It was intended to make the waste of the dam 100 feet, with abutments of eight feet high; but in consequence of the disappointment in regard to the extent of the rock in the river, it was found difficult to obtain the desired length of the water way, and it was concluded to raise the abutment to 12 feet at the lower end, and 15 feet at the upper end, and allow the water way to remain an average length of 90 feet for this height. The natural rock formed the southern abutment, and the aqueduct being on this side, the water was conducted to the gateway at its head, by a tunnel, cut 180 feet through the rock this;

allowed the gateway to be located on solid rock, in a situation not exposed to the floods of the river. The water enters the gate chamber by an archway through the second bulk-head. The gate chamber is provided with a double set of gates one set of guard ;

gates, of cast iron set in cast iron, frames, and one set of regulating gates, made of gun metal, set in frames of the same material ; the gates are all 18 by 40 inches, and there are nine gates in each set. They are all operated by means of wrought iron screw rods.

The gate chamber and bulk-heads are constructed of well dressed masonry, laid up in hydraulic cement.

In the north abutment a waste culvert has been constructed, with suitable gates of cast iron, to draw the water down in the reservoir at such times as it may be necessary, to facilitate the making of any repairs that may be required, and to discharge the river at ordinary times during the construction of the work. From this abutment the old channel of the river was filled by an embankment, with a heavy protection wall on the lower side, which was raised 15 feet above the waste weir of the dam, and designed to be 50 feet wide on the top, but was not completed the full width, when the unprecedented flood of January, 1841, carried it away.