Ancient Extent of (he Glaciers of Chamonix. 79 



between Bonneville and the mountain Saleve, is strewed with 

 erratic blocks. These blocks, however, are wholly wanting 

 on a band of 17 kilometres in length, and of variable breadth, 

 which extends from the entry of the valley of Bornaud as far 

 as Nangy, a village situate on the roa(J from Bonneville to 

 Geneva. This long band, known under the name of Focailles, 

 is almost wholly uncultivated, and its sterility contrasts 

 strongly with the vigorous vegetation of the surrounding 

 plain. The little town of Roche, the villages of St Laurent 

 and Cornier, are built upon the Rocailles, while those of Pers, 

 St Romaine, and Nangy, are placed on its edges. By pene- 

 trating to the middle of these rocks, many of which are 30 op 

 40 metres in height, near the imposing ruins of the Chateaux 

 de la Roche, Chatelet, &c., and the towers of St Laurent and 

 Bellecombe, the geologist finds himself all at once in a calca- 

 reous country. The mineralogical nature of the rocks which 

 surround him, the white mud which covers the road, all con- 

 firm this idea. The botanist immediately recognizes the 

 plants peculiar to limestone mountains, the box, cyclamen, 

 and {dompte-venin) asclepias vincetoxicum ; but these appear- 

 ances are deceitful ; wherever the torrents have ploughed up 

 the ground, we see beds of mollase on which calcareous masses 

 rest. The fossil shells which they contain complete the de- 

 monstration that those masses are not in their place, but that 

 they have been formerly separated from the elevated parts of 

 the mountain of Bornaud, and transported to the plain. We at 

 last come to the conviction that the Rocailles are a great cal- 

 careous moraine, issuing from the valley of Bornaud, at the 

 period when a glacier debouched on this valley, in order to 

 unite itself to that of the Arve. At many points, we may 

 see the granitic moraine and the calcareous one touching 

 each other \vithout becoming confounded ; at the entry, for 

 example, of the town of Roclie on the side of Bonneville, and 

 near the bridge Bellecombe, below the village of Nangy. At 

 a kilometre above the village, all travellers remark two 

 precipitous rocks rising near the road. The one supports a 

 building, the Chateau de Pierre, the other a tuft of pines, 

 having a most picturesque effect. These two rocks are the 

 last blocks of the calcareous moraine of Bornaud, pushed for- 



