222 GEOLOGY OF TRANS-PECOS TEXAS. 



North of the Carboniferous cliffs, which lie directly west of the Eagle Flat 

 Station on the Texas Pacific Railroad, there rises a range of hills composed 

 entirely of fragments of eruptive and metamorphic rocks and of the Carbon- 

 iferous limestones, embedded in a very hard areno-calcareous matrix, which 

 is more or less ferruginous. 



The same great breccia forms two hills about one mile from the southeast 

 slope of the Sierra Blanca Peak, twenty miles west of Eagle Flat, and similar 

 hills are found extending eastward to the pass leading from Carrizo Station 

 to the Hazel mine. 



These conglomerate hills, although rising as high as 600 feet above the 

 surrounding valleys, do not seem to have been caused by any disturbance in 

 the Carboniferous strata against which they lie in closest proximity, and their 

 origin is as yet unexplained. 



About a mile nearly due west of the last Carboniferous cliffs, which mark 

 the south line of the Sierra Diabolo, there is a mass of basalt which has cut 

 through the strongly metamorphosed Carboniferous limestone, and it would 

 seem that the basalt also extended under and was the builder of the rounded 

 hills which lie between its outcrop and the cliffs. It is hard to imagine any 

 other cause for the entire dissimilarity which exists between these hills and 

 the cliffs. 



Greenstone and serpentine dikes are of frequent occurrence in the foot- 

 hills of the Sierra Diabolo, but they disappear entirely in the southern edge 

 of the mountains. The cliffs, composed in their upper part of strata of the 

 Upper Carboniferous epoch, as determined by the fossils found in them, rest 

 on a red and brown sandstone, which becomes coarser in the upper layers 

 and changes into an amygdaloidal conglomerate embedded within a red 

 sandy matrix. The same red sandstone, from which the limestone and the 

 upper coarse layers have been eroded, extends north from Carrizo Station 

 toward the Hazel mine at the southeast termination of the Carboniferous 

 cliffs of the Sierra Diabolo. It continues through the Carrizo Pass toward 

 the large flat north of the Van Horn Station, the soil of which is composed 

 mostly of the detritus of the red sandstone. It also extends along the east- 

 ern side of the Sierra Diabolo Mountains; and on this side the sandstone, as 

 well as some limestone strata which here covers the sandstone in small 

 patches, is penetrated by numerous spar leads and copper outcrops. 



The Carboniferous cliffs of the Sierra Diabolo are capped by elevations 

 rising several hundred feet above the cliffs, and intercalations of eruptive 

 rocks as well as intrusions will probably be found in the northern part of 

 this mountain range, which seems to extend north to the Cornudas and 

 south to the Chinati Mountains, or even farther and into Mexico. 



If this supposition should be confirmed by detailed examination, as can 



