CALCAREOUS TUFA 



KI 



their deposition is principally due to the loss of the solvent CO a . 

 The ancient Lake Lahontan, which formerly occupied part of 

 northwestern Nevada, was the seat of calcareous deposition on 

 a magnificent scale, and every crag and island which its waters 

 touched is sheathed in thick masses of calcareous sinter. Pyra- 

 mid Lake, a remnant of Lahontan, has a remarkable island 



Fig. 56. — Calcareous deposits in Mono Lake, California. (U. S. G. S.) 



of calcareous tufa ; and "Mono Lake, California, is famous for 

 similar deposits, which have assumed curious and whimsical 

 shapes. 



As the concentration of the lake waters proceeds, the next 

 substance to be precipitated is gypsum (CaS0 4 , 2H 2 0),which, 

 though much more soluble than the carbonate of lime, is yet only 

 sparingly so. After all the gypsum in solution has been thrown 

 down, there follows a pause in the deposition, until a further stage 

 of concentration has been reached, and then common salt is pre- 



