264 M. A. Guyot on the DlstribuUon of Rocks 



separates the valley of Langenbruck from ffisingen, and else- 

 where. 



The quartz pebbles are thus the only vestiges of the erratic 

 formation which connects the region of the exterior blocks of 

 the Jura with the erratic formation, as we find it insulated in 

 the bottom of the high valleys of this chain. Here they are 

 associated with the Pennine rocks as usual, but they are pro- 

 portionably more abundant. Lastly, no rock appears in more 

 numerous fragments, nor so far from the Alps. When placed 

 beyond the erratic basin of the Rhone, we approach the re- 

 gions which it occupies in Savoy, in the Jura, as in Argovia ; 

 everywhere we encounter, on the outer margin, the quartz 

 pebbles as the avant-coureurs of the Alpine rocks. It is in 

 this way, that at the eastern extremity of the basin, and most 

 remote from the primitive sites, in the vicinity of Urkheim 

 and Zofingen, not far from the spot where we leave the predo- 

 minating erratic rocks of the Reuss, a great abundance of 

 quartz pebbles suddenly announces the approach of the basin 

 of the Rhone. They are alone at first, but a few hundred 

 metres further on, some granular chlorites shew themselves ; 

 the talc schists and granites finally succeed these, and no 

 longer leave any doubt that we are in the basin of the Rhone. 

 This abundance of quartz pebbles is so mucli the more re- 

 markable, because the blocks of this rock are rare and of 

 small size. Perhaps their number is owing to their almost in- 

 destructible nature, and the absence of large blocks to their 

 being produced by veins rather than from massive rocks. 



To shew briefly the distribution of the species of rocks in the 

 basin of the Rhone, let us cut the basin transversely to the 

 east at first, than to the west of the outlet of the valley from 

 which they issue, each time leaving the Alps to emerge on 

 the Jura ; each of these sections Avill shew us clearly the 

 order of succession which the rocks observe. I draw the 

 first from the neighbourhood of Bulle to Mont de Boudry, 

 near Neuchatel ; the second from Fourches d'Aberre, in 

 Chablais, to Marchairu. 



On leaving the Alps, above Bulle, we find, on the height, 

 the wine-coloured conglomerates which form the superior 

 limit of the erratic formation and the extreme right bank of 



