To turn now from water to land. We have already discussed Aristotle’s idea of the gradual transposition of continents and oceans under the control of the celestial bodies. Pliny describes a large number of local changes of land and sea:[140] the building of new land by alluvial deposits, the sudden appearance of land and islands out of the depths of the waters, the separation of islands from the mainland, the tying of islands to the shore, the total disappearance of entire countries beneath the sea—Plato’s Atlantis is given as an example[141]—the collapse of mountains; but in all this, though he tells where such prodigies took place, he rarely tries to explain how and why they happened. EARTHQUAKES AND VOLCANOES The explanation of the causes of earthquakes and volcanoes, however, was attempted by Plato, Aristotle, Pliny, Seneca, and many other writers of antiquity with no small measure of ingenuity. We have seen that ancient philosophers almost universally were of the opinion that the earth is honeycombed with cavities and subterranean passages. Plato said that some of these cavities were filled with water and air but that others contained mighty swamps and streams of fire, including the immense fiery river Pyriphlegethon. The volcanoes of the earth’s surface were outpourings from these internal streams, and their minglings with the atmosphere and strivings to burst forth were the cause of earthquakes.[142] Aristotle, on the other hand, denied the possibility of subterranean fires. According to his scheme of physics the place for fire in the universe was above the sphere of air. He maintained that the dry and smokelike exhalation which causes the winds of the atmosphere not only penetrates into the cavities of the earth from the outside but is generated within the earth’s interior[143] and that when this exhalation tries to escape and is opposed by any obstacle—for example, by the sea—there is a tremendous upheaval and the land is shaken. Seneca[144] and Pliny[145] ascribed the cause of earthquakes to the winds. Pliny believed that after a great storm, in which wind is driven down and compressed in the interior of the earth, it frequently strives to come forth and in so doing shakes the earth’s surface far and wide. Occasionally, if the pressure is too tremendous to be withstood by the crust of the earth, the winds burst through, accompanied by a violent tempest and a rain of sparks and cinders. Aristotle describes such a volcanic eruption in the Eolian (Lipari) Isles.[146] While this was the explanation of violent eruptions, the quiescent volcanic activity of mountains like Etna was usually attributed to a different cause. Pliny[147] speaks of Etna, Chimaera in Lycia, and various other volcanoes as burning, and it would seem that he connected them with such phenomena as burning naphtha wells and pits of bitumen and sulphur. HEIGHT OF MOUNTAINS