ng instinct in these diminutive
creatures. Their wall of coral, for the most part in situations where the
winds are constant, being arrived at the surface, affords a shelter, to
leeward of which their infant colonies may be safely sent forth; and to
this their instinctive foresight it seems to be owing, that the windward
side of a reef exposed to the open sea, is generally, if not always the
highest part, and rises almost perpendicular, sometimes from the depth of
200, and perhaps many more fathoms. To be constantly covered with water,
seems necessary to the existence of the animalcules, for they do not
work, except in holes upon the reef, beyond low-water mark; but the coral
sand and other broken remnants thrown up by the sea, adhere to the rock,
and form a solid mass with it, as high as the common tides reach. That
elevation surpassed, the future remnants, being rarely covered, lose
their adhesive property; and remaining in a loose state, form what is
usually called a _key_, upon the top of the reef. The new bank is not
long in being visited by sea birds; salt plants take root upon it, and a
soil begins to be formed; a cocoa nut, or the drupe of a pandanus is
thrown on shore; land birds visit it and deposit the seeds of shrubs and
trees; every high tide, and still more every gale, adds something to the
bank; the form of an island is gradually assumed; and last of all comes
man to take possession.

Half-way Island is well advanced in the above progressive state; having
been many years, probably some ages, above the reach of the highest
spring tides, or the wash of the surf in the heaviest gales. I
distinguished, however, in the rock which forms its basis, the sand,
coral, and shells formerly thrown up, in a more or less perfect state of
cohesion; small pieces of wood, pumice stone, and other extraneous bodies
which chance had mixed with the calcareous substances when the cohesion
began, were inclosed in the rock; and in some cases were still separable
from it without much force. The upper part of the island is a mixture of
the same substances in a loose state, with a little vegetable soil; and
is covered with the _casuarina_ and a variety of other trees and shrubs,
which give food to paroquets, pigeons, and some other birds; to whose
ancestors it is probable, the island was originally indebted for this
vegetation.

The latitude of Half-way Island, deduced from that of the preceding and
following noons, is 10 deg. 8' s