CHAPTER VII 

 Coral Reefs 



In the last chapter we learnt something of those animals 

 and plants which are the chief agents of destruction in the 

 sea, in this chapter we are going to deal with animals and 

 plants which, so far from being destructive, are responsible 

 for the formation of many thousands of islands and reefs 

 in the tropical seas. Everyone has heard of coral reefs 

 and probably seen pictures of them, but few, perhaps, have 

 had their imaginations roused by the thought of the amazing 

 manner of their formation. For it is surely a very remark- 

 able thing that animals allied to our common sea anemones, 

 and plants related to the little red corallines, have between 

 them built up — by the slow but persistent process of con- 

 verting the calcium salts in solution in the sea water into 

 hard calcareous rock — dry land where there was before open 

 sea, land on which first of all plants, then animals and 

 finally men, have successfully established themselves. 



Before we go on to speak of the various kinds of coral 

 reefs and islands and of the different theories which have 

 been put forward to account for their formation, we must 

 first say something about the animals and plants which are 

 responsible for their formation. The most important of 

 these are the stony or Madreporarian corals which, as was 

 briefly alluded to in Chapter I, are animals of the sea 

 anemone type which form around and beneath themselves 

 a thick protecting skeleton of carbonate of lime. Although 

 some of these are " solitary " corals like the little cup-coral, 



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