Buffon's Natural History, Volume I (of 10)

Let us now examine the position and formation of the interior strata: the earth, says Woodward, appears in places that have been dug, composed of strata placed one on the other, as so many sediments which necessarily fell to the bottom of the water; the deepest strata are generally the thickest, and those above the thinnest, and so gradually lessening to the surface. We find sea shells, teeth, and bones of fish in these different beds, and not only in those that are soft, as chalk and clay, but even in those of hard stone, marble, &c. These marine productions are incorporated with the stone, and when separated from them, leave the impressions of the shells with the greatest exactness. "I have been most clearly and positively assured," says this author, "that in France, Flanders, Holland, Spain, Italy, Germany, Denmark, Norway, and Sweden, stone, and other terrestrial substances are disposed in strata, precisely the same as they are in England; that these strata are divided by parallel fissures; that there are inclosed within stones and other terrestrial and compact substances, a great quantity of shells and other productions of the sea, disposed in the same manner as in this island. I am also informed that these strata are found the same in Barbary, Egypt, Guinea, and in other parts of Africa; in Arabia, Syria, Persia, Malabar, China, and the rest of the provinces of Asia; in Jamaica, Barbadoes, Virginia, New-England, Brazil, and other parts of America20."

This author does not say how he learnt, or by whom he was told, that the strata of Peru contained shells; yet as in general his observations are exact, I do not doubt but he was well informed; and am persuaded that shells may be found in the earth of Peru, as well as elsewhere. This remark is made from a doubt having been formed some time since on the subject, and which I shall hereafter consider.

In a trench made at Amsterdam, to the depth of 230 feet, the strata were found as follows: 7 feet of vegetable earth, 9 of turf, 9 of soft clay, 8 of sand, 4 of earth, 10 of clay, 4 of earth, 10 of sand, then 2 feet of clay, 4 of white sand, 5 of dry earth, 1 of soft earth, 14 of sand, 8 of argil, mixed with earth; 4 of sand, mixed with shells; then clay 102 feet thick, and at last 31 feet of sand, at which depth they ceased digging21.

It is very singular to dig so deep without meeting with water: and this circumstance is remarkable in many particulars. 1. It shews, that the water of the sea does not communicate with the interior part of the earth, by means of filtration. 2. That shells are found at the depth of 100 feet below the surface, and that consequently the soil of Holland has been raised 100 feet by the sediment of the sea. 3. We may draw an induction, that this strata of thick clay of 102 feet, and the bed of sand below it, in which they dug to 31 feet, and whose entire thickness is unknown, are perhaps not very far distant from the first strata of the original earth, such as it was before the motion of the water had changed its surface. We have said in the first article, that if we desired to find the ancient earth, we should dig in the northern countries, rather than towards the south; in plains rather than in mountainous regions. The circumstances in this instance, appear to be nearly so, only it is to be wished they had continued the digging to a greater depth, and that the author had informed us, whether there were not shells and other marine productions, in the last bed of clay, and in that of sand below it. The experiment confirms what we have already said; and the more we dig, the greater thickness we shall find the strata.

The earth is composed of parallel and horizontal beds, not only in plains, but hills and mountains are in general composed after the same manner: it may be said, that the strata in hills and mountains are more apparent there than in the plains, because the plains are generally covered with a very considerable quantity of sand and earth, which the water has brought from the higher grounds, and therefore, to find the ancient strata, must dig deeper in the plains than in the mountains.

I have often observed, that when a mountain is level at its summit, the strata which compose it are also level; but if the summit is not placed horizontally, the strata inclines also in the same direction. I have heard that, in general, the beds of quarries inclined a little to the east; but having myself observed all the chains of rocks which offered, I discovered this opinion to be erroneous, and that the strata inclines to the same side as the hill, whether it be east, west, north, or south. When we dig stone and marble from the quarry, we take great care to separate them according to their natural position, and we cannot even get them of a large size, if we cut them in any other direction. Where they are made use of for good masonry, the workmen are particular in placing them as they stood in the quarry, for if they were placed in any other direction, they would split, and would not resist the weight with which they are loaded. This perfectly confirms that stones, are found in parallel and horizontal strata, which have been successively heaped one on the other, and that these strata composed masses where resistance is greater in that direction than in any other.

