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There is but one sea, which has so existed no doubt from the beginning of things. It has sources of its own, from which its impulses and tides are derived. As with the raging sea, so with this gentler kind of water, there is a vast supply55 in secret, which no river course can drain dry. The exact explanation of its reserve strength has not yet been discovered. It is only the superfluous portion of it that is released. Now, there are some of these beliefs to which we may safely subscribe; but I hold this further opinion. My firm conviction is that the earth is organised by nature much after the plan of our bodies, in which there are both veins and arteries, the former blood-vessels, the latter air-vessels. In the earth likewise there are some routes by which water passes, and some by which air. So exactly alike is the resemblance to our bodies in nature’s formation of the earth, that our ancestors have spoken of veins (= springs) of water. Again, in our bodies there is not merely blood, but many other kinds of moisture, some essential to life, others tainted and somewhat thick—brain in the head, marrow in the bones, mucus, saliva, tears, and a kind of lubricating substance that suffuses the joints, and enables them to turn more quickly (= synovial fluid).
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So, too, in the earth there are several different kinds of moisture. There are some kinds that grow hard when fully formed. Hence arises all the metalliferous soil, from which our avarice seeks gold and silver. Then there is the kind which turns from liquid into stone. In some localities the earth and its moisture combine to form a liquid like bitumen and other substances of the same kind. There, then, we find the cause of waters produced according to the law and will of nature. But as in our bodies, so in the earth, humours often contract taints of various kinds. A blow, or some shock, or exhaustion of the ground, or cold or heat injures the natural vigour. A vein of sulphur, too, may solidify the moisture, lasting for a longer or shorter time. Therefore, as in our bodies, when a vein is cut, the flow of blood lasts till the blood is exhausted or the incision in the vein has closed up and stopped it, or until some other cause has staunched the blood; in like manner in the ground, when the seams have been loosened and laid bare, a stream or river rushes forth. The way in which the water is used up depends on the extent of the opening in the seam. At one point its flow is checked by some obstacle; at another it heals up, so to speak, into a scar and chokes the path it had made; at another the power of transmutation, which we have said the earth possesses, reaches its limit and cannot longer supply material that may be liquefied: sometimes the exhausted source is replenished, now by energy self-recruited, now by a supply drawn from external sources. For I ought to say that often dry objects placed opposite to wet attract the moisture to them. Earth itself, which easily assumes another form, often wastes away, and is dissolved in moisture. The same phenomenon occurs under the earth as above it in the clouds; becoming too dense and heavy to retain longer its own character, solid begets liquid. There is often a gathering of thin, scattered moisture like dew, which from many points flows into one spot. The dowsers call it sweat, because a kind of drop is either squeezed out by the pressure of the ground or raised by the heat. This slender trickle scarce suffices to form a spring. But if the sources are great and the gatherings great, rivers issue. Sometimes they flow gently if the water merely descends by its own weight, sometimes with violence and loud roar if air be intermingled and eject the water.