CORALS. 125 



the sea by each river that reaches the final destination of 

 its respective watershed. 



What is to become of all this calcareous earth ? If 

 nothing were done with it, the sea would be so con- 

 stantly receiving fresh supplies of solid matter, that the 

 water would be gradually thickened, and daily become 

 more like mud than water. 



It cannot be destroyed, because destruction, as we 

 understand the word, does not exist in nature. But it 

 can be modified, and agencies may be imagined by 

 Avhich the calcareous matter is extracted from the 

 water, and built up into fabrics which, though they 

 differ in form from the chalky mud, are identical with it 

 in material. 



There are many such agencies, silently, slowly, but 

 surely in constant work, and one of them I shall briefly 

 describe in the following pages. 



We know them, or rather the results of their labours, 

 by the very comprehensive word CORAL, under which 

 title are grouped a vast number of forms, all composed 

 of calcareous matter, but differing greatly in the shapes 

 which they assume and the structure of the living 

 agencies which make them. 



We have all heard of " Coral insects " and their work, 

 and scarcely a generation ago the young learner was 

 taught that the Coral Insect was the founder of tropical 

 islands, having raised its edifices from the depths of the 

 ocean, and only being checked in its labours when it 

 reached high-water mark. There is a certain amount of 



