134 THE ILLINOIS GLACIAL LOBE. 



TOPOGRAPHIC EXPRESSION. 



At several places along the border of this drift sheet in Winnebago, Ogle, 

 and Whiteside counties low swells and ridges appear, but they are seldom 

 mure than 10 or 15 feet in height. These serve, however, to give defmite- 

 ness to the margin, although they are very inconspicuous features. In most 

 cases the low swells are plainly independent of drainage erosion, there being 

 instances in which they pass across a valley which had been formed in the 

 earlier drift, dotting its slopes and bottoms and passing onward over the 

 bordering uplands in utter disregard of the drainage lines. Such knolls 

 may be seen near the mouth of Leaf River in Ogle County, and also on the 

 borders of the Pecatonica in Winnebago County. Along portions of the 

 border the separation of the erosion features from the drift aggregations 

 produced by this ice invasion is somewhat difficult, Such is the case on the 

 borders of the lowland tract north and west from Sterling, where the undu- 

 lations are probably in part due to drainage erosion. A similar difficulty 

 is experienced in the narrow belt of lowland east from Geneseo. There are 

 present, however, in both these districts knolls and ridges of drift which 

 appear to be independent of drainage erosion and referable to the inequali- 

 ties of deposition of the ice. 



No paha have been found in Illinois except in western Whiteside and 

 northwestern Henry counties in the districts in which some uncertainty is 

 felt concerning the occupancy by ice at this stage of glaciation. The paha 

 are scattered over the portion of Whiteside County north of Rock River 

 from Round Grove westward to the borders of the Mississippi, but are best 

 developed on the lowland tract south and east from Morrison and on the till 

 tract between Rock and Green rivers, which leads from Spring Hill south- 

 westward to the mouth of Green River. They are' straight ridges, usually 

 a mile or less in length, but occasionally reaching 2 miles. They are often 

 sharp crested, with a width of scarcely 50 feet at top, and present abrupt 

 slopes. Occasionally they reach a width of 40 or 50 rods, including slopes. 

 In height they range from 10 feet or less up to about 50 feet. The trend is 

 quite uniformly about WNW.-ESE. Several of them may be seen in the 

 Clinton topographic sheet, PL XVIII (in pocket). The longest paha noted 

 is found about 4 miles south of Morrison, and leads from the center of sec. 4 

 west-northwest to the north line of sec. 6, T. 20, R, 5 E., a distance of about 



