This plan provided for an aqueduct of masonry, to be rendered more impervious by a cast iron lining; but as it was supposed the Commissioners had power, and no objection having previously been made, on the ground of interference with the the navigation, a structure, conforming nearly to the shape of the valley, and rising to a moderate elevation above the surface of the river, on which iron pipes were to be laid and secured, was recommended, as best adapted for economy, permanence, and more ready execution, to carry the aqueduct across this heavy depression from the grade line. Although adopted by your Board, and put in progress of execution, the law before mentioned compels its abandonment. We are therefore with only the alternatives of the Act of the Legislature, as before mentioned.

The arches of the bridge, originally designed to maintain the grade of the aqueduct, were elevated 112 feet above the high water mark of the river, which is 12 feet higher than the Act requires. It is obvious, therefore, that 100 feet will not be sufficient to maintain an aqueduct of masonry, but will require iron pipes as conduits for the water. This I do not consider an objection, as I am fully satisfied, iron pipes will make the most suitable conduit for the water on such a bridge, and therefore have had a plan prepared, with a view to comply with the law, arid avail of the economy and greater permanence from a less elevated structure. Owing to the less height required for the arches, and by adopting iron pipes for the conduit, the top of the parapets will be 114 feet above high water mark, which is 17 feet lower than the original plan. The superstructure being lighter than necessary for an aqueduct of masonry, a diminished thickness of arch stone may with equal safety be adopted.