2The soft species have this advantage, that when recently taken from the quarry they are easily worked, and answer well under cover; but when used in open and exposed situations, and subjected to the action of the frost and rain, they soon become friable, and moulder away. They are also much affected by the salt near the sea-shore, and are not capable of preserving their strength when exposed to great heat. The Tiburtine stones, and those of a similar nature, resist great weights no less than the action of the weather, but are easily injured by fire. The instant they are exposed to that they are ruined, from their possessing so small a quantity of moisture; their earthy particles, also, are few, and the quantity of air and fire in them considerable. Hence, from the small portion of earth and water which they contain, the fire easily acts upon them, and, occupying the interstices, drives out the air with accumulated violence, and communicates its own hot quality to them.
2All these soft kinds have the advantage that they can be easily worked as soon as they have been taken from the quarries. Under cover they play their part well; but in open and exposed situations the frost and rime make them crumble, and they go to pieces. On the seacoast, too, the salt eats away and dissolves them, nor can they stand great heat either. But travertine and all stone of that class can stand injury whether from a heavy load laid upon it or from the weather; exposure to fire, however, it cannot bear, but splits and cracks to pieces at once. This is because in its natural composition there is but little moisture and not much of the earthy, but a great deal of air and of fire. Therefore, it is not only without the earthy and watery elements, but when fire, expelling the air from it by the operation and force of heat, penetrates into its inmost parts and occupies the empty spaces of the fissures, there comes a great glow and the stone is made to burn as fiercely as do the particles of fire itself.