BASINS OF THE LAURENTIAN LAKES. 203 



bays, when upon the country around Lake MIstassini and upon many 

 other tracts glacial lakes of considerable size must have been formed. In 

 the exploration of that region traces of these former lakes, especially of 

 then- channels crossing the watershed, should be carefully looked for, as 

 not the least important of our records of the Ice age. 



Basins of the Laurentian lakes and of Hudson Bay. — As soon as the 

 border of the retreating ice-sheet was withdrawn across the various parts 

 of the watershed south of the Laurentian lakes, each considerable stream 

 valley and embayment between the height of land and the ice front held a 

 glacial lake. Doubtless hundreds of channels may be traced where these 

 lakes outflowed. But the continuing glacial retreat merged these minor 

 lakes into a few of large size, overflowing at the lowest passes. In the 

 States adjoining on the south, and in portions of Canada on the north, the 

 shores of these glacial representatives of the present Laurentian lakes are 

 recorded by eroded cliff's, beach ridges, deltas, and lacustrine sediments; 

 but along other poi-tions of their Canadian boundaries, where they were 

 held in by the receding ice barrier on the northeast and north, the land 

 shows no shore erosion nor beach deposits. 



The west part of Lake Superior stood about 500 feet higher than now, 

 and outflowed by the St. Croix River. Lake Michigan outflowed by the 

 low divide at Chicago to the Des Plaines and Illinois rivers. The glacial 

 Lake Erie was at first some 200 feet above the present level of this lake, 

 with ovei-flow to the Wabash ; but later it obtained lower outlets, the last 

 being by Chicago, after the glacial lakes Erie, Huron, Michigan, and 

 Superior had been merged into one expanse, which Spencer has named 

 Lake Warren. Lake (Dlntario, or rather its glacial forerunner, named by 

 Spencer Lake Iroquois, becoming by the retreat of the ice separated and 

 distinct from the upper lakes, extended far to the north and northeast of 

 its present limits and poured its waters into the Hudson, at first by the 

 Mohawk and afterward by the way of Lake Champlain, while the continu- 

 ing glacial recession uncovered the country north of the Adirondacks and 

 along the great valley where it now outflows by the St. Lawrence. 



The watershed which divides the upper St. Lawrence basin from the 

 basin of James Bav is crossed bv manv channels of outflow from glacial 



