THE MOUNTAINS OF SWITZERLAND. 
87 
the Rhine at Ilanz — is bounded by ranges ap- 
proximately at right angles to the main direction of 
the mountains. That on the left of the valley cul- 
minates in the Piz Ricin, Crap Grisch, Weissenstein- 
horn, and Barenhorn. In favourable light it can 
easily be seen from the opposite side of the valley, 
that the streams have cut out the valleys and are 
thus the cause of the mountains. This is a par- 
ticularly clear illustration, because the strata are 
uniform along the whole line, so that the structure is 
not complicated by the presence of rocks of different 
character and hardness. 
Indeed if we compare together two maps, in one 
of which the principal chains of mountains, and in 
the other the main river valleys, are brought out 
most prominently, they look at first sight so different 
that we should hardly suppose them to represent the 
same district.* It is evident therefore that the main 
agent which has determined the longitudinal valleys 
is not that which has given rise to the mountain 
summits. The courses of the rivers, though there 
have, as we shall see, been many minor changes, and 
exceptions due to other causes, still were determined 
by the folds into which the surface was thrown; while 
* Heim, Mech. d. Gebirgsb., vol. I. 
