260 LEADING AMERICAN MEN OF SCIENCE 



only volcanic peaks, such as may be formed by submarine volcanic 

 action in regions remote from continental land. 



The history of the Darwinian theory has been a singular one. 

 When first announced, it produced on most scientific minds the 

 same impression of complete satisfaction that it produced upon 

 the mind of Dana. The subsidence of large areas of the ocean 

 bottom which it postulates, is sufficiently probable a priori; and 

 the theory possesses that same charm of simplicity which charac- 

 terizes Newton's conception of gravitation and Darwin's own 

 theory of natural selection. Very naturally, therefore, for three or 

 four decades, it was generally accepted as the one complete theory 

 of barriers and atolls. Later researches, however, have shown 

 conclusively that both barrier reefs and atolls may be formed with- 

 out subsidence. At the southern extremity of Florida, three suc- 

 cessive barrier reefs have been formed, all of which now have their 

 crests almost at the same level, showing that there has been no 

 crustal movement of any consequence. Chamisso long ago showed 

 that an atoll might be formed on a submarine volcano, or on a 

 shoal of any other origin, simply by the more luxuriant growth of 

 corals on the margin than in the middle. Of course it was impossi- 

 ble to believe that several hundred submarine volcanoes had been 

 raised to within about a hundred feet of the same level ; but Murray 

 showed that no such assumption of coincidence was necessary. A 

 submarine volcano that did not rise into the zone of coral growth, 

 could be built up by the accumulation of skeletons of other kinds 

 of marine life until it reached that zone; while a volcano that rose 

 a little above the sea-level might be degraded to a shoal by wave- 

 action. 



But, while it is certain that both barrier reefs and atolls can be 

 formed without subsidence, it still seems probable that there has 

 been a very extensive subsidence in the central part of the Pacific 

 Ocean, and that this subsidence has been an important factor in 

 the origin of the numerous atolls and barrier reefs of that region. 

 In going northeastward from the zone of fringing reefs of the New 

 Hebrides and Solomon Islands, one would traverse successively 

 zones of barrier reefs, large atolls, small atolls, and blank ocean 



