THE CHAMPAIGN MOEAINIG SYSTEM. 225 



Outer Ridge at its widest separation from the Middle one is distant but 8 or 

 9 miles. It is separated from the Middle Ridge for only about 30 miles of 

 the 100 or more miles in which they are exposed to view. The Inner 

 Ridge is distinct from the others for a much longer distance, being combined 

 with them for only about 30 miles of the 100 which the belt occupies. 



It will be observed that the moraines are looped across the Wabash 

 Basin after the fashion of the looping of the late Wisconsin moraines about 

 the basins and large valleys, as brought to notice by Chamberlin in the 

 Third Annual Report of this Survey. The axis of the Wabash Basin is 

 depressed only 150 to 200 feet (aside from the immediate valley of the 

 river) below the borders of its watershed where crossed by this morainic 

 system. This slight amount of depression seems scarcely adequate to be 

 the sole cause for the protrusion of the ice sheet into the valley,* though it 

 no doubt had some influence. 



RELIEF. 



The relief of the combined belt between Blue Ridge and Champaign 

 reaches about 90 feet above the outer-border plain at several points, though 

 it usually is about 60 to 75 feet. The outer-border plain declines from 750 

 feet at Blue Ridge to about 710 or 720 feet east of the Sangamon. The 

 crest of the moraine reaches 820 feet in northern Piatt County, and 800 to 

 810 feet near Rising in Champaign County, but averages only about 775 

 feet above tide. The inner-border plain lying north of this portion of the 

 moraine stands about 730 feet above tide. 



The outer ridge has a measured relief of 45 feet on the outer border 

 and 40 feet on the inner border at the crossing of the Wabash Railway at 

 Tolono, but at the crossing of the Chicago and Eastern Illinois at West 

 Ridge it scarcely exceeds 35 feet on either border. Farther east, near its 

 junction with the Middle Ridge, the relief increases to 70 feet, and one 

 point near Palermo, used by the United States Lake Survey as a site for a 

 geodetic station, stands 90 feet above the general level of the outer border 

 plain. 



The Middle Ridge has a relief of 25 or 30 feet on its outer border 

 throughout the interval in which it is distinct from the Outer Ridge. On its 

 inner border the relief is about 20 feet. At Philo, where the Inner and 

 Middle ridges are combined, the outer-border relief, as shown by the 



MON XXXVIII 15 



