266 
Frank Carney 
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 re- 
maining basins were buried beneath ice. These small lakes grad- 
ually expanded as the ice-cap diminished. So long as each lake i 
maintained an independent overflow southward, it is evident that | 
there had not been disclosed, in the area between these lakes, an f 
altitude lower than the altitude of the overflow channels. As 
soon as any lower point was disclosed by the retreating ice then the [ 
marginal lakes coalesced and continued to drain southward by I 
the lowest col reached. Frequently long intervals of time marked | 
the spacing of these periods of retreat. It is this fact that makes j 
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 I 
revealed when the ice withdrew from the Mohawk Valley area; 
then this great marginal lake reached the Atlantic by the eastern 
outlet. I 
The succession of ice-front lakes, as we today read descriptions j 
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 i 
Superior, represents a long time period. We have difficulty, per- 
haps, in realizing that Lake Whittlesey, or Maumee, probably 
endured quite as long as the present Lake Ontario. When, how- j 
ever, we compare the rock cliff's now bordering the shore of Lake ; 
Erie, the constructed beaches, the barriers, the lagoons isolated 
by development of new bars, the dune sands reaching inland from I 
the shores, with the identical phenomena of these lakes of the past | 
and see how little they differ in scale, in spite of the denuding j 
agencies that have operated upon them since they were formed, * 
then we can better comprehend the very appreciable time inter- 
vals represented by the successive stages in the past history of the | 
Great Lakes. 
The shore of Lake Maumee in the vicinity of Cleveland was | 
