684 PAUL MacCLINTOCK 



Following the retreat of the early Wisconsin ice came a period 

 of erosion during which part of the fill was cut away. The late 

 Wisconsin ice advanced farther and stood across the heads of all 

 four valleys, building valley trains at the level of the low terrace. 

 At the same time the low terrace was being built in the main valley. 



Evidence adverse to this suggestion must be summarized under 

 several heads : 



i) If deposited by glacial waters, the terrace should decline 

 westward more rapidly than the present river, unless the western 

 end had been raised by postglacial tilting. But, judging from the 

 tilting of the glacial beaches of the Great Lakes, this latter possibility 

 is unUkely. 



ii) If deposited by glacial waters the material should be notice- 

 ably coarser at the eastern end grading to fine at the west. This 

 is not the case. 



in) There are three conspicuous examples of small valleys 

 containing only the low terrace, west of the farthest ice advance 

 (just west of Black Earth, south of Arena, and west of Avoca), 

 while there are but two such cases among the valleys heading in 

 the terminal moraine, as previously cited. It would seem that 

 the mere fact that two of the four valleys east of Mazomanie do 

 not have the high terrace is not conclusive one way or the other. 

 In fact, it would be just as plausible to suppose that there was but 

 one Wisconsin advance in this region and that, since the longer 

 valleys drained the ice both earher and later than did the shorter 

 ones, they received more outwash, and so were more aggraded. 

 The thin terminal moraine crossing the valleys means a short stay 

 of the ice-edge at this place, or poverty of debris in the glacier. 



iv) No evidence was seen of weathering of the stratified drift 

 underlying the till of the terminal moraine, as would be expected 

 somewhere in the region if it were early Wisconsin and the till were 

 late Wisconsin, since this interglacial interval is considered by many 

 to be fairly long. The stratified drift may as well be outwash depos- 

 ited by waters which flowed out in advance of the oncoming ice. 



v) The evidence from the larger amount of leaching of the out- 

 wash plain, suggested by Alden and Weidman,^ as showing that 



' W. C. Alden, op. cit., p. 192. 



