THE WORK OF THE OCEAN. 369 



Shalloir-icater Deposits. 



Littoral deposits. — The littoral zone is the zone between high- and 

 low-water marks. It is the zone in which bowlders, gravels, sands, and 

 all coarser materials accimiiilate. though muds are occasionally mst 

 \\ith 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 by 

 rivers from liigh terrestrial regions, or thrown up by the tides and waves 

 of the sea, are here arranged with great diversity of stratification through 

 the alternate play of the ^inds and waves. Twice in the twenty-four 

 hom\s the httoral zone is covered by water and exposed to the direct 

 rays of the sun or the cooling effects of the night. There is a great 

 range of temperature: mechanical agencies produce their maximum 

 effects," ^ and physical conditions in general are most varied. Still 

 greater diA'ersity is introduced by the fact that the zone is inhabited 

 by both marine and terrestrial organisms, wliile the evaporation of 

 the sea-water which flows over tidal marshes and lagoons leads to the 

 formation of sahne deposits. If the length of the coast-lines of the world 

 be taken at 125.000 miles (about 200.000 kilometers), and the average 

 width of tliis zone at half a mile, these deposits are now forming over 

 an area of 62,500 scjuare miles (about 160,000 square kilometers) of 

 the earth's surface. 



Non-Uttoral, mechanical deposits in shallow water. — These deposits 

 are laid down in the zone of the ocean between low-water mark and 

 the 100-fathom hne. They cover about 10,000.000 scjuare miles.^ 

 Theu' composition is much the same as that of the littoral deposits, 

 with which they are continuous, though on the whole they are finer. 

 At their lower hmit they pass insensibly into the fine deposits of the 

 deep sea. Coarse material, such as gravel and sand, prevails, though 

 in special situations, such as depressions and inclosed basins, muddy 

 deposits are foimd. Wliile some of the deposits are whohy composed 

 of inorganic debris, organic remains are freely mingled with others. 

 The mechanical effects of tides, currents, and waves are everywhere 

 present, but become less and less weU marked as the 100-fathom line 

 is approached. The forms of vegetable and animal hfe are numerous, 



1 Murray, loc. cit., pp. 187, 188. - Ibid. 



