290 jR. T. Hill — Texas Section of American Cretaceous. 



paper, to which the former was but introductory, I propose to 

 diagnose more clearly this lower group and to explain many 

 new features of it which- throw much light upon the American 

 Cretaceous section. 



The strata of the Cretaceous period in the Texas region are 

 so uniform and simple in their deposition, and the exposures 

 and contacts of the groups so well marked, that the}' would 

 be easily described, had not the publications by early writers* 

 involved it in much confusion. 



In the paper upon the Topography and Geology of the Cross 

 Timbers, I showed how the westward extension of the upper 

 Cretaceous from the other Gulf States abruptly ended along a 

 line commencing in the vicinity of old Fort Washita, Indian 

 Territory, and how it extended, as shown upon the accompany- 

 ing map, from that point a little west of the cities of Denison, 



Sherman, McKinney, Dallas, 

 'J* ^*~~^\^xC-- '^^0^^>^-^ Waco and San Antonio, and 

 i^^^^W through the cities of Austin, 

 |S? ; ' j San Marcos and New Braun- 

 ^°V-J fels, to a point eighteen miles 

 V \S. west of Eagle Pass where it 

 crossed the Eio Grande into 

 Mexico. In additition to be- 

 ing the line of demarcation 



;vj between the upper, the mid- 



i -- die and lower groups of the 



^"~ Cretaceous formation, it is the 



western limit of the fertile 



E=a Black Prairie Region, and 



t^uwis! separates the reliable agricul- 



.i&tluww^g tural from the grazing region 



a of Texas; a complete change 



";w"-SM5-"iir in the topograph} 7 , meteoro- 



cavWitr^sss ] nry anc [ other natural condi- 



E^£m~« tlons taklD S P lace when tbe 

 line is crossed into the central 



Geologically it is one of the clearest and 



demarcation in America, and along it is to 



be seen what I believe the most comprehensive section of the 



Cretaceous formation to be found on this continent. 



denuded region, 

 sharpest lines of 



The Austin New JBraunfels N on- conformity. 



I have previously shown that along the northern third of 

 this boundan 7 line the country was generally level, with a uni- 



* The writer has made a careful compilation of the literature of the geology of 

 Texas, and endeavored to make a complete reference book for those who wish to 

 trace the development of geological knowledge in that region. See Bulletin No. 

 45, TJ. S. Geological Survey. (In press.) 



