DESCRIPTIVE GEOLOGY. 683 



like those of the Sierra Diabolo, and have an average dip of 30° south and 

 southwest. 



The Carboniferous strata rest non-conformably on the conglomerate and 

 sandstone, with few exceptions (probably slides), in horizontal layers, and the 

 few insignificant folds indicate that post-Carboniferous disturbances in the 

 Sierra Diabolo group, as far as the examination goes up to this time, were 

 confined to the part south of the cliffs toward the Carrizo uplifts and the 

 Eagle Mountains, where we will have to look for the cause of this disturbance. 



At the south slope of the conglomerate hills a gangue of clay slate strikes 

 nearly west with a general dip of about 35° south between the cherty lime- 

 stone strata, which are cut by numerous ferruginous quartz veins. These 

 limestones, sandstones, and igneous intrusions alternate with Carboniferous 

 limestones, and extend north to the cliffs of the Diabolo proper, which on its 

 west side slopes down gradually to the basin (flat) east of Sierra Blanca. 



On the south and east sides the cliffs of the Sierra Diabolo fall nearly per- 

 pendicularly two hundred feet from the top to the sloping accumulations of 

 debris, which lean under an angle of 35° to 45° about four hundred feet high 

 against the perpendicular walls of the Carboniferous strata. The Carbonif- 

 erous limestone forming the top part of the Sierra Diabolo rests on a silty 

 copper and silver bearing layer about six feet thick where exposed to sight, 

 and this on an amygdaloid conglomerated deposit, which, getting finer in its 

 lower parts, changes to the grits mentioned in the Carrizo Mountains which 

 rest on the Diabolo sandstone. If and how far the Carrizo schists extend 

 under the Diabolo Mountains can not be determined at present. Above the 

 cliffs of the Sierra Diabolo Mountains, rounded hills, also Carboniferous, rise 

 to about eighteen hundred feet above the cliffs. Synclines and anticlines ap- 

 pearing occasionally, particularly in the gulches, seem to be caused by slides. 

 The Sierra Diabolo, as far as examined up to the present time, is a monocline, 

 deflecting in a southerly direction; and judging from a view taken at these 

 mountains from the nearest high points, no breaks or disturbances of any 

 consequence will be found in the southern half of the Diabolo range. 



The south cliffs of the Sierra Diabolo begin opposite and about eight miles 

 northwest of Eagle Flat Station, on the Texas and Pacific Railway, extend- 

 ing in an easterly direction, slightly deflecting to the south, taking at the 

 Hazel mine a sharp turn to the northeast, and they run in this direction 

 eight miles to a rough gulch, or ravine, about two miles wide at the mouth, 

 and extending far back into the mountains. From there for about eight 

 miles they follow a northerly direction, and then they turn about 45° to the 

 northwest, getting lower as they approach the Sierra Prieta, and assume the 

 character of a mesa sloping toward the Salt Lake valley. The projection of 

 this last course points towards the Tinaja Pinta, Alamo, and Wind moun- 



