The eupelagic deposits are subdivided by Kriimmel into two main groups; (a) epilophic,' including the pteropod, globigerina and diatom oozes occurring on the rises and ridges and in the less deep troughs.
This is really the case, for all observations show that the Antarctic and Arctic ice-bound seas are enormously rich in diatom life when compared with temperate and tropical regions: the great Antarctic zone of sea-bottom deposit, in which the skeletons of diatoms predominate, covers some ten millions of square miles.
To this inconceivably slowly-growing deposit of inorganic material over the ocean floor there is added an overwhelmingly more rapid contribution of the remains of calcareous and siliceous planktonic and benthonic organisms, which tend to bury the slower accumulating material under a blanket of globigerina, pteropod, diatom or radiolarian ooze.
The irrigation of the claires is entirely under control, and the claires undergo a special preparation for the production of the green oysters, whose colour seems to be derived from a species of Diatom which abounds in the claires.
The silica, in the form of diatom or radiolarian skeletons, is eventually deposited on the ocean floor after the death of the organisms. Most of the fine colloidal clay is, however, deposited as river-sludges when the fresh water carrying it mixes with denser sea-water.