AREAS OF SUBSIDENCE. 263 



the specified height. Again, in the Indian Ocean, 

 there is a space of ocean 1500 miles in length, in- 

 cluding three archipelagoes, in which every island 

 is low and of coral formation. From the fact of 

 the reef-building corals not living at great depths, 

 it is absolutely certain that throughout these vast 

 areas, wherever there is now an atoll, a foundation 

 must have originally existed within a depth of from 

 20 to 30 fathoms from the surface. It is improba- 

 ble in the highest degree that broad, lofty, isolated, 

 steep-sided banks of sediment, aiTanged in groups 

 and lines hundreds of leagues in length, could have 

 been deposited in the central and profoundest parts 

 of the Pacific and Indian Oceans, at an immense 

 distance from any continent, and where the water 

 is perfectly limpid. It is equally improbable that 

 the elevatory forces should have uplifted, through- 

 out the above vast areas, innumerable great rocky 

 banks within 20 to 30 fathoms, or 120 to 180 feet, 

 of the surface of the sea, and not one single point 

 above that level ; for where, on the whole face of 

 the globe, can we find a single chain of mountains, 

 even a few hundred miles in length, with their 

 many suminits rising within a few feet of a given 

 level, and not one pinnacle above it? If, then, the 

 foundations, whence the atoll-building corals sprang, 

 were not formed of sediment, and if they were not 

 lifted up to the required level, they must, of neces- 

 sity, have subsided into it, and this at once solves 

 the difficulty ; for as mountain after mountain, 

 and island after island, slowly sank beneath the 

 water, fresh bases would be successively afforded 

 for the growth of the corals. It is impossible here 

 to enter into all the necessary details, but I ven- 

 ture to defy* any one to explain in any other man- 



* It is remarkable that Mr. Lyell, even in the first edition of his 

 " Principles of Geology," inferred that the amount of subsidence 



