798 DESCRIPTIVE GEOLOGY. 



granitic masses of the Truckee, Pah-tson, and Sali-wave Mountains, but 

 at the same time the range, being higher and more massive, develops certain 

 aspects and modes of weathering which are not so characteristically shown 

 in the more subordinate, narrow ridges. The canons are deeply cut, but 

 the ridges and spurs have in general a rounded outline, in distinction from 

 angular forms, while the peaks, although standing out boldly, have curved, 

 broad, and even dome-shaped summits, and are rarely seen in sharp pinnacles. 



In general, the granite is characterized by a uniform texture, and 

 shows little tendency to form either a fine or coarse-grained rock. It breaks 

 readily under the blow of a hammer. It is made up of translucent quartz- 

 grains, both monoclinic and triclinic feldspars, biotite, and hornblende. All 

 the feldspars are light-colored, and the plagioclase, which is the prevailing 

 form, frequently occurs beautifully striated and characterized by a brilliant 

 lustre. Hornblende, as a constituent of the rock, varies very considerably 

 in different localities as to the amount present, but is always a marked 

 feature of the body. Amber-colored titanite, the variety designated as 

 sphene, is very abundant, with well-developed crystalline faces. 



It may be added that the rock-mass possesses a fresh, unaltered appear- 

 ance, with no recognizable law in the arrangement of the mineral constitu- 

 ents. A specimen collected from the low hills west of Granite Creek Sta- 

 tion may be taken as a typical rock. It was subjected to chemical analy- 

 sis by Prof Thomas M. Drown, of Lafayette College, with the following 

 result : 



Silica 65.83 



Alumina 16.84 



Ferrous oxide 3.90 



Manganous oxide 0.29 



Lime 4.59 



Magnesia 1.84 



Soda 3.84 



Potassa 2.48 



Loss by ignition .- 0.62 



100.23 



