1895.] NATURAL SCIENCES OF PHILADELPHIA. 93 



Into the general section, however, three divisons of the Lisbon 

 stage have to be introduced, all of which, so far as at present known, 

 are peculiar to Texas. There are (a) Frio Clays, (b) Fayette 

 Sands, and (c) Yegua Clays. These overlie the marine beds in the 

 reverse of the order here given and together aggregate a thickness of 

 nearly 1,500 feet in East Texas, while farther west this may be con- 

 siderably exceeded. 



Frio Clays. 



These clays form the uppermost division of the Eocene Tertiary 

 as shown in the Texas section. They comprise a series of dark-blue, 

 red, green, brown, and yellow clays when wet. They weather to pale 

 blue, light red, watery green, gray, and pale yellow upon exposure 

 and drying. In many places they carry numerous calcareous nodules, 

 hard when freshly exposed, but in contact with the air they soon become 

 soft and powdery, coating the exposures of the banks and outcrops 

 with a fine, limy powder, and the clays themselves may be regarded 

 as more or less gypseous throughout. In structure these deposits are 

 sometimes laminated or partially stratified, but throughout their greater 

 extent are massive and heavy bedded. The East Texas deposits ap- 

 pear to be unfossiliferous, but a considerable extinct fauna is reported 

 from the beds lying in the central and western portions of the State. 



Although reported as forming extensive deposits and covering a 

 wide area throughout the region w T est of the Brazos 12 these clays thin 

 out and are so covered by the overlapping Neocene deposits to the 

 east of that river that their existence has only been noted at a few 

 places. East of the Brazos these clays were first observed a short 

 distance east of the town of Corrigan, in Polk County, where the 

 section shows them to be dark- blue gypseous clays 13 and to lie between 

 two beds of sandstone. Thirteen miles farther east, near Fleming, 14 

 an extensive outcrop of the same clays appears. Here, however, they 

 present their calcareous features and appear to be devoid of selenite 

 and are about 160 feet in thickness. Small outcrops appear at in- 

 tervals along the Trinity and Sabine Railway and at Summit, in 

 Tyler County, a section of a cutting on the Southern Pacific Railway 

 shows the Frio clays to be about eighty feet in thickness and to be 



12 Third Annual Keport Geol. Survey of Texas, p. 116. 



13 Third Annual Report Geol. Survey of Texas, pp. 62-63, and 117-118. 



14 Durable, Journal of Geology, Sept., 1894, p. 554. 



