380 THE ILLINOIS GLACIAL LOBE. 



SECTION V. THE LAKE-BOEDER MORAINIC SYSTEM. 



Between the Valparaiso morainic s}^stem and the shore of Lake Michi- 

 gan there is a series of till ridges running nearly parallel with the lake shore. 

 In the Illinois portion three ridges are developed in Lake and northern 

 Cook Comity, but in Lake County, Indiana, at the head of the lake, these 

 ridges are wanting. On the southeast border of the lake two of them reap- 

 pear and a third one sets in north of the mouth of the Kalamazoo River. 

 Though usually distinct, the ridges are in places coalesced, as described 

 below. The gaj) at the head of the lake is so wide that strict correlation 

 between each ridge on opposite sides of the gap can scarcely be made, but 

 there is little room for questioning the interpretation that the ridges on the 

 southeast border belong to the same morainic system as those on the west 

 side of the lake. They not only have the same position with reference to 

 the Valparaiso morainic system, but also are strikingly similar in topography 

 and structure. It is found convenient to take up the discussion of the ridges 

 of each district separately. Those west of the lake, in Lake and Cook coun- 

 ties, Illinois, are first discussed, and then those on the southeast border. 



TILL RIDGES OF LAKE AND COOK COUNTIES, ILLINOIS. 

 THE OUTER OR WEST RIDGE. 



The outer or west ridge enters Illinois from Wisconsin on the west 

 side of the Des Plaines River, its outer border being for a few miles followed 

 by Mill Creek, while its inner extends to the west bluff of the Des Plaines 

 River. Just below Gurnee the river passes through a gap in the ridge, and 

 for several miles south follows closely the outer border. The river then 

 bears away a short distance, and the outer boi'der of the ridge for the 

 remainder of its course lies a mile or more east of the stream. In Lake 

 County the ridge is sufficiently prominent and bulky to constitute a marked 

 feature, and has a general width of about 2 miles. In the south part of the 

 county it sends out a weak spur to join the middle ridge near Deerfield, 

 while the main ridge continues south into Cook County, gradually decreas- 

 ing in strength and dying out in a plain near Mont Clare, in the southwest- 

 ern part of Jefferson Township (T. 40, R. 12 E.). For 5 or 6 miles north 

 from its southern terminus it rises scarcely 10 feet above the bordering 



