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;;;;;;;;;;;;;;; C'I • Q. BUREAU OF ECONOMIC GEOLOGY 0 0 THE UNIVERSITY OF TEXAS AT AUSTIN VI Q. AUSTIN, TEXAS 78712 r:Q ct n.J :IE ..D ..J 0 W. L. F1seER, Director r-"I w r:Q Cl Lt) U"J rn co r-"I a""' n.J Cl . GEOLOGIC QUADRANGLE MAP NO. 48 - .,,.....""' 0

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Cl""' Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas

By VIRGILE. 8A.RNBI

November 1982 THE UNIVERSITY OF TEXAS AT AUSTIN TO ACCOMPANY MAP-GEOLOGIC BUREAU OF ECONOMIC GEOLOGY QUADRANGLE MAP NO. 48

GEOLOGY OF THE MARBLE FALLS QUADRANGLE,

BURNET AND LLANO COUNTIES, TEXAS

VIRGIL E. BARNES

1982

CONTENTS

General setting ...... 2 Crack fillings ...... 8 Geologic formations ...... 2 Houy Formation ...... 8 Precambrian rocks ...... 2 Ives Breccia Member ...... 8 Igneous rocks ...... 2 Doublehorn Shale Member .... . 8 Town Mountain Granite ...... 2 Mississippian System ...... 8 Paleozoic rocks ...... 3 Chappel Limestone ...... 8 Cambrian System ...... 3 Barnett Formation ...... 8 Moore Hollow Group ...... 3 Pennsylvanian System ...... 9 Riley Formation ...... 3 Unnamed phosphorite ...... 9 Hickory Sandstone Member . . . . 3 Marble Falls Limestone ...... 9 Cap Mountain Limestone Member 3 Smithwick Formation ...... 9 Lion Mountain Sandstone Member 3 Mesozoic rocks ...... 10 Wilberns Formation ...... 4 Cretaceous System (Lower Cretaceous) . . 10 Welge Sandstone Member ...... 4 Trinity Group ...... 10 Morgan Creek Limestone Member 4 Shingle Hills Formation ...... 10 Point Peak Member ...... 4 Hensen Sand Member ...... 10 San Saba Member ...... 4 Post-Smithwick? Mesozoic? diabase ..... 10 Ordovician System (Lower Ordovician) . . 5 Cenozoic rocks ...... •. 10 Ellenburger Group ...... 5 Quaternary deposits ...... 10 Tanyard Formation ...... 5 Terrace deposits and colluvium .. 10 Threadgill Member ...... 5 Alluvium ...... 10 Staendebach Member ...... 5 Subsurface geology ...... 11 Gorman Formation ...... 5 Mineral resources ...... 11 Honeycut Formation ...... 6 Construction materials ...... 11 Ordovician System (Upper Ordovician) . . . 6 Dimension stone ...... 11 Burnam Limestone ...... 6 Road materials ...... 13 Silurian System ...... 7 Sand and gravel ...... 13 .... , Starcke Limestone ...... 7 High-calcium limestone ...... 13 ""'(JI Devonian System ...... 7 Water ...... 14 Stribling Formation ...... 7 Lead and zinc ...... 14 ,}5 Mississippian-Devonian rocks ...... 8 References ...... 15 ..,. ~ L ~ ~~ (,t GL Vif'<"') C..uv Bureau of Economic Geology, The University of Texas at Austin

GENERAL SETTING

The geology of the Marble Falls quadrangle is Colorado River drainage basin. The Colorado flows shown on a U. S. Geological Survey 7 .5-minute eastward across the middle of the quadrangle topographic quadrangle map and is the fourteenth through a series of lakes. Tributaries from the geologic map in the Llano region to appear on a north are Elm Creek draining into Lake Lyndon B. modern 1:24,000 scale, 20-foot contour interval Johnson and Deep Creek and Backbone Creek base. The relief in the quadrangle is about 520 feet; draining into Lake Marble Falls. Tributaries of elevations range from 681 feet, pool level of Lake Backbone Creek are Williams Creek, Dry Creek and Travis, to about 1,200 feet at the south border of its branch Dry Branch, Sparerib Creek, Coldspring the quadrangle toward the western side. Creek, and Whitman Branch. Tributaries from the Marble Falls quadrangle is in the eastern part of south are Slickrock Creek and Horseshoe Creek the Llano region, high on the eastern side of the draining into Lake Lyndon B. Johnson and Tiger Llano uplift. Precambrian rocks, in part covered by Creek, Varnhagen Creek, and Flatrock Creek and lakes and some alluvium, occupy about 26 square its branch Little Flatrock Creek draining into Lake miles. Except for some Quaternary deposits and, Marble Falls. A small area in the southeastern part near the south border, some Cretaceous Hensen of the quadrangle drains to Lake Travis mostly by Sand, the rest of the quadrangle is underlain by way of Double Horn Creek. Paleozoic rocks ranging from Cambrian to Pennsyl­ The Marble Falls quadrangle was mapped geo­ vanian in age. These rocks are mostly southeast of logically by Barnes during 1951-1952 assisted by the Marble Falls fault which trends southwest­ W. A. Anderson, T. M. Anderson, and John northeast and divides the quadrangle into two Twining. Discussions of stratigraphic, structural, subequal parts. economic, and geophysical problems are in cited Marble Falls quadrangle is entirely within the references.

GEOLOGIC FORMATIONS

PRECAMBRIAN ROCKS Marble Falls quadrangle is mapped by Keppel as coarse-grained massive granite with no mineral IGNEOUS ROCKS parallelism. Goldich (1941) made a chemical and petro­ Town Mountain Granite graphic examination of granite in the Granite Mountain pluton in the Marble Falls quadrangle Town Mountain Granite of the Granite Moun­ and in the Lone Grove pluton to the northwest in tain pluton occupies the northwestern part of the the Kingsland quadrangle (see Barnes, 1976, for Marble Falls quadrangle, is faulted against Paleo­ locality). Sandell and Goldich (1943) listed the zoic rocks to the southeast, and passes under rarer metallic constituents in the same rocks. Paleozoic rocks to the northeast. Keppel (1940) Zartman (1964) made a geochronologic study of mapped variations in grain size and textures of the the Lone Grove pluton and found that the granite Llano region plutons, and his map of these plutons has a rubidium-strontium age of 1,000 ± 40 million shows areas designated as coarse-grained porphy­ years. Zartman (1965) determined the isotopic ritic, coarse-grained, medium-grained, and fine­ composition of lead in microcline from the same grained granite. All of the granite within the rock. He concluded that this and other granite

