Thus the
difficulty on this head, which appeared so great, disappears.
If, instead of an island, we had taken the shore of a continent
fringed with reefs, and had imagined it to have subsided, a great
straight barrier, like that of Australia or New Caledonia,
separated from the land by a wide and deep channel, would evidently
have been the result.
(PLATE 97. SECTION OF CORAL-REEF. A'A', Outer edges of the
barrier-reef at the level of the sea, with islets on it. B'B', The
shores of the included island. CC, The lagoon-channel. A''A'',
Outer edges of the reef, now converted into an atoll. C', The
lagoon of the new atoll. NB.--According to the true scale, the
depths of the lagoon-channel and lagoon are much exaggerated.)
Let us take our new encircling barrier-reef (Plate 97), of which
the section is now represented by unbroken lines, and which, as I
have said, is a real section through Bolabola, and let it go on
subsiding. As the barrier-reef slowly sinks down, the corals will
go on vigorously growing upwards; but as the island sinks, the
water will gain inch by inch on the shore--the separate mountains
first forming separate islands within one great reef--and finally,
the last and highest pinnacle disappearing.
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