The style of masonry is similar to that before described for the Sing Sing bridge, and the same method of open walls arid cast iron lining is also adopted. That part of the bridge which has no provision for street arches, is composed of a continuous wall of masonry, carried up on a bevel of one-twelfth its rise to the line of the aquegrade duct, where it is 30 feet wide the outside or face of this wall for one foot in breadth, is ;

laid in hydraulic mortar, and the remainder is laid dry. The method of laying up this dry masonry was to lay a course of large stone in such a manner as to give them the greatest solidity, and within a few inches of each other; after the course was laid over the work, the interstices werethoroughly filled with small broken stone, well pounded in,and succeeding course. (The same plan was adopted in all the dry levelled up to receive the foundations which were laid up to support the conduit over low grounds.) After the foundation was carried up to the proper height for the conduit masonry, parapets of hydraulic masonry were carried up to the level of the roofing arch of conduit, between which the conduit masonry of the usual form (excepting the side walls, which were 12 inches ex*

212 MEMOIR OF THE tra thickness) has been constructed, and covered with earth to protect the sides and top from frost ; the earth covering being secured by turfing carried over from parapet to parapet. The work presents a very substantial and finished appearance. RECEIVING RESERVOIR. This reservoir is 1826 feet long and 836 feet wide, and including its embankments contains 35.05 acres, and its area at top water line, 31 acres, divided into two divisions the northern division is designed to contain 20 feet depth of ;