IN THE UPPEK BIO GRANDE EMBAYMENT IN TEXAS. 61 



exposed by an excavation, and here they are seen to be heavily 

 charged with amorphous oxide of iron. Farther to the south- 

 west a seam of practically pure hematite was noted, measuring- 

 from one to four inches in thickness. This was seen to extend for 

 nearly a hundred feet in a recently cut gully. From a general 

 examination of the vicinity it was, however, evident that this 

 deposit is local, the ferruginous character of the clay diminishing 

 in both directions from this place along the exposed outcrop of 

 •the Del Jiio formation in this bluff. This red clay will make an 

 excellent puddling clay. 



Variations in Thickness. 



On Deadman's creek, about five or six miles above its mouth, 

 the Del Rio clay is absent and the Buda limestone directly over- 

 lies the Devil's river limestone. In the country about two miles 

 to the east-southeast of California ranch it measures only thirty 

 feet in thickness. From this point it increases southward to 

 eigthy feet near the centre in survey 20 in block A. Southeast of 

 Del Rio it reaches its maximum thickness, which is probably not 

 much short of two hundred feet. In the region of Turkey moun- 

 tain it averages ninety feet. In general it increases in thickness 

 southwards. 



Geographical Distribution. 



Consisting of clay, this formation yields very readily to ero- 

 sion and has been promptly washed away, except where it is cov- 

 ered by the overlying Buda limestone. Under the edges of this 

 limestone it everywhere forms the slopes and bluffs that limit the 

 level and less elevated flats, from which the clay has been wholly 

 or partly removed. In this way have been formed nearly all of 

 the bluffs which follow on either side of the arroyos in block 1, and 

 in block A west of Devil's river. Most of the tributaries of Evan's 

 creek have cut through the Buda limestone cover, and their course 

 is marked by broad valleys, washed out in the Del Rio clay. The 

 wagon roads in the region usually follow these flats, which a,re 

 comparatively even and free from rocks. In the south half of 

 Block 12 the bluff which parallels the river about a mile to the 

 east is of the same nature. This bluff follows San Pedro creek 

 eight miles, then it swings around to the south side and returns 



