210 Professor Hoffmann on the Geological Investigations 



present day we must often return to the descriptions there 

 given, and by much the larger portion of the observations 

 there communicated have been subsequently confirmed in the 

 most striking manner. 



Volcanic district of Central France. After his first residence 

 in Southern Italy, Buch proceeded in 1802 to the south of 

 France ; he first visited the remarkable district of Auvergne, 

 so celebrated for its richness in extinct vqlcanos, and ex- 

 amined the environs of Clermont and Mont d'Or, upon w^hichso 

 much light had been partially throvi^n by the observations of 

 Guettard, Soulavie, Dolomieu, and Faujas de St Fond. He 

 was the first to bring forward anew the discovery made by 

 Dolomieu, that the volcanos rise through granite, a fact, 

 attention to which had repressed the Wernerian doctrines 

 when in their highest repute. He also pointed out, that 

 most of these volcanos consist of a previously unobserved 

 peculiar felspathic rock, which he termed Trap-porphyry, or 

 Domite, from its forming the Puy de Dome. It was then re- 

 garded by him as a granitic mass altered by the inflation pro- 

 duced by vapours, and by imperfect fusion, and he believed 

 that whole mountains of it, like bubbles in a pasty liquid, 

 could be elevated without bursting at the top, and therefore 

 without exhibiting eruptive phenomena. It is the same rock 

 which now generally receives the name of Trachyte, given to 

 it by Haiiy, and of which we know, and that chiefly from 

 BucVs subsequent observations, that it forms the nucleus and 

 the products of the oldest eruptions of all the accurately de- 

 scribed volcanos of the earth.* 



Buch again saw in Auvergne, and more distinctly than 

 before, basalts which were undistinguishable from those of 

 Germany, breaking out in currents at the foot of trachytic 

 hills; and, although he had certainly changed his views very 

 considerably respecting volcanic phenomena, yet the notions 

 he had originally imbibed, as to the formation of basalts, 

 were so deeply rooted in his mind, that he concluded his ac- 

 count of Auvergne with the following words, — " We thus 

 stand astonished and perplexed with the result to which we 



* Sec an elaborate memoir printed in the Transactions of the Berlin 

 Academy, 1812 and 1813, p. 127. 



