THE NONMETALLIC MINERALS. 399 



and borax, largely supplemented with volcanic sand. This depression, 

 which has an elevation of 1,700 feet above sea level, and an irregular 

 oval shape, is about 10 miles long and 5 miles wide, its longitudinal 

 axis striking due north and south. It is surrounded on every side but 

 the south by high mountains, the Slate Range bounding it on the east 

 and north, and the Argus Range on the west. 



There is no doubt but this basin was once the bed of a deep and 

 wide-extended lake, the remains of a former inland sea. The shore 

 line is distinctly visible along the lower slopes of the surrounding 

 mountains at an elevation of 600 feet above the surface of the marsh. 

 Farther up, one above the other, faint marks of former water lines 

 can be seen, showing the different levels at which the surface of the 

 ancient lake has stood. In the course of time the lake became extinct, 

 having been filled with the sediments from the adjacent mountains. 



What may have been the depth of the lake has not yet been ascer- 

 tained, borings put down 300 feet having failed to reach bed rock. 

 These borings, commenced in 1878, disclosed the following underlying 

 formations: 



First, 2 feet of salt and thenardite [Na 2 SOJ; second, 4 feet of clay 

 and volcanic sand, containing a few ciystals and bunches of hanksite, 

 [4Na 2 SO 4 , Na 2 CO 3 ]; third, 8 feet of volcanic sand and black, tenacious 

 clay, with bunches of trona, of black, shining luster, from inclosed 

 mud; fourth, 8-foot stratum, consisting of volcanic sand containing 

 glauberite, thenardite, and a few flat, hexagonal crystals of hanksite; 

 fifth, 28 feet of solid trona of uniform thickness; sixth, 20-foot 

 stratum of black, slushy, soft mud; smelling strongly of hydro- 

 sulphuric acid, in which there are layers of glauberite, soda, and 

 hanksite. The water has a density of 30 Baume; seventh, 230 feet 

 (as far as explored) of brown clay, mixed with volcanic sand and per- 

 meated with hydrosulphuric acid. 



Overlying No. 5 a thin stratum of a very hard material was encoun- 

 tered. Being difficult to penetrate, and its character not recognized, 

 this was simply called "hard stuff," its more exact nature being left 

 for future determination. 



As is the case with all salines of like character, this has no outlet, 

 the water that comes into it escaping only by evaporation, which proc- 

 ess goes on here very rapidly for two-thirds of the year. 



While most of the water contained in this basin is subterranean, a 

 little during very wet winters accumulates and stands for a short time 

 on portions of the surface. In no place, however, does it reach a 

 depth of more than a foot or two, hardly anywhere more than 3 or 

 4: inches. 



Within the limits of the actively producing portion of the marsh, 

 which covers an oblong area of about 1,700 acres, the water stands on 



