460 On the Coral Formations of the Indian Ocean. [Mar. 22, 



I would be the last to deny that organic material brought by currents 

 must determine the existence of coral polyps in every instance. I 

 have confined nn'self to a discussion of the islands of the Indian 

 Ocean, because I have no practical knowledge of coral formations in 

 other parts of the world, and it would be rash to dogmatise about 

 their structure when the conditions may be different. In the Indian 

 Ocean I may fairly assume that the coral groups are subjected to the 

 same influences that I studied at Diego Garcia. No doubt many of 

 my statements will be contradicted by observers in the Pacific Islands 

 and elsewhere. I can only say that they are true of the group which 

 I have visited, and that within the limits of that group they form 

 contradictions to existing theories. The seas in which coral reefs are 

 formed are not all subject to the same conditions. In the Chagos 

 group there is always a heavy swell on the ocean, and the sea breaks 

 with a great force against the outer shores, and even over the shallower 

 parts of submerged banks ; the breakers are said to reach a height of 

 15 to 18 feet, but I never saw them so large at Diego Garcia. In 

 other groups oi coral formations the sea is wonderfully calm, and the 

 sea rarely breaks on the outer shores with any violence. Some 

 islands are situated in the direct course of great ocean currents, others 

 are not, and are swept by the minor currents caused by prevailing 

 winds. However one looks at the subject one must realise that the laws 

 governing the formation of coral reefs are exceedingly complex, and 

 that many circumstances have to be taken into account before any 

 perfect explanation of their structure can be obtained. Action and 

 reaction, destruction and reconstruction, growth and decay are con- 

 stantly at work ; the result of the multitude of nicely balanced forces, 

 seemingly antagonistic, is the atoll or reef. It seems to me that the 

 current theories of the formation of coral reefs attempt to explain 

 everything by one or two agencies, whereas the agencies are numerous, 

 and interact in a most complicated manner. Mr. Murray is undoubtedly 

 right in laying stress on the necessities of nutrition suitable for coral 

 growth, and the solve at action of sea water, but he has not taken 

 count of other agencies which tend to modify and obscure these, and 

 therefore his theory is not in itself sufficient to explain the question. 

 I cannot expect that my views will be of universal application, since 

 my observations were made on so limited a field, but I hope that com- 

 petent observers will spend some months on coral formations in 

 different parts of the world and give the closest attention to their 

 facies, without overlooking the minutest particular bearing on coral 

 growth on the formation of the reef. Then only shall we be in a 

 position to construct a general theory of coral reefs. 



[Note. — The life history of corals shows that they are not adapted 

 to live in strong and direct currents. The free larvae (planulee) swim 



