Page:The American journal of science, series 3, volume 49.djvu/26

8 8 W. Zfpham — Champlain Subsidence and

Lake Algonquin* — When the glacial melting and retreat at length permitted an outflow from the St. Lawrence basin over a lower pass, which was through central New York to the Mohawk and Hudson, the water surface of the basins of Lakes Michigan, Huron, and Superior, fell only some 50 or 75 feet, from the latest and lowest stage of Lake Warren to its short- lived successor, Lake Algonquin. This lake appears to have been ice-dammed only at low places on its east end, as at or near the heads of the Trent and Mattawa rivers, lying respect- ively east of Lakes Simcoe and Nipissing, where otherwise its w T aters must have been somewhat further lowered to outflow by these passes. Careful study and comparison of the work of Spencer in tracing the Algonquin beach about the southern part of Lake Huron and Georgian bay, and of Taylor in ex- ploration of his " Nipissing beach " from Duluth east along the south coast of Lake Superior and the north side of Lake Huron and Georgian bay to Lake Nipissing, convince me that these beaches were of contemporaneous formation, marking respect- ively the southern and northern shores of Lake Algonquin, and therefore both to be known by the name Algonquin beach of Spencer, according to the law of priority. The earliest and principal stage of Lake Algonquin is shown by these beaches to have coincided closely in area w T ith Lakes Michigan and Superior, but to have been considerably more extensive east- ward than the present Lake Huron and Georgian bay. It held a level which now by subsequent differential epeirogenic movements is left probably wholly below the level of Lake Michigan by a vertical amount ranging from almost nothing to about 40 feet. Its shores were nearly coincident with the western shore of Lake Huron, but eastward they are now elevated mostly 150 to 200 feet above that lake and Georgian bay ; and in the Lake Superior basin they vary from about 50 feet above Lake Superior at its mouth, and along its north- eastern and northern shores, to 25 feet at Houghton, and to a few feet or none at Duluth.

The Algonquin beach at the south end of Lake Huron coin- cides very closely with the land surface there and with the

Chicago to the Des Plaines and Mississippi rivers so lately as about 1,500 years ago, when the Niagara river had cut back its gorge to the Johnson ridge, about a mile north of the present site of the falls. This would have formed a beach 10 to 15 feet above Lakes Michigan and Huron, and about 20 to 25 feet above Lake Erie, around all their shores; and the absence of such a modern and still horizon- tal shore line, slightly higher than the present lake levels, upon all this large area, forbids an acceptance of this hypothesis.

Huron," this Journal, III, vol. xli, pp. 12-21, with map, Jan.. 1891; and other papers before cited. G. K. Gilbert, F. B. Taylor, and Warren Upham, as before cited for Lake Warren. G. F. Wright, Bulletin Geol. Soc. Am., vol. iv, pp. 423- 5 ; with ensuing discussion by Dr. Robert Bell, pp. 425-7.
 * J. W. Spencer, "Deformation of the Algonquin Beach, and Birth of Lake