Page:The Journal of geology (IA journalofgeology21894univers).pdf/406

opment of this uplift, it will be needful to consider it first for the southern half and afterward for the northern half of the glacial lake area.

About thirty successive levels of Lake Agassiz have been recognized by its beaches. A considerable number were due to the gradual erosion and lowering of the outlets, and to their changes of place and direction, first toward the south and later toward the northeast; but probably more than half of this whole series of lake levels are distinctly exhibited only upon the central and northern portions of the lacustrine area, being due chiefly to its differential uplift increasing from south to north, and in a small degree to the decrease in the gravitative attraction of the waning ice-sheet. The five well defined beaches near the south end of this ancient lake, named in descending order the Herman, Norcross, Tintah, Campbell, and McCauleyville beaches, formed at the successive levels of southward outflow as the channel was deepened, are each found to be represented, when they are followed northward, by two, three, or more, so that near the international boundary and in Manitoba, they become subdivided into no less than seventeen beaches, marking the stages of the subsidence of the lake and in larger proportion of the differential elevation of the land. Nearly as many other lower shore lines record the stages of the lake while it outflowed northeastward. My surveys of these shores, with exact mapping and leveling, extend more than 300 miles from the south end, to lakes Winnipeg and Manitoba and the Riding Mountain.^[1]

In this southern half of the whole extent of Lake Agassiz, the shore of its highest or Herman stage, as represented at the north by the uppermost of its divided beaches, has now a northward ascent of about 35 feet in the first 75 miles north from Lake Traverse, which lies in the old channel of southward outlet, about 60 feet in the second 75 miles, and about 80 feet in the