122 Ehrenberg’s Discoveries—Notices of Eminent 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 for 
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 distine- 
tion supplies a key to the most extraordinary phenomena, while 
it 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 fot 
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- 
vergne. But as the main additions to sound theory whieh 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 thei 
present form by the long-continued action of fluviatile watel, 
is ee 
* After mentioning Guettard, he says, “ Les mémoires de M. Desmarest, publi¢s 
quelques années aprés, entrainérent tout-dfait opinion publique.” (p. 20- 
