GRANITE. 219 



granite is found in isolated patches in such uplifts as the Ombe, Gosiute, and 

 Peoquop ranges. The East Humboldt Mountains present the grandest mass 

 of the older crystalline rocks, stretching with the trend of the range over 

 sixty miles in a nearly noi'th and south direction, and is the most extensive 

 area of pre-Cambrian rocks to be found in central Utah and Nevada along 

 the countiy examined by the Fortieth Parallel Exploration. Inunediately 

 westward of this latter range in the country occupied by the Diamond and 

 Pinon ranges, no exposures of granites occur, and it is one of the 

 largest areas knoAvn in the Great Basin, in which all evidences of granite 

 and of an Archean body are wanting. There are good reasons for believ- 

 ing that in early Paleozoic time this area east of the Humboldt Moiuitains 

 was a deep trough of the sea, in which Cambrian, Siliu-ian and Devonian 

 sediments were deposited. At all events, the mountain ranges within this 

 region offer excellent sections of the lower Paleozoic strata, which over large 

 areas of the Great Basin are unknown. 



At Eureka, where the Diamond and Piiion ranges unite in a liroad ele- 

 vated mass of sedimentary beds of great thickness, singularly broken up by 

 great faults into bold mountain ridges, only one obscure outci-oj) of granite 

 is known. It is, however, not without considerable interest, aud whvu the 

 geological position of these granites and allied rocks of the Great Basin 

 come to be studied in detail in their relation to the Ai-chean masses and the 

 U])lifts of the parallel ranges, it may be found to throw nnu-h liglit upon 

 some complex structural problems. Here at Eureka the outcroj) does not 

 occm* rising above the Quaternary plain along the base of a ridge, nor in 

 the bottom of some deeply eroded canyon. On the contrary it is found 

 1,000 feet above the level of Diiimond Valley, at the extreme northern end 

 of Prospect Ridge, on the steep soutli slope of the ravine which separates 

 Rubv Hill from the main ridge. It is so insignificant and so covered with 

 debris derived from the limestone hills above that it might easily escape 

 attention, especially as it presents no inequalities of surface. This granite 

 is best seen on comingup the ravine from the west, and is exposed just above 

 the path, some miners having cut into it, attracted by the red color of the 

 decomposed rock. It extends from the footpath up the steep slope for 300 

 feet to within 50 feet of the top of the hill. 



