FORMATION OF CORAL REEFS AND ISLANDS. 227 



nooks and recesses deep among the corals, the rapidly moving 

 waters, during the heavier swells, must produce whirling ed- 

 dies of considerable force, tending to uproot or break the coral 

 clumps. These disrupting and transporting effects will be 

 less and less as we recede from the shores ; yet all coral depths 

 must experience them in some degree. 



There is another process going on over the coral field, some- 

 what analogous to vegetable decay, though still very different. 

 Zoophytes have been described as ever dying while living. The 

 dead portions have the surface much smoothed, or deprived 

 of the roughening points which belong to the living coral, and 

 the cells are sometimes half obliterated, or the delicate lamellae 

 worn away. This may be viewed as one source of fine coral 

 particles ; and as the process is constantly going on, it is not 

 altogether unimportant. This material is in a fit condition to 

 enter into solution, and it cannot be doubted that the water 

 receives lime from this source, which is afterward yielded to 

 the reef. 



In the Alcyonia family, which includes semi-fleshy corals, 

 and in the Gorgoniae, the lime is often scattered through the 

 polyps in granules ; and the process of death sets these calca- 

 reous grains free, which are constantly added to the coral sands. 

 The same process has been supposed to take place in the more 

 common reef corals, the Madrepores and Astrasas, and it is 

 possible that this may be to some extent the case. Yet it 

 would seem, from facts observed, that after the secretion has 

 begun within the polyp, the secretion of lime going on takes 

 place against the portions already formed and in direct union 

 with them, and not as granules to be afterward cemented. 



The mud-like deposits about coral reefs (pp. 142, 183, 205) 

 have been attributed to the causes just mentioned, but with- 

 out due consideration. There is an unfailing and abundant 



