. Summary of section 44 Top of mesa ; no higher beds preserved. Cox Sandstone : Feet Brushy Canyon Formation: 5. Sandstone, massive, sugary, light-brown: forms Part of main body of formation exposed___ 205 remnant on top of mesa at west end 25 Pipeline Shale Member______33 Campagrande Limestone : 4. Limestone, marly; contains Exogyra and Tri~ Part of Brushy Canyon Formation exposed__ 238 10 Part of Bone Spring Limestone exposed______1,545 3. Nodosaria bed." Limestone, massive, sandy, STRATIGRAPHIC SECTIONS AND FOSSIL COLLECTIONS dark-gray, evenly bedded. Shells of the me­ OF CRETACEOUS ROCKS dium-sized foraminifer Haplostiche ("Nodo­ saria") occur on weathered surfaces, and many Sections 45-54, which follow, were measured in the unidentifiable shells appear in cross section, southern and western parts of the Sierra Diablo dur­ probably mainly oysters (USGS 17828; field ing the present investigation. Some of these are label K 10) ______25 2. Limestone, nodular, light-gray; interbedded with plotted graphically on plate 13 where, to complete the marl; in part conglomeratic 30 stratigraphic picture, four other sections to the south 1. "Cap ledge." Limestone, massive, light-gray; at and west have been included; these were measured by base of slope _ 10 STRATIGRAPHIC SECTIONS OF CRETACEOUS ROCKS 171 Base of section covered by alluvium. Cox Sandstone Continued Feet Summary of section 45 33. Sandstone, massive, brown; crossbedded in part; Feet forms ledges, with a 10-ft bed of marly lime­ Part of Cox Sandstone exposed ______25 stone in lower part 82 Part of Campagrande Limestone exposed- 75 32. Sandstone, friable; forms a slope____ 15 SECTION 46. STREERTTWITZ 31. Sandstone, massive, brown; with many pebbly seams; forms prominent ledges 19 The following is a section of part of the Campa­ 30. On west slope of Dome Peak; red sandy shale grande Limestone in the Streeruwitz Hills, 4^/2 miles interbedded with gray marly limestone; on northwest of Eagle Flat section house (northwestern south slope; represented by a 4-ft layer of con­ part of sec. 22, Block 57). The section was meas­ glomerate, formed of limestone fragments 25 ured by J. Brookes Knight in 1931. The top unit of 29. Sandstone, white or buff, pebbly; forms a slope; contains small pebbles and ferruginous this section appears to be the basal unit of section 45, nodules __ 21 and the two sections combined give an approximate total 28. Sandstone, friable, crossbedded, white 16 thickness of the Campagrande Limestone in the district 27. Sandstone, massive, brown 5 of 205 ft; however, units of the lower part of the Campa­ 26. Sandstone, friable; forms a slope 8 grande in nearby sections in the Streeruwitz Hills are 25. Sandstone, massive, brown; with pebbly seams; much thinner than in section 46, due to overlap on an passes at top into a conglomerate of chert and eroded topography of Hueco Limestone and Precamb- quartz pebbles 5 rian rocks. 24. Sandstone, friable; forms a slope- 6 23. Sandstone, massive, brown- ____ 22 Top of section; no higher beds preserved. 22. Sandstone, shaly, red; with thin beds of coarser Campagrande Limestone: Feet sandstone; forms a succession of benches and 3. "Cap ledge." Limestone, massive, dark- to light- slopes ______40 gray ; nodular in upper part; contains chert peb­ 21. Sandstone, slabby or shaly, white or red; forms bles in lower 4 ft______55 slopes, with several ledges of massive brown 2. Conglomerate, mainly limestone pebbles, but in­ pebbly sandstone in upper part 25 cludes some chert pebbles, in a limestone matrix 20. Sandstone, massive, brown, pebbly 10 that is red below, grayer above______80 1. Conglomerate, red; contains pebbles and cobbles 19. Sandstone, marly, red; forms a slope- 8 of limestone and chert from Allamoore Forma­ 18. Sandstone, massive sugary brown; contains well- tion ______rounded chert and quartz pebbles; in part Unconformity. crossbedded. Small spherical limonite nodules Hueco Limestone at base of section. occur on weathered surfaces. Forms promi­ nent ledge, which breaks out into cubical Summary of section 46 blocks ______18 Part of Campagrande Limestone exposed______140 17. Marl and shale, poorly consolidated, gray or SECTION 47. DOME PEAK purple; at top, a conglomerate of rounded chert pebbles in a yellow marl matrix. In most The following is a section of the Campagrande Lime­ places, poorly exposed on slope and covered by stone and Cox Sandstone on Dome Peak (summit 5485). blocks from bed above______100 The section was measured by P. B. King and J. Brookes 16. Limestone, marly, gray; interbedded with purple Knight in 1931. The Campagrande Limestone was shale ______43 measured a mile south of the peak on the west side of 15. Marl, gray; forms a slope, with a 2-ft ledge of the ridge, southwest from the road from Sierra Blanca gray limestone at top_ _ 12 14. Sandstone, brown, shaly; with a 2-ft ledge of red to the Keen Ranch (east-central part of sec. 28, Block limestone at top______12 51). Two sections of the Cox Sandstone were meas­ 13. Sandstone, thin-bedded, slabby; with small-scale ured, one on the west slope (northeastern part of sec. crossbedding ______10 21, Block 51), the other on the south slope (west half of 12. Sandstone, massive, sugary, brown; crossbedded sec. 22, Block 51); descriptions of units in the two sec­ in part-______16 tions have been combined in the text, and thicknesses Campagrande Limestone: 11. Marl, sandy; forms a slope______5 averaged. No fossils were collected, but they were ob­ 10. Limestone rusty-brown; in 2-ft beds______7 served in parts of the Campagrande Limestone. 9. Marl, nodular, blue-gray to brown______5 Top of Dome Peak; no higher beds preserved. 8. Limestone, light-gray to gray-brown; with marl Cox Sandstone: Feet partings ______9 37. Sandstone, massive, brown______8 7. Marl and thin layers of nodular limestone____ 16 36. Sandstone, shaly, buff______12 6. Limestone, dark blue-gray; contains oysters and 35. Sandstone, massive, sugary, crossbedded; forms rudistids in upper part______6 rimrock at top of Dome Peak______36 5. Shale and marl with beds of brown dense nodu­ 34. Sandstone, friable; forms a slope______25 lar limestone______16 172 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS

Campagrande Limestone Continued Feet Campagrande Limestone Continued Feet 4. "Nodosaria bed." Limestone, dark-gray or gray- 2. Shale, reddish, sandy, poorly exposed 18 brown, sandy; in 1- to 2-f t beds; contains frag­ 1. Conglomerate, formed of pebbles as much as an ments of oysters and echinoids 16 inch in diameter of quartz, chert, and limestone, 3. Marl, nodular limestone, and conglomerate 22 in a coarse sandstone matrix, with thin beds of 2. "Cap ledge." Limestone, massive, nodular light- calcareous sandstone at top 6 gray ; contains chert pebbles at base 8 Unconformity. I. Conglomerate, composed of pebbles of Hueco Hueco Limestone at base of section. Limestone, in a sandy or marly limestone Summary of section 48 matrix ______9 Part of Cox Sandstone exposed- 411 Unconformity. Total Campagrande Limestone 63 Hueco Limestone at base of section; about a mile to the SECTION 49. COX MOUNTAIN southeast the Hueco is truncated and the Campagrande Limestone lies directly on red sandstone of the Hazel The following is a section of the Campagrande Lime­ Formation. stone, Cox Sandstone, Finlay Limestone, and Kiamichi Summary of section 47 Formation on Cox Mountain (sees. 19 and 20, Block Part of Cox Sandstone exposed______599 Total Campagrande Limestone______119 45%. The Cox Sandstone was measured on the north face of the mountain, west of a prominent reentrant, SECTION 48. HOCK CRUSHER the Finlay and Kiamichi at various favorable places The following is a section of the Campagrande Lime­ on the summit of the mountain. The whole section was stone and Cox Sandstone on the north slope of the high originally measured by P. B. King and R. E. King in knob northeast of the Gifford-Hill rock crusher, on the 1928; the Finlay and Kiamichi were measured again opposite side of the Texas and Pacific Railway (summit in more detail by J. Brookes Knight in 1938; the text 5188; north half of sec. 26, Block 67, Twp. 8). The given below contains data from both sections. Fossils section was measured by P. B. King in 1936, but the from the Kiamichi Formation that were collected in 1938 were identified by R. W. Imlay (written commun., sequence here had been described previously by Rich­ 1940), and his determinations are given in the text. ardson (1914, p. 6). No fossils were recorded by King, Fossils collected in 1928 were examined by W. S. Ad- but Richardson observed gastropods, oysters, and an kins (1932, p. 353), who reported virtually the same Exogyra in the Campagrande Limestone. assemblage, which he regarded as of Kiamichi age Top of knob 5188; no higher beds preserved. (see table 11, p. 87). Cox Sandstone: Feet Tertiary: Feet 13. Sandstone, massive, pebbly, crossbedded_____ 10 18. Basalt, vesicular; forms three remnants on top of 12. Sandstone, fine-grained, thin-bedded; forms a mountain; at base, a conglomerate of limestone slope______65 cobbles a few feet thick, partly derived from II. Sandstone, massive, crossbedded; very pebbly Cretaceous rocks, partly from earlier rocks 30 at top______70 Unconformity. 