214 



SCIENCE. 



[Vol. XXII. No. 559 



CORAL FORMATIONS. 



BY G. H. PEEKINS, UNIVERSITY OF VERMONT, BURLINGTON, VT. 



When the old navigators, after long and weary voyag- 

 ing, at last came upon the coral islands of the southern 

 Pacific and gazed with delight upon the circles of green 

 foliage lifted above the frothing breakers, verily they 

 must have thought that they had found the Enchanted 

 Isles. 



Probably no portion of the earth's surface is more like 

 fairy land or more wonderfully beautiful than a typical 

 coral island. But the beauty of these islands, although 

 so exquisite, is not their chief attraction, for as one learns 

 how numerous they are, how unique their structure, how 

 peculiarly they are distributed through the oceans, how 

 unlike other reefs and islands is their form, elevation 

 above sea level, and indeed everything that pertains to 

 them, he becomes eager to know why they are as they 

 are and by what processes they have come into being. 



It soon becomes evident even to a very casual observer 

 that the geological and chemical principles, which are 

 sufficient to explain the existence of other reefs and 

 islands, are not satisfactory when applied to these, and 

 that some different conditions must be sought to account 

 for the different results which have been attained in these 

 singular structures. 



What these conditions are or have been in the past it is 

 not easy to determine, and, although from the time of the 

 first navigator coral formations must have excited curi- 

 osity, no theory to account for them was made known un- 

 til in 1837 Mr. Darwin, after his voyage in the Beagle, 

 published his well-known theory. 



From the first this theory was received with gen- 

 eral approval, nor is this strange, for it is at once so sim- 

 ple and so apparently sufficient that nothing more seems 

 to be needed. This theory was also greatly strengthened 

 by the endorsement of Professor Dana after his return 

 from the Wilkes Expedition in 1842. 



For many years Mr. Darwin's theory was scarcely ques- 

 tioned, and certainly there is nothing improbable in any 

 of the conditions which it requires. The only question 

 is, Do the observed facts warrant its acceptance ? As VTill 

 be remembered, Mr. Darwin supposed that the whole vast 

 area in which coral islands are found has been slowly 

 sinking for a very long time, that islands of the usual 

 sort, which formerly existed, have wholly disappeared 

 through subsidence, aad that about these islands there 

 grew masses of coral which in time formed fringing reefs, 

 that as the island sank the coral grew upward more rap- 

 idly on the outer or seaward side because there food 

 was more abundant, and as the island sank the reef would 

 presently be separated from the island by a strip of 

 water; that is, the fringing reef would become a barrier 

 reef. Finally, the island having disappeared, the reef, 

 would become an island of more or less annular form en- 

 closing a lagoon that is an atoll. 



So long ago as 1851, Professor Agassiz, after studying 

 the Florida reefs, declared that he found no evidence of 

 subsidence, and that the structure of the southern part of 

 Florida must be explained in some other way. 



So also Semper, in the Pelew and Philippine islands. 

 Dr. Guppy in the Solomons, and Dr. Bain in the Ber- 

 mudas, had been studying coral formations, and all these 

 observers found the old theory inadequate to account for 

 the structural peculiarities noticed. 



Later, and more important than these, are the observa- 

 tions of the naturalists of the Challenger at Tahiti, which 

 have led many scientists to reject the commonly received 

 theory. 



However great the dissatisfaction with Mr. Darwin's 



theory may have been, it was not given utterance until in 

 1880 Mr. Murray, one of the Challenger naturalists, pub- 

 lished a theory quite unlike that which had been current. 

 Although first stated by Mr. Murray, this theory is to be 

 regarded as an outgrowth from the objections to the older 

 one. 



Mr. Darwin himself noticed that in some cases corals 

 grew upon submerged platforms or banks and also that 

 the growth was most rapid on the seaward side of a reef 

 where food was most abundant, and all subsequent inves- 

 tigators have noticed the same fact. 



Mr. Murray assumes a sufficient number of such plat- 

 forms to afford foundations for coral growth, and that 

 the peculiar form of reef or island would be determined 

 by well-known conditions. 



Of course the upward growth of the coral would be in 

 a solid mass if growth went on equally, and this is some- 

 times the case, but usually because of the rapid increase 

 of the outer zone of coral and because of the solvent ac- 

 tion of the sea water upon the dead or weakly growing 

 coral in the interior zone the forming island becomes an- 

 nular, that is, an atoll. 



Deep-sea soundings have proved that such submerged 

 banks and islands as are demanded by this theory do ex- 

 ist and are more numerous than has been supposed, and' 

 also that by the accumuiation of shells and all sorts of 

 debris such foundations, if at first too deep, may be 

 raised nearer the surface and into the coral-growing 

 region. 



On the other hand, mountain peaks, rising above the 

 surface, may be worn down below it by erosion. 



As atolls may begin as fringing reefs and may even at 

 first be platforms of coral rock, so barrier reefs may begin 

 as fringing reefs, and as they grow outward the solid coral 

 be dissolved and worn away between the reef and the 

 land, thus changing one into the other. 



There are then these two theories at present before us. 

 Which IS to finally prevail? The naturalists of the Chal- 

 lenger expedition are fully committed to the new view 

 and so are many leading English scientists. 



If one seeking information should chance upon an arti- 

 cle by the Duke of Argyle in the Nineteenth Century of 

 September, 1887, or Professor Geikie's Presidential ad- 

 dress before the Royal Physical Society of Edinburgh, he 

 would probably conclude that the question had been 

 finally settled in favor of Mr. Murray's views. 



If, however, he should turn to the November numb: r 

 of the same periodical he would discover that no such 

 result had been reached and that it is not probable that 

 it soon will be. 



Certainly when such an authority as Professor Huxley 

 can write as he does in the latter article, "I happen to 

 have spent the best part of three years among coral reefs, 

 and when Mr. Murray's work appeared I said to myself 

 that until I had two or three months to give to the sub- 

 ject ***** J mugj; \)Q content to 

 remain in a condition of suspended judgment," it becomes 

 us to be modest in expressing an opinion. 



Should one still seek for information upon this subject 

 he may find in the American Journal of Science and Arts, 

 vol. XXX, 1885, sundry articles by Professor Dana in 

 which there is very strong advocacy of Mr. Darwin's the- 

 ory and opposition to that of Mr. Murray. While it 

 would be idle at present to attempt to decide as to the 

 value of either theory we may perhaps do well to con- 

 sider some of the facts before us. 



That there has been subsidence in great areas of the 

 sea bottom cannot be doubted nor can it be doubted that 

 there are great areas where there has been elevation, and 

 in still other areas there does not appear to have been 

 either rising or sinking. 



