DEVELOPMENT OF THE REEF 251 



suggested that this effect will also be produced on the reef 

 itself, and there are very many facts that go to support this 

 suggestion. The rising reef becomes the site of the pro- 

 duction of much debris, dead colonies are reduced to coral 

 sand by the many sand-producing agencies of the reef; and 

 this sand becomes held in suspension in the water moving 

 over the surface of the reef. The reef, therefore, in a great 

 measure provides its own suspended matter, but added to 

 this is the shower of particles held in suspension in the 

 surface waters. This accumulation of particles will, doubtless, 

 find lodgment on the uneven surface ,of the coral bank ; and, 

 in its to and fro journey ings across the bank, it will tend to 

 exert the maximum of its influence upon the flat central area 

 of the reef. In this way it is easily seen that the central 

 colonies of the reef, just as the central zooids of the colony, 

 will tend to decline in vigour, and their growth will not be 

 so rapid as that of the colonies situated nearer to the edge. 

 The growth of the reef as a whole will, therefore, tend to be 

 more rapid at its margins, and less rapid at the centre ; thus a 

 somewhat concave upper surface to the bank will be developed. 

 The fate of the colony is again reproduced ; sediment becomes 

 accumulated in this central depression, and coral growth be- 

 comes still more reduced ; and a stage is arrived at, in every 

 way comparable to that followed in the Porites colony, of a 

 flat-topped plain, ringed around with a healthy growing edge 

 of coral. So far, it may be objected, this development of the 

 reef is pure hypothesis ; but it is a hypothesis that is capable 

 of receiving very real support from the actual condition of 

 those submarine coral banks which have been at all adequately 

 surveyed. The stage at which we have arrived is exactly that 

 seen in reality in such reefs as the Tizard and Macclesfield 

 Banks in the China Sea. 



Admiral Sir W. L. Wharton has described these banks in 

 Nature, Feb. 23, 1888, and Dr. Bassett- Smith in the paper 

 already quoted. Tizard Bank is 32 miles long and 10 miles 

 wide : it is flat and lies at a depth varying from 30 to 47 

 fathoms, and its raised edge is only some 10 fathoms below 



