56 THE SEAS 



The vast bulk of life in the open sea is composed, not of 

 large and active creatures, such as fish or whales, but of 

 microscopic plants and animals which drift near the 

 surface and make up the all-important plankton. It is 

 their skeletons which form the great proportion of the deep- 

 sea deposits, for their bodies soon disintegrate or are 

 eateu by other animals. From their consistency Murray 

 called these deep-sea deposits Oozes, and distinguished them 

 according to the complete absence or relative abundance of 

 the various kinds of skeletons. 



Particularly around the poles, in the Antarctic ocean 

 especially, the surface waters contain vast numbers of the 

 microscopic plants called diatoms, each individual of which 

 is enclosed in a delicate case of silica, and it is these minute 

 plant " skeletons " which form the chief constituent of the 

 deposits in these regions, hence called diatom ooze. Al- 

 though there is an abundant flora in the temperate and 

 tropic seas, there is a larger proportion of animals, those 

 udth calcareous shells being the commonest. Chief among 

 these are the tiny foraminifera of which one called Globi- 

 gerina is the most plentiful, and ooze, with its limy 

 skeletons as the principal constituent (Plate 21), is extremely 

 widespread covering an estimated area of some 48,000,000 

 square miles, being especially abundant in the Atlantic. 

 A third type of deposit which is really only a variety of the 

 last is called Pteropod ooze ; it takes its name from the 

 predominance in it of the limy skeletons of delicate swim- 

 ming snails known as Pteropods or " sea Butterflies " which 

 are commonest near the equator where this type of ooze is 

 exclusively found, always in shallower water than Globi- 

 gerina ooze and especially near coral islands and on sub- 

 merged elevations far from land. 



Beneath a certain depth cozes with limy shells as their 

 principal constituent are no longer found, all calcareous 



