lx FISHES OF ILLINOIS 



correlated with the Cerro Gordo moraine, crossing this in south- 

 eastern Douglas county. Its course is then slightly west of south 

 for 25 miles, at which point it leaves the Shelby ville or earliest Wis- 

 consin sheet of drift, continuing southward 25 to 30 miles farther, 

 to the neighborhood of Newton, where it changes to the southeast- 

 ward and maintains this course to its mouth, a distance of 50 miles. 



The river rises at an altitude of 750 feet, while its mouth lies only 

 395 feet above tide, making a total descent of 355 feet, or an average 

 descent of two and a third feet to the mile. In the last 53 miles, 

 however, the fall is scarcely more than a foot to the mile. 



The upper part of the river, lying within the Wisconsin drift, 

 drains only a narrow strip and has but few tributaries. This section 

 of its basin is mostly prairie with woodlands skirting the larger 

 streams, and the soil is a deep, black, and very fertile loam. 



Upon emerging from the Wisconsin drift, the river enters at once 

 a much broader valley which appears to have been excavated prior 

 to the Wisconsin stage of glaciation, for the valley gravels connected 

 with the Shelby ville 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 Law- 

 rence 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 gen- 

 erally 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 

 arc 50 feel high in Cumberland and Jasper counties, but much lower 

 near its mouth, although the uplands lie 50 to 100 feet above the 

 watercourses. 



The interesl ing 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 gener- 

 ally, is clearly traceable to differences in age between the two glacial 

 anas through which it flows. 



] l i l I.K WABASH RIVER 



Little Wabash River drains about 3,000 square miles in south- 

 east crn Illinois. It lies in an oval basin, much broader in the middle 



