132 THE GEOLOGY OP MINNESOTA. 



[Lakes and rivers. 



same class, though its rock-rim was formerly covered by drift throughout 

 much of its extent. This has largely been washed off in Minnesota to the 

 hight of about 500 feet above its present level, by the former action of its 

 own waves which have left terraces and other water-marks up to that 

 hight. The lakes of this class extend southward to Vermilion lake, and 

 there they begin to blend with those of the first class. Southwest of 

 Rainy lake they blend with those of the second class. The northern por- 

 tions of Rainy lake, and of lake of the Woods, exemplify the characters of 

 this class, but the southern portions belong to the second class. 



Lakes Traverse and Big Stone, on the western boundary of the state, 

 and St. Croix and Pepin on the eastern, do not belong to either of these 

 classes. They are simply expansions in old river-valleys, not yet filled 

 with sediment ; the former excavated in the drift sheet,* and the latter in 

 the Cambrian rocks. 



Rivers. The waters of the state all find their way to the Atlantic 

 ocean, but they reach that level through three of the cardinal points of 

 the compass north, east and south. The French and English geographers 

 of the last century also located in Minnesota the source of another great 

 river which reached the Pacific ocean toward the west. This river, which 

 was designated as the "river of the west" was sometimes thought to be the 

 Oregon, sometimes tbRio Colorado, and sometimes was confounded with 

 the Saskatchewan river that enters the north end of lake Winnipeg from 

 the west. Without this great western river, however, Minnesota occupies 

 in a pre-eminent degree the summit divide of the waters of North America, 

 at least so far as they exist within the United States. The hight of the 

 main divide in the state, in the region west and southwest of Itasca lake, 

 rises between 1600 and 1700 feet above the sea, and the average elevation 

 of the entire state is probably not far from 1275 feet above the sea, the 

 border of lake Superior, the lowest land within the state, being 602 feet. 

 Hence, the streams which drain the surface area amounting to about 

 84,286.53 square miles, are not characterized by water-falls and rapids, but 

 by their crooked courses and gentle, generally navigable, currents. 



The water area of the state is greater than that of any state or terri- 



*And partly In the Cretaceous. 



