And in this same archipelago,
Mahlos-Mahdoo atoll is divided by a bifurcating channel from 100 to
132 fathoms in depth, in such a manner that it is scarcely possible
to say whether it ought strictly to be called three separate
atolls, or one great atoll not yet finally divided.
(PLATE 99. CORALS.)
I will not enter on many more details; but I must remark that the
curious structure of the northern Maldiva atolls receives (taking
into consideration the free entrance of the sea through their
broken margins) a simple explanation in the upward and outward
growth of the corals, originally based both on small detached reefs
in their lagoons, such as occur in common atolls, and on broken
portions of the linear marginal reef, such as bounds every atoll of
the ordinary form. I cannot refrain from once again remarking on
the singularity of these complex structures--a great sandy and
generally concave disk rises abruptly from the unfathomable ocean,
with its central expanse studded and its edge symmetrically
bordered with oval basins of coral-rock just lipping the surface of
the sea, sometimes clothed with vegetation, and each containing a
lake of clear water!
One more point in detail: as in the two neighbouring archipelagoes
corals flourish in one and not in the other, and as so many
conditions before enumerated must affect their existence, it would
be an inexplicable fact if, during the changes to which earth, air,
and water are subjected, the reef-building corals were to keep
alive for perpetuity on any one spot or area.
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