70 
SCENERY OF SWITZERLAND. 
fore, are rendered more susceptible of disintegration, 
the latter on the contrary acquire greater powers of 
resistance. 
The above diagram, Fig. 14, represents six strata 
(1-6) supposed to be originally of approximately 
equal hardness, but which, after being thrown into 
undulations, are rendered more compact in the 
hollows and less 'so in the ridges. Denudation will 
then act more effectively at A, C, E, than at B, D, 
F, and when it has acted long enough the surface 
will be shown by the stronger line. This will be 
still more rapidly the case if some of the strata are 
softer than others. Where they are brought up to 
the surface erosion will of course act with special 
effect. Hence it often happens that hills have be- 
come valleys, and what were at first the valleys have 
become mountain tops. As an illustration of the 
former I may mention the valley of the Tinitue (Fig. 
98, vol. 11. p. 87); of the latter, the Tremettaz (Fig. 7) 
or the Glarnisch. 
In other eases where the summit is not at the 
very base of the trough, the edges of some stratum 
rather harder than the rest, project as two more or 
less pointed peaks, leaving a saddle-shaped depression 
in the centre. 
Highly inclined strata are often worn away so as 
