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 of the reef, you find that the depth of the water
is not more than from 20 to 25 fathoms--that is about 120 to 150 feet.
Outside that point you come to the natural sea bottom; but all inside
that depth is coral, built up from the bottom by the accumulation of the
skeletons of innumerable generations of coral polypes. So that you see
the coral forms a very considerable rampart round the island. What the
exact circumference may be I do not remember, but it cannot be less
than 100 miles, and the outward height of this wall of coral rock
nowhere amounts to less than about 100 or 150 feet.
When the outward face of the reef is examined, you find that the upper
edge, which is exposed to the wash of the sea, and all the seaward
face, is covered with those living plant-like flowers which I have
described to you.
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