Page:Popular Science Monthly Volume 1.djvu/582

566 plunge over Niagara Falls every minute, all the water of the lakes making the circuit of the Falls, the St. Lawrence, the ocean, vapor, rain, and lakes again, in 152 years. Through the Illinois Canal about 8,000 cubic feet of water are taken every minute from Lake Michigan to the Illinois River; through the Welland Canal 14,000 cubic feet flow every minute from Lake Erie into Lake Ontario, and through the Erie Canal 30,000 cubic feet pass every minute from the same lake into the Hudson. Thus, 52,000 cubic feet of water, which Nature would give to Niagara, are diverted every minute by artificial channels, some into the Mexican Gulf and some into the Bay of New York. Add this to 18,000,000, it is as a drop in the bucket, and would make no appreciable difference in the character of the Falls or their rate of recession. Was there ever a time when the Niagara was appreciably a greater river than now?

Below the Falls, on the Canada side, is a terrace, extending along the river-bank, and attaining a height of 46 feet. It contains river-shells, and is an old river-bank. A corresponding bank is found on the New York side, although much broken and eroded. If a tourist will stand on the New Suspension Bridge and cast his eye along these ancient banks, his first impression will be that the Niagara which flowed against them was vastly greater than the river which flows now nearly 200 feet below him. But, if his eye will follow the Canadian terrace above the Horseshoe, he will see it falling lower and lower, till, at the head of the Rapids, it merges into the present bank. From this point upward the river is contained within low banks, and bounded by a plain whose monotony is not broken by a hill or terrace. A glance at the section (Fig. 1) will make this clear to the eye of the reader. The surface of the river from Buffalo to Lake Ontario is represented by the line R, R; the banks, from Buffalo to the Rapids, by the dotted line t, t and the old banks, from the Rapids to the Whirlpool, by a continuation of the same line. It will be seen that this line rises as the surface of the river falls. The slope from the head of the Rapids to the Falls is nearly 50 feet, and the terrace opposite the Falls attains a height of 46 feet.

We turn now to Goat Island. A walk around the island, by the margin of the river, will show us what immense denudation its limestones have suffered. The extent of this denudation can be seen in our section of the island (Fig. 2). To wear away such beds of limestone, the river, for many ages, must have flowed over the island. And as the upper beds of fluviatile drift, marked, d in our section, are a little below the level of the highest terrace, we must infer that the river, when contained in these ancient banks, covered the island, and was eroding its beds of limestone.

By all this we see that the Niagara itself has made the Rapids, and that, as it cut its way downward, its forsaken banks have assumed the character of terraces. And we see, by the low banks and absence