2S8 CRUISE OF THE PORPOISE. 



the laws of gravity, and descended to the unfathomable depths be- 

 neath them. 



The low coral islands, as far as they have been investigated, both 

 by boring and sounding, have shown a foundation of sand, or what 

 becomes so on being broken up. 



The elevated coral islands which we have examined, exhibit a 

 formation of conglomerate, composed of compact coral and dead 

 shells, interspersed with various kinds of corals, which have evi- 

 dently been deposited after life has become extinct. A particular 

 instance of this was seen at the island of Metia, and the same 

 formation was also observed at Oahu. 



The abrading effects of the sea on all the islands and reefs, was 

 evident, for they exhibited throughout a worn surface. Some living 

 corals are indeed found at the surface, but a few inches beneath it the 

 reef is invariably a collection of loose materials, and shows no regular 

 coralline structure, as would have been the case if it had been the 

 work of the lithophyte. 



All the coral islands lie within an ocean subject to the effects of 

 volcanic action, and we have no reason to doubt that they would be 

 as liable to be upheaved and depressed by it as those of unquestion- 

 able igneous origin. With so great and powerful an agent at hand, it 

 seems to me there is no necessity for resorting to a cause inadequate 

 of itself, and at variance with the facts. It seems almost absurd to 

 suppose that these immense reefs should have been raised by the 

 exertions of a minute animal, and positively so to explain the peculiar 

 mode of construction by which reefs of an annular shape are formed, 

 when in nine cases out of ten they are of other figures. 



Those who will examine the charts of the Pacific Ocean, and view 

 the relations which the coral islands bear to one another, as well as 

 the extent of ocean through which they are spread in groups, will 

 entertain but little doubt that many of them which are now separated 

 have at some remote period been joined, and formed extensive tracts 

 of land. They must also be inclined to believe that their alteration 

 and dismemberment have been brought about by the same causes 

 that affect other lands. If this be the case, there would be no difficulty 

 in accounting for the lagoons, as they now present themselves. Be- 

 fore I reached the coral islands, I had derived an impression, from the 

 attempts to explain the manner of their formation, that all the reefs 

 would be found level with the water, and have a uniform surface ; 

 but so far from this being the case, they are all irregular and much 



