344 THE GEOLOGY OF THE ALPS. [XIV. 



like structure attributed to this last is questioned by Lory, 

 according to whom the strata of this mountain dip uniformly 

 to the southeast, and are overlaid by the great mass of crystal- 

 line talcose schists and micaceous limestones assigned by him 

 to the trias ; but apparently, as we have endeavored to show, 

 a portion of the pre -carboniferous crystalline schists. These 

 rocks are well displayed further on in the mountain of Cra- 

 mont, and are regarded by Favre as identical with those of 

 Mont Cenis.* Lory conceives that the attitude of the rocks of 

 Mont Chetif to the Jurassic strata in the trough at the southeast 

 base of Mont Blanc is due to a great fault with an uplift, which 

 has brought these older rocks to overlie the Jurassic beds. 



With the facts before us, we can with Favre trace the history 

 of Mont Blanc from the time when over a partially submerged 

 region of gneiss and crystalline schists the carboniferous strata 

 with their beds of coal and their plant-remains were being de- 

 posited ; many of the strata being made up from the partially 

 disintegrated crystalline schists and now scarcely distinguish- 

 able from them. After some disturbance, the secondary forma- 

 tions were laid down unconformably alike over the carbonifer- 

 ous and the older strata, followed by the nummulitic beds and 

 their overlying sandstones; the whole, from the base of the 

 trias, having in this region an aggregate thickness of about 

 1,250 metres. Subsequently to this occurred the great move- 

 ments which threw into folds all of these strata, enclosing, as 

 in the Tarentaise, the nummulites, with Jurassic and carbonifer- 

 ous fossils, among the folds of the crystalline schists. This 

 was followed by great denudation, which removed from the 

 broken anticlinals the secondary rocks, leaving, however, in the 

 horizontal Jurassic beds which still cap the Aiguilles Rouges, 

 an evidence of the former spread of these formations, which 

 once extended over what is now the summit of Mont Blanc. 

 It is worthy of note that the highest portions of this latter do 

 not exhibit the underlying gneiss, but are capped by crystalline 

 schists, which may be supposed to rest upon it, as do the sec- 



* See in this connection Hebert, Bull. Soc. Geol. de France (2), XXV. 

 356. 



