Harbor will not be apparent, and it may seem an easy explanation to assume that they have been formed by the ebb and flow of the tide which sweeps through them. The tides at New York, however, do not rise to a great height, and have very little eroding power. It should also be said that the channels are far too deep to have been cut by any agents now in operation. For instance, at Polhemus's Dock the depth of Hell
Fig. 4.—Bird's-eye View of New York Harbor and its Connections.
Gate channel is 170 feet, and there are many places in the East River where the depth is over 100 feet. The greatest depth of water in New York Harbor and the Hudson River is about sixty feet, but this does not represent the true depth of the channels, since they have been very much silted up, and their rock-bottoms are probably 200 or 300 feet below the water-surface. If they could be cleared of clay, sand, and gravel, they would be seen to be narrow gorges cut in solid rock as deep as that of Niagara, and resembling some of the canons of the Western rivers. It is therefore certain that they could not have been produced by tidal action. There are only two ways in which such chasms could be formed: first, by earthquakes, opening fissures in the rocks; and, second, by the erosion of flowing streams. That they are not earthquake fractures is certain, since no such fissures are found in the country about in the line of these channels, and their rocky walls show no sign of disturbance, being similar on opposite sides, and doubtless continuous below. They have, in fact, been formed by draining streams when this part of the continent stood much higher than now above the ocean-level. The evidence of this is cumulative and conclusive. The facts which prove it are, briefly, as follows:
1. The trough of the Hudson has been shown, by the soundings of
