564 DESCRIPTIVE GEOLOGY. 



Toward the riorthern part of the-*ange, in tbe region of Pinto and 

 Baven's is est Peaks, a large amount of siliceous rock forms the foot-hills; 

 the beds are in general more arenaceous, are far coarser, and carry thin 

 sheets of pebbles. On the east side of the valley, and especially toward the 

 northern end of the range', the Pliocene .strata are prominently terraced, 

 but on the west side they slope gradually, becoming a sort of inclined table 

 cut by shallow ravines. 



The depression of Dixie Pass represents a most remarkable point of 

 dislocation. The Cambrian, Silurian, Devonian, and Carboniferous strata, 

 all dipping west, come up to the pass from the south. The pass itself is 

 obscured by trachytic and rhyolitic outflows, while on the hills to the north . 

 the outcrops are those of the Upper Coal-Measure limestone and Weber 

 Quartzite, all dipping to the east, or in an exactly opposite position to the 

 rocks south of the pass. It seems not improbable that the anticlinal south 

 of the pass has been depressed and moved to the eastward, and that the 

 line of fault is now obscured by the Dixie Pass volcanic outflows. 



Robert's Peak. — Only the northernmost slopes of Robert's Peak come 

 within the limit of the map ; but the peak presents so much that is of interest 

 that it will not be out of place to introduce here a few notes made during 

 a hasty examination of the region. The mountain-group of which the peak 

 forms the culminating point lies between the Piiion and Wah-weah Ranges, 

 completely shutting in Keyes Valley to the north, and stands out promi- 

 nently above the surrounding country, partly on account of its great eleva- 

 tion (10,136 feet) above sea-level, but in part also of its isolated position 

 between two long, parallel ranges. The group consists almost entirely of 

 limestone ; and, from the fossils obtained, it is evident that the beds belong 

 to the lower limestone belt. No careful estimate of the thickness of strata 

 could be made, as the structure, somewhat obscure, was not clearly seen, 

 but there must be at least between 2,000 and 3,000 feet of conformable 

 beds which lithologically closely resemble the Pogonip series, compact, 

 dark limestones, more or less siliceous, with interstratified beds of calcare- 

 ous shales, and thin, cherty layers. So far as examined, the beds are 

 inclined uniformly to the eastward, with a varying dip, and a strike north- 

 west and southeast. Along the northern slopes, recorded strikes give from 



