THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS Iv 



through the IMississippi bottoms. With the exception of the ridge 

 on the southern border, which stands 600 to 800 feet above tide, the 

 basin has few points rising above 550 feet, the average level being 

 400 to 500 feet. The immediate borders of the main valley fall 

 below 400 feet and the mouth of the stream at low water in the 

 Mississippi is but 320 feet. The country is made up of gray prairies 

 intersected by rivers whose bottom-lands are below the general 

 level. These rivers are skirted by timber belts, so that a large por- 

 tion of the basin is wooded. The bottom-lands also were formerly 

 timbered, but parts have been cleared and put under cultivation. 

 Over the greater portion of the area the drift is very thin, and rock 

 divides separating the preglacial drainage areas are plainly discern- 

 ible. The basin of the Big Muddy has been subject to long erosion, 

 and consequently the soils are largely made of clays containing little 

 humus and giving acid reactions. 



Big Muddy River has the characteristics of an old stream, in a land 

 long exposed to erosion. It has cut its bed down to drainage level, 

 and it runs its crooked course over a broad flood-plain. It rises in 

 northern Jefferson county, and flows south and then west and south, 

 emptying into the Mississippi about 5 miles below Grand Tower, 

 Jackson county. It is about 127 miles long. Beaucoup creek en- 

 ters from the north 25 to 30 miles from the mouth, and Little Muddy 

 River enters from the same side about 10 miles farther up. These 

 two streams together, drain about the same area as the main stream 

 above the junction, and Beaucoup creek drains about one half more 

 area than the Little Muddy. An eastern tributary, Crab Orchard 

 creek, drains about 250 square miles of the district bordering the 

 Ozark ridge. 



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 ele- 

 vation of from 500 to 600 feet or more above the rock bottom. 

 Just below Murphysboro the valley becomes constricted to a 

 width of about a mile in its passage through the elevated ridge 

 which there borders the Mississippi. In its course through the 



