Corals and coral islands.

CORALS AND CORAL ISLANDS.

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cavities among the living tufts, and in this manner produce
the reef deposit; and the bed is finally consolidated, while
still beneath the water.
The coral zoophyte is especially adapted for such a mode
of reef-making. Were the nourishment drawn from below, as
in most plants, the solidifying coral rock would soon destroy
all life: instead of this, the zoophyte is gradually dying below while growing above; and the accumulations of debris
cover only the dead portions.
But on land, there is the decay of the year, and that of old
age, producing vegetable debris; and storms prostrate forests.
And there are corresponding effects among the groves of the
sea. It has been shown that coral plantations, from which
reefs proceed, do not grow in the "calm and still" depths of
the ocean. They are to be found amid the waves, and usually
extend little below a hundred feet, which is far within the
reach of the sea's heavier commotions. To a considerable extent they grow in the very face of the tremendous breakers
that strike and batter as they drive over the reefs. Here is
an agent which is not without its effects. The enormous
masses of uptorn rock found on many of the islands may give
some idea of the force of the lifting wave; and there are examples on record, to be found in various treatises on Geology,
of still more surprising effects.
During the more violent gales the bottom of the sea is
said, by different authors, to be disturbed to a depth of three
hundred, three hundred and fifty, or even five hundred feet,
and De la Beche remarks, that when the depth is fifteen fathoms, the water is very evidently discolored by the action of
the waves on the sand and mud of the bottom.
In an article on the Force of Waves, by Thomas Stevenson, of Edinburgh, published in the Transactions of the Royal