Vol. 4] Smith. — Upper Region of Main Walker River. 



17 



along the western margin of the valley near the steep eastern 

 face of the Pine Nnt Range; bnt so long as the river is eon- 

 strained to remain in the present canon of the Sing-ats'-e Ridge, 

 the tendency is somewhat offset, and the gradual invasion of 

 the northern bluff is probably only a manifestation of such 

 tendency. The river after emerging toward the open valley con- 

 tinues in the direction of the canon for a short distance, but it 

 soon turns quickly to the north, bearing a little to the west; 

 this being the general direction of the base of the ridge. It is 

 joined by the East Walker at a point about two miles south of 

 the map PI. 1. The East Walker flows in a canon-valley through- 

 out almost its entire length and, therefore, this valley does not 

 show the difference of the valley slopes that is shown in the 

 wider valleys. Walker Lake lies under the steep eastern slope 

 of the Wassuck Range, and from the eastern and southern shores 

 the ground rises gently. So much for the Walker River System. 

 As to the Carson River, which has its source near the West 

 Walker, it flows near the eastern base of the mountains just east 

 of Lake Tahoe, and Carson Valley has a more or less gentle 

 eastward rise to the summit of the Pine Nut Range. 



DESCRIPTION OP THE IGNEOUS ROCKS. 



The numbers on the maps indicate approximately the places 

 where the samples were taken. The hand-specimens and the 

 corresponding thin sections bear the same number as the place. 

 The region was not traversed consecutively, hence the reason for 

 the numbering being apparently at random. 



The Granitic Rocks. — Hand-specimen No. 123 is a fair repre- 

 sentative of the granitic rocks that occur in the southeastern 

 portions of the map PI. 1. This rock has an even grained granitic 

 structure ( allotriomorphic granular), and is made up of feld- 

 spar, quartz, biotite and a greenish ferro-magnesian mineral. 

 The color is grayish and the fracture is irregular. Microscopically 

 the structure is granitic ; no mineral has idiomorphic outline. 

 The essential minerals are biotite, augite, plagioclase, orthoclase, 

 and quartz. Magnetite in somewhat irregular grains, 0.25 mm. 

 in size, is distributed throughout all the essential minerals. This 

 mineral is apparently original when possessing that size in this 

 rock. The biotite is brown and in irregular crystals, often with 



