42 CHICAGO ACADEMY OF SCIENCES. 



LAKE BORDER MORAINIC SYSTEM. 



THE MORAINES. 



Between the Valparaiso moraine and the shore of Lake 

 Michigan there are, in Cook and Lake Counties, a series of nearly 

 parallel till ridges. We can perhaps best describe them as the West 

 Ridge, Middle Ridge and East Ridge. Though usually distinct, 

 the ridges are in places coalesced as described below. 



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 the moraine and for 

 several miles south follows closely the outer border. The river 

 then bears away from the ridge a short distance and the outer 

 border 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 two miles. In the south part of the county 

 it sends out a spur to join the middle moraine belt near Deerfield, 

 while the main ridge continues south into Cook County, gradually 

 decreasing in strength and dying out in a plain near Mont Clare, 

 in the southwestern part of JefTerson Township (T. 40, R. 12 E.). 

 For five or six miles north from its southern terminus it rises 

 scarcely ten feet above the bordering plains, and is distinguishable 

 from them mainly in being more undulatory. Where well de- 

 veloped, as in northern Lake County, the moraine has numerous 

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

 ridge whose relief is nearly twenty-five 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 old lake. A possible continuation 

 southward is discussed below. , The course of the belt is south to 

 north, through Northfield Township, Cook County. Upon enter- 

 ing Lake County it becomes distinct from the spur and remains 



