140 SA LI SB URY A ND A TWO OD 



The slope of the upper surface of the ice at the margm. — The mar- 

 g-inal ridge on the south slope of Devil's Nose leads to an infer- 

 ence of special interest. Its course lies along the south slope of 

 the Nose, from its summit on the east to its base on the west. 

 Throuo'hout this course the ridge marks with exactness the 

 position of the edge of the ice at the time of its maximum 

 advance, and its crest must therefore represent the slope of the 

 upper surface of the ice at its margin. 



The western end of the ridge a (Fig. 2) has an altitude of 940 

 feet, and its eastern end b is just above the i 500-foot contour. The 

 distance from the one point to the other is one and three-fourths 

 miles, and the difference in elevation, 560 feet. These figures 

 show that the slope of the ice along the south face of this bluff 

 was about 320 feet per mile. This, so far as known, is the first 

 determination of the slope of the edge of the continental ice 

 sheet at its extreme margin. It is to be especially noted that these 

 figures are for the extreme edge of the ice only. The angle of 

 slope back from the edge was doubtless much less. 



Devil's Lake. — At the north end of Devil's Lake, and again in 

 the capacious valley leading east from its south end, there are 

 massive terminal moraines. Followed southward, this valley 

 leads off toward the Wisconsin River, and is probably the course 

 of a large preglacial stream. It is now occupied by a small tribu- 

 tary to the Wisconsin, the head of which is separated from the lake 

 by the massive moraine. To the north of the lake, the head of 

 a tributary of the Baraboo comes within eighty rods of the lake, 

 but again the terminal moraine intervenes. From data derived 

 from wells it is known that the drift both at the north and south 

 ends of the lake extends many feet below the level of its water, 

 and at the north end, the base of the drift is known to be at least 

 fifty feet below the level of the bottom of the lake. The drain- 

 ing of Devil's Lake to the Baraboo River is prevented only by 

 the drift dam at its northern end. It is nearly certain also, that, 

 were the moraine dam at the south end of the lake removed, all 

 the water would flow out to the Wisconsin, though the data for 

 the demonstration of this conclusion are not to be had. There 



