It is well known that there are lakes whose waters bear up those 4 who cannot swim. There used to be a pool in Sicily, there still is one in Syria, in which brickbats float, and no objects thrown in, however heavy, will sink. The cause of it is obvious. Weigh any object and compare it with water while they are equal bulk for bulk. If the water is the heavier, it will bear the object that is lighter than itself, and will raise it above its surface to a height proportionate to its lightness; objects heavier than the water will sink in it. But if the weight of water and of the object compared with it in 5 respect of weight be equal, the object will neither go to the bottom nor yet will it stick up; it will just be in equipoise with the water. It will float, it is true, but almost submerged and without any part projecting. The differences in weight give the reason why some logs float almost entirely above water, while some sink to their centre, and some go down until they are in equipoise with the water. For it always holds good that, when the weights of the two are equal, neither yields to the other; but objects heavier than water sink, those lighter are upborne. Now heavy and light do not refer to our judgment of weight, but are 6 relative to the medium by which an object is to be supported. So when water is heavier than the human body or than a stone, it does not allow the inferior weight to sink. So it comes to pass that in some lakes even stones will not go to the bottom; I mean hard solid stones. There are many light pumice stones, of which in Lydia whole islands that float are composed. Theophrastus is my authority for the statement. I have myself seen a floating island in the lake near Cutiliae. Another is carried about in the Vadimonian Lake, another in the lake by Statonia. The island at Cutiliae contains trees and grows grass, and 7 yet it is borne up by the water, and is wafted now in this direction, now in that, not merely by wind, but even by a mere air. So light the breath that moves it that night and day it never remains stationary in one spot. There are two reasons for it: first, there is the weight of the water, which is medicated and therefore heavy; and then there is the portable material of the island itself, which contains no solid body, although it supports trees. Perhaps in the first instance the 8 thick liquid laid hold upon and made fast light trunks and boughs scattered over the surface of the lake. So also whatever rocks are in the island, you will find porous and hollow. They resemble those formed of moisture that has hardened especially near the banks of medicinal springs; in such cases the scourings of the spring coalesce and the foam is solidified. It is necessarily light, being formed by concretions of windy, empty material.