Still, though the ocean includes in its composition every kind of land-water, Sea-water as such is different from them all. Not only in its vast extent, in its enormous depth, but in its strong flavour of Salt.
One of the commonest of substances is Salt. It is in the ground, in air, in water. We even know that it does not belong to our earth alone, but to many heavenly bodies also.
Perhaps one reason for this abundance, at least upon our Earth, is that it is necessary for life. There is salt in the make of blood and of brain, of muscle and of tendon. Salt is perpetually passing out of a man’s body; therefore continual fresh supplies of it are needed. Without a certain amount of salt in his food, he cannot keep in good health.
This at one time was not understood; and salt was looked upon as a mere luxury, easily to be dispensed with. Condemned criminals were forbidden that luxury; and they went through a good deal of suffering, the reason for which was not guessed. If plenty of animal and vegetable food was given to them, they managed to get along, since both contain salt; but if they were kept on purely farinaceous fare, they broke down.
Where all the salt in the Ocean comes from, is a complex question. Large supplies are brought down annually by rivers and streams, from various minerals in their beds, as well as from rock-salt regions. But if we ask, “How comes the rock-salt to be there?” we are told that it is a deposit, once formed beneath ocean-waters, or at least left by the drying up of salt lakes and seas. A proof of the latter theory is found in multitudes of sea-shells, often distributed through layers of rock-salt.
If much sea-salt came originally from rock-salt on land, and if rock-salt came originally from ocean-deposits, we are led into a curious circle of cause and effect—not unlike that of oak and acorn, or of hen and egg, with the attendant puzzle of—Which first? It is a query which we are not able to answer.
In former days the salt used for household and mercantile purposes was almost entirely prepared by the evaporation of sea-water. We no longer depend on this, however; and in England the sea-salt trade has gone down greatly before that of rock-salt, which is found to be the better for table use. It has not the same tendency to stick together in lumps, after being packed in sacks.
Great districts of rock-salt are found in many places—such as those in the Carpathian Mountains, in the Swiss Alps, in Germany, and in Great Britain. One huge mine in Galicia has been worked for six hundred years; and this supply is said to reach through about five hundred miles. From British works alone the quantity carried away every year amounts to a cubic mile of salt.
But land-supplies grow pale and insignificant before the quantities which float in the ocean. It has been reckoned that, if the waters of the whole ocean could be dried up, the amount of salt left lying on the ocean-bed would be something like four-and-a-half millions of cubic miles.
Such an enormous mass hardly conveys a clear idea. Let us think of one single cubic mile of sea-water, separated from the ocean, and see how much it would contain. First, the whole of that cubic mile of water has to be dried up; and then the materials left behind have to be weighed. We should find about thirty-three millions of tons of various kinds of substances, the names of which need not be given. We should also find of common salt a supply which, when weighed, would reach the great figure of one hundred and seventeen millions of tons. All this, be it remembered, floating unseen in a single cubic mile of water. No wonder the sea tastes salt.