Coral and Coral Reefs | Page 8

waters of the Pacific. You must fancy yourself in
the middle of the great ocean, and you will perceive that there is an
almost circular island, with a low beach, which is formed entirely of
coral sand; growing upon that beach you have vegetation, which takes,
of course, the shape of the circular land; and then, in the interior of the
circle, there is a pool of water, which is not very deep--probably in this
case not more than eight or nine fathoms--and which forms a strange
and beautiful contrast to the deep blue water outside. This circular
island, or atoll, with a lagoon in the middle, is not a complete circle;
upon one side of it there is a break, exactly like the entrance into a dock;
and, as a matter of course, these circular islets, or atolls, form most
efficient break-waters, for if you can only get inside your ship is in
perfect safety, with admirable anchorage in the interior. If the ship were
lying within a mile of that beach, the water would be one or two
thousand feet deep; therefore, a section of that atoll, with the soundings
as deep as this all round, would give you the notion of a great cone, cut
off at the top, and with a shallow cup in the middle of it. Now, what a
very singular fact this is, that we should have rising from the bottom of
the deep ocean a great pyramid, beside which all human pyramids sink
into the most utter insignificance! These singular coral limestone
structures are very beautiful, especially when crowned with cocoa-nut
trees. There you see the long line of land, covered with

vegetation--cocoa-nut trees--and you have the sea upon the inner and
outer sides, with a vessel very comfortably riding at anchor. That is one
of the remarkable forms of reef in the Pacific. Another is a sort of
half-way house, between the atoll and the fringing reef; it is what is
called an "encircling reef." In this case you see an Island rising out of
the sea, and at two or three miles distance, or more, and separated by a
deep channel, which may be eight to twelve fathoms deep, there is a
reef, which encircles it like a great girdle; and outside that again the
water is one or two thousand feet deep. I spent three or four years of
my life in cruising about a modification of one of these encircling reefs,
called a "barrier reef," upon the east coast of Australia--one of the most
wonderful accumulations of coral rock in the world. It is about 1,100
miles long, and varies in width from one or two to many miles. It is
separated from the coast of Australia by a channel of about 25 fathoms
deep; while outside, looking toward America, the water is two or three
thousand feet deep at a mile from the edge of the reef. This is an
accumulation of limestone rock, built up by corals, to which we have
no parallel anywhere else. Imagine to yourself a heap of this material
more than one thousand miles long, and several miles wide. That is a
barrier reef; but a barrier reef is merely as it were a fragment of an
encircling reef running parallel to the coast of a great continent.
I told you that the polypes which built these reefs were not able to live
at a greater depth than 20 to 25 fathoms of water; and that is the reason
why the fringing reef goes no farther from the land than it does. And
for the same reason, if the Pacific could be laid bare we should have a
most singular spectacle. There would be a number of mountains with
truncated tops scattered over it, and those mountains would have an
appearance just the very reverse of that presented by the mountains we
see on shore. You know that the mountains on shore are covered with
vegetation at their bases, while their tops are barren or covered with
snow; but these mountains would be perfectly bare at their bases, and
all round their tops they would be covered with a beautiful vegetation
of coral polypes. And not only would this be the case, but we should
find that for a considerable distance down, all the material of these atoll
and encircling reefs was built up of precisely the same coral rock as the
fringing reef. That is to say, you have an enormous mass of coral rock
at a depth below the surface of the water where we know perfectly well

that the coral animals could not have lived to form it. When those two
facts were first put together, naturalists were quite as much puzzled as I
daresay you are, at present, to understand