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.
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