II All waters are classed as either standing or running; they are either gathered in one or occupy different channels underground. Some of them are sweet, others have pungent flavours of different kinds, among them salt, bitter, medicinal. Belonging to the last class one may name sulphur, iron, alum waters. The taste shows the quality. Waters of different kinds have many other differences. First there is touch, hot and cold; then weight, light and heavy; then colour, pure, muddy, dark blue, yellowish; then wholesomeness, wholesome and useful, or deadly or capable of petrifaction. Some waters are thin, some thick; some give nourishment, others pass through the system without benefiting it at all; the use of some removes barrenness. III The lie of the ground makes water either stand or run; on a slope it flows down, a plain keeps it in, causing it to stagnate. Sometimes under pressure of air it is forced uphill; it is then driven, it does not flow. Surface water comes from rain; spring water from a natural fountain. There is, however, nothing to prevent surface and spring water in the same spot. This we see in Lake Fucinus, into which the streams drain all the rainfall of the surrounding mountains, while there are also large springs concealed under the surface of the lake itself. So, even when the torrents discharge into it in winter, it preserves its appearance unaltered. IV Let us inquire therefore, in the first place, how the earth can contain sufficient water to maintain the unbroken flow of the rivers, and where such a vast quantity of water comes from. We are surprised that the ocean is not sensible of the additional water derived from rivers. It is no less surprising that the earth is not sensible of the loss of all the water that issues from it. What is it that has so filled it up that it can from its hidden recesses furnish such quantities and continually make good the loss as it does? Whatever explanation we give regarding a river must apply also to streams and springs. V Some are of opinion that the earth receives back all the water it has lost. The sea, therefore, does not get larger, because it does not assimilate the water that runs into it, but forthwith restores it to the earth. For the sea water returns by a secret path, and is filtered in its passage back.[50] Being dashed about as it passes through the endless, winding channels in the ground, it loses its salinity, and, purged of its bitterness in such a variety of ground as it passes through, it eventually changes into pure, fresh water. [50] The ordinary text, as Koeller saw, is evidently wrong. It runs: “For by a secret path the sea water enters the ground and becomes visible, and returns stealthily, and is filtered, etc.” No author can be supposed to have written such a sentence. The restoration must be conjectural. I have adopted what seems simplest and most in keeping with the context. VI