. Annual report of the United States Geological Survey to the Secretary of the Interior . ent lime-stones has produced some striking effects in places, resulting in apeculiar red-colored cavernous rock composed of the siliceous pseudo*morphs of fossil Mudistes and other shells, the interstitial spaces glit-tering with minute quartz crystals which line them. Where the harder limestones form the summit of extensive plateaus,such as those of the Lampasas Cut Plain and Edwards Plateau south-west of Austin, the flints are sometimes left in great quantities as aresiduum. These often cover large area
. Annual report of the United States Geological Survey to the Secretary of the Interior . ent lime-stones has produced some striking effects in places, resulting in apeculiar red-colored cavernous rock composed of the siliceous pseudo*morphs of fossil Mudistes and other shells, the interstitial spaces glit-tering with minute quartz crystals which line them. Where the harder limestones form the summit of extensive plateaus,such as those of the Lampasas Cut Plain and Edwards Plateau south-west of Austin, the flints are sometimes left in great quantities as aresiduum. These often cover large areas of country. The flints havealso been transported in past geologic times by streams and are dis-tributed over large areas along the margin of the Black Prairie as apart of the post-Cretaceous gravels of that region. These are the onby flint horizons, so far at least as is known to thewriter, in the Cretaceous deposits of the United States. (See Pis. XXXand XXXI.) They occur about the middle of the Lower Cretaceous U. S. GEOLOGICAL SURVEY TWENTY-FIRST ANNUAL REPORT PART VII PL. XXVIII. EDWARDS LIMESTONE, BARTON CREEK, TEXAS. °f ILLINOIS HILL.] FEATURES OF THE EDWARDS LIMESTONE. 229 series, instead of at the top of the upper series, as in England. Itwas from these flints that the ancient and modern Indians made theirimplements, and the ease of their lithologic identification will be of valueto the anthropologist in tracing the extent of the intercourse and depre-dations of former Indian tribes inhabitating this region. Occasionallythe flints, especially an opalescent variety in Comanche County, possessnuclei in the shape of fossils, usually Requienia. In going south theflints first appear in the vicinity of Meridian, but sparingly; theyincrease in number very rapidly to the south, being seen in greatquantities about Belton. South of the Paluxy the formation canalways be distinguished by the immense quantity of these flint nodules,which are embedded in and between the limestones
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