STRUCTURE OF CORAL ISLANDS. 41 



Raraka, Panmotu Archipelago.— 16° 10' S., 145° W. 14 

 miles by 8, trending east and west. Shape somewhat triangular. 

 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 en- 

 trance, 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 projecting parts of the reef. Layers of 

 beach sandrock on the lagoon shores, as well as on the seaward 

 side, inclined at an angle of six or seven degrees : characters as 

 already described. Growing coral in the entrance to the lagoon, 

 within two feet of the surface, mostly a species of Millepora, (M. 

 squarrosa.) Interior of the lagoon not examined for want of 

 time. The water looked as blue as the ocean, and was much 

 roughened by the winds. 



Kawehe, or Vincennes Island, Paumotu Archipelago, 15° 30' 

 S., 145° 10' W. 13 miles by 9, trending north-northwest. 

 Shape irregularly oval. Having a large lagoon, and mostly 

 wooded around, least so to leeward. Between the wooded islets, 

 (as on Raraka and elsewhere,) surface consisted of angular masses 

 of coral rock, (among which the Pontes prevail,) strewed in great 

 numbers together ; and in some parts bearing a few vines and 

 purslane among the blocks, though scarcely any appearance of 

 soil, or even of coral sand. In other parts, not as high, no veg- 

 etation, and surface still wet by high tide. A few large masses 

 of coral on the shore platform, either lying loose, or firmly at- 

 tached below ; some of them were six feet cube, and one was 

 raised seven feet above high-water mark. Those that were at- 

 tached were so firmly cemented to the reef-rock as to seem to be 

 a part of it, and they were partly worn off below by the wash 

 of the sea; the surface was extremely rough, owing to wear 

 by rains. These masses were sometimes single individual corals, 

 and others were conglomerate in character. Shore platform 

 about a hundred yards wide, rather highest at the edge, and much 

 of its surface two to four feet under water at low tide. As else- 

 where, this platform is nothing but a compact coral conglomerate 

 or limestone, having no growing coral over it, except in some 

 shallow pools near its outer margin, where also there are numerous 

 holes in which crabs are concealed, with small fish and other ani- 

 mals of the shores. On the lagoon shore, layers of beach sand- 

 rock, six or seven in number, dipping at an angle of seven degrees 

 towards the lagoon, and outcropping one from beneath the other. 

 Similar layers on the sea-shore side. 



