THE CORAL-REEF PROBLEM. 53 



atoll soundings made at a distance of 60 yards from the coast 

 failed to detect bottom at a depth of 1200 feet, and 500 feet 

 out from Whitsunday Island no bottom was found by Beechey 

 at a depth of 1500 feet. Captain Fitzroy found that at a dis- 

 tance of 6,600 feet from the Keeling Island shores the lead 

 did not strike bottom even after having been run out to a 

 length of 7,200 feet. Seven miles to the north-west of the Ber- 

 muda reef, as has already been seen, the depth of water is 

 2,100 fathoms, but the coast shallows for a considerable dis- 

 tance around the islands. It would 'thus appear that the 

 pitch of the coral island beneath the ocean is at a very steep 

 angle, sometimes considerably exceeding 45 degrees. Indeed, 

 there are some grounds for concluding that in the deeper 

 parts the faces are nearly vertical, rising like gigantic walls 

 from the oceanic abysses. 



In view of the peculiar conditions attending coral growth 

 the limitation of depth to 100 or 120 feet the difficulty of ac- 

 counting for the occurrence of coral structures in some of the 

 deepest parts of the sea at once becomes apparent. It had, in- 

 deed, been assumed that coral islands merely occupied the sum- 

 mits of submerged volcanoes, and that their distribution over 

 the deep-sea was simply an indication of the existence, in the 

 region in question, of an equal number of buried volcanic 

 peaks or mountain backs. Recent researches have, however, 

 failed in the majority of cases to detect the presence of such 

 hypothetical buttresses rising to within a few feet of the sur- 

 face, but, on the contrary, tend to show that at least in some 

 instances the actual coral portion of the island descends of 

 itself hundreds, if not thousands, of feet into the ocean. 



The genius of the late Mr. Darwin has furnished a theoretical 

 explanation of the phenomenon which, even if it cannot be 

 held to be proved or con-elusive, has at least the merit of a 

 strong probability in its favor, and of being in consonance 

 with well-determined geological facts and conditions. This 

 "subsidence" theory, which until recently received the almost 

 unanimous support of geologists, is based upon the evidence of 



