UPPER CRETACEOUS. 



649 



H 14. SOUTHERN TEXAS. 



In describing the Upper Cretaceous of the Rio Grande section near Eagle Pass, 

 Vaughan *^^ adopted with sHght modifications the classification of Dumble ^^ and 

 distinguished the Eagle Ford formation, Austin chalk, Upson clays, and Eagle 

 Pass formation. The Eagle Ford rests upon the Buda limestone of the Comanche 

 series. It is composed of flaggy argillaceous limestones, in places separated by 

 calcareous shaly layers. The thickness is 250 feet or more. 



The Austin chalk is a soft, chalky, argillaceous white limestone, composed in 

 part of Foraminifera. Its thickness is undetermined but was estimated by Dumble 

 at 1,500 feet. 



. The Upson clays are described as yellow at the base and as containing calca- 

 reous septaria; the upper portion is a clay shale. The thickness was estimated by 

 Dumble at 700 feet. 



The Eagle Pass formation is described as comprising three members, called 

 San Miguel beds, Coal series, and Escondido beds. These consist of sandstone and 

 clay with coal beds, of which Vaughan gives many detailed sections. An artesian 

 well near Eagle Pass penetrated 1,512 feet of strata, of which Vaughan assigns 767 

 feet to the San Miguel beds and 745 feet to the Coal series. A summary of the 

 formation is given as follows: 



Resume of characters and thicJcness of the Eagle Pass formation. 



Escondido beds, composed of sandstones and clays, with many fossiliferous horizons, exposed Feet. 



for 26 miles below Eagle Pass 2,600 



Coal series, as determined by artesian well bore, which begins in the uppermost bed 900 



San Miguel beds, the lower 600 feet of the artesian well bore and the thickness of sandstone 



exposed in the hills north of the Carter ranch, 15 miles above Eagle Pass (200?) 800 



4,300 



^Aguilera^*^ has divided the Upper Cretaceous in the coal-bearing area of 

 northern Coahuila, south of Eagle Pass, into the Sabinas, Las Esperanzas, Barro- 

 teran, and Peyotes formations. 



In the Uvalde area, Texas (99° 30'-100° west longitude and 29°-29° 30' north 

 latitude), according to Vaughan,*^^"" the Upper Cretaceous rests upon the Buda 

 limestone and exhibits the following divisions: 



Generalized section of Upper Cretaceous sedimentary roclcs of Uvalde quadrangle, Texas. 



