CHANGES IN OCEANIC REGIONS. 335 



Chagos isles in the Indian Ocean are coral formations of a horse-shoe shape opening to 

 the north-west, while the prevailing wind blows regularly from the south-east. 



The rapidity of the growth of the coral is a point upon which nothing certain can be 

 stated, owing to the w.ant of ancient observations with which to compare those of the 

 present day. The Dolphin reef off Point Venus in Otaheite, when first examined by 

 Captain Wallis in 1^69, had twelve feet of water upon it. Captain Beechey found it in 

 much the same state in 1826 after an interval of fifty six-years. But this reef being 

 within the influence of rivers cannot be taken as a criterion of the increase of coral 

 limestone, owing to the aversion of the zoophytes to fresh water. In the year 1792 the 

 Matilda, a whaler, was wrecked in the night time upon a reef of coral rocks, in latitude 

 22 S., and longitude 138 34'. Upon an island answering to this situation Beechey 

 found unequivocal signs of a shipwreck ; part of a vessel's keel and fore-foot, broken 

 casks, a number of staves, hoops, lances, and harpoons, two anchors, and a leaden pump 

 with the date of 1790 upon it. The date, the nature, and the situation of these remains, 

 left no doubt that they belonged to the unfortunate Matilda ; but whether they had been 

 washed up to their present site by some extraordinary high tide and sea, or whether the 

 reef had since grown upwards, and raised them above the reach of the waves, could not 

 be determined. Beechey thought the former the most probable, but it is evident, as he 

 remarks, that a considerable alteration has taken place since the wreck, as the crew 

 described themselves to have been lost on a reef of rocks, whereas the island is fourteen 

 miles in length, with a deep central lagoon, and has a well-defined aspect, one of its sides 

 being covered nearly the whole way with high trees, which are very conspicuous, and 

 could not fail to be seen by persons in the situation of the crew, had the same appearance 

 been presented there. While the anchors were found not at all overgrown with coral, 

 which may have arisen from the oxide formed being prejudicial to the animalcules, a 

 species of large shell -fish, the Chama gig as, while the animal was yet living, was observed 

 so completely covered, that a space of only two inches was left for the extremity of the 

 shell to open and shut. It is supposed by conchologists that the chima may require 

 upwards of thirty years to attain its full size, but from an isolated fact like this no judg- 

 ment can be formed respecting the rate of advance of the coral formations in general. 

 The augmentation may be slow, but it is steady and constant, for it is perfectly accordant 

 with the instincts of animals to continue working without intermission until their labours 

 are consummated, or their lives extinct ; and it is obvious that until the dissolution of 

 our planet shall arrive, the zoophytes will perpetuate their races, and the ocean keep up 

 its supply of lime. Comparing the state of the coral formations now in progress after the 

 lapse of a century, only a slight alteration may be perceptible, so extensive is their area ; 

 but there can be no question that if we could study them after the lapse of several centu- 

 ries, vast changes would be observable ; the filling up of channels with reefs, and the 

 conversion of reefs into islands. 



c c 



