Here is a body of water 740,000 square miles in extent, subject hourly to the increase of its specific gravity. Upon the surface, a crust of salt is left in the course of every year, sufficient to give a double charge to the depth of six fathoms. To adjust the difference thus created with the ocean, there is but a narrow inlet,—a mere crack upon the side of the vessel, an interval of six miles left in a circumference of four thousand. By this, in its deepest part, the heavier water will have to find its way out, and thus occasion an indraught of water above, besides the demand created by evaporation. It remains to be ascertained by experiment, that the specific gravity of the water in the Straits varies at different levels, and at what level it commences to move outwards. These experiments will present great practical difficulties from the tides at the sides, which will mingle the streams; and, from the shallowness towards the ocean, they must be made in the middle and at the Mediterranean side. The evaporation, and the differences of specific gravity, will give the means of calculating the amount of water passing through in both directions, and the depth and velocity of the two currents. But it may be inferred that the currents will have the greatest speed at the top and the bottom,—that their velocity will diminish towards the centre, and that a neutral space of dead water will remain, not only in consequence of the counter-impetus of the currents, but because of the nearer approach of specific gravity, and the mingling of the two waters, which would destroy the moving power.
With this solution we can at once understand the powerlessness of tides and storms, currents without difference of level, or prevalence of winds: the volume of the stream is accounted for, the mass of salt disposed of, and the apparent rebellion against the laws of Nature put down.
By tables kept for several years at Malta, it appears that the Mediterranean, at that point, varies in level between winter and summer no less than three feet. In winter, when there is no evaporation, and when the quantity of water falling in the immediate vicinity of the Mediterranean is greatest, the level is lowest. The cause, I should take to be the pressure of wintry wind. In like manner, those erratic movements in the Straits may result from difference of atmospheric pressure without and within.
These currents, by the testimony of the ancients, have not held from the beginning—they have been the results of successive modifications of the channel. This is singularly borne out by the traditions of the neighbouring people and the geological features of the coast.
Eldressi narrates, as an old and popular story of his day, that “the Sea of Cham (Mediterranean) was in ancient times a lake surrounded on all sides, like the Sea of Tabaristan (Caspian), the waters of which have no communication with any other seas. So that the inhabitants of the extreme west invaded the people of Andalusia, doing them much injury, which they, in like manner, did to the others, living always in war, until the time of Alexander,[28] who consulted his wise men and artificers about cutting that arid isthmus and opening a canal. Thereupon they measured the earth, and the depth of the two seas, and saw that the Sea of Cham was not much lower than the Sea Muhit, (Ocean); so they raised the towns that were on the coast of the Sea of Cham, changing them to the high ground. Then he ordered the earth to be dug out; and they dug it away to the bottom of the mountains on both sides; and he built there two terraces with stones and lime the whole length between the two seas, which was twelve miles; one on the side of Tankhe (Tangier), and one on the side of Andeluz. When this was done, he caused the mound to be broken, and the water rushed in from the great sea with violence, raising the waters of the Sea of Cham, so that many cities perished, and their inhabitants were drowned, and the waters rose above the dykes, and carried them away, and did not rest until they had reached the mountains on both sides.”
The Moors have also a Myth. “The sea,” they say, “was created fresh, but exalting itself against its Maker, gnats were sent to drink it up. It then humbled itself in the stomach of the gnats, and prayed to be relieved, so the gnats were ordered to vomit it forth again, but the salt remained from the stomach of the gnats an eternal sign of its disobedience.”
Before suggesting the interpretation of these Myths, I will point out the change which the coasts and channel have undergone.
The description of the Straits by Greek and Roman writers is so unlike their present appearance, that, but for the impossibility of doubting the identity of the objects, we must have supposed their words to apply to some undiscovered region. Who could recognize the deep sea and the iron-bound coasts of these narrows, in a plain of sand furrowed by rivers running in from the ocean, which it was difficult to reach, not from the strength of the stream, but the intricacies of the passage—who would imagine the necessity of constructing flat-bottomed boats to get across from Gibraltar to Ceuta, where now there is above one thousand fathoms, or of transferring the ferry to the Atlantic side of the Straits, where at present the depth is not one-sixth of what it is in the other, in order to get more water? Yet there is no doubt that these details apply to these spots, nor can we question the known accuracy of the writers, or escape from the concurrence of their testimony. We are reduced, then, to the necessity of admitting some great revolution in the features of the country, and a total change in the nature of the current.
The explanation is easy: the bank of sand, left by the retiring waters of the Deluge, which covers the western border of Africa, reached to the coast of Andalusia, and the remnants of it still lie on the eastern side of Gibraltar, and fill the caverns exposed to that side; on the depression of the Mediterranean by evaporation, the water of the ocean would filter in, the sand would be gradually removed. The amount of sand on the Mediterranean side of the “Rock,” shows that a plain nearly one thousand feet above the level of the sea, once stretched across to Africa, where now the channel is one thousand fathoms deep. This has been worked out by the overfall, while on the Atlantic side the water shoals to one hundred and eighty fathoms, presenting the character of an estuary with a bar from the rush outward of the under waters, since the Gut was sufficiently deepened to admit of the currents in opposite directions. The centre part of the channel is worn down to the rock or to gravel, every particle of sand has been removed from the bottom. Two inferences may be drawn: 1st. That the process of removal was likely to be accompanied by sudden inbursts, which would submerge the borders. 2nd. That the Mediterranean, in early ages, was fresh, and afterwards became, as it evaporated, very salt, until the channel was deepened to allow of its mixing with the ocean. What else is implied by the Myth of the midges and the fable of Alexander?