THE PLEISTOCENE OR GLACIAL PERIOD. 



459 



are extensively utilized. Calcium carbonate, though not shown in 

 quantity by analyses of the water, is precipitated in the form of oolite 

 about the shores of the lake, probably through the influence of organisms. 



Fig. 539. — Same as Fig. 53S, in contours. (Johnson, U. S. Geol. Surv.) 



Within the area of Lake Bonneville, igneous eruptions (Fig. 540) 

 have taken place during the Pleistocene period. These eruptions appear 

 to have occurred at various stages of the lake's history, and even in post- 



