Tabular View of Oceans and Seas

TABULAR VIEW OF OCEANS AND SEAS The following table gives the average depth, the area, and the volume of the oceans, seas and the hydrosphere according to the 1921 computations of E. Kossinna:— Krtimmel preferred, 1907, to simplify this by grouping the deposits in a single category arranged according to position : (a) Littoral (including Murray and Renard's littoral and shal low water deposits [II. and III.]).

(b) Hemipelagic (including Nos. 6-10 of deep sea deposits).

(c) Eupelagic (including Nos. 1-5 of deep sea deposits).

As so defined the hemipelagic deposits are those which occur in general on the slope from the continental shelves to the ocean depths and in the deep sea basins of enclosed and fringing seas. K. Andree (Geologie des Meeresbodens, 192o) adopts this.

Littoral and Shore Deposits.

The littoral deposits include those of the actual shore on the wash of the waves and of the surface of the continental shelf. Shore deposits are the product of the waste of the land arranged and bedded by the action of currents or tidal streams. On the rocky coasts of high latitudes blocks of stone detached by frost fall on the beach, and becom ing embedded in ice during winter, are of ten drifted out to sea and so carry the shore deposits to some distance from the land. Where the force of the waves on the beach produces its full effect the coarser material gets worn down to gravel, sand and silt, the finest particles remaining long suspended in the water, to be finally deposited as mud in quiet bays. A particularly fine-grained mud is formed on the low coasts of the eastern border of the North sea by a mixture of the finest sediment carried down by the slow running rivers with the calcareous or siliceous remains of plank ton. Pure calcareous sand and calcareous mud are formed by Oceanic Deposits.—It has long been known that the deposits which carpet the floor of the ocean differ in different places, and coasting sailors have been accustomed from time immemorial to use the lead not only to ascertain the depth of the water but also to obtain samples of the bottom, the appearance of which is often characteristic of the locality. Various devices have been attached to leads intended to catch and hold the material when soft enough to be penetrated. One of the most effective early forms was the snapper or "deep-sea clamm" of Sir John Ross, a pair of powerful spring jaws held apart by an arrangement which, when released on striking the bottom, allowed the jaws to close, biting out and holding securely a substantial portion of the ground. A simpler form of collector, now almost universally used, is a plain brass tube, which is driven into the bottom of the sea by the weight of the sounding lead, and in which the deposit may be retained by a valve or other contrivance, though in many cases friction alone suffices to hold the punched-out core. Larger

quantities of deposit may be conveniently collected by means of the Monaco snapper or of the dredge, which can be worked in any depth and brings up large stones, concretionary nodules or fossils, which a sounding-tube could not collect.

The voyage of the "Challenger" supplied for the first time the nucleus of a collection of deep-sea deposits sufficient to serve as the basis for comprehensive classification and mapping. The "Challenger" collections supplemented by those of other expedi tions and of many telegraphic and surveying-ships were studied in detail by Sir John Murray and Prof. A. Renard, whose mono graph ("Challenger" Reports, "Deep Sea Deposits"), published in 1891, laid the foundations and reared the greater part of the structure of our present knowledge on the subject. The classifi cation adopted was a double one, thus :— wave action on the shores of coral islands where the only material available is coral and the accompanying calcareous algae, crus tacea, molluscs and other organisms secreting carbonate of lime. Recent limestones are being produced in this way and also in some places by the precipitation of calcium carbonate by sodium or ammonium carbonate which has been carried into the sea or formed by organisms. The precipitated carbonate may agglom erate on mineral or organic grains which serve as nuclei, or it may form a sheet of hard deposit on the bottom, as occurs in the Red sea, off Florida, and round many coral islands in the Pacific. The very finest sediment is kept in a state of movement until it drops into the gulleys or furrows of the shelf, where it can come to rest together with the finer fragments of the remains of littoral or bank vegetation. Thus are formed the "mud-holes" of the Hudson Furrow. Sand may be taken as the predominating de posit on the continental shelves, often with a large admixture of remains of calcareous organisms, for instance the deposits of rnaerl made up of nullipores off the coasts of Brittany and near Belle Isle. Amongst the most widely-distributed of the deposits actually formed on the continental shelf are phosphatic nodules; these are especially abundant on the east coast of the United States and on the Agulhas bank, where the amount of calcium phosphate in the nodules is as much as 5o%. Sir John Murray finds the source of the phosphoric acid to be the decomposition of large quantities of animal matter.