This, together with the consideration, that the supervision and maintenance of the pipe on the bridge, will be more simple and less expensive, and consequently more satisfactory than that in the tunnel, have induced me to give the preference to the bridge.

By a resolution of your Board, subsequent to the one before mentioned, my attention is called to a suggestion for a wooden bridge, resting on timber piers, sunk in the river, and filled with stone to high water, on which to erect wooden piers, to be connected by arches of the same material. To this has been added a verbal suggestion of your

CROTON AQ.UEDUCT. 171

Chairman, to carry up stone piers above the water, and then erect the wooden structure upon them. Timber piers in the river could not be expected to last more than ten or twelve years, which would be quite temporary for such a work. The least that could reasonably be done, would be to raise the piers to such a height above the water as would be convenient to support the timber work. In my judgment, no calculation should be made, short of carrying the piers to the proper height for the spring arches of masonry, which they should be designed ultimately to support. The estimate for masonry above the spring line of arches, is 224,540 dollars. A timber arch and trunk sufficient for two and a half feet pipes, which would be sufficient to supply the city with water for twenty years, could be erected and covered for about 75,000 dollars, which is about 150,000 dollars less than estimated to complete the work of masonry. Such a bridge would last, if the cover was kept in good repair, probably 30 years. It is quite practicable to raise timber work to support the superstructure from near the water's edge but when it is considered that important bridges for travelled ;