heir existence at a depth of nearly 46
fathoms, buried beneath a mass of _Halimeda_ and foraminifera, is clear
evidence of recent subsidence. _Halimeda_ grows abundantly over the
floor of the lagoon of Funafuti, and has been observed in many other
lagoons. The writer collected a quantity of it in the lagoon of Diego
Garcia in the Chagos group. The boring demonstrates that the lagoon of
Funafuti has been filled up to an extent of at least 245 ft. (nearly 41
fathoms), and this fact accords well with Darwin's theory, but is
incompatible with that of Murray. In the present state of our knowledge
it seems reasonable to conclude that coral reefs are formed wherever the
conditions suitable for growth exist, whether in areas of subsidence,
elevation or rest. A considerable number of reefs, at all events, have
not been formed in areas of subsidence, and of these the Florida reefs,
the Bermudas, the Solomon islands, and possibly the Great Barrier Reef
of Australia are examples. Funafuti would appear to have been formed in
an area of subsidence, and it is quite probable that the large groups of
low-lying islands in the Pacific and Indian oceans have been formed
under the same conditions. At the same time, it must be remembered that
the atoll or barrier reef shape is not necessarily evidence of
formation during subsidence, for the observations of Karl Semper, A.
Agassiz, and Guppy are sufficient to prove that these forms of reefs may
be produced by the natural growth of coral, modified by the action of
waves and currents in regions in which subsidence has certainly not
taken place.

See A. Agassiz, many publications in the _Mem. Amer. Acad._ (1883) and
_Bull. Mus. Comp. Zool._ (Harvard, 1889-1899); J. D. Dana, _Corals and
Coral Islands_ (1853; 2nd ed., 1872; 3rd ed., 1890); C. Darwin, _The
Structure and Distribution of Coral Reefs_ (3rd ed., 1889); H. B.
Guppy, "The Recent Calcareous Formations of the Solomon Group,"
_Trans. Roy. Soc. Edinb._ xxxii. (1885); R. Langenbeck, "Die neueren
Forschungen uber die Korallenriffe," _Hettner geogr. Zeitsch._ iii.
(1897); J. Murray, "On the Structure and Origin of Coral Reefs and
Islands," _Proc. Roy. Soc. Edinb._ x. (1879-1880); J. Murray and
Irvine, "On Coral Reefs and other Carbonate of Lime Formations in
Modern Seas," _Proc. Roy. Soc. Edinb._ (1889); W. Savile Kent, _The
Great Barrier Reef of Australia_ (London, W. H. Allen & Co., 1893);
Karl Semper, _Animal Life_,