GEANITE HILLS. 851 



study of the rocks quite difficult. On the north slope of Peavine Mountain, 

 near the Bevelhymer ledge, occurs, intimately associated with the series 

 just described, a rock which has a much fresher appearance, with the 

 individual minerals more clearly defined. It is a compact dense rock, 

 breaking with difficulty under the hammer, presenting a sharp angular 

 fracture. It carries considerable dull opaque orthoclase, a little plagioclase, 

 with both hornblende and mica. It would seem to be related either to the 

 diorites or syenites. On the north slopes of Peavine Mountain, the beds 

 are traversed by quartz veins. 



East of Peavine Mountain, a low group of volcanic hills, rising but a 

 few hundred feet above the valley, stretches out toward the Virginia Range, 

 and closely connects the intrusive rocks of those mountains with the Sierra 

 Nevada. 



Lithologically, these rocks present some features of interest, as they 

 bear a close resemblance both to basalts and to augite-andesites, and, if 

 classed with the latter, belong more to basalts than to normal andesite. 

 They possess a bright fresh appearance, a conchoidal fracture, a grayish- 

 black color, and a resinous lustre, characteristic of andesite Scarcely any 

 crystals are of sufficient size to permit of determination by the unaided 

 eye, yet the groundmass is brilliant with faces of feldspar crystals. Uiider 

 the microscope, the feldspars are seen to be mainly triclinic forms associated 

 with augite. It is evident that the rock is not a true basalt by the large 

 amount of silica present, a quantitative determination yielding 62.67 per 

 cent., which is somewhat higher than is usually found in augite-andesite. 

 As to the position of these rocks in regard to other volcanic outbursts, there 

 is no evidence. 



Granite Hills. — Along the western border of the map, lying between 

 the Virginia Range and the California State boundary, occurs a large 

 area of granitic rocks. They extend from the southern limit of the map 

 northward to Honey Lake Valle}^, a distance of 40 to 45 miles, with an 

 undulating surface, not forming one continuous range, but broken into 

 numerous ridges, separated by irregularly shaped valleys that are now 

 filled by Quaternary deposits. These valleys everywhere show conclusive 

 evidence that they are merely shallow depressions in the great granite 



