CORAL REEFS. APPENDIX. 225 



end of the Peninsula (Ras Muhammed), or almost in the very 

 region of the islets in question. Further to the north, on the 

 other hand, the reefs are strictly linear and conform rigidly 

 to the coast-line, and are confined within the 10-fathom line. 

 In the region of the islets, opposite to the points where subsi- 

 dence is supposed to have taken place, the depths are much 

 greater. 



S. J. Hickson. " Theories of Coral Reefs and Atolls." Address British Assoc., 1888. 



Some points contained in this paper, which is a broad re- 

 view of the opposing theories of reef-formation, have already 

 been noticed. Prof. Hickson considers himself an adherent 

 of the views of Mr. Murray, but feels doubtful about two points : 

 (1) "Whether the power of solution of sea- water is sufficient to 

 account for the formation of lagoons, and (2), whether in some 

 cases, such as the eastern part of the Feejee Archipelago and 

 the Low Archipelago, the theory of subsidence may not be the 

 correct one." The author believes that from the evidence of 

 the Great Chagos bank alone "the subsidence theory breaks 

 down ," but he gives no facts to support this position beyond 

 the belief that the banks are (or ought to be) rising instead of 

 subsiding, as they were considered to be by Darwin. The all- 

 important fact which Darwin pointed out, on the testimony of 

 Captain Moresby, that the rim of this supposed " drowned atoll," 

 lying at a depth of a few fathoms beneath the surface of the 

 water, consisted almost wholly only of dead coral, Prof. Hick- 

 son believes " requires re-investigation," because " it is difficult 

 upon any theory to see why the rim only nine or ten fathoms 

 below the surface should not be covered with live coral." I 

 fail to see why this assumed fact is opposed to " any theory " 

 of coral growth, except the one which has been advanced or 

 sustained by Murray, Guppy, and Bourne. While it is ad- 

 mitted by both Darwin and Dana that the reef-building zone 

 extends down to ,a depth of 20-25 fathoms, it is well known 

 that in many coral regions the practical limit of coral develop- 

 ment is found at only half this depth. Thus, during the cruise 



