96 Couthouy on Coral Formations 



Crossing the plain, which is overrun with a variety of bur- 

 rowing Crustacea, terrestrial Paguri, and on some islands a 

 species of Birgus, as often found on trees as among stones j 

 we emerge from a tangled thicket upon the light green waters 

 of the tranquil lagoon. This of course, varies greatly in 

 extent and depth, and not less in the character of its bed. 

 Some have the appearance of being very shallow throughout, 

 the water being, except where darkened by occasional gullies, 

 of an uniform pale, yet brilliant green hue. In others, there 

 are large strips and patches toward the centre, where it is 

 nearly as blue as the surrounding ocean. At Aitoho, one of 

 the Disappointment Islands, the whole central portion of the 

 lagoon is of this latter color, as if it were very deep, although 

 less in circuit than many others. From the beach of some, I 

 have waded out for a couple of hundred yards, with the Avater 

 deepening almost imperceptibly, over a bottom of fine sand, 

 with only a few scattered bunches of coral ; while in others, 

 their bed is very unequal, full of large and deep pits, and 

 traversed by gullies several fathoms deep and from ten to 

 three hundred yards wide, occasioned probably by like irreg- 

 ularities in the submerged land. 



At Serle Island, and several other Paumotus, I observed at 

 a couple of miles or so from shore, several small islets and 

 clumps of rock, rising above the surface of the lagoon, nearly 

 as much as its bordering ridge, and apparently encircled by 

 water much deeper than the average. 



It would have been exceedingly interesting, and was cer- 

 tainly of importance in arriving at a correct idea of the struc- 

 ture of these islands, to have ascertained the composition of 

 such islets ; but the circumstances in which I was placed, 

 entirely dependent on the pleasure of those in whose opinion 

 such objects were of merely secondary consequence, and by 

 whom my every movement was limited and controlled, ren- 

 dered it impossible for me to make an examination so desira- 

 ble. Should they hereafter be found to consist of volcanic 

 rock, they would establish beyond all question the theory of 

 subsidence first advanced by Mr. Darwin. Should they, on 

 the contrary, be as I suspect, of coralline formation, this would 



