Book II.

1522 THEORY AND PRACTICE OF ENGINEERING.

be made to roll along the parapet, and by means of a windlass be raised or lowered asrequired.

The Spandrills and Wing-walls should progress as soon as the centres are struck, and wecannot do better than refer to the construction of London Bridge for the manner in whichthey are to be carried up.

CHAP. XXVI.

ON THE CONSTRUCTION OF FASCINES AND BASKET-WORK FOR JETTIES.

—RIVER, SEA, AND DOCK WALLS.

In many parts of Italy gabions made of twigs and branches, in the manner ofbasket-work, are filled with stones laid one on the other, to form rivers and sea walls : thismethod is both expeditious and convenient, and when laid down and covered withsand or mud, it is several years before the basket-work is destroyed, and the stones becomeconsolidated and requirelittle further adjustment:such osier-work may bemade where it is to beused, and as the manufac-ture advances, the basketscan be filled with stones orother hard material.

The cylindrical formgathered in at the top isgiven by placing eight up-right rods on the ground,with a hoop to hold themin at the top; the osiers arethen woven in alternatelyup to the hoop; the eightrods are then united atthe summit, and the wholefinished to the requiredform.

There are several varietiesof this work, which is ad-mirably adapted to thepurpose for which it is em-ployed ; sometimes a breachin a river wall is stoppedby laying in several rowsof these gabions, whichserve the purpose of sand-bags. When shell-fish,muscles, &c. attach them-selves to works of this kind,they should not be removed,as they contribute verymuch to their consolidation;to protect banks so formed from injury from boats, fender piles are driven in at convenieidistances.

Rods 15 or 16 feet in length, interlaced round the heads of several piles driven eitherrows or around a circle, form a very efficient barrier to ordinary streams, and when severrows are repeated, filled in with chalk or stones, will last a considerable time : such was tlpractice on the banks of the Thames, but the wash now produced by the steam-boats hoccasioned this practice to be abandoned, and a more efficient one to be introduced, whiconsists of dressing the slope of the banks and laying on them a pavement of heavy stone.

Wherever sand is deposited by the waters on a coast, and it is desirable to retain it ithe purpose of forming a sea-wall: that which is furthest distant from low water is fi:secured by small bands of osier or basket-work; the winds not having any power to scatlit, in the course of a short time it becomes consolidated; should any clayey or eart

Fig. 2788.

Fig. 2790.

mmm

wm

Fig. 2789.