114 M. BnocHANT on the 



Nevertheless, granites have continued very generally to 

 be admitted in many places in the Alpine chain, especially 

 in the enormous mass of which Mont Blanc is the centre 

 and most elevated point. The rock which is there most 

 abundant, has been, and is still very generally called granite- 

 Geologists had observed, it is true, that this granitic rock 

 of Mont Blanc offered many characters, which caused it sen- 

 sibly to differ from the granites observed in other chains. 

 It had been remarked that it contained talc instead of mica, 

 that it was very frequently disposed to a schistose texture, 

 and that it sometimes possessed it. 



Thus many naturalists have thought it right to describe 

 this rock separately, but always as a variety of granite. 

 M. Jurine alone has proceeded further, and has given it 

 another name, that of protogyn';^ on account of the differ- 

 ences which distinguish it from the true granites, M. 

 Brongniart has mentioned it under this name in his classifi- 

 cation of rocks. 



The greater number of geologists have not doubtless 

 judged this distinction and denomination necessary, since 

 they have not adopted it. I had long since remarked these 

 anomalies of the granitic rock of Mont Blanc, and they 

 struck me much more when I began to search in the Alps 

 for the characters of the different formations, such as they 

 have been very generally recognized in many countries far 

 distant from each other.* 



Besides the presence of chlorite talc instead of mica, and 

 the schistose disposition of this rock, I observed that the 

 quartz was disseminated in it in a peculiar manner, and 

 that it was often wanting. 



* Let me be permitted to observe, en passant, that it is rather extra- 

 ordinary, that we have not as yet a satisfactory geological description 

 of the different primitive formations of the Alps, although it lias so 

 often been visited by able geologists. This no doubt arises from the 

 great elevation of this chain, its immense glaciers, and its escarpments, 

 which render geological determinations much more difficult than in low 



