174 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



the steep granite wall of Weston's Peak rises over 1,500 feet in a distance 

 of about half a mile. At the very summit of the pass is a thin bed of 

 White Porphyrjr, overlying considerable outcrops of Blue Limestone, very 

 much metamorphosed and iron-stained, and dipping from 35"^ to 45° to the 

 north and east. West of this the underlying White Limestone and Lower 

 Quartzite sweep up, at a gradually shallowing angle, almost to the very 

 summit of South Peak. On the eastern side of the pass black shales and 

 quartzitic sandstones of the Weber Grits can be traced for several hundred 

 feet up the fece of the slope. These are suddenly cut off by a bed of 

 white quartzite, standing at an angle of 70° to the westward, and suc- 

 ceeded on the east by granite and gneiss. Between the two is the line of 

 the Weston fault. Following this line southward around the angle of the 

 upper spur to the basin at the foot of Weston's Peak, the quartzite becomes 

 steeper and finally bends over with an angle of 50° to the westward. The 

 actual fault line cannot be traced, inasmuch as it is covered by the talus 

 slope. The thin bed of fine-grained brown conglomerate which forms the 

 base of the Lower Quartzite, in contact with the Archean, is, however, not 

 to be mistaken. Li the Archean itself there seems to be a tendency to a 

 bedded structure parallel with this lower bed of the Cambrian, and, more- 

 over, a sort of actual passage from sedimentary into crystalline rocks, as 

 shown b)^ an increasing development of well-defined crystalline feldspars. 

 These transition beds pass into a peculiar granite of yellowish-red color. 

 It belongs to the coarsely crystalline type, and apparently owes its color to 

 the hydration of the oxide of iron, which gives the flesh-colored tint to the 

 orthoclase of the normal granite of the region. 



South Peak ridge. — Froui Wcstou's pass soutliward the South Peak ridge, 

 which follows approximately the direction of the major strike of the forma- 

 tions, viz, S. 20° to 30° E., constitutes the main crest of the range. The 

 summit of tliis ridge and its eastern slopes are covered with a thin shell of 

 Lower Quartzite beds, whose dip, quite gentle on top of the ridge, steepens 

 to 45° on the eastern spurs. Archean exposures cover the wliole w'estei-n 

 slope of the range south of Weston's pass and are disclosed in the deeper 

 cation cuts on the east side by erosion of the overlying quartzites. 



