36 THE OCEANOGRAPHY OF THE NORTH-WESTERN OCEAN [PART I 



calcareous skeletons of the numerous species of foraminifera which 

 inhabit the upper layers of the sea. Its average range in depth is 

 from about 3000 to 5000 metres and at those depths Atlantic and 

 Norwegian Oceans are alike carpeted by this deposit. 



But beyond a depth of about 5000 metres the remains of 

 organisms possessing a calcareous skeleton form but an insignificant 

 proportion of the oozes on the ocean floor. It takes so long a time 

 for these fragile remains to fall through water of this depth that 

 before reaching the bottom they are almost entirely dissolved. 

 Siliceous deposits take their place. Of such nature is the 

 Radiolarian Ooze which is found at greater depths than 5000 

 metres. The Radiolaria are Protozoa which secrete a siliceous 

 skeleton, and which inhabit nearly all layers of the sea. When 

 they die their bodies sink to the bottom and while the soft parts 

 decompose slowly and disappear the siliceous remains accumulate 

 to form a deep-sea deposit. 



Beyond the limit of depth of the radiolarian ooze we find the 

 Red Clay which lies in the great abysses of the ocean. While 

 some part of this deposit is formed by the remains of living 

 creatures it is nevertheless a substance w^hich is mostly formed 

 from inorganic material. We have seen that pumice and volcanic 

 ash may be carried over wide tracts of ocean surface and that this 

 material finally beccr>ies water logged and sinks to the sea bottom. 

 This is the origin of the red clay. At the profound depths in 

 which it is found almost all organically formed material has 

 disappeared from the deposits, being dissolved by the sea water 

 or perhaps broken down by the action of marine bacteria — a mode 

 of action which conceivably may account for the disappearance of 

 much of the silica and lime which must reach the sea floor fi:-om 

 the upper layers as the skeletons of marine organisms. 



In addition to these substances composing the oceanic bottom 

 deposits there are of course many others. None of them are pure, 

 but each shades off into the others under various conditions and at 

 various depths. Other formations also occur, such as the well- 

 known Diatom Ooze of the Antarctic. At an average depth of 

 about 4000 metres there is a wide band of soft white ooze 

 covering the sea bottom between the parallel of 40° S. and 

 extending to the Antarctic circle and completely surrounding 



