4G4 



GEOLOGY. 



carbonate, which, in the form of calcareous tufa, was deposited during 

 at least three distinct stages of the lake's history (Fig. 545). The 



■■■ 



Fig. 545. — Tufa deposits in the basin of Lake Lahontan. (Russell, U. S. Geol. Surv.) 



oldest tufaceous deposits lined the basin of the lake at the time of its 

 first expansion; the next were made when the lake was low, between 



