72 



DESMABEST. 



[Ch. IV. 



7 







3CC 



showed how the streams of basalt had poured out from craters 

 which still remain in a perfect state.* 



Desmarest. — When sound opinions had thus for twent 

 years prevailed in Europe concerning the true nature of the 



y 



a 



ancient trap-rocks, Werner by his simple dictum caused 

 retrograde movement, and not only overturned the true theory 

 but substituted for it one of the most unphilosophical that 

 can well be imagined. The continued ascendancy of his 

 dogmas on this subject was the more astonishing, because a 

 variety of new and striking facts were d^ly accumulated in 

 favour of the correct opinions previously entertained. Des- 

 marest, after a careful examination of Auvergne, pointed out, 

 first, the most recent volcanos which had their craters still 

 entire, and their streams of lava conforming to the level of 

 the present river-courses. He then showed that there were 

 others of an intermediate epoch, whose craters were nearly 

 effaced, and whose lavas were less intimately connected with 

 the present valleys ; and, lastly, that there were volcanic 

 rocks, still more ancient, without any discernible craters or 

 scorise, and bearing the closest analogy to rocks in other parts 

 of Europe, the igneous origin of which was denied by the 

 school of Freyberg.f 



Desmarest's map of Auvergne was a work of uncommon 

 merit. He first made a trigonometrical survey of the district, 

 and delineated its physical geography with minute accuracy 

 and admirable graphic power. He contrived, at the same 

 time, to express without the aid of colours, many geological 

 details, including the different ages and sometimes even the 

 structure, of the volcanic rocks, and distinguishing them from 



They alone who have care- 

 fully studied Auvergne, and traced the different lava streams 

 from their craters to their termination, — the various isolated 

 basaltic cappings, — the relation of some lavas to the present 

 valleys, — the absence of such relations in others, — can appre- 

 ciate the extraordinary fidelity of this elaborate work. JN° 

 other district of equal dimensions in Europe exhibits, perhaps, 

 so beautiful and varied a series of phenomena ; and, forttt- 



* Cuvier, Eloge de Desmarest. and Mem. de l'lnst., Sciences Mathemat. 



f Journ. de Phys. vol. xiii. p. 115 ; et Phys. vol. vi. p. 219. 



the fresh-water and the granitic. 



] 

 ] 



t 







