XVlll APPENDIX.

produced a solid wall.” The author adds, “ that sand should be procured for this purpose from the sea-coast between CumEe and the promontory of Minerva,” which seems to be considered by him as most efficient in forming the cement here alluded to.

If the beams could not, however, be firmly fixed, on account of the action of tides or currents, or from being too much exposed to a heavy swell from the open sea, a strong buttress is recommended by Vitruvius to be built upon the water’s edge, and a portion somewhat less than half the upper surface of the buttress to be constructed upon a horizontal level, the remaining part inclining towards the sea. Upon the edges of this part of the buttress walls were to be raised to the height of the level part, of a foot and a half in thickness, and the intermediate space filled with sand. Upon this foundation a solid pile, we are told, may be built, which, after being finished, should be left to dry for two months at least. The walls which were raised upon the edges of the inclined surface of the buttress, and which seemed to confine the sand, should then be destroyed ; and the water, in washing away the sand by degrees, will undermine the pile, and cause it to be precipitated into the sea.

This operation should be repeated until the whole is complete.

In places, however, (Vitruvius observes) where this sand is not to be procured, other methods must be resorted to. The space, which the mole is intended to occupy, having been inclosed by a double range of beams connected by planks and chains, the interval between the ranges should be filled with loam, rammed into baskets made of the ulva palustris. The space being filled by masses of this kind, stowed as closely together as possible, the water contained in the inclosed area may be removed by engines calculated for the purpose, such as cochleae, rotae, and tympana ; and when the ground is left perfectly dry, the foundations may be dug of greater width than the walls they are intended to support, and filled in with rough stone, lime, and sand. Piles of charred alder, olive, or oak, must first be driven into the ground if it be soft, and the intervals between them filled with charred wood, in the manner recommended