Page:Popular Science Monthly Volume 48.djvu/288

276* through some natural duct, finds its way to the sea with its burden of salt. But when the waters of the ocean are evaporated to form clouds and rain, the salt is left behind, so that ever more and more salt is being transferred from the land; and this ceaseless transfer has been going on since the first brooks and rills gathered together to form the rivers of the primeval lands. This process of salinification, which is identical with that which takes place in every lake and inland sea, like Great Salt Lake and the Dead Sea, into which streams flow but from which none emerge, has often been looked upon as a sufficient cause for the existing saltness of oceanic waters, for the ocean occupies a great closed basin into which many thousands of rivers flow, but from which none take their source. It must not be overlooked, however, that there is direct evidence to show that in early geological ages, when the continents were small and before the rivers were numerous or large, the waters of the vast ocean of those times were salt.

The salts of the sea have fed, throughout all time, countless living things which have thronged its water and whose remains now form the rocks of continents or lie spread in beds of unknown thickness over 66,000,000 square miles of the 143,000,000 square miles of the ocean's floor; they have lent the substance to build the fringing reefs of the land and all the coral islands of the sea, and there are at present, on the basis of an average salinity of three and a half per cent, in the 290,700,000 cubic miles of water which make up the oceans, 90,000,000,000,000,000 tons, or 10,173,000 cubic miles, of salt. This is sufficient to cover the areas of all the lands of the earth with a uniform layer of salt to a depth of one thousand feet.

It seems that the sea was made salt in the beginning as a part of the grand design of the Creator to provide for the system of evolution which has been going on since the creation. Many distinct species of living organisms exist in the sea as a result of its salinity, and their remains have largely contributed to the growth of continents. The three great factors in accounting for the system of currents in the ocean, by which it becomes the great heat distributer of the globe, are changes of temperature, the winds, and salinity. The last mentioned becomes an important factor through the immediate and essential differences of specific gravity and consequent differences of level that it produces in different parts of the ocean through the action of evaporation and rainfall.

If, through the fall of rain upon a portion of the ocean or through the action of evaporation in the surrounding parts, the waters of that portion become lighter than the rest down to a certain distance below the surface, two different kinds of motion will