2 Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas analyzed "was probably obtained from a rather vated. The Hickory where exposed within the uniform source, which is possibly related to some Marble Falls quadrangle appears to be considerably deep crustal or upper mantle layer ... " thinner than the 340 feet measured in the Morgan Exfoliation domes are common and include Creek area to the northwest and the 276 feet Granite Mountain, Kennison Rock, School Rock, measured in the White Creek section to the Goose Rock, Sow Rock, Hickory Rock, Corner southwest (Barnes and Bell, 1977; Barnes, 1952a). Rock, and numerous other smaller occurrences. The thickness of the Hickory within the Marble Falls Similar domes forming monadnocks were present quadrangle, as shown on an isopach map in the on the surface of the Precambrian when the former publication, ranges from 260 to 300 feet. Cambrian sea invaded central Texas. Two such Cap Mountain Limestone Member.-Steeply exhumed monadnocks are in the northeastern part dipping Cap Mountain Limestone crops out south of the Marble Falls quadrangle, one of which is tall of Alvin Wirtz Dam in a fault sliver off Marble Falls enough to reach the base of the Cap Mountain fault. Cap Mountain Limestone also crops out in Limestone. Another exhumed monadnock just to the northeastern part of the Marble Falls quad­ the north on the Longhorn Cavern quadrangle is rangle. overlapped by Cap Mountain Limestone mineral­ The lower part of the Cap Mountain is sandy, ized by galena and sphalerite. brown, and in part glauconitic; upward, the lime­ In the vicinity of Kennison rock, many of the stone is less sandy and in part light to medium large tabular feldspar phenocrysts are horizontal gray. The upper part of the Cap Mountain is and dark basic-appearing inclusions are vertical. somewhat fossiliferous and glauconitic grading The phenocrysts are of about the same density as upward to the overlying Lion Mountain Sandstone the rock as a whole and probably represent the Member. The lower contact, likewise, is gradational true direction of flow structure. The dark inclu­ to the Hickory Sandstone Member beneath and is sions, which are denser than the rock as a whole, chosen at a distinct topographic and vegetational may have settled and in settling changed their break. The silty and argillaceous upper part of the orientation to vertical. If this interpretation is Hickory Sandstone weathers to a bench; the correct, the use of dark inclusions as a criterion in calcareous sandstone and sandy limestone at the estimating the shape of granite plutons may lead to base of the Cap Mountain, as well as the limestone error. above, are resistant to weathering and mostly form The granite is composed predominantly of rocky, steep slopes. The Cap Mountain supports microcline, plagioclase, quartz, and some biotite cedar and a variety of thorny plants; the Hickory and hornblende. Accessory minerals are scarce and Sandstone supports deciduous oaks, and where consist mostly of magnetite, sphene, apatite, argillaceous, mesquite is common. zircon, and allanite. The thickness of the Cap Mountain Limestone PALEOZOIC ROCKS was not measured in the Marble Falls quadrangle but thicknesses of 204 feet in the Morgan Creek CAMBRIAN SYSTEM area to the northwest, 411 feet in the Riley Mountains to the west, and 497 feet in the White Moore Hollow Group Creek section to the southwest were measured (Barnes and Bell, 1977; Barnes 1952a). An isopach Riley Formation map of the Cap Mountain in the former publica­ tion shows it to range in thickness from 390 to 4 70 Hickory Sandstone Member.-The Hickory feet within the Marble Falls quadrangle. Sandstone Member crops out mostly in the north­ Lion Mountain Sandstone Member.-Two small eastern part of the quadrangle where it rests on an outcrops of Lion Mountain Sandstone are present uneven Precambrian surface with monadnocks within the Marble Falls quadrangle, one in the reaching as high as the base of the overlying Cap narrow fault block south of Alvin Wirtz Dam and Mountain Limestone. Slaughter Mountain, a mesa­ the other in the northeastern part of the quad­ like feature, is capped by Hickory Sandstone. A rangle. The latter forms a narrow bench distinctly fault sliver of Hickory Sandstone is mapped south­ visible on the aerial photograph used in mapping east of Alvin Wirtz Dam, and nearby Castle the outcrop. The only rocks exposed are fragments Mountain on the northwest side of Marble Falls of trilobite coquinite; the greensand weathers to a fault is capped by Hickory Sandstone. sandy soil. An excellent exposure of the Lion The upper part of the Hickory Sandstone in the Mountain Sandstone can be seen in the Kingsland northeastern area forms a bench which is culti- quadrangle (Barnes, 1976) in the cut on the north

3 Bureau of Economic Geology, The University of Texas at Austin side of Ranch Road No. 1431 where it crosses the feet or so is coarse grained to medium and fine nose of Backbone Ridge. grained medium bedded, medium to light gray and The thickness of the Lion Mountain Sandstone greenish gray, glauconitic in some beds, with was not measured within the Marble Falls quad­ patches of brownish-yellow dolomite along the rangle, but Barnes and Bell (1977) measured bedding; scattered dolomite rhombs are common. thicknesses of 49 feet at Lion Mountain to the Trilobites are common throughout the interval, northwest, 33 feet in the Riley Mountains to the and calcareous brachiopods are abundant in the west, and 41 feet in the White Creek section to the upper half with Eoorthis concentrated in a thin southwest. An isopach map (Barnes and Bell, bed near the middle. The top 40 feet of strata 1977) shows thickness of the Lion Mountain to consists of alternating intervals of argillaceous, range from 55 to 65 feet within the Marble Falls fine-grained, thinly bedded limestone, thickly quadrangle. bedded coarse-grained limestone, and some inter­ Phosphatic brachiopods and trilobites are abun­ vals of stromatolites. Silt is common, glauconite is dant in the lower part of the Lion Mountain. While present in some beds, and the rocks are greenish no fossil collections were made within the quad­ gray to brownish gray. Trilobites and brachiopods rangle, Palmer (1954) and Wise (1964) have listed are common. numerous species of phosphatic brachiopods and The thickness of the Morgan Creek Limestone trilobites from the Lion Mountain in the Blowout was not measured within the Marble Falls quad­ and Johnson City quadrangles. rangle, but Barnes and Bell (1977) measured thicknesses of 130 feet in the Morgan Creek section to the northwest, 113 feet in the Riley Wilberns Formation Mountains to the west, and 143 feet in the White Creek section to the southwest. On an isopach Welge Sandstone Member.-Two small outcrops map, they show the Morgan Creek ranging in of Welge Sandstone are present within the Marble thickness from 130 to 145 feet within the Marble Falls quadrangle, one in the narrow fault block Falls quadrangle. south of Alvin Wirtz Dam and the other in the The biostratigraphy of the Morgan Creek Lime­ northeastern part of the quadrangle. The latter stone (Bell and Barnes, 1961, published in Moscow forms a narrow scarp marked on aerial photographs and difficult to obtain) was reprinted in Barnes and by a dark line of vegetation adjacent to the Bell (1977). The reader is referred to the latter sparsely vegetated Lion Mountain Sandstone publication for a summary of the paleontology of bench. the Morgan Creek Limestone and other units of the The Welge is medium to fine grained, massive, Moore Hollow Group. and light brown to grayish brown; the sand grains Point Peak Member.-The Point Peak Member are well rounded and fairly smooth. It is somewhat crops out in normal stratigraphic position in the glauconitic in its lower part. The thickness of the narrow fault block south of Alvin Wirtz Dam but Welge Sandstone was not measured within the appears to have been shuffled somewhat during the Marble Falls quadrangle, but Barnes and Bell faulting. Exposures are very poor and the Point (1977) measured thicknesses of 13 feet at Lion Peak is chiefly identified by the presence of large Mountain to the northwest, 16 feet in the Riley masses of stromatolitic limestone scattered here Mountains to the west, and 11 feet in the White and there. Creek section to the southwest; their isopach map The thickness of the Point Peak Member within shows about 10 feet of Welge within the Marble the quadrangle was not measured, but Barnes and Falls quadrangle. Bell (1977) measured thicknesses of 65 feet in the Fossils were not seen in the Welge within the T. F. Murchison ranch well a short distance to the Marbles Falls quadrangle; trilobites were collected northeast, 114 feet in the Morgan Creek section to from the Welge in the Johnson City quadrangle the northwest, 214 feet in the Riley Mountains to (Barnes, 1963) to the south. the west, and 111 feet in the White Creek section Morgan Creek Limestone Member.-The Morgan to the southwest. On an isopach map they show Creek Limestone crops out in the narrow fault the Point Peak Member ranging in thickness from block south of Alvin Wirtz Dam, and the lower few 50 to 100 feet within the Marble Falls quadrangle. tens of feet of the member crop out in the San Saba Member.-The San Saba Member crops northeastern part of the quadrangle. out in normal stratigraphic position in the narrow The lower 25-foot interval is coarse grained, fault block south of Alvin Wirtz Dam and as with reddish, massively bedded, and highly sandy at the the Point Peak, has been considerably shuffled base, becoming less sandy upward. The next 75 during the faulting. Some calcitic rocks at the base

