CORAL-REEFS. 
Some parts of the ocean are studded with a peculiar kind of rock, 
very narrow, but stretched out to a considerable length. It is called 
a Coral-reef, and is produced by innumerable small zoophytes popu- 
larly called Coral-insects, The Coral-insect consists of a little oblong 
bag of jelly closed at one end, but having the other extremity open, and 
surrounded, by tentacles or feelers, usually six or eight in number, set 
like the rays of a star. Multitudes of these minute animals unite to 
form a common stony skeleton called Coral, or Madrejjore, in the minute 
openings of which they live, protruding their mouths and tentacles 
when under water, but suddenly drawing them into their holes when 
danger approaches. These animals cannot exist at a greater depth 
in the sea than about ten fathoms, and as the Coral islands often rise 
with great steepness from a sea more than three hundred fathoms 
deep, it would seem that a great alteration must have taken place in the 
depth of the ocean since the time when the little architects commenced 
their labours. Their mode of working is, to build up pile upon pile 
of their rocky habitations, until at length the work rises to such a 
height that it remains almost dry at low water. A solid rocky base 
being thus formed, sea-shells, fragments of coral, sea-hedge-hog-shells, 
and prickles, are united by the burning sun and the cementing cal- 
careous sand into a solid stone, which gradually increases in thickness, 
till it becomes so high that it is covered only by the spring tides. 
The heat of the sun so penetrates the mass of stone when it is dry, 
that it splits in many places, and breaks off in flakes. These flakes 
are raised by the active surf, and thrown, with sand and shells of ma- 
rine animals, between and upon the foundation stones, where they offer 
to the seeds of trees and plants, cast up by the waves, a soil upon 
which they rapidly grow, overshadowing the dazzling white surface. 
Trunks of trees, carried by rivers from other countries and islands, find 
here, at length, a resting-place ; with these come small animals, such as 
lizards and insects, as the first inhabitants ; sea-birds nestle there ; 
strayed land-birds take refuge in the bushes ; and at a much later 
period man also appears, and builds his hut on the fruitful soil. 
Reefs are of various forms. In some places they occur at a great 
distance from the land, and run nearly parallel with it : these are 
called barrier -reefs, and are often of enormous dimensions. Usually 
a snow-white line of great breakers, with here and there an islet 
crowned by cocoa-nut trees, separates a broad channel of smooth 
water from the waves of the open sea. In other places Coral-reefs 
fringe the shore, and are separated from it by a narrow channel of 
moderate depth: these are called fringing or shore-reefs. 
But perhaps the most remarkable form of reef is that to which 
the term Lagoon-Island has been applied. In this case the reef ap- 
proaches the form of a circle ; and, surrounding a part of the sea, 
produces a sheet of smooth water called a lagoon, or lake, within which 
are usually several smaller islands. From this circumstance the word is- 
land, as applied to the whole, has been objected to, and the term atoll 
substituted, which is the name given to these circular groups of 
Coral islets by the inhabitants of the Indian Ocean. 
"Every one," says Mr. Darwin, "must be struck with astonishment 
when he first beholds one of these vast rings of Coral rock, often 
many leagues in diameter, here and there surmounted by a low ver- 
dant island with dazzling white shores, bathed on the outside by the 
foaming breakers of the ocean, and on the inside surrounding a calm 
expanse of water, which, from reflection, is of a bright but pale green 
colour. The naturalist will feel this astonishment more deeply after having 
examined the soft and almost gelatinous bodies of these apparently 
insignificant creatures, and when he knows that the solid reef increases 
only on the outer edge, which, day and night, is lashed by the breakers 
of an ocean never at rest." 
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SOCIETY FOR PROMOTING CHRISTIAN KNOWLEDGE. 
