IOWA ACADEMY OP SCIENCES 129 



farther south; and that this ridge played an important part in 

 hindering the advance of the ice until it had accumulated 

 sufficiently to break through into the James river valley, as it 

 did during the Wisconsin epoch. This would be the more 

 easily explained if the ice sheet from the north, i. e., from the 

 Keewatin center was not so vigorous in the earlj^- stages, i. e., 

 in the Kansan and pre-Kansan stages. 



From a general consideration of the extent of the so-called 

 Kansan till as compared with the Wisconsin, we may infer that 

 the natural center during the former stage was further east; 

 probably, northeast of Lake Superior. In fact; we may con- 

 ceive that some of the higher points north of Lake Huron were 

 the first to receive a permanent ice cap. As the region became 

 more chilled, the zone of accumulation would extend naturally 

 along the more elevated surface of the ice and then the great- 

 est accumulation would lie naturally near the edge of the zone 

 and advance slowly outward. In this way, we may perhaps 

 account for the greater vigor of the streams passing down 

 Lake Michigan and Lake Superior during the Kansan stage or, 

 as some would say, the latter during the Kansan stage and the 

 former during the Illinoian stage. If we believe the ice to 

 have here pushed forward southwest in the axis of Lake 

 Superior basin, it is not difficult to conceive that its course 

 would lie diagonally across the state of Minnesota, being con- 

 fined in a broad shallow channel between the highlands about 

 Itasca and the region of central Wisconsin, that it was directed 

 to the Minnesota valley and across it against the high transverse 

 ridge of the ''East Coteau" the high divide separating the 

 Minnesota from the James, which now has an elevation of 

 1,700 to !2,000 feet. From the shape of the land and the course 

 of the stream, it seems not unlikely that the highest elevations 

 were along the axis of this stream. As the Des Moines valley 

 to the south offered an easier slope, we may conceive the ice 

 sheet to have expanded more rapidly in that direction and to 

 have spread out during the Kansan stage, from that valley 

 westward and south into northwestern Missouri. We may 

 account for its failure to press westward over into the James 

 valley by the elevation of the Coteau region and by the divert- 

 ing influence of the Big Sioux valley, which we may suppose 

 had greater effect upon the thinner edge of the ice which there 

 lay in the zone of ablation. 



The failure of the ice to press equally northward may be 



