. Annual report of the United States Geological Survey to the Secretary of the Interior . the prairie proper, the Trinity, Paluxy, Leon, andSan Gabriel type, the alluvium is nearly all derived from the Cretace-ous, but is of two distinct and contrasting types. One of these, derivedfrom the limestone formations, is of the nature of light-colored cal-careous marls Avith pebbles of rolled fossils and Cretaceous limestone,usually accompanied by vast quantities of flint; the other, found onlyin the Leon, Bosque, Paluxy, and Trinity drainage, is made up largelyof sands derived from the Paluxy and Tr
. Annual report of the United States Geological Survey to the Secretary of the Interior . the prairie proper, the Trinity, Paluxy, Leon, andSan Gabriel type, the alluvium is nearly all derived from the Cretace-ous, but is of two distinct and contrasting types. One of these, derivedfrom the limestone formations, is of the nature of light-colored cal-careous marls Avith pebbles of rolled fossils and Cretaceous limestone,usually accompanied by vast quantities of flint; the other, found onlyin the Leon, Bosque, Paluxy, and Trinity drainage, is made up largelyof sands derived from the Paluxy and Trinity formations. The alluvial material of the streams rising within the Black prairiebetween Trinity River at Dallas and Red River is nearly all redepos-ited black, waxy soil, derived from the Navarro. Taylor, and Austinformations and so resembling in composition the adjacent residualsoils, both of which make a mantle of deep black loam, that the twoare almost indistinguishable. The Sulphur River deposits are com-posed largely of the black, waxy material mixed with the Eocene HILL.] VARIOUS TERRACE FORMATIONS. 351 SKIOND-HOTTOM FORMATIONS AN INDEX TO DENUDATION OF CENTRAL PROVINCE. While terraces of the same relative age and level are not always com-posed of similar material, the degradation of the Central province fromlayer to layer has been so uniformly progressive in geologic time thatsufficient data are recorded in this material, when properly referredto its appropriate source, to enable us to interpret the history ofthe denudation of the vast Central Province and the recession of thescarps of the Great Plains and the Black and Grand Prairie it is that the older alluvium of the Colorado and Brazos basinsis largely made up of flint debris derived from the Edwards limestone,which once covered the Central Province, while the newer terraces aresuccessively made up of the older and older formations of the CentralProvince as denudation proceeded downward in
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