THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS xlix 



of preglacial vallej^s which were cut by streams then emptying 

 into Lake Michigan. The present river consequently cuts alter- 

 nately through the divides and valleys of these old rivers. 

 Probably much of the underground drainage now follows these 

 old channels to the lake. 



In its passage through Kane and Kendall counties, the fall 

 of the river is about 3 feet per mile, but in La Salle county it 

 increases to about 5 feet per mile, making a descent of nearly 

 125 feet in the lower 25 miles of its course. Near Elgin it 

 begins a rapid descent to the low plain that lies on the outer 

 border of the Marseilles moraine and follows this to its mouth. 

 The stream here, for a few miles, has cut to a depth of nearly 

 100 feet, but in its passage through the plain its bed is sunk to 

 a depth of only 40 to 50 feet except for a few miles near its 

 mouth, where it cuts 125 feet to enter the Illinois. Its channel, 

 even in the lower 75 miles, has a breadth of only about one 

 eighth of a mile. 



VERMILION RIVER 



Vermilion River of the Illinois (not of the Wabash) , about 90 

 miles in length, -drains an area covering about 1,320 square miles. 

 This is a plain of till about 20 miles wide, which lies immediately 

 south and west of the Marseilles moraine in Ford, Livingston, 

 and La Salle counties. The river rises by several branches in 

 the Bloomington morainic system in southeastern Livingston 

 and Ford counties, the main stream following the western or 

 outer border of the inner range of the system from its source to 

 its mouth, and thus flowing in a northwestward direction and 

 emptying into the Illinois near La Salle. The plain descends 

 with the river, so that for 50 miles scarcely any valley is formed 

 though there is a descent of nearly 100 feet. In the last 40 

 miles, from Pontiac to the banks of the Illinois, it has scarcely 

 20 feet of slope, and was apparently occupied by a shallow lake 

 until a stream had been given time to open a channel from the 

 Illinois back several miles into the plain. There are sandy 

 deposits along the southern border of the plain which tend to 

 confirm this view. In the lower 25 miles the stream corrades 

 rapidly, making a descent of about 150 feet and cutting its 

 valley mainly in rock. The channel is very narrow, steep, and 

 rocky, especially near the mouth of the river, where the walls 

 rise abruptly 150 feet from the water's edge. 



A few miles from the mouth, at a bend in the river, a deep 



