Composition of Sea Water.—It is prob able that every element is in solution in sea water, the great majority, however, present only in exceedingly minute traces. If the average density of sea water be taken at 1,027, pure water being 1,000, then the following would represent the composition of 1,000 cubic centimeters of sea water: Sodium chloride 28.9980 Magnesium chloride 4.0568 Magnesium sulphate 1.7665 Calcium sulphate 1.3425 Potassium sulphate 0.9193 Magnesium bromide 0.8809 Calcium carbonate 0.1287 Water 989.7073 1027,0000 Each base is probably in combination with each acid, so that there are really 16 salts altogether from the mixture of the four bases and four acids. The total amount of sea salts may vary greatly in different samples of sea water, but it has been shown by hundreds of carefully con ducted experiments that the ratio of the constituents of sea salts is nearly every where constant, with one significant ex ception, that of lime, which is in slightly greater proportion in the water from the deeper parts of the ocean basins. Nitro gen remains at all times and places nearly constant; not infrequently the propor tion of oxygen is much reduced in deep water, owing to the process of oxidation and respiration. Carbonic acid free or loosely combined is abundant, and plays a most important role in the economy of the ocean, combining with and render ing soluble normal carbonates of lime and magnesia to solution in the form of bicarbonates. Water, as is well known, is but slightly compressible, and almost any substance that will fall to the bot tom of a tumbler of water will in time fall to the bottom of the deep ocean. Still the compressibility of water must not be neglected in oceanographical ques tions. In the deeper parts of the ocean the pressure amounts to four or five tons per square inch; hence, in an ocean with a depth of 5 miles, were the action of gravity suddenly to cease, the ocean waters would rise 500 feet above their present level from expansion.
Life.—The color of pure sea water is a light shade of blue; it has, however, frequently various shades of green and brown, owing to the presence of organisms and matters in suspension. It has been definitely established that life in some of its many forms is universally distrib uted throughout the ocean. It has long been known that marine plants and ani mals abound in the shallow waters sur rounding continents and islands. Algm disappear from the sea-bed at depths between 100 and 200 fathoms, but a great abundance of animals have been procured in the greater depths. The term "Ben thos" is now used for all the animals and plants which live attached to or creep over the bottom of the ocean, "Plankton" being the term for all the plants and ani Trials which live in, and are carried along by the currents of the ocean. In the great body of oceanic waters life is most abundant in the surface and sub-surface waters down to about 100 fathoms. Pelagic alga;, such as diatoms and oscil latoria, are abundant in this region, and are the principal and original source of food for many pelagic and nearly all deep-sea animals. In the intermediate
depths of the ocean life though present is less abundant.
Deposits.—All marine deposits may be divided into two classes—viz., those made up principally of the debris from the solid land of the globe, laid down in greater or less proximity to the shores of continents and islands, called "terri genous" deposits, and those in which this continental debris is nearly or quite ab sent, laid down in the abysmal regions of the ocean, called "pelagic" deposits. Commencing with the former, there are first the littoral and shallow-water de posits, forming around the land masses from the shore down to a depth of about 100 fathoms, consisting of sands, gravels, and muds derived almost entirely from the disintegration of the neighboring lands. The littoral deposits, laid down between tide marks, cover about 63,000 square miles, and the shallow-water de posits, between low-water mark and 100 fathoms, about 10,000,000 square miles. Proceeding seaward from an average depth of about 100 fathoms, the deposits gradually change in character, the pro portion of land detritus decreasing, while the remains of oceanic organisms increase in abundance till at a considerable dis tance from land and in comparatively deep water the terrigenous deposits pass insensibly into truly pelagic deposits. The terrigenous deep-sea deposits—i. e., those formed at depths greater than 100 fathoms—may be briefly summarized as follows: Blue mud, the most extensive, is gray ish or bluish in color, with usually a thin reddish upper layer, and is char acterized by the presence of fragments of rocks and mineral particles coming from the disintegration of the land. Blue mud is found along the coasts of con tinents and continental islands, and in all inclosed and partially inclosed seas. Blue mud is estimated to cover about 14,500,000 square miles of the earth's sur face-4,000,000 in the Arctic, 3,000,000 in the Pacific, 2,500,000 in the Antarctic, 2,000,000 in the Atlantic, 1,500,000 in the Indian, and 1,500,000 in the Southern ocean. Red mud covers about 100,000 square miles off the coast of Brazil.
Green mud and sand are similar to the blue muds, but are characterized by the presence of the mineral glauconite in isolated grains or in small concretions; the dead shells of calcareous organisms are usually filled with the glauconite, which gives the green color to the de posits. Green mud and sand cover about 850,000 square miles-300,000 in the At lantic, 250,000 in the Pacific, 150,000 in the Indian, 90,000 in the Southern, and 60,000 in the Antarctic.
Volcanic mud and sand are deposited around the oceanic islands of volcanic origin and the name is derived from the presence of fragments and particles of volcanic rocks and minerals, which are larger and more numerous nearer the islands, when the deposit is called a sand. Volcanic mud and sand cover about 600, 000 square miles-300,000 in the Pacific, 200,000 in the Atlantic, and 100,000 in the Indian ocean.