the interior of the earth which
moves all this up and down, and is due to the following cause:--There is
a chasm which is the vastest of them all, and pierces right through the
whole earth; this is that chasm which Homer describes in the words,--

'Far off, where is the inmost depth beneath the earth;'

and which he in other places, and many other poets, have called
Tartarus. And the see-saw is caused by the streams flowing into and out
of this chasm, and they each have the nature of the soil through which
they flow. And the reason why the streams are always flowing in and out,
is that the watery element has no bed or bottom, but is swinging and
surging up and down, and the surrounding wind and air do the same; they
follow the water up and down, hither and thither, over the earth--just
as in the act of respiration the air is always in process of inhalation
and exhalation;--and the wind swinging with the water in and out
produces fearful and irresistible blasts: when the waters retire with
a rush into the lower parts of the earth, as they are called, they flow
through the earth in those regions, and fill them up like water raised
by a pump, and then when they leave those regions and rush back hither,
they again fill the hollows here, and when these are filled, flow
through subterranean channels and find their way to their several
places, forming seas, and lakes, and rivers, and springs. Thence they
again enter the earth, some of them making a long circuit into many
lands, others going to a few places and not so distant; and again fall
into Tartarus, some at a point a good deal lower than that at which they
rose, and others not much lower, but all in some degree lower than the
point from which they came. And some burst forth again on the opposite
side, and some on the same side, and some wind round the earth with one
or many folds like the coils of a serpent, and descend as far as they
can, but always return and fall into the chasm. The rivers flowing in
either direction can descend only to the centre and no further, for
opposite to the rivers is a precipice.

Now these rivers are many, and mighty, and diverse, and there are four
principal ones, of which the greatest and outermost is that called
Oceanus, which flows round the earth in a circle; and in the opposite
direction flows Acheron, which passes under the earth through desert
places into the Acherusian lake: this is the lake to the shores of
which the souls o