158 EFFECTS of HEAT 



eruptions of Mount Vefuvius. Some of thefe, as marble and gyp- 

 fum, are incapable in freedom of refitting the action of fire. We 

 have likewife granite, fchiftus, gneifs,and ftones of every known 

 clafs, befides many which have never, on any other occafion, 

 been found at the furface of our globe. The circumftance of 

 thefe fubftances having been thrown out, unaffected by the 

 fire, proves, that it has proceeded from a fource, not only as 

 deep, but deeper, than their native beds ; and as they exhibit 

 fpecimens of every clafs of minerals, the formation of which 

 we pretend to explain, we need inquire no further into the 

 depth of the Vefuvian fire, which has thus been proved to 

 reach below the range of our fpeculations. 



Volcanic fire is fubject to perpetual and irregular varia- 

 tions of intenfity, and to fudden and violent renewal, after 

 long periods of abfolute cefiation. Thefe variations and inter- 

 miflions, are likewife effential attributes of fire as employed by 

 Dr Hutton ; for fome geological fcenes prove, that the indura- 

 ting caufe has acted repeatedly on the fame fubftance, and that, 

 during the intervals of that action, it had ceafed entirely. 

 This circumftance affords a complete anfwer to an argument 

 lately urged againft the Huttonian Theory, founded on the 

 wafte of heat which mull have taken place, as it is alleged, 

 through the furface. For if, after abfolute cefiation, a power 

 of renewal exifts in nature, the idea of wafte by continuance 

 is quite inapplicable. 



The external phenomena of volcanoes are fufBciently well 

 known ; but our fubject leads us to inquire into their internal 

 actions. This we are enabled to do by means of the foregoing 

 experiments, in fo far as the carbonate of lime is concerned. 



Some experiments which I formerly* laid before this So- 

 ciety and the public, combined with thofe mentioned in this 



paper, 



* Edinburgh I'ranfaBions, Vol. V. Part I. p. 60 — 66. 



