9. The wave, as it advances, possesses a kind of power, which some call the purging of the sea, to eject all foreign substances. It is by this force that dead bodies and wrecks are cast on shore. But on retiring it does not possess sufficient power to carry back into the sea either dead bodies, wood, or even the lightest substances, such as cork, which may have been cast out by the waves. And by this means when places next the sea fall down, being undermined by the wave, the earth and the water charged with it are cast back again; and the weight [of the mud] working at the same time in conjunction with the force of the advancing tide, it is the sooner brought to settle at the bottom, instead of being carried out far into the sea. The force of the river current ceases at a very little distance beyond its mouth. Otherwise, supposing the rivers had an uninterrupted flow, by degrees the whole ocean would be filled in, from the beach onwards, by the alluvial deposits. And this would be inevitable even were the Euxine deeper than the sea of Sardinia, than which a deeper sea has never been sounded, measuring, as it does, according to Posidonius, about 1000 fathoms.[341] 10. Some, however, may be disinclined to admit this explanation, and would rather have proof from things more manifest to the senses, and which seem to meet us at every turn. Now deluges, earthquakes, eruptions of wind, and risings in the bed of the sea, these things cause the rising of the ocean, as sinking of the bottom causes it to become lower. It is not the case that small volcanic or other islands can be raised up from the sea, and not large ones, nor that all islands can, but not continents, since extensive sinkings of the land no less than small ones have been known; witness the yawning of those chasms which have ingulfed whole districts no less than their cities, as is said to have happened to Bura,[342] Bizone,[343] and many other towns at the time of earthquakes: and there is no more reason why one should rather think Sicily to have been disjoined from the mainland of Italy than cast up from the bottom of the sea by the fires of Ætna, as the Lipari and Pithecussan[344] Isles have been.