324 How Volcanic Fires may be Jupported. [Book VI. 



true fources of lava, It feems, however, after all, dif- 

 ficult to conceive that fuch extenfive and intenfe fires 

 fhould be maintained without the accefs of confider- 

 able quantities of air; that fluid may therefore be 

 poffibly fupplied by a communication with fome exten- 

 five caverns, which may themfelves receive it by open- . 

 ings at the difiance of many miles from the crater of 

 the volcano. It does not feetn improbable that the 

 volcanoes, which now burn, may have a communica- 

 tion with the cavities and craters of extinguished vol- 

 canoes, and thence derive a fupply of air Sufficient to 

 account for the inflammation of large beds of pyrites 

 and bituminous matters. M. BufFon fuppofes, that 

 the feat of volcanic fires is fituatcd but a very little 

 way below the bed of the mountains ; but it appears 

 more probable, that it is in general many miles below 

 the fur face of the earth, for the quantity of matter dif- 

 rhargcd from ./Etna alone is fuppofed, on a moderate 

 calculation, to exceed twenty times the original bulk 

 of the mountain, and therefore could not have been 

 derived from its contents alone, but muft come from 

 the deeper recedes of the earth. 



M. Condamine afferts, that all the mountains in the 

 .neighbourhood of Naples exhibit undoubted marks of 

 a volcanic origin. He fays, he could trace the lava, 

 and other productions of Subterraneous fire, from Na- 

 pks to the very gates of Rome, pervading the whole 

 foil, fometimes pure and fometimes differently com- 

 bined. " Wherever I fee," fays he, " on an elevated 

 plain, a circular bafon, fu-rrounded with calcined rocks, 

 I am not deceived by the verdure of the adjacent 

 fields ; I. can difcover, beneath the fnow itfelf, the 

 traces of an extinguished fire. If there is a breach in 

 the circle, I ufually find out, by following the decli- 

 vity of the ground, the traces oa rivulet, or the bed 



of 