10. Sandstone, fine-grained, thin-bedded, poorly ex­ Kiamichi Formation: posed; with a massive sandstone ledge 15 ft 17. Shale, brown, sandy. Contains Oxytropidoceras above base ______59 acuticarinatum (Shumard), O. Iravoense 9. Sandstone, massive, brown, coarse-grained; in Bose, Natica! sp., Trigonia emoryi Conrad, 2- to 10-ft beds, which form prominent ledges Exogyra texana Roemer, GrypJiaea navia Hall, and break out in rectangular blocks. Contains G. cf. O. corrugata Gabb, Pecten (Neithea) dispersed quartz and chert pebbles in places, subalpinus Bose, and Protocardia texana (Con­ and some layers are crossbedded. Weathered rad) (USGS 17838, 17280; field labels K 3 G, surfaces are dark-brown and quartzitic____ 95 K 2) ; horn corals and colonial corals observed. 8. Sandstone, fine-grained, thin-bedded, shaly, gray According to Imlay, correlation with the Kia­ or red. Upper part poorly exposed and much michi is signified by the Gryphaea navia; the covered by float from above. A bed of massive species of Oxytropidoceras range through beds sandstone may occur near middle, but it is rep­ of late Fredericksburg age 15 resented only by loose blocks that might have 16. Sandstone, brown; forms a ledge 3 slumped from above______112 15. Marl, yellowish, sandy. A collection from this Campagrande Limestone: unit, and unit 13 below, contains Oxytropido­ 7. Limestone, buff, dense; with conchoidal fracture; ceras cf. 0. supani (Lasswitz), Nerineal sp., Ty- forms a prominent ledge______4 lostoma sp., Natica"! sp., Pecten (Neithea) sp., 6. Shale, reddish, poorly exposed______17 Exogyra texana Roemer, and Enallaster teas- 5. Limestone, gray, granular; contains limestone anus (Roemer) (USGS 17857; field label K 2 pebbles______j EF). According to Imlay, occurrence of an 4. Shale, reddish, poorly exposed______13 ammonite like Oxytropidoceras supani indicates 3. Limestone, brown, sandy and pebbly; forms a a late Fredericksburg age, but not necessarily ledge ______4 a Kiamichi age 8 STRATIGRAPHIC SECTIONS OF CRETACEOUS ROCKS 173

Kiamichi Formation Continued Feet Cox Sandstone: Feet 14. Sandstone, yellow; contains oysters 2 7. Sandstone, medium-grained, crossbedded, bluff; 13. Limestone, blue-gray, marly; contains abundant contains small limonite nodules___ 20 fossils, such as Pecten, Exogyra, oysters, and 6. Shale, sandy, buff and purple_____ 15 Turritella'i ______15 5. Sandstone, coarse-grained, massive 20 12. Marl and limestone, forming a slope, containing 4. Sanstone, buff, shaly______13 Lunatial sp. (USGA 17836; field label KID) 15 3. Sandstone, medium- to coarse-grained, pink; 11. Limestone, brown; forms a prominent ledge; weathers purple in places, in others to a brown cross sectiions of shells are visible, possibly crust. Texture uneven, in part contains seams rudistids _ -______5 of well-rounded chert and quartz pebbles as much as an inch in diameter, in part cross- 10. Limestone, marly; forms a slope 6 bedded______20 Finlay Limestone: Campagrande Limestone: 9. Limestone, massive, gray; forms 1- to 3-ft ledges ; 2. Limestone, massive, lumpy and nodular, light- contains obscure rudistids, chamids, and other gray ; weathers pale brown and forms a promi­ fossils. This, and lower beds of the formation nent ledge. In places weathered surface con­ are reported to contain the chamid Toucasia sp., tains irregular limonite veinlets 19 and the other mollusks Protocardia filosa Conrad 1. Limestone, sandy and marly, white or buff; with and Tylostoma sp., (DeFord and Brand, 1958, some harder reddish dolomitic layers and a few fig. 11, p. 23)______10 beds of sandstone _ _ 40 8. Marl, forming a slope______5 Unconformity. 7. Limestone, gray; forms a ledge______2 Hueco Limestone at base of section. 6. Limestone, gray, nodular, marly, sandy in part; Summary of section 50 contains gastropod steinkerns, oysters, and many Part of Cox Sandstone exposed 88 other poorly preserved fossils______28 Total Campagrande Limestone- 59 5. Sandstone, yellow-brown, ripple-marked______3 4. Limestone, gray, marly______..______8 SECTION 51. ROBERTS MESA Cox Sandstone: The following is a section of the Finlay Limestone 3. Sandstone and clay, poorly exposed______16 at the east end of Roberts Mesa (east-central part of 2. Sandstone, coarse, yellow-brown; weathers brown; in 5-ft beds that break out into great cubical Sec. 10, Block 39). The section was measured in 1936 blocks. Many layers are crossbedded on a large by J. Brookes Knight. Fossils were identified by K. W. scale, and some bedding surfaces are ripple Imlay (written cominun., 1940). marked. Some layers are conglomeratic, con­ taining quartz 'and chert pebbles as much as 1% Top of mesa ; no higher beds preserved. in. across. Weathered surfaces are dotted with Finlay Limestone: Feet ferruginous pellets. Some purplish shaly sand­ 1. Limestone, marly; contains rudistids_ _ 10 stone is interbedded, but is mostly obscured by 6. Limestone, massive; contains rudistids; forms a float from the more massive layers. About 10 ft ledge at rim of mesa 3 of nodular limestone, with 15 ft of shale beneath 5. Marl, sandy_ ___ 12 is reported 225 ft below the top (DeFord and 4. Sandstone, massive, coarse-grained, crossbedded, Brand, 19561, p. 23, fig. 11), but was not recorded ripple-marked; contains silicified wood. (This in 1928______390 unit is separately shown on geologic map.) 8 Campagrande Limestone: 3. Marl, light-gray, fossiliferous. Contains Natical 1. Limestone, thin-bedded, conglomeratic, white; with cf. N.l pedarnates Roemer, Tylostoma sp., yellow and pink mottling; passes into a more Exogyra texana Roemer, Lima sp., Protocardia massive ledge at top______20 cf. P. texana (Conrad), and Homomya sp. Unconformity. (USGS 17844; field label K 9). According to Hueco Limestone at base of section. Imlay, these fossils are probably of Fredericks- Summary of section 49 burg age 20 Part of Kiamichi Formation exposed______69 2. Shale, sandy, with a 2-ft bed of yellow fine-grained Total Finlay Limestone______56 sandstone at top 15 Total Cox Sandstone______406 1. Limestone, containing abundant poorly preserved Total Campagrande Limestone______20 oyster shells, including Ostrea cf. O. crenuli- margo Roemer (USGS 17843; field label K 8) 3 SECTION 50. BLACK KNOBS Base of section covered by alluvium. Summary of section 51 The following is a section of the Campagrande Part of Finlay Limestone exposed ______71 Limestone and Cox Sandstone on Black Knobs, 5!/£ miles east of Cox Mountain (summit 5480, west-central SECTION 52. NORTON MESA part of sec. 15, Block 44). The section was measured The following is a section of the Finlay Limestone by P. B. King and K. E. King in 1928. on the northeast side of Norton Mesa (southeastern part Top of knobs; no higher beds preserved. of sec. 16, Block 34). The section was measured by 174 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS P. B. King in 1936, and fossils were collected in 1938, Finlay Limestone. From strata 54-82 ft below Kiamichi (?) Formation. Northeastern part of Triple Hill quadrangle, west which have been identified by R. W. Imlay (written of Norton Mesa (Block 35). Collected by J. F. Smith, Jr., and commun., 1940). identified by R. W. Imlay (written commun., 1950). Contains Top of Mesa; no higher beds preserved. Exogyra texana Roemer, Trigonia sp., Protocardia texana Finlay Limestone: Feet Conrad, P. multisriata Shumard P, sp., Cardium! cf. C.! sub- 12. Sandstone, brown, platy 1 congestum Bose, Cypremeria sp., Pecten (Neithea) occidentalis 11. Marl ______2 Conrad, Brachydontes sp., Modiolus concentrice-costellatus 10. Limestone, gray; contains rudistids; forms rim (Roemer), Sphaera cf. S. roblesi (Bose), Tapes! sp., Neritina! of mesa_ _ 3 cf. N.! elpasensis Stanton Tylostoma sp., Gyrodes! sp., Apor- 9. Marl, and nodular limestone, containing Exogyra rhais! sp., Monodonta! sp., Cerithium! cf. C.! pecosense Stan­ cf. E. texana Roemer, Pecten (Neithea) cf. P. ton, and Turritella seriatim-granulata Roemer. occidentalis Conrad, and Natica! sp. (USGS Kiamichi ( ?) Formation. From 34-ft unit of sandstone over­ 17281; field label K 2)______15 lying top limestone layer of Finlay Limestone. Northeastern 8. Sandstone, medium-grained, brown, partly lami­ part of Triple Hill quadrangle, west of Norton Mesa (Block nated, partly crossbedded; forms a prominent 35). Collected by J. F. Smith, Jr., and identified by R. W. ledge on slope of mesa. (This unit is sepa­ Imlay (written commun., 1948). Contains Turritella seratim- rately shown on geologic map.)