4 Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas of the member probably belong to the calcitic block south of Alvin Wirtz Dam, and in a small facies of the San Saba; the bulk of the member is area in the southwestern comer of the quadrangle. dolomite. The dolomitic facies of the San Saba also The Staendebach Member is predominantly fine­ crops out in the northeastern corner of the grained cherty dolomite, and at the upper contact quadrangle. The dolomite is fine grained and a few small outcrops of white, cherty, aphanitic sparingly cherty. The upper boundary is mapped at limestone are present. These patches of limestone a change from fine-grained to coarse-grained may be remnants of a once much more nearly dolomite. continuous limestone that has dissolved. Evidence The thickness of the San Saba Member within for this is the collapsed nature of the upper contact the quadrangle was not measured, but Barnes and of the Staendebach Member in the Marble Falls Bell (1977) measured thicknesses of 280 feet in the and adjacent quadrangles. T. F. Murchison ranch well a short distance to the The thickness of the Staendebach Member was northeast and 21 7 feet in the Riley Mountains to not measured within the Marble Falls quadrangle the west. On an isopach map, they show the San but thicknesses of 433 feet in the T. F. Murchison Saba ranging in thickness from 270 to 360 feet ranch well a short distance to the northeast (Barnes within the Marble Falls quadrangle. and Bell, 1977), 481± feet in the Backbone Moun­ Fossils collected from locality 9-8C, identified tain area, and 353 feet in the Riley Mountains by P. E. Cloud of the U.S. Geological Survey, are (Cloud and Barnes, 1948; Barnes, 1976) were Stenopilus and Finkelnburgia?. measured. Fossils collected from locality 9-8A, identified by P. E. Cloud of the U.S. Geological Survey, are ORDOVICIAN SYSTEM (LOWER ORDOVICIAN) Ophileta cf. 0. supraplana Ulrich & Bridge, Ophileta sp., Turritoma or Gasconadia sp., Ellenburger Group Schizopea sp., and a new genera of trilobites.

Tanyard Formation Gorman Formation Threadgill Member.-In the Marble Falls quad­ rangle the position of the San Saba - Threadgill The Gorman Formation crops out in a broad boundary in reference to the position of the area in the southwestern part of the quadrangle Cambrian-Ordovician boundary is unknown be­ and in two fault blocks in the northeastern part of cause of lack of paleontologic evidence. The the quadrangle; calcitic Gorman is present in two uppermost part of the San Saba could be Ordo­ small outcrops in the southeastern part of the vician or the lower part of the Threadgill could be quadrangle. Both calcitic and dolomitic facies of Cambrian. The boundary between the members, the Gorman have been mapped within the Marble where in dolomite, is placed at the top of the Falls quadrangle. In one fault block in the north­ fine-grained dolomite above the highest Cambrian eastern area, the Gorman is composed of a lower fossils and at the bottom of coarse-grained dolo­ dolomitic facies and an upper calcitic facies, which mite below the lowest Ordovician fossils. is normal for the Gorman in the Llano region. In The Threadgill Member in its coarse-grained the other block in the northeastern area, the dolomitic facies crops out in two fault blocks in Gorman has not been subdivided into facies, but the northeastern comer of the quadrangle where it the Archaeoscyphia bed has been mapped. is estimated to be about 200 feet thick, which is In the southwestern area the calcitic facies has a considerably less than the 390 feet measured in the patchy occurrence and for about a mile is absent in T. F. Murchison ranch well a short distance to the the upper part. From here directly south to the northeast (Barnes and Bell, 1977), and con­ bottom of the Gorman Formation on the Round siderably more than the 91 feet measured on Mountain quadrangle (Barnes, 1978d), only dolo­ Backbone Ridge in the Kingsland quadrangle mite is present. The dolomitic facies is predomi­ (Cloud and Barnes, 1948; Barnes, 1976). nantly microgranular and the calcitic facies is The Threadgill Member in the narrow fault aphanitic. block south of Alvin Wirtz Dam is predominantly Although two complete sections are present, the light-colored aphanitic limestone, and a minor thickness of the Gorman Formation has not been amount grades laterally to coarse-grained dolomite. measured within the Marble Falls quadrangle but Staendebach Member.-The Staendebach Mem­ thicknesses of 483 feet in the Backbone Mountain ber crops out in two fault blocks in the north­ area and 456 feet in the Riley Mountains were eastern part of the quadrangle, in the narrow fault measured (Cloud and Barnes, 1948).

5 Bureau of Economic Geology, The University of Texas at Austin

Three fossil collections were made from the Falls fault. These have not been mapped except Gorman at localities 27T-10-13A, 27T-10-20A, and where the faults have offset younger beds. 149T-3A-4A, the latter for a distance of a quarter In the lower part of the Honeycut massive of a mile along one bed. I have no record of limestone beds containing Archaeoscyphia are identifications having been made for these collec­ common, a few Ceratopea were seen, and tions, and the fossils are now in the U. S. National Xenolasma are common in chert near the base of Museum. the formation. Five fossil collections were made from the Honeycut at localities 9-9A, 10-12A, Honeycut Formation 27T-10-19A, 27T-10-20B, and 149T-3A-4B. P. E. Cloud of the U. S. Geological Survey identified the A broad belt of Honeycut rocks crosses the following fossils from locality 9-9A: Hormotoma southern part of the Marble Falls quadrangle; small sp., Euomphalopsis? sp., "Jeffersonia"? sp., another outcrop in a fault block 2 miles north of and unidentified gastropods and a cephalopod. I Marble Falls was examined by Cloud and Barnes have no record of identifications having been made (1948} p. 350) and was estimated to contain about for the four remaining collections and the fossils 500 feet of Honeycut rocks. A very large collapse are now in the U.S. National Museum. structure in the upper part of this outcrop contains a mixture of Marble Falls Limestone and Honeycut Formation rocks. ORDOVICIAN SYSTEM (UPPER ORDOVICIAN) Cloud and Barnes (1948) estimated that about 450 feet of Honeycut strata is present along Burnam Limestone Slickrock Creek in the southwestern part of the Marble Falls quadrangle. In this section, and in Although pockets of Burnam Limestone have general in the Honeycut of the area, the Honeycut not been recognized in sinks or collapse structures can be subdivided into three units-the lower and within the Marble Falls quadrangle, the Burnam upper units composed of alternating limestone and Limestone is included here because its type locality dolomite beds and the middle unit predominantly is only 800 feet east of Marble Falls quadrangle, microgranular dolomite. Lateral gradation of lime­ half a mile north of the south border of the stone to dolomite is common. Smithwick quadrangle. Also, it is not contemplated The upper part of the Honeycut Formation is that a geologic map of the Smithwick quadrangle especially well exposed along Colorado River and will be included in the present series of Llano Flat Rock Creek, and cores extending 100 feet region maps, although all the rocks to the base of below river level were examined from the Max the Marble Falls Limestone have been mapped. The Starcke Dam site. Thin layers and small masses of Smithwick quadrangle mapping is on large aerial light-green shale are exposed in the spillway of the photographs at a scale of about 8 inches to 1 mile, dam, (locality 10-2B) and similar shale is present in and with prior arrangement can be viewed in the the cores examined as well as in a small quarry in offices of the Bureau of Economic Geology. These the Honeycut south of Alvin Wirtz Dam. photographs bear the index numbers 27T-6-34, Chert, common in the Honeycut, is mostly 6-35, and 6-41 to 6-43. chalcedonic to subchalcedonic and in part porce­ As the Marble Falls and adjacent quadrangles are laneous. A fossiliferous type of chert, referred to as rich in geologic history in the interval between the cannonball chert because of its shape, varies in top of the Ellenburger and the base of the Marble texture from solid granular to porous and chalk­ Falls Limestone, the abstract of the report by like. Barnes and others (1953) is quoted as follows: The lower part of the Honeycut in places is Discovery of Upper Ordovician strata in the Llano collapsed into the top part of the Gorman Forma­ uplift of central Texas is here reported. These rocks, tion through solution of the upper calcitic portion named the Burnam limestone, are considered to be of the Gorman. The upper surface of the Honeycut correlative with some part of the Richmond group is an erosional surface which developed karstic because of the presence in them of Halysites (Catenipora), Streptelasma ruslicum, Austinella, topography at various times, as witnessed by Mcewanella raymondi, Strophomena aff. S. nutans, preservation of formational remnants in collapse Rhombotrypa, and other fossils. Closest correlation is structures, such as the Upper Ordovician Burnam believed to be with the Maquoketa formation and Limestone, the Silurian Starcke Limestone, and equivalents in the Mississippi Valley, but affinities are various Devonian units. also indicated with the type Fernvale formation of Southwest of Alvin Wirtz Dam the Honeycut is Tennessee, the so-called Fernvale limestone of extensively sliced by small faults along the Marble Missouri, Arkansas, and Oklahoma, and possibly with

