678 PAUL MacCLINTOCK 



subangular stones found nowhere else in the outwash material of 

 the valley, together with the patchy character of the drift, suggests 

 deposition directly by the ice. If this view is correct the glacier 

 must have extended from Iowa across the Mississippi into the 

 lower end of the Wisconsin Valley. 



On the other hand, at no place where this older drift occurs was 

 a glacial pavement seen. The drift Kes in most places on deeply 

 eroded and weathered dolomite, while at other places several inches 

 of blue-black clay, weathered from the bedrock, Hes at the base of 

 the brown drift. It is not strange that, in exposures so limited, 

 no pavement was seen; none has been found in Iowa in this vicinity, 

 where the ice is known to have stood to the very edge of the Miss- 

 issippi Valley. It seems probable that if a tongue of ice projected 

 into the Wisconsin Valley for a distance of 4 miles — a condition 

 called for by this hypothesis — ^it would have been at least as wide as 

 the mouth of the valley (i^ miles) so that its shoulders would 

 have rested against the valley walls near the mouth, and have left 

 there glacial material. Some material of this kind is seen for a 

 distance of i^ miles north of the lower end of the Wisconsin Valley. 

 It is however small in size, meager in quantity, and found not strictly 

 on the shoulders but on the lower slopes at heights of never more 

 than 100 feet above the flood-plain. Glacial material on slopes so 

 steep as the shoulders present would not have remained there but 

 would have soon been washed to the flat below. 



The crucial points are: (i) the Bridgeport drift is much higher 

 in altitude than any of the older drift farther up the valley, 

 (2) it is composed of striated, subangular, and grooved material, 

 and (3) it is both stratified and unstratified — the latter material 

 indistinguishable from till. The conclusion then is that this drift 

 is glacial in origin and was deposited by a tongue of ice. It seems 

 clear that the drift at Wauzeka is the outwash material from the 

 same ice invasion, for it is closely akin to the Bridgeport drift in 

 many ways, has the lense and pocked structure of outwash material, 

 and has a suggestion of eastward dipping cross-bedding (Fig. 4). 

 None of this calcareous drift is found farther up the valley because 

 the decHne of this old valley train would have brought its top 

 below the level of the rock benches where drift is now found. 



