HALF AN HOUR WITH THE WAVES. 17 



as carbonate of lime most largely carried into the 

 sea by all rivers are utilised by the molhisca to 

 form their shells with, by the corals to build up their 

 reefs, and by the fishes to construct the bones of 

 their skeletons. The much less quantity of silica 

 finds its way into the frustrules of diatoms, the 

 spicules of sponges, &c., and the iodine, silver, &c., 

 are none the less necessary to the seaweeds on which 

 thousands of marine species feed. Thus the quantity 

 of mineral matter carried into the sea by rivers is 

 exactly compensated for by the animals and plants 

 which live there ; it is quietly but surely stowed out 

 of the way, the sea-water is kept in an equably pure 

 condition, and always fit for animal life to be enjoyed 

 in it whilst, meantime, the accumulating shells of 

 molluscs, the slowly forming reefs of coral, and the 

 still more slowly collecting of the calcareous shells 

 of foraminifera, are laying along the floors of existing 

 seas the foundations of continents yet to be. Surely 

 this must be esteemed by all right thinkers a mar- 

 vellous means of getting over a present difficulty by 

 making it insure a future benefit ! Owing to this 

 arrangement it is that in tropical regions, where the 

 rainfall is greatest, the rivers the longest, the surface 

 of the earth most worn and torn, and therefore where 

 a larger quantity of mineral matter is carried into 

 the sea than in temperate latitudes, the fish are 

 larger, the coral-reefs peculiar to such districts, and 

 the mollusca attain a weight of shell unknown 

 elsewhere. In fact, the greater the difficulty, the 



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