After having passed at least three hours on the crater, we descended, and went to a rising ground, about a mile distant from the upper mountain we had just left, and saw there some remains of the foundation of an ancient building; it is of brick, and seems to have been ornamented with white marble, many fragments of which are scattered about. It is called the Philosopher's Tower, and is said to have been inhabited by Empedocles. As the ancients used to sacrifice to the celestial gods on the top of Etna[23], it may very well be the ruin of a temple that served for that purpose. From hence we went a little further over the inclined plain abovementioned, and saw the evident marks of a dreadful torrent of hot water, that came out of the great crater at the time of an eruption of lava in the year 1755, and upon which phaenomenon the Canonico Recupero, our guide, has published a dissertation. Luckily this torrent did not take its course over the inhabited parts of the mountain; as a like accident on Mount Vesuvius in 1631 swept away some towns and villages in its neighbourhood, with thousands of their inhabitants. The common received opinion is, that these eruptions of water proceed from the Volcanos having a communication with the sea; but I rather believe them to proceed merely from depositions of rain water in some of the inward cavities of them. We likewise saw from hence the whole course of ancient lava, the most considerable as to its extent of any known here; it ran into the sea near Taormina, which is not less than thirty miles from the crater whence it issued, and is in many parts fifteen miles in breadth. As the lavas of Etna are very commonly fifteen and twenty miles in length, six or seven in breadth, and fifty feet or more in depth; you may judge, Sir, of the prodigious quantities of matter emitted in a great eruption of this mountain, and of the vast cavities there must necessarily be within its bowels. The most extensive lavas of Vesuvius do not exceed seven miles in length. The operations of nature on the one mountain and the other are certainly the same; but on Mount Etna, all are upon a great scale. As to the nature and quality of their lavas, they are much the same; but I think those of Etna rather blacker, and in general more porous, than those of Vesuvius. In the parts of Etna that we went over, I saw no stratas of pumice stones, which are frequent near Vesuvius, and cover the ancient city of Pompeii; but our guide told us, that there are such in other parts of the mountain. I saw some stratas of what is called here _tufa_; it is the same that covers Herculaneum, and that composes most of the high grounds about Naples; it is, upon examination, a mixture of small pumice stones, ashes, and fragments of lava, which is by time hardened into a sort of stone[24]. In short, I found, with respect to the matter erupted, nothing on Mount Etna that Vesuvius does not produce; and there