102 HANDY BOOK OF 



hold their own on the surface, this estimate is probahly far 

 beneath the reality. 



The length of time needed for the formation of these 

 colossal Coral-banks may be judged from the fact that 

 D'Urville found the anchors of Perouse's ships lost forty 

 years previously off Vanikoro, at a depth of fifteen feet, 

 covered with only a small crust of Coral, and that the anchor 

 which Anson, the circumnavigator, left off the island of 

 Tinian, in a depth of twenty-two fathoms, when found 

 eighty- five years after was also merely covered with a thin 

 layer of Coral. Thus the naturalist is shown the extreme 

 age of our planet by the reefs of the tropical ocean. 



While some portions of the bed of the sea are sinking, 

 others again are rising. These masses of raised Coral 

 prove that the New Hebrides, Solomon's Islands, New Ire- 

 land, the Friendly Islands, &c, are emerging from the bed 

 of ocean. 



Round Eua Island runs a Coral wall twenty feet high, in 

 which the surf has excavated deep cavities and spouting 

 holes. At such places the in-rolling wave produces inter- 

 mittent springs, which start from the perforated rock with 

 immense force. 



Most interesting is the manner in which lagoon islands 

 and encircling reefs eventually become the residence of 

 man; for the Corals only build up to low- water mark, 

 and, therefore, every tide necessarily lays their labours 

 under water. But where the living architects falter, the 

 destroying surf displays itself as a creative might. It tears 

 fragments and blocks from the exterior of the reef, and 

 hurls them a long distance over its surface. Corals, shells, 

 and sea-urchin houses are converted, by its crushing, grind- 

 ing power, into lime, which gradually rills up the inter- 

 stices of the large, irregularly-piled blocks, and imparts to 

 them greater solidity. In this manner the firm ground 

 rises higher and higher, till at last only the spring tides 

 submerge it. Soon, too, the tropical sun does its part in 



