s. 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 a