3There are some hot springs from which water of an excellent flavour is procured, so pleasant to the taste, that it is inferior neither to that of the fountains of the Camænæ nor of the Martian aqueduct. These are naturally so, on the following account. When fire is generated under ground, and the soil is heated all round, either from abundance of alum, bitumen, or sulphur, the hot vapour ascends to the upper parts, and, if there are therein springs of sweet water affected by its spreading through the pores, they grow hot, without injury to the flavour.
3There are, however, some hot springs that supply water of the best taste, which is so delightful to drink that one does not think with regret of the Fountain of the Muses or the Marcian aqueduct. These hot springs are produced naturally, in the following manner. When fire is kindled down beneath in alum or asphalt or sulphur, it makes the earth immediately over it very hot, and emits a glowing heat to the parts still farther above it, so that if there are any springs of sweet water found in the upper strata, they begin to boil in their fissures when they are met by this heat, and so they run out with their taste unimpaired.