stages o f one tide, is particularly interesting, j When the
tide has left it for some time it becomes dry, and appears
to be a compact rock, exceedingly hard and ragged ; but as
the tide rises, and the waves begin to wash over it, the
coral worms protrude themselves from holes which were
before invisible. These animals are of a great variety of
shapes and sizes, and in such prodigious numbers, that, in
a short time, the whole surface of the rock appears to be
alive and in motion. The most common worm is in the
form of a star, with arms from four to six inches long,
which are moved about with a rapid motion in all directions,
probably to catch food. Others are so sluggish,
that they may be mistaken for pieces of the rock,
and are generally of a dark colour, and from four to five
inches long, and two or three round. When the coral is
broken, about high water mark, it is a solid hard stone, but
if any part of it be detached a t a spot which the tide reaches
■every day, it is found to be full of worms of different lengths
and colours, some being as fine as a thread and several
feet long, of a bright yellow, and sometimes of a blue colour:
others resemble snails, and some are not unlike lobsters in
shape, but soft, and not above two inches long *.
* A large collection, which was at this time made of these Zoophites, was
unfortunately lost in the Alceste,
The growth of coral appears to cease when the worm is no
longer exposed to the washing of the sea. Thus, a reef
rises in the form of a cauliflower, till its top has gained the
level of the highest tides, above which the worm has no
power to advance, and the reef of course no longer extends
itself upwards. The other parts, in succession, reach the surface,
and there stop, forming in time a level field with steep
sides all round. The reef, however, continually increases;
and being prevented from going higher, extends itself
laterally in all directions. But this growth being as rapid
at the upper edge as it is lower down, the steepness of the
face of the reef is still preserved. These are the circumstances
which render coral reefs so dangerous in navigation
; for, in the first place, they are seldom seen above
the water; and, in the next, their sides are so steep,'that a
ship's bows may strike against the rock before any change
of soundings has given warning of the danger.
The island at high water is formed into three parts,
which at low water are joined by reefs; the whole being
about two and a half or three miles from east to west, and
tolerably clear of rocks on the south side; but on the north
it is guarded by a semicircle of coral extending upwards of
a mile from the shore. On the centre island is only one
hut, which, as there was reason to believe it to be the actual