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Early Paleozoic of New Mexico Rousseau H. Flower, 1965, pp. 112-131 in: Southwestern New Mexico II, Fitzsimmons, J. P.; Balk, C. L.; [eds.], New Mexico Geological Society 16th Annual Fall Field Conference Guidebook, 244 p.

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EARLY PALEOZOIC OF NEW MEXICO ROUSSEAU H. FLOWER New Mexico Bureau of Mines and Mineral Resources

INTRODUCTION mations have retained their apparent simplicity. The Early Paleozoic was a long time, extending roughly It was not too long ago that the Early Paleozoic of from 600 to 370 million years ago, and it is perhaps New Mexico was regarded as simple, with almost one too much to hope that the physical history in terms formation for each geological system. Even this was an of periods of deposition and erosion, was any simpler advance, for earlier work lumped the whole of the here than it has been found to be in other regions in Early Paleozoic into one formation, the Mimbres lime- North America. Eastern sections, which have been stone. For mapping on the scale then used, and in- longer under investigation, show quite complex his- deed, in many cases on scales in current use, the Early tories in each of the systems. Paleozoic shows such a narrow belt of outcrop that Figure 1 shows the development of the geologic finer division is impractical. While Kelley and Silver column of the Early Paleozoic of New Mexico. Col- (1952) made an important step in the recognition of umn 1 shows the old broad formations, roughly one to finer units, their units, new formations, had to be a system, which developed from 1906, and are found grouped together in mapping because of scale of the in Darton (1917). Column 2 shows divisions proposed map and the limited areas of outcrop. within these broad units up through 1952—Entwistle It has, however, been necessary to inquire more (1944) for the Montoya, Stevenson (1945) for the closely into the parts of systems represented by the Devonian, Kelley and Silver (1952) for El Paso and deposits in the Early Paleozoic of New Mexico, in Montoya. Column 3 shows the divisions used in this order to arrive at a clearer concept of the geological paper—both formation names and faunal zones are history in terms of periods of deposition alternating given. Column 4 shows the correlation of these divi- with intervals of elevation and erosion. It was necessary sions in terms of a general column for North America. to know what parts of systems were represented and This column is incomplete; major intervals not repre- how the New Mexico sections correlate with those of sented in New Mexico arc omitted. other regions. There are two realities in geology, the Figure 2 relates the Early Paleozoic sediments of actual geological history, and the succession of rocks New Mexico to a generalized column for North as we see them today, and the first is not always ob- America which includes the major divisions of systems vious from the second. A case is shown by the Mon- from Upper Cambrian through the Devonian. The toya Group of New Mexico. In some exposures, the thicknesses of these intervals have no time significance Second Value and the Aleman are distinct, and we and intervals unrepresented in New Mexico sediments have reason to believe that they are separated by a have been reduced in thickness to permit fuller repre- general period of uplift and erosion. Yet where, as in sentation of the New Mexico section. the Sacramento Mountains or in the Mud Springs Mountains, both show advanced dolomitization, lithic differences are obscured, only previously silicified fos- SEQUENCE OF EVENTS sils are retained, and the two units may be so fused "These things," the Golux said, "I hope are true." that it is difficult and in some sections impossible to Thurber—the 13 clocks point out the contact. 1. Deposition of Dresbachian sediments (earliest Interpretation has depended to a large extent upon late Cambrian) in the region athwart the southern the faunas, which have made possible correlations with New Mexico-Arizona border. It is not yet clear other regions. Yet there may be regional peculiarities whether this is a continuation of deposition which be- in zonation, and regions such as New Mexico, which gan earlier in Middle Cambrian time in southern Ari- may be invaded by faunas from both eastern and west- zona, or whether it marks a separate invasion of the ern geosynclinal belts, are particularly apt to show sea. Some complexity of events is suggested by the some zonal anomalies. In some cases established zona- presence of the Cedaria zone, absence of the Crepi- tions have held well. This is particularly true of our cephalus zone, and indications of the next two, the Cambrian. The Canadian, however, shows a faunal Aphelaspis and Dunderbergia zones. succession including mixtures of eastern and western 2. Early Franconian beds of the Elvinia zone, gen- elements, with some endemic features. erally widespread in North America, have been found With closer scrutiny, almost none of the older for- only in one locality, at White Signal, but may be rep- NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 1 1 3 resented by barren beds at Lone Mountain. This Hatchet Mountains, and continue eastward, being period of deposition is greatly restricted. represented largely by calcarenites. In the extreme east 3. Eoorthis zone. Deposition was possibly continu- at this position are dolomites with Apheoorthis cf. ous from the preceding interval into this one, but de- emmonsi. It is not yet certain whether these beds are posits cover a wider area ranging from the Silver City equivalents of the Kainella zone or whether they are region to the Hatchet Mountains. an initial phase of Middle Canadian deposition. 4. Apparent elevation in the succeeding interval, 10. Demingian deposition, comprising the sequence marked by the Conaspis zone (restricted) and the of first endoceroid, first piloceroid zones, oolite, Bridge- Taenicephalus zone. ites reef and gastropod beds above, is general in New 5. Late Franconian deposits of the Ptychaspis- Mexico. At El Paso the beds above the oolite are Prosaukia zone, divisible into three subzones. These wanting. are well developed in the Caballo, Mud Springs Moun- 11. Minor emergence in late Demingian time was tains and on the east side of the Black Range, are confined to the El Paso region and involved nondepo- represented by nearly barren, dominantly glauconitic sition or removal of beds above the oolite. beds in the Silver City region, and continue west into 12. Widespread deposition of Jeffersonian lime- Arizona. There is some indication that these beds may stones. Deposits are thick and contain many stro- be limy in the extreme southwest, in the Chiracahua matolitic beds, particularly well developed in eastern Mountains. sections. 6. Trempealeauan deposition is known only in the 13. A minor break, known only in the east, followed Silver City region. Seas were more restricted, and de- by Cassinian deposition. posits arc conspicuously cross-bedded, coarse sand- 14. Cassinian deposition continued locally to the stones. Presumably New Mexico was emergent east close of the Canadian. of the Black Range. 15. General emergence with warping, and erosion Question: Is the marked faunal change at the top of the El Paso. Warping makes depth of erosion some- of the Cambrian the result of uplift and withdrawal what irregular, but it penetrates increasingly lower of the seas, which then return, bringing in a new asso- levels to the west and to the north. Precise dating is ciation of organisms, or is this a general biological not yet possible. Erosion may have begun as early as change of continental or world-wide significance with- Whiterock and its end is probably no older than Black out a demonstrable cause? This is a question which River. may well be repeated at several other faunal breaks in 16. Deposition of dominantly sandy beds, the ap- the section; as yet we have no sure answer except that parent Harding-Winnipeg equivalents. we are certainly dealing with widespread rather than 17. Elevation, erosion, and reduction of these beds local phenomena, and such changes can occur in re- to mere scattered remnants. gions in which there is no demonstrable serious gap in 18. Red River deposition, originally continuous deposition. north to Winnipeg and Greenland is dated as Late 7. Early Gasconade deposits (Van Buren equiva- Trenton and Eden. lents?) arc dominantly sandy beds in the east, with 19. Elevation, and erosion of the Red River surface, interbedded thin limestone lenses in the central part, probably occupying much and possibly all of Maysville and with dolomites between lower and upper sand- time. stones in the western part of the state. The existence 20. Par Value-Aleman deposition, dominantly dark of correlatives of this interval in Arizona is yet dubious. cherty beds, occupying early Richmond time and pos- 8. Later Gasconade deposition of limestones, largely the Sierrite Limestone, which, locally, grades up from sibly beginning in the late Maysville. the Bliss by a decrease first of sand and then of glau- 21. Minor elevation, producing at least local erosion conite. The Sierrite Limestone shows odd variations of the Aleman surface. in thickness. It is possibly wanting in the southeastern 22. Raven-Cutter deposition, which shows evidence sections, and the greatest thickness is in the Mimbres of onlap from southeast to north and west on the Ale- Valley. man surface. 9. Later Gasconade deposition, absent in most of 23. Elevation and erosion, beveling the Montoya eastern North America and represented there by an surface. erosional break at the top of the Gasconade and its 24. Restricted sediments of probable Early Silurian equivalents, is marked in the Utah-Nevada sections by age. A break at the top is not clearly evident. deposition of zone D, with Kainella and Leiostegium. 25. Middle Silurian deposition, Clinton, possibly Such beds are well developed in New Mexico in the continuing through the Lockport. Exact age-range of 114 NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE the Fusselman is not yet precisely known, but there is sediments. The supposed land mass separating the no indication of Upper Silurian in this region. Early Paleozoic of New Mexico from that of Colorado 26. Elevation and erosion, extending through Early was traversed by seas and sediments several times, pos- and most, if not all, of Middle Devonian time. The sibly in the Franconian, certainly in the Canadian, Fusselman was, by this erosion, restricted to southern Red River, and Richmond with intervening periods of regions, so that in the northern extent of the early elevation and erosion. Possibly this occurred again in Paleozoic the Devonian lies on the Ordovician. Warp- the Silurian, and it certainly did in the western Devon- ing of the erosion surface of the Ordovician cannot be ian in the Ouray and Percha. dated precisely, as it has been found only where no Fusselman is present. Both warping and erosion may SHANDON-BLISS FORMATIONS have been pre-Fusselman, but both or either could The basal Paleozoic of southern New Mexico con- also be post-Fusselman. The region was again faulted sists of dark-weathering, sandy beds which, when seen slightly later, producing some unplaned faults, which at a distance, form a prominent black band between are possibly connected with sinking and return of the the pink-weathering granites of the Precambrian and seas in Onate time. the light-tan to gray-weathering El Paso slope above. 27. Submergence and Onate deposition. The unit shows wide variation. Conspicuous are sandy Elevation and erosion of the Onate surface prior 28. ledges which weather black, with stains of green, red, to purple and yellow from iron and other minerals. Glau- 29. Sly Gap deposition. (Ithaca and Naples equiva- conite is common. There are beds of red-weathering, lents) Frasnian. ferruginous sandstone and beds of quite pure hema- 30. Contadero deposition, late Frasnian, Chemung tite. There are shaly layers, dolomitic sands, in some equivalents. of which a light brown-weathering, dolomitic sand 31. Thoroughgood deposition, known only in the contains pebbles of darker-weathering, dolomitic sand- north San Andres with a remnant in the Sacramentos, stone. There are, particularly in the Caballo Moun- Early Fammenian. tains, thin layers of pure limestone which may be 32. Planation of the Thoroughgood surface. dolomitized locally. Toward the west, a considerable 33. Deposition of the Rhodes Canyon shales. interval of moderately sandy dolomite is found. There 34. Elevation and erosion of the above, with plana- are sedimentary quartzites which may, at the base of tion extending in some places down into the Onate, the Paleozoic, contain Precambrian pebbles. and removing it locally. This interval was assumed to be all one depositional It is still problematical whether the Bella-Box mem- unit in New Mexico, a view which recent findings have ber of the Percha contains some black shale equiva- opposed. It was first named, in New Mexico, the lents of the older Onate and Sly Gap. "Shandon quartzite," from exposures in the southern 35. Deposition of the Percha, late Fammenian. Caballo Mountains, but this name was generally sup- 36. Early Mississippian deposition, Caballero For- pressed in favor of "Bliss sandstone" which was mation, widespread, and with remnants continuing proposed a few years earlier from exposures in the north of the earlier Paleozoic as the Caloso Formation. southern Franklin Mountains. 37. Possibly uplift and minor erosion prior to Lake The Bliss was assigned to the Cambrian on the basis Valley deposition. of early reports of Lingulepis acuminata, a species first 38. Lake Valley deposition, continued north as the described from the Potsdam Sandstone of New York Kelly of the Magdalena area. where it is Dresbachian in age. Some reservations exist, 39. Meramec deposits confined now to extreme however, because linguloid brachiopods are wide-rang- southern New Mexico, but with remnants of the Ar- ing types, and not necessarily reliable guides as to age. royo Penasco in northern New Mexico. Paige (1916) cites Ptychoparia and BilIingseIla from 40. Chester deposition now known only in the ex- the Silver City region which would support Cambrian treme south. age, but the specimens cannot be found, and both 41. General elevation and erosion, truncating pre- determinations are now suspect.* Pennsylvanian beds to their northern limits with re- The Van Horn region of Texas yielded from the moval of Mississippian over much of the Rio Grande "Bliss" gastropods and cephalopods of unquestionable valley. Gasconade age, a find which required review of the age Much of the geological history of New Mexico is involved in periods of uplift and erosion which have *Ptychoparia was then used very broadly. Today it is restricted altered the original picture of deposition materially to Middle Cambrian trilobites. Billingsella has been found, though it is rare in the Silver City region, and the form was more probably and are responsible for the present restriction of the the commoner Eoorthis. NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 115 of the Bliss in New Mexico and elsewhere. A further The whole of the eastern Bliss may be Cambrian. collection from the same locality yielded impressions Recent collecting has yielded true Lingulepis from the of endoceroid siphuncles, showing that the first endo- southern Franklin Mountains, and though the lingu- ccroid zone of the El Paso, ordinarily at least 100 feet loids remain suspect, this find would tend to support above the Bliss, is included in it. The lowest El Paso such a view. While we know age relationships of much there contains the fauna of the first piloceroid zone. of the western "Bliss" the evidence is ambiguous for The recent significant finds in New Mexico include the eastern Bliss, which contains the type section. ( 1 ) discovery by Northrop and students (see Kelley Flower (1959) restricted Bliss to the Canadian beds, and Silver (1952) of the brachiopod Apheoorthis and proposed the name Tonuco for the Cambrian beds, a dendroid graptolite which proved to be Dictyonema and revived the name Shandon for sections where flabelliforme anglicum: (2) discovery of late Francon- both Canadian and Cambrian may be present (figs. 1 ian faunas in Tonuco Mountain, Cable Canyon, and and 2). Readjustment of formational names may be exposures on the east side of the Black Range: (3) required when the age of the type Bliss is definitely discovery of Gasconadian, Lower Canadian, faunas established. A temporary measure might be to restrict above, including the Apheoorthis, Symphysurina, and Bliss to the eastern sections of still uncertain age, and the Dictyonema: (4) discovery of early Franconian to propose another term for the demonstrable Cana- beds in the Silver City region, with Trempealeauan dian portion. beds in the same general area: (5) finds indicat- The faunal zones expressed in the Cambrian Corre- ing earlier beds, Dresbachian, essentially athwart the lation Chart (Howell and others, 1944) have under- southern New Mexico-Arizona border. gone some modification, and from one region to an- The prevalence of glauconite and other features sug- other there are some minor differences in names ap- gest very slow deposition, so slow as to destroy much plied to the zones, and to relative placement of some of the original faunal evidence. It is difficult to estab- horizons as "zones" and others as "subzones", but the lish the geological history, for absence of faunas may general succession is one which has shown a surprising not mean absence of deposits in the time interval in- validity in the light of critical study. A good summary volved. From these finds there has emerged the general in Lochman-Balk and Wilson (1958) shows the gen- picture shown in figure 3. Knowledge is still incom- eral faunal successions and the different faunas de- plete, and the most vexing problem remaining is that veloped contemporaneously in disparate environments. of the "Bliss" of the Sacramento, San Andres and Figure 3 shows the faunas found and the portions of Franklin Mountains. There the main constituents of the Cambrian in which deposits can be established in the faunas are linguloid brachiopods, which seem New Mexico. Future finds may alter the picture. allied to Linguella deltoidea (Flower, ms) of the Gas- Faunas are extremely sparse, and only a combination conadian part of the Bliss. These forms are confined of work and luck has yielded the present results. The to the upper part of the Bliss. The lower beds are section at Carbonate Hill yielded numbers of unidenti- barren, and further, fail to show such Ethic contrast fiable free checks, but after extensive work a piece was as is found in the Caballo Mountains separating Cam- found which bore not one, but two identifiable heads brian from Canadian beds. The evidence suggests that of an Eoptychaspis. the whole of the type Bliss is Canadian. This usage 1. Dresbachian faunas have been found only in the is employed in our present diagrams. Bliss is used for extreme southwest. Flower found material at Dos Ca- Canadian beds, Tonuco (Flower 1959) for the Cam- bezas determined by Balk as representing the Cedaria brian, and Shandon to include both units. Subsequent zone. Sabins (1957) found trilobites indicating the finds may prove the lower beds to be Cambrian. Aphelaspis zone and the Dunderbergia zone (formerly While no clear sedimentary break exists in the south- cite as post-Aphelaspis zone). ern Franklin Mountains, the "Bliss" of the Hueco The Crcpicephalus zone is unrecognized there, but Mountains consists of two contrasting elements. A it is generally far more widespread over North Ameri- lower light gray, medium to coarse-grained sandstone ca than the zones immediately below or above. contains marble-sized pebbles of darker sand, weathers 2. The Elvinia zone at the base of the Franconian with hues of pink and mauve, and occupies the lower is found in 24 feet of ferruginous sandstone at the three-fourths of the sandstone interval. Above, with an base of the section in an outlier southwest of White abrupt contact, are fine-grained black-weathering sand- Signal. It yields abundant Carnaraspis. It is possible stones with abundant linguloid fragments. Traces of that the basal beds, so far barren, at Lone Mountain this facies can be found in the lower part of the type are equivalent. Bliss of the southern Franklin Mountains, but without 3. Eoorthis is a genus which is amazingly wide- a similar sharp sedimentary break below it. spread and confined to one narrow horizon. It is cur- 116 NEW MEXICO GEOLOGICAL SOCIETY—SIXTEENTH FIELD CONFERENCE rently grouped as a subzone of a broadly defined Co- Eoorthis is found. One piece of sandstone was found naspis zone. The grouping depends on the affinities of with a Camaraspis on the bottom, and an Eoorthis on associated trilobites in other regions, but only the the top, with no apparent bedding plane between