______5 granulata Roemer, Cerithium! sp., Ostrea sp., Pecten (Neithea) 7. Marl, sandy______15 sp., Pecten (Syncyclonema) sp., Nucula sp., Nuculana! sp., 6. Sandstone, medium-grained, brown; forms a Cardium cf. C. congestum Conrad, C.! sp., Trigonia emoryi ledge______4 Conrad, Protocardia sp., and Engonoceras cf. E. peirdenale 5. Marl, sandy, buff; contains limestone lumps and (VonBuch). interbedded layers of sandstone and nodular limestone. At west end of mesa contains An- SECTION 63. EASTERN SIERRA PREETA chura! sp., Natica! cf. N. incisa Giebel, Ampul- The following is a section of the Campagrande Lime­ Una! sp., Cardita sp., Protocardia cf. P. texana (Conrad), Homomya! cf. H.t alta Roemer, stone, Cox Sandstone, and Washita Group on the east Exogyra texana Roemer, and Enallaster cf. E. slope of the southeast prong of Sierra Prieta about due texanus (Roemer) (USGS 17900; field label K east of Black triangulation station (west-central part 12). According to Imlay, these fossils are prob­ of sec. 21, Block 68, Twp. 4). A section was measured ably of Fredericksburg age______19 here by P. B. King and R. E. King in 1928, and again 4. Sandstone, calcareous, buff; forms a ledge____ 1 3. Marl, soft, sandy, buff ______10 in more detail by J. Brookes Knight in 1938; the section 2. Sandstone, fine-grained, brown; forms a ledge given here is that by Knight. Fossils collected by Oryphaea and Alectryonia observed______4 Knight were identified by R. W. Imlay (written 1. Marl ______3 commun., 1940). Base of section covered by alluvium. Summary of section 52 Sill of igneous rock at top of mountain. Part of Finlay Limestone exposed______82 Intrusive contact Washita Group: Feet COLUECTIONS FROM FINIiAY UEMESTONE AND KIAMI- 38. Sandstone, marly, pink______8 CHI FORMATION WEST OF ROBERTS MESA AND 37. Marl, gray; partly covered by float of igneous NORTON MESA rock. Contains Cardita sp., Cyprimeria sp., The following three collections amplify the faunas Pecten (Neithea) sp., Alectryonia qtiadriplicata of the Finlay and Kiamichi Formations. They were (Shumard), A. cf. A. subovata Shumard, Gry- phaea washitaensis Hill, Kingena! sp., Nau­ collected in the plateau country west of Roberts and tilus! sp., Enallaster bravoensis BSse, and Norton Mesas, in the Triple Hill quadrangle a short Hemiaster n. sp. (USGS 17914; field label K 14 distance beyond the west edge of the report area. The K). According to Imlay, these fossils do not first was collected during the present investigation, the afford a definite correlation, but the presence second and third during the investigation of C. C. of Alectryonia quadriplicata suggests an age not younger than lower Mainstreet______65 Albritton, Jr., and J. F. Smith, Jr., (1965); all were 36. Sandstone, brown______2 identified by R. W. Imlay. 35. Marl, yellow; mostly covered by float of igneous Finlay Limestone (USGS 17899, field label K 11.) Fossilif- rock. Contains many Gryphaea washitaensis erous marl underlying capping 6-ft limestone ledge. Three Hill (USGS 17913; field label K 14 J)_____ 22 miles southwest of Roberts Ranch and half a mile west of 34. Covered by float of igneous rock; some inter­ road to Sierra Blanca (sec. 19, Block 38). -Collected by P. B. mingled float of brown shale______10 King and J. Brookes Knight in 1938 and identified by R. W. 33. Marl, pink; mostly covered by float of igneous Imlay (written commun., 1940). Contains Anchura! sp., rock. Contains Kingena! sp. (USGS 17912; Tylostoma sp., Nerita sp., Exogyra texana Roemer, Protocardia field label K 14) ______10 texana (Conrad) Lima! sp., and Enallaster cf. bravoensis BSse. 32. Limestone, marly; packed with shells of Gryphaea According to Imlay, these fossils are probably of Fredericks- washitaensis Hill and Pecten (Neithea) tex­ burg age. anus Roemer (U SG S17911; field label K14 H) _ 15 STRATIGRAPHIC SECTIONS OF CRETACEOUS ROCKS 175

Washita Group Continued Feet Washita Group Continued Feet 31. Marl, with a profusion of shells. Contains An- Idiohamites cf. /. fremonti Marcous, /. cf. /. chura'i sp., Tylostomal sp., Turritella sp., Lima comanchensis (Adkins and Winton), Anchura wacoensis (Roemer), Pecten (Neithea) subal- sp., Cercomya sp., Pholadomya cf. P. shattucki pinus Bose, Gryphaea washitaensis Hill, Enal- Bose, Eomomya cf. E. ligeriensis (d'Orbigny), laster cf. E. texanus (Roemer), Tetragramma Trigonia sp., Inoceramus cf. I. comancheamts cf. T. taffl (Cragin), and Pseudopyrina clarki Cragin, Lima leonensis Conrad, L. sp., Pinna (Bose) (USGS 17910; field label K 14 G). sp., Ostrea sp., Alectryonia aff. A. carinata According to Imlay, correlation with Fort (Lamarck), Pecten (Neithea) subalpinus Bose, Worth or Denton is indicated by Pseudopyrina Tapes'! cf. T. chilhuahuensis Bose, Kingenal clarki ______27 cf. K.I leonensis (Conrad), Enallaster texanus 30. Marl; white; with numerous fossils. Contains (Roemer), Pliotoxaster whitei (Clark), Pseu­ Pecten (Neithea) subalpina Bose, Pholadomya dopyrina parryi (Hall), Dumbleal sp., and cf. P. sanctisabae Roemer, Gryphaea washitaen- Phymosa cf. P. mexicana Bose (USGS 17904; sis Hill, Cyprimeria cf. C. crassa Meek, C, cf. C. field label K 14 B). According to Imlay, cor­ texana (Roemer), C. sp., Alectryonia aff. A. relation with the Duck Creek is shown by carinata (Larmarck), Pinna sp., Lima wacoen­ Eopachydiscus brazoense, Idiohamites cf. fre­ sis (Roemer), L. sp., Cercomya sp., Isocardita monti, I. cf. 7. comanchensis, and Inoceramus cf. I. medialis (Conrad), Tapes ? cf. T.I vibray- comancheanus ______30 eana d'OrMgny, Enallaster texanus (Bose), Cox Sandstone: Phymosoma cf. P. texanum (Roemer), Pseudo­ 20. Sandstone, platy, mottled purple, red and white; pyrina cf. P. inaudita (Bose), Dumblea sym- bedding surfaces show sun cracks and fucoidal metrica Cragin, Holaster simplex Shumard, markings______..______10 Holectypus limitus Bose, Engonoceras sp., Mor- 19. Sandstone, fine-grained, massive, crossbedded, toniceras wintoni (Adkins), Prohysteroceras"! light buff; weathers lumpy. Contains a silici- sp., Cymatoceras texanum (Shumard), Tylos- fied log______36 toma cf. harrisi Whitney, Tylostoma sp., and 18. Sandstone, coarse-grained, very massive, cross- Amauropsisl sp. (USGS 17909; field label K 14 bedded, light-brown 10 F). According to Imlay, a correlation with the 17. Sandstone, friable, ocherous 18 Denton or Weno is indicated. Pervinqueria 16. Sandstone, very massive, crossbedded, light- wintoni lias been recorded from the Weno and brown 8 Pawpaw, Dumblea symmetrica ranges as high 15. Sandstone, friable, yellow; mostly covered by as the Weno; Holectypus limitus has been re­ float from unit above- 15 corded from Fort Worth to Mainstreet; Pseudo­ 14. Sandstone, slabby, brown _ 2 pyrina inaudita is known from Fort Worth to 13. Sandstone, friable, marly, yellow; with a thicker Denton ______25 ledge near base_ 15 29. Limestone, containing Gryphaea; forms a ledge_ 1 12. Sandstone, yellow; contains nodules of possible 28. Marl, gray. Contains abundant Gryphaea corru- algal origin 15 gata Say and G. aff. G. washitaensis Hill, as Campagrande Limestone: well as Natica sp., Tylostoma cf. T. harrisi 11. Clay, white______2 Whitney, and Turritella sp. (USGS 17906; field 10. Shale, sandy, ocherous; contains unidentifiable label K 14 E2) ______32 oysters and other pelecypods (USGS 17903; 27. Sandstone, red-brown, platy; interbedded with field label K 14 A) ______5 clay and marl toward top. Contains Trigonia 9. Sandstone, argillaceous, chalky, white 2 cf. T. emoryi Conrad, Lima sp., and Gryphaea 8. Clay ocherous 7 corrugata Say var. (USGS 17907; field label 7. Limestone, mottled, yellow; forms a ledge. Con­ K 14 E)______40 tains nodules of posssible algal origin 2 26. Poorly exposed; one outcrop of yellow clay__ 12 6. Marl, ocherous; contains nodules of possible 25. Sandstone, yellow-brown, slabby. Contains Gry­ algal origin _ 5 phaea corrugata Say (USGS 17906; field label K 14 D)______5 5. Marl, white. ___ 5 24. Clay, gypsiferous, yellow______12 4. Limestone, forming a ledge 2 23. Slope, covered by float of igneous rock_____ 25 3. Marl, gravelly, gray- 8 22. Marl, yellow, sandy; much concealed by float of 2. Limestone, gray, lumpy; forms a massive ledge; igneous rock. Contains Pervinqueria cf. P. contains obscure fossils 7 kiliani (Lasewitz), P. sp. indet., Hamitesl sp., 1. Limestone, light-gray to purple; weathers to Pecten (Neithea) sp., and Kingenal sp. (USGS rounded lumps. Contains algal nodules and 17905; field, label K14 C). According to Imlay, poorly preserved gastropod molds 35 a Duck Creek or Fort Worth age is suggested Unconformity. by Pervinqueria cf. P. kiliani______15 Victorio Peak Limestone at base of section. 