DIRECTIONS OF RIVERS. 
231 
Bagne at Sembranchier. This was facilitated by the 
comparative softness of the Jurassic strata and Grey 
Schists, while the Vallee de Champey is in Protogine, 
Felsite, and Porphyry, which offered a much greater 
resistance to the action of the water.* 
The Trient also has changed its course. Originally 
it ran over the Col de la Forclaz down to Martigny. 
In this case the change is due, not to any difference 
in the hardness of the rock, but to the greater fall, 
and consequently greater erosive power, of the Eau 
Noire. 
It would also seem that some of the Vaud and 
Friburg rivers must be older than the final elevation 
of the mountains at the north-east end of the Lake 
of Geneva. Gillieron points out that the Broye, the 
Mionnaz, the Flon, and I may add the Sarine, from 
Sarnen to below Chateau d’Oex, run towards the 
Lake of Geneva, until they are stopped by the 
mountains between Chatel St. Denis and the Rocher 
de Naye, and forced to return northwards. 
There is also one important change which applies 
to the whole crest of the Alps. 
Watersheds are at first determined by the form 
of the earliest terrestrial surface, and if the slopes in 
* Bodmer, p. 21. 
