IN THE UPPER lilO GRANDE EMBAYMENT IN TEXAS. 71 



while the soft clays and less durable limestone all around it have 

 been washed away more rapidly and reduced to lower land. The 

 Anacacho mountains are wholly due to this difference in re- 

 sistance to destructive forces. The thickness of the formation is 

 300 feet in the west end of the mountains and about 400 feet in 

 the east end. With the other rocks it is tilted to the south, about 

 ninety feet to the mile. The steepness of the slopes on the north 

 side of the mountains is due to the comparatively rapid removal 

 of the underlying clays. The limestone, being more resistant, 

 remains until its foundation is removed. The southward slope 

 of the top of the mountain is due to the dip in that direction and 

 in block 9 the limestone disappears under an overh'ing clay. In 

 wells which have been drilled on this clay the limestone has been 

 encountered at depths increasing with the distance from the 

 mountain. The southernmost exposure noted was about a 

 fourth of a mile northwest of the southeast corner of Kinney 

 county. From this point and from the east end of the Anacacho 

 mountains this limestone constitutes the bed rock as far east as 

 to Turke}^ creek and beyond this. But in this eastern region it 

 lies more nearlj^ horizontal. 



Asphalt. 



The deposit of asphalt which has been worked at Carbonville, 

 three miles south of Cline in Uvalde county, occurs in the lower 

 part of the Anacacho limestone. I find, however, that the ledges 

 which carry the asphalt are of a more coarse texture on Turkey 

 creek than they are farther west. Near the asphalt deposits they 

 have also been affected by-A^olcanic agencies that probabty were 

 instrumental in rendering those agents effective, which brought 

 about the concentration of the asphalt at this point. The only 

 evidence of local disturbance noted in the region of the Anacacho 

 mountains which may be diie to a concealed igneous intrusion is 

 a small, but somewhat abrupt upward fold, now marked by a 

 valley, at a point three and one half miles south and three miles 

 we.st of U, S. bench mark Cline. In the country' where the asphalt 

 occurs chert is frequently observed as an accompanying mineral. 

 No such chert was observed in the Anacacho mountains. While 

 all of this indicates dissimilarity of physical conditions, the pres- 

 ence or absence of asphalt in the lower ledges of these limestones, 

 where these are not exposed, can only be determined by direct 



