TIIEUHY OF CultAL-KEEFS. 



271 



which the section is now represented by unbroken 

 lines, and which, as I have said, is a real section 

 through Bolabola, and let it go on subsiding. As 

 the barrier-reef slowly sinks down, the corals will 



A'A'. Outer eUges of the barrier-reef at the level of the sea, with islets 

 on It. B'B'. The shores of the included island. C C. The lagoon-channel. 



A" A". Outer edges of the reef, now converted into an atoll. C. The 

 lagoon of the new atoll. 



N.B. According to the true scale, the depths of the lagoon-channel and 

 lagoon are much exaggerated. 



go on vigorously growing upwards ; but as the 

 island sinks, the water will gain inch by inch on 

 the shore, the separate mountains first fomiing 

 separate islands within one great reef, and, finally, 

 the last and highest pinnacle disappearing. The 

 instant this takes place a perfect atoll is formed : 

 I have said, remove the high land from within an 

 encircling barrier-reef, and an atoll is left, and the 

 land has been removed. We can now perceive 

 how it comes that atolls, having sprung from en- 

 circling barrier-reefs, resemble them in general 

 size, form, in the manner in which they are grouped 

 together, and in their arrangement in single or 

 double lines ; for they may be called rude outline 

 charts of the sunken islands over which they stand. 

 We can further see how it arises that the atolls in 

 the Pacific and Indian Oceans extend in lines 

 parallel to the generally prevailing strike of the 

 high islands and great coast-lines of those oceans. 

 I venture, therefore, to affirm, that on the theory 



