204 ACTlOy QF HEAT MODIFIED 



But while we remain in suspense as to the prime caus© of thk 

 tremendous agent, many circumstances of importance with 

 regard to it, may fairly become the subjects of observation 

 and discussion. 

 Volcanic fire is Some authors (I conceive through ignorance of the facts) 

 have alleged, that the fire of ^tna and Vesuvius is merely su- 

 perficial. But the depth of its action is sufficiently proved, by 

 the great distance to which the eruptive percussions are felt, 

 and still more, by the substances thrown out uninjured by some 

 eruptions of Mount Vesuvius. Some of these, as marble and 

 gypsum, are incapable in freedom of resiting the action of fire. 

 We have likewise granite, schistus, gneiss, and stones of every 

 known class, besides many which have never, on any other oc- 

 casion; been found at the surface of our globe. The circum- 

 stance of these substances having been thrown out, unaffected 

 by the fire, proves, that it has proceeded from a source, not 

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

 exhibit specimens of every class of minerals, the formation of 

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

 the depth of the Vcsuvian fire, which has thus been pi'oved to 

 reach below the range of our speculations. 

 — and subject Volcanic fire is subject to perpetual and irregular variations 

 andTrreg-iirar ^^ intensity, and to sudden and violent renewal, after long 

 variations. periods of absolute cessation. These variations and intermis- 

 sions, are likewise essential attributes of fire as employed, by 

 Dr. Hutton ; for some geological scenes prove, that the indura- 

 ting cause has acted repeatedly on the. same substance, and 

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

 This circumstance affords a complete answer to an argument 

 lately urged against the Huttonian Theory^ founded on the 

 waste of heat which must have taken place, as it is alleged, 

 through the surface. For if, after absolute cessation, a power 

 of renewal exists in nature, the idea of waste by continuance 

 is quite inapplicable. 



The external phenomena of volcanoes are sufficiently well 

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

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

 ej:pcriments, in so far as the carbonate of lime is concerned. 



•Sor4s 



