R. T. Hill — Texas Section of American Cretaceous. 291 



form, slope of surface to the southeast, that the underlying 

 strata dipped in the same direction at a slightly greater angle ; 

 and that the escarpment lines, originally light or obscure, which 

 mark the eastward recession of the rapidly disappearing forma- 

 tion, faced to the westward. Farther southward the topo- 

 graphic features along each side the line are less easily distin- 

 guishable, as in the vicinity of Waco, McLennan County, and 

 Salado, Bell County. South of the last named place, however, 

 they again become sharp, but the escarpment line increases in 

 prominence, and instead of facing westward faces to the east, 

 so that extending from Georgetown, Williamson County, to far 

 southwest of San Antonio, there is an abrupt step of several 

 hundred feet, the general altitude of the country above sea 

 level diminishing from twelve hundred feet to five hundred 

 within a score of miles. This escarpment passes near the cities 

 of Austin, San Marcos, New Braunfels, the Post Office of Heli- 

 otes, eighteen miles west of San Antonio, and from thence west- 

 ward to Rio Grande. It has long been known as a geographic 

 feature of the country. It was first described by Kennedy, and 

 later more in detail by Roemer, whose labors in Texas were 

 mostly in its vicinity, and who placed it on his map of Texas. 

 The latter utterly misinterpreted its geological features how- 

 ever as will be shown later on. When viewed from the Inter- 

 national and Great Northern railroad, which runs from Austin 

 to San Antonio, east of and parallel to it, the scarp has an 

 irregular and varying appearance, resembling a broken range 

 of distant hills. East of and at the base of the scarp is a gentle 

 undulating plane, averaging twenty miles in width south of 

 the Brazos, and extending the entire length of the State, which 

 I have described previously as the Black Prairie region.* The 

 plateau surmounting the escarpment and extending for hundreds 

 of miles to the westward, is an entirely different country. In- 

 stead of the gentle undulations of the Black Prairie, the topog- 

 raphy, where other than level prairie, has the more sharply 

 defined features of buttes and mesas ; and instead of the wide 

 flood plains and low banks there are steep banks and some- 

 times rugged canons. The color of the soil and underlying 

 rock, it is true, approximates that of the Black Prairie, but 

 in composition, structure and geological age they are entirely 

 different, facts which have been overlooked by most writers. 



A careful study of this escarpment line and the stratigraphy 

 of the adjacent- formations reveals some most interesting re- 

 sults. The underlying structure of the Black Prairie region, 

 as seen all along the foot of the escarpment, which is the same 

 as at Dallas, consists of massive, soft, chalky limestones {A), 



* This is the "gently undulating, or hilly region" of Roemer, and the "soft 

 lime rock region" of Roberts. ' 



