THE LAKE-BOEDER MORAINIC SYSTEM. 381 



plains, and is distinguishable from them mainly in being- more undulatory. 

 Where well developed, as in northern Lake County, the moraine has numer- 

 ous knolls, 20 to 25 feet in height, and these stand upon a basement ridge 

 whose relief is nearly 25 feet. A noticeable feature of this and also of the 

 other ridges of this system is the difference in the breadth of the outer and 

 inner slopes, the usual breadth of the outer slope being scarcely one-half 

 that of the inner. 



THE MIDDLE RIDGE. 



As already noted, this ridge is joined to a spur from the west ridge south 

 from Deerfield. The combined belt finds its southern terminus near the 

 head of the Chicago River and at the border of the Glacial Lake Chicago. 

 A possible continuation southward is discussed below. The course of the 

 belt is south to north, through Northfield Township, Cook County. Upon 

 entering Lake County it becomes distinct from the spur and remains a 

 distinct ridge for a distance of 15 miles. It there, in sec. 18, Waukegan 

 Township (T. 46, R. 12 E.), becomes united with the east ridge and remains 

 united with it as far north as it has been examined. On each side of this 

 ridge there is a narrow sag or slough. The sag on. the east is marshy its 

 entire length from Winnetka, in Cook County, northward to the latitude of 

 Waukegan, a distance of nearly 20 miles. For a couple of miles at its 

 southern end it has a width of one-half mile or more, but the usual width 

 is only one-fourth mile. The sag on the western or outer border contains 

 a marsh from Rondout Station southward to the Lake and Cook County 

 line, a distance of about 9 miles. 



This ridge, like the west ridge,- has low knolls along its crest, 8 to 15 

 feet in height, but the coalesced ridge in northern Cook County is more 

 billowy and. carries knolls 20 feet or more in height. There are basins and 

 winding sloughs among the knolls, which add to the morainic expression. 



THE EAST RIDGE. 



The southern terminus of the east ridge is at Winnetka, where Lake 

 Michigan cuts it off. It has apparently had its entire east slope and a 

 portion of the crest removed by the lake, there being a descent immediately 

 from the bluff on the lake to the slough, which lies west of the ridge. 

 Following the ridge north to Highland Park the crest and east slope appear. 



