All the purposes and objects to be obtained by the project, will as well be attained by the plan of a low bridge as by that of the high bridge, and at an expense of more than half a million of dollars less. 3d. The experience in sinking piers in so great a depth of water and mud, in order to reach the rock bottom, being very limited, and their great number and immense height from the rock to the spring of the arches, although their construction is practicable, it must be attended with many unforeseen difficulties and casualties and should the least ;

variation from plumb occur, or the least settlement on the foundation take place, it would carry with it very injurious results to the work while with the low bridge and iron ;

pipes, the same occurrence would be attended with but trifling injury, and could very soon be repaired. 4th. The water in the large aqueduct of masonry would, with much more uncertainty, be protected from frost on the high bridge, from the greatly elevated exposure and difficulty in surrounding it with a sufficient quantity of earth, than when constructed on

the land ; while the iron pipes, from their comparative size, may be bedded in earth of sufficient depth and compactness, to avoid all possibility of being affected by the frost.

5th. The effects of leakage have been found very injurious to the aqueduct bridges on our canals, and it is therefore a part of our contract to line the aqueduct, when the crossing of streams on bridges is necessary, with plates of cast iron, in order to avoid the possibility of repairs, which might require the shutting out of the water while effecting them, and thus be attended with serious consequences to the city.