. Annual report of the United States Geological Survey to the Secretary of the Interior . rate, and this united Basement bedascends the sloping Paleozoic floor as a deposit synchronous withthe lower part of the Glen Rose beds and continues to representthe attenuated littoral of the latter to north of Nix. At Burnet thematerial consists of coarse conglomerate and grit embedded in areddish clay matrix, as seen in Hamilton Creek and Post Mountain,south, west, and north of the town. In this area the Basement bedscontain the debris of the granite, Algonkian, Cambrian, and Silu-rian rocks. 180 BLACK
. Annual report of the United States Geological Survey to the Secretary of the Interior . rate, and this united Basement bedascends the sloping Paleozoic floor as a deposit synchronous withthe lower part of the Glen Rose beds and continues to representthe attenuated littoral of the latter to north of Nix. At Burnet thematerial consists of coarse conglomerate and grit embedded in areddish clay matrix, as seen in Hamilton Creek and Post Mountain,south, west, and north of the town. In this area the Basement bedscontain the debris of the granite, Algonkian, Cambrian, and Silu-rian rocks. 180 BLACK AND GRAND PRAIRIES, TEXAS. From Burnet northward to Nix the Basement sands are thin andrepresent the interior margin of the upper Glen Rose formation as faras the center of western Lampasas County, when they begin todescend and thicken at the northward slope of the Burnet highland ofthe Paleozoic floor. The following section at Twin Sisters Peak, Lam-pasas County, shows the nature of the Basement sands in this generallocality. (See fig. 16.) The section includes Cretaceous rocks from. Fig. 16.—Section of Twin Sisters Peaks, Lampasas County, Texas. (For explanation of lettering see PI. XVI, p. 110.) the Carboniferous to tne base of the Caprina limestone in Twin Sis-ters Peaks, and is given in descending order. The base of the Cre-taceous is 160 feet below the Fredericksburg division. Section No. II.—Twin1 Sisters Peaks, Lampasas County (Taff). Feet. 5. Caprina limestone; indurated chalky limestone forming cap rock of the butte. 84. Comanche Peak limestone from below the cap of the peak to top of theWalnut bed. The rock is soft, white, heavily bedded, almost pure lime-stone. Numerous fossils of EnaUaster texanus, Diplopodia, and gasteropodsoccur at base of bed. The lower 25 to 30 feet is a chalky limestone verylike the above. Schloenbachia acutocarinata, Cyprimeria texana, Area, Enal-laster texanus, Diplopodia texanum, and gasteropods occur in the lower chalky limestone 67 3
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