IN THE UPPER RIO GRANDE EMBAVMENTIN TEXAS. 87 



it certain that no mineral deposits of anj' consequence will 

 be found associated with it in these localities. 



It is probable that the intrusives come from the Uvalde 

 countiy on the east. In that region similar rocks have a much 

 greater development and the fissures through which the molten 

 masses rose, are no doubt to be found in that direction. This 

 hypothesis would also account for a westward thinning which is 

 evident in the remnants of the flow found in Kinney county. The 

 measurements taken are given in the following table. 



Table Showinb Approximate Thickness of the Igneous Rocks in Kinney 



County. 



Thickness 

 in feet. 



Turkey mountain 200 



Elm mountain 35 



Las Moras mountaia 90 



Hill two miles north of Las Moras 70 



Little Pinto mountain 15 



Pinto mountain 30 



Palmer hill 30? 



In all probability other exposures of this intrusive are found 



at some points to the south and west of Palmer hill, for small 



boulders of it are present in the land drift between Fort Clark 



and Spofford. 



GEOLOGICAL STRUCTURE. 



In its great features the structure of this whole region is quite 

 simple, as will be apparent from the facts already presented. 

 There is a general slow descent of the formations to the southeast. 

 In the distance of a hundred miles, from Del Eio down the Rio 

 Grande, 3872 feet of stratified rocks go under the river. The 

 descent of the river itself in this distance amounts to nearly 200 

 feet, and thus the dip averages some forty feet to the mile. 



The whole region must be regarded as a single structural 

 unit, a wide and low monocline tilted to the southeast. This mo- 

 nocline is however itself affected by minor flexures and by some 

 small faults. Thus we find a rather abrupt reversal of the gener- 

 al southward dip in Devils river about one mile north of the 

 bridge of the Southern Pacific railroad. At this place there is a 

 small anticlinal fold with its axis extending from east to west for 

 several miles. To the north of this axis the ledges of the Devil's 



