FRESHENING OF LAKES BY DESICCATION, 223 



Section 3.— DESICCATION PEODUCTS. 



During the centuries that witnessed the deposition of the vast amount 

 of calcareous tufa now found in the Lahontan basin, other salts were 

 contributed to the lake in varying proportions. Upon the evaporation of 

 the waters these more soluble salts were eventually deposited, and, as the 

 lake never overflowed, they must still be retained in the basin. 



Instances of the deposition of salts by the evaporation of inclosed 

 lakes are common, and may be illustrated by many examples in the Gri'eat 

 Basin. The salt fields in Osobb Valley; the saline deposits left by the 

 evaporation of the Middle Lake in Surprise Valley, California, in 1872; 

 and by the broad salt field now covering the desiccated basin of Sevier 

 Lake in Utah, are all cases in point. 



In the Lahontan basin, deposits of this character, which have resulted 

 directly from the evaporation of the former lake are nowhere to be found. 

 The accumulations of common salt, sulphate of soda, etc., occurring in 

 considerable quantities at certain localities, have in all cases been deposited 

 since the evaporation of the former lake. In some instances these accumu- 

 lations are due to the leaching of saline clays, and the evaporation of 

 the resultant brine in restricted areas, as in the case of the salt fields in 

 Alkali Valley; at other times saline deposits of considerable thickness 

 have resulted from the evaporation of spring waters. Over very large 

 areas the Lahontan beds are frequently whitened with a saline efflorescence, 

 which also owes its accumulation to secondary causes, as will be described 

 a few pages in advance. 



Wherever the Lahontan sediments have been examined they have 

 been found more or less highly charged with salts of the same character as 

 those that were most common in the waters of the former lake. The total 

 quantity of saline matter thus imprisoned is certainly very great, and is 

 assumed to represent the more soluble substances contributed to Lake 

 Lahontan. 