6 Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas some part of the upper Montoya limestone and upper and of probable Wenlock age. Seddon (1970) Maravillas chert of West Texas. discusses the conodonts of the Starcke Limestone, The only outcrops of the Burnam limestone known especially in the light of reworking of Starcke at present are preserved in a collapse structure in conodonts into younger formations. Seddon re­ southern Burnet County, Texas. This limestone is vised the maps in figure 1 of the Silurian publica­ exceptionally pure, very coarse-grained, light-colored, tion (Barnes and others, 1966) showing later and fossiliferous. Large and relatively solid fossils information. such as corals and cephalopods show evidence of breakage and wear, but smaller and normally buoyant ones such as brachiopods are not worn, although they DEVONIAN SYSTEM are commonly disarticulated. Environment of deposi­ tion may have been near a wave-breaking organic reef Stribling Formation (or reefs) or near pre-existing coral beds. Rocks equivalent in age to the Burnam limestone The Stribling Formation (Barnes and others, are to be expected in the subsurface of north-central 1945, 1947a) crops out in two areas just east of and West Texas, as well as in the Llanoria channel of the Starcke Limestone outcrop about 4,000 feet the Ouachita trough. The growing list of relict south-southwest of Max Starcke Dam. The eastern Paleozoic formations being found around the margins outcrop forms a small hill in which about 10 feet of the Llano uplift indicates the probability of a more of strata is fairly well exposed. The lower part of complete subsurface Paleozoic succession in Texas the Stribling in this hill is dolomite and the upper than was formerly supposed. part is Leptocoelia-bearing limestone. The lime­ Since that report was written, outcrops of stone and dolomite are both microgranular and Burnam Limestone have been found 700 feet yellowish gray to olive gray, Both contain sub­ east-northeast and 900 feet southeast of the type chalcedonic chert in shades of yellowish gray, olive locality (Barnes and others, 1966). The Burnam is gray, and grayish white. coarse grained, yellowish gray, and fossiliferous, The western outcrop is collapsed into Honeycut with occasional pebbles of fine-grained yellowish­ Formation rocks and consists of three units. The gray to pearl-gray limestone. basal unit is a carbonate rock, brownish in color, Merrill (1965) reports on the conodonts from with sand, glauconite, phosphatic pellets, and the Burnam Limestone and concludes that two conodonts. Seddon (1970, p. 24) concludes that ages of conodonts are present, Late Ordovician and this member, on the basis of conodonts is "correla­ Early Devonian. The Late Ordovician conodonts tive with the Edgecliffe Limestone Member and indicate a correlation with the Maquoketa Forma­ Springvale Sandstone Bed at the base of the tion of Iowa. The Early Devonian conodonts are Onondaga Limestone." thought to be fissure fillings and compare favor­ The other two units are in contact with the basal ably with forms from the Emsian Series of unit, but because of the collapse their stratigraphic Germany. Seddon (1970, pp. 8-10) further dis­ position in reference to each other is uncertain. cusses the conodont evidence furnished by Burnam The eastern end of the outcrop is normal cherty rocks. Stribling similar to that on the hill to the east. The western end of the outcrop is coarse-grained, SILURIAN SYSTEM yellowish-gray limestone (locality 10-3A) that has not been seen elsewhere in the Llano region. It Starcke Limestone contains abundant conodonts. Seddon (1970, p. 24) states, "The conodont evidence suggests that The Starcke Limestone type locality (locality the type section at Honeycut Bend, the nearby 10-3B) is situated on the C. H. Dean ranch, 4,000 section at Honeycut Hollow, and the limestone at feet south-southwest of Max Starcke Dam. One locality 27T-10-3A are coeval and correlative with other outcrop of Starcke Limestone is known, the Nedrow-Moorehouse interval of the Onondaga southeast of the type locality of the Burnam Limestone." Limestone on the Smithwick quadrangle. Boucot and Johnson (1967), on the basis of The Starcke Limestone "is medium-to-coarse­ brachiopods, correlate the Stribling Formation at grained, pinkish gray, massive, and locally brecci­ the type section with the Esopus Formation of ated. It crops out in an area about 50 feet across, New York and the limestone at locality 10-3A but exposures are discontinuous because of soil with the Schoharie Formation. The brachiopod cover, and neither top, bottom, meaningful esti­ evidence suggests, therefore, that the limestone at mate of thickness, nor sequence can be given" locality 10-3A is the middle member of the (Barnes and others, 1966). Fossils are abundant Stribling.

