Now such a structure as this is what
is termed a "fringing reef." You meet with fringing reefs of this kind
not only in the Mauritius, but in a number of other parts of the world.
If these were the only reefs to be seen anywhere, the problem of the
formation of coral reefs would never have been a difficult one. Nothing
can be easier than to understand how there must have been a time when
the coral polypes came and settled on the shores of this island,
everywhere within the 20 to 25 fathom line, and how, having perched
there, they gradually grew until they built up the reef.
But these are by no means the only sort of coral reefs in the world; on
the contrary, there are very large areas, not only of the Indian ocean,
but of the Pacific, in which many many thousands of square miles are
covered either with a peculiar kind of reef, which is called the
"encircling reef," or by a still more curious reef which goes by the
name of the "atoll." There is a very good picture, which Professor
Roscoe has been kind enough to prepare for me, of one of these atolls,
which will enable you to form a notion of it as a landscape.
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