THE SERIES OE MORAINES 239 



farther east the Eose Hill moraine is found, bnt does not at present pro- 

 ject quite so far south. The space between this and the Gale wood mo- 

 raine is occupied by the Chicago River. Going farther north, there are 

 renniants of a parallel moraine above Evanston. These all seem to be 

 lateral moraines formed when the ice in shrunken quantities extended 

 toward the south end of the lake, but the erosion of the water has very 

 likely removed their extreme southern ends, so that their existence can 

 only be inferred; but Mr. Leverett thinks it not at all improbable that 

 the Rose Hill moraine extended southward to Blue Island, which is cer- 

 tainly a moraine formation 6 miles long, since the rock does not appear 

 underneath it until a depth of 50 or fiO feet is reached, while it rises more 

 than 60 feet above the lake level. 



It would seem also likely that the Galewood moraine extended to Mount 

 Forest Island, v^hich is deeply covered with moraine material. As a 

 partial proof of this, it is to be noted that the 60-foot terrace extends 

 southward from Galewood through Oak Park well on toward Mount 

 Forest Island. 



History of the Chicago Outlet 



It is true that this 60-foot beach through Oak Park, like the 40-foot 

 beach which extends toward Blue Island, is composed of stratified sand 

 and gravel; but as the erosive agencies of the lake when at its higher 

 levels probably operated for several thousand years, and as these agencies 

 are known at the present time to be eating into the bank at rates varying 

 from 2 to 3 feet a year, there was ample opportunity for them to level 

 these narrow moraines and so in part to account for the material forming 

 the present Glen wood and Calumet beacbes in that vicinity. 



But this is preliminary to considerations bearing on the opening of the 

 outlet followed by the Drainage Canal and the Des Plaines River. This 

 channel, as well as both the Sag and Des Plaines outlets which join to 

 form it, is from 1 to 2 miles wide, with rocky sides rising at La Grange, 

 on tlie north, 60 feet above the lake, and at Lemont, on the south side, to 

 the same height. Farther in the interior moraine deposits rise to a 

 height of 160 feet above the lake. The level of the rock bed of the outlet, 

 as already said, is 8 feet above the lake. 



Two suppositions have been resorted to in accounting for the accumu- 

 lation of peat underneath the Calumet beach. Mr. Alden sus'gested that 

 the water fell to the level of the Tolleston beach by being drained off 

 eastward as the ice had receded and opened up channels in that direction, 

 and that this continued for sufficient time for the peat to accumulate, 

 when a readvance of the ice closed up those outlets and raised the water 



