IX THE UPPEK EIO GEAXDE EMBATMENT IN TEXAS. 73 



mostly composed of siliceous material, but they contain occa- 

 sional ledges consisting of organic fragments. In this respect the 

 formation resembles the Anacacho limestone, to a part of which 

 these beds clearly are equivalent. Green grains of glauconite are 

 also present. 



But the best exposures of these beds occur in the bluffs of the 

 Rio Grande all the way from two to six miles below the mouth of 

 Hackberrj- creek, also called Canyon Chiquito. The sandstones are 

 interbedded with clays or shales. These shales increase in thick- 

 ness and frequency in the upper parts of the beds, which are ex- 

 posed farther down the river. A section of the lower part of the 

 beds seen in the river bluff near the old village of San Miguel is as 

 below: 



Sandstone 8 feet. 



Clay 5 



Sandstone 7 



Clay 9 



Calcareous sandstone S 



Clay 10 



Soft sandstone 18 



Clay, only partly seen 7 



These same ledges were again seen near the old Stone ranch 

 northwest of Paloma, and on survey 86 in block 7 northeast of 

 Paloraa. From the last place their outcrop was traced in a 

 northeast direction for four miles, but beyond this they could not 

 be identified. 



Near Paloma a ledge of sandy limestone runs parallel with 

 the outcrops just described, at a distance of a mile to the south 

 of there. About 100 feet of clay separates these two ledges. The 

 upper Paloma ledge is overlain by another heavy bed of clay and' 

 above this there is more sandstone, which is soft and friable and 

 of a dark rusty brown color. On Elm creek the thickness of the 

 San Miguel beds does not-much exceed 4:00 feet. From the log of 

 a boring which was made near Eagle Pass many years ago and 

 which penetrated to the shales below these beds,* it is clear that 

 the upper part of these beds consists of clays which measure some 

 230 feet. These might perhaps as well be classified with the over- 

 lying coal series. 



• Thomas W. Vaughan, Bull. 164. U. S, Geol, Surv.. p. 24. 



