IN THE UPPER KIO GRANnE EMBAVMENT IN TEXAS. 57 



and 28 in block D, on both sides of f'edar creelc, the difference in 

 weatherinf^ of these several horizons is perhaps most clearly ex- 

 hibited, viz: 



1. The ledges in which the river is now cutting yield but slow- 

 ly, and the channel is contracted and bordered by narrow, rocky 

 and sloping benches formed by the lowermost indurated ledges. 

 One of these was seen to contain some sand and a faint impregna- 

 tion of bituminous material. 



2. A slight recesssion of the bluffs above this level marks the 

 presence of somewhat softer beds. 



3. Then there is a shoulder in the bluff, which again consists 

 of more heavily bedded strata. 



4. These are overlain by other more rapidly disintegrating 

 beds. 



5. Uppermost the bluffs are carved into buttes consisting of 

 the highest member in the Edwards limestone, which is quite as 

 resistant to the destructive agencies at work as any of the lower 

 horizons. 



6. The limestone which follows above this corresponds to the 

 Georgetown limestone. Everywhere along the river this forms 

 the outer border of the dissected plateau. It weathers in such a 

 manner as to leave in the thin residual soil, usually present on the 

 surface, a number of angular boulders, which render the wagon 

 roads exceedingly uncomfortable for travel. 



This entire formation consists of limestone, but there is con- 

 siderable difference in the texture of different ledges. The broad 

 statement is true that all ledges consist of open sea sediments 

 and that foraminiferal shells constitute a large ingredient in 

 the calcareous material of which they are composed. Some of 

 the lower indurated ledges near Indian creek contain these minute ■ 

 shells in great abundance. In the thinly bedded ledges there is 

 more of comminuted fragments of these shells. The upper indur- 

 ated ledges show a crystalline texture, typical of much of the Ed- 

 wards limestone elsewhere. Certain of the ledges are more porous 

 than the rest, and these have become the conduits of underground 

 water, and frequently exhibit in their outcrops deeply etched sur- 

 faces. One of these ledges lies only about one hundred feet below 

 the top of the formation. It may be seen in the banks of Evan's 

 creek above the railroad bridge in the southeast quarter of sec- 

 tion 19 in block A. Another such ledge remains a,s a porous and 



