510 PLEISTOCENE OF INDIANA AND MICHIGAN. 



the front of the ice advancing down to the northern side of the Driftless Area in Wisconsin. 

 Over the middle of the outer part of Keweenaw Bay, say 20 miles directly south of Keweenaw 

 Point, the ice surface must have been at least 500 or 600 feet higher than on the high ground 

 north of Champion. Thus, by an estimate based on minimum values throughout, the depth of 

 ice at the maximum of the Wisconsin sheet over the present surface of Lake Superior in the 

 central part of Keweenaw Bay was 2,900 to 3,000 feet, or considerably more than twice the 

 depth assumed by Lane. Applying to this depth of ice the ratios used by Lane, the amount of 

 uplift due to elastic resilience would be nearly 600 feet and to this must be added that due to 

 hydrostatic inflow amounting to nearly 1,000 feet, making a total uplift of 1,500 to 1,600 feet in 

 Keweenaw Bay. 



The total amount of uplift actually determined by observation near Calumet on the Kewee- 

 naw Peninsula is only a little over 500 feet, this amount being recorded in the Algonquin beach. 

 To this may be added by inference 150 to 200 feet for the first period of uplift, which is recorded 

 in the Michigan, Huron, and Erie basins, but which is not shown by the beaches of Lake Superior. 

 The absence of such evidence in the Lake Superior basin is not, however, a safe reason for in- 

 ferring that the early uplift did not affect that basin, because the basin lies well within the 

 uplifted region and none of its old shore lines extend south of the Algonquin hinge line, or even 

 near to it. Thus the total uplift, recorded and inferred, was 650 to 700 feet, agreeing closely 

 with Lane's estimate on the assumptions which he made, but amounting to less than half that 

 which would correspond to the revised estimate of the thickness of the ice. 



The selection of the Lake Superior region, however, as a place for testing the hypotheses of 

 elastic resilience and hydrostatic readjustment appears to be unfortunate, in the light of recent 

 investigations. Studies by Leverett and Sardeson in 1910, the results of which were announced 

 in a paper presented by Sardeson at the Minneapolis meeting of the American Association for 

 the Advancement of Science, indicate that the region west and north of the west end of Lake 

 Superior became free of ice in an early part of the Wisconsin stage of glaciation. It was open 

 territory at the time the Keewatin ice field had its greatest eastward extent in northern Minnesota, 

 for the Superior lobe at that time extended but little beyond the western end of the basin. The 

 only glaciation which this region experienced in the Wisconsin stage seems to have been from a 

 weak ice advance southward from the high country between the Superior and Winnipeg basins. 

 At the height of the Wisconsin stage of glaciation this country seems to have had a covering of 

 ice which was thin in comparison with that in the basins on either side, and before the earliest 

 uplift recorded in the Huron-Erie basin it seems to have been free from ice. It is not yet known 

 how far northeast this ice-free region extended, but it seems to widen toward the Canadian 

 border. The existence of this area along the north side of the western part of the Lake Superior 

 basin changes the glacial status of that whole region and puts the ice lobe of the western arm 

 of Lake Superior into the category of strongly protruding marginal lobes, like the others farther 

 south. The deep basin of the western arm of the lake was near the ice border toward the north- 

 west as well as toward the south. And yet this whole region is well within the area of Algonquin 

 uphft and both of the hinge lines shown in figure 14 (p. 503) pass far south of it. 



ICE LOBES AND DRIFTLESS REENTRANTS. 



If the problem be considered in connection with another differently situated ice lobe, a 

 more certain and a very different light is thrown on the relations of uphft to ice weight. The 

 best subject is the Great Lakes lobe. The base line of this lobe is 600 miles long and extends 

 from the northeast angle of the Driftless Area in Wisconsin to the reentrant angle at Salamanca, 

 N. Y. It happens that this base line is almost exactly coincident with the Algonquin hinge line 

 in the Lake Huron basin. It lies only a few miles south of this line and has almost the same 

 trend. Within the area of this lobe there is no evidence whatever of either depression or ele- 

 vation of the land in Wisconsin glacial time before the movement which raised the land north 

 of the first or Whittlesey hinge line. The whole lobe, therefore, the part north of the first hinge 

 fine alone excepted, lies within the area of horizontally, and as the base fine of the lobe is sub- 

 stantially coincident with the Algonquin hinge line, it may be said that only that part of the 



