1 64 CORALS AND CORAL ISLANDS. 



Ahii, or Peacock's Island, Paumotu Archipelago. — 14° 30' 

 S., 146° 20'' W. 13 miles by 6, trending N. E. by E. Shape 

 irregularly oblong. A large lagoon, having an entrance for 

 small vessels on the west. Reef wooded throughout nearly its 

 whole circuit. Lagoon shallow, and much obstructed by 

 growing coral, the latter giving the water over it a clear light 

 green colour. Platform, or outer coral shelf of the island, 

 about two hundred and fifty feet wide ; under water except at 

 the lowest tides. Margin highest, and covered with Nullipore 

 incrustations, which give it a variety of delicate shades of 

 colour, mostly reddish, of peach-blossom red, rose, scarlet. 

 For thirty to fifty feet from the margin, very cavernous, and 

 containing many Tridacnge, lying half imbedded, with the 

 variously tinted mantle expanded when the surface is covered 

 with water. Rock of the platform either a compact white 

 limestone or a solid conglomerate ; dead over its surface, ex- 

 cepting a few Madrepore tufts or Astrseas near the margin in 

 pools. In this shelf there were long fissures, extending nearly 

 parallel with the shore, a quarter to half an inch wide at top, 

 and continuing sometimes a fourth of a mile or more. These 

 fissures were commonly filled with coral sand. The higher 

 parts of. the island either consisted of loose blocks of coral or 

 were covered with some soil ; the soil mostly of comminuted 

 coral and shells, with dark particles from vegetable decom- 

 position intermingled. On the bottom, exterior to the shore 

 platform, observed the same corals growing as occurred in frag- 

 ments upon the island ; but the larger part of the bottom was 

 without coral, or consisted only of sand. 



Rai^aka, Paumotu Archipelago. — 16° 10' S., 145° W. 14 

 miles by 8, trending east and west. Shape somewhat tri- 

 angular. North side nearly continuously wooded ; south angle 

 and south-west reef bare. A large lagoon, with an entrance 

 for small vessels on the north side. A rapid current flows from 

 the entrance, which it was difiicult for a boat to pull against. 

 Shore platform, as usual, about a hundred yards wide, with the 

 edge rather higher than the surface back ; the platform mostly 

 bare of water at low tide. Several large masses of coral and 



