destruction could not have been adduced. Thus have we traced the
history of these great rings of coral-rock, from their first origin
through their normal changes, and through the occasional accidents of
their existence, to their death and final obliteration.
In my volume on "Coral Formations" I have published a map, in which I
have coloured all the atolls dark-blue, the barrier-reefs pale-blue,
and the fringing reefs red. These latter reefs have been formed whilst
the land has been stationary, or, as appears from the frequent presence
of upraised organic remains, whilst it has been slowly rising: atolls
and barrier-reefs, on the other hand, have grown up during the directly
opposite movement of subsidence, which movement must have been very
gradual, and in the case of atolls so vast in amount as to have buried
every mountain-summit over wide ocean-spaces. Now in this map we see
that the reefs tinted pale and dark-blue, which have been produced by
the same order of movement, as a general rule manifestly stand near
each other. Again we see, that the areas with the two blue tints are
of wide extent; and that they lie separate from extensive lines of
coast coloured red, both of which circumstances might naturally have
been inferred, on the theory of the nature of the reefs having been
governed by the nature of the earth's movement. It deserves notice
that in more than one instance where single red and blue circles
approach near each other, I can show that there have been oscillations
of level; for in such cases the red or fringed circles consist of
atolls, originally by our theory formed during subsidence, but
subsequently upheaved; and on the other hand, some of the pale-blue or
encircled islands are composed of coral-rock, which must have been
uplifted to its present height before that subsidence took place,
during which the existing barrier-reefs grew upwards.
Authors have noticed with surprise, that although atolls are the
commonest coral-structures throughout some enormous oceanic tracts,
they are entirely absent in other seas, as in the West Indies: we can
now at once perceive the cause, for where there has not been
subsidence, atolls cannot have been formed; and in the case of the West
Indies and parts of the East Indies, these tracts are known to have
been rising within the recent period. The larger areas, coloured red
and blue, are all elongated; and between the two colours there is a
degree of rude alternation, as if the rising of one had balanced the
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