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NATURE FOR ITS OWN SAKE 



red mud bottoms have reddish waters and 

 others with sandy bottoms have yellow waters. 

 Black streaks in the water are often indicative 

 of hidden rocks or dark masses of seaweed, and 

 a sunken mud-bank will occasionally produce a 

 silver-gray stripe for miles across an inlet. 



But however the bottom may change the local 

 color in shallow waters, it has little or no effect 

 upon the great seas. Their coloring is produced 

 ! largely by particles of salt and other substances 

 ! held in the water. The dust and moisture par- 

 | ticles floating in the atmosphere are productive 

 of the blue sky, and if we regard the waters of 

 the sea as colored by similar phenomena, we 

 shall not go far astray, though the analogy may 

 not be quite exact in every way. It is doubtless 

 the salt-particles in sea- water having the power 

 of reflecting blue that make the Mediterranean 

 such a dark ultramarine ; and the rock-par- 

 ticles carried down from the Alps by the Rhone 

 make the water of that stream assume a beauti- 

 ful green-blue tone even when the reflecting 

 blue sky is shut out by clouds. Again, the ef- 

 fect of the Blue Grotto, near Capri, is produced 

 by light shining through the water from beneath 

 and striking particles that apparently turn to 

 blue and produce that tone throughout the cave. 



