684 TRANS-PECOS TEXAS. 



tains and the Cornudas, the Carboniferous rocks forming the cliffs of the 

 south and east side of the Sierra Diabolo slope, and run out on the west side 

 into decomposed rock and newer deposits. 



East of the Diabolo and Carrizo range opens a broad valley towards the 

 Salt Lake basin, into which open a number of extensive draws or valleys, 

 evidently the drainage channels of the mountains and formerly existing (Cre- 

 taceous) sea basins of New Mexico, probably to the White Mountains and all 

 the ranges and groups east of the drainage area of the Sacramento River. 

 This valley, between the Diabolo and Carrizo mountains and the southern ex- 

 tension of the Sierra G-uadaloupe, widens from six miles at the northern 

 end of the Carrizo Mountains to about, fifteen miles at the end of the Sierra 

 Diabolo, and is bordered on the east side by cliffs similar to those of the 

 Sierra Diabolo, with many deep cut ravines. How deep the bottom of this 

 valley is covered with debris of the igneous rocks of the New Mexico moun- 

 tains, the Carboniferous strata of the high plateaux bordering the valley, and 

 probably also Cretaceous and Quaternary material, can not even be guessed 

 at present, but it seems probable that the original erosion reaches to the crys- 

 talline schists, which probably extend from the Carrizo Mountains towards 

 the Sierra Guadaloupe. 



With reference to the petrographic character the Davis Mountains differ 

 in many respects from the more western mountain ranges and mountain 

 groups. True we find there hornblendic rocks similar to those of the Sierra 

 lilanca group, granites resembling those of the Quitman Mountains, the lavas 

 of the Chispa range and only slightly differing from those of the Chinatti 

 Mountains, also sand and limestone partly excessively metamorphic, partly 

 only slightly altered ; but conspicuous before all others are the flinty siliceous 

 ridges which, beginning at the former Barrel Spring Station on the old Fort 

 Davis and El Paso stage line, were known by the name of Marble Hills. 

 They extend in a northeast direction about two miles, rise in beautifully (yel- 

 low, pink, purple, etc.) colored cliffs above Gaines Ranch, and appear as occa- 

 sional intrusions through and above the stratified metamorphic rocks. 



Coarse trachytic rocks rise in sharp saw-tooth like ridges over seven thou- 

 sand feet high above the sea level, and slope very steeply down into the nar- 

 row valleys, which, not filled in to any considerable depth with debris, show 

 more springs and creeks than the valleys of the other Trans-Pecos mountain 

 ranges. 



Near Fort Davis porphyritic trachytes rise in steep, frequently perpendicular 

 cliffs, resting, in many places exposed to view, on a yellowish sandstone. 

 These trachytic rocks are also found east and south of Fort Davis, along the 

 Limpia Canyon, which at Dog Canyon opens into a more flat country (Cre- 

 taceous and newer) about twelve miles east of Fort Davis. In this canyon 



