Coral and Coral Reefs | Page 6

lime in the interior of the combined polype body, formed by budding
and by fission in the way I described. You will perceive that there is no
necessary limit to this process. There is no reason why we should not
have coral three or four times as big; and there are certain creatures of
this kind that do fabricate very large masses, or half spheres several feet
in diameter. Thus the activity of these animals in separating carbonate
of lime from the sea and building it up into definite shapes is very
considerable indeed.
Now I think I have said sufficient--as much as I can without taking you
into technical details, of the general nature of these creatures which
form coral. The animals which form coral are scattered over the seas of
all countries in the world. The red coral is comparatively limited, but
the polypes which form the white coral are widely scattered. There are
some of them which remain single, or which give rise to only small
accumulations; and the skeletons of these, as they die, accumulate upon
the bottom of the sea, but they do not come to much; they are washed
about and do not adhere together, but become mixed up with the mud
of the sea. But there are certain parts of the world in which the coral
polypes which live and grow are of a kind which remain, adhere
together, and form great masses. They differ from the ordinary polypes
just in the same way as those plants which form a peat-bog or
meadow-turf differ from ordinary plants. They have a habit of growing
together in masses in the same place; they are what we call
"gregarious" things; and the consequence of this is, that as they die and
leave their skeletons, those skeletons form a considerable solid
aggregation at the bottom of the sea, and other polypes perch upon
them, and begin building upon them, and so by degrees a great mass is
formed. And just as we know there are some ancient cities in which
you have a British city, and over that the foundations of a Roman city;
and over that a Saxon city, and over that again a modern city, so in
these localities of which I am speaking, you have the accumulations of
the foundations of the houses, if I may use the term, of nation after
nation of these coral polypes; and these accumulations may cover a
very considerable space, and may rise in the course of time from the
bottom to the surface of the sea.

Mariners have a name which they apply to all sorts of obstacles
consisting of hard and rocky matter which comes in their way in the
course of their navigation; they call such obstacles "reefs," and they
have long been in the habit of calling the particular kind of reef, which
is formed by the accumulation of the skeletons of dead corals, by the
name of "coral reefs," therefore, those parts of the world in which these
accumulations occur have been termed by them "coral reef areas," or
regions in which coral reefs are found. There is a very notable example
of a simple coral reef about the island of Mauritius, which I dare say
you all know, lies in the middle of the Indian Ocean. It is a very
considerable and beautiful island, and is surrounded on all sides by a
mass of coral, which has been formed in the way I have described; so
that if you could get upon the top of one of the peaks of the island, and
look down upon the Indian Ocean, you would see that the beach round
the Island was continued outward by a kind of shallow terrace, which is
covered by the sea, and where the sea is quite shallow; and at a distance
varying from three-quarters of a mile to a mile and a half from the
proper beach, you would see a line of foam or surf which looks most
beautiful in contrast with the bright green water in the inside, and the
deep blue of the sea beyond. That line of surf indicates the point at
which the waters of the ocean are breaking upon the coral reef which
surrounds the island. You see it sweep round the island upon all sides,
except where a river may chance to come down, and that always makes
a gap in the shore.
There are two or three points which I wish to bring clearly before your
notice about such a reef as this. In the first place, you perceive it forms
a kind of fringe round the island, and is therefore called a "fringing
reef." In the next place, if you go out in a boat, and take soundings at
the edge