Every strata, whether horizontal or inclined, has an equal thickness throughout its whole extent. In the quarries about Paris the bed of good stone is not thick, scarcely more than 18 or 20 feet: in those of Burgundy the stone is much thicker. It is the same with marble; the black and white marble have a thicker bed than the coloured; and I know beds of very hard stone, which the farmers in Burgundy make use of to cover their houses, that are not above an inch thick. The different strata vary much in thickness, but each bed preserves the same thickness throughout its extent. The thickness of strata is so greatly varied, that it is found from less than a line to 1, 10, 20, 30, or 100 feet thick. The ancient and modern quarries, which are horizontally dug, the perpendicular and other divisions of mines, prove that there are extensive strata in all directions. "It is thoroughly proved," says the historian of the academy, "that all stones have formerly been a soft paste, and as there are quarries almost in every part, the surface of the earth has therefore consisted, in all these places, of mud and slime, at least to certain depths. The shells found in most quarries prove that this mud was an earth diluted by the water of the sea, and consequently that the sea covered all these places; and it could not cover them without also covering all that was level with or lower than it: and it is plain that it could not cover every place where there were quarries, without covering the whole face of the terrestrial globe. We do not here consider the mountains which the sea must also at one time have covered, since quarries and shells are often found in them.

"The sea," continues he, "therefore, covered the whole earth, and from thence it proceeds that all the beds of stone in the plains are horizontal and parallel; fish must have also been the most ancient inhabitants of the globe, as there was no sustenance for either birds or terrestrial animals." But how did the sea retire into these vast basins which it at present occupies? What presents itself the most natural to the mind is, that the earth, at least at a certain depth, was not entirely solid, but intermixed with some great vacuums, whose vaults were supported for a time, but at length, sunk in suddenly: then the waters must have fallen into these vacancies, filled them, and left naked a part of the earth's surface, which became an agreeable abode to terrestrial animals and birds. The shells found in quarries perfectly agree with this idea, for only the bony parts of fish could be preserved till now. In general, shells are heaped up in great abundance in certain parts of the sea, where they are immovable, and form a kind of rock, and could not follow the water, which suddenly forsook them: this is the reason that we find more shells than bones of the fish, and this even proves a sudden fall of the sea into its present basins. At the same time as our supposed vaults gave way, it is very possible that other parts of the globe were raised by the same cause, and that mountains were placed on this surface with quarries already formed, but the beds of these quarries could not preserve the horizontal direction they before had, unless the mountains were raised precisely perpendicular to the surface of the earth, which could happen but very seldom: so also, as we have already observed, in 1705, the beds of stone in mountains are always inclined to the horizon, though parallel with each other; for they have not changed their position with respect to each other, but only with respect to the surface of the earth22.

These parallel strata, these beds of earth and stone, which have been formed by the sediment of the sea, often extend to considerable distances, and we often find in hills, separated by a valley, the same beds and the same matters at the same level. This observation agrees perfectly with that of the height of the opposite hills. We may easily be assured of the truth of these facts, for in all narrow vallies, where rocks are discovered, we shall find the same beds of stone and marble on both sides at the same height. In a country where I frequently reside, I found a quarry of marble which extended more than 12 leagues in length, and whose breadth was very considerable, although I have never been able precisely to determine it. I have often observed that this bed of marble is throughout of the same thickness, and in hills divided from this quarry by a valley of 100 feet depth, and a quarter of a mile in breadth, I found the same bed of marble at the same height. I am persuaded it is the same in every stone and marble quarry where shells are found; but this observation does not hold good in quarries of freestone. In the course of this work, we shall give reasons for this difference, and describe why freestone is not dispersed, like other matters, in horizontal beds, and why it is in irregular blocks, both in form and position.

We have likewise observed that the strata are the same on both sides the straits of the sea. This observation, which is important, may lead us to discover the lands and islands which have been separated from the continent; it proves, for example, that England has been divided from France; Spain from Africa; Sicily from Italy; and it is to be wished that the same observation had been made in all the straits. I am persuaded that we should find it almost every where true. We do not know whether the same beds of stone are found at the same height on both sides the straits of Magellan, which is the longest; but we see, by the particular maps and exact charts, that the two high coasts which confine it, form nearly, like the mountains of the earth, correspondent angles, which also proves that the Terra del Fuega, must be regarded as part of the continent of America; it is the same with Forbisher's Strait and the island of Friesland, which appear to have been divided from the continent of Greenland.

The Maldivian islands are only separated by small tracts of the sea, on each side of which banks and rocks are found composed of the same materials; and these islands, which, taken together, are near 200 miles long, formed anciently only one land; they are now divided into 13 provinces, called Clusters. Each cluster contains a great number of small islands, most of which are sometimes overflowed and sometimes dry; but what is remarkable, these thirteen clusters are each surrounded with a chain of rocks of the same stone, and there are only three or four dangerous inlets by which they can be entered. They are all placed one after the other, and it evidently appears that these islands were formerly a long mountain capped with rocks23.

Many authors, as Verstegan, Twine, Somner, and especially Campbell, in his Description of England, in the chapter of Kent, gives very strong reasons, to prove that England was formerly joined to France, and has been separated from it by an effort of the sea, which carried away the neck of land that joined them, opened the channel, and left naked a great quantity of low and marshy ground along the southern coasts of England. Dr. Wallis, as a corroboration of this supposition, shews the conformity of the ancient Gallic and British tongues, and adds many observations, which we shall relate in the following articles.

