the coral-trees."

"Yes, I understand that; but how do you make out that this island was
made by them?"

"Almost all the islands in these seas have been made by the labour and
increase of these small animals. The coral grows at first at the bottom
of the sea, where it is not disturbed by the winds or waves: by degrees,
as it increases, it advances higher and higher to the surface, till at
last it comes near to the top of the water; then it is stopped in its
growth by the force of the winds and waves, which break it off, and of
course it never grows above the water, for if it did the animals would
die."

"Then how does it become an island?"

"By very slow degrees; the time, perhaps, much depending upon chance:
for instance, a log of wood floating about, and covered with barnacles,
may ground upon the coral reefs; that would be a sufficient
commencement, for it would remain above water, and then shelter the
coral to leeward of it, until a flat rock had formed, level with the
edge of the water. The sea-birds are always looking for a place to rest
upon, and they would soon find it, and then their droppings would, in
course of time, form a little patch above water, and other floating
substances would be thrown on it; and land-birds, who are blown out to
sea, might rest themselves on it, and the seeds from their stomachs,
when dropped, would grow into trees or bushes."

"I understand that."

"Well then, William, you observe there is an island commenced, as it
were, and, once commenced, it soon increases, for the coral would then
be protected to leeward, and grow up fast. Do you observe how the coral
reefs extend at this side of the island, where they are protected from
the winds and waves; and how different it is on the weather side, which
we have just left? Just so the little patch above water protects the
corals to leeward, and there the island increases fast; for the birds
not only settle on it, but they make their nests and rear their young,
and so every year the soil increases; and then, perhaps, one cocoa-nut
in its great outside shell at last is thrown on these little patches--it
takes root, and becomes a tree, every year shedding its large branches,
which are turned into mould as soon as they decay, and then dropping its
nuts, which again take root and grow in this mould; and thus they
continue, season after season, and year after year, until the island
becomes as large and as thickly covered with trees as