inclination inwards, and I have no doubt it is of general occurrence,
although, according to Ehrenberg, the reefs of the Red Sea offer an
exception. Chamisso observes that "the red colour of the reef (at the
Marshall atolls) under the breakers is caused by a Nullipora, which covers
the stone WHEREVER THE WAVES BEAT; and, under favourable circumstances,
assumes a stalactical form,"--a description perfectly applicable to the
margin of Keeling atoll. (Kotzebue's "First Voyage," volume iii., page
142. Near Porto Praya, in the Cape de Verde Islands, some basaltic rocks,
lashed by no inconsiderable surf, were completely enveloped with a layer of
Nulliporae. The entire surface over many square inches, was coloured of a
peach-blossomed red; the layer, however, was of no greater thickness than
paper. Another kind, in the form of projecting knobs, grew in the same
situation. These Nulliporae are closely related to those described on the
coral-reefs, but I believe are of different species.) Although Chamisso
does not state that the masses of Nulliporae form points or a mound, higher
than the flat, yet I believe that this is the case; for Kotzebue (Kotzebue,
"First Voyage," volume ii., page 16. Lieutenant Nelson, in his excellent
memoir in the Geological Transactions (volume ii., page 105), alludes to
the rocky points mentioned by Kotzebue, and infers that they consist of
Serpulae, which compose incrusting masses on the reefs of Bermudas, as they
likewise do on a sandstone bar off the coast of Brazil (which I have
described in "London Phil. Journal," October 1841). These masses of
Serpulae hold the same position, relatively to the action of the sea, with
the Nulliporae on the coral-reefs in the Indian and Pacific Oceans.), in
another part, speaks of the rocks on the edge of the reef "as visible for
about two feet at low water," and these rocks we may feel quite certain are
not formed of true coral (Captain Moresby, in his valuable paper "on the
Northern atolls of Maldivas" ("Geographical Journal", volume v.), says that
the edges of the reefs there stand above water at low spring-tides.)
Whether a smooth convex mound of Nulliporae, like that which appears as if