72 ON CORAL REEFS AND ISLANDS. 



We must, therefore, allow that some effect will be produced 

 upon the coral groves. There will be trees prostrated by gales, 

 as on land, fragments scattered, and fragmentary and sand accu- 

 mulations commenced. Besides, masses of the heavier corals 

 will be uptorn, and carried along over the coral plantation, which 

 will destroy and grind down everything in their way. So many 

 are the accidents of this kind to which zoophytes appear to be 

 exposed, that we might believe they would often be extermina- 

 ted, were they not singularly tenacious of life, and ready to 

 sprout anew on any rock where they may find quiet long enough 

 to give themselves again a firm attachment. 



But it should be observed, that the sea would have far less 

 effect upon the slender forms characterizing many zoophytes, 

 among which the water finds free passage, than on the massive 

 rock, against whose sides a large volume may drive unbroken. 

 Moreover, much the greater part of the strength of the ocean is 

 exerted near tide level, where it rises in breakers which plunge 

 against the shores. Yet, owing to the many nooks and recesses 

 deep among the corals, the rapidly moving waters, during the 

 heavier swells, must produce whirling eddies of considerable 

 force, tending to uproot or break the coral clumps. These dis- 

 rupting and transporting effects, will be less and less as we re- 

 cede 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 afterwards yielded to the reef. 



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

 the Gorgonise, the lime is often scattered through the polyps in 

 granules ; and the process of death sets these calcareous grains 

 free, which are consequently added to the coral sands. The 

 same process has been supposed to take place in the more com- 

 mon 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 afterwards cemented. 





