80 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



of the vats is usually fibout 10 inches thick and shows two divisions, the 

 upper layer, or " winter soda," being the more crystalline. The salt thus 

 obtained is removed to drying sheds, where it loses its excess of water, at 

 the same time crumbling to a fine powder, and is then ready for the market. 

 A sample of this material was found on qvialitative examination to consist 

 principally of sodium carbonate, together with considerable quantities of 

 chloride and sulphate of soda, and traces of ])hosphoric and boracic acid 

 and potash. /^ 



The manufacture of soda in the smaller pond has been carried on for 

 about eighteen years, with an annual production of between four and five 

 hundred tons, as I am informed by Mr. B. F. Gray, the present superin- 

 tendent. 



The walls of the smaller crater are of the same nature as those that 

 surround the larger lake, and exhibit sections of stratified tuff containing 

 ejected blocks of basalt that depress the strata on which thev rest. An 

 illu.stration of the smaller Soda Lake will be found on Plate XXII, Vol. II, 

 and of the larger lake on Plate XXVI of Vol. I, of the rejiorts of the 

 U. S. Geological Exploration of the Fortieth Parallel. 



The mineral matter now dissolved in the water of the Soda Lakes is 

 unquestionably derived from the springs that supply them, and has been 

 dissolved from the lacustral beds and lapilli deposits through which their 

 waters percolate during their subterranean passage. 



The data given on Plate XVI enable one to calculate approximately 

 the volume of the larger of the Soda Lakes; and from the analj'ses of its 

 waters that have been made we can determine the quantity of the various 

 salts it contains. Making- these calculations for the salts of greatest economic 

 importance, we find that the lake contains nearly 428,000 tons of sodium 

 carbonate; sodium sulphate amounts to nearly four-fifths of this quantity; 

 while the sodium chloride is somewhat less than three times as great. The 

 total of all salts dissolved in the lake is in the neighborhood of two million 

 tons. 



