of the coast of the mainland, it may be.expected that any outlying
islands would have formed lagoon islands. Now Bligh
and otliers distinctly state that some of the islands there are
precisely similar to the well-known lagoon islands in the
Pacific; there are also encircled islands, so that the three
classes supposed to be produced by the same movement aie
there found in juxtaposition; as likewise happens, but in a
less evident manner, at New Caledonia and in the Society
Archipelago.
The New Hebrides line of islands, may be observed to bend
abruptly at New Britain, thence to run nearly east and we st;
and, lastly, to resume its former north-west direction in
Sumatra and the peninsula of Malacca. The figure may be
compared to the letter S laid obliquely, but the line is often
double. We have shown that the southern part, as far north
as New Ireland, abounds with proofs of elevation, so is it
with the rest. Since the time of Bougainville every voyager
adduces some fresh instance of such changes throughout a
great part of the East Indian archipelago. I may specify
New Guinea, Wageeoo, Ceram, Timor, Java, and Sumatra.
Coral reefs are abundant in the greater part of these seas, but
they merely skirt the shores. In the same manner as we
have followed the curved hne of elevation, so may we that
of subsidence. At Keeling Island, I have already mentioned
that there exist proofs of the latter m ovement: and it is a very
interesting circumstance, that during the last earthquake, by
which that island was affected, Sumatra, though distant
nearly 600 miles, was violently shaken. Bearing in mind
that there is evidence of recent elevation on the coast of the
latter, one is strongly tempted to believe that as one end of
the lever goes up, the other goes down: that as the East
Indian archipelago rises, the bottom of the neighbouring sea
sinks and carries with it Keeling Island, which would have
been submerged long ago in the depths of the ocean, had it not
been for the wonderful labours of the reef-building polypi.
As I have remarked, the islands in this great archipelago
are only skirted with reefs; and it appears from the state-
April, 1836. a u k a s o f Ai / i ' i i i i xA T n m o v e m h x t s . f)65
ments of those who have visited them, as well as from an
examination of the charts, that lagoon islands are not founci
there. This in itself is remarkable, but it becomes far more
so when it is known, that according to all accounts (and
distinctly stated by Mr. De la Beebe*) they are likewise absent
in the West Indian sea, where coral is most abumiant:
now every one is aware of the numerous proofs of recent
elevation in most parts of that archipelago. Again, Eliren-
berg has observed that lagoon islands do not occur in the
lied Sea: in LyelFs Geology, and in the Geographical Journal,
proofs are given of recent elevation on the shores of a
large part of that sea. Excepting on the theory of the form
of reefs being determined by the kind of movement to which
they have been subjected; it is a most anomalous circumstance,
and which has never been attempted to be solved, that
the lagoon structure being universal and considered as characteristic
in certain parts of the ocean, should be entirely
absent in others of equal extent.
I may here also just recal to mind the cases of skirting
reefs mentioned by M. Quoy (to which number several others
might be added), where proofs of elevation occurred. Some
general law must determine the marked difference between
reefs merely skirting the shore, and others rising from a deep
ocean in the form of distant rings. We have endeavoured to
show that with a subsiding movement, the first and simple
class must necessarily pass into the second, and more remarkable
structure.
To proceed with our examination: to the westward of the
prolongation of the line of subsidence, of which Keeling
Island is the index, we have an area of elevation. For on
the northern end of Ceylon and on the eastern shores of
India, elevated shells and corals, such as now exist in the
neighbouring sea, have been observed. Again in the middle
of the Indian ocean, the Laccadive, Maldive, and Chagos
line of atolls or lagoons show a line of subsidence. The
* Geo lo g ical M a n u al, p . 14,1.