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Page:Popular Science Monthly Volume 73.djvu/301

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dividing currents on either side. Thus for perhaps half of the river from the Goat Island side, I have estimated the mean depth of the water over the rock rim as not exceeding two feet. Indeed, much of it is not over a foot in depth. Nearer the Canadian side it increases to nine feet (see figures 3 and 5).

PSM V73 D301 Rim of the first cascade at niagara falls.png

Fig. 3. Profile of Rim of First Cascade, with forebay of Ontario Power Company in foreground.

12. Portion of Falls in Immediate Peril.—As the river is so shallow over the rock rim on the Goat Island side of the main channel, it forms only a thin sheet of water on the eastern side of the Canadian or Horseshoe Falls, for a distance of 800 feet from the Goat Island end. Indeed, from the changes already effected, this sheet of water has been reduced in depth by sixteen inches, thus in many places exposing the shelf of rock over which the rapids are passing (figure 4). This portion of the falls I had considered as being in most immediate peril, even more so than the American Falls, but recent soundings, about the head of Goat Island, show that a rocky floor extends almost across to the main shore of New York, which in the future must divert to a large degree the supply of water from the American channel between the island and the shore. Accordingly, the American Falls are in equal danger with the eastern side of the Canadian cataract.

I hope that in this study of the physics of the river, the importance of this rim has been sufficiently emphasized; for any lowering of the water in the basin, will cause the draining of the higher parts of this rocky barrier, which extends nearly two thirds of the breadth of the