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Wonders of the Deep: Williamson Submarine Expedition, The Formation of Coral Reefs

Wonders of the Deep: Williamson Submarine Expedition, The Formation of Coral Reefs: How the reef is formed with details of the research conducted by Charles Darwin. The coral reef island, its structure and vegetation.

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The Coral Architect (continued)

After a time the coral polyp, having lived its full term of existence, dies, and presently the soft portion of the animal decomposes and is washed away by the moving water, leaving behind the hard, stony skeleton. Parts of this skeleton mass are broken off from time to time by the currents, or the waves, and the loose blocks of coral are frequently flung with considerable force against the mass, breaking off other portions, and gradually grinding a great deal of this into fine coral sand, which eventually fills the numerous holes and crevices. In the course of a long period the whole mass thus becomes cemented into hard reef rock, and in this way a kind of island is formed down on the ocean bed.

This is always going on, and thus the low island gradually rises through the addition of further rock material brought to it by the ocean waves and currents, until at last the reef has grown as high as the surface of the water.

Before long the reef becomes covered with a layer of soil, which is washed on to it by the waves. The seeds which this soil may contain, and those which may be dropped on to it by the birds, germinate, and not very long after varied forms of tropical and subtropical plant life begin to make their appearance, and in this way the coral island, originally quite bare, is clothed with a most luxuriant vegetation. In some instances the original island has completely sunk below the level of the water, leaving the fringe of a reef surrounding a central lagoon. Charles Darwin, one of the most eminent scientists of the nineteenth century, made a special study of the structure and distribution of coral reefs. He has described the lagoon islands, or atolls, as they are called, as "vast rings of coral rock, often many leagues in diameter, here and there surmounted by a low, verdant 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.” He further adds: “The naturalist will feel a deeper astonishment 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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How coral reefs are formed

Charles Darwin

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