After the frame is sunk to its place and well secured, the driving of the sheet-piling, filling in with water-tight earth, and, in general, all other work, will be similar to that proposed for coffer dams for the piers ; with such additional security as its larger dimensions demand. The coffer dam being completed, it is proposed to erect two fifty horse power steam engines, with suitable pumps, to clear the pit from water. The sand and rock within the coffer dam will then be excavated to the proper level of foundation of the masonry ; in the progress of which the bottom of the coffer, below the frame, will require to be secured by suitable prop or stay timbers. MASONRY. It is proposed to lay down a foundation course of concrete, formed to receive an inverted arch of brick, from which will rise curved walls to form abutments for the upper arches of the tunnel, all of which will be of brick masonry supported by concrete, and the exterior protected on the sides by well set stone, and the top by a covering of well jointed coping. The iron pipes are proposed to be of metal, 1 3-8 inches in thickness, for the part that passes the tunnel, and 1^ inches until they extend to a point 40 feet above the level of the river. Branch pipes and waste cocks will be required in the main pipe, above the high water mark of the river, as a means to force out the sediment that may be deposited in the bottom of the pipe. This means of clearing the pipes would probably be sufficient, if the waste pipes could be placed in, and discharge freely from the bottom of the bend ;