So, too, in the earth there are several different kinds of moisture. There are some kinds that grow hard when fully formed. Hence arises 4 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 5 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 6 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, 7 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. XVI