630 DESCEIPTIVE GEOLOGY. 



tion. Driven by the southwest winds, the clouds would pass from the 

 Dome across Cortez Valley to Mount Tenabo, and from there on to the high 

 peaks of the Humboldt Range. 



So far as examined, the Dome consists of nearly white quartzite beds. 

 The rock is quite compact, with a slight arenaceous texture, has a vitreous 

 lustre, and a brittle, splintery fracture. In places, it has more or less of a 

 grayish tinge, and carries minute specks of oxide of iron, or ferruginous 

 earth,* scattered through it. In the hand-specimen, the rock cannot be 

 distinguished from that of Carico and Railroad Peaks, the microscopical 

 analysis failing to detect any points of difference. Liquid-inclusions in the 

 quartz-grains are abundant, and easily recognized under the microscope. 



The structure of this great quartzite body was not clearly ascertained, 

 but it would seem most probable that it forms a broad anticlinal fold, with 

 a low, gentle dip to the west, but inclined at a higher angle to the east. 



Overlying the Dome quartzites, on the east side, occur a series of 

 beds of siliceous and argillaceous slates, which pass up into compact 

 gray limestones, considerably metaphorsed, and dipping to the eastward. 

 It cannot be stated positively that the slate and limestone series overlie 

 the quartzites conformably, although no apparent unconformity was ob- 

 served ; and inasmuch as in the same range to the southward nearly iden- 

 tical beds are seen resting conformably on massive beds of white and gray 

 quartzites, it would seem more than probable that similar structural relations 

 exist here in the region of the Dome. No fossils were found. 



North of the Dome, the beds sink rapidly downward, and, with the 

 exception of a long tongue of quartzite extending nearly to Carico Valley, 

 the entire region, like so many others where the Palaeozoic beds suffer a 

 sudden depression, is deluged .with vast accumulations of rhyolite. These- 

 rhyolites stretch westward to Reese River, rising in irregular-shaped hills 

 between 1,000 and 1,500 feet above the valley. 



In the eroded basins and valleys worn out in the rhyolite, noticeably 

 on Silver and Boone Creeks, the underlying beds of Truckee Miocene are 

 well exposed. These beds consist almost completely of cream- and ash- 

 colored strata, made up of extremely fine, impalpable powder, so fine that 

 when crushed and agitated with water the liquid will remain turbid for days 



