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THE POPULAR SCIENCE MONTHLY. 



Harbor will not be apparent, and it may seem an easy explanation to as- 

 sume 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 Yoke Hakbor 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 dis- 

 turbance, being similar on opposite sides, and doubtless continuous be- 

 low. 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 



