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Birth of a coral island
How has this enormous reef, or more correctly, series of reefs, come into existence? We cannot answer this question with complete certainty, but at least we know that the conditions—clear water, warm and shallow—were ideal for the growth of coral. With these conditions to its liking, the coral flourished. But as it grew many agencies were at work destroying it; and as generation after generation of coral disintegrated into coral sand the living coral rose higher and higher till in places it thrust its head above the surface of the sea. Here it continued to grow, to die, and to disintegrate, till at length an island was formed, made up entirely of coral sand. fringing reef of coral, they are not coral Birds rested on it; their droppings islands. In the distant past they formed vitalized it; and when seeds of trees carried by the currents or attached to the feathers of birds were deposited on it they were able to take root and to grow.
Thus was a coral island born; thus will many others be born as the submerged reefs build their way to the surface.
The coral islands of the Great Barrier Reefs are all coral cays, so called to distinguish them from coral atolls, which form a complete ring of coral exposed to the air and enclosing a permanent lagoon. A coral cay is just a great sand heap, and most of the Barrier Reef cays are barely above high water level.
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