^54 CORALS AND CORAL ISLANDS. 



formed from the guano deposits on a coral island, Sombrero, 

 in the Caribbean Sea. 



Lord Byron, of the Blonde, mentions that phosphate of 

 lime (apatite) was collected by him on Mauke, an elevated 

 coral island of the Hervey Group, west of the Society Islands, 

 but its exact condition in the rock is not stated. 



Coral islands are exposed to earthquakes and storms like 

 the continents, and occasionally a devastating wave sweeps 

 across the land. During the heavier gales, the natives some- 

 times secure their houses by tying them to the cocoanut trees, 

 or to a stake planted for the purpose. A height of ten or 

 twelve feet, the elevation of their land, is easily overtopped by 

 the more violent seas ; and great damage is sometimes expe- 

 rienced. The still more extensive earthquake-waves, such as 

 those which have swept up the coast of Spain, Peru, and the 

 Sandwich Islands, would produce a complete deluge over these 

 islands. We were informed by both Grey and Kirby, that effects 

 of this kind had been experienced at the Gilbert Islands ; 

 but the statements were too indefinite to determine whether 

 the results should be attributed to storms or to this more 

 violent cause. 



But while coral islands have their storms, the region in 

 their vicinity is generally one of light winds and calms, even 

 when the trades are blowing strongly all around them. The 

 heated air which rises from the islands lifts the currents to 

 a considerable height above the island. J. D, Hague men- 

 tions that on Jarvis's and the two neighbouring islands, under 

 the equator, near i8o° in longitude from Greenwicli, he " often 

 observed the remarkable phenomenon of a rain-squall approach- 

 ing the island, and, just before reaching it, separating into two 

 parts, one of which passed by on the north, the other on the 

 south side, the cloud having been cleft by the column of heated 

 air rising from the white coral sands." 



