The cross walls are four feet thick at bottom, and have one offset of six inches on each side at 8 feet below the spring line of connecting arches ; they have an opening 6 feet high, and 1^ feet wide, at a suitable level near the bottom, to allow a drain to be formed, to collect any water that mayleak through the work, and carry it off in sewers provided for that purpose, and also to allow persons to go in and examine the work. Some modifications in the cross walls are made to accommodate the gate chambers, and connect the corners of the work. On each corner of the reservoir, pilasters 40 feet in width are raised, projecting four feet from the main wall, and in the centre, on the streets and 5th Avenue, there are pilasters 60 feet wide and projecting 6 feet from the wall. The pilaster in the centre, on the 5th Avenue, rises 7 feet above the main wall, and all the others 4 feet above. Doors are placed in the central pilasters on 40th and 42d streets, which give access to the pipe chambers, to work the influent and effluent stop-cocks, from which chambers, an entrance is made to the openings in the walls. In the central pilaster on the 5th Avenue, an entrance is made by a door to a stairway that leads up to the top of the walls. On the outside walls, an Egyptian cornice is laid, which accords with the general style of the work. The pilasters are laid in courses, and well dressed ashlar face, and the main wall with coursed rubble work, rough hammer-dressed. Inside of the walls of masonry, a thorough puddled embankment of suitable earth is formed, fifty-eight and one-third feet wide at the line of reservoir bottom, and sloping on the inside face one and a half to one for 24 feet high, and one to one for the remaining 16 feet high, arid making with the walls on top a width of 17 feet the faces ;