21. Marl, gray, abundantly fossiliferous. Contains Summary of section 53 Cymatorceras texanum (Shumard), Eopachy- Part of Washita Group exposed______356 discus brazoense (Shumard), E.I sp. juv., Total Cox Sandstone- _ 129 Mortoniceras cf. M. leonensis (Conrad), M. sp., Total Campagrande Limestone 80 176 GEOLOGY OF THE SIERRA DIABLO REGION, TEXAS OTHER FOSSIL COLLECTIONS FROM WASHITA GROUP here has been edited to agree with the styling of the IN EASTERN SIERRA PRIETA other sections of this report, and additional data on The following three collections of fossils were made fossils have been added from notes furnished by Adkins from the Washita Group of the eastern part of the (oral commun., 1930). A section was also measured by Sierra Prieta, and supplement the data given in sec­ P. B. King and E. E. King in 1928 at a locality about tion 53. three-quarters of a mile farther south, but is less USGS 17915 (field label K 15 C). Washita Group, 25 ft complete. above top of Cox Sandstone, a quarter of a mile south of the line Sill of igneous rock at top of mountain. of section 53 (southwestern part of sec. 20, Block 68, Twp. 4). Intrusive contact. Collected by J. B. Knight in 1938 and identified by E. W. Imlay Washita Group: pee^ (written commun., 1940). Contains Eopachydiscus lacvicanic- 14. Limestone, light-gray; largely a shell coquina. ulatum (Roemer), E. brazoense (Shumard), Pervinqueria Contains Macraster sp., echinoid fragments, trinodosa (Bb'se), P. Jciliani (Lasswitz), and P. n. sp. Accord­ Prohysteroceras whitei (Bb'se), and Pervin­ ing to Imlay, a Duck Creek age is indicated by Eopachydiscus queria trinodosa (Bose). The two ammonites brazoense; the listed species of Pervinqueria are recorded from indicate a correlation with Bose's unit 5 of the both the Duck Creek and Fort Worth Formations. Cerro de Muleros section, which may be of Fort USGS 17901 and 18091 (field label K 13). Washita Group, Worth or Denton age______50 first 25 ft of beds above Cox Sandstone, west side of southeast 13. Marl, calcareous, with thin seams of gray nodular prong of Sierra Prieta, southwest of Black triangulation station limestone. Contains Dumblea symmetrica (center of sec. 19, Block 68, Twp. 4). Collected by J. Brookes Cragin, Enallaster bravoensis (Bb'se), Diplo- Knight in 1938, and identified by E. W. Imlay (written com­ podia sp., Phymosa sp., Pyrina sp. (abundant) mun., 1940). Contains Eopachydiscus brasoense (Shumard), Salenia sp., Gryphaea washitaensis Hill, and Cymatoceras texanum (Shumard), (7.? sp., Pervinqueria sp., Pecten n. sp. This distinctive assemblage is P. cf. P. Jciliani (Lasswitz), Montoniceras cf. M. leonensis (Con­ like one at a similar level in the Washita Group rad), Pleurotomaria sp., Alectryonia quadriplicata (Shumard), at Cerro de Muleros, and may be equivalent A. aff. A. carinata (Lamarck), Astartel sp., Gryphaea cf., Cf. to the Denton _ 40 washitaensis Hill, Lima sp., Pholadomya cf. P. shattucJci Bose, 12. Marl, brown, and interbedded flaggy limestone 40 Homomya aff. H. Ligeriensis (d' Orbiguy), Pecten (Neithea) 11. Marl and limestone _ 22 subalpinus Bose, Trigonia sp., Spondylus sp,. Kingena cf., K. leo­ 10. Limestone, yellow-brown, platy 1 nensis (Conrad) K. cf. K. ivacoensis (Eoemer), K. spp., Enal- 9. Marl, yellow-brown; contains Pecten subalpinus Bb'se and Gryphaea sp_ 11 laster texanus (Eoemer), Pliotoxaster whitei (Clark), Holec- 8. Conglomerate, massive; composed of heterogene­ typus sp., Pseudopyrina parryi (Hall), and Phymosoma cf. ous rounded pebbles as much as 5 mm in diam­ P. mexicanum Bb'se. eter, in a calcareous matrix _ _ 1 The first two and the fourth of the ammonites listed above 7. Marl, yellow-brown. Contains Eopachydiscus are of exceptionally large size and are represented only by brazoense (Shumard), Pervinqueria nodosa fragments, some of which are several feet across. (Bose), P. trinodosa (Bb'se), P. spp., Mortoni- According to Imlay, these fossils indicate a Duck Creek or ceros leonensis (Conrad), and Idiohamites spp., Fort Worth age. The large Eopachydiscus indicates a Duck which are typical Duck Creek fossils___ _ 10 Creek age. Ammonites similar to or identical with Pervinqueria Cox Sandstone: kiliani and with Mortoniceras leonensis occur in both the Duck 6. Sandstone, fossiliferous in part______95 Creek and Fort Worth Formations. Phymosoma mexicanum 5. Sandstone, thin-bedded, crossbedded, brown; has been recorded only from the Fort Worth and Denton forms a bluff______26 4. Sandstone, crossbedded, brown; massive above, Formations. nodular below. Top beds contain abundant USGS17902 (field label K13 A). Same locality as preceding, Exogyra texana Eoemer, Alectryonia carinata higher beds of Washita Group. Collected by J. Brookes Knight (Lamarck) (casts and molds), Pecten sp., in 1938 and identified by E. W. Imlay (written commun., 1940). Limal sp., Plagiostomal sp., and gastropods; Contains Pervinqueria, cf. P. trinodosa Bose, Gryphaea washi­ this is a Fredericksburg fauna 40 taensis Hill, Enallaster sp., Macraster sp., and Kingenal sp. 3. Sandstone, crossbedded, nodular, brown. Con­ tains irregular sandy inclusions as much as SECTION 54. WESTERN SIERRA PRIETA a foot long______8 The following is a section of the Campagrande Lime­ 2. Sandstone, massive, yellow 20 Campagrande Limestone: stone, Cox Sandstone, and Washita Group at the west­ 1. Limestone, called Hueco limestone in published ern end of Sierra Prieta ("at northwest corner of Black section, but probably Campagrande; thickness Mountain or Sierra Prieta"), probably below the west­ not stated (?) ern angle of the igneous sill (summit 5110, northwestern Base of section concealed by alluvium. part of sec. 27, block N). The section was measured Summary of section 54 Part of Washita Group exposed- ______175 by J. W. Beede and W. S. Adkins in 1921, and has been Total Cox Sandstone______189 published by Adkins (1932, p. 354). The text given Part of Campagrande Limestone exposed (?) REFERENCES CITED 177

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Osann, C. A., 1893, Report on the rocks of trans-Pecos Texas: Streeruwitz, W. H. von, 1890, Geology of trans-Pecos Texas: Texas Geol. Survey 4th Ann. Kept. (1892), p. 123-141. Texas Geol. Survey, 1st Ann. Rept. (1889), p. 219-235. Plummer, F. B., and Moore, R. O., 1921, Stratigraphy of the 1891, Report on the geology and mineral resources of Pennsylvanian formations of north-central Texas: Texas trans-Pecos Texas: Texas Geol. Survey 2d Ann. Rept. Univ. Bull. 2132,237 p. (1890), p. 665-713. Plummer, F. B., and Scott, Gayle, 1937, Upper Paleozoic am­ 1892, Trans-Pecos Texas: Texas Geol. Survey, 3d Ann. monites in Texas, Pt. 1 in Upper Paleozoic ammonites and Rept. (1891), p. 383-389. fusulinids, v. 3 of The Geology of Texas: Texas Univ. Bull. 1893, Trans-Pecos Texas: Texas Geol. Survey, 4th Ann. 3701, p. 13-516. Rept. (1892), p. 141-175. Pray, L. C., 1958, Stratigraphic section, Montoya group and Fusselman formation, Franklin Mountains, Texas: West Thompson, M. L., 1942, Pennsylvanian system in New Mexico: Texas Geol. Soc. Field Trip Guidebook, 1958, p. 30-42. New Mexico Bur. Mines and Mineral Resources Bull. 17, Ransome, F. L., 1915, The Tertiary orogeny of the North Amer­ 92 p. ican Cordillera and its problems, in Problems of American Twiss, P. C., 1959, Geology of Van Horn Mountains, Texas: geology: New Haven, Conn., Yale Univ. Press, p. 287-376. Texas Univ. Bur. Econ. Geology Geol. Quad. Map 23. Richardson, G. B., 1904, Report of a reconnaissance in trans- Warner, L. A., Holser, W. T.( Wilmarth, V. R., and Cameron, Pecos Texas north of the Texas and Pacific Railway: Texas E. N., 1959, Occurrence of nonpegmatite beryllium in the Univ. Bull. 23 (Mineral Survey Ser. Bull. 9), 119 p. United States: U.S. Geol. Survey Prof. Paper 318, 198 p. 1908, Paleozoic formations in trans-Pecos Texas: Am. Warren, W. C., 1955, Introduction to field trip, in Permian field Jour. Sci., 4th serv., v. 25, p. 474-484. conference, Guadalupe Mountain, October 21-22, 1955: Soc. 1909, Description of the El Paso district: U.S. GeoL Econ. Paleontologists and Mineralogists, Permian Basin Survey Geol. Atlas, Folio 166,11 p. Sec. Guidebook, p. 11-14. 1914, Description of the Van Horn quadrangle: U.S. Geol. Winterer, E. L., and Murphy, M. A., 1960, Silurian reef com­ Survey Geol. Atlas, Folio 194, 9 p. plex and associated facies, central Nevada: Jour. Geology, Scalapino, R. A., 1950, Development of ground water for irri­ v. 68, p. 117-139. gation in the Dell City area, Hudspeth County, Texas: Yochelson, E. L., 1956, Permian Gastropoda of the southwestern Texas Board Water Engineers Bull. 5004,38 p. Sellards, E. H., 1933, Pre-Paleozoic and Paleozoic systems in United States; [Pt.] 1, Euomphalacea, Trochonematacea, Pseudophoracea, Anomphalacea, Craspedostomatacea, and Texas, Pt. 1 in Stratigraphy, v. 1 of The geology of Texas: Platyceratacea: Am. Mus. Nat. History Bull., v. 110, p. Texas Univ. Bull. 3232, p. 15-238. Smith, J. F., Jr., 1940, Stratigraphy and structure of the Devil 179-275. Ridge area, Texas: Geol. Soc. America Bull., v. 51, p. 1960, Permian Gastropoda of the southwestern United 597-638. States; 3, Bellerophontacea and Patellacea; Am. Mus. Stehli, F. G., 1954, Lower Leonardian Brachiopoda of the Sierra Nat. History Bull., v. 119, p. 209-293. Diablo: Am. Muss. Nat. History Bull., v. 105, p. 261-358. Yochelson, E. L., and Bridge, Josiah, 1957, The Lower Ordo- Stevenson, F. V., 19451, Devonian of New Mexico: Jour. Geology, vician gastropod Ceratopea: U.S. Geol. Survey Prof. Paper v. 53, p. 217-245. 294, p. 281-304.

