Ch. VI. DISTRIBUTION OF CORAL-REEFS. 183 



mountains of the Society Islands, — a group of islands 

 encircled by barrier-reefs, and which, therefore, must 

 have recently subsided. Thus at Tahiti, Mr. Stutchbury 

 found on the summit of one of the highest mountains, 

 between 5,000 and 7,000 feet above the level of the sea, 

 6 a distinct and regular stratum of semi-fossil coral;' 

 but we cannot infer from such evidence as this that the 

 island has been elevated within the recent period ; and 

 on the other hand, several naturalists, including Mr. 

 Dana and myself, have in vain searched near the coast 

 for upraised shells and corals, where if present they 

 could not have been overlooked. Two of the Harvey 

 Islands, namely, Aitutaki and Manouai, are formed of 

 upraised coral rocks, and have probably been elevated 

 within a recent period ; nevertheless they are encircled 

 by reefs extending so far from the land, that I have 

 coloured them blue, though with much hesitation, as 

 the space within the reef is shallow, and the encircled 

 land is not abrupt. If these reefs really belong to the 

 barrier class, we have here another instance of subsi- 

 dence having followed elevation, both movements having 

 been effected apparently within the recent period. There 

 are also many cases of coral-formations, such as Elizabeth 

 Island, Metia, Mangaia, several of the Friendly and one of 

 the Loyalty Islands, which it can hardly be doubted once 

 existed as atolls, and were originally formed during sub- 

 sidence, but have since been elevated, and are now sur- 

 rounded by fringing-reefs. We have, however, no 

 reason to feel surprise at occasional or even frequent 

 alternations of level of the above two kinds. 



