( 3°/- ) 

 I fliould wander beyond the limits I 

 have propofed to myfelf, fhould I proceed 

 to confider the nature of the ftony fub- 

 ftances which have been a£ted on by vol- 

 canic fires out of Italy, and have been de- 

 fcribed by naturalifts of experience and 

 worthy of credit. I fhall only fay that 

 thefe defcriptions are fufficient to fhow that 

 they are all, or almoft all, rocks or com- 

 pound flones. As therefore the fires of 

 volcanos extend to a prodigious depth, 

 as may be deduced from the vafi; moun- 

 tains they raife above the earth ; it follows 

 that thefe rocks, befides conftituting nu- 

 merous chains of very lofty mountains, 

 defcend to an immenfe depth, even in 

 thofe places where we fhould not know- 

 that they exifted, were they not difcover- 

 ed by fiery eruptions. We thus perceive 

 how extenfively thofe rocks contribute to 

 form the rind, or fuperficial coating, of 

 this globe ; the only part of it which 

 man is permitted to examine ; and which 

 we never could have obtained knowledge 



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