102 THE WATEES. 



the Grulf of Mexico, although the return current does not 

 go by the name of Grulf- Stream. This great stream of water 

 warmed by the tropical sun serves the same two purposes 

 described under the section "Air" as being fulfilled by the 

 trade-winds, namely, a circulation and distribution of the 

 superfluous heat of the equatorial regions, warming the 

 northern countries and cooling by the return of under- 

 currents those in the tropics. The fogs of Newfoundland 

 are caused by the great current of warm water entering the 

 cold region and carrying with them surface-currents of 

 moist air, which the cold condenses into fog, just as the 

 breath is visible in a cold atmosphere. England owes its 

 moist and mild climate to the same cause. 



The sand which lies upon the sea-shore is produced by 

 the action of the waves constantly dashing against the earth 

 and rocks of the coast, and is mostly composed of what 

 chemists call " silex," or silica, which is a chief constituent 

 of most rocks and earths ; these, being worn down by the 

 action of the waters, form sand. The fragments of these 

 rocks (especially granite) and those which contain silica in 

 the form of minute crystals, are soon rolled and rubbed 

 together until they are ground to powder, but it is doubtful 

 whether any sand exists at the bottom of the deep seas far from 

 shore, as the waters there lie and must have laid perfectly 

 quiet ever since they were seas, for the greatest storm that 

 ever rages does not affect the tranquility of the sea more than 

 a few fathoms beneath its surface, so that a stone dropped 

 in the middle of the Atlantic Ocean, could be picked up 

 after a hundred years exactly where it fell, were it possible 

 for any to find out the spot and descend ; but the bottom 

 of some deep seas, as in the antarctic regions and the north 

 Atlantic Ocean (as the soundings between Ireland and 

 America have lately shown), is covered to an unknown depth 

 with what had been supposed to be sand, but which is not 

 sand at all, but a wonderful collection of minute shells and 

 coralines, which to the unassisted eye have the appearance 

 of sand. They are the silicious shells and coverings of 

 minute vegetables and animals, these creatures, being coated 

 with silica (a substance indestructible by age and the 



