Coral Reefs and Islands. 291 



VI. Conclusion. 



With the theory of abrasion and solution incompetent, all 

 the hypotheses of objectors to Darwin's theory are alike weak ; 

 for all have made these processes their chief reliance, whether 

 appealing to a calcareous, or volcanic, or mountain-peak base- 

 ment for the structure. The subsidence which the Darwinian 

 theory requires has not been opposed by the mention of any 

 fact at variance wth it, nor by setting aside Darwin's arguments 

 in its favour; and it has found new support in the facts from 

 the 'Challenger's* soundings off Tahiti that had been put in 

 array against it, and strong corroboration in the facts from 

 th© West Indies. 



Darwin's theory therefore remains as the theory that 

 accounts for the origin of coral reefs and islands. 



VII. Central-Pacific Subsidence. 



Darwin, as has been said, took a step beyond direct obser- 

 vation in his inference that the subsidence attested to by each 

 atoll extended over the intermediate seas and characterized a 

 large central area of the ocean. He may be wrong here (and 

 the writer with him), while not wrong in his theory. But, 

 considering the distribution of the Pacific atolls in the ocean, 

 their relation in this respect to the distribution of other 

 Pacific lands, and the facts connected with the history of 

 coral reefs and islands, the generalization appears to be well 

 sustained. The question is here left without further argu- 

 ment, to be considered over the best geographical map of the 

 ocean to be had, and the best bathymetrical map that can be 

 made, only asking that the doubts which physical theory has 

 set afloat may not be allowed by the geologist to warp the 

 judgment or cripple investigation*. 



My own agreement with Darwin as to the area of coral- 

 reef subsidence was promoted by an early personal study of 

 the oceanic lands. For more than five years previous to pass- 

 ing my third decade I was ranging over the oceans, receiving 

 impressions from a survey of the earth's features. I was 



* One point often encountering an a priori doubt is the slowness of the 

 required subsidence. The subsidence over the Appalachian region which 

 preceded the making- of the Appalachian Mountains amounted, according 

 to well -ascertained facts (as stated by Hall and Leslie), to at least 30,000 

 feet. The great trough, nearly a thousand miles long, was in progress 

 through all of Palaeozoic time. If the Palaeozoic ages covered only 

 20,000,000 years (a low estimate) the mean annual rate was 0*018 inch, 

 which is less than half a millimetre per year. Such a fact is no evidence 

 as to the rate of the atoll-making subsidence; but, whatever the cause to 

 which the Appalachian subsidence is to be attributed, it is suggestive as 

 to possibilities and probabilities connected with the earth's movements. 



