154 



ANIMAL LIFE OF THE DEEP SEA BOTTOM 



almost pure iron. We also know that sedimentation on the deep-sea floor 

 far from the coasts takes place very slowly, it being estimated that in many 

 places a layer of one centimetre represents about a thousand years. We 

 had the idea that, whereas iron meteors are very difficult to locate on the 

 earth, we might expect, if we raked the bottom with a magnet, to find a 

 number of the small pellets of iron which arise when drops of glowing 

 iron strike the surface and sink to the bottom, from where specimens had 

 previously been taken up in bottom samples. We obtained a series of very 

 powerful magnets and had them mounted on our shooting-star rake, 

 which we may call a sort of magnetic harrow (see figure on previous 

 page). It gave successful results on the few occasions when we found the 

 bed suitable for tests, and is a method which should certainly be developed 

 and employed in the future. 



While the significance of pressure and the nature of the bed to the 

 distribution of the various animals remains obscure, there is one last factor 

 which we must consider, one on which we ourselves are greatly dependent. 

 We can overcome the cold or warmth of our environment and we can 

 overcome many other things, but we must have food. 



Professor E. Steemann Nielsen har discussed the origin of all sea-food 

 in the plants of the uppermost water levels (see page 52). But the means 

 by which it gets down to a depth of 4,000 — 6,000 metres, and right down 

 to the abyssal 10,000 metres, is far from being fully elucidated. 



It is commonly believed that a "rain" of dead plankton organisms sinks 

 down to the bottom from the surface layers. But we must bear in mind 

 that dead organisms are as rare a sight in the sea as they are on land. 

 Sick or weak animals fall a prey to stronger enemies and are devoured; 

 at most, a large whale or giant shark might sink to the bottom without 

 being completely eaten. The microscopic plants sink very slowly, and 

 must be consumed in the first few hundred metres; lower down they can 

 certainly be traced only in very scanty quantities. This, no doubt, is why 

 the discontinuity layer between the water masses in the warm, upper 



Vegetable matter trawled at 4,040 metres, south of Ceylon. 



