ATOLL AND REEF FORMATION 229 



more rapidly than it can be dissolved. Then a lagoon is 

 formed because the solution exceeds the accumulations, and 

 this on the same spot, and in still shallower and less power- 

 fully dissolving water." 



The late Mr. T. Mellard Keade has also pointed out that if 

 solution does in reality form the lagoon at the top of the 

 bank, it ought to dissolve the bank itself much more easily 

 {Nature, March 22, 1888), and Mr. Hedley in the same journal 

 (August 4, 1904) has also shown this weakness of the theory. 

 As a matter of fact the work of Murray and Irvine appears to 

 show very clearly that at the surface of the sea calcareous 

 deposits take place, whilst at greater depths they tend to 

 become dissolved ; certainly calcareous deposits take place in 

 atoll lagoons. It is easily seen that brecciated rock and sand- 

 stone are formed in the lagoon by the actual deposition of 

 calcium carbonate. The deposition of calcium carbonate is a 

 very widespread phenomenon in the lagoon, so that, granting 

 that sea water dissolves coral, its action cannot be a very 

 destructive one where rapid deposition of calcium carbonate is 

 taking place. 



There are some features of a fully developed atoll which 

 have been urged in support of the theory of solution. In 

 Sir John Murray's first paper, he says (p. 515): "At the 

 Admiralty Islands, on the lagoon side of the islets on the 

 barrier reef, the trees were found overhanging the water, and 

 in some cases the soil washed away from their roots. It is a 

 common observation in atolls that the islets on the reef are 

 situated close to the lagoon shore. These facts point out the 

 removal of matter which is going on in the lagoons and 

 lagoon channels." 



Now with regard to the first statement, it is fair to say 

 that it is identical with Darwin's observations in the Cocos- 

 Keeling atoll, which gave him such strong confirmation of 

 his own theory. That any real weight could be attached to it 

 was denied by the objectors to Darwin's theory — and quite 

 rightly, for the condition is only one of those temporary 

 phases of atoll life which come and go with seasons and winds. 



