DELATION OF ILLINOIS AND IOWA ICE LOBES. 151 



bluff of the Mississippi Valley, opposite the broad sandy bottoms, such as 

 occur in southwestern Carroll and northwestern Whiteside counties, sandy 

 knolls and ridges are found which are evidently due to wind action. Some 

 of them are in process of drifting even to-day, for the sand is too barren to 

 nourish an adequate protective cover of vegetation. These ridges are 

 irregular in form and trend and seldom bear a resemblance to the canoe- 

 shaped ridges of loess. A few sandy ridges are found on the strip of drift 

 in southwestern Carroll County, above noted, where the loess is scanty, 

 which like the canoe-shaped ridges of loess have a general WNW.-ESE. 

 trend. They are, however, more irregular in form and are usually broader 

 than the loess ridges. Possibly they should be classed with the dunes. 



If all the features of the region just discussed be considered, it appears 

 that positive evidence of the invasion of the Iowa ice into northwestern 

 Illinois at the Iowan stage of glaciation is at best very weak. The features, 

 however, appear to favor rather than to antagonize the hypothesis of such 

 an invasion. The debatable ground is restricted to a belt but 10 or 15 

 miles wide on the north and east borders of unquestioned Iowan drift. It 

 embraces northern Clinton and southern Jackson counties, Iowa, and south- 

 western Carroll, western Whiteside, and possibly neighboring portions of 

 Rock Island County, Illinois. Were this belt low, like the tracts occupied 

 by the Iowan drift in Clinton and Scott counties, Iowa, the extension might 

 be granted, even with a very limited occurrence of fresh-looking drift. But 

 the fact that the debatable region, both on the north and east, stands 100 

 to 300 feet above the low plain of Iowan drift, necessitates a very careful 

 study of the evidence in the light of all applicable hypotheses. Having set 

 forth the available data, the question is left open with the hope that either 

 by the light of further data or by more mature reflection a satisfactory 

 solution may be reached. 



RELATION OF THE ILLINOIS AND IOWA ICE LOBES. 



In concluding this discussion a few remarks seem necessary concerning 

 the probable relation of the Illinois and Iowa ice lobes at the Iowan stage 

 of glaciation. In his paper on northeastern Iowa, above quoted, McGree 

 considers it probable that at the invasion now called Iowan the ice from the 

 Iowa side culminated earlier than that on the Illinois side, and caused a 

 displacement of the drainage of the Mississippi near Clinton, southeastward 



