ILLINOIS EIVEE DEAINAGE BASIN. 513 



several parallel tributaries in this curving portion of its course. Its deflec- 

 tion from a southwestward course is caused by the change in the course 

 of the moraine which lies on its northern and western border. This moraine 

 furnishes only small northern and western tributaries to the main stream. 



The watershed, with the exception of the great moraine on the north 

 and west borders, shows a perceptible southwestward descent, amounting 

 generally to several feet to the mile. In the headwater portions the main 

 creek and also its tributaries have formed only shallow ditches, but in the 

 lower course they have trenched deeply into the drift deposits, as may be 

 seen by reference to the Hennepin topographic sheet. 



Between the mouth of Bureau Creek and the city of Peoria, a distance 

 of about 50 miles, the Illinois River receives no important tributaries. The 

 largest is East Crow Creek, which has a drainage area of 226 square miles. 

 Sandy Creek, another eastern tributary, drains 147 square miles; and 

 Senachwine Creek, a western tributary, drains 132 square miles. No others 

 have an area exceeding 100 square miles. The smallness of the western 

 tributaries is due to the close approach of the bulky Bloomington morainic 

 system to the west bluff of the Illinois. In most cases these tributaries 

 lead somewhat directly from the moraine down to the vallev, but Senach- 

 wine Creek has been deflected by a drift ridge into a course parallel with 

 the moraine, and thus drains a larger area than the neighboring tributaries. 

 The eastern tributaries lead directly westward across a slightly undulatory 

 plain, which apparently offered conditions rather unfavorable for stream 

 development, there being very little descent. The streams, however, have 

 overcome this impediment by trenching deeply near then* mouths, and have 

 thus opened a fair drainage in that region. The features are well shown in 

 the Hennepin, Lacon, and Metamora sheets. 



K1CKAPOO CREEK. 



Kickapoo Creek, which enters the Illinois from the west at the city of 

 Peoria, has a drainage area of 310 square miles, mainly situated on the 

 Illinoian drift outside the limits of the Shelbyville moraine. The headwater 

 portion, however, drains a narrow strip between the Shelbyville and Bloom- 

 ington morainic systems, passing through the Shelbyville moraine just below 

 the village of Dunlap. The relation of this stream to the morainic ridges, 

 mon xxxviii 33 



