Topo(jriiphij I if the Pennine Alps. 327 



Chermontane and the mer de glace of the great Oteninia, 

 scarcely exhibit anything else, in their numerous moraines, 

 than very diversified varieties of these same rocks, generally 

 of a dull colour, among which we can distinguish many rich 

 in epidote. The mountain of the great Otemma itself is, in 

 a great measure, formed of chloriteous gneiss. Tliis rock 

 loses more and more its slaty structure, as we advance to the 

 top of the chain, and near that point it assumes the appear- 

 ance of a granite, with large ill-defined crystals of felspar, 

 and of a slight rose-colour. 



The opposite chain, which comprehends the mass of the 

 Trumma de Bouc, and which is prolonged by the Col de Cre- 

 stasetz as far as Val-Pelline, is likewise composed of chlori- 

 teous gneiss, in which the proportion of the constituent parts 

 is very variable, according to the localities. In the last men- 

 tioned valley, tlie rock seems to pass, by almost insensible 

 transitions, into a true syenite. The chloriteous gneiss, but 

 not the arkesine, is still frequently found in the Val-Pelline, 

 or, on ascending the valley, we see it alternating with the 

 syenites, and other rocks less distinctly characterised. To- 

 wards the bottom of this valley, as far as the glacier of Li - 

 sette, amphibolic rocks and talcose limestones or cipolius 

 succeed, and present petrographic forms of the highest in- 

 terest in reference tothetheory of metamorphism. 



At the Col de Collon, and along the glacier of Arolla, the 

 chloriteous gneiss and arkesines reappear, but under less 

 normal forms. The proportion of the amphibolic rocks, sye- 

 nites, and species which may be more directly connected with 

 the green granite, greatly increase. It may even be said, 

 that they are dominant as far as the tributary of the grand 

 Otemma, which brings specimens whose forms approach more 

 and more to the types of the two rocks in question. 



But the true granitoidal arkesine and chloriteous gneiss 

 with shining particles, such as they are usually found in the 

 plain, reappear in the masses which surround the glacier of 

 Fei'pecle. The tributary glaciers which descend from the 

 Dent Blanche in particular, carry along with them scarcely 

 any other rocks than arkesines ; and these are, in part, dis- 

 tinguishable from those of the Otemma and Chermontane, by 



