Our Salt-JVater World 323 



needs light to reduce the carbonic acid required for its 

 existence. Some require more, and others may want 

 less; without it, however, no vegetation can live. The 

 actual depth to which light penetrates obviously would 

 vary in different localities, but generally speaking it may 

 be said that at depths of 600 feet no light can be re- 

 ceived from the sun, and even at depths considerably 

 less the amount that filters through is so feeble as to 

 have little or no Influence on life. 



Every year approximately 475,000,000 tons of salts 

 and other chemicals dissolved from the land are carried 

 into the ocean by the rivers of North America alone. 

 There exists at present in solution in the sea, 4,800,000 

 cubic miles of salts; this quantity is more than enough 

 to cover the surface of the United States one and one- 

 half miles deep. Of the eighty odd known elements, 

 thirty-two have been proved to exist in sea water; and 

 It Is quite probable that as the analytical methods of 

 chemistry become more refined, the presence of nearly 

 all the rest will be revealed. Seaweeds and corals 

 contain many of the metals, but gold and silver have 

 actually been found in solution. It has been estimated 

 that nearly one fifth of a grain of silver Is contained 

 In a ton of sea water; there is, then, dissolved in the 

 sea nearly fifty thousand times as much of this precious 

 metal as has been mined throughout the world since 

 the discovery of America. But this is Insignificant 

 as compared with the quantity of gold it is presumed 

 to contain. Gold is estimated to be five times as plen- 

 tiful as silver in the sea. Needless to say, man has 

 constantly and unsuccessfully attempted to extract the 

 gold from the water. 



