inst the steep
slopes. Cliffs stand shattered and ready to fall in ruins. And
here the forces at work readily reveal themselves. An occasional
wreath of white smoke among

32

the far-off peaks, followed by a rumbling reverberation, marks
the fall of an avalanche. Water everywhere trickles through the
shaly _debris_ scattered around. In the full sunshine the rocks are
almost too hot to bear touching. A few hours later the cold is
deadly, and all becomes a frozen silence. In such scenes of
desolation and destruction, detrital sediments are actively being
generated. As we descend into the valley we hear the deep voice
of the torrents which are continually hurrying the disintegrated
rocks to the ocean.

A remarkable demonstration of the activity of mechanical
denudation is shown by the phenomenon of "earth pillars." The
photograph (Pl. IV.) of the earth pillars of the Val d'Herens
(Switzerland) shows the peculiar appearance these objects
present. They arise under conditions where large stones or
boulders are scattered in a deep deposit of clay, and where much
of the denudation is due to water scour. The large boulders not
only act as shelter against rain, but they bind and consolidate
by their mere weight the clay upon which they rest. Hence the
materials underlying the boulders become more resistant, and as
the surrounding clays are gradually washed away and carried to
the streams, these compacted parts persist, and, finally, stand
like walls or pillars above the general level. After a time the
great boulders fall off and the underlying clay becomes worn by
the rainwash to fantastic spikes and ridges. In the Val d'Herens
the earth pillars are formed

33

of the deep moraine stuff which thickly overlies the slopes of
the valley. The wall of pillars runs across the axis of the
valley, down the slope of the hill, and crosses the road, so that
it has to be tunnelled to permit the passage of traffic. It is
not improbable that some additional influence--possibly the
presence of lime--has hardened the material forming the pillars,
and tended to their preservation.

Denudation has, however, other methods of work than purely
mechanical; methods more noiseless and gentle, but not less
effective, as the victories of peace ate no less than those of
war.

Over the immense tracts of the continents chemical work proceeds
relentlessly. The rock in general, more especially the primary
igneous rock, is not stable in presence