INDEX

[Italic numbers indicate major references]

A Page Page Page Barnett Shale- 41 Bend Formation_ 42, 43 Abrigo Limestone of Middle and Late Cam­ age- . 41 Berdan, Jean, fossils identified by _ . 133 brian age--. 32 J^-J-jlf1 f«?«? OO Beryllium ...... _ ...... Acknowledgments_ 3 lithology and thickness, 41 Black John Canyon, beds of Devonian age Adkins, W. S., fossils identified by . 88,8Q regional features ..... 42 molluscan ledges. . section measured by- 176 stratigraphic relations.. 41 stratigraphic section.. . 159 Agricultural areas... 17,121 stratigraphic section stratigraphic section, south of... - 158 Aleman Cherty Member of Montoya Dolo­ Black Knobs, Cretaceous rocks.._.. . . 82, 83 mite___-_-_____-___- 35, 56 Basin and Range province_ 11,99,107, 118 stratigraphic section.. . . 173 fossils.....- 38,37,185,128-131 Bass Canyon, stratigraphic section... 136 Black Rock Formation of Arkansas. .. . 33 in Caballo Mountains of New Mexico _ SB, 56 Bat Cave, stratigraphic section - 145 Blackshaft mine_.._ _ . 119 Alkali flats, Salt Basin....__.______15,97 Bat Cave fault_-_____..._ 112 Bleaching, red sandstone of Hazel Formation- 27, Allamoore Formation. . 16,25,29 Bat Cave Formation in Caballo Mountains of 103 Bean Hills . ___._ 108 New Mexico_ S4 sandstone of the Van Horn Sandstone... - fossils__ _ ...... _...___ % Bat guano, nitrate ___ . . 121 Bliss Sandstone £0,30,34 jasperoid. SB Baylor Mountains...... ___ 15, 30,104,107,109, 110 limestone beds_ ...... 2S beds of Devonian age_ 40 calcareous division . SO marble_ _ ...._ __ 180 beds of Middle(?) Ordovician age. . 54 distribution.... SO minerals in veins... 119 Bone Spring Limestone___ 61,66,72,139-141 fossils . 30, 31,123,124,187,128 phyllite___..- ....__..._ 84, 101,119 Cretaceous outliers______- 85 main body of formation... SO rock alteration_. ..._..._ 85,101,119 El Paso Limestone______58,53,110 regional relations.._ 31 stratigraphic relations.....__ ___ SB escarpment-...... _...... IS, 34,38 stratigraphic relations.--.-. SI structure_ ... __ 101 fault block. __...... _____ 13, 111, US stratigraphic sections-. _ 183,184,127,128 talc in phyllite units .. __ 24,110 Fusselman Dolomite_ 58 thickness.- ..... SO Tumbledown Mountain... 23, 25, 108 Hueco Limestone___...... 49, 50,52,110 Block faulting, Cenozoic time. - 99,104 volcanic rocks...... _ 84,28 joints __....__.______... 116 of Sierra Diablo. - 94 Alluvial deposits, older...... _...___ 98 Montoya Dolomite 35, SS Bluff Mesa Formation- 81,82 younger. .. .. 98,99 Permian rocks __.... __ 46, US fossils.______83 Alluvial fans._.__ ..___ 15,97,98,109, 110 stratigraphic sections.. .. 187,128,129,1S8, HI Bolsa Quartzite of Middle Cambrian age 51 Alluvial slopes. IS, IS Victorio Peak Limestone_ 73,74 Bone Canyon. __ 60 Bone Spring Limestone 14, 60, 90,92, 93 Analyses, hornfels, Bone Spring Limestone_ 93 Beach Mountain_ ... . 14, hornfels, Powwow Member of Hueco Apache Tank... 64 15,28, 29, SO, 105, 107,119, US, 124 Baylor Mountains...... 61,66,72,139-141 Limestone .. ..__ 98 El Paso Limestone______S8,SS,S4 marble and limestone from Hueco Lime­ correlation of faunas....._ 78 faults . .-. Ill, US Delaware Mountains... 60 stone. _ 9S, 95 Hueco Limestone_._.-. -.-__ 49,52 Annotated bibliography __ 5 faunal assemblages.-. . 66 joints-. . 116 fossils. 49,6S, 1S8-141,146-15S, 169-164,166,167-170 Anticlines...... __ 101,105 Montoya Dolomite_ - 35,86 Apache Canyon. - ___ IS, 15,61, 111, 160 fossils and correlation... 66 Permian rocks.. ___.. ..__ 46 Guadalupe Mountains .... 60 Hueco Limestone . . ... 49, 50,54 stratigraphic sections___ __ 123-127, W northern marginal belt of Bone Spring lithology and fades 81 Limestone- ... __ 64 Bean Hills. - _-_-___ 14, 16,101,102 molluscan ledges... 63,66,67,72 stratigraphic sections. .._...___ 168 AUamoore Formation._ . 102 northern marginal belt_.. 64 Apache Mountains ... 117 talc mined from phyllite units. . 24,120 outcrop 81 faults . .-. . _.... 107 Campagrande Limestone. 83 reefs and banks... 61,63,64,65 wells drilled for oil - . __ S5,122 Beds of Devonian age, distribution and thick­ Sierra Diablo escarpment 81 Apache Peak, reef mass on ______65 ness. S9 southern marginal belt .. 65 stratigraphic section ... _ 160 fossils-.._ .. . . 40 stratigraphic relations__ 72 Apache Spring, Fusselman Dolomite. _ S8 lithology..- . - 40 stratigraphic sections 1S8-141,146-160,168-170 stratigraphic section . ___ 1S2 regional relations_ 40 Brand, J. P., fossils identified by. 87 Apache Tank, Bone Spring Limestone...... 4 stratigraphic relations..._ . 40 Branson, C. C., section measured by. 129,130 stratigraphic section ... 166 stratigraphic sections_ . 129 Bridge, Josiah, fossils identified by.. 124,125 Arizona.. . . . 31,82,118 Beds of Middle(?) Ordovician age..__ 84 sections measured by 123,132 Colina Limestone of Naco Group.- 57 fossils .. _...__...__. 34,129 Brucite. - - 121 Arkansas, Atoka Formation. . 45 stratigraphic section ______129, ISO Brushy Canyon Formation. 78 Black Rock Formation.. . 33 BedsofPennsylvanianage.. 42 Pipeline Shale Member..... 79 Atoka Formation in eastern Oklahoma and age. - 43 stratigraphic section 169 western Arkansas__ 45 distribution-... 43 Buda Limestone in foothills of Eagle Moun­ fossils - - - 48,134 tains .. 88 B local features 43 Babb Canyon .. 63 regional relations..... 4$ Babb flexure...... 14,.61, 73,77, 82, 106, 107, 109 stratigraphic relations. __ . . 43 Barnes, V. E., quoted .. 31,34 stratigraphic section. 184 Cable Canyon(?) Sandstone Member of Mon­ section measured by -. 124 Beede, J. W., section measured by. -.... 176 toya Dolomite- . 34,56 181 182 INDEX

Page Page Fault Continued Caballo Mountains of New Mexico, subdivi­ Cutoff Shale.--...... 81,74,79 East Baylor.. 107, 110 sions of El Paso Limestone.. . 34 age 78 East Diablo-_ _ 107, 109, 111, lit, 113; subdivisions of Montoya Dolomite ..-. 35,36 "Dos Alamos gypsum member" 77 Grapevine..__- __ - 29,102,103,113 Caballos Novaculite of Marathon region_ 41 fossils...... 78,167 Hillside.-.___ . 105,114,117 California, faults...... 118 Guadalupe Mountains..... 74 North Baylor __ - . 107,109- Camp Creek Shale Member of Pueblo Forma­ lithologic features...-- 77 North Diablo- ._ 107,111,112 tion..___.. . 56 stratigraphie relations.... 78 Red Hills thrust . ... lOff Campagrande Limestone______81,82, S3 stratigraphic section 167 Sheep Peak._ - lit BeanHills.______... 83 Cutter Formation of Montoya Dolomite. 35, 38,37 South Diablo-___- 105, 106, lit Cox Mountain_ 83 Streeruwitz thrust - 22,23,25,27, 100- Finlay Mountains_ _.___._ 83,84 D Sulphur Creek... 105,lit, 114 fossils. .__ 84,170-172,176 Dallas fault 29, 103, 114 West Wylie.. - - 110 Sierra Diablo Foothills . - . 83 Dallas mine______. -- 119 Fault blocks .- _- IS, 19,32,35, 39, 41, US, 116. Sierra Prieta.._____.______..... 83 Davis Mountains__ 122 Faults-_...... IS, 14,96,103,105,107,112, 159,169 stratigraphic sections. _____ 170-173,175 Delaware basin. 46,61,99,104, 106, 122 Apache Mountains. 107 western Sierra Diablo - __------83 Delaware Mountains. 14,46, 78,98, 169 Baylor Mountains.-.- - 111,113' Campo Grande Arroyo in Finlay Mountains.. 83 Bone Spring Limestone .. . 60, 73,169 Beach Mountain.-. . 111,118 Canutillo Formation, in Franklin Mountains. 40,41 Brushy Canyon Formation_ 78,79, 169 bordering the mountains... 