SHOSHONE EANGE. 635 



broad flat plain composed of thick plastic muds and fine sands. In the dry- 

 season, a thin efflorescence of alkaline salts covers the ground over extended 

 areas. From a number of localities in the valley, in the region of rhyolitic 

 hills, this fine surface soil was collected for examination, and found to be a 

 highly arenaceous clay, charged with varying quantities of carbonate and 

 sulphate of lime, and small percentages of soluble alkaline salts, chiefly 

 sulphate and chloride of sodium. 



