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, 
stil we may, I think, regard that of 
the Isére from Chambery to Albertville, 
of the Rhone from Martigny to its source, 
of the Urseren Thal, of the Vorder Rhine 
from its source to Chur, of the Inn from 
Landeck to below Innsbruck, even perhaps 
of the Enns 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 Isére, the Rhone, the Vorder Rhine, 
the Inn, and the Enns. That the valley of 
