From the considerations before detailed, I have however come to the conclusion, that under the modificationnow presented, it is better to adopt it, than the plan of carrying the aqueduct by a tunnel under the river. Could I have the same confidence in the estimate for the tunnel that I have in the bridge, I should have less in coming to this conclusion than I now feel for although the tunnel estimate includes all that appears ;

tangible, with an apparent liberality for all contingencies, still we know experience in similar work, much more limited in extent, proves how difficult it is to anticipate all the circumstances that will swell the cost of construction. If we have not calculated much more accurately for this work, than was originally done for the Thames Tunnel, we shall find our contingent allowance much too low. 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