From these remarks on the surface-tratsr, we pass on briefly to notice the difference of sea-water in different depths. On this subject, the result obtained from the analyses of specimens of sea-water taken from different regions, is so contradictory that we shall simply quote the sentence with which Forchhammer commences this department of his subject: " It would be natural to suppose that the quantity of salts in sea-water would increase with the depth, as it seems quite reasonable that the specific gravity of sea water would cause such an arrangement. But this difference in specific gravity, rela tive to the increase in the quantity of salts, is counteracted by the decreasing tempera ture from the surface to the bottom. We have parts of the sea where the quantity of solid salts increases with the depth; in other parts, it decreases with the increasing depth; in other places, hardly any differences can be found between surface and depth; and, lastly, I have found one instance where water of a certain depth contained more salt than both above and below. These differences are, to a great extent, dependent upon currents both on the surface and in different depths."—Op. cit., p. 229. Some times salinity of the surface-water is the same as that of the deep: or one or more ingredients may vary in its proportions: for example, in the Mediterranean, while the deep water, generally, is richer than the surface-water in sulphuric acid, in some pans, as between Sardinia and Naples, the surface-water is the richer in that ingredient. There are few observations on the specific gravity of sea-water at different depths. For the following observations we are indebted to sir James Ross: "At 39° 18' s. lat., 177* 2' w. long., the specific gravity of the surface-water was 1.0274; at 150 fathoms. 1.0272; and at 450 fathoms, 1.0268; all tried at the temperature of 60° Fahr., and showing that the water beneath was specifically lighter than that of the surface, when brought to the same temperature; our almost daily experience confirmed these results." —Voyage, etc., vol. ii. p. 133.
it important question, How did the salts which now occur in the sea come into it? Is It the land that forms the sea, or is it the sea that makes the land? Are the salts that are now found in sea-water washed out of tile land by the atmospheric water ? Has the sea existed from the beginning of the earth? And has it slowly but continually given its elements to form the land? and their answers constitute the last part of Foreh hammer's most philosophical and laborious Memoir. The following is, in a condensed form, his reply to these questions: Suppose a river had its outlet in a valley, with no communication with the sea; the valley would be filled with water till its surface was so great that the annual evaporation was equal to the annual supply. There would then be a physical, but not a chemical equilibrium, because the annual loss would consist of pure water, while the received water would contain various mineral or saline matters, which would gr on increasing till chemical changes would occasion precipitation of dif ferent salts. Now, in the water of the assumed river, we should find the bases prevail
ing in the following order—lime, magnesia, soda, iron, manganese, and potash;- • while the acids, similarly arranged, were carbonic, sulphuric, muriatic (chlorine), and . Now, all these substances are found in although in very different 'proportions The ocean is, in point of fact, such a lake as we have here supposed, with all the carrying their dissolved matters into it. " then," our author asks, "do we not observe, a greater influence of the rivers? Why does not lime, the prevailing base of river-water, occur in a greater proportion in the water of the In all river-water the number of equivalents of sulphuric acid is much smaller than that of lime, and yet we find in sea-water about three equivalents of sulphuric acid to one of lime. There must thus be in sea-water a constantly acting cause that deprives it again of the lime schieh the rivers furnish, and we find it in the shell-fishes, the corals, the bryozoa, and all the other animals which deposit carbonate of lime." These animals not only deprive the water of its carbonate of lime, but they likewise decompose the sulphate of lime—a decomposition probably depending upon the carbonate of ammonia formed by the vital processes of these animals. The silica, which is always present in river-water, is appro priated by the varied sponges, diatoms, etc., and hence its scantiness in sea-water. With regard to the sulphuric acid conveyed into the sea, a small part enters into the ompositiou of shells, corals, etc., and a greater part is attracted by sea-weeds, in which it undergoes reduction, as already described, while the balance remains in the sea water. The magnesia of the river-water enters in small quantity into marine shells and corals, but only a small quantity is thus abstracted from sea-water, while the soda and muriatic acid, or chlorine, form, as far as we know, by the pure chemical, or ergano-chemical action that takes place in the sea, no insoluble compound. "Thus," he concludes, " the quantity of the different elements in sea-water is not proportional to the quantity of elements which river-water pours into the sea, but inversely to the facility with which the elements in sea-water are made insoluble by general chemical or organo-chemical actions in the sea; and we may infer that the chemical composition of the water of the ocean in a great part is owing to the influence general and organo chemical decomposition has upou it, whatever may have been the composition of the primitive ocean."