120 M. Brochant on the 



granitic rocks of Mont Blanc, whilst on the contrary, the 

 delations already established between this rock and the tal- 

 cose felspathic schists, make it already presumable that they 

 are two products of the same deposit, in one of which crys- 

 tallization was more developed than in the other. 



If we now add the geological indications I have given to 

 these mineralogical characters, and if we recollect that the 

 rocks of Mont Blanc which have furnished us with these 

 granitic rocks, also afford many rocks decidedly schistose, 

 nearly all mixed with talc, and even completely talcose, 

 since serpentines are met with in it very analogous to other 

 rocks of this kind existing in great masses in the Alps ; 

 lastly, hornblende rocks, actynolite, &c. we cannot help 

 recognizing a striking analogy between this association and 

 that which I have shewn to be common to the true talcose 

 rocks, whilst on the contrary this union of rocks has not yet 

 been observed in the true granites. 



Lastly, to complete these resemblances, our talcose fel- 

 spathic schist exists even in the midst of the granitic rocks 

 of Mont Blanc ; I have observed it in many places, and par- 

 ticularly near the glacier of Talefre ; this talcose schist al- 

 together enters into what is called chlorite schist ; it possesses 

 all its characters ; it is even mixed with oxidulated iron, but 

 it also contains perfectly formed crystals of felspar.* 



This last example appears to me to place the identity of 

 formation as much beyond a doubt as the identity of compo- 

 sition. 



We are led then to admit that the granitic rocks of Mont 

 Blanc can no longer be regarded as granites, not only ac- 

 cording to the mineralogical acceptation at present given to. 

 that denomination, but also according to the geological ac- 

 ceptation ; they are rather extreme varieties of the talcose 

 felspathic schists I have described, rocks forming a part of 

 the talcose rocks of the Alps 3 the granitic mass of Mont 



* Fragments of rocks are often met with on the sides of Mont Blanc, 

 the half of which is chlorite schist, and the other a granitic rock. There 

 exists in the cabinet of M* de Dree a very beautiful specimen which be- 

 longed to Dolomieu, 



