1826.] Dr, Daubeny on Volcanos, 2J^ 



in such a supposition, for we have instances of lakes formed in a 

 similar manner, in Auvergne, if not near the Rhine ; and remarks, 

 that, ".if the little rivulet that flows at the foot of the Puy de la' 

 Vaclie in the former country was adequate to produce the lake^ 

 of Aidat, there seems no disproportion in attributing to a river 

 of the size of the Jordan, to say nothing of other streams nowise' 

 inconsiderable which must have been affected by the same 

 cause, the formation of a piece of water, such as the Dead Sea ; 

 which, according to the best authorities, is, after all, not more 

 than twenty-four leagues in length, by six or seven in breadth."^ 

 P. 287. ' '■ 



In his account of the volcanos of the New World, it will be' 

 seen that the Professor concurs with Humboldt, with respect to- 

 the formation of Jorullo ; indeed the views of that naturalist,' 

 though expressed, perhaps, in language more metaphorical, like 

 that employed by the Roman poet in speaking of the sudden' 

 rise of the Promontory of Trsezue in ^rgolis,* are, upon the' 

 whole, conformable with those entertained by our author, relative' 

 to the origin of the dome-like masses of trachyte in Auvergne, 

 and even the basaltic dykes, (if they may be so called,) of Hessia. 



The three first lectures or chapters, being occupied by a detail 

 of facts with regard to volcanos, the author proceeds, in the 

 fourth, to some general conclusions on the ph-aenomena them- 

 selves. 



He begins, by considering the theories which have been pro-' 

 posed to explain the cause of volcanos, and having decided in 

 favour of the one suggested by Sir H. Davy's discovery, with" 

 respect to the metallic bases of the earths and alkalies, endea- 

 vours to deduce, in detail, the phsenomena attendant on an 

 eruption from this hypothesis. 



" Let us suppose," he says, "that the nucleus of the earth at 

 a depth of three or four miles either consists of, or contains as a 

 constituent part, combinations of the alkaline and earthy metal- 

 loids, as well as of iron, and the more common metals, with, 

 sulphur, and possibly with carbon. '; 



" These sulphurets are gradually undergoing decomposition, 

 wherever they come into contact with air and water, but, 

 defended by the crust of the globe, just as a mass of potassium 

 is by a coat of its own oxide, when preserved in a dry place, the 

 action goes on too slowly to produce any striking eliect, unless 

 the latter of these agents be present in sufficient quantity. 



'^ Hence, under our continents, the elastic fluids generated by 

 this process are compressed by the superincumbent mass of 

 rock, until they enter probably, into new combinations, or diffuse! 

 themselves through the solid strata. 



* .Extentam tumefecit huraum, ceu spiritus oris 

 Tendore vesciam solet, aut derepta bicornis 

 Terga capri,— Owi'rf, Mctam. 



