This plan, it will be perceived, has, in its general appearance, a great degree of similarity to what has, for distinction, been called the high bridge. It

will, however, in consequence of its being of less height, and adapted to support a lighter superstructure, be 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 designed 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 $ 320 200 cubic yards of excavation of rock for foundations on shore, at $3 600 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 $104,000 $104,920 500 tracing piles, for foundations of land piers not on rock, at $5 2,500 1,700 cubic yards of concrete masonry, at $6 10,200 10,600 cubic yards of masonry in large piers, at $20 212,000 3,800 cul^ic yards of masonry in small piers, at $15 57,000