THE GLACIAL LAKE CHICAGO. 429 



Lake Chicago in that State, being nowhere less than 2 and in places 12 

 miles back from the shore. In Michigan it is absent for a short distance 

 at the "clay banks," north of New Buffalo, where the present shore 

 stands farther east than the shore of Lake Chicago. It is also absent for 

 the same reason for a few miles near the line of Berrien and Van Buren 

 counties, north of St. Joseph, Michigan. Tracing in detail the course of 

 this beach is as follows: 



From the Wisconsin line southward to South Waukegan it stands only 

 1 to 2 miles back from the shore of Lake Michigan and comes out to that 

 shore at the point where the bluff of till sets in south of Waukegan. This 

 bluff of till stands above the highest lake level as far south as Winnetka. 

 From Winnetka a cut bank, nearly 20 feet in height, extends south along 

 the face of the east till ridge noted above to its terminus, perhaps 1 mile 

 from the point where the old shore departs from the present shore of the 

 lake. From the terminus of this ridge a bar was built out southwestward 

 5 or 6 miles, terminating about a mile east of Chicago River, in the west- 

 ern part of T. 41, R. 13 E. The bar sends out two prominent spurs to the 

 west, a distance of nearly 1 mile. These probably mark the termini in its 

 early stages of growth. The average width of this bar is about one-fourth 

 mile, and it was built up to a height of 10 to 20 feet above the bottom of 

 the bay back of it. It consists largely of gravel, but has a liberal admix- 

 ture of sand. The bay back of this bar extended to the valley of the 

 Chicago River and has a width of 2 to 3 miles. The northern end finds a 

 narrow extension northward in Skokie Marsh. The site of this old bay is 

 now largely under cultivation, though some portions are still marshy. 



The question naturally arises whether this accumulation of gravel and 

 sand was formed by the lake currents and waves independent of the Chicago 

 River, or was largely formed as a delta from that stream. This deposit is 

 not in the form of a delta built up at the debouchure of the river into the 

 lake, but lies some distance to the east of the river valley, thus indicating 

 that it was formed by the lake. Moreover, to make it still more evident 

 that it was the lake and not the river which contributed the great bulk of 

 the beach deposit, it is found that the river valley above the point where it 

 entered the old lake has very little assorted material, such as would accu- 

 mulate above a delta. 



