Page:EB1911 - Volume 19.djvu/1015

Rh deeper water, which aided by the increased pressure adds to the solvent power of the water for carbonate of lime. It is, however, a curious question how, considering the increase of carbonic acid by the decomposition of organic bodies and possible submarine exhalations of volcanic origin, the water has not in some places become saturated and a precipitate of amorphous calcium carbonate formed in the deepest water. The whole subject still requires investigation.

Amongst the foreign material found embedded in the red clay are globules of meteoric iron, which are sometimes very abundant. Derived products in the form of crystals of phillipsite are not uncommon, but the most abundant of all are the incrustations of manganese oxide, as to the origin of which Murray and Renard are not fully clear. The manganese nodules afford the most ample proof of the prodigious period of time which has elapsed since the formation of the red clay began; the sharks’ teeth and whales’ ear-bones which serve as nuclei belong in some cases to extinct species or even to forms derived from those familiar in the fossils from the seas of the Tertiary period. This fact, together with the extraordinarily rare occurrence of such remains and meteoric particles in globigerina ooze, although there is no reason to suppose that at any one time they are unequally distributed over the ocean floor, can only be explained on the assumption that the rate of formation of the epilophic deposits through the accumulation of pelagic shells falling from the surface is rapid enough to bury the slow-gathering material which remains uncovered on the spaces where the red clay is forming at an almost infinitely slower rate. Sir John Murray believes that no more than a few feet of red clay have accumulated in the deepest depressions since the close of the Tertiary period. The red clay is the characteristic deposit of the Pacific Ocean, where about 101,000,000 sq. km. (39,000,000 sq. m.) are covered with it, while only 15,000,000 sq. km. (5,800,000 sq. m.) of the Indian Ocean and 14,000,000 sq. km. (5,400,000 sq. m.) of the Atlantic are occupied by this deposit; it is indeed the dominant submarine deposit of the water-hemisphere just as globigerina ooze is the dominant submarine deposit of the land-hemisphere.

Radiolarian ooze was recognized as a distinct deposit and named by Sir John Murray on the “Challenger” expedition, but it may be viewed as red clay with an exceptionally large proportion of siliceous organic remains, especially those of the radiolarians which form part of the pelagic plankton. It does not occur in the Atlantic Ocean at all, and in the Indian Ocean it is only known round Cocos and Christmas Islands; but it is abundant in the Pacific, where it covers a large area between 5° and 15° N., westward from the coast of Central America to 165° W., and it is also found in patches north of the Samoa Islands, in the Marianne Trench and west of the Galapagos Islands.

The total areas occupied by the various deposits according to the latest measurements of Krümmel are as follows:—

Geologists are agreed that littoral and hemipelagic deposits similar to those now forming are to be found in all geological systems, but the existence in the rocks of eupelagic deposits and especially of the abysmal red clay, though viewed by some as probable, is totally denied by others. There is even some hesitation in accepting the continuity of the chalk with the globigerina ooze of the modern ocean. From the obvious rarity of true abysmal rocks in the continental area Sir John Murray deduces the permanence of the oceans, which he holds have

always remained upon those portions of the earth’s crust which they occupy now, and both J. Dana and Louis Agassiz had already arrived at the same conclusion. This theory accords well with the enormous lapse of time required in the accumulation of the red clay.

Salts of Sea-water.—Sea-water differs from fresh water by its salt and bitter taste and by its unsuitability for the purposes of washing and cooking. The process of natural evaporation in the salines or salt gardens of the margin of warm seas made the composition of sea-salt familiar at a very early time, and common salt, Epsom salts, gypsum and magnesium chloride were recognized amongst its constituents. The analyses of modern chemists have now revealed the existence of 32 out of the 80 known elements as existing dissolved in sea-water, and it is scarcely too much to say that the remaining elements also exist in minute traces which the available methods of analysis as yet fail to disclose. Many of the elements such as copper, lead, zinc, nickel, cobalt and manganese have only been found in the substance of sea-weeds and corals. Silver and gold also exist in solution in sea-water. Malaguti and Durocher estimate the silver in sea-water as 1 part in 100,000,000 or 1 grain in 1430 gallons. If this estimate is correct there exists dissolved in the ocean a quantity of silver equal to 13,300 million metric tons, that is to say 46,700 times as much silver as has been produced from all the mines in the world from the discovery of America down to 1902. No quantitative determination of the amount of gold in solution is available. E. Sonnstadt detected gold by means of a colour test and roughly estimated the amount as 1 grain per ton of sea-water, and on this estimate all the projects for extracting gold from sea-water have been based.

The elements in addition to oxygen which exist in largest amount in sea salt are chlorine, bromine, sulphur, potassium, sodium, calcium and magnesium. Since the earliest quantitative analyses of sea-water were made by Lavoisier in 1772, Bergman in 1774, Vogel in 1813 and Marcet in 1819 the view has been held that the salts are present in sea-water in the form in which they are deposited when the water is evaporated. The most numerous analyses have been carried out by Forchhammer, who dealt with 150 samples, and Dittmar, who made complete analyses of 77 samples obtained on the “Challenger” expedition. Dittmar showed that the average proportion of the salts in ocean water of 35 parts salts per thousand was as follows (calculated as parts per thousand of the sea-water, as percentage of the total salts. and per hundred molecules of magnesium bromide):—

As Marcet had foreshadowed from the analysis of 14 samples in 1819, the larger series of exact analyses proved that the variations in the proportion of individual salts to the total salts are very small, and all analyses since Dittmar’s have confirmed this result. Although the salts have been grouped in the above