270 PAUMOTU GROUP AND 



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 exer- 

 tions 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 rup- 

 tured, some wholly above the water, others awash, and some again 

 altogether submerged, having various depths of water over them. 



As the coral islands have sand and limestone for their base, it would 

 appear possible to account for the formation of the lagoons by sup- 

 posing that, after the several portions of the pre-existing continent 

 were separated from each other, the outer edge or line of coral, une- 

 qually worn by the sea, had become more compact in some cases than 

 in others. Thus, while the border of the island resisted in one place, 

 it might be torn asunder in others, and through the washing influx 

 and efflux of the sea, strata underlying the centre might be carried 

 off into the deep sea in the shape of sand and mud, or in solution. 

 The centre, thus undermined, from want of support would cave in, 

 and form the inverted cone or tunnel-shaped lagoon, generally found 

 in the centre of these islands, surrounded by an outer rim, variable in 

 width and elevation. 



Actual observation proves that the reefs and islands are undergoing 

 dissolution, for at many points where former navigators have laid 

 down shoals of coral, none now exist. One reef, in particular, noticed 

 by those who visited Tahiti ten years before we did, was found by 

 Captain Belcher, of H. B. M. ship Sulphur, to exist no longer. This 

 officer states that he visited and surveyed the place where it is laid 



