DRIFT SHEETS OF NORTHWESTERN ILLINOIS 275 



but there are serious objections to such an interpretation. If these 

 ridges were the product of a southwestward-moving glacier, we 

 should expect to find (i) the ridges represented north as well as south 

 of the Kishwaukee River, (2) the drift of northern Boone County 

 showing the same evidences of age as that to the south, (3) the eskers 

 trending northeast-southwest, (4) the striae on the bedrock trending 

 northeast-southwest, and (5) the axis of such a lobe situated to the 

 east. Checking on these points, it should be stated that (i) 

 there is no continuation of these ridges north of the river; (2) the 

 drift of northern Boone County is more weathered than that south 

 ' of the Kishwaukee River and in places in the northern part the drift 

 is separated from the overlying loess by an old soil, whereas no such 

 relationship was found in the southern part; (3) an esker-like ridge 

 less than ^ mile long situated about i mile south of Cherry Valley 

 parallels the Kishwaukee River in a northeast-southwest direction, 

 but a much larger esker on the upland near Irene station trends 

 at right angles to this in conformity to the supposed radial flow of 

 the Belvidere lobe; (4) striae have been observed on the bedrock at 

 the quarry i mile southwest of Belvidere trending a few degrees 

 north of west;^ and (5) a projection of the axis of the Green Bay 

 lobe would place it west of this area rather than east. The axis could 

 scarcely lie east of this area without encroaching upon the territory 

 wliich would more likely be occupied by the master lobe, the Lake 

 Michigan lobe. Unfortunately the lithology of the till lends no aid 

 in the solution, because the formations which would be crossed by a 

 Green Bay lobe would be the same for this locality as those crossed 

 by the Lake Michigan lobe. 



The best explanation which the writer has to offer for these ridges 

 is that their materials were deposited in re-entrant angles and crev- 

 assed zones of a radial-spreading lobe, the crevasses on. this side 

 of the lobe trending in a northwest-southeast direction. Melting 

 was more rapid along these crevassed zones than elsewhere and with 

 the ice and glacial waters continually bringing material forward, 

 greater accumulations took place here than elsewhere beneath the 

 ice. The quantity of gravel in these ridges is in harmony with this 



^ Rollin D. Salisbury and Harlan H. Barrows, "The Environment of Camp Grant," 

 Illinois Geological Survey Bulletin jp (191 8), p. 44. 



