We did not return on board till late in the evening, for we stayed
a long time in the lagoon, examining the fields of coral and the
gigantic shells of the chama, into which, if a man were to put his
hand, he would not, as long as the animal lived, be able to
withdraw it. Near the head of the lagoon I was much surprised to
find a wide area, considerably more than a mile square, covered
with a forest of delicately branching corals, which, though
standing upright, were all dead and rotten. At first I was quite at
a loss to understand the cause; afterwards it occurred to me that
it was owing to the following rather curious combination of
circumstances. It should, however, first be stated, that corals are
not able to survive even a short exposure in the air to the sun's
rays, so that their upward limit of growth is determined by that of
lowest water at spring tides. It appears, from some old charts,
that the long island to windward was formerly separated by wide
channels into several islets; this fact is likewise indicated by
the trees being younger on these portions. Under the former
condition of the reef, a strong breeze, by throwing more water over
the barrier, would tend to raise the level of the lagoon.
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