107 Capitan Limestone___ . ______155 faults... _ 107,110 Delaware Mountains. 107,110> Carlsbad Limestone of Guadalupe Mountains. 74 wells drilled for oil - -- 35 on east side of Salt Basin 110 Carrizo Mountain Formation. _._..._..19,114 Permian rocks______-_ 46,60, 169 Precambrian age.. 117 igneousrocks intrusive into.... tt, 25, SB, 101, ISO stratigraphic section- 189 Red Tank Canyon.. . 113- metamorphie features_ ._._ 21 Dell City.______17 with strike-slip displacement . 10% sequence in Carrizo Mountains._____ gO,lgl Devil Ridge thrust fault 82,86,106 Faults and related structures within the stratigraphic relations_...... & Devonian, beds of Devonian age . 39 mountains- 111 Carrizo Mountains.__... 14,23,28,^00,101,*^, 138 regional relations... 40 Faunal assemblages, Bone Spring Lime­ crushed stone______.. ISO Diabase, dikes and sills... 96 stone. 66~ Hueco Limestone-...... 49, 52 Diablo Plateau IS, 14,83,85,94,96, 99,106 Figure Two Ranch, water wells... m, Itt Pennianrocks ... .. 46 Diablo platform....._ . . 48, 99 Fillman, Louise, quoted 42 vein deposits of metallic sulflde minerals_ 119 Dikes.______90,9g,94 Finks, R. M., fossils identified by.... 58,59,68,76,80' Carrizo Spring fault______103, 113 Dome Peak, stratigraphic section 171 Finlay Limestone. - 85, 87 Cave Peak, beryllium_.______ISO "Dos Alamos gypsum member" of Cutoff age. - 8& igneousrocks______65,90,91 Shale. . 77 Cox Mountain-. . 8ff Cherry Canyon Formation, typical, of Dela­ Drainage of region.. 14,15,121 Finlay Mountains. 85 fossils ___. - 86,173,174 ware Mountains______79 Drake, D. A., fossils identified by.. 134,136 Dunbar, C. O., fossils identified by. - 134, local features... 86 Cherry Canyon Formation sandstone tongue. 79, Norton Mesa. 8ff 167 147,149,152,153,155,157-159,167,169 Dunean, Helen, fossils identified by .. 58, Roberts Mesa.. . . 8ff fossils...... _.____ 167 stratigraphic sections 173~ stratigraphie section- ______167 59,68,76,80,133 Dunes- . . 16,98 Finlay Mountains, Campagrande Limestone. 83,84 Chihuahua tectonic belt.. _____ 106, 107, 115 Cox Sandstone.. 84 Circle Ranch fault zone___-______112 E Finlay Limestone_ 85 Cisco Group of central Texas______56 Flexures-.______- IS, 105,113,116, 117 Climate.. .______...._.___.. is, 16 Eagle Flat, ground water in unconsolidated Flower, R. H., quoted 32 Cloud, P. E., Jr., quoted. --_____ 31,34,63 depositsof Cenozoicage 121, \ Fossils, Aleman Cherty Member of Montoya section measured by...______124 intermontane plain. 13, 14, 16,22, < Dolomite__ -__ 36, 87,125,128-lSt Colina Limestone of Naco Group in southern stratigraphic sections. 141,170 Allamoore Formation. -. 24 Arizona______57 Eagle Ford Formation. 88 Barnett Shale . - . 41,133 Comanche Series.__ ....____... 81 Eagle Mountains-___ - 20,106,119 beds of Devonian age 40 Conglomerate, Hazel Formation __.... SB bedsof Middle (?) Ordovicianage. . 34,129 Van Horn Formation- ___- _____ 28 Early Mesozoic age, structures of 105 bedsofPennsylvanianage . 48,184 Early Tertiary age, structures of 106 Cooper, Q. H., fossils identified by_____ 129 Bliss Sandstone 30, SI, 123,124,1*7,128 East Baylor fault... . 107, 110, 114 Bluff Mesa Formation 83 Copper, production___ ...____ 17,119 East Diablo fault-. 107, 109, 111, US, 113 Cornudas Mountains_ ..______81,96 Bone Spring Limestone .. 49,63,138- Economic geology.. 118 141,146-156,159-164, 166, 167-170 Cox Mountain, Campagrande Limestone_.. 83 Edwards Limestone 81,86 Brushy Canyon Formation- . 79, 169 Cox Sandstone.._ ..______84 El Paso Limestone.. Sg, 123 Campagrande Limestone. _ 84, 170-172,175 Finlay Limestone...______88 age.__._____ ' S3 Cox Sandstone.. 85 flow of vesicular basalt . ______96 Baylor Mountains_ 32, S3, 127 Cutoff Shale...-.______. 78,167 Kiamichi Formation..______87 Beach Mountain. . 32,33,124 El Paso Limestone_ __ St, S3,123-128,128-1SO stratigraphic section __.. l?g distribution and thickness_ 32 Finlay Limestone. _ . 86,173,174 Cox Mountain fault... ___ 32, 112 fossils ____ Sg, S3,12S-128,128-1SO Fusselman Dolomite 39 Cox Sandstone...... __ 81,84,95 regional relations . 34 Goat Seep Limestone. 49, SO, 167 Finlay Mountains.. ______84 stratigraphic relations..-. S3 Hueco Limestone - - 48, fossils and age.. . ______86 stratigraphic sections. 123,125, 127-182 50,52,54, 55, 68,135-159,162-167 outlying areas. ..______._ 85 subdivisions_.... 52 Kiamichi Formation - . 87,172 Sierra Diablo foothills and Cox Mountain. 84 Elgin Limestone Member of Maquoketa Permian rocks . 4,17,49,134-170 Sierra Prieta-..______85 shale of Iowa_ 37 Victorio Peak Limestone . .. 49,73,74, southwest of Eagle Flat... ______84 Ellenburger Group of central Texas.... SI, S3,84, 123 76,136,150,154,155,160-164,166,168 stratigraphic sections...... _ 170-176 Eureka prospect.. 103,119 Yucca Formation_ 82 Cretaceous System___...______80 Washita Group - 88,174 Cretaceous rocks... ______80 Fractures and fracture zones, Hazel Formation. 27, angular discordance with older rocks.... 81,105 103,119 mineral deposits in Eagle and Quitman Fanglomerate along edges of Salt Basin-- 15, 98, 110 Franklin Mountains, Bliss Sandstone. SO, 31 Mountains..__ ._____ 119 Fault, Bat Cave-_ lit Canutillo Formation 40,41 stratigraphic sections and fossil collections.. 170 Canizo Spring.__ _ 103, 113 El Paso Limestone_._ 32,34 stratigraphy...... _...______80 Cox Mountain-.-.. lit Fusselman Dolomite_ 38,39 Crushed stone. ___-______.. 120 Dallas 29, 103, 114 Montoya Dolomite. 35,37 Cutoff Mountain.__ ___.. __.._. 74 Devil Ridge thrust- - - 106 Paleozoic formations 5 INDEX 183

"Pug* Page L Page Furnish, W. M., fossils identified by . 42,70,161 History..... _ . 16 Landslides-.....__ _ 41,43,97 quoted.. 42 Hollingsworth, K. V., fossils identified by. 134 Late Cretaceous age, structures of... ..- 106 FusselmanDolomite.....__ ...... 35, 36,38,105 Honeycut Formation of central Texas.... 33,34 Late Tertiaryage, structuresof. 107 distribution-_ . 38 Hornfels, chemical analyses and mineralogy. 92,93 Lee, D. E., quoted . 95,96 fossilsandage SS Hot Wells, Southern Pacific railroad well_ - - - 15, Leonard Series.... ._ 48, 49, 61, 78,105,106 99, 122 litbology - - 38 of the Glass Mountains.-- 66,72 regional relations 39 Howe, H. J., fossils identified by_ 128 in West Texas region_ . 72 stratigraphie relations__.. 39 sections measured by__ - 128 Llano uplift of central Texas___ 34,38,41,45 stratigrap hie sections... 125,128,129,131 Hueco Limestone _ 5, IS, 49, Lobo Flats district, ground water.. _ 15,17, 121,122 thickness.. - - 38 65,90,92,93,95,101, 106, 109, 111, 127 Lone Mountain Formation, Nev._ ... 39 Apache Canyon. --__ 49,50,54 Love Hogback_ _ 82 G Baylor Mountains____ ...._ 49,50, 52,110 Lowland areas.. . 14 Geography... . 11 Beach Mountain_ 49 Luedere Limestone, central Texas 57 human... - 16 central Sierra Diablo_ 54 Gifford-Hill rock crusher, ...... 114,120,172 fossils. . 49,50,52,54, 55, 56,135-159,162-167 Gillerman, Elliot, section measured by.. 170 fossils and correlation_ - ... 55 M Gilliam Limestone of the Glass Mountains.... 74 Hueco Mountains.. 49 Girty, G. H., fossils identified by.. . 134,136,138 inclusions in Sierra Prieta intrusive_ 95 McAdoo Ranch, stratigraphic section_.. - 143 Glen Kose Formation in central Texas_.. 