corrupt elements of the earth were concentrated in the Western Sea and that waters coming from that quarter were very dangerous unless boiled.[909] The Southern Sea harbored an immense quantity of venomous worms and small animals, and consequently waters from it were not good for cooking or drinking. As we shall see in the next chapter,[910] Giraldus Cambrensis’ discussion of the different qualities of the East and West was probably based in some measure on observation. The same can hardly be said of Hildegard’s theories. We cannot but feel that they were the offspring of an unusually ingenious imagination, though the prophetic abbess undoubtedly attributed them to divine inspiration. Hildegard went on to assert that swamp waters are dangerous from whatever part of the earth they come, since they contain vile and noxious damp elements of the ground and the poisonous spume of worms. Such waters should not be used unboiled except for washing. Well and spring waters which flow from swamps are equally bad, though as a general rule all waters arising from an unsanitary source become purer the farther they flow. Water from deep wells is usually better and smoother (_suavior_) for cooking, drinking, and other uses of man than the water of flowing springs; the latter, in turn, is better than river water, which should be avoided because of the impurities it receives from the air. The water of small, clear, pure rills is excellent for both men and cattle. EFFECT OF LAND ON WATERS WHICH SPRING FROM IT The land itself might produce varying effects on the water within it, and thus on the wells and fountains which spring from it. In summer, William of Conches tells us,[911] the pores of the earth are open, and the warm vapor (_fumus_) contained therein can escape. Consequently the heat of the earth is loosed, and the springs and wells are cooler than in winter, when the cold constricts the earth’s pores and keeps the heat in. It is very easy to understand what gave rise to such a theory when we consider the fact that water always preserves a more uniform temperature than the surrounding air. Hot and putrid springs, the _De imagine mundi_ tells us,[912] are caused by the ground water coming into contact with subterranean caves full of sulphur that is sometimes ignited by the winds. In some places serpents, by poisoning the earth and the ground water which passes through it, indirectly cause the water sources of a region to become noxious.[913] Michael Scot, in a somewhat repetitious and not wholly clear passage, explained in effect that the hot and boiling springs of Italy and Sicily are produced by waters arising out of subterranean cavities where the native heat of the interior of the earth in combination with the winds produces a violent combustion of sulphur and “white-hot rocks” (_petre calidissime_).[914] MIRACULOUS WELLS AND SPRINGS; GEYSERS