It is laid level across the bottom, three inches thick at the centre of the inverted arch, and curved on its upper surface, to form a bed for the arch, which brings it 12 inches thick at the spring line, and is carried three inches thick under the side walls or abutments. The abutments are 2 feet 8 inches thick at the spring line of the inverted arch, and 2 feet at the top, or spring line of the roofing arch. The inverted arch is of brick, 4 inches thick. The roofing arch is also 8 inches thick. The abutments, or side walls, are of rubble stone, with a brick facing 4 inches thick. Spandrels of stone are carried up solid from the exterior angle of side wall, on a line that is tangent to the arch.
When the bed of concrete is formed for the inverted arch, a heavy course of plastering is laid over it, on which the arch is laid. When the stone work of the side walls was up, the face that received the brick lining had its irregularities filled with successive courses of plastering, and finally a uniform course of a quarter of an inch in thickness over the whole, in front of which the brick facing was laid up. A course of plastering was also put over the roofing arch. The concrete masonry was formed by mixing one part hydraulic cement, three parts clean sand, and three parts fine broken stone ; in some cases fine pebbles were in part substituted for broken stone.
The masonry was all laid up in hydraulic cement, obtained mostly from the hydraulic lime of Ulster Co. The mortar for the stone work was composed of one measure of cement to three of clean sharp sand, and for the brick masonry and plastering, one of cement to two of sand.