I08 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



So far as I have been able to form an opinion, I entirely agree 

 with the views expressed by my friend Prof. Bonney in the Appendix 

 to the third edition of Darwin's ' Structure and Distribution of 

 Coral Eeefs.' The evidence brought forward by Mr. John Murray, 

 Prof. Agassiz, Dr. Guppy, and others, certainly shows that an atoll 

 with a shallow lagoon may originate in an area that is stationary or 

 even undergoing slow elevation. At the same time I cannot concur 

 in the theory of the origin or deepening of atoll-lagoons by solution. 

 If sea-water were capable of dissolving corals to this extent, it is 

 difficult to understand how any marine limestones can have origi- 

 nated, especially such as the chalk, which is chiefly composed of 

 minute Foraminifera. It has been urged by Mr. John Murray that 

 coral atolls may be founded on submarine banks raised to within the 

 limits at which reef-building corals grow (whether this be 15, 20, or 

 25 fathoms or more) by the deposition of shells from small floating 

 MoUusca, Crustacea, Foraminifera, &c. Some explanation is neces- 

 sary why the sea-water should be incapable of dissolving these 

 minute shells, but yet should have the power of forming deep lagoons 

 by solution of the far more solid corals. In the lagoon, it must be 

 remembered that the sea-water is far less quickly renewed than in 

 the open sea, and must be quickly saturated, and also that the 

 higher temperature of the lagoon-water, by diminishing the amount 

 of carbonic acid in solution, would lessen the quantity of calcium 

 carbonate that the water could dissolve. I believe, however, that 

 very few observers are now prepared to accept the hypothesis of the 

 formation of the atoll-lagoons by the solution of the coral rock * ; 

 and if this be not accepted, it is difficult to understand how lagoons 

 40 fathoms deep and upwards, as in some of the Maldive Islands 

 and on the Chagos and Saya de Malha banks, can have been formed 

 without subsidence. 



There is another point to which Darwin especially called atten- 

 tion, but which has, I think, been greatly overlooked in the recent 

 discussions, the cumulative nature of the evidence f. The frequent 

 occurrence of atolls in groups is noteworthy. The Laccadive and 

 Maldive atolls are together more than 30 in number, and on the 

 theory of subsidence, with the understanding that, as the land sank, 

 coral-reefs formed gradually and grew jiciri passu with the depres- 

 sion, it is easy to understand how it occurs that all are now at one 



* Mr. G-. C. Bourne's remarks, Pnoc. Roy. Soc« xliiu 1888, p. 449, are very 

 important. 

 t See ' Coral Eeefs,' ed. ix. pp. ix, 125, &c. 



