822 DE30KIPTIVE GEOLOGY. 



All over this delta group of hills may be traced the Lake La Hontan 

 tufas, exposing a variable thickness, much of it having been carried away 

 by erosion. It reaches a maximum thickness of perhaps 35 feet, and was 

 obviously formed of a rude growth of crystals, which have been often 

 cemented together, built upon, and partly enveloped in the amorphous 

 tufa. Whenever and wherever this deposit is found, the traces of crystals 

 abound through it in such a way as to leave no doubt that the formation 

 was at one time mainly made up of them. 



The Truckee River bifurcates and empties into both Winnemucca and 

 Pyramid Lakes, separated by the Lake Range, and as neither of them have 

 any outlet, retaining by constant and rapid evaporation approximately the 

 same level through a long series of years, their waters are necessarily 

 charged with alkaline salts. The waters of Winnemucca Lake have never 

 been analyzed, but inasmuch as their conditions are apparently the same as 

 those of Pyramid Lake, the chemical composition of the two waters would 

 probably show few points of difference. Winnemucca Lake is about 25 

 miles long by scarcely 4 wide, and, judging from the configuration of the 

 shore and valley, is probably quite shallow. Everywhere along the shore 

 and cliffs, below the level of the ancient Lake La Hontan waters, incrusta- 

 tions and fragments of calcareous tufa are abundant, but having the same 

 habit as those found in the region of Truckee Valley and Pyramid Lake. 



Pyramid Lake lies between the Virginia and Lake Ranges, and is 

 almost completely encircled by high rugged mountains, frequently coming 

 down to the water's edge in steep precipitous ridges with ever-varying out- 

 lines, which make the lake by far the most picturesque sheet of water to be 

 found among the Nevada Valleys. It is 30 miles in length by 12 in width 

 at its broadest expanse. It is crossed just below the centre by the 40th 

 parallel, and the extreme western shore lies 15 miles to the eastward of 

 the California State boundary. Barometric measurements place the altitude 

 of Pyramid Lake at 3,890 feet above sea-level, which varies but little from 

 the level of Carson Lake and the Mud Lakes to the north. Above the 

 present water-level, the terraced benches of La Hontan Lake arc easily 

 followed, cutting deeply into the volcanic rocks, four of them standing out 

 prominently and more boldly than the others. Careful measurements by 



