Considerations on Volcanoes. 367 



form a basalt ; while it is esteemed a fact in support of this opi- 

 nion, that very different lavas are produced from the same vent. 

 Here the author quotes many references, and as we have not 

 remarked it before, we must not let this pass without saying that 

 wherever there are facts of this nature required, the references 

 are sufficiently numerous for any useful purpose. 



The seventh chapter treats of volcanic mountains ; and though 

 we might, perhaps, esteem it, in some measure, a repetition of 

 much that has gone before, as had also struck us in the previous 

 parts of the work, we have no doubt that the author has perfectly 

 good reasons for his arrangement, and as little doubt in accusing 

 ourselves of want of care and attention in examining the valid 

 causes which have led to this mode of disposing his materials. 



Mr. S., like preceding writers, attributes the well-known circu- 

 lar lakes found in various places, to the destruction of the upper 

 parts of volcanic cones by eruption, and to the consequent lodg- 

 ment of water in the crater, or to the action of an eruption on the 

 sides of the fissure through which it has made its way; which 

 last process, in particular, he dwells upon with some detail ; and 

 he also thinks that such lakes, formed in volcanic craters, may, by 

 their pressure, have burst through the sides, and thus have been one 

 cause of the demolition of volcanic cones. The aqueous eruptions 

 of South America, and the torrents of fish, are, of course, enu- 

 merated among the rest of these phenomena. Those waters which 

 he calls eluvial eruptions, necessarily entangle and carry down 

 stones and mud, forming deposites, which he calls eluvial, and 

 which sometimes are so consolidated as to produce rocks. In 

 these rocks the "divisionary" structure takes place, and he 

 considers that to be regulated by the same laws as the similar 

 struetures occurring in lavas or rocks which appear to have been 

 in fusion ; but which, of course, according to the proofs which 

 he has given, are only rendered fluid by being suspended in hot 

 water and vapour, being, like the others, but mud ; red-hot mud, 

 would, we suppose, express his meaning : but we must refer our 

 reader to this chapter itself; as we fear that we at least should 

 be guilty of repetition, if we were to attempt an abridgment of it, 

 and thus, perhaps, appear to throw blame on the arrangement. 



The eighth chapter on subaqueous volcanoes follows. The phe- 

 nomena have been so often described, that we need not repeat 

 them here. The most important new conclusions drawn are, 

 first, u that when the expansive force of the confined lava has, at 

 length, overcome its antagonist, the tension of the mass, and its 

 temperature, must be proportionately intense ;" and, second, "that 

 the vapour which escapes from the lava, owing to its excessive 

 tension, will be speedily refrigerated," <^c. ; in short, that the cold 

 ocean will condense the hot steam; though we] must beg the 



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