FORMATION OF CORAL REEFS AND ISLAND'S. 191 



The coral zoophyte is especially adapted for such a mode 

 of reef-making. Were the nourishment drawn from below, as 

 in most plants, the solidifying coral rock would soon destroy 

 all life : instead of this, the zoophyte is gradually dying below 

 while growing above ; and the accumulations of debris cover 

 only the dead portions. 



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 effects among the groves of the 

 sea? It has been shown 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 a hundred feet, which is far within the 

 reach of the sea's heavier commotions. To a considerable 

 extent they grow in the very face of the tremendous breakers 

 that strike and batter as they drive over the reefs. 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, to be found in various treatises on geology, of still 

 more surprising effects. 



During the more violent gales, the bottom of the sea is 

 said, by different authors, to be disturbed to a depth of three 

 hundred, three hundred and fifty, or even five hundred feet ; 

 and De la Beche remarks, that when the depth is fifteen 

 fathoms, the water is very evidently discoloured by the action 

 of the waves on the sand and mud of the bottom. M. Siau 

 mentions {Comptes Re?idus t. xii. 744) that ripple-marks are 

 formed on the bottom by the motion of the water, which may 

 be readily distinguished at a depth of at least twenty metres. 

 The hollows between such ridges or zones are occupied by the 

 heavier substances of the bottom. Similar ripple-marks were 

 distinguished at a depth of one hundred and eighty-eight 

 metres, to the north-west of the St. Paul's Roads. 



In an article on the Force of Waves, by Thomas Stevenson, 

 of Edinburgh, pubhshed in the Transactions of the Royal 

 Society of Edinburgh (vol. xvi., 1845), it is stated as a deduc- 



