M. Fournet's Researches on the Geology of the Alps. 95 



particularly the metamorphism, and we are happy to find a 

 work so carefully and accurately executed in this respect as 

 that of M. Fournet. 



De Saussure had likewise described a portion of the section 

 from Martigny to St Maurice, and he did it with his usual 

 admirable precision. He particularly attached himself to the 

 study of petrosilex. But, in his time, the theory of metamor- 

 phism, at least such as it is now understood, had not been 

 promulgated ; consequently, M. Saussure' s work and that of 

 M. Fournet, regard the subject in two very different points 

 of view. 



The valley of the Rhone, between Martigny and St 

 Maurice, in the Valais, intersects the prolongation of the 

 axis of elevation of Mont Brevent, (valley of Chamonix) ; this 

 axis is formed of rocks of crystallisation ; it is parallel to the 

 axis of Mont Blanc, and it has upraised sedimentary rocks be- 

 longing for the most part to the Jurassic formation. All 

 these rocks have been traversed by a great number of veins 

 which are the principal cause of the metamorphic effects. 

 These veins appear upon the escarpments, sometimes under 

 the form of transverse bands, sometimes under that of large 

 lenticular masses parallel to the stratification ; they are found 

 in all the rocks placed between the slates of La Bathia (near 

 Martigny) and the ravine of Saint Barthelemy, below the 

 Dent du Midi. They are composed of quartz, pure felspars, 

 or associated with quartz, or rather with some crystals of am- 

 phibole (?), protogine, and rocks allied to serpentine. These 

 rocks are frequently ill defined and confusedly crystallised. 



The rocks which are thus traversed with veins are the 

 following, going in the direction from Martigny to St Maurice, 

 that is to say, from the superior to the inferior. 



At Bathia. we see slates slightly micaceous, with small 

 veins of calcareous spar and milky quartz, thin grey slates 

 passing into unctuous slates, crossed by veins of quartz and 

 a felspar rock. These latter, by their contact, determine the 

 formation of the petrosilex or palaiopetres of Saussure. 



Further down, near Trient, are various kinds Qi gneiss , as- 

 sociated with petrosilex, or even mingled with them ; and 

 amonffst the debris we find saccharoidal limestone with ido- 



