THE PHYSICAL CONDITIONS OF THE ABYSS 37 



sideration is that presented by the floor of the great 

 oceans. The floor of the ocean, if it were laid bare, 

 would probably present a vast undulating plain of 

 fine mud. Not a rock, not even a stone would be 

 visible for miles. 



The mud varies in different parts of the globe 

 according to the depth, the proximity to land, the 

 presence of neighbouring volcanoes or the mouths of 

 great rivers. 



The Globigerina ooze is perhaps the best known ' 

 of all the different deep-sea deposits. It was dis- 

 covered and first described by the officers of the Ameri- 

 can Coast Survey in 1853. It is found in great 

 abundance in the Atlantic Ocean in regions shallower 

 than 2,200 fathoms. Deeper than this, it gradually 

 merges into the c Red mud.' It is mainly composed of 

 the shells of Foraminifera, and of these the different 

 species of Globigerina are the most abundant. It is 

 probably formed partly by the shells of the dead 

 Foramimfera that actually live on the bottom of the 

 ocean and partly by the shells of those that live near 

 the surface or in intermediate depths and fall to the 

 bottom when their lives are done. 



So abundant are the shells of these Protozoa that 

 nearly 95 per cent, of the Globigerina ooze is com- 



