ON THE ORIGIN AND CAUSES OF SUBTERRANEAN THINGS, BOOK I

heat does indeed dry and warm the earth soaked with water, and it produces various humors and performs many other works of nature. However, its power is not so great that it can warm even cold waters to the point of boiling, or warm veins soaked with humor so that their vapors reach the highest degree of heat. Furthermore, the hot springs of the island opposite the Timavus a river in Italy, which, as Pliny writes, increase and decrease in tandem with the tides of the sea, sufficiently indicate that hot waters do not arise from hot vapors but from a confluence of waters.

A fifth opinion remains, which is that the material through which the waters flow warms them, and that for this reason, some hot waters smell of the poison of sulfur, because they emanate from sulfurous veins. They say this should seem not at all surprising to us, for we can see every day that water poured onto quicklime boils. We, however, although we do not deny that the material through which they run gives hot waters their odor and taste, and even many of their powers, we do not concede that sulfur, bitumen, or anything else that easily catches fire can warm the waters. This is because fire does not lie hidden in them as it does in quicklime, which, when water is poured onto it, is stimulated and warms the water.

Therefore, neither the heat of the sun, nor the wind, nor motion, nor internal heat of the earth, nor the material through which the waters flow can be the cause of hot waters; but rather fire itself, whose property alone it is to place things in the highest degree of heat. But now we must consider again whether that fire, placed under the channels of the waters, warms them, or whether the channels themselves contain it in their bed. The former is an ancient opinion, namely that of Empedocles. He believes that subterranean waters are warmed by fires if they are situated under the ground through which they run their course; no differently than how water is warmed by fires placed underneath while permeating through pipes made of bronze, shaped into dragon-like coils and other twisted and bent figures, so that the cold water entering into them may sustain the same power of the fires for a longer time and be able to exit hot.

However, since the earth’s channels—in order for metals to be generated in them—do not consist of metal but of rocks or earth, they are not similar to bronze pipes but to stone or earthen tubes. Moreover, miners of metals know that fire breaks even the hardest of rocks. And we see that vessels—even if earthen or clay—soaked with moisture cannot endure the lasting and intense heat of fire for long; but they suffer damage and break apart. Therefore, water that flows hot from the same source for many centuries cannot heat up in the channels of the earth as it does in bronze pipes with fire placed underneath. This is perhaps what caused others, when they had judged this with natural sense, to depart somewhat from the opinion of Empedocles and to think that a burning spirit, which is generated by secret subterranean fires, enters the veins, veinlets, and fissures of the rocks into the channels of the water and warms their inner walls, not unlike the heating of baths when fire is poured into them through pipes from burning furnaces.

But a burning spirit cannot warm so much and such perennial water to such a degree...