apprehension of such a result. Well completed, the bridge, in the simplicity and economy of its operation, and its architectural appearance, would, no doubt, be the most satisfactory structure. In the foregoing estimates and remarks, I have endeavored to call your attention to all the essential circumstances and considerations that have a bearing in deciding on the plan most appropriate to be adopted. The question is one of great importance, and surround- ed with embarrassing difficulties, which in some respects are of a nature that do not ad- mit of exact, or even hardly approximate, computation. In relation to the time required for the completion, I think five years as little, as should be calculated for the bridge ; while the tunnel, if successful in putting down the coffer dam, may be completed in four years. It is not probable that either plan can be executed as early as other parts of the aqueduct ; and it will be proper to lay down a temporary pipe, which may be sufficient for the introduction of the water ; as for the want of suitable fixtures, some time will probably elapse, after its first introduction, before it will get into general use in the city. A twenty-two inch main may be laid down and protected for $30,000, and when the work is completed may be taken up and used to supply the city mains, by which the extra expense will not be much, if any, over $20,000. In making up an opinion which of the two plans should be adopted, I have felt the question to be one involving great responsibility. The high bridge I have heretofore en- deavored to avoid, as a work of great expense, and attended with much difficulty in its execution. From the considerations before detailed, I have however come to the conclu- sion, that under the modification now 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 atten- tion 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 connect- ed 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 conve- nient 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 roads, are usually supported by piers of stone, and aqueducts for canals almost invariably so, we could not, I think, do less than give that degree of permanence and durability which would be obtained by carrying up the piers as above suggested. In