512 THE ILLINOIS GLACIAL LOBE. 



LITTLE VERMILION RIVER, ETC. 



Little Vermilion River enters the Illinois directly opposite the mouth 

 of the Vermilion River, and sustains a similar relation to the inner ridge of 

 the Bloomington morainic system, that ridge being immediately east of 

 each stream. Its watershed, however, comprises only 150 square miles. 

 The size and slope of its valley and the slope of bordering uplands, as well 

 as the relation to the morainic ridge east of it, are well displayed on the 

 Lasalle topographic sheet. The same sheet also brings out clearly the 

 features of a neighboring small tributary of the Illinois — Spring Creek — 

 which enters the river at Spring Valley. The features of another small 

 northern tributary — Negro Creek — are brought out on the Lasalle and 

 Hennepin topographic sheets. 



The same sheets also bring out the features of All Forks Creek, a small 

 southern tributary of the Illinois, entering the river about 5 miles above 

 Hennepin. All Forks Creek, it will be observed, occupies a shallow 

 depression leading westward parallel with the Illinois River. This depres- 

 sion was perhaps utilized, if not produced, in the early stages of drainage 

 development by a portion of the Illinois River. It will be observed that 

 a similar shallow depression also leads westward on the north side of the 

 Illinois, passing just north of the cities of Peru and Spring Valley, which 

 may also have been formed by the river in the early stages of its develop- 

 ment. A more careful investigation of this portion of the Illinois, where 

 the postglacial stream enters the preglacial valley, is necessary to bring out 

 fully the history of the development of the present lines of drainage. 



BUREAU CREEK. 



Bureau Creek, which enters the Illinois from the northwest at the great 

 bend of the river, has a drainage area of about 480 square miles. This 

 watershed, as previously shown, is included mainly between the two promi- 

 nent members of the Bloomington morainic system which are developed in 

 the district north from the bend of the Illinois. In addition to the main 

 creek there are several nearly parallel tributary streams, all flowing south- 

 westward across the northeastern and eastern portions of Bureau County. 

 The main stream swings around to the south and east, gathering in the 



