THE ILLINOIS GLACIAL LOBE. 427 



THE GEACIAE LAKE CHICAGO. 



The name-" Lake Chicago" was introduced by the writer in a recent 

 bulletin issued by the Chicago Academy of Sciences. 1 The need for a 

 name for this glacial lake and the reason for the selection of this name arc 

 set forth in the following statement: 2 



The introduction of the name " Lake Chicago " for the glacial lake which was held 

 in the southern end of the Lake Michigan Basin seems convenient, if not necessary, 

 inasmuch as its area was not coincident with that of Lake Michigan and its outlet 

 was in the reverse direction. It is also in keeping with the custom of students of 

 glacial lakes, who find it advantageous to employ a special name for each of the 

 temporary bodies of water in the several basins. The name "Lake Chicago'' seems 

 especially pertinent, since the glacial lake extended about as far beyond the present 

 limits of Lake .Michigan in the vicinity of Chicago as at any part of its border. It is 

 also a name which readily suggests Wie position of the lake, and it is in keeping with 

 the name which has come into use for the outlet, namely, the "Chicago Outlet." 



The name "Lake Chicago" is applied provisionally to all the stages at which 

 there was a southwestward outlet, but it is not yet certain whether they were all 

 formed during the occupancy of a portion of the Lake Michigan Basin by the ice sheet. 



The precise relations of these beaches to the ice sheet, or points of 

 connection with it, have not as yet been determined. The writer's study 

 has been carried no farther north than to the line of Wisconsin and Illinois 

 on the west side and to Grand River on the east side of Lake Michigan. 

 Professor Chamberlin's studies left the precise extent of the higher beaches 

 undetermined. Mr. Taylor's observations have been confined to the north- 

 ern portion of the basin, and as yet no one has examined the intervening 

 districts, where it appears probable that the higher beaches terminate. 

 Probably the most favorable field for investigation will be found on the 

 Wisconsin side, since extensive deposits of wind-drifted sand on the border 

 of the lake in Michigan make it difficult to determine the extent of water 

 action. The long stretches of high bluff, however, interrupt the beaches so 

 greatly that some difficulty is anticipated in making precise correlations on 

 the Wisconsin side. 



Enough is known to make certain that the general direction of retreat 

 of the ice sheet was northeastward. The southern and western portions of 

 the Great Lake basins were, therefore, the first to become free from ice and 



1 The Pleistocene features and deposits of the Chicago area, by Frank Leverett: Bull. No. 2, 

 Geol. and Nat. Hist. Survey, Chicago Academy of Sciences. Issued May, 1897. 



2 Op. cit., p. 65. 



