The Olive-Tree is likewise very serviceable, if it be put in the Foundations, and Walls of Cities; for after it has been singed a little, and interlaced among the Stones, it lasts for ever, and is out of all danger of Corruption.
Lime is made of White Stones or Flinty Pebbles, the harder the Stones are which 'tis made of, the better it is for Building. That which is made of soft Spongy Stones, is proper for Plastring.
There are five sorts of Sand; viz. Sand that is dug out of the Ground, River Sand, Gravel, Sea-Sand, and Pozzolana, which is a Sand peculiar to some Parts of Italy.
The best Sand is that which being rubb'd between the Hands makes a little Noise, which that Sand does not, which is Earthy, because it is not rough. Another Mark of good Sand is, that when 'tis put upon any Thing that is White and shak'd off, it leaves no Mark behind.
The Sand which is dug out of the Earth has all these Qualities, and is esteem'd the best. Vitruvius makes four sorts of it; viz. White, Black, Red, and Bright like a Carbuncle.
If it happen that there be no good Place to dig Sand in, we may make use of Sea-Sand, or River-Sand, which is likewise better for Plastering than the Sand which is digged, which is excellent for Building, because it drys quickly. Gravel likewise is very good, provided the grosser Parts be taken away. Sea-Sand is worst of all, because 'tis long adrying; and for this Reason, where 'tis made use of in Building, they are forc'd to desist sometimes till it dry.
The Sand which is found near Naples call'd Pozzolana is so proper to make good Mortar, if it be mixed with Lime, that not only in the ordinary Fabricks, but even in the very bottom of the Sea it grows into a wonderful hard Body. In Old Times they made use of it for Moles or Ports of the Sea, for after having made with Piles and Boards a Partition, they fill'd up the whole Compass of the Partition with this Mortar, which dry'd of it self in the middle of the Water and became a solid Body.
ART. II.
Of the Use of the Materials.