688 PAUL MacCLINTOCK 



sin terminal moraine. The eastern end of the region at this time 

 stood relatively higher than it does now, so that the glacial waters 

 flowing down the Wisconsin Valley had a steep gradient and trans- 

 ported coarse debris. The glacial drainage from at least a hundred 

 miles of ice-front to the north must have flowed southward to the 

 vicinity of Portage, and then westward down the Wisconsin River. 

 In its course, along the ice margin, the river must have cut against 

 the edge of the ice, at least in places, and must have broken off 

 blocks of debris-laden ice, floating them into the Wisconsin Valley. 

 Here many of them must have grounded and, upon melting, have 

 deposited their loads. The adequate source of bergs, the abundant 

 supply of glacial material, and the swift and powerful glacial river 

 seem sufficient to account for the older drift deposited on the terraces 

 of the mid-course of the valley. After the ice had stood long enough 

 to build a valley train to a height of at least 75 feet above the present 

 flood-plain in the mid- course of the valley, it withdrew and erosion 

 cut away the valley train till all that remained were the terrace 

 remnants on rock benches along the sides of the valley. It is not 

 known how deeply this erosion progressed, but probably the valley 

 was largely re-excavated. 



At some time after this first valley train was built and before 

 the next glacial advance, the eastern end of the region was depressed 

 relative to the western end. A depression of 150 to 250 feet would 

 not have been unlikely and would account for the phenomena 

 observed. 



The Kansan ice advanced across Iowa, crossed the Mississippi 

 River in the neighborhood of Prairie du Chien, and projected a 

 tongue of ice into the lower end of the Wisconsin Valley. The 

 Mississippi was dammed, diverted into the Wisconsin Valley, and 

 flowed eastward, carrying with it not only great quantities of coarse 

 and fine outwash material, but abundant icebergs broken from the 

 ice-front farther north as it encroached upon the Mississippi Valley. 

 An eastward sloping valley train of coarse material was built. 

 When the ice withdrew, erosion cut away the moraine and valley 

 train, save where remnants are left on rock benches at Bridgeport 

 and Wauzeka. The depth of this erosion is not known accurately, 



