108 
MOUNTAINS AND THEIR ORIGIN. 
mountain-scenery, may be found the most fertile 
growth, the richest pasturage, the brightest flow 
ers. Where such a patch of arable soil has a 
southern exposure on a mountain-side, we may 
have a most fertile vegetation at a great height, 
and surrounded by the dark pine-forests. Many 
of the pastures on the Alps, to which from height 
to height the shepherds ascend with their flocks 
in the summer, — seeking the higher ones as the 
lower become dry and exhausted, — are due to 
such alternations in the character of the rocks. 
In consequence of the influence of time, 
weather, atmospheric action of all kinds, the 
apparent relation of beds has often become so 
completely reversed that it is exceedingly diffi- 
cult to trace their original relation. Take, for 
instance, the following case. An eruption has 
upheaved the strata over a given surface in such 
a manner as to lift them into a mountain, crack- 
ing open the upper beds, but leaving the lower 
ones unbroken. We have then a valley on a 
mountain-summit between two crests resembling 
the one already shown in Figure 4. Such a nar- 
row passage between two crests may be changed 
in the course of time to a wide expansive valley 
by the action of the rains, frosts, and other disin- 
tegrating agents, and the relative position of the 
strata forming its walls may seem to be entirely 
changed. 
