VOL. LI.] PHILOSOPHICAL TRANSACTIONS. 453 



been sometimes found floating on the sea, at so great a distance from the shore, 

 as well as from any known volcano, that there can be little doubt of their being 

 thrown up by fires subsisting under the bottom of the ocean. 



From these instances, we may with great probability conclude, that the fires 

 of volcanos produce earthquakes. He does not however suppose that the earth- 

 quakes, which are frequently felt in the neighbourhood of volcanos, are owing 

 to the fires of those v^olcanos themselves ; for volcanos, giving passage to the 

 vapours that are there formed, should rather prevent them, as in the instance at 

 St. Christopher's, before mentioned. We also m.eet with frequent instances 

 confirming the same thing among the Andes. Antonio d'Ulloa (speaking of 

 what happens among these mountains) says, * Experience shows us, that on the 

 fresh breaking out of any volcano it occasions so violent a shock to the earth, 

 that all the villages which are near it are overthrown and destroyed, as it hap- 

 pened in the case of the mountain Carguayraso. This shock, which we may 

 without the least impropriety call an earthquake, is seldom found to accompany 

 the eruptions, after an opening is once made; or if some small trembling is per- 

 ceived, it is very inconsiderable; so that after the volcano has once found a vent 

 the shocks cease, notwithstanding the matter of it continues to be on fire.' The 

 greater earthquakes therefore seem rather to be occasioned by other fires, that 

 lie deeper in the same tract of country; and the eruptions of volcanos, which 

 happen at the same time with earthquakes, may with more probability be as- 

 cribed to those earthquakes than the earthquakes to the eruptions, w^henever at 

 least the earthquakes are of any considerable extent. 



Sect. 3. It may be asked perhaps why we should suppose that several subter- 

 raneous fires exist in the neighbourhood of volcanos? In evidence of this, we 

 have frequent instances of new volcanos breaking out in the neighbourhood of 

 old ones : Carguayraso, just mentioned, may supply us with one example to 

 this purpose; and in the night of the 28th of October 1/46, in which Lima and 

 Callao were destroyed, no less than four new ones burst forth in the adjacent 

 mountains. To the same purpose we may allege the instances of many volcanos 

 lying together in the same tract of country: as for example, the many places, 

 not so few as 40, among the Azores, which either do now, or have formerly 

 sent forth smoke and flames ; the many volcanos also among the Andes, already 

 mentioned: thus Etna, Strombolo, and Vesuvius, and Solfatara too, are all in 

 the same neighbourhood : and Mons. Condamine says he has traced lavas, ex- 

 actly like those of Vesuvius, all the way from Florence to Naples. In Iceland 

 also we have, besides Hecla, not only several other volcanos, but also a great 

 number of places that send up sulphureous vapours. But the examples of this 

 kind are so frequent that there are few instances to be produced of single vol- 

 canos, without evident marks either that there have been others formerly in 



