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CHAPTER IX. 



WHAT BECOMES OF THE "DUST" CORAL ISLANDS, ETC. 



What becomes of Nature's "Dust" The Invisible made Visible Rivers 

 supply the Inhabitants of the Ocean Oyster-shells, Mother-of- Pearl, 

 and Pearls The Largest existing Shell Coral Polyps, their Stony 

 Skeletons, Coral Reefs, Coral Islands Depths of the Ocean Micro- 

 scopic Shells Stone Lilies- -Limestone and Marble. 



SAND and mud do not by any means represent all that 

 is carried down into that universal receptacle, the 

 great ocean, which is receiving fresh additions every moment 

 of the day and night, and yet never gets overfull. The 

 clearest of clear streams is as surely conveying some- 

 thing to it as the mud-laden river ; and as everything that 

 water can dissolve reaches the sea at last, sea-water contains 

 at least a trace of every soluble mineral and metal in the 

 world. 



Roughly speaking, however, the average composition of 

 1,000 grains of sea-water is as follows : 



Water . 962-0 



Sodium chloride * 27*1 



Magnesium chloride 5 '4 



Potassium chloride 0*4 



Bromide of magnesia . cri 



Sulphate of magnesia i'2 



Sulphate of lime 0*8 



Carbonate of lime o'l 



* Common salt. 