81, 83 lithology and subdivisions.. ___ - 50 Magdalena Limestone.. ____ 42,46 Goat Seep Limestone.. . 79 marble and altered limestone.. .__ 95, 121 Mainstreet Formation, north-central Texas... 88 age ... - 80 outcrop_ . 49 Malone Mountain _ 106 fossils....__ .. ..._.... 49,80,169 Powwow Member______50, Marble ___ 95, 120 Guadalupe Mountains. __ __ . 79,80 52,53,54,92,114,115, 117, 136-139 analyses. . 93, 95,121 lithologic features- . 79 regional relations of fauna. . 55 Marble Canyon.... 43,45,46,54,61,63,109 stratigraphic relations.... 80 stratigraphic relations__ 57 fossil collections from Hueco Limestone stratigraphic section 167 stratigraphic sections______- 135-145, near. ....___ 156 Gordon, Mackenzie, Jr., fossils identified 147-148,150-160,162-167 stratigraphic sections_ ..____ 134,156 by .-____..__-__ 41-43,133,134 subdivisions In Apache Canyon area.. . 54 Marble Canyon-Mine Canyon intrusive com­ quoted..__ ...... ____.__ 42,45 thickness. . . 50 plex. .. 112 German Formation of central Texas. ... 31,33,34 Wylie Mountains....-.-. .._ 49,50 Marble Canyon stock___.____ 65,90, 92, 93,121 Grape Creek Limestone Member of Clyde Hueco Mountains, beds of Devonian age_ 40,41 petrology . 90 Formation__... ___ . 57 Bliss Sandstone...... 31 Marvin-Judson prospect . ..____ 119 Grapevine fault .- .. _. $9,102,103,113 El Paso Limestone_...... _ 34 Metarhyolite, intrusive into Carriao Moun­ Grayson Formation in fDothills of Eagle Hueco Limestone 49 tain Formation. ____ 22, Mountains..... 88 Magdalena Limestone.. - - 46 25,28,101,105,114,115,120 Grayton Lake, alkali flat 97,99 Montoya Dolomite_.... 37 klippen of Streerawitz thrust sheet___ 100,101 Greenstone, Intrusive into Carrizo Mountain Human geography 16 Middle Mesa...... _____ 79,80,109 Formation__... ..___._ 22,03 Middle Ordovician Simpson Group __.. 18t Ground water.... _. ______16, 121 quality. 181 Igneous rocks_ _ ... 22,25,89,92 Miller, A. K., fossils identified by. ____ 42,70,161 Guadalupe Mountains__...... 14,96 intrusive Into Carrizo Mountain forma­ Millican Hills. r . __ 14, / 0,22,100,/Of,//9 Bone Spring Limestone_-_ .-... 60 tion.- - 88,86 conglomerate of Hazel Formation...... Cenozoic block faulting..-. 104 outlying 92 talc._. Cutoff Shale....- 74 Sierra Prieta...... _ ___ - _ 95 Mine Canyon.... . 43,46,48,64,61, M, 65 Goat Seep Limestone_ ... 79,80 Imlay, R. W., fossils identified by. ._ 86-89, stratigraphic sections...... /33, 157 Joints-___....__-______._ 107 172-174,176 Mine Canyon stock 90,91,92,120 Permian rocks______48, 60 IndiansinTrans-Peco Texas______IS rock units __ 91,120 Victorio Peak Limestone__ - 73 Indio Mountains. . ... 106 Mines, Blackshaft- . ___ 102, 119 Guadalupe Series... __.-. 14, 48,72,78, 79,82,105 Investigations, present_.. 2 Dallas.. .._._ 119 Gulf Series..._.____..__....__._ 8/,88 previous_ 4 Hazel . 17, 102,103,113, 119 Gypsiferous clay, hills 15,97 related,__ _ 4 Mohawk_ ..... 119 Pecos . .. 103,109,113,119 H St. Elmo- ...... 102,119 Hackberry Creek. - 14, IB, 18,98, 102,110 Jasperoid, Allamoore Formation_ S5 Saneho Panza. 102, 119 Hass, W. H., fossils identified by.-.-_ _ 40 Jefferson City Formation of Missouri_.. 33 Missions founded by Franciscan monks... 16 quoted_ ... . 40 Joints...._.__..______95, 103, 111, 116 Mississippian, stratigraphy. .. 41 Hawkins Tank, stratigraphic section-.. .. 30, ISO Baylor Mountains.... 116 Missouri, Roubidoux Formation.. 33 Hazel Formation...... 25,100 Beach Mountain_ _ 116 Montoya Dolomite . 33,35,38,113,114 conglomerate- . . 16,25,108 Guadalupe Mountains.._ - 107 age. 57 fracture zones . . 103,119 Sierra Diablo fault block.._ - 116 AlemanCherty Member_ ... 35,35 joints...... lie Cable Canyon (?) Sandstone Member. 34, 36 red sandstone -. ----- 14, 16, 25, 28,109,112 Cutter Formation__ 36, S7 Kelley, V. C., quoted___ 32 fossils...-._ . 36,37,126,129-138 rock alteration . 27 Kiamichi Formation.._ .. 85,87 stratigrapbic relations...... _. . 27 Hueco Mountains...- 37 Cox Mountain - 87,172 regional relations . 37 structure.-...... -_ ._ 101 stratigraphic section.. 172 stratigraphic relations__ S6 Hazel fracture zone...... 103 King, P. B., sections measured by. 123, stratigraphic sections... 124, 125,128-133 Hazel mine .. 119 124, 127, 128, 130, 131, 134, 136, 138, Upham Member___.... . 36, 125 stratigraphic section .. . 144 144, 147, 149, 153, 155, 157, 159, 160, Mountain areas.... /3 166, 167, 170-174, 176. Helms Formation._ .... _ . 41,42 Murata, K. J., analyst-_ . 24,74,83,90,92,93,95 King, R.E., fossils identified by_ - 56, Henbest, L. G., fossils identified by__ 56, Murray fracture zone of the Pacific Ocean 134, 136, 138, 147, 149, 153, 157, 160, 58, 67, 76, 80, 136, 142, 145, 146, 148, basin. - . 118 167, 169. 149, 153, 154, 157, 160-164, 166, 167, sectionsmeasuredby-..-. - 128, 169. 134, 136, 138, 147, 149, 155, 157, 160, N quoted . 64 166, 167, 169, 172-174, 176. Hess Limestone of the Glas;3 Mountains.. 72,74 Knight, J. Brookes, sections measured by- 123, Nevada, Lone Mountain and Roberts Moun­ Hills of gypsiferous clay .. 97 124,127-129,132-134,136,138,141-146, tains Formations.- 39 Hillside fault. 14, 52, 105,114, W 149,153,155,157-159,162-166,170-174. Pogonip Group 35 184 INDEX Page New Mexico, Aleman Formation of Montoya Red Tank Canyon______... 53,85 Sohn, I. G., fossils identified by... 70,159 Dolomite __ SB,S6 faults-...... ___.__. 113 South Diablo fault.. . 105,106,112 Bat Cave Formation of ElPaso Limestone. S4 Red Valley___ __-_.... _ 14,87,29 South Mesa _. 77,78,79,80,109 Bliss Sandstone- 31, S2 folds....--_. . __..._...... 103 stratigraphic section_.-.___.____ 167 Cable Canyon Sandstone of Montoya joints ... . 118 Southern Pacific railroad..______16 Dolomite ___-_ _._ SB, SB Red Wash...... __.... 15,98,99 Stehli, F. G., quoted_ -__ ....._ 72 Cutter Formation of Montoya Dolomite S5 Reef and bank deposits in Bone Spring Lime­ Stratigraphic classification of Permian rocks.- 48 Fusselman Dolomite S9 stone______61,64,65 Stratigraphic nomenclature of Precambrian Onate formation. 40 Regional metamorphism of sedimentary rocks rocks, development______SO Pennsylvanian rocks 45 of Carrizo Mountain Formation.. SS Stratigraphy....______17 Percha Shale___ 40 Relief. - IS, 14,104,103 Streerawitz Hills.-_-_-_....__ 14, 16,101, 102 Sierrite Limestone of El Paso Limestone Sj. Rhyolite intrusive into Carrizo Mountain Campagrande Limestone . ___ 85 Up ham Dolomite of Montoya Dolomite 35 Formation.... _ Si Hazel Formation______.. 26,102 Nitrate prospect HI Rhyolite porphyry and breccia, Mine Can­ Hueco Limestone.__...__ _ 49,50,52 North Baylor fault.. - 107,^09 yon stock 91 stratigraphic sections. ______142,171 North Diablo fault zone. 107, 111, 112 Roberts Mesa, Finlay Limestone. 86 talc mined from phyllite units of Alla­ North Mesa...__ 77,78, 79,80, 109 stratigraphic section.... 17S moore Formation.. __ 24,120 Norton Mesa, Finlay Limestone - 86 Roberts Mountains Formation, Nev..... - 39 Tertiary intrusive rock__.... __. 96 stratigraphic section. 17S Rock formations--...__ 17 Streerawitz thrust fault- __- 22,23,25,27, 100,101 Ross, C. S., quoted-. 95 Structural features______100 Roubidoux Formation of Missouri_. _ 33 Sulphur Creek,....-______15,16,98, 99,110 Ochoa Series- 48 Sulphur Creek fault.______105,^0,114 Old Circle Ranch, stratigraphic section 144 Surface of pre-Cretaceous rocks _ __. 