396 ANNUAL KEPORT. 



sheet; second, those having rock basins formed either by glacial 

 erosion or through the interruption of a geological formation as 

 shown by Lake Saganaga, on the northern boundary of the state ; 

 and in the third place the glacial lakes, of which class lakes Min- 

 netonka and Heron are types. Lakes of the last named class are 

 by far the most numerous ; they lie in the valleys left by the 

 moraines of the retreating masses of ice at the close of the glacial 

 period. In shape they are more irregular than the lakes of the 

 other classes as they fit in between or wind around the moraine 

 ridges, as their contour will permit. We do not find them equally 

 distributed over the state since they owe their distribution to the 

 retreating ice sheets of the succeeding glacial waves which swept 

 over the state, each one weaker than the preceding and constantly 

 northward bearing till the southern limit wholly left the state, 

 and the Red River began to flow northward and the source of the 

 Mississippi was changed to what is now the northern central por- 

 tion of Minnesota. For the origin and law of distribution of the 

 glacial lakes, therefore, we must look to geology; the scope of this 

 paper will only permit us to call attention to this fact, that where 

 the piles of glacial debris lie thickest and highest, there we find 

 these sheets of water most numerous. 



A glance at the map will show that a belt some 50 miles wide, 

 extending northwesterly from Lake Minnetonka through Otter 

 Tail with its 430 lakes, into Becker county, turning a right angle 

 toward the northeast, and crossing into the Canadian dominion, 

 will include that part of the state which contains the greatest 

 number of lakes. 



The altitude of these bodies of water is not great, as the following 

 figures show: 



Lake Minnetonka 922 feet. 



White Bear 9l0 " 



MilleLacs 1346 " 



Itasca 1500 " 



Red Lake 1140 " 



Otter Tail 1325 " 



Lake Ida 1400 " 



Eagle Lake 1125 " 



Lake Miltona 1400 " 



Heron 1405 " 



Lake of the Woods 1062 " 



Of river expansions we have: 



Lake Traverse 970 feet. 



Lake Pepin 664 '' 



Big Stone Lake 962 " 



St. Croix (low water) 655 " 