Column I Column 2 Column 3 Column 4 1906 — 1917 1917 — 1952 Flower—this paper A Standard Column for North America Bella Box BoBox Perch° Percha UPPER Silver Ready Pay Ready Pay Rhodes Canyon (Percha of Stainbrook) I Fammenian — PERCHA Thoroughgood ■ z Contadero 0 (Devonian) Contadero > i Frasnian w Sly Gap Sly Gap 1?

Onate Onate late Middle ? FUSSELMAN FUSSELMAN Middle FUSSELMAN SILURIAN (Silurian) (Cutter variably included) Lower

Poleofavosites -P, Raven Cutter Valmont late 0, Hebertella V , if0 , Rhynchotrema I, Coral Zone _ Anataphrus o (Ordovician) 0 Cooks Range Upham Second Value EDEN— cr UUphamp h Second Value (Red River) LATE TRENTON Cable Canyon Cable Canyon unnamed Harding equivalents Black River ? (remnants) C Florida Cassin i an B2b Scenic Drive 3rd piloceroid McKelligon 2nd piloceroid Jeffersonian McQueenoceras Pistol Range EL PASO Gastropod beds Snake Hills — Bridgeites reef Mud Springs 0 Bat Cave (Canadian) Oolite Jose < 1st piloceroid Victoria Z Demingian 1st endoceroid Cooks < Big Hatchet S i e r r i t e Sierrite Gasconad an Bliss %.S" Trempealeauan BLISS 0 -9 A) Bliss Tonuco 4f X) ("Cambrian") ,6) Franconian -P/ -P 1 1, Dresbachian

FIGURE 1 Development of Formational Units in New Mexico NEW MEXICO GEOLOGICAL SOCIETY—SIXTEENTH FIELD CONFERENCE 117

