It must be conceded, as the Commissioners think, that the building of the proposed dam would be an obstruction of more or less magnitude to the navigation of the river; for although a vessel may be locked through in 10 or 15 minutes, as asserted by Mr. Seymour, still, if we revert to the great number of vessels passing and repassing the proposed site of the dam, it can hardly be otherwise, but that there would be much detention.

4th. Not having found any data in the office of the Street Commissioner, by which to estimate the difficulties to be encountered, in building the contemplated dam, we can only refer to the known obstructions frequently experienced in sinking piers and bulkheads in both the East and North rivers, owing principally to the large accumulation of mud at the bottom of those rivers, which offen baffles the calculations and art of the builder. We have been informed too that the water, 400 feet from the shore, some distance above the site of the proposed dam, is about 30 feet in depth, and the mud at the bottom not less than 8 or 10 feet and it is conjectured, that in the channel of the river, the water :

and mud is not less than 40 or 50 feet deep. The width of the river is more than a mile across, and whether a dam of sufficient solidity and strength can be erected in a river of this width, and with a current running at the rate of the Hudson, and capable of withstanding the pressure of the immense body of water that would be behind it when the tide is down, are questions the Commissioners are not prepared to answer.