THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS Ixv 



valley gravels connected with the Shelbyville moraine head 

 down the river bottom in a way to indicate the existence of this 

 valley at the time of their deposition. The valley increases in 

 width from one mile in Cumberland county to 2 miles in Jasper 

 county, and 3 to 5 miles in Crawford and Lawrence counties. 

 Below Newton its course is determined largely by a preglacial 

 line of drainage, which possibly extends up the valley as far as 

 the vicinity of Greenup, 18 miles above Newton. In this sec- 

 tion of the basin strips of timber-land border the streams, and 

 the bottoms are somewhat swampy and subject to overflow, 

 but are generally sufficiently dry to admit of some cultivation 

 when cleared. In Lawrence county, between the Embarras 

 and the Wabash rivers, there is an extensive marsh, known as 

 Purgatory swamp, about 10 miles long and from 2 to 4 miles in 

 width. The banks of the river are 50 feet high in Cumberland 

 and Jasper counties, but much lower near its mouth, although 

 the uplands lie 50 to 100 feet above the watercourses. 



The interesting contrast between the upper and the lower 

 courses of this stream, in respect to the number of its tributaries, 

 the extent of its flood-plain, and the development of its drainage 

 system generally, is clearly traceable to differences in age 

 between the two glacial areas through which it flows. 



LITTLE WABASH RIVER 



Little Wabash River, with a length of 160 miles, drains 

 about 3,190 square miles in southeastern Illinois. It lies in an 

 oval basin, much broader in the middle than in its lower and 

 upper parts. It extends, on the west, to the watershed of the 

 Kaskaskia and on the east to the Embarras and Bonpas water- 

 sheds. The entire basin lies in the Illinoisan drift, and is 

 made up of rolling prairies lying between the broad belts of 

 woodland which skirt the streams. The difference in level 

 between the creek bottoms and the adjacent highlands does 

 not usually exceed 50 to 75 or 100 feet. 



The river rises in southwestern Coles county, and flows south 

 through Shelby and Effingham counties. In northern Clay 

 county it turns southeast for about 50 miles, and then flows 

 alternately southwest and southeast until it empties into the 

 Wabash at the boundary line between Gallatin and White 

 counties, eight miles, in a direct line, from the junction of the 

 Wabash with the Ohio River. The length of the river is about 

 180 miles. Its source is in the Shelbyville moraine at an eleva- 



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