Considerations on Volcanoes. 369 



elevation of the strata beneath ; and this portion of the chapter is 

 accompanied with a list of useful references, for which we must, 

 ourselves, refer to it. 



" Systems of volcanoes'* forms the title of the ninth chapter ; 

 and this is assuredly one of the most interesting departments in 

 the history of volcanoes. In this case, also, the linear arrange- 

 ment is a very remarkable fact ; and as the author's collection of 

 examples is too long for us even to abridge, we must again refer 

 to the original, which is accompanied by a sketch. It is probable 

 that the open volcano, on any one line of extinct ones, is a spiracle 

 to a large portion of the internal fissure ; and a casual obstruction 

 of it thus leads to earthquakes and new eruptions. Safety-valve, 

 our author's term, is very explicit. 



In Venezuela and the adjacent country, after each set of earth- 

 quakes, fissures are produced in the rocks, and after each the 

 levels are observed to be raised. And reasoning on the proba- 

 bility, that the " transmission of caloric," as the author expresses 

 it, from the centre to the circumference of the globe, is coeval 

 with creation, he concludes, as others have concluded before him, 

 that the phenomena of elevated and fractured rocks are thus 

 explained ; or that volcanoes are but the continuation of that 

 force, now operating partially, which once, more energetic and 

 acting through longer periods, has elevated all the mountains of 

 the globe. 



Another general conclusion is rather more purely the author's 

 own. It is this, if we can contrive to explain in a few vulgar 

 words the matter of pages, that wherever the volcanic power has 

 found vent, there the strata are least elevated, and that, re- 

 versely, where it has not escaped, we find the highest mountains. 

 For the proofs themselves, being given at some length, and not a 

 little controverted, and again answered by the author himself, we 

 7w?/^ refer once more to the book, as they are far beyond abridg- 

 ment. But considering that he has demonstrated it, he concludes, 

 as others also have supposed, that, as he expresses it in his own 

 peculiar language, " a subterranean bed of intensely heated crys- 

 talline rock, from whose gradual increase of temperature and 

 consequent expansion" " volcanic phenomena arise, must extend 

 generally beneath the surface of the whole globe." And the 

 successive expansive shocks of this subterranean bed, which have 

 elevated the continents, incidentally gave rise to contempora- 

 neous eruptions, or " partial outward intumescences of this mat- 

 ter" on the prolongation of the elevated strata, " more or less 

 distant from the line of maximum elevation, fyc. 



Now, we presume, we have arrived at a general theory of the 

 earth, in the tenth chapter, though that title does not occur till 

 some time afterwards. If it is not very new, it is so much the 

 better, because it will have the support of other opinions. The 



