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attempt is made to illustrate these changes of land level, in 

 relation to the unchanging sea level, by drawing three successive 

 lines SI, S 2, S3, to represent the surface of the sea at three 

 different periods of time, as if the sea had risen, instead of 

 the land forming the sea bottom having been depressed. 



The island (a, a, b) represented in section, is surrounded by a 

 Coral strand or Fringing reef, (Fr, rF, SI) which grew in shallow 

 water, like the Florida Keys, or Coral banks of the present day. 

 Then suppose the island to sink slowly and gradually, so that the 

 sea flows more and more over it, (S2) until the reef stands at a 

 distance from the land, and separated therefrom by a shallow 

 channel or encirchng lagoon, (1, 1) the reef forms a Barrier round 

 the subsiding island, ks in the case of the island of Bolabola. As 

 the land sinks, the distance between the Barrier reef (Br , r B) 

 and the land (a, a, b) increases, and the lagoon channel widens. 

 When the highest peak of the land disappears, (S 3) and the 

 Barrier reef becomes an Atoll (Af ) or ring reef, without a 

 central island, then the lagoon channels unite and form a central 

 lake (1.) 



Although this theory cannot be supported by proofs as direct 

 and positive as those which result from observations long 

 continued on the same points, or be proved by geometrical 

 measurements made to attest the change of level on the land, 

 stiU there are facts which are highly significant in support 

 of the explanation. For example, we remark that the Atolls 

 show, in their general distribution, the form or the direction 

 of the land around which the base of the reefs had been 

 originally constructed. In the South Pacific Ocean three principal 

 groups of islands lie in a direction of north-west by south-east, 

 like almost all the land in this part of the globe. North 

 of the Equator the Caroline Archipelago extends east and 

 west ; and south of the line, the islands of Ceram, New Britain, 

 and New Ireland, have a similar direction. In the Indian Ocean 

 the Laccadives and the Maldivas Atolls extend in a Hne parallel 

 with the chain of the Ghauts on the adjoining Asiatic continent. 

 There is hkewise a considerable resemblance between the general 

 form and disposition of the Atolls and that of ordinary islands. 



