THE OCEAN AND ITS LIFE. 93 



pests cannot raise the waves higher than some thirty feet, 

 nor does it ever disturb the habitual calm of the ocean 

 below the depth o a few fathoms, so that divers do not 

 hesitate to stay below, even when the hurricane rages 

 above. Gentle in its appearance, though grand in its effect, 

 this mighty wave shows its true power only when it meets 

 obstacles worthy of such effort. Where strong currents 

 oppose its approach, as in the river Dordogne, in France, 

 it races in contemptuous haste up the daring stream, and 

 reaches there, for instance, in two minutes, the height of 

 lofty houses. Or it rolls the mighty waters of the Amazon 

 river into huge dark masses of foaming cascades, and then 

 drives them steadily, resistlessly upwards, leaving the calm 

 of a mirror behind, and sending its roar and its thunder 

 for miles into the upland. 



Still less known and less observed is the third great 

 movement which interrupts the apparent calm and peace 

 of the ocean. For here, as everywhere, movement is 

 life, as rest would be death. Without this ever-stirring 

 activity in its own bosom, without this constant moving 

 and intermingling of its waters, the countless myriads of 

 decaying plants and animals which are daily buried in the 

 vast deep, would soon destroy, by their mephitic vapors, 

 all life upon earth. This greatest of all movements, never 

 resting, never ending, is the effect of the sun and the heat 

 it generates. Like all bodies, water also contracts, and 

 consequently grows heavier as the temperature sinks ; but 

 only to a certain point, about three degrees Eeaumur. 

 This is the invariable warmth of the ocean at a depth 

 of three thousand six hundred feet, and below that. If 



