PACIFIC OCEAN. 199 



although numerous pieces of coral are thrown up on the beach ; 

 the sea close to its shore is very deep (see Zool. of Beechey's 

 Voyage, p. 164) ; left uncoloured. Gambier Islands (see Plate I. 

 fig. 8) are encircled by a barrier-reef: the greatest depth 

 within is 38 fathoms; coloured pale blue. Metia or Aurora 

 Island lies N.E. of Tahiti, close to the large space coloured 

 dark bine in the map ; it has been already described as an 

 upraised atoll ; as it is said by Captain Wilkes (Narrative of 

 U. S. Exploring Expedition, vol. i. p. 337) to be surrounded 

 by fringing- reefs, in one part 500 feet in width, it has been 

 coloured red. But I must remind the reader of the discussion 

 in the sixth chapter, showing that if an upraised atoll were to 

 subside again, the reef would probably retain for a long time 

 or for ever, its fringing character, owing to the steepness of 

 the submarine flanks. 



The Society Akchipelago is separated by a narrow space 

 from the Low Archipelago ; and in their parallel direction they 

 manifest some relation to each other. I have already described 

 the general character of the reefs of these encircled islands. 

 In the atlas of the CoquilWs Voyage there is a good general 

 chart of the group, and separate plans of some of the islands. 

 Tahiti, the largest island in the group, is almost surrounded, 

 as seen in Cook's chart, by a reef from half a mile to a mile 

 and a half from the shore, with from 10 to 30 fathoms within 

 it. Some considerable submerged reefs, lying parallel to the 

 shore, with a broad and deep space within, have lately been 

 discovered on the N.E. coast of the island, (Naut. Mag. 1836, 

 p. 264,) where none are laid down by Cook. At Eirneo the 

 reef, ' which like a ring surrounds it, is in some places one or 

 two miles distant from the shore, in others united to the 

 beach ' (Ellis, Polynesian Eesearches, vol. i. p. 18, 12mo. 

 edit.). Cook found deep water (20 fathoms) in some of the 

 harbours within the reef. Mr. Couthouy, however, states 

 (Remarks, p. 45) that both at Tahiti and Eimeo, the space 

 between the barrier-reef and the shore has been almost filled 



