THEORETICAL SUCCESSION IN SALINE DEPOSITS. 189 



for a long period, or if evaporation were to exceed supply, we should 

 expect that other salts would be deposited in a definite succession. The 

 probable composition of the waters of Lake Lahontan, if a single evapora- 

 tion is considered, indicates that, as concentration took place, the dissolved 

 salts would be deposited, with some intermixture it is true, but mainly in the 

 following order: (1) Calcium carbonate; (2) calcium sulphate; (3) sodium 

 sulphate; (4) sodium carbonate; (5) sodium chloride, followed by the precipi- 

 tation of the more deliquescent salts In nature, however, this order would 

 be altered by fluctuations of temperature, variations in density, and other 

 disturbing conditions. Should the desiccation be incomplete the remaining 

 waters would form a dense mother-liquor, rich in magnesia, potash, and 

 soda, and containing some of the less common substances, as lithium, bo- 

 racic acid, etc. 



On entering the Lahontan basin — which, as we know, never over- 

 flowed — with this theoi'etical history before us, we are surprised to find 

 that, with the exception of immense deposits of calcium carbonate, there 

 are no accumulations of saline precipitates to be seen. Moreover, the 

 water-bodies now occupying the lowest depressions in the bed of the 

 former lake, are not dense mother-liquors, but, on the contrary, contain 

 even less than half of one per cent, of total solids in solution. It is evi- 

 dent, therefore, that the history we are endeavoring to trace is an excep- 

 tion to the rule sketched above, which seemed self evident when considered 

 in a theoretical way. As we proceed we hope to explain this apparent 

 anomaly, at least in part. 



CALCAREOUS TUFA. 



The deposits of calcium carbonate occurring in the Lahontan basin 

 are most abundant in the valleys where the former lake was deepest, and 

 are usually inconspicuous or, perhaps, entirely wanting in places where the 

 waters were shallow. The best localities for the study of these chemically 

 formed rocks are on the borders of the Carson Desert and about the shores 

 of Pyramid and Winnemncca lakes. The steep rocky sides of these secon- 

 dary basins, and the isolated buttes occurring in them, seem to have been 



