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;
Footnote 1Hom. Il. 8.14 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.