WEST HUMBOLDT KANGE. 715 



lias a coarse friable* texture, crumbling readily. Under the hammer, it 

 breaks with difficulty into rough, irregular pieces. In color, it is dull gray, 

 but mottled by segregations of dark mica. Both monoclinic and triclinic 

 feldspars are present, but an opaque, cream-colored and white orthoclase 

 is the prevailing species. The quartz occurs as translucent crystalline frag- 

 ments, generally in masses of considerable size. Mica is abundant in segre- 

 gated bunches of dark bronze color. A typical specimen of this granite col- 

 lected from the first canon north of Wright's Canon has been analyzed by 

 Prof. Thomas M. Drown, of Lafayette College, who reports the following 

 composition : ■ 



Silica 68.58 



Alumina 16.51 



Ferrous oxide > 2.52 



Manganous oxide 0.11 



Lime 2.91 



Magnesia 0.47 



Soda . . 4.28 



Potassa * 4.34 



Ignition 0.45 



100.17 



Along its northern and western edge, the granite mass is overlaid by a 

 series of metamorphic schists and of light-colored mica-gneisses, in turn 

 overlaid by a fine, white, knotted schist. The strike of these beds is north 

 38° east, standing nearly vertical. The contact of the granite and schists is 

 extremely interesting, showing in horizontal plane an irregular angular intru- 

 sion of the former into the latter, outlying masses of schist lying in the 

 granite and extending as promontories from the main mass of schist for 400 

 or 500 feet. 



The line of demarcation between the two bodies is easily observed, 

 and there seems to be no tendency of the schist to pass by gradations into 

 the granite itself The granite is here traversed by structure-planes having 

 a stiike parallel to the bedding of the schist ; there is also another set of 

 lines approximately at right angles to the former. These northwest planes 



