ioo Introduction to Life of the Lakes. 



the Cascade mountains was first elevated 

 above the surface of the sea, it at once cut off 

 from the ocean and made an inland sea of the 

 great body of water between that dyke on 

 the west and the shore line of the Wasatch, 

 Bitter Root and Coeur d'Alene mountains on 

 the east. In the northern portion of this in- 

 land sea, the large irregular island we have 

 called Shoshone must have formed a fine re- 

 lief feature in so vast a water waste. The 

 level at which the water stood around it 

 would, of course, determine its extent and 

 outline, and these must have varied from age 

 to age, for surface disturbances have left many 

 records of their continued activity. 



The slow elevation of this region devel- 

 oped, as already described, a drainage system 

 southward that in time became the Colorado 

 river, along whose watershed can be found 

 the record of its successive changes. The mid- 

 dle portion with its grand list of Tertiary lakes 

 we may dismiss as outside our theme for con- 

 sideration; but we will center our thought on 



