122 N. H. WINCHELL GLACIAL LAKES OF MINNESOTA 



that since these lakes existed the shore line of lake Superior has sufiered 

 a differential elevation, increasing toward the north and east, amount- 

 ing to about three inches per mile. Making allowance for this change, 

 the distance between the outlets being about 40 miles, the Brule outlet 

 would be found to have been at least 10 feet lower than the Nemadji 

 outlet. As long as these outlets to the Mississippi basin continued, the 

 Saint Lawrence basin was deprived of a large amount of the surface 

 drainage which now passes over Niagara falls. 



17. Lake Nicollet^ 



It has been stated that the line of contact and confluence of the two 

 great ice-lobes passes northwestwardly from the central part of the state, 

 sa)'^ Dakota county, and that in the retreat of these lobes the drift of this 

 contact line was left in a state of confusion and overlapping complexity. 

 This can be followed to the vicinity of Itasca lake, where it turns east- 

 wardl3^ The interlobate area first uncovered was uniformly one of greater 

 elevation than the areas covered by the ice adjoining. On the retreat of 

 these ice-lobes from the vicinity of Itasca lake the included area next 

 eastward naturally sloped eastward, and the interlobate area hence be- 

 came covered with a glacier lake. This lake was hemmed in 'l)y higher 

 land toward the west, partly morainic, and by the two glaciers toward 

 the northeast and the southeast. Here gathered a great Victoria Nyanza, 

 destined later to be the perennial gathering place of the initial waters of 

 the Mississippi. Across this area the line of confluence of the retreating 

 ice-margins is screened by the accumulations of lacustrine sediments. 

 It reappears on the east in the compound moraine which runs eastward 

 from Pokegama falls and Grand Rapids, approximately coinciding with 

 the Mesabi Iron range nearly as far east as Birch lake. The level of this 

 lake was about 1,390 feet above the sea, and its outlet was through the 

 valle}^ occupied by the " chain of lakes," extending from the southwestern 

 arm of Leech lake across Hubbard county to the upper waters of the 

 Crow Wing river. When this lake was drained, Leech lake appeared at 

 a level of about 95 feet lower, Winnibigoshish about 100 feet, and Cass 

 lake about 90 feet. Tliese lakes are connected by a sluggish, winding 

 stream, which continues with about the same characters to near Poke- 

 gama falls. 



18. Lake Beltrami 



Another interlobate lake was farther north, and was apparently more 

 dependent on the northern glacier than on the southern. It had its 



♦This large lake is named Nicollet from the great geographer of the fifth decade of the century, 

 whose indefatigable labor first represented this upper region of the Mississippi on a suitable chart. 



