Plate X. is a representation of the entablature over the mouth of the tunnel, showing the inscriptions upon it, relating to the date of the commencement of the dam and its completion, the persons who had contracts for building it, and those having charge of the work during the time. Plate XI. is a view taken from a point below the dam and shows the relative positions of the dam and the gate chamber at the head of the Aqueduct. The original channel of the River where the dam is built,

;

was about 120 feet wide ; the average depth of water at this

place was about 4 feet ; and the greatest depth 10 feet. The left bank of the river arose abruptly with rock, the channel was gravelly, and on the right bank a sandy table land about 3 feet above the ordinary surface of water extended about 80 feet ; then a sandy hill arose on a slope of about forty-five degrees. In making the plan for a dam at this place it was determined to fill the main channel and the table land on the right bank with an embankment of earth ; and on the left bank where rock was found, to build a body of masonry against the slope to the requisite height for the surface of the Reservoir and connect it with the embankment in the channel ; this masonry formed the overfall for the water,

and the rock in the side of the hill adjacent to it was excavated down to the level of the overfall, thereby extending it