As Far As The Actual Reef Of Coral Is Concerned, There Is Not
The Smallest Difference, In General Size, Outline, Grouping,
And Even In Quite Trifling Details Of Structure, Between A
Barrier And An Atoll.
The geographer Balbi has well remarked,
that an encircled island is an atoll with high land rising out
of its lagoon; remove the land from within, and a perfect
atoll is left.
But what has caused these reefs to spring up at such
great distances from the shores of the included islands? It
cannot be that the corals will not grow close to the land;
for the shores within the lagoon-channel, when not surrounded
by alluvial soil, are often fringed by living reefs;
and we shall presently see that there is a whole class, which
I have called Fringing Reefs from their close attachment
to the shores both of continents and of islands. Again, on
what have the reef-building corals, which cannot live at
great depths, based their encircling structures? This is a
great apparent difficulty, analogous to that in the case of
atolls, which has generally been overlooked. It will be
perceived more clearly by inspecting the following sections
which are real ones, taken in north and south lines, through
the islands with their barrier-reefs, of Vanikoro, Gambier,
and Maurua; and they are laid down, both vertically and
horizontally, on the same scale of a quarter of an inch to
a mile.
It should be observed that the sections might have been
taken in any direction through these islands, or through
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