OCEAN WORK. The most powerful agent of erosion in the ocean is the wind-wave. By its direct blow, and by hurling and grinding rock fragments together, waves are wearing coast-lines back. From the cliffs thus formed much ma terial is supplied by weathering, which is assisted by the influence of the salt and other soluble substances with which the rock is sprinkled by the ocean spray. The waves, approaching the coast diagonally, drift the rock fragments along the coast, and this movement is further aided by the wind and wave-formed currents. These frag ments often find lodgment in embayments, form ing beaches. Such beaches are mills in which the rock fragments are further ground down. The finer fragments obtained by the waves, added to those brought by the rivers, the wind and weath ering agencies, are in part drifted out to sea by the undertow, the wind-formed currents, and the tidal currents. Rarely the tides have an erosive influence; but with ocean currents and ocean drifts they are important transporting agents. The currents and drifts are also geo logical factors in modifying climate, and in bring ing food to sea-animals. The materials derived from the land by the various agencies are strewn over the sea bottom near the land, the coarsest near the coast, the finest out to sea. Sometimes the sediment comes to the sea in greater quan tities than the agencies of the ocean are able to remove. Then they accumulate as bars along the coast and the waves expend their energies on the bars,' leaving the protected coast behind the bars untouched. if the sea bottom is sinking, great beds of conglomerate, sand, and clay may be accumulated; if it is rising, the beds pre viously formed are added to the land, as along the Eastern United States south of New York. More than half of the rocks of all the continents were formed on subsiding sea beds near land areas and made of the land waste. Later they were elevated to form parts of the continents and they have often been built into great mountains, such as the Alps, Appalachian, and Rocky.moun
tains.
In the sediments accumulating on the sea floor animal remains are always present; and as the distance from the coast increases these become of increasing importance because of the diminution of the supply of rock waste. Far from the coasts, in the open ocean, the contributions of land waste are so slight that the sea-floor deposit is made almost exclusively of animal remains, especially of the tests of minute surface animalculie which have dropped to the sea floor. This forms an ooze, variously named from the animal forms predominating. Of these the most numerous are usually the Globigerina, low forms of Forami nifera. Chalk beds are made of Globigerina ooze, raised to the surface and consolidated. In the very deepest oceans only the insoluble residue of these shells continues to the bottom, forming a red clay deposit. In this clay are found also volcanic dust, meteoric iron, and the ear-bones of whales, indicating its extremely slow accumu lation. About one-third of the tea floor is covered by red clay, and one-third by ooze; yet red clay is not found on the continents, and ooze rarely. This seems to indicate a permanency of the deep ocean basins, and that the ocean-formed rocks of the land were mostly made in those shallow parts of the ocean which bordered the continent areas.
Organic influences are not confined to the de posits of the deep sea. Grass-like plants, and, in tropical regions, mangrove trees, are effective in aiding deposit on many coasts, especially in pro tected spots. Shell-building animals also form deposits in addition to contributing to the elastic sediments. But far the most important of the coastal organic influences are those of the corals, which build reefs along the coasts, and islands on shoals in the sea. The coral fragments are built into islands by uplift, by waves and winds; and coral ooze is strewn over the sea floor near the reefs by the grinding of the waves and transpor tation by the currents. By these means beds of limestone are being accumulated. See OCEAN;