FISHES OF ILLINOIS 



The river is very sluggish, and its volume is extremely 

 variable. In the first eleven miles it makes a descent of about 

 100 feet, but below this the fall is not more than a foot to the 

 mile. In times of spring flood its broad stream is overloaded with 

 silt and its bottom a creeping mass, shifting its contour with 

 every change in rate of flow; and during the summer drouths 

 it shrinks to little more than a chain of nearly stagnant pools. 



Throughout the greater portion of its course Big Muddy 

 River occupies a preglacial line of drainage and meanders about 

 in broad bottoms which have been filled with drift and alluvium 

 to an elevation of from 500 to 600 feet or more above the rock 

 bottom. Just below Murphy sboro the valley becomes con- 

 stricted to a width of about a mile in its passage through the 

 elevated ridge which there borders the Mississippi. In its 

 course through the 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 

 Mwphysboro the banks are neither abrupt nor high, and they 

 and the bed of the stream are chiefly clay. 



At Murphy sboro, about 6 miles below the junction of 

 Beaucoup creek, where the stream is about 160 feet wide, the 

 water has sometimes 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, 

 includes also about 8,770 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 Shelbyville 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 



