22 CHICAGO ACADEMY OF SCIENCES. 



belts often cross smooth plains having only occasional develop- 

 ments of morainic topography. 



The moraines which these bowlder belts accompany are usu- 

 ally a strong phase of the swell and sag type bordering on the 

 knob and basin type. They are moraines which in their north- 

 ward continuation in Eastern Wisconsin assume a pronounced 

 knob and basin type. 



In northern Kane and McHenry Counties there are bulky mo- 

 raines with strong expression, which do not have. definite soutfh- 

 ward continuation, unless it be in the bowlder belts. It is not cer- 

 tain whether they are to be correlated with the much feebler, 

 bowlder strewn moraines of Eastern Illinois and Western In- 

 diana, with w'hich the bowlder belts give them a possible con- 

 nection. They may prove to belong to tlie Early Wisconsin series. 

 In that case they were overridden without being obscured by 

 the very bowldery drift sheet. 



Valparaiso Morainie System — This system consists of a more 

 or less complex belt, which sweeps around the head of Lake 

 Michigan, passing through the western and southern part of the 

 Chicago Area. It receives its name from the city of Valparaiso, 

 Ind., situated on its crest. As it is fully discussed on subsequent 

 pages, further description at this point is unnecessary. 



Lake Border Morainie System — This system embraces a se- 

 ries of till ridges well displayed along both the western and eastern 

 borders of Lake Michigan. Those in Lake and Cook Counties, 

 Illinois, are discussed in detail in this paper. Similar ridges appear 

 in Porter and Laporte Counties, Indiana, and in the western 

 counties of Midhigan as far north as investigations have been 

 carried (to the mouth of Kalamazoo River). 



THE LAKE BEACHES. 



Upon the retreat of the ice sheet from the head of Lake 

 Michigan a body of water collected in the southern end of the basin 

 and discharged southwestward by the "Chicago , outlet" to the 

 Desplaines River. This period of discharge appears to have been 

 followed by a period in which the water level was too low to dis- 

 charge in that direction.v There then succeeded another period of 

 discharge through the southwestward outlet. This period of 

 disciharge was followed by the present lake stage with northward 

 outlet. As tjhis complicated lake history is discussed in some de- 

 tail farther on, it is left here with this passing word. 



