23 2 
SCENERY OF SWITZERLAND. 
each side are equal they will be permanent; on the 
other hand if, as in the Alps, one side is much 
steeper than the other, it will be worn back more 
rapidly. Hence the whole crest of the Alps is, though 
of course very slowly, moving northwards. This is 
specially marked in the case of the Engadine (see 
vol. ii. p. 240). 
These changes and struggles have by no means 
come to an end. In some cases we can already 
foresee future changes. For instance, the Nolla, 
which falls into the Hinter Rhine at Tliusis, is rapidly 
eating back into the mountains near Glas, and in, 
geologically speaking, a comparatively short time it 
will probably invade the Valley of the Versam, carry 
off its upper feeders, and appropriate the waters from 
the upper valley. So rapidly is the change progress- 
ing that after even a few hours’ rain the Nolla be- 
comes quite black. In its upper part the Biindner- 
schiefer is saturated with water, and reduced almost 
to a black mud. The ground may be said to be 
continually in slow movement down to the valley, and 
the houses of Glas and Tschappina have to be con- 
tinually repaired. Some have moved as much as 
60 metres downwards in thirty years. 
