186 Davis — DancCs Confirmation of 



the subsequent degradation of an uplifted fringing reef ; the 

 margin of such a reef " would generally during a slow rise of 

 the land be either partially or entirely worn down to that level 

 at which corals could renew their growth on its upper edge. 

 On some parts of the coast-land of Mauritius there are little 

 hillocks of coral rock, which are either the last remnants of a 

 continuous reef, or of low islets formed on it " (55). It is but 

 a step from this case to that of the uplifted and worn-down 

 atolls, which later exploration has brought to light, but the 

 failure to recognize the action of solution made this step diffi- 

 cult : " the supposition . . . that the upraised parts [of atolls] 

 have been worn down by the surf, and thus have escaped 

 observation, is overruled by the considerable depth of the 

 lagoons of all the larger atolls ; for this could not have been 

 the case if they had suffered repeated elevation and abrasion " 

 (146). Darwin attentively examined the possibility of the 

 outward growth of reefs from a still-standing foundation, and, 

 although he overlooked the process of solution in forming a 

 lagoon, accepted this process, as above indicated, for certain 

 special cases (52, 75), but rejected it for most barrier reefs, 

 presumably because they show only a " small quantity of low 

 alluvial land at the foot of the mountains" (128 ; also, 43-4-5) ; 

 possibly also because of the extravagantly large amount of 

 coral waste that outward growth demands in the formation of 

 a reef of increasing perimeter in water of great depth, in com- 

 parison with the economy of coral waste in a reef, the peri- 

 meter of which decreases as the depth of the sea is increased 

 (71, 101). If he did not recognize the possible value of solu- 

 tion in the formation of lagoons, he did explicitly mention the 

 movement of water " thrown over the outer edge " of a reef ; 

 " the current thus produced would tend to prevent the chan- 

 nel being tilled up with sediment, and might even deepen it 

 under certain circumstances" (54; also 45). He concisely 

 stated the unanswerable objection to the theory of veneering 

 barrier reefs on wave-cut platforms, which had been suggested 

 for the Society Islands even in his time : " It will, perhaps, 

 occur to some that the actual reefs formed of coral are not of 

 great thickness, but that before their first growth the coasts of 

 these encircled islands were deeply eaten into, and a broad but 

 shallow submarine ledge thus left, on the edge of which the 

 coral grew; but if this had been the case, the shore would 

 have been invariably bounded by lofty cliffs, and not have 

 sloped down to the lagoon channel, as it does in many instances" 

 (48, 49). 



And yet this most able and impartial investigator, who so 

 logically deduced many consequences from all the theories of 

 coral reefs that had been invented in his time, failed to go one 



