6 PHILOSOPHICAL TRANSACTIONS. [aNNO 1770. 



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, it may very well be the ruin of a temple that served 

 for that purpose. Hence they went a little further over the inclined plain above- 

 mentioned, 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. 

 Luckily this torrent did not take its course over the inhabited parts of the moun- 

 tain, as a like accident on mount Vesuvius in l631 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 Sir W. rather believes thpm to pro- 

 ceed merely from depositions of rain water in some of the inward cavities of 

 them. They also saw from hence the whole course of an ancient lava, the most 

 considerable as to its extent of any known here ; it ran into the sea near Taor- 

 mina, which is not less than 30 miles from the crater whence it issued, and is in 

 many parts 15 miles in breadth. As the lavas of Etna are very commonly 15 

 and 20 miles in length, 6 or 7 in breadth, and 50 feet or more in depth, we 

 may judge of the prodigious quantities of matter emitted in a great eruption of 

 this mountain, and of the vast cavities there must nero^^^rily be within its 

 bowels. The most extensive lavas of Vesuvius do "Oi exceed 7 miles in length ; 

 the operations of nature on the one n^-^'iiain and the other are certainly the 

 same ; but on mount Etna, f " '"^ on a great scale. As to the nature and qua- 

 lity of their lavas, th-j >^^^ much the same ; but he thinks those of Etna rather 

 blacker an'' -'" g<^"eral more porous, than those of Vesuvius. In the parts of 

 p^ .- tnat they went over they saw no stratas of pumice stones, which are fre- 

 quent near Vesuvius, and cover the ancient city of Pompeia ; but their guide said, 

 that there are such in other parts of the mountain. Sir W. saw some stratas of 

 what is called here TufFa, it is the same that covers Herculaneum, and that 

 composes most of the high grounds about Naples ; it is on examination a mix- 

 ture of small pumice stones, ashes, and fragments of lava, which is by time har- 

 dened into a sort of stone. In short he found, with respect to the matter 

 erupted, nothing on mount Etna that Vesuvius does not produce, and there 

 certainly is a much greater variety in the erupted matter and lavas of the latter, 

 than of the former ; both abound with pyrites and crystallizations, or rather 

 vitrifications. The sea-shore at the foot of Etna, indeed, abounds with amber, 

 of which there is none found at the foot of Vesuvius. At present there is a 

 much greater quantity of sulphur and salts on the top of Vesuvius than on that 

 of Etna ; but this circumstance varies according to the degree of fermentation 



