THE TOPOGRAPHY AXD HYDROGRAPHY OF ILLINOIS xlv 



mile, and its bed expands at frequent intervals into lakes and marshes 

 between which are short stretches having narrow and well-defined 

 channels. The river, here, has no valley, but the stream averages 

 150 to 200 feet in width, flowing between gravel and clay 1 anks. In 

 some places it runs close to the bluff, while in others a low flood-plain 

 intervenes. Its tributaries in this section are very small, all occupy- 

 ing deep parallel valleys running in an east and west direction and 

 only turning southward when they reach the lowlands bordering the 

 river. All of the lakes lie along the line of these intermorainic valleys. 

 Among those tributary to Fox River are Lake Geneva, Muskego, 

 and Pewaukee. Fox Lake is simply a widening of the river-bed. 



From the vicinity of Elgin to Yorkville the bed of the river is 

 alternately rock and mud. This is due to the fact that the present 

 course of the river lies almost at right angles to a series of preglacial 

 valleys which were cut by streams then emptying into Lake Michi- 

 gan. The present river consequently cuts alternately through the 

 divides and valleys of these old rivers. Probably much of the under- 

 ground 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 chan- 

 nel, 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 1,413 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 1 (ranches in the Blooming- 

 ton 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 thai 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 



