2That these lands are affected with heat, as surmised, is evident, because in the mountains of Cumæ and at Baiæ, sweating places are excavated, in which the hot vapour rising upwards from the intensity of the fire, strikes through the earth, and so escapes in these places that they are singularly beneficial for the purpose. It is moreover said that in former times fires under Vesuvius existed in abundance, and thence evolved flames about the fields. Thus that which we call sponge-stone, or Pompeian pumice-stone, burnt from another species of stone, appears to be acted on by fire so as to possess a quality of this sort.
2That there is burning heat in these regions may be proved by the further fact that in the mountains near Baiae, which belongs to the Cumaeans, there are places excavated to serve as sweating-baths, where the intense heat that comes from far below bores its way through the earth, owing to the force of the fire, and passing up appears in these regions, thus making remarkably good sweating-baths. Likewise also it is related that in ancient times the tides of heat, swelling and overflowing from under Mt. Vesuvius, vomited forth fire from the mountain upon the neighbouring country. Hence, what is called “sponge-stone” or “Pompeian pumice” appears to have been reduced by burning from another kind of stone to the condition of the kind which we see.