420 THE ILLINOIS GLACIAL LOBE. 



Taylor. — Mr. F. B. Taylor has published in the American Geologist obser- 

 vations on high beaches in the northern portion of the basin of Lake Michi- 

 gan. 1 These beaches, he thinks, pass beneath the present lake level before 

 reaching the southern end of the basin. This being the case, they have no 

 connection with the outlet under discussion. 



Davis. — Prof. W. M. Davis has published a description of the Chicago 

 Outlet in the Popular Science Monthly. 2 His paper was based upon a per- 

 sonal inspection of the channel with the United States topographic sheets 

 in hand, and is a very clear, though brief, discussion of the features. 



THE CHICAGO OUTLET. 



The name " Chicago Outlet" has come into use b)~ geologists and engi- 

 neers, without definite announcement t>r conference among writers, to desig- 

 nate the line of southwestward discharge from the basin of Lake Michigan 

 across the low divides near Chicago and thence down the Des Plaines and 

 Illinois to the Mississippi. It may appropriately embrace both points of 

 discharge from the lake to the Des Plaines — namely, the one entering at 

 Summit and the one at Sag Bridge. 



When the lake was occupying the highest beach, the north or main 

 outlet was entered about 3 miles southwest of Summit; when occupying 

 the second beach, the outlet was entered at Summit; when occupying the 

 third beach, the point of entrance appears to have been transferred eastward 

 nearly to the present shore of Lake Michigan, as explained below. Simi- 

 larly the southern outlet was lengthened eastward with the lowering of the 

 lake, the point of entrance at the time of the highest beach being about 5 

 miles east of Sag Bridge, at the time of the second beach near Blue Island, 

 and at the time of the third beach at Riverdale. This relationship of the 

 several beaches to the outlets and the eastward lengthening of the outlets 

 may be readily understood by a glance at the accompanying map (PL XVII). 



There have been several surveys which have contributed contour maps 

 of portions of the Chicago Outlet and of the plain covered by the lake in 

 the vicinity of Chicago. The Chicago Drainage Commission have prepared 

 an excellent map with 5-foot contours which covers nearly all of Cook 



1 American Geologist, Vol. XIII, May, 1894. 



-The aueieut outlet of Michigan, by Prof. W. M. Davis: Popular Science Monthly, December, 

 1894, pp. 218-229. 



