Ch. VI. DISTEIBUTION OF COEAL-EEEFS. 175 



with a level summit ; and, according to Mr. S. Wilson, 1 is an 

 upraised reef; ' and there are in the central hollow, formerly 

 the bed o£ the lagoon, many scattered patches of coral- rock, 

 some of them raised to a height of forty feet. ' These knolls 

 of coral-rock were evidently once reefs within the lagoon of 

 an atoll. Mr. Martens, at Sydney, informed me that this 

 island is surrounded by a terrace-like plain at about the 

 height of 100 feet, which probably marks a pause in its 

 elevation. From these facts we may infer that the Cook and 

 Austral Islands have been upheaved at a not very remote 

 period. 



Savage Island (S.E. of the Friendly group) is according 

 to Forster about 40 feet in height, and according to Williams 

 about 100 feet. Forster 2 describes the plants as already 

 growing out of the dead but still upright and spreading trees 

 of coral ; and the younger Forster 3 believes that an ancient 

 lagoon is now represented by a central plain : here we cannot 

 doubt that the elevatory forces have recently acted. The 

 same conclusion may be extended to the islands of the 

 Friendly Group, which have been well described in the 

 second and third voyages of Cook, and recently by Dana. 

 The surface of Tongatabou is low and level, but with parts 

 50 or 60 feet high ; the whole consists of coral-rock, ' which 

 yet shews the cavities and irregularities worn into it by the 

 action of the tides.' 4 On Eoua the same appearances were 

 noticed at an elevation of between 200 and 300 feet. Vavao, 

 also, at the opposite or northern end of the group, consists, 

 according to the Eev. J. Williams, of coral-rock. Tonga- 

 tabou, with its northern extensive reefs, resembles either an 

 upraised atoll with one half originally imperfect, or one un- 

 equably elevated ; and Anamouka, an atoll equably elevated, 



1 Couthouy's Kemarks. p. 34. 



2 Observations made during Voyage Bound the World, p. 147- 



3 Voyage, vol. ii. p. 163. 



4 Cook's Third Voyage (4to edit.), vol. i. p. 314. 



