Chap. VI.
221
25 feet 6 inches. To limit the width of the foundation, two lines were set out not quiteparallel, because the depth increasing as they proceeded, rendered it necessary to increasethe width, at the same time that of the channel was made equal throughout, the difierencebeing given to the exterior face of the jetty. Some of the earth being removed, the firstbed of fascines was laid, and to prevent the sea from undermining the work, a trench wasdug and filled in with well-rammed clay ; fascines united in masses were covered with heapsof clay, which filled up the inequalities and holes in the shore, before the work was broughtto a level.
When the necessary trenches were cut, several layers of fascines were laid within themG or 7 feet in length, and from 18 to 20 inches in circumference; when laid across theintended jetty they formed a bed of about 12 inches in thickness. The ends of each layerwere dressed to the form required by the slope; small stakes 3 feet in length were driventhrough them at the distance of 18 inches, and rows were so formed at every 3 feet. Rods15 to 16 feet in length were then worked round the heads of the stakes, and the wholesecurely wattled together.
The beds of fascines were repeated in a similar manner, until the whole mass was broughtup to the height required, care being taken that the rows of stakes were placed in variousplaces to unite the upper layer with that below it. This work was only carried on after thetide had retired, and it was found necessary to load it with large stones, to avoid anymovement that might take place from the rolling in of the sea.
The entire surface was covered with a grillage of fir timber, 4 or 5 inches square, leavingcompartments of 2 feet square. Piles were required to maintain them in their position,one being driven slantways in each mesh of the square, they were from 12 to 13 feet inlength, and 12 inches in circumference at top, gradually diminishing towards the point; ahole was bored at the head, through which a stake about 18 inches in length was passed,to retain the timber grillage, and prevent its moving. The squares were filled with stone,laid dry, placed on edge, and well rammed with wooden rammers, that the stone might notfracture. The crevices were filled with smaller pieces of stone, or the chippings from thequarry.
The whole of the work was protected by piles, to prevent any injury from thepassage of the vessels to and from the harbour, and these also served to support a smallcontinued line of bridges that communicated with the forts. The slopes and top beingcompleted with fascines, a series of framing was laid throughout, at distances of 9 feet,similar to those used in the construction of quays. Each frame being formed of a protect-ing pile from 36 to 40 feet in length, 16 or 17 inches square at top, and capped with timberabout 12 inches by 8, so as to unite the whole line together. These piles were retained intheir position by' tyes, which ran through the entire width of the jetty; each bay wasstrengthened in various directions by cross timbers, 12 inches square.
The jetties so constructed of fascines did not continue more than twenty years, when itwas found necessary to construct them more solidly, and Marcclial Vauban approving ofthe plans suggested by M. Clement, he was directed to form them of timber and stone.
The old fascines were removed to within 3 feet of high water mark; those belowhad become so consolidated by the deposit of sand and other matter, as to be renderedstrong enough to support the weight intended to be put upon them. Lines were drawnat every 20 feet, and piles driven at about 2 feet 9 inches apart, which were cut off at auniform height, leaving a tenon to mortice into the longitudinal timbers placed over them.Rows of piles were driven between these lines, and these were repeated at every 8 feet, thewidth of each bay. On these rested the sill of the framing, halved on to the longitudinaltimbers, and morticed to the heads of the five intermediate piles, on which was constructedthe framing.
The piles were 9 or 10 inches square, and the long timbers which capped them 13 or14 inches square, 25 feet long, and their scarfing joints 3 feet long. The transverse timberswhich formed the sill of the frames were 25 feet in length, and 13 inches square; theirends were dovetailed into the longitudinal timber to the depth of three inches. The middlehorizontal timber was 13 inches square, and the upper one 12 inches square; these weredovetailed into the side timbers which formed the slopes.
The St. Andrew’s crosses were formed of timber, 9 inches square, morticed and tenoned atthe ends. The struts were 9 inches square, dovetailed at the ends, and the upright postwas of the same scantling.
The slant parts of the exterior were 12 inches square. The binding pieces the samescantling, and 25 feet in length. The whole was planked throughout, and capped at thetop.
After the framing was complete, it was filled in with hard stone, laid carefully by handand without mortar, fine gravel being substituted.
The celebrated Ilisban or fort, which was constructed in masonry to guard the entrance ofthe port of Dunkerque, was distant 550 toises from the bastion, and SO’from the mouth ofthe canal : the length of each of its three sides was fifty toises, and it rose 16 feet above the