OCEANIC DEPOSITS AND BOTTOM FAUNA 25 



10 million square miles of the earth's surface. These deposits 

 are also built up entirely of material derived from the land. 

 Their constituent materials are smaller in size than those of 

 the littoral deposit, but larger, as a rule, than deep-sea deposits. 

 Gravels, sands, and coarse material predominate, but mud is 

 by no means uncommon in grooves and depressions, especially 

 in enclosed basins. The mechanical effects of erosion are 

 everywhere recognisable, naturally more marked in the 

 shallower regions. These effects are due to waves, and tides, 

 and currents. 



Areas of Oceanic Deposits 

 (Expressed as percentages). 



Littoral and shallow-water deposits ... ... 9*1 



Deep-sea deposits (Terrigenous) ... ... 15*4 



Pelagic 



Globigerina ooze ... ... ... 29*2 



Pteropod ooze ... ... ... '4 



Diatom ooze ... ... ... 6*4 



Red clay ... ... ... ... 36*1 



Radiolaria ooze ... ... ... 3*4 



75'5 



lOO'O. 



Deep -Sea Deposits. 



These are found on the sea bottom beyond the ico-fathom 

 line down to the greatest oceanic depths. They cover con- 

 siderably more than one-half of the earth's surface and over 

 90 per cent, of the sea-area (see table above). 



Gravels and sands are only met with accidentally in deep- 

 sea deposits, where depths over 100 fathoms are near the land. 

 The chief deposits are muds, clays, and oozes, the last of 

 organic origin. In certain areas the deposits are appreciably 

 affected by the detritus deposited by floating ice. There is in 

 general an absence of the phenomena of erosion. Since sun- 

 light penetrates very little beyond 100 fathoms, it follows that 

 plant remains are scanty except near that limit. Animal life, 



