ROMANCE OF DEPTHS OF THE SEA 99 



No less than 22,500,000 square miles of the 

 Atlantic bed is covered with the shells of these 

 organisms. Some twenty kinds have been classi- 

 fied. The commonest genus amongst them is the 

 Globigerina, and hence the deposit itself is known 

 as Globigerina ooze. At what rate the deposits 

 thicken we do not know, but those whose business 

 it is to lay marine cables have evidence that in 

 some places about one inch is deposited in ten 

 years. Like other unicellular, floating organisms, 

 Foraminifera are kept floating whilst alive by the 

 secretion of either air-bubbles or oil-globules 

 lighter than water. When the animals die the 

 floats cease to act and their bodies sink slowly 

 down in a never-ceasing rain of marine dust, 

 covering and obliterating inequalities on the 

 ocean floor, and clothing the sea-bottom with a 

 mantle of monotony. 



These monotonous plains, which Kipling has 

 called 



" The great grey level plains of ooze," 



are as a rule at a depth of about 2,000 to 3,000 

 fathoms : only in a very few places does the 

 Atlantic bottom sink over 3,000 fathoms below 

 the level of the ocean surface. 



