40 THE WORLD'S WONDERS. 



But there are coral reefs of far greater magnitude. The 



O O 



grandest is that extending along the northeast coast of Australia. 

 Rising from an unfathomed ocean, it extends for 1,000 miles 

 along the coast, with a breadth of from 200 yards to a 

 mile, and at an average distance of twenty or thirty miles, 

 though sometimes double that space. This long, narrow lagoon 

 is never less than ten fathoms deep, and often six times as much, 

 so that the " Great Eastern," the hugest vessel that ever floated, 

 if it once passed through one of the openings in the reef, 

 might sail as though in a tranquil harbor for 1,000 miles in sight 

 of land on either side, without its keel for an instant reaching 

 half-way to the bottom. 



The direct influence of the ocean upon the islands of the 

 tropical world is great in every respect. It gives an almost tem- 

 perate climate to low lands lying under the equator, and thus 

 modifies their fauna and flora, in accordance with known laws of 

 nature. But the ocean and air in their currents also determine 

 the vegetable, animal and human life of the islands of the 

 tropical world in an accidental manner. 



Time was when the volcanic islands of the tropics were 

 masses of naked rock, the coralline islands patches of barren 

 sand. The elements disintegrated the surface of the rock and 

 ground the coral into the soil. Some day a fruit perhaps a 

 cocoa or bread-fruit drifted along by currents, touched the 

 island ; or a bird, swept far out to sea, having in its crop an 

 undigested seed, rested its weary wing upon solid land. The 

 chance-planted fruit or seed took root and grew, and produced 

 its kind, and in time the waste island was clothed with verdure. 

 Other birds found a home in the new forests, built their nests, 

 and raised their young, so that the islands became populous with 

 the winged tribes. Animals, of course, could only rarely cross 

 the waste of waters. Hence the comparative paucity of this 

 form of life in islands remote from the main land. Swine were 

 almost the only quadrupeds which the early European navi- 

 gators found in Polynesia ; and they were doubtless brought 

 there by human means. Mankind reached the islands iu a like 



