trenailed strongly together, and is filled with ballast, to the very top. The upper slope is covered with five inch pine plank, jointed and perfectly tight; the lower With five and three inch hemlock plank.— The crest, terminating at the sluice, near the middle of the overfall, is level, and covered entirely with stone eight feet in length, and strongly secured with iron straps and bolts. The sluice, sixty feet in length, is covered in the same manner, and is about twenty inches lower than the wings. The walls of the Lock are 170 feet in length, its chamber 101 feet by 28 1-3 feet in the clear, with a single lift; the west wall serves as the eastern abutment of the Dam—it is 28 feet thick at the base, graduated to 25 at the top. The head and east walls are of corresponding strength.— Both are built wholly of granite. The face courses hammered, bed and joint, rabbitted, and laid in ce- ment, and the rabbit filled with cement The floor of the Lock is constructed of timber fifteen inches deep, and covered with five inch pine plank, tongued and grooved, with an additional flooring of five inch hard wood plank, commencing at the head of the Lock and ex- tending fourteen feet. The main gates of the Lock, and /guard gates of the Canals, are of white oak from the Chesapeake, and the wicket gates of cast iron. The large stone piers above the Dam, for the pro- tection of the Lock and abutments, are each 30 feet square on the base, graduated to 25 feet on the top, and about 34 feet high, and built of granite, clamped and strapped with iron. |
The Canals on each side of tbe river are 50 feet wide in the clear, carrying 10 feet of water from tbe level of the top of the dam. The walls are 22 feet bigh, 7 1-2 feet thick at the base, and 5 feet at the top. They are finished as far as, and including, the guard gates. The gates are of great strength, built of heavy oak timber, and in the most substantial manner, revolving in stone coins, with which stone and sheet-piling is connected, extending across and 25 feet into each bank, and driven 10 feet below the bottom of the Canals.
' The walls on the banks of the river, above and below the Dam, extending about 500 feet, are of the same height as the Canal walls, and 8 feet thick at the base. On the upper side of the Dam is a sheet of timber-piling, tongued and grooved, and either resting on the bare ledge, or driven as far as they could be made to penetrate into the solid bed which covers a portion of its surface, and is connected with the piling which passes under and across the Lock into the east hank, and also with that which is driven in the west bank of the river.— Above this, and extending to the top of the Dam, so as to cover the entire planking of the upper slope, is a mass of gravel from 20 to 30 feet deep.
2,500,000 feet of timber and about 25 tons of iron have been used in constructing the Dam, and about
75,000 tons of ballast have been de- posited in it.
The Lock, Piers, River and Mill walls, with the Canal walls, ex- tending to and including tbe guard gates, contain about 800,000 cubic feet of stone.
During the progress of the work, and especially while the course of the river was contracted to a space of 17 feet wide by 24 deep (a time peculiarly favorable for forming an estimate, and rarely offered in a stream of this magnitude) repeated observations were made upon the velocity of the current, and at no time was there found a less quanti- ty than 2,500 cubic feet per second. It is proper to add that the seasons of 1836 and 1837, were both re- |