7 Bureau of Economic Geology, The University of Texas at Austin

In the southeastern corner of the Marble Falls likely Stribling Formation. In this area the Ives is quadrangle, broad areas of soil with Stribling-type composed of chert from the Stribling, and where chert have been mapped as Ives, CDhi?, because of this chert is distributed through the soil the the inability to distinguish chert derived from the identity of the underlying formation is uncertain. Stribling from chert derived from the Ives Breccia, Ives was not seen west of U. S. Highway No. 281. which is composed predominantly of Stribling In a few areas of poor outcrop, the Ives Breccia chert in this area. appears to surround boulders of Ellenburger up to 5 feet in size, similar to its occurrence in the bed of MISSISSIPPIAN-DEVONIAN ROCKS Double Horn Creek on the Spicewood quadrangle (Barnes, in press). The maximum thickness of Ives Crack Fillings Breccia seen within the quadrangle is about 2 feet. Much of the chert in the Ives appears to have been Carbonate crack or joint fillings of post­ derived from Stribling rocks. Ellen burger rock, common in the upper 20 feet or Doublehorn Shale Member.-The Doublehom so of the Honeycut Formation, mostly range from Shale Member is confined to the southeast comer dull yellow to yellowish brown and dark brown of the quadrangle in a soil-covered belt about 100 and commonly contain sand grains, dolomite to 500 feet wide between the Chappel Limestone rhombs, and occasionally glauconite grains. The and Barnett Formation and rocks mapped as CDhi? crack fillings are predominantly Devonian in age, which probably include both Ives Breccia and but the presence of crack fillings of Mississippian Stribling Formation. Excellent exposures of the or even of Pennsylvanian age is possible where Doublehom Shale are in the Spicewood quadrangle rocks of these ages rest directly on the Ellen burger. (Barnes, in press) to the southeast and in the Conodonts must be relied upon for age determina­ Smithwick quadrangle (Cloud and others, 1957) to tion. Crack fillings are noted on the map by the the east. symbol +D?. Crack fillings were mapped 300 feet west, 600 MISSISSIPPIAN SYSTEM feet south (localities 10-3C, 10-3D), and 1,100 feet west-northwest of the Starcke Limestone outcrop; Chappel Limestone one is near the eastern edge of the Marble Falls quadrangle 1.3 miles from the south border; and Chappel Limestone is present in numerous out­ another (locality 10-lA) is at the south edge of crops in the east-central and southeastern parts of Lake Marble Falls. the Marble Falls quadrangle. Eight outcrops were seen along several miles of Barnett-Honeycut con­ Houy Formation tact in the western part of the quadrangle. The Chappel, up to 2 feet thick, consists of crinoidal Cloud, and others (1957, pp. 511-512) state: debris in a matrix of fine-grained limestone. The The Houy Formation is the representative in limestone is tough and medium to rather dark gray Central Texas of the widespread Upper Devonian and with a brownish cast. Conodonts are the chief Lower Mississippian black-shale succession that in· fossils used in correlation (Hass, 1959) and other eludes such well-known eastern and midcontinent fossils present include brachiopods and trilobites. deposits as the Chattanooga, Ohio, New Albany, and An unidentified tooth was found in the Chappel at Woodford Shales. locality 10-2A. The deposits included in the Houy Formation comprise several distinctive lithic types and may well be an unnatural agglomeration of discrete micro· Barnett Formation units. It is generally possible, also, through laboratory studies of the conodonts found in them, to assign a Unlike the Silurian, Devonian, and Mississippian probable age to any given thin interval, bed, or rocks so far discussed, the Barnett Formation pocket of the Houy Formation. forms a continuous outcrop beneath the Marble The type sections of the Houy Formation and Falls Limestone. Excellent exposures are found in the Doublehorn Shale Member are along Burnam road cuts and road material pits south of Colorado Branch where it enters Double Horn Creek about River in the vicinity of Max Starcke Dam. The 0.8 mile east of the Marble Falls quadrangle. Barnett is mostly dark-gray oil-bearing shale that Ives Breccia Member.-Ives Breccia crops out in contains limestone concretions 2 feet or so in many places in the east-central part of the Marble diameter and 6 inches or so thick; they may Falls quadrangle. In the southeast corner of the contain live oil in interior cracks. In the south­ quadrangle, part of the area mapped as Ives is very eastern corner of the quadrangle, some chert

8 Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas

present in the Barnett is similar to that described in The interval above the reef and spiculite is the Spicewood quadrangle (Barnes, in press). mostly limestone, cherty limestone, and spicu­ Within the quadrangle the Barnett probably liferous limestone with 21 feet of spiculite at the averages 15 feet thick. top. The limestone is mostly very fine grained Fossils, other than conodonts, were not seen in and either pale yellowish brown and between the Barnett during mapping of the quadrangle. yellowish brown and light olive gray. A few beds Hass (1953) has described the conodonts of the are highly crinoidal and crinoid fragments are Barnett Formation. common in most beds. Some of the massive limestone is highly oolitic and most is crowded with microfossils. PENNSYLVANIAN SYSTEM The chert in the Marble Falls is mostly in thin nodules and branching forms parallel to the Unnamed Phosphorite bedding. The chert is black, grayish black, grayish brown and is commonly spiculiferous. Two deposits of low-grade phosphorite up to 11 The Marble Falls Limestone forms a broad feet thick (locality 10-lOA) are present about 0.2 outcrop north of Colorado River, northeast of mile west of U.S. Highway No. 281 at a point Marble Falls, which continues southwestward along nearly 1.5 miles south of Colorado River (Barnes, the northwest side of a fault to Varnhagan Creek. 1954). The phosphorite is composed of ooids From here it continues westward to a branch of mostly between 0.1 and 0.6 mm in diameter, the Marble Falls fault, and beyond the fault it is structureless pellets, and phosphatic fossil debris. A present as outliers. South of the Colorado along basal 3-inch, reddish-brown, phosphatic conglom­ the eastern edge of the quadrangle, the Marble erate and three 4- to 6-inch impure limestone beds Falls occurs as outliers and in fault blocks. The are present in the phosphorite. Marble Falls also is dragged up along Marble Falls Conodonts from a limestone bed in the phos­ fault near Granite Mountain and, further northeast phorite and from phosphorite adhering to the bed along the fault, occurs as a steeply northeastward­ were identified by W. H. Hass of the U. S. Geologi­ dipping outcrop of the entire formation. cal Survey as predominantly Lower Pennsylvanian Microfossils, spicules, and crinoid debris are in age. abundant. Corals and brachiopods are fairly com­ mon and gastropods were noted. Silicified brachio­ Marble Falls Limestone pods are scarce.

The type locality of the Marble Falls Limestone is along Colorado River downstream from Marble Smithwick Formation Falls. Prior to completion of Max Starcke Dam, Barnes (1952b) measured and described the The Smithwick Formation crops out in the 385-foot-thick type section now beneath the water western part of the city of Marble Falls, forming a of Lake Marble Falls. In that publication the belt 1.3 miles wide which extends from a point various facies of the Marble Falls Limestone were 2 miles north of Marble Falls to a point 4 miles mapped in the vicinity of the type section, southwest of Marble Falls. The Smithwick is including a reef facies in the lower part, about limited to the northwest by the Marble Falls fault 115 feet thick, which grades laterally to spiculite. or by fault slivers of older rocks dragged up along Thin beds of dolomite were noted at localities the fault. 10-lB and 10-lC. Fresh outcrops of dark grayish-black shale are The spiculite is dark gray, fissile, and hard. The scarce; mostly the Smithwick is weathered yellow­ associated limestone is fine grained, highly spicu­ ish green or is masked by cover which in the liferous, and medium gray to medium dark gray. Marble Falls quadrangle consists of large areas of The spiculite and spiculiferous limestone weather terrace deposits and alluvium. to form porous to honeycombed tripolitic chert of Sandstone beds were seen only in the western a russet color. part of the outcrop north of Colorado River. The reef limestone is very fine grained, massive, Plummer (1950) described 301 feet of Smithwick medium olive gray ranging toward light brownish shale in a section east of Granite Mountain. He also gray and is a high calcium limestone. lists fossils found in the Smithwick.

9 Bureau of Economic Geology, The University of Texas at Austin

MESOZOIC ROCKS possible that the two belong to the same igneous event. Basic rocks somewhat similar in appearance CRETACEOUS SYSTEM (LOWER CRETACEOUS) to the diabase have been mapped in the Blowout quadrangle (Barnes, 1952a) and adjacent area. Trinity Group Their age is unknown.

