393 



through which they pass to be purely fortuitous. He then states, 

 that he believes Dr. Boud* was the first to point out, in a general 

 manner, the relative position of metalliferous veins and primary un- 

 stratified formations ; and thus to lead to thejinference, that the me- 

 tals were deposited in the former by sublimation from the latter : and 

 he adds, that Baron Humboldt f accounts for the association of the 

 mines of the Oural and Altai mountains with granite, porphyry, and 

 syenite, by supposing all of them to be the effect of volcanic agency, 

 taken in its most extended signification. 



This doctrine, the sublimation of the metalliferous contents of veins 

 from igneous matter, the author states, occurred to him twelve years 

 ago, from observing the deposition of specular iron on the crust of a 

 stream of lava flowing down the side of Vesuvius ; and he was in- 

 duced from that circumstance to institute a series of inquiries, and in 

 further prosecution of the subject, he proposes in the memoir the fol- 

 lowing questions : — 



1st, Is there near each of the known metalliferous deposits any 

 unstratified rock ? 



2ndly, If none is to be found in the immediate vicinity of such de- 

 posits, is there no evidence, derived from the geological constitution 

 of the district, which would lead to the belief that an unstratified 

 rock may extend under the metalliferous district, and at no great 

 distance from the surface of the country ? 



3rdly, Do there exist metalliferous deposits entirely disconnected 

 from unstratified rocks ? 



With respect to the first of these questions, the author shows, by 

 copious references to works on England, Scotland, Ireland, Norway, 

 France, Germany, Hungary, the southern Alps, Russia, and the north- 

 ern shores of the Black Sea, that the great mining districts of all 

 these countries are immediately connected with unstratified rocks ■ 

 and in further support of this solution of the first question, he men- 

 tions the metalliferous porphyries of Mexico, and the auriferous gra- 

 nite of the Orinoco ; but he observes that his knowledge of the 

 mining countries of South America is not sufficient to enable him to 

 state their general geological connexions. 



With reference to the second question, — the probable association 

 of metallic veins with unstratified rocks, though the latter are not 

 visible in the immediate neighbourhood of the former j — the author 

 gives a section of the country between Valorsine and Servoz, and 

 points out the probable extension of the granite of Valorsine under 

 the Aiguelles Rouges and Breven, composed of protogine, chlorite, 

 and talcose schists, to the immediate vicinity of the mines of Servoz, 

 which are situated in the latter formation. He also refers the reader 

 for further illustration to the metallic deposits of Wanlockhead and 

 the Lead-hills ; to the mines of Huelgoet and Poullavaen in Brittany j 

 to those of Macagnaga and Allayna at the foot of Mount Rosa, of 

 Cardinia, Corsica, and Elba j to the metalliferous veins[of the Vosges, 



* Memoire Geologique sur V Allemagne. 



t Essai de Geologie et de Climatologie Asiatique. 



