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That, where volcanic fire exifts, it will burfl out fuddenly, 

 fometimes in one place and fometimes in another, as it hap- 

 pens to find more or lefs reiiftancc, is well known ; it is alfo 

 certain that the matter of its ejedions muft be various, as the 

 fubftances chance to be, that lie within the fphere of its adivity, 

 or fall within its vortex. That Vefuvius, for inftance, (not to 

 fpeak of extind and dubious volcanoes,) ha^, at fome periods 

 thrown out an immenfe quantity of marble, and other calcareous 

 ftones, in various degrees of calcination, the beft naturalifts that 

 have defcribed that volcano affert, and I can fully confirm, both 

 from adual obfervation, and from the fpecirnens which I col- 

 leded there, and have had the honour to prefent to the Academy. 

 Why then may we not fuppofe that other, and more ancient 

 volcanoes, may have aded upon calcareous matter as well as 

 Vefuvius, and ia a greater quantity? The circumftances of the. 

 prefent cafe feem to demand fuch a fuppofition ; and if it is 

 not inadmiflible on ftrong negative grounds, it invites our affent 

 by giving a clear and eafy explanation of the feveral efFeds in 

 queftion. 



Although, for reafons which I fhall mention, it appears to 

 me evident that the prefent fituation of the filh quarries of 

 Bolca cannot be that of their original formation, yet the great 

 bulk of the maffes that compofe them, will not allow us to be- 

 lieve, that they could ever have been feated very remote from 

 their prefent beds. But as it is abundantly clear, that the place 

 where they were formed muft have been covered with the fea, 

 it feems reafonable to conclude tjjat the fea did then approach 



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