Shingle Hills Formation (Barnes, 1948) CENOZOIC ROCKS

Hensell Sand Member.-A thin mantle of Hensen QUATERNARY DEPOSITS Sand rests on the Paleozoic rocks in a few places in the southeastern part of the Marble Falls quad­ rangle. East of Flatrock Creek a deep channel filled Terrace deposits and colluvium.-Most of the by conglomerate derived from Paleozoic and Pre­ terrace deposits within the Marble Falls quadrangle cambrian rocks crosses State Highway No. 71. The rest on Smithwick Formation. Those south of Hensen is mostly reddish in color, conglomeratic, Colorado River are notably siliceous and are very poorly sorted, and ranges from boulders, derived from the more resistant rocks of the cobbles, pebbles, and granules through the various Precambrian, Paleozoic, and Cretaceous. Slumping sand sizes to silt and clay. The more siliceous of the gravel onto the soft shale of the Smithwick portions, where not cultivated, support a growth of has rendered the mapping of the boundary of the broad leaf oak. deposits uncertain in some areas. Another large area of terrace deposits just north POST-SMITHWICK? MESOZOIC? DIABASE of the Colorado has been mapped chiefly on the basis of its topographic expression and should be Diabasic rock is present intermittently along the similar to the deposit south of the river. Marble Falls fault for a distance of at least 3 miles High on the landscape north of Marble Falls, a within the Marble Falls quadrangle. The thickest large area of terrace deposit in the upper reach of body, perhaps as much as 70 feet thick, is a quarter Whitman Creek includes considerable colluvium. It of a mile northeast of Colorado River. Exposures is likely that Hamilton Creek, now entirely to the are poor and the dike was mapped mostly on the east on the Smithwick quadrangle, originally fol­ basis of a depression along the Marble Falls fault lowed Whitman Creek and flowed into the Colo­ and an occasional outcrop of spheroidally rado at Marble Falls, and that the large deposit of weathered diabase. A quarter of a mile southwest terrace and colluvium is related to this ancient of Colorado River (locality 10-17 A), diabase course of Hamilton Creek. Hamilton Creek, in its occurs as sheets separated by mylonitic Town lower reaches, is now entirely in Smithwick Forma­ Mountain Granite. In an outcrop along Backbone tion and it seems likely that some headward­ Creek (locality 9-20A) the diabase is brecciated, eroding stream tapped Hamilton Creek diverting it but elsewhere brecciation was not seen. In these to its present course. last two localities the diabase outcrops were too Alluvium.-At the time Marble Falls quadrangle small to show. was mapped before Max Starcke Dam was com­ P. T. Flawn, in a thin section examination of pleted, the alluvium along Colorado River was this rock, "found about 75 percent plagioclase subdivided into frequently flooded river-bottom (about labradorite) in ophitic arrangement, 6 per­ alluvium and a low alluvial terrace that was seldom cent carbonate, 8 percent chlorite probably altered flooded. As much of the river-bottom alluvium is from pyroxene, 6 percent magnetite or ilmenite, now flooded, this distinction has not been main­ 4 percent leucoxene, and about 1 percent rutile." tained. Areas of alluvium have been mapped along The age of this intrustion is unknown. The Flat Rock Creek and Backbone Creek and its Marble Falls fault is post-Smithwick in age; the branches Dry Creek, Sparerib Creek, and Whitman intrusion follows the fault and in one place is Branch Narrow belts and patches of alluvium interleaved with mylonite produced by the fault­ follow many of the lesser drainages in the quad­ ing. This evidence indicates that the intrusion is rangle but are insignificant and have not been post-faulting in age. Cretaceous igneous rocks in mapped. Much of the alluvium along Colorado the Balcones fault zone, 30 miles to the southeast, River and some of the alluvium along lesser are more basic than the diabase, yet it may be drainages has been cultivated.

10 Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas SUBSURFACE GEOLOGY

About a third of the quadrangle surface is The following thicknesses of Paleozoic units underlain by Town Mountain Granite of the within the Marble Falls quadrangle are chiefly from Granite Mountain pluton, and it seems likely that Barnes and Bell (1977), Cloud and Barnes (1948), the Paleozoic rocks of most of the rest of the and Barnes (1952b): quadrangle will also be underlain by Town Moun­ Thickness in feet tain Granite. Monadnocks present on the Precam­ Pennsylvanian System­ brian surface when the Cambrian sea invaded Smithwick Formation 300+ central Texas are preserved as buried hills, two of Marble Falls Limestone ...... 385 which have been partly exhumed in the north­ Mississippian and Devonian Systems ...... 10-50 eastern part of the quadrangle. Another is present Ordovician System (Ellenburger Group)- Honeycut Formation ...... 600-7 50 in the Longhorn Cavern quadrangle just to the Gorman Formation ...... 475-485 north and others are probably nearby in the Tanyard Formation ...... 550-650 subsurface. On the basis of gravity data Cambrian System (Moore Hollow Group)- (Bhatrakarn, 1961; Youash, 1961), the edge of the Wilberns Formation ...... 520-560 San Saba Member ...... 270-360 Granite Mountain pluton appears to be about Point Peak Member ...... 50-100 1 mile northeast of the exhumed monadnocks. Morgan Creek Limestone Member ...... 130-145 Further speculations considering the size and shape Welge Sandstone Member ...... 10± of the pluton of which the Granite Mountain Riley Formation ...... 670-750 Lion Mountain Sandstone Member ...... 55-65 pluton is a part are discussed by Barnes (Spice­ Cap Mountain Limestone Member ...... 390-470 wood quadrangle, in press). Hickory Sandstone Member ...... 260-300

MINERAL RESOURCES

The known mineral resources of the quadrangle analyses are given for a few of the building stones. are limited to nonmetallic substances and water. A Four samples of Town Mountain are described. small deposit of lead and zinc just north of the The chief locality, Bu-5, is the Granite Mountain Marble Falls quadrangle in Cap Mountain Lime­ locality analyzed by Goldich (1941). Clabaugh and stone indicates the possibility of the presence of McGehee (1972) give an up-to-date resume of the similar deposits in the subsurface in the north­ operation at Granite Mountain as follows: eastern comer of the quadrangle. Outside of soil, much of which is suited only for ranch land, the The Granite Mountain quarry was opened in 1882 on an exfoliation dome about a mile northwest of most important nonmetallic resources are construc­ Marble Falls. The rock is coarsely crystalline granite tion materials. of the Town Mountain type composed chiefly of microcline, plagioclase, and quartz with minor CONSTRUCTION MATERIALS amounts of biotite, hornblende, rutile, apatite, zircon, and allanite. A few of the large microcline Dimension stone.-The building stones of the crystals are complexly zoned and mantled by Marble Falls quadrangle were described by Barnes plagioclase. Dark biotite-bearing xenoliths and and others (194 7b ), including four localities of schlieren are not uncommon in the granite. Town Mountain Granite, one locality of Cap The Texas Pink Granite Company took over Mountain Limestone, three localities of Ellen­ operation of the quarry in 1893, and in 1895 the burger limestone and dolomite, and three localities owners agreed to donate sufficient granite for con­ of Marble Falls Limestone. For each deposit the struction of the State Capitol Building. Prison labor was used to operate the quarry, and a narrow-gauge following information is included: locality and railroad was built by the State to haul more than geology, megascopic description, microscopic 15,000 carloads of granite from the quarry to the description, and recommendations; for selected Capitol Building site in Austin. Granite Mountain also samples, physical properties are given, including provided the stone for the Galveston seawall and compressive strength, specific gravity, percent most of the jetties along the Gulf Coast of Texas and absorption, and durability tests. Also, chemical Louisiana. By 1940 approximately 34 million tons of

