Chap. XXVI.

SEA AND DOCK WALLS.

1531

ties may be placed at regular distances, for protection against the vessels, and rings maybe inserted to make them fast. Sheet-piling should never be omitted to protect the foun-dations.

t~Tt

Fig. 2823.

Where the foundations are chiefly composed of sand, or of an earth liableabsolutely necessary to continue a row of sheet-piling to tile stratum beneaththe piles a crab engine with a ram of 10 cwt. may be made use of, with airom 8 feet to 18 feet, or 12 feet on an average, which will generally drive anstroke. '

to slip, it isit: to drivefall varyinginch at each

Fig. 2824.’

Platforms of carpentry, when laid upon the heads of piles, should be perfectly level, andhoarded through in the longitudinal, as well as transverse, direction; taking proper carefirst to drag between the heads of the piles, and render the intervals solid, by throwing inloose stones or a mass of concrete.

. ^hen foundations are upon gravel, it is very necessary that they should be consolidated,cither by dropping in large stones, or by piling, and afterwards laying over the whole atimber platform, at such depth below low water that it cannot be affected by the tide.