into angular chip-stone by the same process.

It is on mountain tops and in high latitudes that the effects of
frost are most plainly seen. "Every summit" says Whymper, "amongst
the rock summits upon which I have stood has been nothing but a
piled-up heap of fragments" (Fig. 7). In Iceland, in Spitsbergen,
in Kamchatka, and in other frigid lands large areas are thickly
strewn with sharp-edged fragments into which the rock has been
shattered by frost.

ORGANIC AGENTS

We must reckon the roots of plants and trees among the agents
which break rocks into pieces. The tiny rootlet in its search for
food and moisture inserts itself into some minute rift, and as it
grows slowly wedges the rock apart. Moreover, the acids of the
root corrode the rocks with which they are in contact. One may
sometimes find in the soil a block of limestone wrapped in a mesh
of roots, each of which lies in a little furrow where it has eaten
into the stone.

Rootless plants called lichens often cover and corrode rocks as
yet bare of soil; but where lichens are destroying the rock less
rapidly than does the weather, they serve in a way as a
protection.

CONDITIONS FAVORING DISINTEGRATION AND DECAY. The
disintegration of rocks under frost and temperature changes
goes on most rapidly in cold and arid climates, and where
vegetation is scant or absent. On the contrary, the decay of rocks