DEFORMATION OF SHORE LINES. 507 



Ontario, and from the beginning of that stage until the ice front had retreated approximately 

 to the position A 'A' no uplift occurred. 



This conclusion is supported by the fact that the upper group of Algonquin beaches (see 

 pp. 415, 433) extend to the northern highlands of the lake region, reaching 1,220 feet on the hills 

 north of Trout Creek, Ontario, 25 miles south of North Bay, and about 1,500 feet (as observed 

 by Coleman) at Gondreau Lake, north of Lake Superior. These high beaches have not been 

 continuously traced to the beaches farther south, and their places in the group are not definitely 

 known; but they are strong and show characteristics that indicate the work of heavy waves of 

 wide waters, and their altitudes agree hi a general way with the planes of the upper members 

 of the upper group produced. 



3. When the ice front was approximately at the position A 'A', the second and greatest 

 period of uplift began. It was this movement that produced the remarkable deformation of 

 the Algonquin beaches and caused the northward splitting that amounted to 365 feet at Sault 

 Ste. Marie to 550 feet near North Bay, and apparently to 850 or 900 feet at Gondreau Lake, 

 150 miles north of Sault Ste. Marie. 



The relative rapidity of the middle part of this uplift is remarkable. By the time the ice 

 front had retreated from the position A'A' (fig. 14, p. 503), approximately to the position 

 A' A" (about 150 miles on the lowest line of retreat), the greater part of the Algonquin uplift- 

 had been completed. That for a considerable time the movement must have been relatively 

 slow is shown by the great strength of the beaches of the upper group. That all the move- 

 ments turned on the Algonquin hinge line shown in figure 8 (p. 439) and figure 14 has been estab- 

 lished by the wye-level surveys of the beaches made in 1907 and 1908 by Goldthwait and the 

 writer. From Mackinac Island, Mich., and from Kirkfield, Ontario, all the numerous beach 

 ridges of the Algonquin groups were found to converge southward to this one hinge line. 



4. The most characteristic quality of the Nipissing beach is its great strength and relatively 

 mature development, which seem to show stable condition of the land. The beach is stronger 

 near the Mazokama-North Bay isobase than elsewhere, but it is strong for a long distance 

 south of this line; so far south, indeed, that some part of its strength should probably be attrib- 

 uted to the two-outlet stage when the overflow was divided between Port Huron and North 

 Bay. These characters seem to imply either stability or extremely slow uplift. Hence, during 

 the time of the Nipissing Great Lakes and perhaps for a time during their closing two-outlet 

 stage, the elevation of the land had ceased or was extremely slow. This period covered the 

 time of the retreat of the ice from the position A"A" and may have included the entire dis- 

 appearance of the Labrador ice sheet. 



5. Finally, the movement of elevation was renewed and has continued rather slowly and 

 spasmodically to or nearly to the present time. In this time North Bay has been uplifted a 

 trifle more than 100 feet and the lands farther north still more. This period may possibly 

 include the last fading stage of the ice sheet, but in all probability it began after the complete 

 disappearance of the latter. 



In the marine area in the east it is not yet possible to divide the time of the uplifting 

 movements into periods corresponding to those so clearly defined in the Great Lakes region. 

 From Boston to Quebec the isobases shown on the map range from zero to 600 feet. It seems 

 significant that the first hinge line of the Great Lakes region, if bent in harmony with the 440- 

 foot isobase of the Iroquois beach and produced eastward, seems naturally continued in the zero 

 line of the marine area. There seems to be no reason to doubt that this apparent relation 

 represents the real relation. It can not be safely inferred, however, that the isobases shown 

 around Quebec record the whole amount of uplift that has affected that region, for, as in the 

 Great Lakes region, the early uplifts raised a large area of the land still covered by ice, along 

 with a part of that which had just been uncovered. Thus, the lands for 100 miles or more 

 south and east of Quebec may have been and probably were elevated several hundred feet 

 while still covered by the ice sheet. It follows that the marine beaches observed near Quebec 

 and along the south side of the St. Lawrence probably belong to a different and later period 

 from those near Boston. It may at some time become possible to recognize stages of uplift 