General Classification New Mexico Sediments

.-.B0 x _- - - —__ --L-- -- o ° — P Conewangoann _ — -- Recly-__ e r c Rhodes Canyon h Thoroughgood a Upper Chautouquan ? Con 1 ade ro Z __ --Sly Gap------"-= — p ^= ? O Senecan — --- ay W — _-0-rielti7=--- CI Erian Middle Ulsterian Oriskanian Lower H elder berg ian Water lime Cayugan Salina --ameralI NAI■airmr Guelph 7INIVI■MIMI■I --■IIIE■■11/411111/1111110%■ C -or ■11■IIIIIIII•"— Niagaran Racine c ne ..,,,,miwaramaim Fusselman Slail■•— -...MIfillIMIAIIII■IANIA• _J Clinton A=WWA11WMIIAMM•■-- IIIIIIII■IMIIi■..----- MAINEfia•••••••--- Alexandrian Medina I■■■■-- Cutter Raven almOnt_ Richmond _ Zeman -Far Nalues. Cincinnatian Maysville _ IM.—...■■••1= Cobourg - Eden Upham /NW (..) Second Value Cable Canyon.-- > Trenton 0 Mohawkian River 0 Black Harding-Winnipeg erosion remnants fr Porterfield . 0 Ashby Chazyon Marmour M Whiterock L Odenville K C lialb.... Cassinian Black Rock J B2b MM."- Smithville I AMIIII■e■__ eras/on Su foc Powell 11 1 Cotter 1111 Z Jeffersonian III i 11111 1 Theodosia Beal I 1 1 il I 11_11 < JC : 11 E Rich Fountain I I 1111111 gastropod beds °I MM.. Z reef AgallaillIMMIM. =NM= , 11" EL PASO GROUP 4:1 Demingian oolite III I 1 1 11111111 C.) B1 i I L 1 I pil. 11 II 11 I 1 11 1 1 1 1 1 1 1 11 11 1 1 1 1 1 I end. 1 11 I I I 1 1 Kainella zone D ---7.- I I 1 I 1 I I I I 1 I moo= Sierrite mmlimm Gasconadian Gasconade C momma•■ IMEN■IM ■IMEMIN■∎ ∎ Van Buren A-8 Bliss Trempealeau ..:..V

Croixian . ."`<::..:1 <— Franconia 0 cc . :.• . co ° --Shandon Dresbach 0 ...------Albertan 0 < (..)

FIGURE 2 Correlation of the Early Paleozoic of New Mexico 118 NEW MEXICO GEOLOGICAL SOCIETY—SIXTEENTH FIELD CONFERENCE

Zones and Subzones

a Dictyonema flabelhforme anglicum / X X X X h . 0 \ 6. / 0 ci Symphysurin I X X X X X X X‘ co 1L L L L / Co Apheoorthis mehta X X X X X _ _ __•••x -, / 0 / o 1 <: o / 1 Saukio I h h X X i ,z \ A.` ° / . ..-/

Prosaukia-Briscoia X W h w X 1 Prosaukia 0 o Ptychospis strict° • X h h X - - Ptychospis granulosa - - - - - _. P -- Ptychospis _ Stigmocephalus oweni . X / 0 0 O. Taenicephalus 0 ct a Conospis Conaspis 0 ..• - kk Eoorthis / X X Xsi —_ , • -- El y inia , X -- -....- - -- -- Dunderbergia / S

o Aphelaspis S .0 G..". 0 o Crepicepholus o f-. ... 0 Cedaria k F .. _

FIGURE 3 Faunal zones of Cambrian and Early Canadian found in New Mexico

X-diagnostic fauna found L-linguloid fauna H-horizon recognizable without faunas W-Westonia P-probable development of fauna B-Billingsella S-reported by Sabins 1957 F-reported by Flower Dotted lines suggest regional extent of depositional units. In the Gasconadian no faunal succession is implied by the vertical distribution of the faunal elements, except that the Dictyonema is always found just below the top. them. At White Signal Eoorthis occupies 9 feet of us above. No evidence of these two subzones has been gray, tan-weathering sandstone of medium texture. At found anywhere in New Mexico. For a time I thought Lone Mountain it occupies hematitic sandstones 20-28 they might be present in glauconitic sands above the feet above the base of the Paleozoic. Zeller has re- Eoorthis zone, but the whole of this interval is reason- ported the genus from the Hatchet Mountains. ably assigned to the succeeding horizons, as indicated 4. There is no general agreement as to nomenclature by the find of a Billingsella in the Lone Mountain of the next two subzones. I have regarded the lower section. one as characterized by true Conaspis ( the broader 5. The Ptychaspis-Prosaukia zone is divisible into Conaspis zone was based on an older and somewhat a number of subzones. The nomenclature arises from wider usage of that generic name) , with Taenicephal- the overlapping of the genera in these several sub- NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 119 zones. The former correlation chart indicated Briscoia occurs there (Stoyanow, 1949) in a limestone, and and Prosaukia as separate zones, a view now aban- Sabins reported Billingsella, diagnostic of this horizon, doned, and the first Dikellocephalus zone is now in a limestone also. treated as Trempealeauan. Present collections are far Known Trempealeauan deposition is confined to from satisfactory owing to scarcity of good specimens, the Silver City region and consists of rather coarse, and precise zonation is obscured by poor exposures. cross-bedded sandstones. The faunas from the east side of the Black Range come from a poorly exposed section, and most speci- GASCONADIAN SANDSTONES mens are in loose pieces. Eoptychaspis, a genus of the These sandstones, to which the name Bliss is ten- Stigmacephalus zone, has been found only in the Car- tatively applied, show considerable regional variation. bonate Hill section. The P. granulosa horizon is sug- In the Caballo and Mud Springs Mountains 2 feet of gested by forms obtained from Pierce Canyon in the crossbedded coarse sand at the base grade up into a suc- Black Range, where overlying zones are better de- cession of thin sandy beds alternating with silty glau- veloped. Ptychaspis striata and a Chariocephalus are conitic layers, and some dolomitic sandstones which abundant in a 2-foot bed on Tonuco Mountain, and may contain pebbles of sandier, darker material. There both genera have been found in the Black Range. A are thin beds and lenses of limestone, 4 inches thick 1.5-foot bed in Cable Canyon of the Caballo Moun- at the maximum. In Cable Canyon these are common- tains yielded large Prosaukia and Briscoia, and the ly fossiliferous, and some are composed of fragments same horizon has been found in the Black Range. of Symphysurina, Apheoorthis or Girvanella. In Cable Both of these upper subzones yielded a broad Billing- Canyon these lenses are good limestone; elsewhere sena in abundance. The same brachiopod was also they show recrystallization or dolomitization. Near the found in dominantly barren glauconitic beds at Lone top, a few feet of yellow-green silt and shale occur, Mountain. Billingsella was found by Sabins in the Blue yielding Dictyonema flabelliforme anglicum. This Mountain section at the Arizona border, where it oc- shale, and the graptolite, persist on the east side of the curred not in sandstone, but limestone which he called Black Range. On the west side, the shale horizon is El Paso. This is the same species which occurs with recognizable as far as Lone Mountain, but the grapto- Prosaukia at Cable Canyon. lite has not been found. Light gray, light-tan-weathering, coarse cross-bedded In the Caballo and Mud Springs Mountains the sandstones at Lone Mountain and White Signal have Bliss-El Paso contact is gradational, marked by a de- yielded a Trempealeauan fauna. The Cambrian Corre- crease in sand and glauconite. On the east side of the lation Chart indicated a number of zones in the Trem- Black Range the top of the Bliss is a slightly calcar- pealeauan. It is now recognized that varied facies in eous sandstone, weathering to ledges with rounded a section with sandstones, siltstones and some dolo- surfaces, and yielding Symphysurina. The same sand- mite control the faunal succession in the Minnesota- stone is traceable through the Cooks Range into Lone Wisconsin region where these zones were established. Mountain. No continent-wide zonation within the Trempealeau- In the Mimbres Valley and at Lone Mountain and an has been established. At Lone Mountain this zone White Signal, sands mark the base and top of the occurs in 12 feet of sandstone, the uppermost unit in Bliss, but the middle portion is a nearly sand-free 89 feet of Cambrian, overlain by 72 feet of Gascona- dolomite. dian, sandstone. Thicknesses (in feet) for the basal sands, Shandon, Figure 3 suggests a picture of the depositional his- in these regions are: tory consisting of several discrete periods of deposition. The first, in Dresbach time, is confined to the south- Tonuco Bliss ern Arizona border. The second in early Franconian Tonuco Mt. 60 69 time, is at first restricted to White Signal, but later Cable Canyon 67 83 spreads throughout the Silver City region south to the Mud Springs Mtns. 72 91 Hatchets. Presumably, the Conaspis and Taenicephal- Carbonate Hill 68 95 us subzones represent a short period of emergence. Lone Mt. 89 72 The Ptychaspis-Prosaukia interval thus appears as a White Signal 123 116 distinct period of invasion of the sea, depositing dom- Cooks Range 67 99 inantly sandy beds in the region of the Caballos west to the east side of the Black Range, but dominantly EL PASO GROUP barren glauconitic sands in the Silver City region. Re- The El Paso Group consists dominantly of calcilu- lationships with Arizona are not clear, but the fauna tites, and weathers light gray to tan, commonly form- 1 2 0 NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE ing a slope between the dark sandy Bliss below and the faunas are in the process of description. Kelley and more massive cliff-forming Montoya above. Its thick- Silver (1952) raised the El Paso to a group, and recog- ness ranges from 1200 to 75 feet largely as the result nized two formations in it: Sierrite Limestone, the of later erosion. Wide lithic variations can be observed lower thin-bedded calcilutites with stylolitic beds and in short intervals. The calcilutites may be massive or siliceous seams, but generally free from chert, and the thin bedded. Frequently calcareous shales separate the Bat Cave Formation, the upper more massive beds of more massive beds, but these layers are usually cov- varied lithologies, with cherts and stromatolites. The ered. Stromatolites are common from the base of the boundaries proved gradational on lithology, and the Middle Canadian upward, and occur as biostromes, two units are unsatisfactory. The zones of Flower have and some bioherms. Interstices in the algal reefs con- been given geographic names (Flower, 1964) and tain poorly sorted material, fossil hash, calcarenites, or treated as formations, but difficulties in placing bound- pebble beds. Horizons with limestone pebbles and aries precisely are such that member status would be some sandy layers may occur throughout. Dolomitiza- equally acceptable. Study of these intervals has indi- tion is local, but in eastern sections, several horizons cated some variations in the history of deposition, with are persistently dolomitic. breaks in the section particularly evident in the more With the underlying Canadian beds included in the easterly exposures. Bliss, the El Paso represents nearly continuous deposi- tion throughout Canadian time. This interval is here LOWER CANADIAN-GAS CONADIAN regarded as a system apart from the Ordovician. This The Lower Canadian begins with sandy beds, in- interval of time involves complex events of varied cluded in the Bliss Sandstone. The transition into the types of deposits, and an intricate history of deposi- El Paso is gradational, and is marked by a decrease in tion and erosion, with changing patterns of the seas. first sand and then glauconite. The Gasconadian part For eastern sections a standard section is accepted in of the El Paso is composed of thin beds of calcilutite, the Ozark uplift. There the following formations are often dolomitized. Faunas are poorly preserved, but recognized: include Symphysurina, Apheoorthis melita, Lytospira Black Rock gyrocera, a few Ellesmeroceratidae, Girvanella and Smithville some undescribed tubular algae. These beds are thicker Powell in the northern than in the southern exposures, and it Cotter may be that none of these beds are present in the El Theodosia Paso section. Previously assigned beds may belong to Rich Fountain Jefferson City Group an overlying interval. Rouhidoux In the Hatchet Mountains the Sierrite lithology is Gasconade not typically developed. Its equivalent may be repre- Van Buren sented by some beds altered to massive dolomites. Above them are massive dolomites interbedded with The faunas which characterize these formations dolomitic shales which have yielded Leiostegium and have been only partly described. A nearer and much Kainella, indicating the position of zone D of the better understood section (Cloud and Barnes, 1948) Utah-Nevada sections, and still higher beds with is that of the Llano uplift of Texas. Unfortunately, spheroidal cherts. These beds, thinning, can be traced this section has been eroded to a level in the later part into the more eastern sections, and seemingly grade of the Jefferson City Group, but enough is known to into the Sierrite unit below, but differ from it by the supply some basis for correlation. occurrence of minor chert, and the dominance of cal- In northern Utah are the Garden City and Swan carenites. This interval is not recognized in the eastern Peak Formations, and in western Utah and Nevada the sections. Pogonip Group. These formations have been zoned by Ross (1951) and Hintze (1953), with the zones indi- MIDDLE CANADIAN-DEM INGIAN cated by letters. Their zonation is based primarily on trilobites. Correlation of the El Paso with these west- The Middle Canadian part of the El Paso shows a ern sections is still incomplete, because the El Paso varied Ethic section and a signficant succession of does not yield many trilobites. There is some indica- faunas. The units hold well over the state and are in tion that the trilobites obtained belong to another ascending order: realm and some genera, as Leiostegium, show some- First cndoccroid zone (Cooks Formation) . Calcilu- what different ranges. tites in which there appear stromatolitic biostromes, Flower (1958, 1959) zoned the El Paso, and the with calcarenite and fossil hash in the interstices, and NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 121

