But it is otherwise in the greater part of the ocean which
lies in the warmer parts of the world, comprised within a distance of
about eighteen hundred miles on each side of the equator. Within the
zone thus bounded, by far the greater part of the ocean is inhabited by
coral polypes, which not only form very strong and large skeletons, but
associate together into great masses, like the thickets and the meadow
turf, or, better still, the accumulations of peat, to which plants give
rise on dry land. These masses of stony matter, heaped up beneath the
waters of the ocean, become as dangerous to mariners as so much ordinary
rock, and to these, as to the common rock ridges, the seaman gives the
name of "reefs."
Such coral reefs cover many thousand square miles in the Pacific and in
the Indian Oceans. There is one reef, or rather great series of reefs,
called the Barrier Reef, which stretches, almost continuously, for more
than eleven hundred miles off the east coast of Australia. Multitudes
of the islands in the Pacific are either reefs themselves, or are
surrounded by reefs. The Red Sea is in many parts almost a maze of such
reefs, and they abound no less in the West Indies, along the coast of
Florida, and even as far north as the Bahama Islands. But it is a very
remarkable circumstance that, within the area of what we may call the
"coral zone," there are no coral reefs upon the west coast of America,
nor upon the west coast of Africa; and it is a general fact that the
reefs are interrupted, or absent, opposite the mouths of great rivers.
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