81 Ofiate formation of New Mexico 40 St. Peter Sandstone of the northern interior Oil possibilities - - - in region. - 34 Oklahoma, Simpson Group. 35 Salt Basin.-. - 13, 14, 46,48,73, 107,109, 111, 113 Ordovician, stratigraphy... SO alkali flats. ... _ 15,97 Talc, to phyllite units of Allamoore Forma­ Ozark uplift in Missouri_ 33 deposits of fanglomerate along edges.. 98 tion. .______deposits of floor...__ . 97 production______17, 120 faults 110,117 Tanyard Formation in central Texas_____ 31, 34 ground water in unconsolidated deposits of Tectonic history___ -...__ iOO Pacific Ocean basin, fracture zones . 118 Cenozoic age___ - lit Tectonics_ ___ 99 Paleozoic rocks... 17 interior drainage____-_ ^4.15 regional interpretations and synthesis__ 117 Paluxy Sandstone.- . 81 Salt lakes. - 15, 97 Tertiary rocks______17 Patterson Hills ...... 107 Sancho Panza mine__. 119 Texas and Pacific Railway__ 14,16,19,22,114, ISO Pecosfracture zone... 103 Sandstone, Hazel Formation__ 26 Texas Construction Materials Co_ ___ 1S1 Peneplain, pre-Cretaceous. 82 Van Horn Formation. __ £8,29 Texas lineament ______115, 118 Pennsylvanian, stratigraphy . 4% Sandstone tongue of Cherry Canyon For­ Threemile Mountain, Hueco Limestone___ 50,5a Percha Shale, N. Mex~ 40 mation-.. __.__ 79,167 stratigraphic section___.-._...___ 136 Permian, stratigraphy 46 Settlements, early.._____ . 16 Threemile Mountain area, fossils. ______138 Permian age, structures of.... . 105,117 Seven Rivers Limestone of Guadalupe age 74 Topography______... _._____ 13,99 Permian rocks, fossils._ 17,49,134-170 Sierra Blanca___.__ __ 115 Torbet, ground water____...______122 paleontologic data 49 yield of wells. ______122 Trans-Pecos Texas.-._____.______4,5, stratigraphie classification.. 48 Sierra Diablo, description.... IS stratigraphic sections. 134-170 16, 31, 34, 39, 40, 41, 42, 45, 49, 61, 80, northern part, faults and related struc­ 87, 96, 103, 104, 107, 117, 118, 119 thickness... 17 tures______.__._ 111 Phyllite, Allamoore Formation..-.. ££,101 southern part, faults and related structures. US Transverse Ranges, Calif. __. 118 Pipeline Shale Member of Brushy Canyon Sierra Diablo escarpment__...- IS, Travis Peak Formation of central Texas___ 81,82 Formation.-... 79 25, 26, 27, 28, 29, 43, 46, 50, 54, 61, Tumbledown Mountain______29,133,124 Pogonip Group of Nevada 35 73, 83, 84, 102, 106, 107, 110, 143, Allamoore Formation__ .. 23, 25, 10S Powwow Member of Hueco Limestone 50, 144, 145, 146, 153, 155, 157, 169. faulting ___ -. . __- 103 53,54,92,114,115,117 Sierra Diablo fault block, joints.... 116 Tungsten__ __. ISO fossils-...... - __ 50,52,54,55,136-137, Sierra Prieta ...... 13,81,88 Turquoise in copper prospects __. 1S1 14$-14S, 145,151-153,156,158 Campagrande Limestone. 83 Threemile Mountain. 50,52 Cox Sandstone...____.- 85 Victorio Peak...... 54 Hueco Limestone______-__ 55 Precambrian and Precambrlan(?) rocks, igneous rocks...______94,95,166 structure_ ...... ___ 100 marble.______... 95 Unconformities, angular. .. 17,53,99 Precambrian rocks_...... _ 17,19, 100 stratigraphic sections. 166,174 Unconformity between beds of Pennsylva­ vein deposits of copper and silver .._.. 119 Washita Group______87 nian age and Hueco Limestone. 43, Precambrian(?) rocks.__ ...... ___ 19 Sierra Prieta intrusive, structure...___... 95 99, 104 Precambrian surface, structure_ ___ 103 Sierrite Limestone, N. Mex__ 34 Bliss and Van Horn Sandstones 29,30,99 Pre-Permian Paleozoic rocks, structure.. 17,^04 Sheep Peak, fossil collections from Hueco Hazel Formation and Van Horn Sand­ Pump Station Hills, red rhyolite porphyry... 28 Limestone._____ 146 stone S7 Sheep Peak fault..______113 Hueco Limestone and Bone Spring Lime­ Q Sills_ __ 20,22,23,90, 92,94,95, 96,97,112 stone______5S,53,60 Silver, Caswell, quoted____...__ 32 Leonard and Guadalupe Series...--__ 78 Quaternary age, structures-.... ___ 107 Silver, discovery______._ 17 Unconsolidated deposits of Quaternary age... 96 unconsolidated deposits_ 96 production______- 17,119 Upham Member of Montoya Dolomite_... 36, 125 Quitman Mountains...- 106,115,119 Silurian, stratigraphy_____.... 38 fossils... - 36,37 Simpson Group of Middle Ordovician__ 34,35, Hi N. Mex.. 35 R Sixmile Mountain, stratigraphic section_ 1SS Railroads, construction ._.-...___ 16 Skinner, J. W., fossils identified by__ 134, Rainfall- - ...... __ IS 147, 149, 153, 155, 157-159, 167, 169 Rancheria Formation.._. . ___ 42 Slaughter Ranch well.______122 Van Horn. _ _ 13,15, 16 Ransome, F. L., quoted._.-_-______118 Smith, J. Fred, Jr., sections measured by__ 170 ground water. 1S1,122 Red Hills thrust fault. ______106 Smithwick Shale of Llano uplift in central Van Horn dome 104 Red sandstone, Hazel Formation_____ Texas____.____ 45 Van Horn Mountains__ __. 20,21 INDEX 185

Page Page Page Van Horn quadrangle...... ___._ S Victorio Peak Limestone..__ 14, 61, 65, 72,107,109 West Texas basin..... 34,38,39,41,42,45,122 Van Horn Sandstone. .. 14, SB, 27,110,114 Baylor Mountains__ . __. 73,74 West Wylie fault___.___._._____ 110 age .. 29 fossils 49,73, Wichita Group of central Texas. ___.__ 56 bleached.. .._ . . 89 74,76,1S5,150,154,155,160-164,166,168 Wichita paleoplain of Hill___.______81 conglomerate . 28 Guadalupe Mountains.._ ... 7S Wildhorse Creek.. . . 15,98,121 joints - .. .__... 115,116 joints______... 112 Wildhorse Valley, irrigation district_ 15,17,97, 121 sandstone__...... _ . 28, S9 northeastern calcitic facies.______7S Wolfcamp Series______-___ 48,49, 55, 105 stratigraphic relations . 89 southwestern dolomitic fades ... 74 Woodford Chert of Late Devonian and Early structure .. 103 stratigraphic relations__-__ __ 74 Mississippianage. _ .. 41 Vein deposits containing metallic sulfide min­ stratigraphic sections .. 1S5, Word Formation of Glass Mountains____ 80 erals, in Precambrian rocks_.... 119 147,140,150,154-156,160,162-169 Wylie Mountains______... 20,61, 110 Wylie Mountains-_ . .. 73,74 Hueco Limestone 49,50,52 Veins, Allamoore Formation.. ____ _ 23 Volcanic rocks, Allamoore Formation....__. i4 stratigraphic section . ... 134 calcite, in Hueco Limestone 113 basaltic, of Tertiary age 96 Victorio Peak Limestone.. ______7S, 74 Carrizo Mountain Formation__... 23 Victorio Canyon...... IS, 15,54, 105,109, 111 W Cretaceous rocks .. 82 Washita Group...... 81,87.95,97 Montoya Dolomite. .. SB, SB, 105 fossils....______..____ 88,174 Yates Ranch, stratigraphic section 183 stratigraphic sections. .. . 158 Sierra Prieta. ______.____ 87, 176 Yearwood Formation of the Apache Moun­ vesicular basalt_ .. . 96 southwest of Eagle Flat 87 tains.__-______83,84 Victorio flexure- ... IS, 49,50,54,61, stratigraphic sections. 174-178 Yoehelson, E. L., fossils identified by..... 41,43,58, 63,65, 66, 73, &?, 82,86, 106, 107, 110,112 Wells. . .. 14, SV, 111, 121,122 59, 70, 76, 80, 133, 134, 136, 138, 140- West & Armour, 1 Davis Investment 142,146,148,149, 153-155,157-163,166, fault along_._ __...... ___ _ 105 et al ______...___ 97 167,169. Victorio Peak...... 46,7S,152 Van Horn, yield.______.____ 181 quoted__._... . 45,63,72 Hueco Limestone____.....____-_ 49,50 Wildhorse Valley irrigation district.__- 97 Yucca Formation. 81,88 Powwow Member..__.....___...... 54 Weno Formation, north-central Texas. .. 87 fossils . 82