498 THE ILLINOIS GLACIAL LOBE. 



The Illinois River, as far down as Peoria, has its course through a 

 district covered by drift of Wisconsin age. Below that city as far as 

 southern Pike Count)", its bordering- uplands are coated with Illinoian drift, 

 and this is capped by loess. From Pike County southward the uplands on 

 the west are nearly free from glacial drift, but are heavily coated with 

 loess. Those on the east have a moderate amount of Illinoian drift capped 

 by loess. 



Much of the Kankakee Basin and the headwater portion of Fox River 

 afford very imperfect drainage and contain extensive marshes. They also 

 contain small lakes and marshy shallow lakes, as well as the wet marshy 

 prairies. Elsewhere within the limits of the Wisconsin drift the marshes, 

 bogs, and lakes connected with the Illinois River drainage are of small 

 extent, but there is, on the whole, a rather imperfect development of drain- 

 age lines. Often areas of several square miles, and occasionally entire 

 townships, are without a well-defined channel for the discharge of water. 

 It is only by a judicious system of ditching, including both surface ditches 

 and tile drains, that this area has been brought into its present fair condi- 

 tion for cultivation. Much still remains to be done before the full resources 

 of the rich soil will be at command. 



Within the portion of the drainage basin in which loess forms the 

 surface and Illinoian drift the substratum the drainage is markedly better 

 developed than within the portion covered by Wisconsin drift. Swamps or 

 marshes are of very limited extent, but there are not a few swales or 

 shallow valleys which are poorly drained. Tile draining is found very 

 advantageous on the level portions of the uplands, and the drains are often 

 continued along the shallow valleys or swales into the well-defined valleys. 



The Illinois Valley is naturally divided into two parts, the upper and 

 lower Illinois. The upper Illinois comprises the westward-flowing portion 

 from the junction of the Des Plaines and Kankakee down to the bend 

 near Hennepin, a distance of about 50 miles ; the lower comprises the 

 southward-flowing portion extending from Hennepin to the mouth, a 

 distance of about 200 miles. The upper Illinois is excavating a new course 

 and its bed is usually on the rock, while the lower Illinois occupies a pre- 

 glacial channel in which the rock bottom lies nearly 100 feet below the bed 

 of the present stream. This preglacial channel, as above indicated, con- 



