PAH-SUPP MOUNTAINS. 801 



SECTION yii. 



WINNEMUCCA LAKE EEGION. 



BY ARNOLD HA.GUE. 



Pah-supp Mountains.— The Pah-supp group lies directly west of the 

 Pah-tson Mountains, the depressed valle}" between them measuring scarcely 

 more than 5 miles in width. The 119th meridian west from Greenwich 

 passes through the central portion just to the westward of the main ridge, 

 whose highest summits reach an altitude of 2,000 to 2,500 feet above the 

 desert of the Mud Lakes, rising abruptly on the east side, but falling away 

 gently to the westward. In a north and south direction, the mountains are 

 about 20 miles in length, with a width of 12 miles from base to base. With 

 the exception of the low foot-hills of slate skirting the eastern flanks, the 

 entire mass of the Pah-supp Mountains consists of granite, whose physical 

 attitude, as well as mineralogical composition, presents, wherever visited 

 along the main ridge, a striking uniformity of character and a marked 

 resemblance to the later granites of the Pah-tson Mountains, a resemblance 

 seen even in the modes of weathering and in the detailed topographical 

 structure of the higher slopes and valleys. 



A specimen of granite in the collection taken from the highest peak in 

 the southern portion of the group, nearly due west from Pah-keah Peak, 

 cannot be told from the rock in the region of Grass Canon, Pah-tson Mount- 

 ains, Both hornblende and mica are well developed, the crystals of the 

 former being frequently one-half an inch in length, with broad faces of a 

 dark-green color, while the thin laminae of biotite seem fresh and unal- 

 tered. Plagioclase appears to be abundant, but in small crystals. No 

 titanite was observed in the specimen collected. Under the microscope, in 

 thin sections, the feldspars are shown to be impregnated with specular iron 

 and hornblende dust. 



Other specimens from the northern end of the ridge are somewhat 

 lighter in color, but have an identical mineralogical composition. The 



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