REPORT OF THE STATE GEOLOGIST. lxXXV 



to three hundred feet in places, and a continued rise toward the west to 

 a height of three thousand one hundred feet. West of the Pecos the 

 rise is much more rapid, being about fifteen feet per mile. The dip of 

 the strata, which on the east is toward the northwest not exceeding 

 forty feet to the mile, is reversed, that is, it is to the southeast, and 

 brings the edges of the strata to the surface again after crossing the 

 river. In the southeast corner of this region we find the Archaean area 

 of Llano County, around which the upturned edges of the older Paleo- 

 zoic rocks are exposed at a considerably greater elevation than that of 

 the basin north of them, giving the overlying rocks of the basin itself 

 a northward dip. 



The western extension of this southern border has not been exam- 

 ined. We find the northern border of our basin in the Wichita Moun- 

 tains in the Indian Territory, where the edge of the Silurian rocks is 

 again exposed at a higher altitude than the interior portion of our re- 

 gion. This region is, therefore, of a basin form of structure, with the 

 exposed edges of its lower members and the underlying rocks topo- 

 graphically higher on the northern, western, and southern borders than 

 on the east or in the center. 



The formations which occupy this basin, if we except some overlying 

 Cretaceous and the Plains formation, are almost entirely confined to the 

 Carboniferous and Permian systems. These consist of beds of lime- 

 stone, sandstone, sands, clays, and shales, with coal, gypsum, and salt 

 as associated deposits. The general dip of all the strata in the eastern 

 portion of the basin is to the northwest, but its elevation along the east- 

 ern border is less than in almost any portion of it ; consequently there 

 can be little hope of finding artesian water from any catchment area on 

 this side, although some of the strata (the lower sandstone and shales) 

 are well adapted for carrying water, and where suitable topographic 

 conditions exist do furnish artesian water. An instance of this is found 

 in the flowing well at Gordon, but such cases are the exception and not 

 the rule. The same series of sandstones and shales are exposed on the 

 southeastern border, and the flowing wells at and around Trickham 

 and Waldrip find their supply in them. The conditions are very favor- 

 able in the valley of the Colorado and some distance north between the 

 99th and 100th meridians for similar wells. The rocks of this age are 

 covered by later deposits in the Wichita Mountains, and it is therefore 

 impossible to judge of the possibility of their water-bearing character 

 there. Similar rocks are exposed on the western border of this basin, 



