GEOLOGY 



TKANS-PECOS TEXAS 



PRELIMINARY STATEMENT.* 



W. VON STREERUWITZ. 



As has "been mentioned, the mountains and hills of Trans-Pecos Texas rise 

 generally (seemingly, at least) in isolated ridges and groups from broad flats, 

 abruptly in most cases, and either without foothills or surrounded only by 

 those of limited extent and height. This is particularly the case with the 

 eruptive mountains. 



But even a superficial examination shows that in spite of the great variety 

 in rock material there exists an essential connection between all of the erup- 

 tive mountain ranges and groups, and that the flats and basins between these 

 ranges and groups, however extensive they may be, are in fact deep valleys, 

 having depths of even 1000 feet and more (as has been proved by borings), 

 and filled in with the debris not only of eruptive material, but also with that 

 of Carbonic, Cretaceous, and possibly intermediate strata. This is often cov- 

 ered in turn with Quaternary detritus, which is in some cases more than 100 

 feet thick. 



In the Quitman Mountains, or at least in their northern part, we have to 

 deal with eruptive rocks only; with granites of at least two ages, and with 

 porphyries, the latter evidently younger than the granites. 



The Sierra Blanca group of mountains rises north of the first ridge of 

 the Quitmans, and is separated from them by a valley two miles in width, 

 which slopes gently from the mountains on either side, and west towards the 

 river. The group consists of four isolated, moderately flattened cone-shaped 

 mountains, the highest of which, the Sierra Blanca Peak, has a height of 

 nearly 7200 feet above the sea level, or 2000 feet above the surrounding 

 flat. Up to the present time no granites similar to those of the Quitman 

 range have been detected in the Sierra Blanca group, and outcrops of dioritic 



* As this is merely a preliminary statement of some few facts observed while engaged in 

 preparatory work in the region, no reference has been made to existing literature on the 

 subject. This will be done in a following report. 



