PEAVINE MOUNTAIN REGION. 849 



have a dull white color, quite unusual in rhyolites, and are frequently three- 

 quarters of an inch in length, carrying- impurities, which may be recognized 

 by the aid of an ordinary magnify in g-glass. Mica is very abundant and of 

 a brilliant black color, while the hornblende, which is also black, plays 

 quite a subordinate part. The quartz-grains are large, but by no means 

 frequent, and resemble those usually found in that somewhat limited group 

 known as quartz-trachytes;' that is to say, they appear more like an acces- 

 sory mineral than a primary constituent of the rock. They are quite clear 

 and colorless, and apparently free from microscopical impurities. Under 

 the microscope, minute crystals of apatite may be recognized. The pres- 

 ence of quartz and the microscopical structure of the groundmass relate 

 this rock to the rhyolites. 



Peavine Mountain Region. — That portion of the Truckee Valley lying 

 directly west of the Virginia Range is a broad open basin covered by a 

 thick deposit of Quaternary sands and gravels obscuring all the Tertiary 

 strata below ; these appear, however, farther up the valley, just above the town 

 of Reno, and extend thence westward to the California boundary. These 

 Tertiary beds line the valley on both sides of the river, and form a distinct 

 deposit quite unlike those described from the Lower Truckee Valley. 

 They lie inclined at angles varying fi-om 10° to 15°, in general dipping to 

 the southward away from Peavine Mountain, but considerably disturbed 

 by local outbursts of volcanic rocks. Inasmuch as the beds are so highly 

 inclined, and are older than many of the intrusive rocks of the region, they 

 have been referred to the Miocene age, although they differ somew^hat in 

 lithological character from the Miocene strata of the Kawsoh Mountains 

 and Montezuma Range, having much less volcanic material in their com- 

 position. They consist mainly of sandstones, with interstratified beds of 

 friable sands, clays^ and thin shales of prevailing light colors. So far as 

 known, no animal remains have" as yet been found in these beds, although 

 stems, leaves, and partially carbonized vegetable matter are abundant in 

 certain layers of shale. Perhaps the most characteristic feature of the 

 basin, and one that suggests the Green River beds of the Elko region, is 

 the presence of a number of seams of impure coal and carbonaceous shales. 

 Outcrops of coal occur on both sides of the river north of the town of Verdi, 



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