24 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 15, 



The cleavage planes form a succession of arches or anticlinals, one of 

 which is disturbed by eruptive felspathic rocks near Livrogne *, which 

 also distort the slates and alter their mineral character in the neighbour- 

 hood. For almost twelve miles from Val Ferret, nearly to Livrogne, 

 the beds all dip eastward, presenting an enormous succession of 

 slates, which probably include the Anthraxiferous series, the Lias, 

 and the lowest portion of the Jurassic beds. From the general 

 resemblance of these slates, the rarity of organic remains in them, and 

 their deceptive mineral characters, dependent on their degree of 

 metamorphism, I fear that it will be long before our Swiss colleagues 

 succeed in reduchig them to intelligible arrangement. 



Section 1, from St. Maurice to Sembranchier, following first the 

 valley of the Rhone, then that of the Drance, in both of which the 

 rocks are for the most part well exposed, shows us their relations a 

 little north of the chain of Mont Blanc, and is most instructive vrith 

 reference to the connexion between the cleavage of the slates and the 

 foliation of the crystalline rocks. Commencing on the north-west, 

 there is an anticlinal axis between St. Maurice and Miville, formed 

 partly of the cleavage of the lower Jurassic slates, partly of the folia 

 of the mica-schist, bounded eastward by a line of vertical foliation 

 near Miville, which is probably a continuation of the line of vertical 

 cleavage of Mont Baat. A second anticlinal axis, very narrow and 

 steep, occurs at the Pissevache, and a third at the valley of the Trient, 

 both of which combine the planes of cleavage and foliation. A fourth 

 anticlinal is seen in the foliation of the mica-schist at Martigny, 

 which is the continuation of that of the valley of Chamounix. A 

 fifth anticlinal occurs between Bovernier and Sembranchier, com- 

 bining the foliation of the mica-schist with the cleavages of the slates ; 

 this is the continuation of the central anticlinal axis of Mont Blanc. 

 This section ends here, but the Val d'Aosta section, No. 4, PI. I., 

 shows a continuation to the eastward of the same arrangement of the 

 cleavage-planes in anticlinals or arches. 



The various sections referred to as Nos. 1-5, PL I., are drawn on 

 parallel lines across the chain of Mont Blanc, with the view to show the 

 connexion between them ; each anticlinal has the same number in every 

 section ; and each line of vertical cleavage, or, in the language of the 

 Swiss geologists, each fan-shaped arrangement of the planes is marked 

 by the same letter, commencing in each case on the western side. 



In chapter 48, devoted to the valley of the Rhone from St. Mau- 

 rice to Martigny, Saussure describes all the slate-rocks as vertical, or 

 inclined only a few degrees from the perpendicular f ; ha\ing taken 

 the planes of cleavage for those of bedding, and regarded the bedding 

 as a series of parallel joints ; and this not from inadvertence, for after 

 a careful description and comparison of the two sets of divisional 

 planes, he decides that the more vertical ones, are the couches or 

 planes of bedding, the more horizontal ones fentes or joints ; and 

 that the whole mountains have been raised from a horizontal to their 



* See Studer, vol. i. p. 205, and note, p. 15, ante. 

 t These slates are shown in my Section, No. 1, PI. I. 



