Page:The American journal of science, series 3, volume 49.djvu/20

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Well marked old channels of outflow are found extending southward, at the levels of the deserted beaches, from Lake Agassiz and from the glacial lakes which are now represented by the diminished, but still large, modern lakes Superior, Michigan, Huron, Erie, Ontario, and Champlain. The outlets prove that the great Pleistocene water bodies which occupied these basins were lakes, not gulfs or arms of the sea; and the differential uplifts of the basins, increasing toward the central part of the area of the continental ice-sheet, show that no land barriers, but the ice itself in its retreat, held in these lakes on their northward sides.

The basin of the St. Lawrence during the glacial recession held successively, and in part contemporaneously, no less than eight important glacial lakes, distinguished by their different areas, heights, and places of outlet. They are named the Western Superior and Western Erie glacial lakes; Lake Warren, the most extensive, into which the two foregoing were merged; Lake Algonquin, the successor of Lake Warren in the basins of Lakes Huron, Michigan, and Superior; Lake Lundy, the glacial representative of Lake Erie; Lake Iroquois, in the basin of Lake Ontario; Lake Hudson-Champlain; and Lake St. Lawrence, into which the two last named became merged. The glacial Lake St. Lawrence, which is the only one of the series hitherto unnamed, extended over the Ottawa, Champlain, and St. Lawrence valleys previous to the melting away of the ice barrier, remaining latest in the vicinity of Quebec, by which event the sea, at a lower level than the former lake, was admitted to these valleys.

The Western Superior glacial lake. —In the west part of the basin of Lake Superior the receding ice-sheet held a lake which outflowed southward through northwestern Wisconsin, across the present watershed between the Bois Brulé and St. Croix rivers. The highest shore line of this lake at Duluth is 535 feet above Lake Superior (which has a mean level 602 feet above the sea); on Mt. Josephine, about 130 miles northeast from Duluth, its height, according to leveling by Dr. A. C. Lawson, is 607 feet; and at L'Anse and Marquette, Mich., 175 and 225 miles east of Duluth, it is found by Mr. F. B. Taylor about 590 feet above the lake. The northeastward