ii Desmarest on the Origin of Valleys 65 



Thus the doctrine of the origin of valleys by the 

 erosive action of the streams which flow in them, though 

 it has been credited to various writers, 1 was first clearly 

 taught from actual concrete examples by Desmarest. The 

 first attempt to trace back the history of a landscape, to 

 show its successive phases, and to connect them all with 

 the continuous operation of the same causes which are still 

 producing like effects, was made by this illustrious native 

 of France. 



So satisfied was Desmarest with the proofs furnished 

 by Auvergne regarding the volcanic origin of basalt, that 

 he coined the term " basalt-lava," with an apology to the 

 mineralogists, and remarked that when once the characters 

 of this rock have been appreciated, it may be recognized 

 everywhere, in spite of the most stupendous degradation. 

 Casting his eye over the map of Europe, and noting the 

 localities from which the occurrence of basalt had been 

 reported, he saw two great regions of ancient volcanic 

 activity in the heart of the continent. One of these lay to 

 the east, along the confines of Saxony and Bohemia into 

 Silesia, from Freiberg to Lignitz ; the other stretched from 

 theEhine above Cologne, through Nassau, Hesse-Darmstadt, 

 and Cassel. 



The map which has been already referred to as accom- 

 panying this remarkable memoir, depicts with great clear- 

 ness the grouping of the volcanoes over a large part of 

 Auvergne. It represents them by distinct kinds of 

 engraving, so as to show four classes differing from each 



1 Thus by Lyell and Murchison it was ascribed to Saussure, Playfair, 

 and Montlosier, Edin. New Phil. Journ. vol. vii. (1829), p. 15. In Eng- 

 land it lias been more commonly assigned to Hutton and Playfair, and to 

 Scrope. 



F 



