678 TRANS-PECOS TEXAS. 



Mexico. The material of which this mesa is composed, judging from the 

 character of its southern slope, from borings, and the general aspects of its 

 surface, consists to a considerable depth of only slightly consolidated sand, clay, 

 gravel, and calcareous cementing, resting probably on rock relating to that of 

 the Hueco Mountains and their southern extension towards Findlay, where, 

 about eight miles north of this station, we find Carboniferous rocks, which 

 evidently constitute the flanking and partly the capping of the Hueco Moun- 

 tains. In their southern outrunner these Carboniferous strata are tilted in 

 every direction by crystalline hornblendic rock, seemingly the same which 

 by intrusion between the stratified sandstone uplifted the cones of the Sierra 

 Blanca group two thousand feet above the surrounding flats and Cretaceous 

 hills (about seventy-two hundred feet above the sea level). 



East of the Sierra Blanca group, which seemingly is of laccolitic character, 

 a number of Cretaceous hills rise, tilted by a porphyritic rock of light reddish 

 color, which also caused the tilting of the Cretaceous hill groups south and 

 southwest between Sierra Blanca Junction and the Quitman Mountains. In 

 the group of hills one mile west of Sierra Blanca Junction these porphyries 

 in their contacts with crystalline limestones show a number of iron outblows, 

 which a few feet below the surface are distinctly copper stained, and show 

 the same character as the outcrops of the Hunter district. They also contain 

 uranium, which is one of the characteristic properties of the ore of the 

 Hunter district. The green garnet leads found at the foot of these hills, and 

 in the prospects higher up, are the same as those in the northern part of the 

 Quitman Mountains, and would prove the relation of these two elevations even 

 if the porphyritic, chloritic, and hornblendic rocks which tilt the overlying 

 strata were not so plainly exposed. 



In the northern part of the Quitman Mountains, the highest peak of which 

 rises to seventeen hundred feet (barometric measurement) above the flat be- 

 tween this range and the Sierra Blanca Peak, the reddish granite prevails. 



Bowlders from two to twenty feet in diameter and rounded by weathering 

 are piled upon and against each other on the slopes, covering the solid rock in 

 many places from twenty to thirty feet deep, making it difficult, in many 

 places impossible, to ascertain the limits where the granites of different ages 

 meet and where the porphyritic intrusions, extrusions, and protrusions are in 

 contact with the granites. 



Neverthless it can be ascertained that the northern part of the Quitman 

 Mountains is built up of three granites, different in strike, grain, weathering, 

 and, no doubt, also in age. 



The oldest, mostly of very coarse grain, partly decomposed, has a nearly 

 true north-south strike. It forms the foot of the mountains, and only now 

 and then rises to a few hundred feet above the level of the flat. 



