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CHAPTER VI. 



ON THE DISTRIBUTION OF CORAL-REEFS WITH REFERENCE TO 

 THE THEORY OF THEIR FORMATION. 



Description of the coloured map — Proximity of atolls and barrier-reefs — 

 Belation inform and position of atolls with ordinary islands — Direct 

 evidence of subsidence difficult to be detected — Proofs of recent elevation 

 where fringing-reefs occur — Oscillations of level — Absence of active 

 volcanos in the areas of subsidence — Immensity of the areas which have 

 been elevated and have subsided — Their relation to the present distri- 

 bution of the land — Areas of subsidence elongated — Their intersection 

 and alternation with those of elevation — Amount, and slow rate of the 

 requisite subsidence — Becapitulation. 



It will be convenient first to give a short account of 

 the appended map of the Pacific and Indian Oceans 

 (Plate III.) ; a fuller one, with the data for colouring 

 each spot, is reserved for the Appendix, and every 

 place there referred to may be found in the Index. 

 A larger chart would have been desirable ; but, small 

 as the adjoined one is, it is the result of many months' 

 labour. I have consulted, as far as I was able, every 

 original voyage and map ; and the colours were first 

 laid down on charts on a large scale. The same blue 

 colour, with merely a difference in the tint, is used 

 for atolls or lagoon-islands, and for barrier-reefs; 



