GEOLOGICAL AND NATURAL HISTORY SURVEY. 43 



a distinct ridge for a distance of fifteen miles. It there, in Sec. i8, 

 Waukegan Township (T. 46, R. 12 E.), becomes united with 

 the east ridge and remains so 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 twenty 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 con- 

 tains a marsh from Rondout station south to the Lake and Cook 

 County line, a distance of about nine 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 twenty feet or more in 

 height. There are basins and winding sloughs among the knolls, 

 which add to the expression of the moraine. 



The East Ridge. — The southern terminus of the east ridge is 

 at Winnetka, where the present lake 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 blufif 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. 

 Continuing north to Lake Forest, a narrow till plain appears on 

 the east of the ridge, the inner border of the ridge lying back a 

 half mile or more from the lake front. Still farther north at Wau- 

 kegan, the inner border lies back about two miles from the lake 

 front. The usual width of this ridge, where complete, is about 

 one mile. The crest of the ridge usually stands no to 125 feet 

 above the lake. At Winnetka, the higher portion being removed, 

 it rises but 80 feet above the lake. The till plain east of the ridge 

 stands 75 to 90 feet above the lake. 



The rate at which the lake bluff is being encroached upon by 

 wave action has become a matter of much concern to the residents. 

 It is estimated by old settlers that from Waukegan to Evanston 

 there has been, during the thirty years from i860 to 1890, a strip 

 about 150 feet in width, undermined and carried into the lake. 

 This amounts to about 500 acres, representing at present valuation 

 nearly one million dollars' worth of property. 



Relief. — The west ridge rises with a somewhat abrupt slope 

 about twenty-five feet above the plain along the Des Plaines 

 River. On the inner (eastern) side there is a gradual descent of 



