the greatest depths they descend, i. e. twenty fathoms, the bottom of the sea is so troubled by the agitation of the waters, that the mud and shells are carried to considerable distances, consequently transportations of this kind are made in every part of the sea, and this matter falling must form eminences, composed like our mountains, and in every respect similar; therefore the flux and reflux, by the winds, the currents, and all the motions of the water, must inevitably create inequalities at the bottom of the sea.
Nor must we imagine that these matters cannot be transported to great distances, because we daily see grain, and other productions of the East and West Indies, arriving on our own coasts.[25:A] It is true these bodies are specifically lighter than water, whereas the substances of which we have been speaking are specifically heavier; but, however, being reduced to an impalpable powder, they may be sustained a long time in the water so as to be conveyed to considerable distances.
It has been supposed that the sea is not troubled at the bottom, especially if it is very
deep, by the agitations produced by the winds and tides; but it should be recollected that the whole mass, however deep, is put in motion by the tides, and that in a liquid globe this motion would be communicated to the very centre; that the power which produces the flux and reflux is a penetrating force, which acts proportionably upon every particle of its mass, so that we can determine by calculation the quantity of its force at different depths; but, in short, this point is so certain, that it cannot be contested but by refusing the evidence of reason.
Therefore, we cannot possibly have the least doubt that the tides, the winds, and every other cause which agitates the sea, must produce eminences and inequalities at the bottom, and those heights must ever be composed of horizontal or equally inclined strata. These eminences will gradually encrease until they become hills, which will rise in situations similar to the waves that produce them; and if there is a long extent of soil, they will continue to augment by degrees; so that in course of time they will form a vast chain of mountains. Being formed into mountains, they become an obstacle to and interrupt the common
motion of the sea, producing at the same time other motions, which are generally called currents. Between two neighbouring heights at the bottom of the sea a current will necessarily be formed, which will follow their common direction, and, like a river, form a channel, whose angles will be alternately opposite during the whole extent of its course. These heights will be continually increasing, being subject only to the motion of the flux, for the waters during the flow will leave the common sediment upon their ridges; and those waters which are impelled by the current will force along with them, to great distances, those matters which would be deposited between both, at the same time hollowing out a valley with corresponding angles at their foundation. By the effects of these motions and sediments the bottom of the sea, although originally smooth, must become unequal, and abounding with hills and chains of mountains, as we find it at present. The soft materials of which the eminences are originally composed will harden by degrees with their own weight; some forming parts, purely angular, produce hills of clay; others, consisting of sandy and crystalline particles, compose those enormous masses of
rock and flint from whence crystal and other precious stones are extracted; those formed with stony particles, mixed with shells, form those of lime-stone and marble, wherein we daily meet with shells incorporated; and others, compounded of matter more shelly, united with pure earth, compose all our beds of marle and chalk. All these substances are placed in regular beds, and all contain heterogeneous matter; marine productions are found among them in abundance, and nearly according to the relation of their specific weights; the lightest shells in chalk, and the heaviest in clay and lime-stone; these shells are invariably filled with the matter in which they have been inclosed, whether stones or earth; an incontestible proof that they have been transported with the matter that fills and surrounds them, and that this matter was at that time in an impalpable powder. In short, all those substances whose horizontal situations have been established by the level of the waters of the sea, will constantly preserve their original position.
But here it may be observed, that most hills, whose summits consist of solid rocks, stone, or marble, are formed upon small eminences of much lighter materials, such for instance as
clay, or strata of sand, which we commonly find extended over the neighbouring plains, upon which it may be asked, how, if the foregoing theory be just, this seemingly contradictory arrangement happens? To me this phenomenon appears to be very easy and naturally explained. The water at first acts upon the upper stratum of coasts, or bottom of the sea, which commonly consists of clay or sand, and having transported this, and deposited the sediment, it of course composes small eminences, which form a base for the more heavy particles to rest upon. Having removed the lighter substances, it operates upon the more heavy, and by constant attrition reduces them to an impalpable powder; which it conveys to the same spot, and where, being deposited, these stony particles, in the course of time, form those solid rocks and quarries which we now find upon the tops of hills and mountains. It is not unlikely that as these particles are much heavier than sand or clay, that they were formerly a considerable depth under a strata of that kind, and now owe their high situations to having been last raised up and transported by the motion of the water.
To confirm what we here assert, let us more closely investigate the situation of those materials which compose the superficial outer part of the globe, indeed the only part with which we have any knowledge. The different beds of strata in stone quarries are almost all horizontal, or regularly inclined; those whose foundations are on clays or other solid matters are clearly horizontal, especially in plains. The quarries wherein we find flint, or brownish grey free-stone, in detached portions, have a less regular position, but even in those the uniformity of nature plainly appears, for the horizontal or regularly inclined strata are apparent in quarries where these stones are found in great masses. This position is universal, except in quarries where flint and brown free-stone are found in small detached portions, the formation of which we shall prove to have been posterior to those we have just been treating of; for granite, vitrifiable sand, argol, marble, calcareous stone, chalk, and marles, are always deposited in parallel strata, horizontally or equally inclined; the original formation of these are easily discovered, for the strata are exactly horizontal and very thin, and are arranged above each other like the leaves