8 LIFE IN THE SEA [CH. 



The materials forming the sea floor at shallow 

 depths would mostly be familiar to us, but near the 

 edge of the continental shelf they would becor;^ 

 quite unlike anything that we know on the la .n. 

 All the coarser detritus washed away from the land 

 surface would have settled down, and everywhere 

 the sea-bottom would be covered with soft, fine, 

 muds or oozes, varying in colour through tints of 

 blue, green, red or grey. These are the terrigenous 

 muds and they consist of the very finest particles 

 of mud borne in suspension by rivers and currents, 

 and floating in the water for immense distances. 

 Nearly everywhere they would be modified in com- 

 position by the action of decomposing organic matter 

 resulting from the dead bodies of marine organisms. 

 Here and there would be volcanic debris, scoriae, 

 fine dust, or even fragments of lava, either ejected 

 from submarine volcanic vents, or settling down on 

 the ocean floor after having been drifted about in 

 the sea or in the atmosphere. Beyond this area of 

 terrigenous muds we should encounter that of the 

 pelagic deposits ; and nearly everywhere at depths 

 of 1500 fathoms to rather over 3000 fathoms the sea 

 bottom deposits consist mainly of the shells or 

 skeletons of animals and plants which live in the 

 upper layers of the sea, and dying sink down to the 

 bottom to form the abyssal oozes. 



In many parts of the world the characteristic 



