In some places it contains voids that have no moisture. Though there is no light there to show the distinctions in the air, yet I venture to assert that cloud and mist settle in that gloom. Above ground 2 cloud and mist surely do not exist because they are seen; but, rather, they are seen because they exist. Well, there too rivers none the less exist that they are not seen. You must understand that down there rivers flow equal in size to our own. Some glide gently, others resound as they tumble down headlong over the broken ground. So must not you equally allow that there are some lakes underground and some water in pools without an exit? This being so, it is of necessity that 3 the air be charged with moisture, and that, being charged, it lean in one direction, raising the wind by its propulsion. We must recognise, therefore, that from those subterranean clouds blasts of wind are raised in the dark, what time they have gathered strength sufficient to remove the obstacles presented by the earth, or can seize upon some open path for their exit, and from this cavernous retreat can escape toward the abodes of men. Now it is obvious that underground 4 there are large quantities of sulphur and other substances no less inflammable. When the air in search of a path of escape works its tortuous way through ground of this nature, it necessarily kindles fire by the mere friction. By and by, as the flames spread more widely, any sluggish air there may be is also rarefied and set in motion; a way of escape is sought with great roaring and violence. This point I will elaborate in more detail when I go on to treat of earthquakes. XV You must now allow me to tell you a little story! Asclepiodotus 1 vouches for the tale. Once on a time a large party of miners was sent down by Philip into an old mine, long since abandoned, to ascertain its prospects and condition, and to see whether ancient avarice had left anything for posterity to glean. Down they went with plenty of light to last for days. In due time, when they were quite tired by the length of the road, they saw a sight to make their hair stand on end--huge rivers and vast reservoirs of sluggish waters, equal in size to any above ground, not pressed down either with a weight of earth above, but overarched with an open vault. I confess I felt lively satisfaction in reading the story. It showed me that the vices from which our age 2 suffers are not new; they have been handed down from ancient days. Nor is it in our age that avarice has for the first time ransacked the reefs of soil and stone, searching in the dark for treasure badly hidden. Those ancestors of ours, whom we are always vaunting, our declension from whose standard we constantly bemoan, were also lured by hope to cut down the mountains and stand beneath the ruins to gloat over their filthy lucre.