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CORAL REEFS -
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known as " talus,” and this in the courseof time forms a
foundation for the further outward extension of the reef.
The action of the sea, whose breakers unceasingly beat
against the edge of the reef, causes portions of coral,shells
and the like, to be thrown on to the “ reef at ” aS't—he
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attened surface of the reef is
As a result, the
outer edge is marked by the presence of a long mound,
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known as the “ boulder zone,” which projects above the
surface of the sea.
On the seaward side of the boulder
zone, in the region where the surf breaks upon the reef,
the surface becomes cemented forming a smooth “ reef
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crest.”
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The region immediately below water level on the Outer
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edge of the reef is the area of most active.coral growth.
On
the other hand, the_reef at
the. boulder zone and
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the land becomes hollowed
to form a shallow, lagoon—like
channel, sometimes deep enough for the passage of. native
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beats.
It is not known - denitely exactly how these
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channels are produced, but probablythe principal agencies
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at Work'are the scouring action of the sea as the waves
rush over the surface of the reef at, the action ofthe
multitudinous boring bivalves, worms, sponges and so
forth and, much more doubtfully, the direct dissolution of
the limestone by the sea water.- OcCasion‘ally, when an
especially deep channel has been formed in this manner-,
living corals may beable to establish themselves once m0re
in this region and, by their subsequent growth, ll up.the
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channel.
Finally, nearest the shdre will be a second at ;
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very often formed of coral on its outer side” only, the inner
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part being of land Origin, having been formed by the sea '
which, at the end
rush across the reef at, has cut.
its… way into the land.
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This explanation of the formation of fringing reefs clearly
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cannot be applied
reefs or atolls,the outer slopes
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