VII. 



The Exploration of Coral Reefs by Borings. 



AFTER the years of controversy upon the respective merits of the 

 opposing theories of the origin of coral reefs, an effort is now 

 being made to apply the test which is generally considered to be the 

 only final one. Considering how much is involved by the coral 

 question, with its bearings on the geological history of the whole 

 Central Pacific area, on the permanence of oceans and continents, 

 on zoological distribution, and on the relation of subsidence to vol- 

 canic action, it seems surprising that no attempt has previously 

 been made to secure an adequate series of borings. An influential 

 committee has, however, now been appointed by the British Asso- 

 ciation to arrange for this to be done. The subject having thus 

 been brought within the range of practical science, one is led to 

 consider the questions connected with the choice of a site that 

 would be accepted by all parties as a good test case, and with the 

 mechanical difficulties that have frustrated previous attempts to 

 apply this method of investigation. 



In the selection of a test locality, it is obvious that the Dar- 

 winians should have the main voice, for there are many cases where 

 reefs occur on submerged banks and shoals, and where a boring 

 would be an absolute waste of money. It is, therefore, for the 

 believers in the subsidence theory to point out a reef where this 

 chance is reduced to a minimum. Fortunately, there are plenty of 

 data with which to do this. Darwin himself remarked that the 

 smallness of many coral islands is an argument for subsidence, and 

 Dana has clearly indicated the characters by which a sinking reef 

 may be distinguished from one that is stationary. In the latter, the 

 debris from the reef would accumulate as a beach around the island 

 and thus increase its size ; the slopes around the beach-line would 

 be made steeper ; storms would throw material into the lagoon and 

 fill it up ; and the island would tend to become well wooded. On 

 the other hand, a sinking reef would decrease in size ; the lagoon 

 would rarely be more than partially filled up ; the surface of the 

 island would rise but slightly above the sea ; and it would be largely 

 tide-washed, and thus kept free from trees. Further, Dana has 

 shown that the islands of these two classes are distributed on a 

 definite plan, which affords, probably, the strongest argument for 

 the subsidence theory. 



