1524

THEORY AND PRACTICE OF ENGINEERING.

Rook II.

extent; these were by degrees united, until large tracts of very valuable land were obtained :Spanish broom and twigs of various trees, as the alder and willow, are well adapted forthis purpose.

The general plan in Tuscany for forming sea or river walls is to lay down a framework forround timbers, which being well secured, bundles of faggots or branches of trees in onedirection are laid upon them, and another layer or several in a contrary direction ; this isrepeated several times, and where the water deposits any earthy matter, it is effectuallyretained.

An earth bank covered with fascines formed in this manner is generally sufficiently pro-tected, and will continue sound for several years.

Fig. 2796.

lisas

pass

Jetties at the entrance of small harbours are frequently for the sake of economy formed withfascines, and the same kindof work is sometimes adopted as a temporary expedient, to facilitatethe construction of others more solid : the height to be given to jetties of this descriptionshould be always proportionate to their extent of base, which generally is as 1 to 3 ;so that a jetty 24 feet in height, where the summit is to be left 5 or 6 feet in width, shouldbe at least 78 feet in width at its base. In setting out the work due regard must be hadto the increasing depth of the water and to the necessary spreading of the base.

To prevent the fascines from being displaced after they are laid, they may be covered

Fig. 2791

Fig. 2799

with a framework of rough timber, over which rods, planks, or boarding may be nailed ortied down : timber 4 or 5 inches in diameter laid with the proper inclination, and securedto the heads of inclined piles driven for the purpose, may be covered with smaller timberlaid in squares, and the interstices filled either with stone, chalk, or gravel; where there isa deposit from the water, land may be gained by allowing filtration through such em-bankments, taking care to retain the solid matter, for which purpose baskets closely wovenare well adapted; the foot of such jetties should be well protected at the toe by a row ofpiles.