THE PLEISTOCENE OR GLACIAL PERIOD. 



468 



below the moraines. The partial removal of these deposits has 

 developed terraces (Fig, 551). 



Fig. 549. — Lateral moraine in the valley of the North Fork of Clear Creek, Bighorn 

 Mountains, Wyo. (Blackwelder.) (See also Fig. 278, Vol. I.) 



Glacial lake deposits. — By obstructing valleys, the mountain glaciers 

 of the west gave rise to numerous temporary lakes in which extensive 



Fig. 550. — The moraines about the lower end of a mountain valley. 

 Bloody Canyon, Cal. 



beds of lacustrine sediments were laid down. The extent of such 

 lakes in the west and northwest has not been determined, but where 



