"Yes. Think of a steamboat on Lake Erie sucked along by the stream that flows to Ontario. This lake lies 300 feet lower than Erie, and about half-way between the two lakes the water passes over a sharp bar and plunges with a thundering roar into the depth below (Plate XXXIII.). The barrier itself, which is a thousand yards broad, is formed of a huge stratum of sandstone, and the rocks under it are loose slates. Erosion proceeds more rapidly in the slates than in the hard limestone, which, therefore, overhangs like the projecting leaf of a table, and the collected volumes of water hurl themselves over it. But when the limestone is so far undermined that it is no longer able to bear the weight of the water, fragments break off from time to time from its edge and fall into the abyss with a deafening noise. Thus in time the fall wears away the barrier and Niagara is moving back in the direction of Lake Erie."
"Moving, do you say? The movement can surely not be rapid."
"Oh no; Niagara needs about seventeen thousand years to move half a mile nearer to Lake Erie."
"That's all right, for now I can be sure it will be there when I visit it at some future opportunity."
"Yes, and you would find it even if a crowd of railway lines did not run to it. You hear the roar of the 'thunder water' forty miles away, and when you come closer you see dense clouds of foam and spray rising from the ravine 150 feet below the threshold of the Fall. Yes, Niagara is the most wonderful thing I have seen. In all the world it is surpassed only by the Victoria Falls of the Zambesi, discovered by Livingstone. One feels small and overawed when one ventures on the bridges above and below the Fall, and sees its 280,000 cubic feet of water gliding one moment smooth as oil over the barrier, and the next dashing into foam and spray below with a thundering noise."
"It would not be pleasant to be sucked over the edge."
"And yet a reckless fellow once made the journey. For safety he crept into a large, stout barrel, well padded inside with cushions. Packed in this way, he let the barrel drift with the stream, tip over the edge of the barrier, and fall perpendicularly into the pool below. As long as he floated in the quiet drift, and even when he fell with the column of water, he ran no danger. It was when he plumped down on to the water below and span round in the whirlpools, bumped against rocks rising up from the bottom, and was carried at a furious pace down under the watery vault. But the traveller got through and was picked up in quiet water."
"I suppose that there are bridges over the Niagara River as over all the others in the country?"
"Certainly. Among them is an arched bridge of steel below the Falls which has a single span of 270 yards, and is the most rigid bridge in the world."
"Tell me, where does all this water go to below Niagara?"