VIII RIVERS AND LAKES 293 



them eventually breaking through into a 

 transverse valley. 



The Pusterthal in the Tyrol offers us an 

 interesting case of what is obviously a single 

 valley, which has, however, been slightly 

 raised in the centre, near Toblach, so that 

 from this point the water flows in opposite 

 directions — the Drau eastward, and the Rienz 

 westward. In this case the elevation is 

 single and slight : in the main valley there 

 are several, and they are much loftier, 

 still we may, I think, regard that of 

 the Isere from Chambery to Albertville, 

 of the Ehone from Martigp.y to its source, 

 of the Urseren Thai, of the Vorder Rhine 

 from its source to Chur, of the Inn from 

 Landeck to below Innsbruck, even perhaps 

 of the Bnns from Radstadt to Hieflau as 

 in one sense a single valley, due to one of 

 these longitudinal folds, but interrupted by 

 bosses of gneiss and granite, — one culminat- 

 ing in Mont Blanc, and another in the St. 

 Gotthard, — which have separated the waters 

 of the Isere, the Rhone, the Vorder Rhine, 

 the Inn, and the Enns. That the valley of 



