CHAPTER X 

 SUBMARINE DEPOSITS 



The deposits which are forming on the floor of the ocean 

 are derived partly from the wearing down of the land and 

 partly from accumulations of the harder parts of the animals 

 and plants that live in the water. The material from the 

 land, forming " terrigenous " deposits, is partly carried to 

 the sea by rain and rivers, and partly washed or worn off 

 the coast by waves and currents. AU such materials from 

 the land may be either carried off in suspension or dissolved 

 in the water. The greater part of this work which leads 

 to the formation of terrigenous deposits is performed by 

 rivers : they carry down thirty-three times as much sediment 

 as is worn off the coasts by wave action. These sediments 

 from the land are deposited in shallow water along the coasts 

 of the continents as gravels, sands and muds of various 

 grades and kinds, which farther from land become mixed 

 with the remains of organisms either Hving on the bottom 

 (" neritic ") or floating on the surface (" pelagic "). Some 

 continental shores have a much greater quantity of terri- 

 genous deposits than others, on account of the larger amount 

 of sediment brought to them by rain and rivers. For ex- 

 ample, about half of the world is drained into the Atlantic 

 Ocean, and most of this into the North Atlantic. More than 

 half the total rainfall is on the Atlantic drainage area ; and 

 in consequence, the deposits of the Atlantic are more terri- 

 genous than those of other oceans. 



Marine plants and animals take up mineral substances 

 in solution from the sea and build up their shells, skeletons 



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