part that offers the slightest obstruction to their escape and regain their channel above ground. So when Lycus has been swallowed up by the yawning earth, He comes forth far thence, and is born from another source. So is now drunk up, now gliding with silent stream, Is restored to its Argolic waves the mighty Erasinus. In the East as well as the West this happens. The Tigris is absorbed 4 by the earth and after long absence reappears at a point far removed, but undoubtedly the same river. Some fountains cast out their scourings at a fixed period; the fountain Arethuse does so every fifth summer during the Olympic festival. Thence comes the belief that the Alpheus makes its way right from Achaia to Sicily, stealing under sea by secret sluice, and reappearing only when it reaches the coast at Syracuse. On that account, during the days on which the Olympic festival is taking place, the dung of the victims offered in sacrifice being thrown into the stream of the river (Alpheus) turns up in quantity away in Sicily. You have yourself told the story, my dear Lucilius, in your own poem, 5 and so has Virgil, who says in his address to Arethuse: So when thou glid’st beneath Sicilian seas, Never may sea nymph mingle bitter salt waves with thine. In the Carian Chersonese there is a fountain of the Rhodians which at long intervals sends up from its depths certain foul excretions of mud, until it is set free of them by being cleaned out. At certain places 6 wells throw up not merely mud but also leaves, and bits of crockery and any other filthy things that have accumulated in them. The sea does the same everywhere, its nature being to drive ashore all filthy impurities. In the neighbourhood of Messana and Mylae as it boils and tosses in storms it throws up on the beach something actually like ordure, which has a vile smell too. Whence comes the fable that the oxen of the sun are stalled in that neighbourhood. In certain cases of this kind it is difficult to reach the true explanation, especially when the time of the occurrence in question has not actually been observed and is therefore doubtful. But though the immediate and 7 special cause cannot be discovered, there is a general one worth mentioning; all waters when standing and enclosed tend to throw off impurities. In water that has a current the impurities cannot settle, as they are carried down and expelled by the mere force of the stream. The waters which do not throw off foreign bodies that settle in them always boil more or less. As for the sea, it drags from its lowest depths dead bodies, refuse of vegetation, and all kinds of wreckage, and purges itself of them, not merely when its billows rage in a storm but likewise in its calm and peaceful moments. XXVII