J. D. Dana, Esq., on Coral Beefs and Islands: 223 



whereas coral is itself an enduring rock material, undergoing 

 no change except the mechanical one of comminution. The 

 animal portion is but a mere fraction of the whole zoophyte. 



In these few hints, we have the whole theory of reef-mak- 

 ing : not a speculative opinion, but a legitimate deduction 

 from a few simple facts, and bearing close analogy to opera- 

 tions on land. The coral debris and shells fill up the inter- 

 vals between the coral patches, and the cavities among the 

 living tufts, and in this manner produce the reef-deposit, 

 which is finally consolidated while still beneath the water. 



The coral zoophyte is especially adapted for such a mode 

 of reef accumulation. Were the nourishment drawn from be- 

 low, as in most plants, the solidifying coral rock would soon 

 destroy all life : instead of this, the tree is gradually dying 

 below while growing above ; and the accumulations cover only 

 the dead portions. Moreover, to prevent accident, where 

 these accumulations do not keep pace with the progress of 

 death, organic incrustations cover the lifeless trunk, and pro- 

 tect it from the dissolving waters. 



But on land, there is the decay of the year, and that of old 

 age, producing vegetable debris ; and storms prostrate forests. 

 And are there corresponding efi'ects among the groves of the 

 sea ? It has been shewn that coral plantations, from which 

 reefs proceed, do not grow in the " calm and still" depths of 

 the ocean. They are to be found amid the very waves, and 

 extend but little below 100 feet, which is far within the reach 

 of the sea's heavier commotions.* Here is an agent which 

 is not without its effects. The enormous masses of uptorn 

 rock found on many of the islands may give some idea of the 

 force of the lifting wave • and there are examples on record, 



* During the more violent gales, the bottom of the ftea is said, by different 

 authors, to be disturbed to a depth of 300, 350, or even 500 feet ; and Sir H. De 

 la Beche remarks, that when the depth is 15 fathoms, the water is very evidently 

 discoloured by the action of the waves on the sand and mud of the bottom. In 

 the Comptes Mcndus, t. xii., 774, M. Siau mentions that parallel ridges are 

 formed on the bottom by the motion of the water, which may be readily distin- 

 guished at a depth of at least 20 metres. The hollows between such ridges or 

 zones are occupied by the heavier substances of the bottom. Similar zones were 

 distinguished at a depth of 188 metres to the north-west of the St Paul's Heads. 



