in the Erratic Basin of the lihone. 269 



as far as Mont de Sion. The Pennine rocks form a large 

 central moraine, partly immersed in the waters of the lake, 

 and which covers the plain of Geneva, and Pays de Gex, as 

 far as Mont de Sion and the Jura. The moraine of Mont 

 Rosa, marked by a greater abundance of euphotides, serpen- 

 tines, and secondary rocks of the same group, passes along 

 the vicinity of Nyon and Coppet, running in a westerly di- 

 rection as far as the very foot of the chain. The moraine of 

 Haut Valais, characterised by numerous and huge blocks of 

 white granite, is the beginning of the right lateral moraine, 

 passing by Morges, Bussy, Aubonne, and Biere. Lastly, the 

 Yalorsines, particularly numerous in the environs of Lau- 

 sanne and Cossonay, and often in connexion with limestones, 

 form the extreme right lateral. The granites of Mont Blanc, 

 which are found in the latter regions, and as far as the Jura, 

 undoubtedly belonged to the left lateral moraine during the 

 period of the first divergency, and must have been carried to 

 the west at the time when the change of direction in the 

 progi-ess of the glacier took place. 



In this part of the glacier, we may consider the blocks ac- 

 cumulated at the extreme limit of the basin, on the summit 

 of Mont de Sion, from the road to Frangy, along the declivi- 

 ties of Vouache and the Jura, as far as the vicinity of Fau- 

 cille and Divonne, as the frontal moraine ; for, in the whole 

 of that space, we scai'cely meet with anything else than the 

 Pennine rocks and those of Mont Rosa. 



Here, again, as in the eastern part, the left lateral moraine 

 is more extended than the right lateral moraine ; but the dis- 

 proportion is far from being so great, a circumstance per- 

 fectly accounted for by the relief of the basin. 



It is thus tliat we explain, by this successive effusion of 

 the glacier in two opposite directions, the complicated but 

 still normal distribution of the species of erratic rocks of the 

 basin of tlie Rhone. The order of succession appears to me 

 fixed, not only by the nature of the reliefs, as I have ex- 

 plained above, but still further by that of the rocks them- 

 selves. Although the characteristic rocks are the same in 

 the eastern as in the western portion of the valley, yet we 

 scarcely find among the former any others but the species 



