40 ATOLLS. Ch. I. 



ing the surface. The channels, like the submerged and 

 effaced parts of the reef, occur very generally, though 

 not invariably on the leeward side of the atoll, or on 

 that side, according to Beechey, 1 which, from extending 

 in the same direction with the prevalent wind, is not 

 fully exposed to it. Passages between the islets on 

 the reef through which boats can pass at high-water, 

 must not be confounded with ship-channels by which 

 the annular reef itself is breached. The passages 

 between the islets occur, of course, on the windward 

 as well as on the leeward side ; but they are more 

 frequent and broader to leeward, owing to the lesser 

 dimensions of the islets on that side. 



At Keeling atoll the shores of the lagoon shelve 

 gradually where the bottom is of sediment, and irregu- 

 larly or abruptly where there are coral reefs ; but this 

 is by no means the universal structure in other atolls. 

 Chamisso, 2 speaking in general terms of the lagoons in 

 the Marshall atolls, says the lead generally sinks ' from 

 a depth of two or three fathoms to twenty or twenty- 

 four, and you may pursue a line in which on one side 

 of the boat you may see the bottom, and on the other 

 the azure-blue deep water.' The shores of the lagoon- 

 like channel within the barrier-reef at Vanikoro have 

 a similar structure. Captain Beechey has described a 

 modification of this structure (and he believes it is not 

 uncommon) in two atolls in the Low Archipelago, in 

 which the shores of the lagoon descend by a few broad, 



1 Beechey' s Voyage, 4to ed. vol. i. p. 189. 



2 Kotzebue's First Voyage, vol. iii. p. 142. 



