DRIFT PHENOMENA IN WISCONSIN 1 39 



ridge (west of ^) and a minor one on the north side of the last 

 (southwest ofy). The first and third are but minor irregularities 

 on the sides of the great loop, the head of which is at e. 



The significant fact in connection with these irregularities in 

 the margin of the moraine is that each loop stands in the lee of 

 a prominence. The meaning of this relation is at once patent. 

 The great quartzite range was a barrier to the advance of the ice. 

 Acting as a wedge, it caused a reentrant in the advancing margin 

 of the glacier. The extent and position of the reentrant is shown 

 by the course of the moraine in Fig. i. Thus the great loop in 

 the moraine, the head of which is at e, (Fig. 2) was caused by 

 the quartzite range itself. 



The minor loops on the sides of the major are to be explained 

 on the same principle. Northeast of the minor loop on the north 

 side of the larger one (/, Fig. 2) there are two considerable hills, 

 reaching an elevation of nearly 1500 feet. Though the ice 

 advancing from the east-northeast overrode them, they must 

 have acted like a wedge, to divide it into lobes. The ice which 

 reached their summits had spent its energy in so doing, and 

 was unable to move forward down the slope ahead, and the 

 thicker bodies of ice which passed on either side of them, failed 

 to unite in their lee. The application of the same principle to 

 the loop on the Devil's Nose is evident.' 



Constitution of tlic marginal ridge. — The material in the mar- 

 ginal ridge, as seen where erosion has exposed it, is till, abnormal, 

 if at all, only in the large percentage of widely transported 

 bowlders which it contains. This is especially true of the sur- 

 face, where 90 per cent, of the large bowlders are in some places 

 of very distant origin, and that in spite of the fact that the ice 

 which deposited them had just risen up over a steep slope of 

 quartzite, which could easily have yielded abundant bowlders. 

 In other places the proportion of foreign bowlders is small, no 

 more than one in ten. In general, however, bowlders of distant 

 origin predominate over those derived close at hand. 



'It is at k, Fig. 2 that the preglacial gravel referred to in Vol. Ill (pp. 655-67) 

 of this Journal is found. 



