XXI
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We Stoics also are convinced that it is only air that can attempt such a feat as the production of an earthquake, for than it nothing in the whole realm of nature is more powerful, more energetic; in absence of it even the elements that are most violent lose their force. It is by air that fire is kindled; if you withdraw wind, water is sluggish. Water becomes impetuous only when the blast tosses it with violence. This force it is that has power to scatter vast spaces of earth, to raise from the depths new mountains, and to set in mid-ocean islands hitherto unseen. Can any one doubt that There and Therasia and this island which in our days under our very eyes rose out of the Aegean Sea, were carried up to the light by the force of air?
3
Posidonius will have it that there are two different varieties in the movements of the earth, each with its distinctive name. The one is a quaking when the earth is shaken and moves up and down; the other is a tilting when, like a ship, it leans over to one or other side. I am of opinion that there is still a third variety, which we have a special term to denote. Our forefathers had good reason for speaking of a trembling of the earth, for it is unlike either of the other kinds of movement. On such an occasion things are neither all shaken nor all tilted, but they quiver. In a case of this kind no great damage is usually done; while, on the other hand, a tilting is far more destructive than a shock; for unless a contrary movement set in very quickly from the other side to restore the level, downfall follows of necessity.