THE REUSS. 
213 
by debris, through which the river cuts a gorge 
(Fig. 144, III), and having done so, begins again to 
saw through the solid rock (Fig. 144, IV). 
Thus we have a succession of sawing, widening, 
filling, removal, and then sawing again. 
Owing to the nearly vertical position of the rocks 
they present the same character from the highest 
peaks to the bed of the river, and we are brought 
irresistibly to the conclusion, however incredible it 
may at first appear, that the whole valley has been 
cut out by the river. 
The Upper Reuss is evidently of great antiquity. 
It is older than the lateral valleys which drain into it, 
for it cuts across the ranges of mountains which 
divide them from one another. It must therefore be 
anterior to these chains, and we get an inkling how 
slowly they must have been raised, because the river 
must have had time to cut down into them during 
their elevation, so as to maintain its course. 
The valley shows clear evidence of glacial action. 
The hard rocks are in places quite polished. This is 
especially the case with the buttresses which stand 
like doorposts where the lateral glens open into the 
main valley, and particularly on the right side of the 
eastern glens, the left of the western, where of course 
the pressure of the ice was greatest. Among the 
