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 ;

of the banks are lined with a course of rubble hydraulic masonry 15 inches thick, and coped with dressed stone. The bottom is a very impervious hard-pan, on which two feet of puddled earth is laid, and this covered by 12 inches of hydraulic concrete. The reservoir is divided into two divisions by a wall of hydraulic masonry, at the toe of which a sloping bank of puddled earth is raised 18 feet high and covered with rubble masonry ;

this wall is 19 feet thick at the bottom, six and two-third feet thick at top water line, and four feet at top. In this wall a waste weir is placed, with a well of two falls, together 52 feet, from which the waste water enters a sewer in 42d street, and passes off about one

14 MEMOIR OF mile to the Hudson river. In each division there is a waste cock to draw the water from the bottom. The reservoir is designed for 36 feet of water, and, when full, will stand 115 feet above mean tide. The walls rise 4 feet above the water line. An iron railing is to be placed around the walls on top of the cornice. The capacity of this reservoir is 20,000,000 imperial gallons. GRADE LINE OF AQUEDUCT.