272 TOILERS IN THE SEA. 



It remains briefly to sketch the hypothesis 

 advanced by Darwin, sanctioned by Humboldt, 

 supported by Dana, and generally adopted. This 

 theory is based upon the fundamental fact of the 

 gradual subsidence, or elevation, of islands in the 

 Pacific, that is to say, on changes of level in the 

 Pacific Ocean. Professor Dana devotes an entire 

 chapter in his work to the substantiation, and 

 elucidation, of this fundamental position. Those 

 interested in ascertaining the data for this position 

 must consult that volume, as it would occupy too 

 much space to recapitulate here. Further, that the 

 extent of subsidence has been very considerable. 

 That, in connexion with the origin of coral islands, 

 and barrier reefs, in the Pacific, it must have 

 amounted to several thousands of feet, perhaps fully 

 ten thousand. And it is further urged that this 

 change of level is not greater than the elevation 

 which the Rocky Mountains, Andes, Alps, and 

 Himalayas, have each experienced since the close 

 of the Cretaceous era, or the early Tertiary ; and 

 perhaps it does not exceed the upward bulging in 

 the Glacial era of part of northern North America. 



Humboldt gives the briefest, and most succinct, 

 summary of this hypothesis, when he writes "According 

 to Darwin the following is the process of formation. 

 An island mountain closely encircled by a coral reef 

 subsides, while the fringing reef, that had sunk with 



