Granitic Rocks of Mont Blanc. 123 



crystals of felspar that are so well known, appeared to me 

 to belong to the same granite formation. It is known to be 

 worked much on the great scale, principally for buildings, 

 but also to be cut and polished. There exists yet another 

 working of this kind near Domo d'Ossola, and another near 

 Turin ; no doubt the Lago Maggiore, near which the two 

 first quarries are situated, which allows the transport of their 

 products throughout the whole of Lombardy, and the neigh- 

 bourhood of a capital for the other, facilitates this kind of 

 commerce ; but it Is rather extraordinary that they should 

 be, at least according to the information I could collect, the 

 only granite quarries in the Alps from Mont Cenis to St. 

 Gothard ; and this fact alone gives some reason for presum- 

 ing that this kind of rock, and consequently the true granite 

 formation, is at least very rare there. 



This existence of true granite on one of the sides of the 

 Alps, is analogous to that which has been observed in the 

 Pyrennees, where it is known that the granite most com- 

 monly only shews itself at some distance from the centre of 

 the chain. 



This character however, taken separately, could not lead 

 to any opinion on the geological nature of the granitic rocks 

 of Mont Blanc ; it only acquires importance when it is joined 

 to the direct observations that I have made known, I shall 

 add yet another to it, which is not by itself more decisive, 

 but which appears to me equally to add some weight to my 

 first proofs. 



In the granite formation, and especially in those of gneiss 

 and mica slate of other chains, ores of metals are very often 

 found, and generally, more frequently in veins or lodes than 

 in beds or masses. 



In the Alps on the contrary, from Mont Cenis to St. 

 Gothard, the ores of metals are scarce, in all the mines that 

 . I have seen, and in all the situations I have observed, the 

 , ores of lead (at Pesey, Macot, la Thuile, and Corraayeur), 

 those of copper of Olomon, St. Marcel, Servoz, and all the 

 mines of oxidulated iron, are in beds or masses. I am ac- 

 quainted with but two examples of metalliferous veins that 



