DESCRIPTIVE GEOLOGY. 679 



A newer granite protrudes and extrudes through this, including frequently 

 bowlders from one-half inch to four feet in diameter, of a dark gray color, 

 with -magnetic iron sand. This granite strikes nearly east- west, and in its 

 contacts with the intrusive light colored porphyries most of the ore indica- 

 tions, outcrops, and prospect holes are found. Most of the bowlders covering 

 the slopes are fragments of this granite, and frequently show semi-globular 

 holes left by the included gray bowlders which, loosened in weathering, rolled 

 out, and are found around the reddish rocks, particularly on the northern 

 slopes near the contacts between the light colored porphyry and the granite. 



The second range of the Quitman Mountains is separated by a flat valley 

 about one mile broad in its widest part from the first one. The greater part 

 of the bottom of this valley consists of the oldest granites, with occasional 

 protrusions of later ones and intrusions of a light colored porphyritic rock. 



In the second range of the Quitman Mountains, besides the oldest granite 

 (probably identical with the Burnetian of the Central Mineral Region) and 

 the second one (which might range with the Fernandian), intrusive granitic 

 dykes appear, which strike north 30° to 50° west. This intrusion shows 

 locally a seemingly gneissoid structure, evidently the effect of strong pressure. 

 This structure is visible also in an outrunner from the first range. In some 

 places crystalline limestone older than the Cretaceous is thrown up on the 

 hillsides conformably to this granite. This limestone is so completely mar- 

 bleized that not even the slightest traces of fossils can be detected. 



The intrusive granites, together with the porphyritic intrusions, seem to be 

 the principal cause of the bowlders covering the mountain slopes. 



The ore gangues of this range (in its granitic part), like most of the first one, 

 are on contacts between the granite and porphyry, and the outcrops are indi- 

 cated by kaolinized streaks. On the southwest side of the second range, be- 

 sides the kaolinized streaks there are a number of outcrops like those of the 

 Hunter district, and on the hill group one mile west of Sierra Blanca they 

 are strongly ferruginous, particularly so nearer the foot of the mountains and 

 in the gulches. 



Two and one-half miles east of the most northern end of the second range, 

 south of Zimpelman's Pass, the Quitman Peak rises, a mountain of many- 

 colored porphyritic rocks, and south from this main peak to the Quitman Pass 

 a number of lower peaks of alternating granitic and porphyritic rocks, with 

 frequent metamorphic limestone layers, greenstone and basaltic dykes, show 

 numerous promising prospects, particularly in the Big Gulch, which again 

 forms a kind of pass over the second Quitman range. 



In and near the Quitman Pass the granites give place to, or rather disap- 

 pear under, strongly altered sandstones and less metamorphosed Cretaceous 

 limestones, tilted in every direction and flanking both sides of the pass. 



