502 



THE ILLINOIS GLACIAL LOBE. 



moraine westward the channel found no prominent drift barriers to remove, 

 but has been compelled to cut down 50 to 75 feet into the rock in opening 

 an outlet from the Moms Basin into the valley of the lower Illinois. 



In the 41 miles to the foot of the rapids near Utica the stream falls 47 

 feet, or slightly more than 1 foot to the mile. This fall is far from regular, 

 there being a series of rock rapids separated by pools. The following 

 table of variations is based upon data published by Cooley. 1 In the first 

 mile a fall of 44 inches is made, after which for nearly 12 miles the fall 

 is less than 4 inches to the mile, and in the next 12 miles is but 8£ inches 

 to the mile (if the Marseilles dam were removed). This portion apparently 

 crosses lines of preglacial valleys, for wells indicate that the drift extends 

 in places 50 to 60 feet below the river level. Near Marseilles a fall of 10 

 feet is made in about 1 £ miles, below which for over 5 miles a rate of fall is 

 continued which averages about 2 feet to the mile. The rate then decreases 

 to less than 6 inches to the mile. This is maintained for 6.7 miles. Another 

 rapid is then passed, with a fall of 6.8 feet in 2.6 miles, when a pool is 

 reached, near Utica, that is formed by the dam at Henry, 20 miles below. 

 The above conditions are set forth in the following table: 



Table showing variations in bed of upper Illinois River. 



Low water Fall per 

 (abovetide)J mile. 



Mouth of Kankakee River. 



One mile below 



Head of Marseilles pool ... 



Marseilles, below dam 



Foot of Marseilles rapids . . 



Mouth of Fox River 



Head of rapids 



Foot of rapids near Utiea. . 



Miles. 

 



1 



11.7 

 12.7 

 1.5 

 5.3 

 6.7 

 2.6 



Feet. 



485.3 

 481.6 



477.9 

 468.8 

 458.3 

 447.9 

 444.9 

 438.1 



44.04 

 3.80 

 8.59 



84.00 



23.54 

 5.37 



31.38 



This portion of the Illinois Valley, although of post-Wisconsin age, 

 has a channel more than a mile in average width and nearly 100 feet in 

 average depth. Yet at present it is the line of discharge for an area of 

 only 12,000 square miles. The influence of the waters discharged from 



' Lake and Gulf Waterway, by L. E. Cooley, 1890. 



