32 THE FAUNA OF THE DEEP SEA 



none of the coldest water will ever get across it, 

 and from tlie level of the ridge to the bottom of the 

 sea on the equatorial side the water will have the 

 same temperature as the water at the level of the 

 ridge on the polar side. 



It follows from this that in places where there are 

 deep holes in the bed of the ocean surrounded on all 

 sides by considerable elevations, the temperature ot 



EquBtcr -< Pole 



^ — ——sarx Superficial 



20'] waters 



Intermediate 

 waters 



Fig. 1.— Diagram illustrating the passage of an 

 ocean current across a barrier (A). 



the water at the bottom will be the same as the 

 temperature of the water on the summit of the 

 lowest ridges that surrounds them. ' 



This explains why it is that we find that the bottom 

 temperature for a given depth is frequently less in 

 one place than it is in another, even in places of the 

 same parallel of latitude. One or two examples may 

 be taken to illustrate these points. The temperature 

 off Rio Janeiro in lat. 20° S. was found by the 