If we consider the form of lands, the position of mountains, and the windings of rivers, we shall perceive that generally opposite hills are not only composed of the same matters on the same level, but are nearly of an equal height. This equality I have observed in my travels, and have mostly found them the same on the two sides, especially in vallies that were not more than a quarter or a third of a league broad, for in vallies which are very broad, it is difficult to judge of the height and equality of hills, because, by looking over a level plain of any great extent, it appears to rise, and hills at a distance appear to lower; but this is not the place to give a mathematical reason for this difference. It is also very difficult to judge by the naked sight of the middle of a great valley, at least if there is no river in it; whereas in confined vallies our sight is less equivocal and our judgment more certain. That part of Burgundy comprehended between Auxerre, Dijon, Autun, and Bar-sur-seine, a considerable extent of which is called la Bailliage de la Montagne, is one of the highest parts of France; from one side of most of these mountains, which are only of the second class, the water flows towards the Ocean, and on the other side towards the Mediterranean. This high country is divided with many small vallies, very confined, and almost all watered with rivulets. I have a thousand times observed the correspondence of the angles of these hills and their equality of height, and I am certain that I have every where found the saliant angles opposite to the returning angles, and the heights nearly equal on both sides. The farther we advance into the higher country, where the points of division are, the higher are the mountains; but this height is always the same on both sides of the vallies, and the hills are raised or lowered alike. I have frequently made the like observations in many other parts of France. It is this equality in the height of the hills which forms the plains in the mountains, and these plains form lands higher than others. But high mountains do not appear so equal in height, most of them terminate in points and irregular peaks; and I have seen, in crossing the Alps, and the Apennine mountains, that the angles are, in fact, correspondent; but it is almost impossible to judge by the eye of the equality or inequality in the height of opposite mountains, because their summits are lost in mists and clouds.

The different strata of which the earth is composed are not disposed according to their specific weight, for we often find strata of heavy matters placed on those of lighter. To be assured of this, we have only to examine the earth on which rocks are placed, and we shall find that it is generally clay or sand, which is specifically lighter. In hills, and other small elevations, we easily discover this to be the case; but it is not so with large mountains, for not only their summits are rocks, but those rocks are placed on others; there mountains are placed upon mountains, and rocks upon rocks, to such a considerable height, and through so great an extent of country, that we can scarcely be certain whether there is earth at bottom, or of what nature it is. I have seen cavities made in rocks to some hundred feet deep, without being able to form an idea where they ended, for these rocks were supported by others; nevertheless, may we not compare great with small? and since the rocks of little mountains, whose bases are to be seen, rest on the earth less heavy and solid than stone, may we not suppose that earth is also the base of high mountains? All that I have here to prove by these arguments is, that, by the motion of the waters, it may naturally happen that the more ponderous matters accumulated on the lighter; and that, if this in fact is found to be so in most hills, it is probable that it happened as explained by my theory; but should it be objected that I am not grounded in supposing, that before the formation of mountains the heaviest matters were below the lighter; I answer, that I assert nothing general in this respect, because this effect may have been produced in many manners, whether the heaviest matters were uppermost or undermost, or placed indiscriminately. To conceive how the sea at first formed a mountain of clay, and afterwards capt it with rocks, it is sufficient to consider the sediments may successively come from different parts, and that they might be of different materials. In some parts, the sea may at first have deposited sediments of clay, and the waters afterwards brought sediment of strong matter, either because they had transported all the clay from the bottom and sides, and then the waves attacked the rocks, possibly because the first sediment came from one part, and the second from another. This perfectly agrees with observation, by which we perceive that beds of earth, stone, gravel, sand, &c. followed no rule in their arrangement, but are placed indifferently one on the other as it were by chance.

But this chance must have some rules, which can be known only by estimating the value of probabilities, and the truth of conjectures. According to our hypothesis, on the formation of the globe, we have seen that the interior part of the globe must have been a vitrified matter, similar to vitrified sand, which is only the fragments of glass, and of which the clays are perhaps the scoria; by this supposition, the centre of the earth, and almost as far as the external circumference, must be glass, or a vitrified matter; and above this we shall find sand, clay, and other scoria. Thus the earth, in its first state, was a nucleus of glass, or vitrified matter; either massive like glass, or divided like sand, because that depends on the degree of heat it has undergone. Above this matter was sand, and lastly clay. The soil of the waters and air produced the external crust, which is thicker or thinner, according to the situation of the ground; more or less coloured, according to the different mixtures of mud, sand, clay, and the decayed parts of animals and vegetables; and more or less fertile, according to the abundance or want of these parts. To shew that this supposition on the formation of sand and clay is not chimerical, I shall add some particular remarks.

