Seneca discusses the nature of earthquake motion. He recognises three kinds of movement--quaking (_succussio_), tilting (_inclinatio_), and trembling (_vibratio_)--and he gives illustrations of the kind of causes to which they may be referred (252). He believes that the extent of country convulsed by an earthquake depends upon the area of the subterranean cavern in which the wind performs its exploits, and as these internal cavities do not continuously underlie vast tracts of the earth’s surface, no large spaces of that surface are simultaneously shaken. In his day there appears to have been no record of a shock affecting the whole basin of the Mediterranean Sea. He thinks that no earthquake ever extends as much as two hundred miles. He cites the recent calamity in Campania, which did not pass beyond that district, though marvellous tales about it had spread far and near, and he gives other examples of the markedly local character of the phenomena, so far as then known. He affirms that maritime districts are those most frequently shaken (255, 257), in proof of which he gives various instances, including the late disaster to Pompeii and Herculaneum in a region which had never been known to be shaken before. He had received information about the Campanian shock, and the narrative in which he embodies it has the interest of being the most detailed account of an earthquake that has come down to us from antiquity. First of all, as already mentioned, he states that the movement was confined to the district of Campania, no mention being made of its having been felt even so near as Rome. He notices the injury done to Herculaneum and to Naples by the damage of public and private buildings; bronze statues were split open and some people were driven out of their minds. He records that Campania continued to tremble for some days after the great shock. He had heard that a flock of six hundred sheep was said to have been killed near Pompeii. Accepting the report as true, he sees no reason to suppose that the animals died of fright, but thinks it not unlikely that they were poisoned by the ascent of pestilential vapours from the ground. This conjecture of his receives perhaps some support from the fact that in this volcanic district, after an eruption of Vesuvius, so much carbonic acid gas has been said to escape from the ground as to suffocate hundreds of hares, pheasants, and partridges. But the most vivid experience of the earthquake which he narrates is that of a grave philosophic friend who, when in his bath, saw the tiles of the floor separate from each other, allowing the water to sink through the opened joints, while the next moment, as the pavement closed again, the water was forced out all bubbling. A better illustration of the transit of a wave of shock could not be desired.