908 GEOLOGY 



abundant. Great Salt Lake is estimated to contain 400,000,000 

 tons of common salt, and 30,000,000 tons of sodium sulphate. 



Igneous eruptions (Fig. 596) have taken place within the basin 

 at various stages of the lake's history, even since Lake Bonneville 

 disappeared. Since this time, too, there has been faulting in the 

 basin (Figs. 598 and 599), with displacements of as much as 40 feet. 

 Furthermore, the shore lines of the former lake have been deformed 



Fig. 598. Faulting on the shore of Lake Bonneville (Church). 



so that some parts of the Bonneville shore line are more than 300 

 feet higher than others (Fig. 596). 



Farther west, but still in the area of the Great Basin, were other 

 lakes, probably contemporaneous with Bonneville. Among them 

 Lake Lahontan 1 was of importance. Its history and i liaf of a. lake 

 which occupied a part of Mono Valley, California, 2 were similar to 

 that of Lake Bonneville. 



Glacial effects. The extent of glaciation in the western moun- 

 tains has been outlined in the early part of this chapter. Tin 1 

 erosive work of the mountain glaciers was considerable, 2 us shown 

 both by the extensive deposits of glacial drift, and by the form 

 the valleys which the glac-iors occupied. The most massive arrnnm- 



1 Russell, Mono. XI, U. S. Geol. Surv. 



2 Eighth Ann. Kept., U. S. Geol. Surv. 