some calcarenites generally light in color. The horizon have been named the Pistol Range member,* and can bears the first endoceroids known in the section asso- be traced widely. The succeeding beds show a wide ciated with the brachiopod Diaphelasma, and assem- variation in lithology but include at El Paso massive blage of gastropods including such forms of Lower stromatolites, some true bioherms replete with sponges Canadian aspects as Ophileta and Ozarkina, and a and piloceroids—the second piloceroid zone. The unit new form allied to Liospira ( identified erroneously as is widely developed, but in some places is not obvious- Raphistoma trochiscus in some early reports) . The ly stromatolitic. At El Paso there is an alternation of beds contain minor chert. stromatolitic beds, and massive and thin-bedded lime- First piloceroid zone (Victorio formation) : This is stones for over 400 feet. In the Florida Mountains and an interval characterized by dark-weathering massive Cooks Range, where these beds are well developed and beds with abundant stromatolites, containing pilocer- of comparable thickness, stromatolites are less conspic- oid siphuncles distinguishable from the siphuncles of uous. Often this horizon may yield no obvious fossils the first endoceroid zone by their larger size, and forms other than sponges and stromatolites. The fauna shows showing curvature or rapid expansion or both. Sponges relationships with the Jefferson City and Cotter. are conspiciuous for the first time and silicified frag- ments showing a fenestrate pattern suggest fenestellid CASSINIAN bryozoa. No bryozoa are known in the Canadian. The Cassinian portion of the El Paso Group is found Some beds in interstices in the biostromes are lime- in units B2b and C of Cloud and Barnes. In the south- stone conglomerates. Ordinarily, these conglomerates ern Franklins it is marked by conspicuous cross-bedded are readily recognizable from the darker, dirty, poorly dolomitic sandstone at the base, passes upward into sorted sediments which make up much of the material arenaceous dolomites, overlain by 200 feet of thin- between the stromatolites. bedded limestone, the Scenic Drive Formation. The Oolite ( Jose Formation) . Here are as much as 40 uppermost beds are dominantly ledge-forming calcar- feet of a most distinctive, dark gray to black weather- enites with some calcilutites and orange-weathering ing limestone unit. The limestone is oolitic, and some calcareous siltstones, the Florida Formation. beds are crowded with fragments of an asaphid tri- The Scenic Drive Formation is unquestionably the lobite. Other beds include pinkish weathering nod- equivalent of the Smithville and Fort Cassin Forma- ules, probably algal in origin. Small gastropods are tions. Correlation to the west is less precise. It certain- conspicuous. ly includes the general fauna of Zone J of the Wahwah Bridgeites reef, (Mud Springs Mountain Forma- limestone, though the Pseuclocybele fauna appears to tion) : Succeeding the oolite with a few feet of transi- be confined only to its upper half. tion of light thin-bedded calcilutites, is a massive The Florida Formation is unit C of Cloud and stromatolitic reef, usually 25-35 feet, generally cliff Barnes. In the Franklin Mountains it contains con- forming, and with a sparse fauna, the most characteris- spicuous orange weathering silts in addition to calcar- tic form of which is a large flat gastropod Bridgeites enites and some calcilutites. The silts are absent in the (ms.). Florida Mountains. This bed contains a distinctive The uppermost unit is thin-bedded nondescript cal- fauna which Cloud and Barnes (1948) regarded as cilutites in places filled with small gastropods, but also equivalent to the latest Canadian, the Odenville of containing the trilobite Leiostegium. These calcilu- Alabama and the Black Rock of the Ozarks. The brach- tites, which may be 45 feet thick in the Cooks Range, iopods, larger than those below, and quite distinc- are the Snake Hills Formation. tive, include Syntrophopsis, and Tritoechia. There are These units prevail throughout the New Mexico some gastropods, including Maclurites cf. M. sordida, sections, but to the southeast the upper beds are want- and the cephalopod Buttsoceras. This general fauna is ing, and at El Paso sand separates a thin remnant of found in the Wahwah Limestone of western Utah in the oolite from beds below, and there is another sand a few feet of calcarenitc just below the Hesperonomi- above which is the base of the Jeffersonian. ella minor bed. The Buttsoceras has been found in the Garden City Limestone, in upper cherty beds below JEFFERSONIAN the upper 20 feet with the early Whiterock Rossoceras- Williamsoceras fauna. This is the youngest Canadian MCKELLIGON FORMATION known, and is not, as has been suggested, post- At El Paso this unit begins with a sandstone over- Canadian. lain by a massive stromatolitic biostrome, dolomitized This was named from the pistol range on the Scenic Drive at and characterized by abundant tiny endoceroid siphun- El Paso. The name was no sooner published than the "Pistol Range" cles, none much over 1/4 inch across. These beds was changed to the "Police Academy." 122 NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE

