514 PLEISTOCENE OF INDIANA AND MICHIGAN. 



lived glaciation, therefore, is set back so far into the area of uplift that if it is as large as seems 

 likely (including the marginal belt of relatively thin ice) it seems to constitute a serious obstacle 

 to the hypothesis of depression by ice weight. 



The greatest amount of uplift yet recorded is that found by Coleman at Gondreau Lake, 

 northeast of Lake Superior. Lake Kaministiquia, supposed by the writer to have been a local 

 ice-dammed lake, seems likely from Mr. Leverett's recent results to be merely a bay of Lake 

 Duluth, or possibly of Lake Algonquin, 1 with an upper limit more than 1,500 feet above sea 

 level. These shore lines suggest that 900 to 1,000 feet of uplift has affected the northern part 

 of the plateau referred to, and this inference will have to stand, unless facts are found that dis- 

 prove it, which now seems decidedly unlikely, especially in view of Coleman's recent account of 

 Lake Ojibway. 3 Coleman presents many facts relating mainly to high-level lake clays overlying 

 the drift north of Height of Land between Lake Nipigon and Lake Abitibi and to terraces, 

 belts of sand, and gravel at higher levels. He finds higher old water levels passing above 

 the cols across Height of Land and regards them as temporary arms of Lake Algonquin reaching 

 across to the Hudson Bay slope and covering narrow belts of this slope in front of the retreating 

 ice sheet. They are not so high as the beach at Gondreau Lake, but they appear to mark 

 levels not far below it, and though as yet they can not be positively proved to belong to Lake 

 Algonquin, they indicate the great uplift suggested for the plateau west of Lake Nipigon. 

 The plateau corresponds to the supposed island in the preceding discussion. 



These old lake levels are several hundred feet above the upper limit of marine submergence 

 (about 450 feet above Hudson Bay) as marked by beds of fossil marine shells farther north 

 on the same slope. The fossil-shell beds could not have been deposited until after the ice sheet 

 had disappeared from the region where they are found, and the movement by which they were 

 elevated consequently came still later. The withdrawal of the ice from the southwest slope 

 of the James Bay basin could hardly have been earlier than the later stages of Lake Algonquin 

 and was probably considerably later. Yet, if the plane of the Nipissing beach in the northern 

 part of the upper lake region be produced northward to the shell bed on Albany River, it would 

 indicate an uplift of only 200'to 250 feet. Tins suggests that the shells may have been raised 

 150 to 200 feet before the uplift recorded in the Nipissing beach. The data are still too few 

 to permit final conclusions, but they seem thus far to be in accord with the conclusions reached 

 from the study of the Great Lakes. 



SHIFTING OF THE HINGE LINE. 



For such difficulties as these, which seem strongly unfavorable to resilience following 

 depression by ice weight, the northward shifting of the hinge line and the time relations of the 

 uplifting movements to the retreat of the ice seem to be partial if not equal offsets. The ice 

 front rested close north of the line WW (fig. 14, p. 503) when the first period of uplift began, and 

 the hinge line shifted almost to the Algonquin hinge while the ice retreated to the position AA. 



The northward shifting of the hinge line during the retreat of the ice is shown diagram- 

 matically in figure 15 (p. 505), the positions of the lines being only roughly determined. The 

 movements appear to have been spasmodic, and they cover altogether the retreat of the ice from 

 the late phase of Lake Maumee, not far from the time of the Yale moraine, nearly to the time 

 of the Port Elgin moraine (AA, fig. 14). The Warren hinge line is 15 to 17 miles north of the 

 Whittlesey hinge line, the Grassmere and Lundy about 40 miles north of the Warren, and the 

 Algonquin 15 to 17 miles north of the Grassmere and Lundy. A more pronounced rise begins 

 about 40 miles north of the Algonquin line and appears to correspond to the time of the Bat- 

 tlefield beaches, when the rate of uplift was most rapid. 



The retreat of the ice front from the extreme limit to the line WW was synchronous with 

 the lowering of the entire ice surface in the north by probably 1,500 to 2,000 feet, and this much 

 ice removed from the top of the sheet where it was probably at least 10,000 to 15,000 feet thick 



1 Notes on the abandoned beaches of the north coast of Lake Superior: Am. Geologist, vol. 20, 1897, pp. 117-119. 



2 Coleman, A. P., Lake Ojibway, the last of the great glacial lakes: Eighteenth Ann. Eept. Bur. Mines, Ontario, 1909, pp. 284-293, particu- 

 larly pp. 286-2S7. 



