THE WORK OF THE OCEAN 317 



of continental plateaus and ocean-basins. Because the latter are 

 a little- overfull, the water runs over their rims, covering about 

 10,000,000 square miles of the borders of the continental protuber- 

 ances. 



Aside from the deposits made by organisms, shallow-water 

 deposits are divisible into two groups (1) those immediately 

 along the shore, the littoral deposits, and (2) those made between 

 the littoral zone and the 100-fathom line. Both are terrigenous 

 chiefly, though chemical and organic deposits occur in both zones. 

 The deep-sea deposits likewise are divisible into two principal 

 groups, (1) the terrigenous deposits near the land, and (2) the pelcigw 

 deposits, made up chiefly of the remains of pelagic organisms, and 

 the ultimate products arising from the decomposition of rocks 

 and minerals. The former predominate in the less deep waters 

 relatively near shore; the latter in the deeper water far from land. 

 The shallow- and deep-water deposits grade into each other in a 

 belt along the 100-fathom line. 



Shallow-water Deposits 



Littoral deposits. The littoral zone is often defined as the zone 

 between high- and low-water marks, but in common speech, the 

 very shallow water a little farther from the coast-line is often in- 

 cluded. It is the zone in which bowlders, gravels, sands, and all 

 coarser materials accumulate, though muds are occasionally met 

 with in sheltered estuaries. Generally speaking, the nature of 

 these deposits is determined by the character of the adjoining 

 lands and the nature of the local organisms. The heavier materials 

 brought down by rivers or worn from the shore by waves are here 

 spread out by waves and shore-currents. Twice in the twenty- 

 fours hours the littoral zone is covered by water, and twice parts 

 of it are exposed to the direct rays of the sun or the cooling effects 

 of the night. Physical conditions in general are here most varied. 

 Still greater diversity is introduced by the fact that the zone is 

 inhabited by both marine and terrestrial organisms, while the 

 evaporation of the sea-water which flows over tidal marshes and 

 lagoons leads to the formation of saline deposits. The length of 

 the coast-lines of the world is some 125,000 miles (about 200,000 



