parallel to the generally prevailing strike of the high islands and
great coast-lines of those oceans. I venture, therefore, to affirm,
that on the theory of the upward growth of the corals during the
sinking of the land, [13] all the leading features in those wonderful
structures, the lagoon-islands or atolls, which have so long excited
the attention of voyagers, as well as in the no less wonderful
barrier-reefs, whether encircling small islands or stretching for
hundreds of miles along the shores of a continent, are simply explained.
It may be asked, whether I can offer any direct evidence of the
subsidence of barrier-reefs or atolls; but it must be borne in mind how
difficult it must ever be to detect a movement, the tendency of which
is to hide under water the part affected. Nevertheless, at Keeling
atoll I observed on all sides of the lagoon old cocoa-nut trees
undermined and falling; and in one place the foundation-posts of a
shed, which the inhabitants asserted had stood seven years before just
above high-water mark, but now was daily washed by every tide: on
inquiry I found that three earthquakes, one of them severe, had been
felt here during the last ten years. At Vanikoro, the lagoon-channel
is remarkably deep, scarcely any alluvial soil has accumulated at the
foot of the lofty included mountains, and remarkably few islets have
been formed by the heaping of fragments and sand on the wall-like
barrier reef; these facts, and some analogous ones, led me to believe
that this island must lately have subsided and the reef grown upwards:
here again earthquakes are frequent and very severe. In the Society
archipelago, on the other hand, where the lagoon-channels are almost
choked up, where much low alluvial land has accumulated, and where in
some cases long islets have been formed on the barrier-reefs--facts
all showing that the islands have not very lately subsided--only feeble
shocks are most rarely felt. In these coral formations, where the land
and water seem struggling for mastery, it must be ever difficult to
decide between the effects of a change in the set of the tides and of a
slight subsidence: that many of these reefs and atolls are subject to
changes of some kind is certain; on some atolls the islets appear to
have increased greatly within a late period; on others they have been
partially or wholly washed away. The inhabitants of parts of the
Maldiva archipelago know the date of the first formation of some
islets; in other parts, the corals are now flourishing on water-washed
reefs, where holes made for graves attest the former existence of
inhabited land. It is difficult to believe in frequent changes in the
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