11 Bureau of Economic Geology, The University of Texas at Austin

stone had been shipped from the quarry for use in pany as the Granite Shoals Division of the company. buildings and monuments throughout the country, The first shipment from this deposit was made June including two wings of the American Museum of 4, 1964, and during the next 4 years approximately Natural History in New York, the Times Building in half a million tons of granite jetty stone was shipped. Los Angeles, the Northwestern Life Insurance Build· This granite was used for repair and new construction ing in Seattle, and surprisingly, the Leif Erickson of jetties on the Gulf Coast. Memorial in Iceland. Mr. Johnnie Petrick, superintendent, gave the During 1950 the Texas Granite Corporation following description of the operation: "Once the acquired Granite Mountain. This company is a subsid· face was opened to the natural horizontal bed, some iary of the Cold Spring Granite Company of 50 feet in depth, the ends of the face were broached Minnesota, which operates quarries at several other out with Gardner-Denger channel bars. Line drilling places in the United States and Canada and dis­ at the face was done with Gardner-Denver air tracks tributes at least 24 different colors of commercial drilling 21h inch holes to the depth of the bedding. granite. Stone from Granite Mountain is currently Prima cord was used with cement for stemming to lay marketed as "Sunset Red"; it was formerly known as the burden down in large blocks. After the blast, jack "Texas Pink." Among the buildings built of this stone hammers were used to start the feathering and in recent years are the new State office buildings near wedging process to make specification blocks, which the Capitol in Austin, the Los Angeles County ranged from 2-18 tons. These blocks were loaded on Courthouse, and the Prudential Life Insurance Build­ rail cars and switched 41h miles north to the main line ings in Houston and Minneapolis. The Texas Granite of the railroad." Corporation also operates a second quarry a few miles west of Granite Mountain, from which it produces a Anderson Rock (Corner Rock on Marble Falls popular grayish-pink granite marketed as "Texas quadrangle), locality Bu-13, is 1 mile south of Hog Pearl." This granite was recently used in construction Mountain. The granite both in Anderson Rock and of the First National Bank Building in Chicago, the at Hog Mountain is of excellent quality and is world's tallest granite-clad building. suitable for all purposes for which a coarse-grained In the quarry, blocks of granite are cut free chiefly granite can be used. The Sherwood Shores Devel­ by wire sawing in which twisted strands of tough steel opment had reached the base of the rock by 1967, wire rapidly move a slurry of water and abrasive and by now it is likely that Anderson (Corner) through a slot in the stone. Other methods, including Rock is out of bounds as a quarry site. closely spaced drilling, wedging, and blasting are also used. Especially effective is a method of "jet Locality Bu-6, Kennison Rock, 2 miles south piercing" or burning channels into the granite with a west of Granite Mountain, is another large granite jet of oxygen and kerosene flame. This method is dome. The granite is of good quality in a favorable expensive, but it can be used to free large blocks of position to quarry but contains inclusions pre­ strained granite that would expand and bind drills cluding use for building stone because of the and cutting wires. considerable waste involved However, the granite Most of the granite is sawed into relatively thin is excellent for jetty stone. slabs for facing buildings, and the slabs are polished Many other granite domes and knobs, including by conventional methods. An interesting method Sow, Hickory, Goose, and School Rocks, are which produces a very attractive rough frosty finish is present between Ranch Road 1431 and Colorado also used. The sawed surface of the stone is heated rapidly by moving it through a set of blowtorch River, all of which are excellent granite. The flames followed immediately by a line of cooling supply of easily obtained stone in this area is so water jets. A thin layer of the granite spalls off to the large that it is practically inexhaustible. natural mineral cleavages in a snow of flakes. The A deposit of Cap Mountain Limestone, locality resulting surface is preferred for granite floors and Bu-15, along U. S. Highway No. 281 at the bound­ walks and for nonreflecting walls. ary of the Marble Falls and Longhorn Cavern A granite dome, known as Hog Mountain (un­ quadrangles is in beds up to 18 inches thick in an named on quadrangle), just south of Ranch Road interval in excess of 20 feet thick. The limestone is No. 1431, is partly in the Marble Falls quadrangle dark greenish gray and dark brown and is unlikely but mostly in the Dunman Mountain quadrangle to be used as a building stone because of its somber (Barnes 1978b) to the west. This locality, Bu-12, color. was visited in connection with the Fourth Annual Two deposits in the Honeycut Formation, one Forum on Geology and Industrial Minerals held in of limestone (locality Bu-31) and the other of Austin, Texas, March 14-15, 1968 and the follow­ dolomitic limestone (locality Bu-4), are along ing information is from an unpublished guidebook Flatrock Creek 2 miles by road south of Marble prepared by Barnes and L. E. Garner: Falls. The limestone is just north of the old A granite quarry was opened at Hog Mountain in Spicewood road (now abandoned) and the dolo­ January 1964 by Texas Construction Material Com- mitic limestone is just south of the road. The

12 Geology of the Marble Falls Quadrangle. Burnet and Llano Counties, Texas limestone crops out downstream a half mile or where the Colorado breaks out of its gorge in the more; at the first bend the limestone is chert free, Honeycut Formation on to the lowland of Smith­ has now been quarried, and will be discussed under wick Formation. high-calcium limestone. The dolomitic limestone is The aggregate for Alvin Wirtz Dam is crushed in beds 10 to 18 inches thick and is of little use Ellenburger rock from south of the dam, and except possibly as thick ledge stone or for crushed rip-rap was obtained from a nearby exfoliation stone. dome of granite. Most of the Ellenburger and much A quarry (locality Bu-44) east of U. S. Highway of the Marble Falls Limestone within the quad­ No. 281 in the dolomitic facies of the Gorman rangle is suitable for the production of crushed Formation is about 3 miles north of Marble Falls. stone. The dolomite is down faulted against Hickory Sandstone and is brecciated. The dolomite is red, HIGH-CALCIUM LIMESTONE in part white veined, takes a good polish and has been used for terrazzo chips. Although the stone is Barnes (1952b) reported on the chemical com­ beautiful, the deposit is not sufficiently large and position of the reef in the Marble Falls Limestone free enough of chert to produce saw blocks for use and pointed out that the reef is composed of as a building stone. high-grade limestone. Most of the reef is now The Marble Falls Limestone was sampled in probably off limits for production because of three localities in or near Marble Falls. One sample, encroachment by Marble Falls. The one attempt at locality Bu-14, was collected along U. S. Highway quarrying this reef was in a tongue of the reef high No. 281 south of the Colorado; another, locality on the landscape. Solution features filled with red Bu-19, was collected in a road cut about 1 mile sediment, probably introduced from the Creta­ southwest of Marble Falls; and the other, locality ceous and now gone at the surface, contaminated Bu-45, was collected within the north city limits of the otherwise pure limestone. The quarrying opera­ Marble Falls (locality not recovered during map­ tion was moved in mid-1957 to a limestone bed ping). Sample from locality Bu-14 is black with a that I had mapped in the Honeycut Formation grayish cast, faintly mottled, and has been used for along Flat Rock Creek and that had been men­ terrazzo chips. Sample from locality Bu-19 is dark tioned previously by Barnes and others (1947b, gray somewhat speckled by very small black and locality Bu-31). brown specks, and inch-sized, widely spaced, dark­ This operation is described by Barnes (in Barnes colored areas are present. This stone is rather and Maclay, 1976) as follows: somber and the deposit appears to be small. In 1964 underground mining was started, however, Sample from locality Bu-45 is black, maybe of some limestone is still quarried along Flatrock Creek. value for terrazzo chips, but is too highly jointed About 5 acres a year is mined underground and to to be of value as a building stone. date the area mined out totals about 60 acres. The Thick limestone beds in the Honeycut Forma­ working face is 48 feet wide by 24 feet high and tion along Little Flat Rock Creek and massive pillars are 28 feet square. Each round of shots breaks limestone in the upper part of the Gorman down about 1,000 tons of limestone. For quarrying Formation in the southern part of the quadrangle percussion drilling on a wagon drill is used, and blasting is with ammonium nitrate activated by might be of value for dimension stone. detonators. A Caterpillar 977 track frontend loader is Road materials.-Some base course material for used. Texas Highway No. 71 was obtained from Hensen The rock is trucked to a plant in Marble Falls and conglomerate south of the highway. Weathered in a primary crusher is reduced to -3/4 inch. Part of spiculiferous material from the Marble Falls Lime­ this feed goes to a Bradley ring roll mill which stone has been used extensively in the vicinity of reduces it to 16 mesh. This material goes to 4 Marble Falls. Tyler-Hummer screens. The top deck takes out the Sand and gravel.-The terrace deposits are rather -16 mesh and the lower deck takes out the -40 mesh coarse, contain considerable chert and quartz, and which goes to a 16-foot air separator that removes the those along the Colorado River contain partly -200 mesh. The -200 mesh goes to superclassifiers rotted Precambrian metamorphic rocks; in general which remove the -10 micron material. Some of the 3/4-inch feed goes to two Raymond mills then to the deposits are of little value for the production superclassifiers to take out the -10 micron material. of sand and gravel. The alluvial deposits along The following products are produced: Colorado River should be of some value for -16 mesh, most of dust removed-for glass manu­ production of sand and gravel. Sand and gravel for facture. construction of the Max Starcke Dam was pro­ -40 mesh, with maximum of 10 percent duced just east of the Marble Falls quadrangle -200 mesh-for asphalt tile and shingles.

