382 THE ILLINOIS GLACIAL LOBE. 



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 Waukegan, the inner border lies 

 back about 2 miles from the lake front. The usual width of this ridge 

 is about 1 mile. The crest of the ridge usually stands 110 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 feet or more 

 above the lake. 



In this connection it may be remarked that 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 early settlers that from 

 Waukegan to Evanston there has been, during the thirty years from 1860 

 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 81,000,000 worth of property. 



PROBABLE CONTINUATIONS. 



None of these ridges have been found to have connection at their 

 southern end with the massive Valparaiso morainic system, nor do they 

 admit of continuous tracing around the southern end of the lake within 

 (north of) that moraine. The weak development in that district seems the 

 more remarkable since there is on the east side of Lake Michigan, north- 

 ward from Porter County, Indiana, a series of ridges of similar size and 

 complexity to that under discussion and which are probably its continua- 

 tion. The conditions which affected the southern end of the ice lobe at the 

 time these belts were forming are so poorly known that it may be difficult 

 to ascertain what caused this wide gap. The question naturally arises 

 whether the expanded lake and its old outlet may not have removed the 

 ridges. 



In the case of the western ridge this suggestion seems inapplicable, 

 since the terminus at Mont Clare is outside the well-defined beaches and 

 above their level. The ice sheet here, however, may have terminated in 

 water held between its front and the inner slope of the Valparaiso morainic 

 system in the brief period required for the cutting down of the outlet to the 

 level of the upper beach. But in that case, "n hile wave action may have 

 removed weak morainic features, it seems scarcely probable that there could 



