122 Ehrenberg^s Discovei^ies — Notices of Emijient Men. 



of igneous origin in the rocks of that district : and the elder Des- 

 marest, whose examination of them began in 1763, had made that 

 classification of them, which is the basis, and indeed the main 

 substance, of the views still entertained with regard to the struc- 

 ture of that most instructive region. His map of the district, pub- 

 lished in 1774 (in. the Transactions of the Academy of Paris /or 

 1771,' according to a bad habit of that body still prevailing,) ex- 

 hibits the distinction of modern currents of lava, ancient currents, 

 and rocks fused in the places where they now are, which distinc- 

 tion supplies a key to the most extraordinary phenomena, while 

 ii reveals to us a history more wonderful still. But striking and 

 persuasive as this view was, and fitted, apparently, to carry with 

 it universal conviction, the theory which it implied, collected, as 

 it seemed at the time, from one or two obscure spots in Europe, 

 was for a while resisted and almost borne down by the opposite 

 doctrine of the aqueous origin of basalt ; which came from the 

 school of Freyberg, recommended by the power of a connected 

 and comprehensive system,— a power in science so mighty for 

 good and for evil. Montlosier's Essay on the Volcanos of Au- 

 vergne, which appeared first in 1788, was, however, not written 

 with any direct reference to this controversy, but was rather the 

 exposition of the clear and lively views of an acute and sagacious 

 man, writing from the fullness of a perfect acquaintance with the 

 country which he described, in which, indeed, his own estate and 

 abode lay. In its main scheme, although Desmarest's is men- 

 tioned with just praise,* the object of this Essay is to criticise and 

 correct a work of M. Le Grand d'Aussy, entitled Voyage en Au- 

 nergi\e. But as the main additions to sound theory which this 

 work contains, (a point which here concerns us far more than its 

 occasion and temporary effect,) we may, I think, note the mode 

 in which he traces in detail the effects which the more recent 

 currents of lava (those which follow the causes of the existing 

 valleys) must have produced upon the courses of rivers and the 

 position of lakes ; and the idea, at that time a very bold and, I 

 believe, a novel one, that lofty insulated ridges and pinnacles of 

 basalt, which tower over the valleys, have been cut into their 

 present form by ,tlie long-continued action of fluviatile waters, 



* After mentioning Gueltard, he says, " Les incmoires de M. Desmarest, publics 

 quelques annees apres, entrainerent tout-ufait I'opinion publique.\' (p. 20.) 



