Proceedings of the Ohio State Acadeiiiy of Science 229 



From the dispersion centers of Labrador and Keewatin the ice 

 fed outward, sometimes maintaining a stationary front because 

 melting and feeding were balanced, retreating when wastage was 

 the more active, and advancing with the ascendancy of the feed- 

 ing. 



Wherever the great plain over which the ice was spreading 

 sloped away from the ice, drainage moved freely ; where, how- 

 ever, this plain sloped toward the coming ice, the water gath- 

 ered, forming lakes. 



The record of the bodies of water marginal to the Wiscon- 

 sin ice-sheet has long been known with much accuracy. As soon 

 as the ice in its retreat came to a halt within the basins of the 

 present Great Lakes, then frontal water accumulated ; thus there 

 were small lakes in the Michigan and in the Erie basins, while 

 the remaining basins were buried beneath ice. These small lakes 

 gradually expanded as the ice-cap diminished. So long as each 

 lake maintained an independent overflow southward, it is evi- 

 dent that there had not been disclosed, in the area between these 

 lakes, an altitude lower than the altitude of the overflow chan- 

 nels. As soon as any lower point was disclosed by the retreat- 

 ing ice then the marginal lakes coalesced and continued to drain 

 southward by the lowest col reached. Frequently long intervals 

 of time marked the spacing of these periods of retreat. It is this 

 fact that makes it possible today to deliminate the extent of these 

 temporary lakes. A time did come, however, when the whole 

 front of the gradually receding ice-sheet was skirted by a body 

 of water which reached the ocean by a single overflow channel. 

 The first of these more expanded bodies of water overflowed by 

 way of the Illinois river, past the present location of Chicago. 

 A lower outlet was revealed when the ice withdrew from the 

 Mohawk Valley area ; then this great marginal lake reached the 

 Atlantic by the eastern outlet. 



The succession of ice-front lakes, as we today read descrip- 

 tions of their succeeding overflow channels, include so many 

 positions that we fail to comprehend the time involved. We 

 feel that the shore line of any particular one of the present Great 

 Lakes, as Superior, represents a long time period. We have 



