perhaps by the Congress of the United States. If all navigable rivers are common highways, it is a question at least, whether obstruc- tions can be placed in them without interfering with the powers of Congress to regulate the Commerce of the Nation. 3rd. It must be conceded, as the Commissioners think, that the building of the pro- posed 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 deten- tion. 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 bulk- heads 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 buil- der. 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 with- standing 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. 5th. Mr. Seymour is of opinion that no injury will be done to the land on the banks of the Hudson by the rise of water within the dam ; but, the Commissioners think, the rising of the water permanently, two feet above its ordinary level, together with the occa- sional freshets which occur, must cause a covering with water, on some of the low lands lying on the margin of the river, for several miles above the city. Whe.ther the damming the river at the place proposed, will be the means of removing the alluvial bars below Troy and Albany, or permitting vessels of a large class to proceed to Albany and Troy, without obstruction, as contended by Mr. Seymour, the Commissioners have no means of deciding. 6th. If the river, as low down as the proposeds ite for the dam, will be closed by a CROTON AQUEDUCT. 133 covering of ice for three months in the year, we should think the cutting off so much of the navigation would produce more injury than the privilege of proceeding to Albany on the ice, or of procuring a supply of that article for the use of those who require it, would produce benefits. 7th. The shad fishery on the Hudson is considered of much importance to those who follow the business, as well as to those who consume the article, and we should pre- sume the erecting of the contemplated dam would totally destroy the fisheries, and ruin the business of those who depend on it for a living. 8th. In addition to the above, the Commissioners have obtained the opinion of Fred- erick Graff, Esq. the Superintendent of the water works at Fairmount. He thinks a dam of 24 inches above high tide will not answer the purpose intended, as the space of time that the wheels could work in pumping the water to the reservoir, would be entirely too short to insure a supply. That although the dam on the Schuylkill river is raised six feet six inches above the highest tides, the delay in pumping, occasioned by the tides, average seven hours out of the twenty-four ; and in full moon tides, from eight to nine hours. He considers the impediments to the trade on the river, by locking vessels through the dam, so objectional, that he is induced to conclude that the project cannot be beneficial. To raise the dam higher, appears to be out of the question, as it would not only destroy all the wharf and store property of the city, above the dam, but would also destroy so much land as to occasion the damage claims alone, a reason for abandoning the project. He thinks the advantages calculated on by the proposer of the plan,