By what has been said in the Articles I, VII, VIII, and IX, it appears that great and general changes have happened to the terrestrial globe; and it is as certain, from what we have related in other articles, that the surface of the earth has undergone particular alterations. Although the order, or succession, of these particular alterations is not perfectly known, yet we are acquainted with the principal causes; we can even distinguish their different effects; and if we could collect all the facts, which Natural and Civil History furnishes on the subject of the revolutions which have happened to the surface of the earth, we do not doubt but that the Theory of the Earth which we have, laid down would receive additional support.
One of the principal causes of these alterations is the motion of the sea; a motion it has endured from the earliest ages; for since the sun, moon, earth, waters, air, &c. have existed from the time of the creation, the effects of the tides, the motion of the sea from east to west, as well as that of the winds and currents, must have been felt for the same space; and if even we should suppose the axis of the globe had formerly another inclination, and that the continents, as well as the sea, had another disposition, it does not destroy the motion of flux and reflux, nor alter the cause and effects of the winds: it is sufficient that the immense quantity of waters, which fill the vast space of the sea, is found in some part on the globe of the earth, for wherever they had been collected they would have still been subject to the same motions, and produced similar effects.
When it was once supposed that our continent was formerly the bottom of the sea, there was soon no doubt remaining thereon. The devastations of the sea, which are every where to be met with; the horizontal situation of the strata of the earth; and the correspondence of hills and mountains, appear as so many convincing proofs; for by examining the plains, vallies, and hills, we clearly perceive that the surface of the earth has been formed by the waters. It is equally evident, when we look into the interior parts of the earth, that those stones which contain sea-shells, have been formed by the sediments of the waters, since the shells are found filled with the same matter as that which surrounds them; and lastly, by reflecting on the corresponding angles of opposite hills, we cannot doubt that their directions are the works of the currents of the sea. It is true, that since the earth has been left uncovered, the original form of the surface has been constantly changing; the mountains have diminished in height; the plains have been elevated; the angles of hills become more obtuse; many matters washed away by floods, or rivers, have taken a round shape; beds of gravel, soft stone, &c. have been formed; but the essential matter is still remaining, the ancient form is still apparent, and I am persuaded that all the world may be convinced by their own inspection of what has been advanced on this subject; and whoever attends to the observations and proofs I have given, will not doubt, the earth was formerly covered by the waters of the sea, and that it is the currents of the sea which have given to the surface of the earth, the form we at present perceive.
The principal motion of the sea is, as we have already observed, from east to west. It also appears that the sea has gained above 500 leagues of ground on the eastern coasts of both the old and new continents; for the proofs of which we refer to those given in [Article XI]. and shall only add thereto, that all straits which join two seas, are directed from east to west; the straits of Magellan, Frobisher, of Hudson, of Ceylon, and those of the seas of Corea and Kamtschatka have all this direction, and appear to have been formed by the currents of the waters, which being impelled from east to west, opened these passages in the same direction, and in which they preserve a more considerable motion than in any other; for in these straits there are high and violent tides, whereas in those situated on the western coasts, like that of Gibraltar, Sund, &c. the motion of the tides is almost insensible.
The inequalities of the bottom of the sea change the direction of the water's motion; they have been successively produced by the sediments of the water, and by matters transported by the tides or other motions; for we do not consider the motion of the tides as the sole cause of those inequalities, but only as the principal and first, because it is the most constant and acts without interruption; the action of the winds is another cause; the action of which beginning at the surface, extends to considerable depths, as is plain from the matters that are loosened and thrown up by a storm from the bottom of the sea, and which never happens but in tempestuous weather.
We have already mentioned that between the tropics, and even some degrees beyond them, an east wind continually blows; this wind, which contributes to the general motion of the sea from east to west, is as ancient as the flux and reflux, since it depends on the rarefaction of the air, produced by the heat of the sun. Here then are two united causes of motion, the greatest of which is near the equator. The first, the tides which are more sensibly felt in southern latitudes: and the second, the east wind which blows continually in the same climates. These two causes have concurred, ever since the formation of the globe, to produce a motion in the waters from east to west, and to agitate them more in that part of the globe than in all the rest. It is for this reason that the greatest inequalities of the surface of the globe are found between the tropics. The part of Africa, comprehended between these two circles, is only a group of mountains whose different chains extend for the most part from east to west, as is evident from the direction of the great rivers of this part of the world; it is the same with those parts of Asia and America which are comprised between the tropics.
From the combination of the general motion of the sea from east to west, with the flux and reflux of the currents, and the winds, an infinite number of different effects has resulted, both on the bottom of the sea, and on the coasts. Varenius says, it is very probable that the gulphs and straits have been formed by the reiterated efforts of the ocean against the land; that the Mediterranean sea, the gulphs of Arabia, Bengal, and Cambay, have been formed by the eruption of the waters, as well as the straits between Sicily and Italy, between Ceylon and India, between Greece and Eubœa, and that it is the same with respect to the straits of the Manillas, Magellan, &c. that one proof of these eruptions, and that the sea has forsaken different lands is, that but few islands are to be met with in the great seas, and never a great number of islands close to each other; that in the immense space occupied by the Pacific sea, not above two or three small islands are to be found towards the middle of it; that in the vast Atlantic ocean, between Africa and the Brazils, we only find the small islands of St. Helena and Ascension; but that all islands are near the great continents, as those of the Archipelago, near the continents of Europe and Asia, the Canaries, near Africa, all the islands of the Indian sea, near the eastern coast of Asia; the Antille islands, close to that of America, and that only the Azores lie at any great distance in the sea between Europe and America.
The inhabitants of Ceylon say, that their island was separated from the peninsula of India by an eruption of the ocean; and this popular tradition is very probable. It is also imagined the island of Sumatra has been separated from the continent, and the great number of shoals and sand banks are a strong proof of it. The Malabars assert, that the Maldivian islands formed a part of the continent of India, and in general it may be reasonably supposed that all the eastern islands have been divided from the continents by eruptions of the ocean.[AQ]
[AQ] See Varenius Geography, page 203, 217, and 220.
There is an appearance that formerly the island of Great Britain was part of the continent, and that England was joined to France; the similarity of the stones on the two coasts, and the narrowness of this strait seem plainly to indicate it. By supposing, says Dr. Wallis, "that England formerly communicated with France, by an isthmus between Dover and Calais, it must follow that the sea would be carried against both sides of it with great violence by the tides twice in every twenty-four hours, the German ocean, which is between England and Holland, striking of it on the eastern side, and that of France on the west, would be sufficient in time to wear away so narrow a neck of land, as we have supposed. The tides acting with great violence, not only against this isthmus but also against the coasts of France and England, must have washed away a great quantity of sand, earth, and clay, from every part against which the sea was forced: but, being stopt in its course, it would not deposite, as might be supposed, their sediments against this isthmus, but transported them into the great plain that now forms Romney Marsh, which is eight miles long by four broad; for whosoever has seen this plain, cannot doubt but that it was formerly covered with the sea, as it would be still overflowed by spring tides if it was not for the Dikes of Dimchurch."