A GREAT LESSON. 253 



grown old in Lis own early couvictions, was at least ready to entertain 

 it, and to confess that serious doubts had been awakened as to the 

 truth of his famous theory. 



If, however, Mr. John Murray has not been cheered by the ac- 

 clamations which greeted his illustrious predecessor, if the weight of 

 a great accepted authority and of preconceived impressions has kept 

 down the admiration which ought ever to reward the happy sugges- 

 tions of laborious research, he has had at least the great satisfaction 

 of observing the silence of any effective criticism. But more than 

 this — he is now having the still greater satisfaction of receiving cor- 

 roborative support from the observations of others. His own series 

 of facts as ascertained during the voyage of the Challenger consti- 

 tuted an array of evidence tolerably conclusive. But since he read 

 his paper in Edinburgh, an island has been discovered in the Solomon 

 group by another naturalist, Di*. Guppy,* which lifts into the light 

 and air a complete record of the series of operations beneath the 

 waters of the Pacific to which Mr. Murray ascribes the origin of 

 countless other islands, islets, and atolls. Here the barrier-reef and 

 the atoll have been elevated from their bed, and all their foundations 

 have been shown. Those foundations are not solid rock, but are just 

 what Darwin assumed they could never be — deep-sea deposits. These 

 had been originally, of course, laid down in more or less oceanic 

 depths. But elevation, not depression, had begun the work. The 

 deep deposit had ceased to be deep because the crust of the earth, on 

 which it lay, had been bulged upward by subterranean force. The 

 deep bottom had become a shoal, rising to the required distance from 

 the surface-level of the sea. The moment it reached the thirty or the 

 twenty fathom depth, the reef-building corals seized upon it as their 

 resting-place, and began to grow. Possibly some process of induration 

 may have affected the deposit before it reached this point. Probably 

 it was consolidated or indurated by the luxuriant growth of myriads 

 of deep-sea creatures at depths greater than thirty fathoms. ' 



It has recently been discovered, by another naturalist of the Chal- 

 lenger schooljf that there may be a special explanation of this part 

 of the operation. It is found that shoals have the immediate effect of 

 converting the tidal wave of deeper water into a current. This cur- 

 rent sweeps off the looser deposits covering the shoal. Deep-sea 

 corals then settle upon it. These may, and often do, build up their 

 walls to a great height, and if this height reaches the zone of the true 

 reef -building species, a firm basis is at once provided for their opera- 

 tions. Shoals have lately been discovered off the African coasts of the 

 Atlantic, which in tropical seas would probably have become coral 



* Surgeon of H. M. S. Lark. " Transactions of the Roval Society of Edinburgh," 

 June, 1885. 



f " On Oceanic Shoals discovered by the steamship Dacia," by J. Y. Buchanan, 

 F. Pi. S. E., "Proceedings of the Royal Society of Edinburgh," October, 1883. 



