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Page:Popular Science Monthly Volume 49.djvu/180

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166
POPULAR SCIENCE MONTHLY.

which commenced with the submergence of the lake district to sea level.

The Tilting of the Ancient Shore Lines.—The shore lines of ponds, lakes, or seas are alike water levels. In this respect the

PSM V49 D180 Ancient bowlder pavement of algonquin beach.jpg

Fig. 10.—Ancient Bowlder Pavement of Algonquin Beach, whose crest rises one hundred and eighty-seven feet above Georgian Bay, upon the northeast side of Blue Mountains of Collingwood, Ontario.

elevated coast lines present a striking difference from those now being formed, for the abandoned strands are everywhere tilted toward the northeast (see Figs. 11, 12, 15).

The tilted beach represents the deformation of the Algonquin beach. At the head of Lake Erie the deformation of the old water planes is not over a very few inches in a mile, while it

PSM V49 D180 Section of lake district from ny state to north of lake huron.jpg

Fig. 11.—Section of the Lake District from the Highlands of New York to those or the Laurentian Hills North of Lake Huron, along a Line passing through Buffalo and Lake Nipissing. Length of section, four hundred miles; heights given in feet; t is a ridge of drift north of Lake Ontario. The tilted beach represents the Algonquin plain deformed.

increases toward the northeast, so that it amounts to four feet per mile northeast of Lake Huron, and seven feet per mile near the outlet of Lake Ontario and north of the Adirondack Mountains, to which locality the writer himself has traced the deserted shores