differs from this
structure essentially in the gently shelving bottom of the sea all round
to some distance; in the absence of the defined circular reefs, and, as
a consequence, of the defined central pool or lagoon; and lastly, in
the height of the land. Bermuda seems to be an irregular, circular, flat
bank, encrusted with knolls and reefs of coral, with land formed on one
side. This land seems once to have been more extensive, as on some parts
of the bank farthest removed from the island there are little pinnacles
of rock of the same nature as that of the high larger islands. I cannot
pretend to form any precise notion how the foundation of so anomalous an
island has been produced, but its whole history must be very different
from that of the atolls of the Indian and Pacific oceans--though, as
I have said, at first glance of the charts there is a considerable
resemblance.

LETTER 533. TO C. LYELL. [1842.]

Considering the probability of subsidence in the middle of the great
oceans being very slow; considering in how many spaces, both large ones
and small ones (within areas favourable to the growth of corals), reefs
are absent, which shows that their presence is determined by peculiar
conditions; considering the possible chance of subsidence being more
rapid than the upward growth of the reefs; considering that reefs not
very rarely perish (as I cannot doubt) on part, or round the whole, of
some encircled islands and atolls: considering these things, I admit as
very improbable that the polypifers should continue living on and
above the same reef during a subsidence of very many thousand feet; and
therefore that they should form masses of enormous thickness, say at
most above 5,000 feet. (533/1. "...As we know that some inorganic causes
are highly injurious to the growth of coral, it cannot be expected that
during the round of change to which earth, air, and water are exposed,
the reef-building polypifers should keep alive for perpetuity in any
one place; and still less can this be expected during the progressive
subsidences...to which by our theory these reefs and islands have been
subjected, and are liable" ("The Structure and Distribution of Coral
Reefs," page 107: London, 1842).) This admission, I believe, is in no
way fatal to the theory, though it is so to certain few passages in my
book.

In the areas where the large groups of atolls stand, and where likewise
a few scattered atolls stand between such groups