a thin stratum of sand, and this is followed by a stratum of sand and large boulders intermixed below the stratum of boulders, or detached rock, there has been found in the cof- ;

fer dams for two piers, Nos. 8 and 9, a compact marble rock, and in the coffers for Nos. 7 and 10, a stratum of clay and sand, that is quite impervious to water, and affords a good medium for piling. The general plan of the bridge now in progress of construction, is as follows :

Across the river there are 8 arches, each of 80 feet span, resting on piers that are at each extremity and in the centre 20 feet wide at the spring line of the arches, with intermediate piers that are 14 feet wide at the spring line on the south of this range of large arches ;

there is one arch, and on the north 6 arches, each of 50 feet span, resting on piers 7 feet wide at the spring line, and two abutments that terminate the arch work of the bridge. From the abutments a continuous foundation wall of dry stone work is extended to the gate chambers on each side.

210 MEMOIR OF THE" The whole length of the bridge is 1450 feet the height of the river piers above high ;

water line is 60 feet to the spring of the arches, and 95 feet above the lowest foundation that has been put down ; the arehes are semicircular, and the height 100 feet to the soffit. or under side, at crown to the top of the parapets 114 feet above the ordinary high water line of the river, and 149 feet above the lowest foundation of the piers that have been commenced. The width across, on the top of the parapets, is 21 feet the exterior ;