POST-EL PASO PRE-MONTOYA EROSION moved all of the earlier Paleozoic, but must have cut Sections of the El Paso in New Mexico show in deeply into the then-existing pre-Cambrian surface. general a beveling of the El Paso surface beneath the The absence of Early Paleozoic in northern New Montoya to depths which increase in general north Mexico and southern Colorado is the result of several and west from the Florida and the southern Franklin major periods of erosion of which this is the earliest Mountains. The Cassinian portion of the El Paso is clearly demonstrable, though an earlier one in Trem- present in the southern Franklins ( though it is gone pealeauan time is suspected. at Ranger Peak), in Beach Mountain in Texas, and in Dating of the erosion interval on the El Paso surface the Florida Mountains in New Mexico. The Hatchet is uncertain. It is older than the Second Value which Mountains show only part of the McKelligon Forma- equates with the Rcd River. On it are remnants tion, enough to establish the development of the sec- of sandy beds which the writer has tentatively cor- ond piloceroid zone. The same is true of Round Valley related with the Harding Sandstone of Colorado, in the Chiracahua Mountains, north of Portal, Ari- rather, than, as previously proposed, with the Simpson zona. At Dos Cabezas we find the first piloceroid zone of Oklahoma.* at the top, and at Clifton and Morenci nothing above The El Paso surface may bear remnants of more the first endoceroid zone is preserved. The Montoya is than one period of deposition. An odd endoceroid unknown at Dos Cabezas, so later erosion may also be siphuncle found in the pre-Second Value remnants involved. However, a remnant of Montoya found at proves to have only one known American relative, a Clifton, Arizona, suggests that pre-Montoya erosion is new genus known from one species in the Juab Lime- responsible for the El Paso erosion surface there. To stone (lowermost Whiterock) of western Utah. the north, the Cassinian is absent in the Cooks Range. The sections around Silver City and the Mimbres val- MONTOYA GROUP ley show a good development of the second piloceroid zone, but not the top of the McKelligon formation. The Montoya is dominantly a massive, cliff-forming At Cable Canyon in the Caballo Mountains the El dolomite. Recently Kelley and Silver (1952) raised it Paso top beds are in the McKelligon formation. At to group status and treated its divisions, which are Mud Springs Mountains only the base of this forma- quite distinctive, as formations. Generalized sections tion is present, and on the northeast side of the San of the Montoya are shown in Figure 4. Mateo Mountains there are 75 feet of El Paso below The divisions in Ncw Mexico may be summarized. the Cable Canyon, representing part of the Lower Ca- (1) Unnamed remnants, probable Harding equiva- nadian. Similarly in the San Andres Mountains there lents. (2) Second Value massive cliff-forming beds, is a rapid northward thinning. At Rhodes Canyon the with chert minor. A basal unit, the Cable Canyon top lies in the higher beds of the Demingian, at Sly Sandstone, is a conspicuous dark-weathering coarse Gap only the Lower Canadian is present. sandstone in dolomite. Above, massive dark beds com- There is a lithic, faunal and zonal accord between prise the Upham Dolomite (a limestone locally), the El Paso of New Mexico and the Manitou of Colo- which may have some chert, as large spheroidal masses, rado which is not shared by the known Ordovician to near the top. Restricted to the Cooks Range and Lone the east (Arbuckle) or west (Garden City and Pogo- Mountain is a white granular calcarenite, the Cooks nip) and which suggests that the beds were laid down Range member. (3) The Aleman-Par Value, dark do- in a sea continuous over northern New Mexico and lomites with conspicuous bands of chert. (4) The Cut- southern Colorado where today no early Paleozoic ter-Raven, dominantly light gray, noncherty dolomite. exists. The Manitou shows, just above the red beds The Montoya represents three, probably four peri- with Apheoorthis cf. melita, a good development of ods of deposition separated by intervals of erosion. the first endoceroid zone, and 80 feet higher, of the Earliest are sandy beds of approximate Black River first piloceroid zone. The Manitou, though usually dol- age, probably southern equivalents of the Harding omitized, is Ethically much like the El Paso, a light Sandstone of Colorado. Elevation and erosion has re- yellow to gray limestone as developed in the exposures stricted them to their present small limits. The second of the Sacramento Mountains. The El Paso tends to a period of deposition occurred in Rcd River time, darker hue, of medium to blue grays, in more westerly which can now be dated within the limits of late Tren- sections. ton and Eden, probably in part equivalents. Much of the northward and westward thinning of *Simpson is not at all precise. It ranges from Whitcrock probably the El Paso results from erosion beneath the Montoya to Black River, or at least into the Ashby-Porterfield. In the Simp- son, sand increases to the east, not to the west. Dating of the Hard- Group. The beveling evident in the northern expo- ing is uncertain. It possibly lies in the Ashby-Porterfield, or may be sures, projected farther north, not only would have re- as young as the Black River.

NEW MEXICO GEOLOGICAL SOCIETY—SIXTEENTH FIELD CONFERENCE 12 3

erosion surface Favistello Beatricea Paleofavosites light gray, Raven Cutter fine-grained dol

, —pelecypod zone Richmond minor erosion interval equivalents

Megaripple zone facies change ••• Rhynchotrema capax zone dark gray, medium to coarse - grained cherty Is or dol Aleman Rafinesguina zone Par Value Zygospira zone

••• •ww Anataphrus zone

erosion inter vol Maysville ?

3 Cooks Range member 6 oz• AO al. WO .0 — ••• •111. IND I -EMI I I 1 spheroidal chert I i I ••I i I I I I 1 I I I I I I i —7- upper massive assive I Red River Upham I. 1 I I I I 1 1 I I I ICI I 1 I I calcarenite 1 i 1 I equivalents . i —1— i 1 ii I 1 1 1 i —I 7 Second Value - ...... ,::::.:::::;.:::•4.-...... ::::::.: -- —tr lower massive 1 I I I able Canyon S. I

erosion interval Harding-Winnipeg

...10111NW equivalents

FIGURE 4

Generalized sections of the Montoya Group in New Mexico, showing periods of deposition and erosion, names, lithic variation, and zonation of the units.

1. Rhodes Canyon section 4. Southern Franklin Mountains 2. Hembrillo Canyon section 5. Cooks Range 3. Ash Canyon section 6. Lone Mountain This deposition was followed by elevation and bevel- Cooks Range and 12 feet in the Hatchets. The Hard- ing of the warped surface to varying depths. Par Value- ing itself shows ( Sweet, 1954) an isopach pattern Aleman deposition followed, leaving a series of cherty suggesting beveling of a depressed basin prior to beds, dominantly dolomitic, within which a good zon- later (Red River) depositon. Remnants of a fish- ation is shown both by fossils and lithology. There was bearing sandstone beneath the Bighorn Group are minor elevation and erosion following Aleman deposi- logical equivalents. In Manitoba, some faunal ele- tion. The succeeding Cutter-Raven shows evidence of ments indicate that part of the Winnipeg Sandstone onlap deposition from southeast to north and west. is a probable equivalent, though it is in large part a This brief history is part of a pattern of physical basal sand of the Red River deposition. On the west events which prevailed over a surprisingly wide area, side of Hudson Bay no corresponding deposits are figure 5. The similarity of pattern from New Mexico known. The suggestion in figure 5, that the Gonioceras to Greenland indicates a uniformity of history, and Bay Limestone and the Troedsson Cliff Limestone are the covering of the whole region by seas which left equivalents in northern Greenland, is inferential. Sub- continuous deposits. Harding deposition, dated as ap- sequent uplift and erosion reduced this deposit to proximately Black River in age, was widespread. It remnants preserved in discrete basins. includes the unnamed sandy remnants in New Mexi- A second period of deposition resulted in marine co, usually only a few feet thick, but 10 feet in the deposits of Red River age. Where these are not altered FIGURE 5

Geologic history of the later Ordovician of west-central North America. The Montoya is shown as a local expression of a general pattern extending from New Mexico and Texas to Greenland.

A. Deposits of essentially Black River age. D. Late Richmond deposits. B. Red River deposits. f- apparent fusion of discrete beds by dolomitization C. Early Richmond deposits, may include late Maysville.

