STRUCTURE OF CORAL ISLANDS. 201 



pore incrustations, which give it a variety of delicate shades of 

 color, mostly reddish, of peach-blossom red, rose, scarlet. For 

 thirty to fifty feet from the margin, very cavernous, and con- 

 taining many Tridaciue, lying half imbedded, with the variously 

 tinted mantle expanded when the surface is covered with wa- 

 ter. Rock of the platform either a compact white limestone or 

 a solid conglomerate ; dead over its surface, excepting a few 

 Madrepore tufts or Astraeas 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 com- 

 monly 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 decomposition intermingled. On 

 the bottom, exterior to the shore platform, observed the same 

 corals growing as occurred in fragments upon the island ; but 

 the larger part of the bottom was without coral, or consisted 

 only of sand. 



fiaraka, Paumotu Archipelago.— 16° 10' S., 145° W. 14 

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

 gular. North side nearly continuously wooded ; south angle 

 and southwest 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 difficult 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 coral rock, one to four hundred cubic feet, 

 on the platform and upon the higher parts of the island, some 

 of which stood five and six feet above high- water mark ; they 

 were cemented to the reef- rock below, and appeared like project- 



