Page:Popular Science Monthly Volume 13.djvu/676

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THE POPULAR SCIENCE MONTHLY.

An old channel at least 200 feet deep connects Lake Huron and Lake Erie. Detroit is situated on the western side of it, and the rock lies there 130 feet below the surface.

Many of the streams now flowing into Lake Erie were once tributaries to the ancient river which traversed its valley and joined it far below the present water-level.

The old channel connecting Lake Erie and Lake Ontario apparently passed through Canada between Long Point and Hamilton. Heavy beds of drift, by which it is filled and concealed, here occupy the surface. The Niagara now flows over a rock-bed, for this is a comparatively modern river, which, following the line of lowest surface-levels, passed over a spur from the south shore of the lake-basin when the old channel was filled by glacial drift.

Some of the streams draining into the basin of Lake Ontario in former times cut their channels below the present ocean-level. All the salt-wells of Syracuse are sunk in one of these, which is filled with gravel and sand saturated with brine issuing from the Salina group that forms its walls. The rock-bottom of this old river-bed was reached in some of these wells at a depth of fifty feet below the present level of tide-water.

PSM V13 D676 Old drainage of the great lakes basin.jpg
Fig. 5.—Map showing Old Drainage og the Lake Basin.

The valley of the Mohawk is a very deep channel of erosion, now half filled, which must have been traversed by a large stream flowing eastward at a level below that of the present ocean; and everything indicates that this was the ancient outlet of the basin of the Great Lakes.

The channel of the Hudson is apparently the only possible continu-