THE BLOOMINGTON MORAINIC SYSTEM. 25.1 



the districts on the west and an even greater height above the narrow plain 

 between the ridge and the river bluff. Aside from, this main ridge there are 

 minor ridges trending parallel with it on its inner or eastern border. These 

 minor ridges are a mile or less in width, 25 to 50 feet in height, and are 

 maintained for only a few miles in a place. The surfaces are much smoother 

 than that of the main ridge. They are similar to the slight ridgings found 

 between the inner and outer belts in eastern Bureau County, and, like those 

 ridges, have an influence on the course of drainage. One of the most con- 

 spicuous instances of the governing of drainage is that of Senachwine 

 Creek, in southwestern Marshall County, which owes its southward course 

 to a low drift ridge on its east border. 



The main ridge has a topography similar to that of its northern con- 

 tinuation in central and northern Bureau County. In places a sharply 

 outlined crest is developed, but usually the higher part of the ridge is 

 broken up into knolls and sharp disjointed ridges which rise 20 to 40 feet 

 above neighboring- basins or sags. Shallow basins are a common feature 

 along- this portion of the moraine. On the outer face the border is irregular, 

 being indented by valley-like extensions of the outer-border plain, which 

 in some cases reach a mile or more back into the moraine. Between these 

 indentations there are spur-like, projections. The moraine is nowhere cut 

 through by any of these low tracts, though a line along its crest occasion- 

 ally oscillates 100 feet or more within a space of 2 or 3 miles. On the 

 whole, this section is scarcely surpassed in strength by any other portion of 

 this morainic system. 



Between the Illinois and Mackinaw rivers. — The section embraced between the Illi- 

 nois and Mackinaw rivers has a well-defined outer or southwest border, but 

 its inner or northeast border is difficult to determine. It merges on the 

 northeast into an elevated tract with a gently undulating surface, whose 

 general altitude is about as great as that of the portion of the belt which 

 presents stronger morainic expression. This elevated tract extends as far 

 east as Cazenovia. Should the entire district between Cazenovia and the 

 outer border be included in the moraine, it would have a breadth of about 

 14 miles, or more than twice the breadth of the bulky outer ridge formed on 

 the west side of the river. The strongly morainic expression is confined, 

 however, to the outer or southwest face in a belt only 3 or 4 miles in 

 width. This face presents a series of drift billows 20 to 30 feet in height, 