1. Sandy remnants, unnamed 13. Cape Calhoun Formation (pars) 2. Harding Sandstone 14. Par Value-Aleman 3. Remnants of fish-bearing sandstones of the Bighorns 15. Upper massive Fremont Dolomite 4. Lower sands in the Winnipeg Sandstone 16. Upper beds of massive Bighorn Dolomite 5. Deposits unknown 17. Stony Mountain Formation 6. Gonioceras Bay Limestone and Troedsson Cliff Lime- 18. Churchill River Group ( Shamattawa limestone) stone 19. Richmond beds of Arctic Archipelago 7. Second Value formation, with Cable Canyon a local, 20. Upper part of Cape Calhoun Formation prevalent basal sandy facies 21. Raven-Cutter Formations 8. Lower Fremont Limestone. 22. Priest Canyon member of the Fremont 9. Lower Bighorn Dolomite, with basal Lander Sand- 23. Leigh member of the Bighorn, with a local massive stone dolomite at top 10. Red River limestone, and local shaly evaporites, most 24. Stonewall Formation of Winnipeg Sandstone a basal sandy facies 25. Red Head Rapids Formation 11. Nelson Limestone and Bad Cache Formation 26-27. Equivalents not known 12. Beds with Red River faunas in the Arctic Archipelago NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 125 to dolomite, they show massive poorly-bedded struc- of Wyoming. In the Winnipeg region, the equivalent ture, with vermicular markings, though there is wide is found in the Stony Mountain Formation, which, variation in details. The Upham Dolomite is massive with its several members, is distinct. This condition and vermicular, particularly in its lower part, and dupli- continues to the north where it passes into a mottled cates, except in the darker color, the Selkirk facies of limestone facies formerly confused with the Selkirk the Red River Formation. The fauna of large Recepta- facics of the Red River. On the west side of Hudson culites, large gastropods and cephalopods, and large Bay the equivalent is in the Churchill River Group corals is much the same from New Mexico to Green- (the former Shamattawa limestone) . Farther north, land though species are different. The uneven thick- beds overlying the Red River may equate with this in- ness, and removal of the upper units of the Second terval at several localities, as the Akpatok Island sec- Value in New Mexico is evidence of a break in depo- tion; and the upper part of the Cape Calhoun of sition at the close of this interval. Where dolomitiza- Greenland is a possible equivalent. tion is advanced, lithic and faunal boundaries between Previously it was thought that deposition was gen- this and the overlying unit may be obscured. This is erally continuous from early to late Richmond, but the true of the Montoya in some New Mexico sections, New Mexico sections show clear evidence of a break. and is common in the Fremont and Bighorn Groups. There is evidence both of erosion of the Aleman sur- The Winnipeg area escaped dolomitization, and here face, and of progressive onlap of the Cutter-Raven the contact is clear. Subsurface work has shown the beds. The break was of short duration, in terms of the presence of evaporites developed in restricted seas at Ordovician column of other regions, and is placed in the close of deposition. Emergence for a significant Liberty or Early Whitewater time. interval of time is suggested. On the west side of The later Ordovician of all the regions show similar- Hudson Bay is the Nelson Limestone which Nelson ities. The beds arc generally light-colored dolomites (1963) proposes to name the Bad Cache Group. containing some shaly zones, and have often been con- In the Arctic Archipelago similar beds and similar fused with the Silurian beds. Darton included part or faunas are known from a number of localities. The all of the Cutter with the Silurian in New Mexico, and most important and most closely studied, are on Baffin it is only recently that the Stonewall of Manitoba was Island. The Cape Calhoun Formation of Greenland demonstrated to be Ordovician rather than Silurian. contains a Red River fauna, and beds both older and Some confusion surrounds separation of Cutter and younger are present but not yet differentiated. Older Aleman on lithic grounds. In part this is due to differ- beds are suggested by V aginoceras, Gonioceras and ences in interpretation, but in some southern expo- Actinoceras of Black River species groups. Koch pro- sures, the upper beds of the Aleman become lighter in posed separating the lower beds as the Troedsson Cliff color, and have been identified with the Cutter. The Formation, but it is not yet possible to say whether this final phase of Ordovician deposition in New Mexico is interval was the sole source of some of the seemingly the Raven-Cutter light-colored dolomites with at least older faunal elements. Certainly the higher beds of the one shaly interval. The upper part of the Fremont Cape Calhoun are younger than the Red River. Limestone of Colorado, the Priest Canyon member, One can argue the equivalence of the units dated is similar in lithology and equivalent in age. In the with the Harding Sandstone of Colorado, but evidence Bighorns the equivalent Leigh member of the Bighorn of erosion almost to the point of obliteration is clear Group contains shaly units, but locally, higher massive prior to Red River deposition. The remarkable uni- dolomites are preserved at the top ( fide Teichert ) . In formity of Red River beds and faunas over the region Manitoba the Stonewall Formation is a light dolomite, is incompatible with the concept of deposition in dis- not shaly, and was fomerly grouped with the Silurian. crete embayments. There is good evidence for post- The Red Hcad Rapids Formation, possibly an equiv- Red River general emergence and erosion, but it is not alent, is a fine-grained dolomite more like Silurian than clear whether the Red River beds were at this time Ordovician beds in lithology. The section on Akpatok completely confined to the basins in which they are Island is thick, and should extend into the very late now preserved. Richmond, but upper beds which may be equivalent Early Richmond deposition was general over the re- to the above units cannot be identified. Whether there gion, and may have begun in late Maysville time. The are equivalent beds in the Cape Calhoun of Greenland Aleman is distinct from the beds below in some sec- is not clear. tions, but where it is a massive dolomite it is difficult Subsequent erosion has limited these beds and in to distinguish from the Second Value and appears New Mexico folding preceded peneplanation. There is fused to the lower beds. The same dolomitic fusion is evidence that some peneplanation preceded Silurian general in the Fremont of Colorado and the Bighorn deposition, but the roost striking cases of erosion on a 126 NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE folded and faulted Ordovician surface are not demon- cherty layers at 85 feet, but other sections are too thin. strably pre-Silurian for they occur in sections where In the Cooks Range a 12-foot layer of white granular the Silurian is absent. limestone is the Cooks Range member and only a remnant of the member, 3 inches to 2 feet thick, re- MOHAWKIAN REMNANTS mains at Lone Mountain. The Second Value, where it is a limestone, contrasts Between the El Paso Limestone and the base of the strongly with the Aleman but where both show ad- Second Value there are erosion remnants of an inter- vanced dolomitization the contact may be difficult or vening period of deposition, probable equivalents of impossible to place. The erosion interval between the the Harding Sandstone of Colorado. They are domin- two may be completely obscured. antly elastic, but show some variation. In the Mimbres The Second Value Formation is of Red River age, Valley there may be 2-3 feet of a white saccharoidal and has yielded typical Red River forms including the sandstone which contrasts sharply with the darker, familiar Receptaculties, the large Maclurites, and a coarser Cable Canyon Sandstone above. In Hembrillo variety of large cephalopods. The fauna is known from Canyon 4 feet of gray silt appear on one side of the New Mexico and Western Texas north to Greenland, canyon, but not on the other. In the Cooks Range but the deposits occur now as isolated remnants. The there is 14 feet of a massive dolomitic sand, full of fauna is found in the lower Fremont of Colorado, the large sand-filled worm borings. A similar sand occurs lower Bighorn Dolomite, the Red River Formation of locally in Lone Mountain. In the Hatchet Mountains Manitoba, the Nelson Limestone on the west side of the unit is more dolomitic, 12 feet thick, but shows Hudson Bay, in various localities in the Arctic Archi- variation in thickness due to deposition on the uneven pelago, and in the Cape Calhoun Formation of Green- El Paso surface. land. Necessarily hasty collecting, largely of materials The dating of these beds is uncertain in the absence loose at the foot of the cliffs, obscured the zonation in of fossils. Harding equivalence is an assumption, but a the Cape Calhoun Formation of Greenland, where logical one. It is possible that there are remnants of certainly an upper fauna with "Leptaena" unicostata more than one period of deposition. Lithic variation is of apparent Richmond age is also present. such as might reasonably be expected in one formation The age of the Red River faunas was long a prob- over the area involved. lem, because they do not appear in eastern beds. It was argued that since relatives of these forms appear in the SECOND VALUE FORMATION east in Richmond time, all the faunas should be Rich- The Second Value Formation consists of massive mond. It was also thought that since the eastern ap- poorly bedded limestones, of Red River age. The basal pearance of these forms was a clear case of migration beds are commonly a sandstone which ranges from 0 they might be older in their source region. Later work to 35 feet in thickness. The name Upham has been discovered Red River species in the late Trenton, par- used for the massive limestones, which are often al- ticularly in Quebec, Ontario, the Tennessee basin, and tered to dolomite. The lithic succession is (1) lower less abundantly in the Eden of Cincinnati. Red River dark massive beds (2) a middle calcarenite, thin, light- species occur in the Stewartville of Minnesota, the colored and crinoidal to the east, somewhat thicker, McCune of Missouri and the late Viola of Oklahoma. darker, and populated mainly by brachiopods in the Furthermore, these Red River equivalents are suc- west, and ( 3) an upper massive layer which may con- ceeded by others containing faunas of Richmond as- tain cherts, some scoriaceous and irregular, others con- pect. spicuous round nodules. The upper beds with chert nodules, and a frequently associated horizon with sili- PAR VALUE-ALEMAN cified brachiopods, are not found everywhere. They arc present in the thicker sections, but absent in the thin- This formation consisted originally of rather thin- ner sections. Local post-Second Value erosion is re- bedded limestones, medium to coarse grained, dark sponsible for the removal of these upper beds. The gray to black. In most sections it is altered to dolomite, round chert nodules occur 87-92 feet above the base in but the extent of alteration is variable. Dolomitization the 117 feet of the Second Value at Rhodes Canyon; has obscured the bedding locally but, in the lower in the 80 feet present in Hembrillo Canyon, the cherts beds, horizontal chat bands or bands of isolated chert are absent; in Ash Canyon where the section is 125 nodules reveal the bedding. Where dolomitization is feet thick, the cherts are developed at 80-90 feet above advanced, only silicified fossils, commonly brachiopods the base; in the southern Franklins the upper surface is are found. Four definite fossil zones ( fig. 4) are usually uneven enough so that some sections just reach the found in New Mexico. NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 127

