( 54 ) 



by a thick clou'd of the fumes nfiul there, 

 were already half decompofed, though they 

 were evidently parts of that ciiTfent wMch, 

 but a few months before, had been difgorged 

 Jjy the fide of the jnountainv ^ Laftly, ac- 

 cording to the different qualities of th« 

 lavas, arid as they may be ."compofed more 

 or lefs of calcareous, argillaceous, or martial 

 principles, all combinable with fulphureous 

 acidS) a greater of • kfe deGohlpolltioa will 

 be produced* ^ -I J-!03oo i ty:dhi\ 



- The different degrees' of d^eompofition 

 in lavas render them fometimes more, and 

 fbthetimes lefs fufceplible of fufi^n in the 

 furnaee. The parts notydecbinpofed will 

 fufe. A beginiiing decompofidbft renders 

 them ftubborn, andy whtii 4t is complete, 

 they entirely refift the fire. TheCaufe of 

 thefe differences appears to. me fufficiently 

 evident. The more earths are pure the 

 more they refifh fufion. All thofe hitherto 

 known are.infufible, except in .very violent 

 ^res. Their mixture facilitates their fufion, 

 as they thus become a reciprocal flux j and 



