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 - Relation in form 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 volcanoes in the areas of subsidence — Immen- 
sity of the areas which have been elevated and have subsided — 
Their relation to the present distribution of tne land — Areas of 
subsidence elongated — Their intersection and alternation with 
those of elevation — Amount, and slow rate of the requisite sub- 
sidence — Recapitulation. 
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 barrior-reefs ; 
