244 THE ILLINOIS GLACIAL LOBE. 



The relief on the outer border seldom falls below 50 feet and in places 

 approaches 200 feet. The average relief is probably 75 or 100 feet. The 

 least relief is found in portions of Ford and Champaign counties, Illinois, 

 where it is about 50 feet. The greatest relief is found in southern Lee and 

 northern Bureau counties, where the moraine is bordered on the west by 

 the Green River Basin. The moraine here has an altitude of 900 to 1,000 

 feet or more above tide, while the basin on the immediate borders of the 

 moraine rises from scarcely 700 feet at the west to about 850 feet at the 

 east, thus giving the moraine a relief of 150 to 200 feet. 



Between the ridges of this system there is very little depression in 

 Dekalb and Lee counties. But on the inner border of the system in these 

 counties there is nearly as pronounced relief as on the outer border. 

 •Indeed, in places it exceeds that on the outer border, and probably it 

 averages 100 feet. The relief on the inner border continues prominent 

 southwestward into Bureau County, but falls off rapidly in that county, 

 becoming scarcely perceptible in the vicinity of the Illinois River. The 

 outer ridge, however, maintains its great relief throughout Bureau Count)* 

 and rises 100 feet or more above the plain and lower ridge on its inner 

 border in the eastern part of the county. In southern Bureau, western 

 Marshall, and northeastern Peoria counties it stands 150 feet or more above 

 the narrow upland between it and the Illinois Valley. This prominent 

 ridge probably includes both the Shelbyville and Bloomington systems, for 

 the former separates from it in eastern Stark county, as noted above. Upon 

 crossing the Illinois into Woodford County the uplands on the inner border 

 of the Bloomington moraine are found to stand but a few feet lower than 

 the crest, and eastward from this county there is generally a very gradual 

 descent on the inner border of the main ridges, a descent seldom exceeding 

 25 or 30 feet to the mile. 



The small ridge which leads across northern McLean County has a 

 relief of but 30 to 50 feet on its outer border and a gradual descent on its 

 inner border. The ridge leading northwestward from Chatsworth to Earl- 

 ville usually rises 30 to 50 feet above the outer border, but reaches about 

 75 feet in places in central Lasalle Count}'. The relief on the inner bor- 

 der is nearly as great as on the outer, but is usually more gradual 



