less expensive. In the first instance, it is proposed to put down two three-feet pipes, which will probably be sufficient to supply the city for at least fifty years ; but to adapt the work to receive two four-feet pipe, which will be sufficient when the full CROTON AaUEDUCT. 165 capacity of the aqueduct shall be required. As there will be only a head of about 15 feet, no difficulty will be experienced in the use of pipes of this dimension. To guard more effectually against the influence of frost, the parapet walls are de- signed to be hollow. The same arrangement for influent and effluent gate houses, also for waste cocks, that was proposed for the low bridge, will be required in this. The plans herewith submitted, though not, in all their details, entirely complete, it is believed, with the foregoing description, will explain fully to the Board the character of the plan under consideration. Estimated Expense of the Aqueduct Bridge. '2,000 cubic yards of excavation of earth for foundations on shores, at 16 cents 200 cubic yards of excavation of rock for foundations on shore, at $3 7 coffer dams, including pumping, excavation of pits, and earth filling, as per detailed estimate in report of December, 1837, at $13,000 - $91,000 Add for extra excavation of mud, and extra sheeting of frame 13,000 500 tracing piles, for foundations of land piers not on rock, at $5 1,700 cubic yards of concrete masonry, at $6 10,600 cubic yards of masonry in large piers, at $20 3,800 cul^ic yards of masonry in small piers, at $15 490 cubic yards of water table and cornice on piers, at $30 3,020 cubic yards of large arches, at $30 1,020 cubic yards of small arches, at $25 1,060 cubic yards of pilasters, at $15 3,150 cubic yards of exterior spandrils, at $13 - 3,650 cubic" yards of interior spandrils, and hance walls, at 250 cubic yards of flagging, to connect hance walls, at 1,300 cubic yards of parapet walls, at $12 520 cubic yards of brick walls and wells, at $12 250 cubic yards of coping on parapets, at $30 4,400 cubic yards of foundation walls at ends, at $2 400 cubic yards of side wall on do. at $6 - 42 $ 320 600 $104,000 212,000 57,000 90,600 25,500 40,950 21,900 2,000 15,600 6,240 7,500 8,800 2,400 $104,920 2,500 10,200 269,000 14,700 116,100 15,900 62,850 64,850 29,340 11,200 166 MEMOIR OF THE 6,500 cubic yards of earth filling over pipes, at 40 cents - 2,600 350 superficial yards turfing, at 30 cents - 105 2,705 1,000,000 ft. board measure, pine timber arid plank for centering and scaffolding, at $35 - 35,000 300,000 ft. board measure, oak timber and plank for centering and scaffolding, at $45 - 13,500 48,500 580 tons cast iron pipe, at $75 43,500 Lead, yarn, tallow, and laying down, estimated 9,000 2 pipe chambers, as per estimate detailed in report December, 1837, - 15,642 Waste cocks, as per report December, 1837, - 2,500 70,642 $760,557 Add for contingencies 10 per cent. 76,056 $836,613 Tunnel under the Channel of the River. By the Act before mentioned, it is required that the top of the work put down for the tunnel, shall not be above the bed of the river in the channel ; and it is understood as re- quiring the tunnel to extend entirely across the channel, which at the line of aqueduct is 300 feet wide. The bed of the river is about 18 feet below common high water mark. The channel is not this depth for its whole width, but slopes very flat on the sides. The out- line of the plan, is to make a tunnel of masonry, of sufficient dimensions to allow four iron pipes, each three feet diameter to be laid within it. The tunnel to be made of two sec- tions, or of two arched vaults, laid close to each other, and each sufficient for two pipes. The tunnel to terminate at each end, in abutments of masonry, having such slopes and curves as will afford the most favorable flow of water, that the situation will permit. A horizontal vault in each section will carry any water that may gather in the tunnel, to the vertical welts in the abutments, where it may be cleared by pumps. The tunnel at each end will open in the top of the abutments, and thence the iron pipe will pass from the tunnel, rising to a suitable level above the river, and enter the embankment by which it will be covered. To protect the pipes from frost and provide for convenient entrance into the tunnel, a house is to be erected over this opening. It is proposed to make the tunnel, by first excavating the mud