nd no earth-worms, therefore, there can be no soil;
and under those circumstances we get what we familiarly know as a
desert.

The normal course of events where new land rises above the sea is
something like this, as oceanic isles have sufficiently demonstrated.
The rock when it first emerges from the water rises bare and rugged like
a sea-cliff; no living thing, animal or vegetable, is harboured anywhere
on its naked surface. In time, however, as rain falls upon its jutting
peaks and barren pinnacles, disintegration sets in, or, to speak plainer
English, the rock crumbles; and soon streams wash down tiny deposits of
sand and mud thus produced into the valleys and hollows of the upheaved
area. At the same time lichens begin to spring in yellow patches upon
the bare face of the rock, and feathery ferns, whose spores have been
wafted by the wind, or carried by the waves, or borne on the feet of
unconscious birds, sprout here and there from the clefts and crannies.
These, as they die and decay, in turn form a thin layer of vegetable
mould, the first beginning of a local soil, in which the trusty
earthworm (imported in the egg on driftwood or floating weeds)
straightway sets to work to burrow, and which he rapidly increases by
his constant labour. On the soil thus deposited, flowering plants and
trees can soon root themselves, as fast as seeds, nuts or fruits are
wafted to the island by various accidents from surrounding countries.
The new land thrown up by the great eruption of Krakatoa has in this way
already clothed itself from head to foot with a luxuriant sheet of
ferns, mosses, and other vegetation.

First soil, then plant and animal life, are thus in the last resort
wholly dependent for their existence on the amount of rainfall. But in
deserts, where rain seldom or never falls (except by accident) the first
term in this series is altogether wanting. There can be no rivers,
brooks or streams to wash down beds of alluvial deposit from the
mountains to the valleys. Denudation (the term, though rather awful, is
not an improper one) must therefore take a different turn. Practically
speaking, there is no water action; the work is all done by sun and
wind. Under these circumstances, the rocks crumble away very slowly by
mere exposure into small fragments, which the wind knocks off and blows
about the surface, forming sand or dust of them in all convenient
hollows. The frequent currents, produced by the heated air that lies