In the spring and summer of 1807, the earthen-bank was carried forward to near the end of the timber work for the cofferdam. The first leading frame was begun in August, and put together on the beach, near high water mark, that it might be floated off to its situation. The first leading frame was begun by fishing together end to end, two beams 13 inches square, by pieces 20 feet long, 13 inches broad, and 6 inches thick, laid on op posite sides of the beams across the joints, and fastened by four screw bolts, which passed through the whole. The length of these beams, when joined, was 95 feet. In order to form the sides of the leading frames, from the ends of these last-mentioned beams, two others, each 63 feet in length, were laid with au inclination to each other, that left their inner ends 65 feet apart. They were tastened to the ends of the long beam by half chucking or gaining, and two screw bolts through each corner. There was a beam 38 feet long laid across each angle, and fastened down to the front and side leading beams by screw bo.ts. At the height of the springs this first leading frame was floated off, and at low water adjusted in its precise situation, and sunk to the bottom by means of a number of large stones being placed up on it. A considerable degree of attention was bestowed in adjusting this first frame, because upon this depend ed the having the cofferdam, and, of course, the entrance and wings of the sea-lock, in a proper direction. On the upper side of this leading beam, previous to sinking it, there were mortices cut, three on each side, and three in the front, which were to receive tenons made on the lower end of the standard, which were placed up right therein, and cut off at the level of one foot below high water neap tides, in order to receive the middle leading frame. This last mentioned frame, after hay ing been made on the shore, in all respects similar to the first, was floated into its place ; but, after two or three fruitless attempts to rest it on the top of the upright standards as the tide left it, this mode was abandoned, it being found impracticable, in so strong a tide, to steady such a large frame on such low unconnected points. This led to placing a pile engine upon the deck of a sloop, and driving three piles along the front, and two on each side, all close to the outer side of the lower lead ing frame. Large brackets were nailed to the inside of these piles, level with the tops of the upright stand ards. The frame was then floated again into its place, when it rested upon the brackets, and upon the top of the standards, and was screw-bolted to the piles. Upon the second leading frame were also upright standards fixed in mortices, and cut off at the level of of a high spring tide. The upper leading frame was floated off and fixed upon the standards. For doing this, advantage was taken of one of the highest spring tides in the beginning of October. This frame was likewise bolted to the piles. A temporary scaffold was made above the top frame, by laying large beams across, and driving piles in the inside of the space to support them. The whole was now loaded with stones. A large pile engine was placed on the scaffold, and a num ber of piles driven around the outside of these frames, at fifteen and twenty feet apart from each other. They were bolted to the uppermost frame, to keep the whole %teady during the winter storms.
In March 1808, the work was recommenced by put ting down the main or framing piles, and fixing them in the rock by means of iron-dowels. For this operation there was first constructed a cylinder of three inch fir plank, 22 inches diameter in the inside, and eight feet long. The joints were made perfectly correct, and dowelled together ; and it was hooped with flat iron bars. The lower end was shod with a circular iron shoe, fit ted on the edge of the timber, to prevent it from being damaged by stones while driven down to the rock. Near the upper end, and on the opposite sides of the cylinder, two strong eyes were fixed by means of strong iron clamps, which embraced the cylinder, and were rivetted to its sides. This was done in order to receive a strong chain to lift up the cylinder, and also for drawing it out of the sand and mud after the pile was fixed. At low water, this cylinder was placed in the situation where the centre of the main pile was to lie. At this spot there were three feet of low water, and eight and a half of silt and gravel upon the top of the rock. The cylinder
being lifted by ropes fixed on the top of the pile engine frame, it was set perpendicularly on the surface of the sand, and close to the inside of the lower leading frame. On the top of it was placed a block of ash timber, two feet high ; on the lower end of this six inches were turned, to fill exactly the inside of the cylinder, to pre vent the block from shifting, and also to prevent the cy linder from crushing during the driving. This block was strongly hooped with iron, as was also a pile, twelve inches square, that stood on the top of it, and reached as much above the top of the upper scaffold as the cy linder had to sink into the mud. The whole were now lashed, in such a manner as to keep them perpendicular, and, at the same time, allow them to sink. The driving was then commenced with a pile engine 30 feet high, and a rant 1008 lb. At first the cylinder went freely ; but, by the time it had sunk three feet and a half, it went so stiffly, that it was found advisable to begin emptying the matter out of the inside. For this purpose an in strumen.t, named a sand auger, was made, (Sec Plate XCVI I.) having a quadrant of a circle of the same dia meter as the inside of the cylinder. The circular side, and one of the straight sides of this quadrant, for six. inches high, were made close, of thin rolled iron rivet ted to the ribs, which were fastened to the corners of the quadrant, from which proceeded an upright shaft, the other straight side being open. To the bottom of it four flat teeth, two inches and a half long, were fixed, with an inclination downwards ; so that, when the auger turned round, these teeth loosened the sand, and prepa red it to enter easily into the body of the auger. To keep it steady while turning, there was fastened to the lower side of that corner of the quadrant which is the centre of the circle, a pivot, six inches long, which pass ed into the sand, and served as a centre for the auger to turn upon. Immediately above this pivot stood the upright shaft, which for ten feet was of iron, one inch and a half square, and for twelve feet more a piece of ash timber four inches square. Upon this two cross handles were placed, to turn it with ; and they were to slide up and down as the auger rose and fell. At five feet below the upper scaffold, where the pile engine stood, a temporary scaffold was erected, on the top of the second leading beam, where four men might stand and turn the auger. In this lower scaffold was a round hole, through which the wooden shaft of the auger pass ed, and kept it steady. When at work, two complete turns filled it. It was then lifted up above the water, by a purchase from the top of the pile engine, and the sand was cleaned out with a small shovel, by a man who stood in a boat for that purpose. The operations of bor ing and cleaning out were repeated, until the sand was taken out to the bottom of the cylinder ; which was then driven farther down, and a similar operation of sand boring gone through ; driving and boring alternately, till the lower part of the cylinder rested upon the rock, and all the sand was taken out, as low as the pivot would al low for the rock. There was then a frame, which fit ted the inside of the cylinder, introduced into its upper end, and sunk to the bottom by means of two half bun dyed weights. Down a square hole in the middle of this frame, was introduced a pipe, four inches square at the top, and tapered to three inches at the bottom. This was driven down to the rock through the small quantity that the auger could not clear. The sand which was inclosed by the pipe was cleared off the rock by a cylindrical iron tube, three inches in diameter on the outside, and three feet long, which had a valve fixed witilin two inches of the bottom, and rested on a small ring fastened in the inside of the tube for that purpose. On the top of the tube was a screw, by which it was fas tened to a set of boring rods. It was then passed down the inside to the bottom of the square wooden pipe, and, by working it by short and quick strokes, the before mentioned sand and small gravel worked above the valve by the agitation of the water. The tube was then taken up and emptied of the sand ; and this operation was re peated, until the rock within the square tube was per fectly clean. It was found absolutely necessary to clear away this sand, as otherwise it entirely prevented the jumper from turning on the rock.