Volcanos. 1 39 



The author then adverts to the mineral nature of the general 

 subterranean bed of crystalline rock, (or lava.) This he con- 

 cludes to be probably granitic ; and supposes that some of the 

 elevated portions of it, may, by the effect of repeated intumes- 

 cences, and reconsolidations, under varying circumstances of 

 temperature and pressure, by which the component minerals 

 would be more or less disintegrated, decomposed, and their ele- 

 ments recombined in new proportions, and on separate points, 

 have been converted into syenite, greenstone, porphyry, com- 

 pact felspar, serpentine, diallage rock, fee. The analogy of or- 

 dinary volcanic rocks, in which such changes to a certain extent, 

 indisputably take place under similar circumstances, supports 

 this conjecture ; and since all the above varieties of rock are 

 found in nature to graduate into one another, it cannot be unrea- 

 sonable to suppose all may have been elaborated from the same 

 raw material." 



The sequel of the analysis might be omitted with less in- 

 jury than the preceding, because the authors views are more 

 hypothetical ; but long as this article has been, we are not 

 willing to suppress the remainder. 



"*The work would appear to have terminated naturally here, 

 at least the author is anxious to keep the part of which we have 

 now given a summary, and in which he has endeavored to con- 

 fine himself within the bounds of strict logical inference, (dedu- 

 cing from the evidence of the volcanic phenomena, a certain de- 

 gree of knowledge as to the nature and mode of operation of 

 subterranean caloric, and applying this knowledge to account a3 

 well for the detail of these phenomena, as for the inequalities in 

 the surface of the globe,) separate from the concluding chapter, 

 which contains theoretical matter of a more general and less sub- 

 stantial character ; in short, an attempt to sketch the outline of 

 what may be called the History of the Globe. 



" To this, indeed, the author was naturally led by the results 

 of his previous investigations ; for having proved the existence 

 of a vast subterranean reservoir of caloric, the effect of which is 

 still to occasion violent changes in the superficial crust of the 

 globe, and which appears to have formerly produced similar 

 changes of far greater magnitude, it is impossible not to suppose 

 the same cause to have had a large share in the original forma- 

 tion and disposition of that crust. In fact, the elevating process, 

 which, in the foregoing chapter, is shown to have produced the 

 present irregular disposition of the superficial rocks, presupposes 

 a peculiar arrangement of these beds, previous to their eleva- 

 tion above the sea level. 



