A jumper was then passed down the square direct ing-pipe, and worked by a lever on the upper scaffold, until a hole two inches and a half in diameter, and twenty inches deep, was bored into the rock, to receive an iron dowell two inches square. This dowel' was fix ed in its place, by fastening it into a square socket made in the end of an inch and a half square iron bar by a small cord, to prevent it from falling out of the socket while lowering down the square directing-pipe to the rock. It was driven into the hole in the rock, by strik ing with a large hammer on the head of the bar. When it had been driven eighteen inches into the hole, the timber was lifted by a sudden jerk, which broke the cord, and left the dowel' in its intended situation. The frame and square directing pipe were then lifted out of the cylinder. The pile, previous to being let down, had two hoops put on its lower end, and a hole cut to receive the end of the iron dowel' which stood in the rock. And, from the side of this hole to the inside of the lower hoop, four pieces of iron were driven into the end of the pile, to prevent the timber at the sides of the dowell from giving way, when the lateral pressure came upon the pile. On the four sides, near the lower end of the pile, pieces of timber were nailed, to increase its size to twenty-two inches, this being the inside diameter of the cylinder. By this means the hole was kept in its precise situation, and was formed to pass exactly upon the dowell. It was then set hard to the rock by a stroke of the pile engine. This completed the fixing of one main pile. A strong chain was then fastened to the top of the cylinder, and, after the main pile was, wedged down, to prevent it from rising, a strong purchase of ropes and blocks was applied, to raise the cylinder out of the sand ; but all the power which could be applied was ineffectual. A beam of fifty feet in length was there fore procured for a lever. The fulcrum of this lever was laid on the top of the main pile. The outer end of it was lifted up by ropes and blocks from the mast of a sloop, that was laid along the outside of :he dam for this purpose. The chain from the top of the cylinder was now fixed to the inner end of the lever, and six men got on the outer end, and set it in motion. The cylinder at length started; but, before it moved, it took a pur chase of nearly fifty tons. After it was worked up a little by the lever, the ropes and blocks were again ap plied, and lifted the cylinder over the top of the pile. The head of the pile was now forced against the inside of the upper leading frame, and a screw-bolt put through both. The whole apparatus was then shifted to the situ ation of the next main pile, and similar operations took place, until the whole of the main piles were fixed, ex cepting in some instances where the sand was shallow, and then the cylinder was lifted without employing this enormous lever.
The main piles having been all properly fixed at the bottom, and fastened at the heads, temporary leading beams were bolted on the outside of the piles formerly described as driven 15 or 20 feet apart, all round the outside of the main leading frames. These spaces were now filled up with piles set close side by side, and dri ven down to the rock : then the lower temporary leading frame was taken off, the upper one being left to steady the piles until the puddle was brought up in the coffer dam. The inside braces were now put in ; they rested
upon brackets fastened to the main piles, and also upon the tops of these piles which were driven to the rock under the main•stretching brace. The braces were be sides prevented from floating, by brackets nailed above them, and by stones laid on temporary scaffolds. The outer row of piles, in front of the cofferdam, was begun by placing a pile engine on a float made of large fir logs from 40 to 50 feet long, and one foot square. These were fastened together by half logs spiked across them. The width of this float was 14 feet, which just filling the space between the rows of piles, was thereby kept steady ; and this was also the means of getting readily into a straight line the outer row of piles which stood at twenty feet apart. These being driven, a long leading beam was made by fishing, as formerly described, and bolted to the outside of these piles on a level with the inside leading frame. A temporary leading beam was then fixed on the inside of the outer row of piles, one foot lower than the outside beam ; there was then a scaffold erected on the top over the space between the rows of piles, by which means were taken to secure the outer piles from any motion they might otherwise have had with the tide. The piling engine was next got on this scaffold, and an outside leading beam bolted at the same level with the middle leading frame on the inside. The space betwixt the first-mentioned piles was now filled up by others set close together and driven down to the rock ; by the time the outside and two return rows of piles at the angles were all driven, the bank and pud dle at each side of the dam was brought forward to the front of the inner row of piles.
The connecting bolts were now put in, one through each main pile, opposite the middle leading frame, through which it went, also across the puddle, and through the front leading beam on the outside of the outer row of piles. These connecting bolts were fasten ed by a strong cottcrel through each end, with a strong iron-plate under them. There were likewise two of these connecting bolts through each main pile in the front of the dam ; one through the middle leading frame, and the other one foot below low water common spring tides, at which place the lowest leading beam on the outer row of piles was fixed. The two rows of piles were kept together at the tops by means of a piece of strong timber being gained on the side of each main pile on the inside of the dam, and being spiked down on the outside leading beam.
This description, with the representation in Plate XCVII. will, ‘N e trust, convey a distinct notion of the progress of this difficult operation. The description may, no doubt, to some appear minute, but those engaged or interested in similar works will not think it more than sufficient ; and we consider it a fortunate circumstance, to be enabled to furnish so minute and faithful an account of it.