scientist, J. D. Dana, but others found gaps in the 

 Darwinian theory and rival theories were advanced. 

 None of these have supplanted that of Darwin, but 

 each has added something to the general understanding 

 of reef formation. 



One of the two principal objections to the universal 

 application of the subsidence theory was based on the 

 fact that fringing reefs were found in the same general 

 area as barrier reefs. Since on this theory fringing reefs 

 may only continue existence on a stationary coast and 

 barrier reefs may only form on a subsiding coast, the 

 areas in question would of necessity be in the paradox- 

 ical situation of both sinking and remaining stationary. 

 This objection, however has been partially answered by 

 the recent observations of Davis and of his predecessors, 

 who suggest that a tilting of the earth might occur, 

 which would bring about sinking in one place and 

 rising in another close by. 



The subsidence theory would lead one to expect 

 that as a result of sinking of the earth, atolls should 

 exist with lagoons considerably deeper than the 180 

 feet, which is the maximum actually observed. Further- 

 more the widespread and prolonged sinking of the 

 earth's surface in all the coral seas simultaneously, 

 which Darwin's theory demanded was considered by 

 many to be highly improbable. These and other ob- 

 jections finally led to the theory put forward by Sir 

 John Murray, one of the great scientists who took part 

 in the celebrated four year expedition of H.M.S. 

 Challenger, which began in 1 872. 



Murray concluded that the platforms on which reefs 

 are built originate as submarine ridges, probably of 

 volcanic origin. These would not necessarily come 



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