124 M. Brochant on the 



are well determined, one of auriferous pyrites, and the othfef 

 of copper pyrites ; but the latter is met with precisely in the 

 environs of Baveno, near the granite formation, and iu the 

 mica slate resting upon it ; and the first in a valley (the Val 

 Anzasca), in the neighbourhood of which the same formation 

 occurs. 



Some other unworked veins of lead and copper have been 

 noticed, that I could not visit, and on which I might raise 

 some doubts ; but many are still, if not in well characterized 

 granite, at least in rocks which I presume to be very nearly 

 allied to it, and not belonging to the talcose formation. 



It is at least very certain that metallic veins are extremely 

 rare in that part of the chain I have noticed, in which the 

 talcose formation predominates ; and that the only two ex- 

 amples I was able to discover, are, the one certainly, and 

 the other very probably in a different formation. 



No doubt geologists have not yet assembled a sufficient 

 number of facts on the occurrence of the ores of metals, so 

 as to assign their existence in beds or veins to epochs relative 

 to the rocks containing them ; yet we cannot help observing 

 a great difference between their mode of occurrence in the 

 Alps and other primitive countries, which might seem, in the 

 first instance, to possess analogies to those I have described. 



I am fully sensible that it will be necessary to endeavour 

 to observe the junction of the true granite of the Alps, and 

 the talcose rocks of the high summits I have noticed, and 

 tinder which I have every reason to believe it dips ; but it 

 has as yet been impossible for me positively to determine this 

 superposition, and I invite geologists, who may visit the 

 Italian Alps, to endeavour to verify it. 



I have not, after all, any want of this last proof for es- 

 tablishing the little relative antiquity of the granitic rocks of 

 the centre of the chain, as it is principally founded on the 

 raineralogical and geological relations of these supposed gra- 

 nites with the talcose felspathic schists, and generally with 

 all the talcose formation so abundant in the Alps. 



Perhaps some would raise an objection drawn from the 

 rarity of the granitic rocks in the talcose formation to which 



