]0-2 NIXETEFA'TII U Kl'()i{T. 



\\'itli the melting away of tlic irt- from the Bayfield Peninsula and 

 other })rominent parts of the district south of Lake Superior, the ponded 

 waters all became merged into a single body of water, Lake Dulutli, 

 which had the level of Lake Brule, and utilized its outlet to the St. 

 Croix River and Mississippi. This outlet channel has a floor about 420 

 feet above Lake Sujierior at tlie present summit swamp, and beaches 

 turning into it are still higher, for the outlet was deepened by the 

 discharge of the lake waters through it. The ice seems to have melted 

 from the Keweenaw Peninsula soon after Lake Duluth had been formed, 

 for strong beaches of Lake Duluth are found on the Keweenaw Peninsula 

 as far northeast as Calumet. 



The ice held its front on the Huron Mountains for a relatively long- 

 time, and thus formed the eastern limit of Lake Duluth. With the 

 recession of the ice border down the east slope of the Huron Mountains 

 the glacial waters soon found a passage around the edge of the ice 

 southward and discharged into Lake Algonquin, which by that time was 

 occupying the Michigan as well as the Huron Basin. The recession 

 from the Huron Mountains opened lower and lower passages until the 

 lake in the western ])art of the Superior Basin was drawn down to the 

 level of Lake Algonquin and became a part of that lake. 



The lowering of the lake waters from the Algonquin to the Nipissing 

 level occurred when the Ottawa Valley became freed from ice. This 

 seems to have taken place soon after the waters in the western end of 

 the Superior Basin were lowered to Algonquin level, for the Algonquin 

 beach is very weak in the western Sujierior Basin. It is not as yet 

 known whetlier the ice had entirely disaj)peared from the eastern part 

 of the Superior Basin before the Ottawa ^'^allev was freed from ice. 

 There is thus a possibility that part of the northern and eastern border 

 of the Superior Basin does not have an Algonquin beach. So far as the 

 Michigan part of the Lake Superior Basin is concerned, there was com- 

 plete disappearance of the ice sheet prior to the Nipissing stage. The 

 Nipissing shore is strong all along the south shore of Lake Superior 

 as far west as it stands above the level of Lake Superior. West from 

 the Bayfield Peninsula tlu' Ni])issing shore is below Lake Superior level. 



Ann Arbor. Mich. 



