Chav. VI.

FRANCE.

237

prismatic caissoons, two forming the base, the others placed above them ; these were boardedon the outside, and filled with stone, gravel, and earth. The length of the mole was 160toises ; six drains were formed to carry off any water that might find an entry to it.

De Cessart also executed the sluice for scouring the harbour by means of a caissoon, inlength 54 feet 8 inches, in width 93 feet, and in height 15 feet; the area was 5080 feet.

To put the platform together ten rows of piles, each containing eighteen, were driven;they were in length 10 feet, and 9 inches square, the heads of the piles were capped, and thewhole brought to a level; on this w*as put the bottom of the caissoon, composed of fouroutside timbers, 14 inches square, and four others laid within of the same scantling.

The width was divided into three bays, of 21 feet 4 inches each ; these bays were filled inwith timber 10 inches square, nicely jointed, and made level at the bottom ; over these wereother transverse timbers securely bolted to the bottom, and between them a course of

The whole was secured by four

X

Fig. 250. FKAMING

61,342 pounds, and it drew 2 feet

inch and 4 lines

r

4-inch planks, also crossing the lower timbers at right angles,iron bars, 2 inches in thickness, whichwere screwed up and rendered the platforma compact mass.

After this was done, a course of timber10 inches by 8 was laid around the outside,and above this, four others of the samescantling, into which the uprights of thesides were to be framed ; these were 15 feetin height, and composed of ninety-six up-right timbers, 12 inches by 6, lined on theoutside with 6-inch planks, and again crossedby others 4 inches thick; additional strengthwas given by forty interties, 18 feet 6 incheslong, and 12 inches by 10. When the cais-soon was ready to float, a layer of moss andclay was introduced beneath it, to preventany infiltration from taking place.

The weight of the caissoon wasof water.

It was towed out by two capstans andropes, and in less than ten minutes wasfirmly fixed in its place. By some ac-cident the bottom carried with it some ofthe small timbers of the platform, uponwhich it was constructed, which pre-vented the caissoon from being laid onthe bed of moss prepared to receive it.

These were removed by passing smallrollers by means of ropes under thebottom, which fished out all that ob-structed it.

To attach the lower course of masonryto the timber platform, each alternatestone was usually fastened by two bolts,one entering the stone, and the otherthe main timber on which it rested, but De Cessart,not finding this always effectual, adopted anotherplan ; after the first course of stones was placedupon the platform, he secured the second by irons,and the timbers which were worked into the masonryto receive the planking of the aprons above andbelow the lock, were attached by bent irons placedat regular distances of 3 feet, 14 lines in thickness. 252 ’

Bordeaux is a fine harbour on the Garonne , and although situated at a distance of aboutseventy miles fVom its mouth, there is sufficient depth of water in this noble river to enablelarge vessels to come up to the quays of the city.

At the entrance into the river, the distance between Point de la Coubre on the northand Point de Grave on the south is nearly four leagues; there are, however, extensivesand-banks which are dangerous to the navigation, and some considerable rocks, on one ofwhich is placed the celebrated Tour de Cordouan, which has now a revolving light, some-times showing brilliantly, then feebly, and then eclipsed ; in clear weather it may be seen foreight or nine leagues.

Marseilles is a sea-port of great antiquity, and situated in 43° 17' north latitude, and5° 22J' east longitude. The harbour, surrounded by strong fortifications, is a capacious

ft— tf-

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Fig. 251.

ELEVATION.