88 A DESCRIPTION OF THE [Ch. V. 



limestones, chlorite-schist mixed frequently with magnetic 

 ironstone, and, lastly, talc- schist; in the midst of which, the 

 felspathic talc-rocks occur, either in the form of subordinate 

 beds, or connected with them by gradually passing into each 

 other. 



This felspathic talc-rock is the granitic rock of Mont 

 Blanc. Its principal constituent parts are felspar and talc : 

 the talc is generally of a greenish colour, and often traverses 

 the rock in the form of small veins. This rock has always a 

 tendency to the slaty texture, and even becomes sometimes 

 decidedly foliated ; and it is worthy of remark, that the speci- 

 mens taken from the summit of Mont Blanc present the same 

 character. The only difference between these massive and 

 slaty rocks is, that in the granitoid rock, the felspar most 

 abounds ; and in the schist, the talc : just as the analogous 

 case of greenstone and syenite. Quartz is, indeed, also found 

 in this granitic rock, but it is of rare occurrence; and it 

 exists rather as scattered nodules, irregularly grouped, than 

 as crystalline grains uniformly disseminated throughout the 

 mass, after the manner of true granite. 



These mineralogical characters, says M. Brochant, con- 

 joined with the geological relations of this rock (viz. its 

 association with talc-schist, serpentine, and greenstone, and, 

 above ah 1 , its containing and gradually passing into felspathic 

 talc-schist,) clearly indicate that this rock is not a granite, 

 but only a crystalline variety of the felspathic talc-schist with 

 which it is interstratified. And it may be farther remarked, 

 that the metallic minerals generally occur in true granite, in 

 gneiss, and in mica-slate, in the form of veins ; whilst, in the 

 talcose rocks of the Alps, they are seldom met with : and 

 when found, are always in the state of bunches or beds. 



Although true granite is not to be met with in the highest 

 parts of the Alps, this rock is not entirely wanting in this 

 mountain range : for the lower parts on the side of Piedmont, 

 from Yvree, and indeed from Turin, as far as Lago Maggiore, 

 are composed of granite. This rock is well characterised, 



