850 DESCRIPTIVE GEOLOGY. 



dijDping to the southward 10°. Another coal-seam has been opened a long 

 time on Dog Creek, a short distance north of Crystal Peak, but, so far as 

 known, none of the deposits have as yet proved of any economical import- 

 ance. No accurate measurements of the thickness of these Tertiary strata 

 liave been made, but there cannot be less than 500 or 600 feet of con- 

 formable beds. 



A short distance south of the river, the Tertiary is hemmed in by 

 masses of dark -gray sanidin-trachyte, to the south of which, in the region 

 of Verdi, ai-e outlying masses of Sierra granite. 



On the opposite side of the river, and lying just within the borders of 

 the State of Nevada, is situated Peavine Mountain, an outlying ridge, or 

 rather peak, belonging properly to the Sierra Nevada Range of California. 

 It stands somewhat isolated, forming a prominent landmark in the immediate 

 region, partly on account of its commanding elevation, and partly from 

 its striking outlines, which offer marked contrasts to the forms of Tertiary 

 volcanic outbursts, which characterize the Virginia Range and the country 

 to the eastward. It attains an elevation of 8,217 feet above sea-level and 

 about 3,700 feet above the river, rising in abrupt but long regular slopes to 

 the summit. 



Geologically, Peavine Mountain is formed of a series of highly altered 

 quartzites and fine-grained feldspathic rocks, which have been referred to 

 the Archaean series; but their definite relations to other crystalline rock- 

 masses has not been made out, nor can they be referred to any beds of 

 precisely similar petrographical habit. They stand at a highly inclined 

 angle, with a strike varying from north 50° to 65° east, agreeing approxi- 

 mately in strike with the Archaean rocks of the West Humboldt and Pah- 

 Ute Ranges, but quite at variance to the direction of the Mesozoic uplifts. 

 The entire series of beds is characterized by a fine-grained texture, and all 

 the beds seem more or less decomposed, the purer quartzites being pene- 

 trated by fissures and cracks filled by ferruginous material. In the quartz- 

 ites are also minute grains of magnetite and occasionally a little yellowish- 

 green epidote. In the feldspathic beds, similar iron seams are even much 

 more abundant, and many of the rocks are stained bright red from the 

 discoloration produced by the ferruginous earth, rendering the lithological 