In the southern sections the basal beds are common- Most conspicuous are one to three zones in the middle ly barren, but carry conspicuous bands of chert. North- or upper part characterized by silicified corals, mainly ward they thin and are absent at Rhodes Canyon and Paleofavosites. A soft nonresistant siltstone is persist- in Mud Springs Mountains. Fossils are not silicified. ent in eastern sections. It occurs 32-40 feet above the The horizon has yielded an asaphid trilobite, deter- base in Hembrillo Canyon, at 23 feet in Rhodes Can- mined by Whittington as Anataphrus. Allied forms yon, at 9 feet on Nakaye Mountain, and is the basal occur in the lower Maquoketa shale of Iowa. Higher unit of the Cutter in Mud Springs Mountains. It has beds, also with horizontal seams of chert nodules, are yielded pelecypods and brachiopods, appears to be a commonly filled with Zygospira, Dalmanella and Cor- single horizon, and suggests onlap of the Cutter from nulites. A very slender ramose bryozoan, probably southeast to northwest. The spheroidal cherts occur Bythopora, is conspicuous but less common. The over- mainly in beds below this interval, where they exist. lying beds contain more massive cherts often joined In the Rio Grande valley from Mud Springs Moun- and fused into irregular masses across successive layers. tains to Nakaye Mountain, there are two persistent This horizon is dominated by large Rafinesquina. A thin, conspicuous, ledge-forming, blue-weathering lime- succeeding bed, commonly barren, has yielded a sig- stones a little above the silty pelecypod zone. nificant coral assemblage in the Franklin Mountains. The Cutter fauna suggests a late Richmond age, It is developed also at Lone Mountain, but is not within the limits of the Whitewater, Saluda and Elk- found in the intervening areas. The commonest species horn of the Cincinnati arch. Equivalent units through- is Paleophyllum thorni. The upper beds of the Aleman out western and northern North America are discussed yield a large fauna, with many brachiopod genera, on pages 123-125. Rhynchotrema capax most common, Platystrophia, Strophomena, and many orthoids. Southward, this zone thickens, and may be further subdivided. The SILURIAN lower beds are commonly filled with bryozoa. To the FUSSELMAN DOLOMITE north and east, the highest bed shows conspicuous For the Silurian rocks of New Mexico there is only megaripples, and has yielded only a sparse fauna. This one formation name, the Fusselman Dolomite. The bed may be absent in some sections to the south, but dolomites are massive, generally dark and dark weath- elsewhere in the south it is apparently represented by ering, with silicified fossils, and conspicuous chert a continuation upward, with some variation, of the locally. Reports of thickness give wide variations. Cer- Rhynchotrema capax zone. Some recently discovered, tainly the extreme thickness reported in the Florida anomalously thin sections, with the upper faunas mis- Mountains is the result of thrusting of the formation sing, suggest that the Aleman was eroded priod to the upon itself. deposition of the Raven-Cutter. Dolomitization is general, has altered original lithol- The R. capax zone of the Aleman suggests the ogies and destroyed most fossils which are not silicified. Vaureal of Anticosti and the Waynesville of the Cin- These features are largely responsible for failure thus cinnati section. The lower beds contain faunas with far to recognize significant divisions or to give precise long-ranging forms. They may be Arnheim, (which dating of the interval. If it is not composed of several itself shows faunal anomalies as it is traced around the units representing different parts of the Silurian, it will Cincinnati arch ), but there is nothing in the lower be the only one of the old seemingly simple formations beds that is demonstrably early Richmond. Thus, de- which is not so composed. position may have begun in late Maysville time. The basal Fusselman in Lone Mountain has yielded small silicified cup corals identified as Streptelasrna by Miss Helen Duncan. This is a genus unknown in the RAVEN-CUTTER-VALMONT Silurian, and Miss Duncan has suggested that possibly Succeeding the Aleman are finer grained dolomites these fossils were silicified, weathered from the Cutter, light gray in color, generally light weathering, and with and redeposited. If this is true, and it is the only rea- minor chert. The lower beds may contain small sonable suggestion, we have not yet found a bed in the smoothly rounded chert nodules, contrasting with the Cutter yielding such forms. It may well be that, since irregular masses found in the Aleman. In higher beds the Raven-Cutter-Valmont unit is known to be eroded chert is sparse or absent. The upper beds may contain to varying depths, the youngest beds of these deposits vugs lined with quartz crystal. We have three names have been completely destroyed. for this lithic unit, the Raven of Entwhistle, the Cutter Pray (1953) reported a fauna in the lower Fussel- of Kelley and Silver, the Valmont of Pray. The Cutter man regarded as of Early Silurian age. The writer has is largely barren, but a few fossils have been found. questioned the age assignment because the fossils were 128 NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE stated to be poorly preserved, leaving some question as tent of the Onate and also in the Canutillo Formation. to species, and are members of genera which range up The faunas are dominated by brachiopods and some into the Clinton, if not into the Lockport. These fos- nondescript forms, the use of which in correlation is sils may be Alexandrian. They are certainly from lower complicated by the fact that records, descriptions, and beds, which are somewhat lighter in color and coarser- illustrations of western Devonian faunas have lagged textured than the regular Fusselman. far behind discoveries. The Devonian brachiopods of Reports of large pentameroid brachiopods have New Mexico are in the process of study by Dr. G. A. listed Pentamerus and Conchidium. The most com- Cooper and Dr. T. E. Dutro, and their results, which mon forms seem to belong to neither of these genera, may be expected in a few years, should contribute but to a Virgiana close to the northern Virgiana decus- materially to current problems. I am indebted to both sata. This species is a zone marker throughout the for much information included in the following pages. north-central Silurian, and is succeeded by beds with Leperditia hisingeri fa bulina and Pterinea occidentalis. ONATE FORMATION The latter beds are succeeded by the Discosorus- Huronia faunas. These faunas are certainly Clinton in As originally defined, the Onate was distinguished age, early rather than late Clinton. The Virgiana beds from the overlying Sly Gap shales by the predomin- have been variously considered as the base of the Clin- ance of silty rather than shaly beds, and the presence ton or the top of the Alexandrian. Difficulties in re- in it of a different fauna. Stevenson cited a large Leio- moving good specimens have resulted in incomplete rhynchus and the bryozoan Sulcoretopora (readily collections for the Fusselman; there is no faunal zona- recognized as it consists of flat fronds which bifurcate tion yet established. A core from eastern New Mexico regularly). Stevenson also mentioned Spirifer cf. ac- yielded true Pentamerus. The Fusselman probably =hiatus from Hayes Gap. This form (fide Cooper) contains Alexandrian, certainly the Virgiana horizon, is actually related to the Ithaca species Spirifer and may extend into late Clinton or Lockport. (Lock- mesastrialis. port is used here in the sense of containing the two The top of the Onate of the San Andres Mountains intervals, Racine and Guelph. Both are present in the was considered to be an orange-weathering siltstone or type Lockport.) There is no indication of Salina or fine sandstone, usually 1.5-2.5 feet thick, which forms Cayuga beds of Upper Silurian.* a prominent ledge. However, the soft shales above the ledge differ Ethically and faunally from the typical Sly DEVONIAN Gap. These are clay shales, some beds with limy nod- ules, that weather to a resistant clay. They have yielded The Devonian of New Mexico is dominantly a slope- Warrenella, Rhipidomella cf. vanuxemi and other forming shale, and good outcrops are scarce. East of forms, alien to the Sly Gap faunas. Such shales vary the Rio Grande thicknesses are less than 100 feet. In from 2 to 18 feet thick in the San Andres and are the Caballo and Mud Springs Mountains the Devon- directly overlain by shales carrying the Mcgeea zone. ian was eroded and is thin; at Whiskey Canyon in the the lowest of the Sly Gap faunules. Variation in thick- Mud Springs Mountains there is a 5-foot covered in- ness of these upper shales of the Onate may be caused terval between Ordovician and Pennsylvanian. The by differential warping and uneven deposition, or may Devonian may even be absent there. In the typical be the result of post-Onate erosion. If the Onatc is development of the Percha, from Hillsboro to the Sil- Middle Devonian, there is a potential time interval for ver City region, thicknesses range up to 250 feet, and such erosion in the early Late Devonian. exceed 300 feet in the extreme southwestern part of Most of the Devonian shales of the Rio Grande the state. valley from Palmer Park, Derry and north through the Formerly only one formation, the Percha Shale, was Caballo Mountains should be assigned to the Onate recognized. Closer study has shown that the deposi- rather than the Sly Gap. Where the base is seen, there tional history was complex, and six formations are cur- is a lower limy layer of thin, moderately resistant beds rently recognized, to which might be added two more, with Ambocoelia and Chonetes cf. aurora. Higher the the Canutillo of the Frankin Mountains, and the shales are of somewhat variable aspect, with silts and "Swisshelm" of the extreme southwest. Lithologies in- sands to the south, some good sandstones at Derry, clude shales, siltstoncs, some sandstone, argillaceous and dominantly clay shales to the north. These beds shales and limestones, with chert in the northern ex- have a distinctive fauna with a large Atrypa, Schiz- *Upper Silurian is a term which at present is ambiguous. It ap- ophoria, Eatonia and Warrenella. In Mud Springs pears that the beds we have been calling upper Middle Silurian, Mountains these beds have yielded the "Receptacu- notably the Guelph and Port Byron, have their British equivalents in part at least of the Upper Silurian of the type section. lites", more properly named Sphaerospongia, and the NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 129 characteristic Sulcoretopora. At Chise the beds are a Canyon Formation above. As restricted, the Contadera dark gray siltstone with Atrypa and a stropheodontid. at Rhodes Canyon consists of 45 feet of shaly beds, be- At Hermosa the lower Chonetes beds arc a sequence coming limy at the top. The lower 14 feet consist of of quite pure limestones with a varied fauna, including thin fissile shales with widely-spaced, thin layers of Hypothyridina; above are the clay shales with Warren- siltstone, the under surfaces of which show abundant ella and other forms, and at the top are gray shales and strand markings. Near the top some silty limestones limestones with Sulcoretopora. Here the contact with alternate with shale containing an abundant and dis- the overlying Sly Gap is marked by a 4-inch limonitic tinctive brachiopod fauna. The top is a 3-foot bed of band. hard limestone, nodular, weathering bluish, largely bar- The age relationship of the Onate involves the ques- ren at this locality. tion of conflicting interpretations in other regions, as At Sly Gap the basal beds of the Contadero show to whether the Tully limestone is to be considered late 20 feet of similar fissile shale and siltstone, barren ex- Middle or early Upper Devonian. Chonetes aurora is cept for the top foot which yields the same fauna as a species characterizing the Tinkers Falls, the basal that found at Rhodes Canyon. Above this is a 1-foot member of the Tully in New York. Hypothyridina bed of limy siltstone, the coral bed of Stevenson, makes its first appearance there in the overlying Apulia which yielded many large solitary corals; but only one member. One may suggest that the Warrenella is allied colonial form was found. Stevenson seems to have to "Spinner" laevis of the Sherburne