WEATHERING 123 
places the disintegration is only that of chemical 
change. 
Forest Protection. —So, also, a tree-covering influ- 
ences the rate of decay. Where there are trees, there 
is the deep action of roots, and there is always present 
a goodly supply of chemical substances in the layers 
of decaying vegetation through which the water must 
Fia. 55. 
pains blocks near the top of Pikes Peak, Colorado, showing characteristic 
mountain surface strewn with frost-riven bowlders. 
pass; but on the other hand, the forest keeps the soil 
from being removed either by the action of wind or of 
rain-wash, and so in this respect protects the rock 
(see Fig. 56, and compare this with Fig. 57). There 
are cases in France, where the removal of forests from 
hillsides has been followed by the disappearance of 
the soil, so that fertile farms have been transformed 
to barren wastes of rock. 
