THE TOPOGRAPHY AND HYDROGRAPHY OP ILLINOIS XXXI 



entered. Outcrops of the Niagara formation occur frequently 

 along the bluffs. 



PLUM RIVER 



Plum River rises in the northeast corner of Carroll county, 

 and, following a westerly and southerly direction through many 

 windings and abrupt turns, finally empties into the Mississippi 

 in the center of the western boundary of Carroll county. It 

 rises at an altitude of 900 feet but descends to 800 feet in the 

 first 3 miles, to 700 feet in the next two and one half miles, and 

 to 590 feet in the remaining 32 miles of its course. The banks 

 are often 150 feet high, and in some places are very abrupt, 

 while at other points a narrow valley of one eighth to one fourth 

 of a mile intervenes. It is 33 miles long, and drains an area of 

 307 square miles. 



THE MISSISSIPPI BLUFF DRAINAGE 



Under this head are included all of the small streams of 

 western Illinois directly tributary to the Mississippi below those 

 of the northwestern area. Those here briefly described are 

 Edwards River, Pope creek, Henderson River, Bear creek, Bay 

 creek, and Cahokia River. The character of a multitude of 

 others may be sufficiently inferred from those of this list. The 

 area drained by these western streams includes two strips of 

 land bordering the Mississippi, one above and the other two 

 below the Illinois basin. It consists of the eastern Mississippi 

 bottoms, varying in width from one to ten miles, and of high 

 bluffs rising from 150 to 250 feet above the river, usually of loess, 

 but occasionally with precipitous rock exposures. Many of the 

 streams rise beyond this range of bluffs on the western prairies. 



EDWARDS RIVER. 



Edwards River rises in southeastern Henry county, in two 

 branches, and flows westward through this and Mercer county. 

 In the western part of the latter it turns southward for a short 

 distance before emptying into the Mississippi about one and one 

 half miles below New Boston. Below the junction of its two 

 headwater streams the course of the river is remarkably straight 

 and it has few tributaries. This is due to the fact that its basin 

 lies in a narrow and shallow valley between two ridges having a 

 general east- west direction, and so the river drains only this 

 narrow strip. Pope creek, which flows parallel with it on the 