Sandstone, but mistakenly attributed to this horizon the abundant the resemblances may be superficial. Spirifer mesas- colonial forms which occur at the top of the Sly Gap. trialis is an Ithaca species, appearing not at the base, Another foot of calcareous siltstone with the Conta- but in the Williams Brook member. The Rhipidomel- dero fauna may occur above, but in places this bed is la cf. vanuxerin from Sly Gap is a species common in absent. the upper Hamilton of New York. The Onate can The Contadero fauna is being studied by Cooper certainly be placed within the limits of late Middle and Dutro The fauna includes abundant Hystricina, Devonian or lowermost Upper Devonian. a small fimbriate Spirifer, several stropheodontids, a large Camarotoechia, abundant small Ambocoelia, SLY GAP FORMATION several genera of pelecypods, a gastropod fragment and unidentifiable small smooth orthoconic cephalopods. This interval consists of shales with limy bands and It is probably Chemung in age. Some difficulty has nodules. At the type section it is 40 feet thick; at possibly arisen from collecting specimens, weathered Rhodes Canyon the thickness is 37 feet, and other from the Contadero, on the Sly Gap slope, leading to sections are thinner. With the underlying Onate, the the idea that the Contadero and Sly Gap faunas had Sly Gap grades southward in the Sacramento and San much in common. Andres Mountains into a black fissile shale which has been called the Percha, but this may be too broad an identification. THOROUGHGOOD FORMATION The Sly Gap has yielded a large fauna dominated The Thoroughgood Formation consists of the top by brachiopods (Stainbrook, 1948) , is allied to the 10-12 feet of the Devonian section at Sly Gap. It is Independence Shale of Iowa, and is lower but not dominantly tan-weathering, light gray sandstones and lowermost Upper Devonian. It has yielded Manticoc- siltstones, varying in hardness and calcareous content. eras. It is generally absent in the Caballos Mountains, The basal layers, called the fish bed by Stevenson (but is present in only one small area of the Mud Springs our collections contain no fish remains) have phos- Mountains, is absent at Chise, and is found again at phatic black nodules which include fragments of a Hermosa. The present distribution results from post- slender orthoconic nautiloid, unidentifiable, as no Sly Gap erosion, difficult to date, but clearly prior to specimens have been found preserving the interior, and the deposition of the Percha which lies on an eroded a high spired gastropod of the aspect of Loxonema, in Sly Gap-Onate surface from Mud Springs Mountains addition to brachiopods. Throughout the formation to Hermosa. brachiopods are common. The dominant types are a Leiorhynchus cf. mesacostalis of the Three Forks (the CONTADERO FORMATION species is from the "Ithaca and Chemung" of New The type Contadero is in Rhodes Canyon, where it York) as figured by Raymond, and a "Spinner," closely was originally defined as the whole of the Devonian allied to Cyrtospirifer portae of the Devils Gate lime- exposed above the Sly Gap. The upper part is removed stone of Nevada. Less closely allied are C. monticola as the Thoroughgood Formation, with the Rhodes of the Three Forks, C. whitneyi of the Ouray and C. 1 30 NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE kindlei of the Percha. A 2-11-inch remnant of this for- chiopods which weather readily from the shales and mation is present in Rhodes Canyon, and has yielded limy nodules. The commonest form is a small Cleio- the same Cyrtospirifer. thyridina, but more conspicuous are Cyrtospirifer kindlei, Schizophoria australis, and Paurorhyncha coop- RHODES CANYON FORMATION er/. Closely allied faunas are found in the lower Ouray beds of southwestern Colorado and the Dyer The Rhodes Canyon Formation was proposed for Dolomite of northwestern Colorado. Precise dating in the 73.5 feet of shale which overlies the remnant of the Devonian involves some differences of interpreta- the Thoroughgood Formation in the Rhodes Canyon tion. House (1962) would place the horizon only a section. The shales are largely fissile, with some silt- little higher than the Three Forks Shale, but Cooper stones, dominantly gray and finely micaceous. The sec- placed it considerably above that interval, and would tion is:— now regard it as possibly very late Upper Devonian. The dating of the Silver-Ready Pay member of the F. 20 ft. dominantly soft fissile clay shale with a few Percha still is uncertain. It may not be materially older beds of resistant siltstone; siltstone gray, weather- than the Box member, or it may contain equivalents of ing tan; shales weather in pale green and pale rose the Onate and Sly Gap. If it does, there is an erosional layers; a few calcareous lenses; contains sparse fos- break within it, a hiatus represented farther east by sils of C and E. the Contadero, Thoroughgood and Rhodes Canyon E. 10 ft. dominantly of silty shales with several beds beds. of soft calcareous siltstones; yields a brachiopod In the Sacramento and San Andres Mountains the fauna with conspicuous productids, Athyris, and a Onate and Sly Gap show a southward change into a Leiorhynchus. black shale facies, but this is not necessarily identical D. 20 ft. dominantly fissile noncalcareous shales with with the Silver shale. The Sly Gap and to a lesser ex- 1/4- to 1/2-inch thick widely-spaced siltstones; very tent the Onate show a facies change to darker and sparse fauna. more fissile shale from Mud Springs Mountains to C. 8 ft. fissile shales, light gray to white, finely mica- Hermosa. A change to a perfectly black fissile shale at ceous, slightly calcareous, with large brachiopod Hillsboro, 22 miles to the south, the type section of fauna including a Camarotoechia resembling C. the Percha, would not be unreasonable. A reported sobrina. Manticoceras (specimen lost) from the Percha at Sil- B. 6 ft. shales darker gray, moderately silty. ver City would also support this interpretation. How- A. 3 ft. gray silty shales. ever, dark fissile shales do lie disconformably on the The fauna is largely of brachiopods, and has not yet Onate-Sly Gap. At Mud Springs Mountains there are been adequately studied. It is this interval which, near 15 feet of such shale above the Sly Gap; at Chise, Rhodes Canyon, yielded the species which Stainbrook there are about 100 feet, which lie on Onate, with the ascribed to the Percha. My collections have been on Sly Gap missing; at Hermosa there are 137 feet above loan to Washington for some years, and are not im- the Sly Gap. These shales could represent the Silver, mediately available for review. Cooper has considered the Bella, or the whole Percha. An impression of this a fauna of possible Three Forks age. Cyrtospirifer kindlei, too fragile to be preserved, found in the upper part would suggest an equivalence with PERCHA SHALE the Bella-Box member. The Percha Shale, 184 feet thick at the type locality In the extreme southwestern part of the state, near (Stevenson, 1945), consists of 120 feet of black barren Portal, Arizona, the Devonian consists of black shales fissile shale, 12 feet of gray argillaceous shale grading like those of the Silver-Ready Pay member, overlain by up into 46 feet of calcareous shale with limy nodules, calcarenites with a mucronate "Spirifer." This speci- which locally may be so numerous as to constitute lay- men Cooper (in Sabins 1957) considered of probable ers of nodular limestone with shaly partings. Chemung age. The writer has found similar mucronate Keyes proposed the name Silver shale for the lower spirifers in the top of the Dyer Formation of north- fissile shales, the Bella member for the upper calcar- western Colorado, lying above beds with a fauna of eous part. Stevenson proposed the Ready Pay member Bella-Box aspect. In the Hatchet Mountains, the black for the lower fissile shales, the Box member for the shales of the Devonian grade up into limy beds with a upper part. It is misleading to speak of a Percha fauna, different fauna, as yet undescribed and not precisely because the known fauna is confined to the upper dated. Bella-Box member. The ammonoids contribute to the problem of dat- The Bella-Box fauna consists dominantly of bra- ing the New Mexico Devonian. The Sly Gap has NEW MEXICO GEOLOGICAL SOCIETY-SIXTEENTH FIELD CONFERENCE 1 31 yielded Manticoceras. This genus is confined to the Flower, R. H., 1958, Cambrian-Mississippian of southern New Mexi- co: Roswell Geol. Soc. Field Trip guidebook for 1958, p. 61-78. upper part of the lower half of the Upper Devonian , 1959, Cambrian-Devonian beds of southern New Mexico: (the Frasnian of Europe). In the east, Pharciceras, in Guidebook for joint field conference, Permian Basin Sec., Soc. the Tully Limestone, Pontoceras and Koenites in the Econ. Paleontologists and Mineralogists, p. 154-171, 2 figs. Geneseo-Sherburne, precede Manticoceras which , 1964, The nautiloid order Ellesmeroceratida: New Mexico Bur. Mines and Mineral Res. Mem. 12, 234 p., 32 pls., 53 figs. ranges through the Ithaca and Chemung. The upper Hintze, L. E., 1951, Lower Ordovician detailed sections for western part of the European Devonian, the Fammenian, is di- Utah: Utah Geol. Min. Survey Bull. 39, 99 p., 11 figs. vided in Europe into the zones of Cheiloceras, Platy- Hintze, L. E., 1953, Lower Ordovician trilobites from western Utah and eastern Nevada: Utah Geol. MM. Survey Bull. 48, 249 p., clymenia, Clymenia, and Wocklumeria. House (1962) 28 pls. has recognized Cheiloceras in the Gowanda Shale of House, M., 1962, Observations on the ammonoid succession of the New York. The Three Forks Shale contains PIatycly- North American Devonian. Jour. Paleontology, v. 36, p. 247-284, pls. 43-48, 15 figs. menia. Cyrtoclyrnenia and Falciclymenia in the Bella- Kelley, V. C. and Silver, C., 1952, Geology of the Caballo Moun- Box member of the Percha he placed slightly higher in tains: Univ. New Mexico Pub. in Geol., No. 4, 286 p., 19 pls., the same zone, and recognized in the Chonopectus 26 figs. Lochman-Balk, C., and Wilson, J., 1958, Cambrian biostratigraphy sandstone of Missouri forms assignable either to the of North America: Jour. Paleontology, v. 32, p. 312-350, 18 figs. Clymenia or the Wocklumeria zone. Nelson, S. J., 1963, Ordovician paleontology of the northern Hudson The reported Manticoceras (determined by Miller, Bay lowland: Geol. Soc. America Mem. 90, 152 p., 37 pls., 5 figs. the specimen unfortunately lost), from the lower Per- Paige, S., 1916, Description of the Silver City quadrangle, New Mexico: U.S. Geol. Survey Atlas, Silver City Folio, No. 199, 19 p., cha near Silver City, has not yet been duplicated. If 1 pl., 3 maps. correct, it would indicate an equivalent of the Sly Gap Pray, L. C., 1953 Upper Ordovician and Silurian stratigraphy of the in the lower Percha at that locality. The only ammo- Sacramento Mountains, Otero County, New Mexico: Am. Assoc. Petroleum Geologists Bull. v. 37, p. 1894-1918, 10 figs. noid from the Onate so far is a crushed Tornoceras, Ross, R., 1951, Stratigraphy of the Garden City formation in north- too poorly preserved to be diagnostic. eastern Utah, and its trilobite faunas: Yale Univ., Peabody Mus. Nat. Hist. Bull. 6, 161 p., 36 pls., 4 figs. Sabins, F. F., 1957, Stratigraphic relationships in the Chiracahua and REFERENCES Dos Cabezas Mountains, Arizona: Am. Assoc. Petroleum Geol- Cloud, P. E. and Barnes, V. E., 1948, The Ellenberger group of ogists Bull., v. 41, p. 466-510, 15 figs. central Texas: Univ. of Texas, Bur. Econ. Geol., Publ. 4621, 473 Stainbrook, M. A., 1947, Brachiopoda of the Percha shale of New p., 44 pls. 8 figs., 3 tables. Mexico and Arizona: Jour. Paleontology, v. 21, p. 297-328, pls. Cooper, G. A., 1956, Chazyan and related brachiopods: Smiths. 44-47. Misc. Coll., v. 127, 2 v., 1024 p., 3 figs., 269 pls. , 1948, Age and correlation of the Devonian Sly Gap beds Darton, N. H., 1917, A comparison of Paleozoic sections in south- near Alamagordo, New Mexico: Am. Jour. Sci., v. 246, p. 765-790, ern New Mexico: U.S. Geol. Survey Prof. Paper 108-c, p. 29-55, pls. 1-2. 15 figs. Stevenson, V. F., 1945, Devonian of New Mexico: Jour. Geology, Entwistle, L. P., 1944, Manganiferous iron ore deposits near Silver v. 53, p. 217-245, 14 figs. City, New Mexico: New Mexico Bur. Mines and Mineral Res. Sweet, W. C., 1954, Harding and Fremont formations of Colorado: Bull. 19, 70 p., 11 figs., maps. Am. Assoc. Petroleum Geologists Bull., v. 38, p. 284-305, 4 figs.