I conceive, that the earth, in its first state, was a globe, or rather a spheroid of compact glass, covered with a light crust of pumice stone and other scoria of the matter in fusion. The motion and agitation of the waters and air soon reduced this crust into powder or sand, which, by uniting afterwards, produced flints, and owe their hardness, colour, or transparency and variety, to the different degrees of purity of the sand which entered into their composition.

These sands, whose constituting parts unite by fire, assimilate, and become very dense, compact, and the more transparent as the sand is more pure; on the contrary, being exposed a long time to the air, they disunite and exfoliate, descend in the form of earth, and it is probable the different clays are thus produced. This dust, sometimes of a brightish yellow, and sometimes like silver, is nothing else but a very pure sand somewhat perished, and almost reduced to an elementary state. By time, particles will be so far attenuated and divided, that they will no longer have power to reflect the light, and acquire all the properties of clay.

This theory is conformable to what every day is seen; let us immediately wash sand upon its being dug, and the water will be loaded with a black ductile and fat earth, which is genuine clay. In streets paved with freestone, the dirt is always black and greasy, and when dried appears to be an earth of the same nature as clay. Let us wash the earth taken from a spot where there are neither freestone nor flints, and there will always precipitate a great quantity of vitrifiable sand.

But what perfectly proves that sand, and even flint and glass, exist in clay, is, that the action of fire, by uniting the parts, restores it to its original form. Clay, if heated to the degree of calcination, will cover itself with a very hard enamel; if it is not vitrified internally, it nevertheless will have acquired a very great hardness, so as to resist the file; it will emit fire under the hammer, and it has all the properties of flint; a greater degree of heat causes it to flow, and converts it into real glass.

Clay and sand are therefore matters perfectly analogous, and of the same class; if clay, by condensing, may become flint and glass, why may not sand, by dissolution, become clay? Glass appears to be true elementary earth, and all mixed substances disguised glass. Metals, minerals, salts, &c. are only vitrifiable earth; common stone and other matters analogous to it, and testaceous and crustaceous shells, &c. are the only substances which cannot be vitrified, and which seem to form a separate class. Fire, by uniting the divided parts of the first, forms an homogeneous matter, hard and transparent, without any diminution of weight, and to which it is not possible to cause any alteration; those, on the contrary, in which a greater quantity of active and volatile principles enter, and which calcine, lose more than one-third of their weight in the fire, and retake the form of simple earth, without any other alteration than a disunion of their different parts: these bodies excepted, which are no great number, and whose combinations produce no great varieties in nature, every other substance, and particularly clay, may be converted into glass, and are consequently only decomposed glass. If the fire suddenly causes the form of these substances to change, by vitrifying them, glass itself, whether pure, or in the form of sand or flint, naturally, but by a slow and insensible progress, changes into clay.

Where flint is the predominant stone, the country is generally strewed with parts of it, and if the place is uncultivated, and these stones have been long exposed to the air, without having been stirred, their upper superficies is always white, whereas the opposite side, which touches the earth, is very brown, and preserves its natural colour. If these flints are broken, we shall perceive that the whiteness is not only external, but penetrates internally, and there forms a kind of band, not very deep in some, but which in others occupies almost the whole flint. This white part is somewhat grainy, entirely opaque, as soft as freestone, and adheres to the tongue like the boles; whereas the other part is smooth, has neither thread nor grain, and preserves its natural colour, transparency, and hardness. If this flint is put into a furnace, its white part becomes of a brick colour, and its brown part of a very fine white. Let us not say with one of our most celebrated naturalists, that these stones are imperfect flints of different ages, which have not acquired their perfection; for why should they be all imperfect? Why should they be imperfect only on the side exposed to the weather? It, on the contrary, appears to me more reasonable that they are flints changed from their original state, gradually decomposed, and assuming the form and property of clay or bole. If this is thought to be only conjecture, let the hardest and blackest flint be exposed to the weather, in less than a year its surface will change colour; and if we have patience to pursue this experiment, we shall see it by degrees lose its hardness, transparency, and other specific characters, and approach every day nearer and nearer the nature of clay.

What happens to flint happens to sand; each grain of sand may possibly be considered as a small flint, and each flint as a mass of extremely fine grains of sand. The first example of the decomposition of sand is found in the brilliant opaque powder called Mica, in which clay and slate are always diffused. The entirely transparent flints, the Quartz, produce, by decomposition, fat and soft talks, such as those of Venice and Russia, which are as ductile and vitrifiable as clay: and it appears to me, that talk is a mediate between glass, or transparent flint, and clay; whereas coarse and impure flint, by decomposing, passes to clay without any intermedium.