13 Bureau of Economic Geology, The University of Texas at Austin

·200 mesh-for dry wall products Goint cements, generally good, but erratic, with median concentra­ etc.), latex filler, rice polishing, feed supple· tions in mg/I (milligrams per liter) of Si, 49; S04 , ment. 61; Cl, 83; N03 , 21; Fe, 0.07; and total hardness ·10 micron-for filler for adhesives, rubber, plastics, (as CaC03 ), 302.... The water samples with high paint. nitrate concentration typically are from wells near This limestone is so constituted that a much larger proportion of it reduces to the -10 micron higher septic systems or livestock pens." priced material with the same expenditure of energy Within the Marble Falls quadrangle, Landers as used in reducing other limestones. Because of the (1972) lists four water analyses in mg/I; these high quality of the -10 micron material and the low analyses are quoted as follows: cost of production this grade is competitive through­ Total out the United States. A very large reserve remains. Well hardness Core drilling is in progress and to date reserves for 57 number Si 804 Cl F N03 as CaC03 P04 to 100 years have been blocked out. 57302-01 175 24 65 2.5 10 330 0.03 The calcitic upper part of the Gorman Forma­ 57302-02 36 30 0.6 60 230 0.82 tion along Flatrock Creek is massive and relatively 57302-03 13 40 1.8 8 60 0.04 free of impurities. It is possibly of chemical grade; 57304-01 120 100 210 1.2 10 380 0 no analyses have been made. Ellenburger rocks and the San Saba Member contain water along joints and solution features; WATER several springs issue from the Honeycut Formation. Springs are also present at the top of the Marble The availability of water in Town Mountain Falls Limestone. Some water is present in solution Granite has been discussed by Landers (1972) and features in the Marble Falls Limestone but the Landers and Turk (1973), and their conclusions quality of water is likely to be poor. have been summarized by Barnes (1976, 1977a, The Hickory Sandstone is an aquifer in some 1977b, and 1977c) for Kingsland, Click, Dunman parts of the Llano region especially where it is Mountain, and Cap Mountain quadrangles, respec­ thick. The Hickory exposed in the northeastern tively. part of the quadrangle is thin, no springs were seen, In a study of the ground-water resources of the and water in it is likely to be scarce. Southeast of crystalline rocks of the Llano region, Landers the Marble Falls fault the Hickory is deep, far from (1972) included the resources of the Town Moun­ its recharge area, and possibly may be mineralized. tain Granite of the Marble Falls quadrangle. Within The Welge and Lion Mountain Sandstones the quadrangle he inventoried 77 wells of which 12 within reach of the drill are of limited occurrence are in granite, 56 are in granite grus, and 9 are in within the quadrangle and their quality as aquifers fractured granite. Average yield of wells from these is unknown; it is unlikely that they will contain three kinds of rock are 6.6, 21.8, and 13.7 gpm much water. (gallons per minute) respectively. The average production for all wells within the quadrangle is LEAD AND ZINC 18.5 gpm which is somewhat higher than the average value of 14 gpm found by Landers and The Slaughter Gap prospect (Barnes, 1956) is Turk (1973) for all wells in crystalline rocks of the just north of the Marble Falls quadrangle in the Llano region. They found a median depth of Longhorn Cavern quadrangle. Within the Marble 76 feet for the wells of the Llano region, whereas Falls quadrangle, buried hills of granite reaching the median depth for wells in the crystalline rocks into the Cap Mountain Limestone could be present of the Marble Falls quadrangle is 62 feet. in an area of approximately 0.8 square mile. In the Concerning quality of ground water in the Llano region lead and zinc deposits are mostly crystalline rocks of the Llano region, Landers and confined to Cap Mountain Limestone around such Turk (1973) state: "Quality of ground water is buried hills.

14 Geology of the Marble Falls Quadrangle, Burnet and Llano Counties, Texas REFERENCES

Barnes, V. E., 1948, Ouachita facies in central Texas: Univ. Internat. Geol. Cong., 1956, v. 3, p. 484-503. [Published Texas, Bur. Econ. Geology Rept. Inv. No. 2, 12 p. in Moscow.] 1952a, Geology of the Blowout quadrangle, Bhatrakarn, Tanakarn, 1961, Correlation of gravity observa· Gillespie, Blanco, and Llano Counties, Texas: Univ. tions with the geology of parts of Burnet, Blanco, and Texas, Bur. Econ. Geology Geol. Quad. Map No. 5. Llano Counties, Texas: Univ. Texas, Master's thesis, 59 p. 1952b, High purity Marble Falls Limestone, Boucot, A. J., and Johnson, J. G., 1967, Paleogeography Burnet County, Texas: Univ. Texas, Bur. Econ. Geology and correlation of Appalachian province Lower Rept. Inv. No. 1 7, 27 p. Devonian sedimentary rocks: Tulsa Geol. Soc. Digest, 1954, Phosphorite in eastern Llano uplift of v. 35, p. 35-87. central Texas: Univ. Texas, Bur. Econ. Geology Rept. Clabaugh, S. E., and McGehee, R. V., 1972, Precambrian Inv. 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A., 1972, Ground-water resources of the ---- 1978d, Geology of the Round Mountain quad· crystalline rocks, Llano area, Texas: Univ. Texas, Austin, rangle, Blanco, Burnet, and Llano Counties, Texas: Univ. Master's thesis, 99 p. Texas, Austin, Bur. Econ. Geology Geol. Quad. Map ----,and Turk, L. J., 1973, Occurrence and quality of No. 46. ground water in crystalline rocks of the Llano area, ___ In press, Geology of the Spicewood quadrangle, Texas: Ground Water, v. 11, no. 1, p. 5·10. Blanco, Burnet, and Travis Counties, Texas: Univ. Texas, Merrill, G. K., 1965, Conodonts from the Burnam Lime· Austin, Bur. Econ. Geology Geol. Quad. Map No. 50. stone of central Texas: Texas Jour. Sci., v. 27, ----,and Bell, W. C., 1977, The Moore Hollow Group p. 345-403. of central Texas: Univ. Texas, Austin, Bur. Econ. Palmer, A. R., 1954, The faunas of the Riley Formation in Geology Rept. Inv. No. 88, 169 p. central Texas: Jour. Paleont«llogy, v. 28, p. 709-786. ----, Boucot, A. J., Cloud, P. 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