CHAPTER VI. 



ON THE DISTRIBUTION OF CORAL-REEFS WITH 

 REFERENCE TO THE THEORY OF THEIR FOR- 

 MATION. 



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

 — Relation in form and position of atolls zvith ordinary islands. — 

 Direct evidence of subsidence difficult to be detected. — Proofs of 

 recent elevation where fringing-reefs occur. — Oscillations of level. — 

 Absence of active volcanoes in the areas of subsidence. — Immensity 

 of the areas which have been elevated and have subsided. — Their 

 relation to the present distribution of the land. — Areas of sub- 

 sidence elongated, their intersection and alternation with those 

 of elevation. — Amount ', and slow rate of the subsidence. — Re- 

 capitulation. 



It will be convenient to give here a short account of the 

 appended map (Plate V.) : 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 larger scale. The same blue colour, with merely a 

 difference in the depth of tint, is used for atolls or lagoon- 

 islands, and barrier-reefs, for we have seen, that as far as 



