Granilic Rocks of Mont Blanc. 125 



they have been referred, and especially from the position of 

 that of Mont Blanc in the midst of the enormous mass of 

 which it is as it were the centre, a position analogous to that 

 yery generally given to true granites in other chains. 



It may in the first place be answered that this last cha- 

 racter ought never alone to serve in establishing a conclusion 

 on the anteriority of a rock, and that it can in no way 

 weaken the proofs I have drawn from the mixtures of this 

 rock, and the associations and gradations that unite it with 

 others ; but moreover, what is there extraordinary in meet- 

 ing with the most crystalline rocks of a formation towards 

 the centre and most elevated parts of the masses that it con- 

 stitutes ? it appears, on the contrary, that reasoning leads 

 one to presume that it ought generally to be so, since these 

 more crystalline masses would better resist all the causes 

 of destruction than others ; following up this idea, which is but 

 natural, one is led to conjecture that Mont Blanc remains 

 now the highest and most central eminence of the formation 

 of which it is a part, only because it has been, at its forma- 

 tion, the most crystalline part of it, and consequently the 

 most solid. 



Summing up all the geological facts which I have endea- 

 voured to prove in the course of this memoir, it appears, — 



1st. That the granitic rocks of Mont Blanc, and others 

 resembling them of the high summits of the Alps (from the 

 Mont Cenis to St. Gothard), are not granites, and that con- 

 sequently there does not appear to be any true granite in 

 these high crests ; 



2d. That these granitic rocks are but extreme varieties 

 (more crystalline and more abounding in felspar) of a talcose 

 felspathic rock much more abundant in the Alps, and with 

 which it is found united ; 



3d. That this talcose rock, also associated with other 

 talcose rocks, constitutes a peculiar formation, predominant 

 in a great part of the Alps ; 



4th. That ores of metals almost always occur as beds in 

 this formation ; 



