MICHIGAN ACADEMY OF SCIENCE. 



29 



feet higher than the bed of the outlet, but in parts of the border the 

 shore is very Aveak and ill defined/ The red clay of the Green Bay basin 

 wliich Upham considered a deposit of the lake bed has been found by 

 Alden to be a glacial deposit. It was on the withdrawal of the ice after 

 depositing the red drift that the hike reached its gi-eatest extent, and it 

 only persisted until the ice had melted far enough back to give an east- 

 ward discharge into the Lake Michigan basin. 



Scale 



Miles 



Fig. 3. Beginnings of lakes in Superior, Green Bay, Micliigau. and Erie basins, witli 



correlative ice border. 



MICHIGAN BASIX. 



In the Michigan basin there was at first a chain of lakes along the 

 eastern side of the southern portion and a narrow strip of water at the 

 south and southwest which discharoed down the Des Plaines valley. 

 The ice filled the basin at that time a little beyond the limits of the 

 present lake, its border being at Blue Island ridge in Illinois, and at 

 the narrow moraine north of Chesterton, Indiana. 



^Personal communication. 



