THE CAKSON DESERT. 745 



the Truckee Valley througli the gap south of the Kawsoh Mountains, and 

 piled up in ever-shifting mounds on the eastern side of the desert. 



Like the Nevada valleys, tree-growth is wanting on the desert, vege- 

 tation being still more limited than on the so-called sage-brush plains, and 

 over a greater part of the area is restricted to a scattered growth of stunted 

 alkaline shrubs, of which HalostacJiys occidentalis is the prevailing species, 

 producing a monotonous dulness of mingled dull-gray plant-life and blind- 

 ing white sands. 



Over the entire area there is but a single elevation rising above the 

 general level, and that one scarcely reaching 200 feet. It is situated mid- 

 way between the Carson River and Mirage Lake, just east of the old Emi- 

 grant Road, and stands up like an island in a sea of sand. From a hasty 

 examination, it would appear to be a basaltic outburst, penetrating and 

 uplifting the underlying Miocene Tertiary beds, which are exposed along 

 the base. More or less encrusting the entire hill are heavy deposits of the 

 aqueous tufas, which have been eroded in the most curious manner; the rock 

 upon which it Avas deposited weathering much more readily than the compact 

 and homogeneous sediment, leaving the latter standing like a wall or fortifi- 

 cation 3 and 4 feet in height and frequently 2 and 3 feet in thickness. In 

 places, the tufa shows a concentric structure resting in dome-like masses 

 upon the underlying rock. 



An analysis of this tufa was made by Mr. R. W. Woodward for the 

 purpose of comparison with the similar deposits observed on the Truckee 

 Desert and at Pyramid Lake, and was found to have an almost identical 

 composition. 

 It yielded: 



Alumina 0.77 0.82 



Lime .. : 50.88 50.92 



Magnesia 3.86 401 



Soda 0.77 0.76 



Potassa... 0.15 0.17 



Carbonic acid 41.35 41.43 



Silica 2.23 2.19 



Phosphoric acid trace trace 



Sulphuric acid. trace trace 



100.01 100.30 



