340 PROCEEDINGS OF THE ACADEMY OF [1893. 



7. — The Trans-Pecos Region. 



(a) Topographic Description. — This is almost a terra incognita. 

 It is in brief a region of mountains and basins, the highest mountains 

 being the Guadalupe Mountains which extend from New Mexico 

 into Texas. This is a faulted monocline, rising to the south, where, 

 at Guadalupe Peak, it has an elevation of fully 8,000 feet above sea 

 level and 3,000 feet above the plateau, being terminated by a sheer 

 precipice 2,000 feet in height. It is a mountain of Carboniferous 

 limestone faulted in the western side. Other mountains are associa- 

 ted with igneous action, but our knowledge of them is extremely 

 limited. 



(6) Erosion in the Guadalupe Mountains.™ — I introduce here a 

 few notes on the topography of the Guadalupe Mountains taken 

 during a brief sojourn there. The dip of the strata is to the east, 

 gently at the base of the mountains, increasing to an angle of fifteen 

 degrees or thereabout, then becoming nearly horizontal to the west 

 bounding fault beyond which the dip is steeply west. The west 

 dipping rocks, the downthrow of the fault, form the western foot 

 hills. The drainage is chiefly to the east, being consequent on the 

 structure, and therefore long canons enter from the east well up 

 to the western edge of the mountains, and the west flowing streams 

 are small and short. 



Of the east flowing streams McKitterick canon is a typical exam- 

 ple. For two miles from its exit from the mountain, this mountain 

 gorge is accessible to wagons, but beyond this travel on foot is possi- 

 ble only Avith difficulty. It is extraordinarily rough, being bounded 

 by precipices and steeply sloping sides rising to a height of fully 

 two thousand feet, and the valley is littered with huge bowlders and 

 fragments of the cliff which have dropped down from the valley 

 side. The slope of the valley walls is rarely less than thirty degrees 

 and there are sheer precipices of magnesian limestone rising to a 

 height of from one thousand to eighteen hundred feet. There are 

 several hundred of these precipices and it is only rarely that the 

 mountain top is accessible from the interior gorges. There is no 

 soil on these slopes which are either bare bed rock or bowlder 

 strewn. The vegetation is of the arid type, except in the shaded 

 valleys or well up on the mountain top, where fair sized pines and 

 cedars grow. Snow accumulates in the canons but disappears in 



30 See Bull. 3 Texas Geol. Survey, 1892, Reconnoissance of the Guadalupe 

 Mountains, by R. S. Tarr. 



