1895.] NATURAL, SCIENCES OF PHILADELPHIA. 99 



Jackson, and a considerable portion of the Claiborne stages are ab- 

 sent throughout the whole of this part of Texas. 



Yegua Clays. 



Immediately underlying the Fayette sands comes an extensive series 

 of clays and lignites known to the Texas geologists as the Yegua 

 clays. In the First Annual Report of the Survey these clays were 

 considered as forming a portion of the Fayette beds of Prof. Penrose 

 and were by him placed at the base of that division M and belonging 

 to the same Grand Gulf series as the overlying gray sandstones of the 

 Fayette sands as now known. The discovery of Eocene fossils in 

 the overlying sandstones as well as in the clays themselves naturally 

 relegated the whole to an olderstageof deposition than that to which the 

 Grand Gulf was supposed to belong. The wide lithological variation be- 

 tween the sandstones and thinly stratified and laminated lignitic sands 

 and clays led to the separation of the two into independent stages 

 more in keeping with their structure and evidently widely separated 

 manner of formation and deposition and the designation "Yegua 

 Clays ' ' has been applied to them from their development on the river 

 of that name. 



These beds comprise a series of dark blue, brown and gray clays 

 and blue-brown and gray sands and sandy clays. Extensive de- 

 posits of lignites are also found throughout the areas occupied by 

 them. The clays are laminated, thinly stratified and massive and 

 characterized by the great quantities of gypsum either in the form 

 of selenite crystals or as irregular masses in a crystalline form dis- 

 tributed throughout the various beds. In the eastern portion of the 

 area the laminated gypseous clays are more prevalent than farther 

 west. In Angelina County these beds are thinly stratified blue clays 

 containing small clusters of minute crystals of gypsum and occasional 

 streaks or pieces of lignite which at their contact with the overlying 

 Fayette sands on the Neches River have a thickness of over thirty- 

 five feet. The section at Clark's Crossing shows: 27 



22. Gray sandstone stained brown forming base of 



Fayette sands 3 feet. 



23. Thinly stratified or laminated blue clay with gyp- 



sum in crystals, to river level 35 " 



26 First Annual Report Geol. Survey of Texas, 1889, pp. 47-51. 



27 Third Annual Report Geol. Survey of Texas, 1801, p. 62. 



