12 bulletin: museum of comparative zoology. 



for the breakers cannot cut on the shores of the island/ and they do not 

 often tear up and cast inside fragments from the outer edge of the reef, 

 while every streamlet carries away its mud through breaches iu the 

 reef. ... A fringing reef, if elevated in a perfect condition above the 

 level of the sea, would present the singular appearance of a broad dry 

 moat bounded by a low wall or mound." 



Darwhi, when meeting Semper's objection that the existence of atolls 

 or barrier reefs in a region of elevation was a fatal argument against 

 his (Darwin's) views, is obliged to say that therein ''seems to me no 

 improbability in their having originally subsided, then having been up- 

 raised . . . and again having subsided." ^ He further says, " The exist- 

 ence of atolls and of barrier reefs in close proximity is manifestly not 

 opposed to my views." Certainly not, but their existence in an area of 

 elevation as claimed by Semper is. Darwin also says that, ""When the 

 land is prolonged beneath the sea in an extremely steep slope, reefs 

 formed there during subsidence will remain closely attached to the 

 shore, and will be undistinguishable from fringing reefs." ^ This seems 

 to me impossible. The disintegration of the inner edge of the fringing 

 reef, the action of the sea upon this disintegrated material, the solvent 

 action of sea water, all will tend to form a channel between the outer 

 parts of the reef and the shore, as is evidently tlie case in almost all 

 fringing reefs, which show either an incipient cliannel where boats may 

 circulate at high water, or a belt of considerable width in which the coi'al 

 fringing the land has been killed by the silt brought down from the ad- 

 jacent slopes, and has been decomposed, and, crumbling to sand or mud, 

 is gradually being carried off at each high tide, forming a channel which 

 when wide enough and deep enough becomes sufficiently prominent to 

 change the fringing r^ef into a barrier reef. 



The difficulties encountered in attempting to meet the many sugges- 

 tions made by Darwin regarding reefs which he did not examine are 

 well exemplified in the account which he gives of Rose Island, one of 

 the Samoa group.* 



1 This would depend upon the widtli and slope of the fringing reef. Many of 

 the narrow fringing reefs in Fiji have a uniform slope towards the lagoon, and do 

 not present the structure described by Darwin. 



2 Darwin's Coral Reefs, 3d ed., p. 228. 



3 Ibid., p. 229. 



* Ibid., p. 212 : " The lagoon is very shallow, and is strewn with numerous large 

 boulders of volcanic rock." (Negro-heads, A. Ag.) He further says : " This island, 

 therefore, probably consists of a bank of rock, a few feet submerged, with the 

 outer margin fringed with reefs. Hence it cannot be properly classed with atolls, 



