EFFLORESCENCES. 



231 



The genesis of the efflorescent salts that appear on desert surfaces is not 

 difficult to explain. During- the rainy season the clays become saturated 

 with moisture, but on the advance of summer they dry at the surface at 

 the same time that moisture rises from below through the action of capillary 

 attraction. The waters saturating the beds are rendered saline by the salts 

 they dissolve from the clays, and on evaporating at the surface deposit all 

 foreign matter as a surface incrustation. The incrustations thus formed 

 are frequently five or six inches in thickness. They frequently dissolve and 

 disappear during the winter, only to reappear when the heat of summer dis- 

 sipates every drop of moisture from the surface of the deserts. 



From the manner in which saline efflorescences are formed, it is evident 

 that they give a very fair indication of the character of the more soluble 

 salts impregnating the lacustral beds wliicli floor the valleys. The anal- 

 yses inserted below are of representative samples gathered on the surface 

 of the deserts at widely separated points in the Lahontan basin, and may 

 be taken as indicating approximately the relative abundance of the more 

 soluble salts in the sediments of the ancient lake. Local variations occur, 

 but in general they consist mainly of the more common salts of soda, as 

 has been shown by qualitative tests of a large number of samples in addi- 

 tion to the quantitative analyses here introduced,'* which were made by 

 Dr. T. M. Chatard. Sample No. 1 is from the surface of the desert, a few 

 miles north of the northern end of Walker Lake. No. 2 is from near Black 

 Rock Point in the Black Rock Desert. Efflorescent incrustations are nearly 

 always mingled with portions of the sand and clay on which they rest, but 

 in the following analyses only the portion soluble in water is considered : 



" See also Reports of U. S. Geological Exploration of tUe Fortieth Parallel, Vol. I, Table of chem- 

 ical analyses, No. V. 



