Phaedo (111-112)

Phaedo. And the earth there is adorned with all the jewels and also with gold and silver and everything of the sort. For there they are in plain sight, abundant and large and in many places, so that the earth is a sight to make those blessed who look upon it. And there are many animals upon it, and men also, some dwelling inland, others on the coasts of the air, as we dwell about the sea, and others on islands, which the air flows around, near the mainland; and in short, what water and the sea are in our lives, air is in theirs, and what the air is to us, ether is to them. And the seasons are so tempered that people there have no diseases and live much longer than we, and in sight and hearing and wisdom and all such things are as much superior to us as air is purer than water or the ether than air. And they have sacred groves and temples of the gods, in which the gods really dwell, and they have intercourse with the gods by speech and prophecies and visions, and they see the sun and moon and stars as they really are, and in all other ways their blessedness is in accord with this. Such then is the nature of the earth as a whole, and of the things around it. But round about the whole earth, in the hollows of it, are many regions, some deeper and wider than that in which we live, some deeper but with a narrower opening than ours, and some also less in depth and wider. Now all these are connected with one another by many subterranean channels, some larger and some smaller, which are bored in all of them, and there are passages through which much water flows from one to another as into mixing bowls; and there are everlasting rivers of huge size under the earth, flowing with hot and cold water; and there is much fire, and great rivers of fire, and many streams of mud, some thinner and some thicker, like the rivers of mud that flow before the lava in Sicily, and the lava itself. These fill the various regions as they happen to flow to one or another at any time. Now a kind of oscillation within the earth moves all these up and down. And the nature of the oscillation is as follows:

Phaedo. One of the chasms of the earth is greater than the rest, and is bored right through the whole earth; this is the one which Homer means when he says:

Far off, the lowest abyss beneath the earth;

[*]and which elsewhere he and many other poets have called Tartarus. For all the rivers flow together into this chasm and flow out of it again, and they have each the nature of the earth through which they flow. And the reason why all the streams flow in and out here is that this liquid matter has no bottom or foundation. So it oscillates and waves up and down, and the air and wind about it do the same; for they follow the liquid both when it moves toward the other side of the earth and when it moves toward this side, and just as the breath of those who breathe blows in and out, so the wind there oscillates with the liquid and causes terrible and irresistible blasts as it rushes in and out. And when the water retires to the region which we call the lower, it flows into the rivers there and fills them up, as if it were pumped into them; and when it leaves that region and comes back to this side, it fills the rivers here; and when the streams are filled they flow through the passages and through the earth and come to the various places to which their different paths lead, where they make seas and marshes, and rivers and springs. Thence they go down again under the earth, some passing around many great regions and others around fewer and smaller places, and flow again into Tartarus, some much below the point where they were sucked out, and some only a little; but all flow in below their exit. Some flow in on the side from which they flowed out, others on the opposite side; and some pass completely around in a circle, coiling about the earth once or several times, like serpents, then descend to the lowest possible depth and fall again into the chasm. Now it is possible to go down from each side to the center, but not beyond, for there the slope rises forward in front of the streams from either side of the earth.