lvi FISHES OF ILLINOIS 



Mississippi bottoms its eastern shore hugs the bluff, which rises 200 

 to 300 feet above the river. On its west are the low, flat flood- 

 plains of the Mississippi. Above Murphysboro the banks are 

 neither abrupt nor high, and they and the bed of the stream are 

 chiefly clay. 



At Murphysboro, about 6 miles below the junction of Beaucoup 

 creek, where the stream is about 160 feet wide, the water has some- 

 times risen 30 feet, flooding the surrounding flats. Backwater from 

 the Mississippi is felt at that point. The river is very properly 

 named, as it carries great quantities of alluvium which the current is 

 'constantly shifting from one place to another. 



The Wabash System 



The Wabash basin, which covers the greater part of Indiana, in- 

 cludes also about 8,600 square miles of eastern Illinois, drained by 

 the Big Vermilion, the Embarras, and the Little Wabash rivers, and 

 by several smaller streams in the southeastern part of the state. 

 The greater part of its surface lies at an elevation varying between 

 300 and 700 feet, with the highlands around its headwaters and the 

 region of the Shelby ville moraine rising approximately 100 feet 

 higher. This moraine marks the southern limit of the Wisconsin 

 glaciation, beyond which lies the lower Illinoisan. It divides the 

 Wabash valley in Illinois into two distinctly different regions, the 

 northern of which has the characteristics of a comparatively recent 

 glaciation, and the southern those of a glaciated area long exposed 

 to erosion. In the northern part the streams are few, and their 

 branches are few and comparatively short. The uplands were poorly 

 drained originally, and contained many marshes, sometimes very 

 large, and many shallow lakes. The soil here is deep, black, rich in 

 organic matter, slightly alkaline in reaction, porous, and rather 

 coarsely granulated. In the southern section the soil has been 

 washed and eroded for thousands of years, leaving it as an extremely 

 fine-grained, slightly acid residue, from which most of the organic 

 matter has disappeared. The streams of this long-exposed south- 

 ern area have developed themselves freely in comparatively deep 

 channels, through which their currents have a sluggish flow, and 

 have lengthened their branches back to the uplands, which are 

 thus effectually drained by natural processes. The large streams, 

 especially in their lower courses, have formed extensive bottom- 

 lands liable to overflow, and, owing to the thorough natural drainage 

 of the country, the waters recede to a very low level during times of 

 drought. 



