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Ch. XLIX .] 



DEPTH AT WHICH COKALS GROW. 



583 



immense 



so 



that Pharaoh may have looked upon these same individuals 

 in the Eed Sea.'^ They certainly imply, as he remarks, 

 that the reef on which they grow has increased at a very 

 slow rate. After collecting 



mor 



none 



of them covered with parasitic zoophytes, nor any 

 instance of a living coral growing on another living coral. 

 To this repulsive power which they exert whilst living, against 

 all others of their own class, we owe the beautiful symmetry 



3 Mseandrince, and other species which adorn our 

 museums. Yet Balani and Serpulse can attach themselves to 

 the dermal tissues of living corals, and holes are excavated 

 in tliem by boring moUusks. 



At tlie island called Taaopoto, in the South Pacific, the 

 anchor of a ship, wrecked abont 50 years before, was observed 

 in seven fathoms' water, still preserving its original form, but 



t 



seem 



to form 

 dif&cnlt. 



not only according to the species of coral, but according to 



may 



from 



of light, the temperature of the water, its freedom from 

 sand or mud, or the absence or presence of breakers, which 

 is favourable to the growth of some kinds and is fatal to that 

 of others. It should also be observed that the apparent 

 stationary condition of some coral reefs, which according to 

 Beechey have remained for centuries at the same depth under 

 water, may be due to subsidence, the upward growth of the 

 coral having been just sufficient to keep pace with the sinking 

 of the solid foundation on which the zoophytes have built. 

 We shall afterwards see how far this hypothesis is borne out 

 by other evidence in the regions of annular reefs or atolls. 



In one of the Maldive Islands a coral reef, which, within a 

 few years, existed as an islet bearing cocoa-nut trees, was 

 found by Lieutenant Prentice, ^ entirely covered tvith live coral 

 and madrepore.^ The natives stated that the islet had been 



* See Ehrenberg's work above cited, 



p. 751. 



t Stuchbury, West of England Jour- 

 nal, No. i. p. 49. 



