262 



PHYSICAL GEOLOGY 



12,500 feet) and in practically every latitude, they are, never- 

 theless, distributed very unevenly over the surface of the land. 

 Lakes abound in the recently glaciated areas of northeastern 

 United States, Canada, and Europe. Nearly one third of 

 the surface of Finland is covered with lakes and marshes. 

 Maine has 1620 lakes, and it is said that Minnesota may 

 have 8000. Figure 278 illustrates their abundance in parts 

 of Michigan. In these regions, as already indicated (p. 214), 



FIG. 279. Lake in an ice-scoured rock basin. Northern Washington. 

 (Russell, U.S. Geol. Surv.) 



they commonly occupy (1) ice-scoured rock basins, (2) hol- 

 lows in the unevenly deposited drift (Fig. 225), or (3) the un- 

 filled depressions of drift-choked preglacial valleys. Lakes are 

 numerous also in northwestern United States, western Canada, 

 the Alps, and elsewhere, in glaciated mountain valleys. Most 

 of them fill depressions (1) behind morainic dams (Figs. 238 

 and 240), or (2) gouged out by the glaciers which formerly 

 occupied the valleys (Figs. 239 and 279). Lakes are common 



