326 M. Guyot on the 



Orta, we distinctly distinguish the character and superposi- 

 tion of the two formations. 



These facts, in themselves so significant, are not the only 

 ones of this nature observed in this valley. M. the Canon 

 Carrel has proved the existence, on a large scale, of all the 

 same phenomena in the neighbourhood of the city of Aoste. 

 Many years previously, M. Guyot had pointed out very beau- 

 tiful polished rocks at the foot of Mont Blanc, above Cour- 

 mayeur, whei'e they were likewise seen by MM. Agassiz and 

 Forbes. This assemblage of facts authoi-ises us, in M. Guyot's 

 opinion, to consider the valley of Aoste, viewed in relation to 

 the development of the erratic phenomena, as analogous to 

 the valley of the Rhone. It is, in regard to the southern de- 

 clivity of the Pennine chain, and the Italian side of Mont 

 Blanc, what the Valais is to the northern declivity of these 

 two chains ; it is even superior to the latter in the number and 

 evidence of polished and moutonneed rocks, and, in this re- 

 spect, it does not yield even to the classical valley of the Aar. 



As to the essential object M. Guyot had in view in this ex- 

 ploratory journey, namely, to determine the precise site of 

 the species of rocks of the erratic basin of the Rhone, the 

 origin of which was not sufficiently clear, he has completely 

 succeeded in attaining it. 



He was particulai'ly careful to obtain specimens in situ of 

 the chloriteous gneiss and arkesine scattered in such great 

 abundance in the plain. No one had previously done this. M. 

 Guyot had only indicated the bottom of the valley of Bagnes 

 and the valley of Viege, whei'e these rocks had been ob- 

 served in an erratic state by himself, and previously by MM. 

 Studer and Forbes, as the extreme limits of their extension. 

 He soon convinced himself that these rocks and their varie- 

 ties, accompanied with diverse amphibolic rocks, constitute, 

 in a great measure, the central mass and the highest sum- 

 mits of the Pennine chain. In the bottom of the valley of 

 Bagnes, after passing the region of the chlorites, we imme- 

 diately find the chloriteous gneiss and arkesine in great 

 abundance on the glacier of Brena, at the western base of the 

 Champriond, where these rocks, almost of themselves, form 

 the fine, frontal moraines left by this glacier. The glacier of 



