President's Address. 13 



As the atoll increases in size, the lagoon becomes propor- 

 tionately larger, partly from its water being less supplied 

 with pelagic food, and tlierefore less favourable to the growth 

 of the more massive kinds of coral, partly from the injurious 

 effects of calcareous sediment upon coral growth there, and 

 partly also from the solvent action of the carbonic acid of the 

 sea-water upon the dead coral. This process of solution of 

 dead calcareous organisms by sea-water is undoubtedly one 

 of the most interesting facts in the chemistry of the ocean 

 which has been brought to light by tlie naturalists of the 

 " Challenger " Expedition. 



Moreover, a connected chain of atolls might be formed on 

 a long submarine bank, and similar conditions of growth 

 would then be displayed, as in the case of the single atoll. 

 The marginal atolls, having a better supply of food, would 

 grow more vigorously than those towards the centre, and 

 would tend to assume elongated forms, according to the shape 

 of the bank beneath them. Many of them might coalesce, 

 and might even ultimately give rise to one large atoll. Such 

 a chain of atolls as that of the great Maldive group may be 

 thus explained without the necessity for any disseverment 

 by oceanic currents, as Darwin supposed. On the other 

 hand, the submerged coral banks of the Lakadive, Caroline, 

 and Chagos Archipelagos may be regarded as representing 

 various stages in the growth of coral-reefs; some of them 

 being still too deep for reef-builders, others with coral-reefs 

 which have not yet quite grown up to the surface. But 

 scattered among these banks are some of the most completely 

 formed atolls. Mr Murray contends that it is difficult to 

 conceive how such banks can have been due to subsidence, 

 when their situation -with respect to each other and to the 

 perfect atolls is considered. He reverses the order of growth 

 as given by Darwin, who cited the great Chagos bank as 

 probably an example of an atoll which had been carried down 

 by a subsidence more rapid than the rate at which the corals 

 could build upwards. 



From a careful study of barrier-reefs, Mr Murray concludes 

 that in their case also, all the phenomena can be explained 

 without having recourse to subsidence. He found, from per- 



