The Avaste cocks for the tunnel pipe, being 32 feet above the lower part of the bend, rendering it probable the sediment must be removed, to a great extent, by manual labor, through the man holes, will make the clearing of the pipes much more difficult and expensive than the bridge pipe. The supervision and care, necessary to keep the tunnel pipe in good condition and guard against sudden failure, will be much greater than required for the bridsre pipe. In regard to the masonry, a defect or failure in either plan would be very difficult and expensive to remedy and we should not anticipate any, or ;

rather the work should be so well guarded as to leave no 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 surrounded with embarrassing difficulties, which in some respects are of a nature that do not admit 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 ;