Therefore it cannot be doubted but that the tides produce currents whose direction always answers that of the opposite hills and all mountains between which they flow. Currents produced by winds, also follow the direction of those hills which are under the water, seldom running opposite to the wind which produces them, any more than those which are occasioned by the tides follow the direction of their original cause.
To give a clear idea of the productions of currents, we shall first observe they are to be met with in every sea; that some are rapid, and others slow; that some are of great extent, both in length and breadth, and others short and narrow; that the same cause, whether the wind or tides, which produces these currents, frequently gives to each of them a velocity and direction very different; that a north wind, for example, which should give the water one general motion towards the south, on the contrary, produces a number of currents, separated from each other, and very different both in extent and direction; some flowing towards the south, others south-east, and others south-west; some are very rapid, others slow; some long and broad, others short and narrow; in fact, their motions are so various that we have no idea left of their original cause. When a contrary wind succeeds, all these currents take an opposite course, and follow in a contrary direction, precisely in the same manner as would be the case upon land between two opposite and adjacent hills, provided it was covered with water, as is seen at the Maldiva and all the islands of the Indian seas, where the currents run, and the winds blow, for six months in a contrary direction. The same remark has been made on currents between shoals and sandbanks. In general all currents, whether caused by the motion of flux or reflux, or the action by the wind; have the same extent and direction throughout their whole course, yet differ from each other in most respects, which can proceed only from the inequalities of the hills, mountains, and vallies, at the bottom of the sea, it being certain that the current between two islands follows the direction of the coasts; and the same is observable between banks of sand, shoals, &c. we must, therefore, look on the hills and mountains of the bottom of the sea as banks which direct the current; and hence a current is a river, the breadth of which is determined by that of the valley through which it flows: its rapidity depends on the force which produces it, combined with the breadth, of the interval through which it must pass: and its direction is traced by the position of the hills and inequalities between which it must take its course.
We shall now give a reason for the singular correspondence between the angles of mountains and hills, which are to be met with in every part of the world. We have already remarked that when a river, &c. forms an elbow, one of the borders forms on one side a projection inland, and the other forms a point from land, and that through all the sinuosities of their course this correspondence is always found. This fact is founded on the laws of hydrostatics. It would be easy to demonstrate the cause of this effect; but it is sufficient that it is general and universally known, and that all the world may be convinced of it by their own eyes, that when the banks of a river form a projection inland to the left hand, the other shore forms a projection from land to the right.
Hence the currents of the sea must be looked upon as great rivers, subject to the some laws as those on land, and will, like them, form in the extent of their course many sinuosities, whose projections or angles will correspond; and as the banks of currents are hills and mountains, above or below the surface of the water, they will have given these eminences the same form as is remarked on the shores of rivers; therefore we must not be astonished that our hills and mountains, which have been formerly covered by the sea, and formed by the sediments which the waters have left, should, by the motion of its currents, have taken this regular figure, and all the angles are alternately opposite; they have been the shores of the currents or rivers of the sea, and have therefore necessarily taken a figure and direction similar to those of the shores of the rivers of the earth.
This alone, independent of the other proofs we have given, would be sufficient to evince that the earth of our continent and islands have been covered with waters of the ocean, and doubtless throws great light upon the Theory which I have endeavoured to prove well founded; for it was not sufficient to have proved that the strata of the earth were formed by the sediments of the sea; that the mountains were elevated by the successive accumulation of such sediments; and that they were composed of shells and other marine productions; but it required also a reason why the angles of mountains so exactly correspond; this could only be done by an investigation into the real cause, which had not hitherto been attempted, and which, being united with the rest, forms a body of proofs as complete as may be had in physics, and establishes my Theory to be founded on facts, independent of all hypothesis.
The principal currents of the ocean are those observed in the Atlantic Sea, near Guinea. They extend from Cape Verd to the Bay of Fernandes. Their motion is from west to east; that is contrary to the general motion of the sea. These currents are so rapid that vessels sail in two days from Moura to Rio de Benin, a course of 150 leagues; but they require six or seven weeks to return; nor would it be possible to get out of these climates if advantage was not taken of the tempestuous winds which suddenly rise in them; but there are entire seasons during which vessels cannot stir, the sea being continually calm, excepting what arises from the currents, which is always directed towards the coasts, and never extend more than 20 leagues from shore. Near Sumatra there are rapid currents, which flow from south to north, and which probably formed the gulph at Malacca. There are also considerable currents between Java and Magellan, the Cape of Good Hope, and the island of Madagascar, especially on the coast of Africa, between Natal and the Cape. In the Pacific Sea, on the coast of Peru, and the rest of America, the sea moves from south to north, and a south wind continually blowing there seems to be the cause. The like motion is observed on the coasts of Brazil; from Cape St. Augustine to the Antilles; from the mouth of the Manilla strait to the Philippine islands; and in the port of Kubuxiu at Japan[D].
[D] See Varen. Geography, page 140.
There are violent currents in the sea adjacent to the Maldivian islands; and between those islands these currents flow, as already observed, constantly for six months from east to west, and during the other six months they follow the direction of the monsoons, and it is probable they are produced by those winds.