[Sidenote: Description of the interior of the earth and of the subterranean seas and rivers.] Such is the nature of the whole earth, and of the things which are around the earth; and there are divers regions in the hollows on the face of the globe everywhere, some of them deeper and more extended than that which we inhabit, others deeper but with a narrower opening than ours, and some are shallower and also wider. All have numerous perforations, and there are passages broad and narrow in the interior of the earth, connecting them with one another; and there flows out of and into them, as into basins, a vast tide of water, and huge subterranean streams of perennial rivers, and springs hot and cold, and a great fire, and great rivers of fire, and streams of liquid mud, thin or thick (like the rivers of mud in Sicily, and the lava streams which follow them), and the regions about which they happen to flow are filled up with them. And there is a swinging or see-saw in 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 112 describes in the words,— ‘Far off, where is the inmost depth beneath the earth;’ [Sidenote: _The four rivers of the world below._] 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