"It is certain, by the number of fossil-shells in the quarries and mountains, that this country, as well as many others, must have formerly been covered with the sea. But how has the American or Indian sea reached thither? To explain this, and many other wonderful phenomena, it may be supposed, with much probability, that the sea originally covered the whole terrestrial globe: but this supposition will not hold good, because how were terrestrial plants to exist? It evidently, therefore, must have been great inundations which have conveyed the plants of one country into the others.
"M. de Jussieu thinks, that as the bed of the sea is continually rising, in consequence of the mud and sand which the rivers incessantly convey there, the sea, at first confined between natural dykes, surmounted them, and was dispersed over the land, and that the dykes were themselves undermined by the waters and overthrown therein. In the earliest time of the formation of the earth, when no one thing had taken a regular form, prodigious and sudden revolutions might then have been made, of which we no longer have examples, because the whole is now in such a permanent state, that the changes must be inconsiderable and by degrees.
"By some of these great revolutions the East and West Indian seas may have been driven to Europe, and carried with them foreign plants floating on its waters, which they tore up in their road, and deposited gently in places where the water was but shallow and would soon evaporate."
ARTICLE IX.
ON THE INEQUALITIES OF THE SURFACE OF THE EARTH
The inequalities which are on the surface of the earth, and which might be regarded as an imperfection to its figure, are necessary to preserve vegetation and life on the terrestrial globe. To be assured of this, it is only requisite to conceive what the earth would be if it was even and regular. Instead of agreeable hills, from whence pure streams of waters flow, to support the verdure of the earth; instead of those rich and flourishing meadows, where plants and animals find agreeable subsistence; a dismal sea would cover the whole globe, and the earth, deprived of all its valuable qualities, would only remain an obscure and forsaken planet, at best only destined for the abode of fishes.
But independent of moral considerations, which seldom form a proof in philosophy, there is a physical necessity why the earth must be irregular on its surface; for supposing it was perfectly regular in its origin, the motion of the waters, the subterraneous fires, the wind, and other external causes, would, in course of time, have necessarily produced irregularities similar to those now seen.
The greatest inequalities next to the elevations of mountains, are the depths of the ocean; this depth is very different even at great distances from land; it is said there are parts above a league deep, but those are few, and the most general depths are from 60 to 150 fathoms. The gulphs bordering on the coasts are much less deep, and the straits are generally the most shallow.
To sound the depths of the sea, a piece of lead of 30 or 40lb. is made use of, fastened to a small cord; this is a good method for common depths, but is not to be depended upon when the depth is considerable; because the cord being specifically lighter than the water, after it has descended to a certain degree, the weight of the lead and that of the cord is no more than a like volume of water; then the lead descends no longer, but moves in an oblique line, and floats at the same depth: to sound great depths, therefore, an iron chain is requisite, or some substance heavier than water. It is very probable that for want of considering this circumstance, navigators tell us that the sea in many places has no bottom.
In general, the profundities in open seas increase or diminish in a pretty uniform manner, and commonly the farther from shore the greater the depth; yet this is not without exception, there are places in the midst of the sea where shoals are found, as at Abrolhos in the Atlantic; and others where there are banks of a very considerable extent, as are daily experienced by the navigators to the East Indies.
So likewise along shore the depths are very unequal, nevertheless we may lay it down as a certain rule, that the depth there is always proportionate to the height of that shore. It is the same in great rivers, where the high shores always announce a great depth.
It is more easy to measure the heights of mountains, whether by means of practical geometry, or by the barometer. This instrument gives the height of a mountain very exactly, especially in a country where its variation is not considerable, as at Peru, and under the other parts of the equator. By one or other of these methods, the height of most eminences has been measured; for example, it has been found that the highest mountains of Switzerland are about 1600 fathoms higher than Canigau, which is one of the most elevated of the Pyrennees; those mountains appear to be the highest in Europe, since a great quantity of rivers flow from them, which carry their water into very remote and different seas, as the Po, which flows into the Adriatic; the Rhine, which loses itself in the sands in Holland; the Rhone, which falls into the Mediterranean; and the Danube, which goes to the Black Sea. These four rivers, whose mouths are so remote from each other, all derive a part of their waters from Mount Saint Godard and the neighbouring mountain, which proves that this place is the highest in all Europe. The highest mountains in Asia are Mount Taurus, Mount Imaus, Caucasus, and the mountains of Japan, all which are loftier than those of Europe; the mountains in Africa, as the Great Atlas, and the mountains of the Moon, are at least as high as those in Asia, and the highest of all are in South America, particularly those of Peru, which are more than 3000 fathoms above the level of the sea. In general the mountains between the tropics are loftier than those of the temperate zones, and these more than the frigid zones, so that the nearer we approach the equator, the greater are the inequalities of the earth. These inequalities, although very considerable with respect to us, are scarcely any thing when considered with respect to the whole globe. Three thousand fathom difference to 3000 leagues diameter, is but one fathom to a league, or one foot to 2200 feet, which on a globe of 2-1/2 feet diameter, does not make the 16th part of a French line. Thus the earth, which appears to us crossed and intersected by the enormous height of mountains, and by a frightful depth of sea, is nevertheless, relative to its size, but slightly furrowed with irregularities, so very trifling, that they can cause no difference to the general figure of the globe. In continents the mountains are continued and form chains. In islands, they are more interrupted, and generally raised above the sea, in the forms of cones or pyramids, and are called peaks. The peak of Teneriffe, in the island of Fer, is one of the highest mountains on the earth; it is near a league and a half perpendicular above the level of the sea; the peak of St. George, in one of the Azores, and the peak of Adam, in the island of Ceylon, are also very lofty. These peaks are composed of rocks, heaped one upon the other, and they vomit from their summits fire, cinders, bitumen, minerals, and stones. There are islands which are only tops of mountains, as of St. Helena, Ascension, most of the Azores, and Canaries. We must remark, that in most of the islands, promontories, and other projecting lands in the sea, the middle is always the highest; and they are generally separated by chains of mountains, which divide them in their greatest length, as (Gransbain) the Grampian mountains in Scotland, which extend from east to west, and divide Great Britain into two parts. It is the same with the islands of Sumatra, Lucca, Borneo, Celebes, Cuba, St. Domingo, and the peninsula of Malaya, &c. and also Italy, which is traversed through its whole length by the Apennine mountains.
Mountains, as we find, differ greatly in height; the hills are lowest, after them come the mountains of a moderate height, which are followed by a third rank still higher, which, like the preceding, are generally loaded with trees and plants, but which furnish no springs except at their bottoms. In the highest mountains we find only sand, stones, flints, and rocks, whose summits often rise above the clouds. Exactly at the foot of these rocks there are small spaces, plains, hollows, and kinds of vallies, where the rain, snow, and ice remain, and form ponds, morasses, and springs, from whence rivers derive their origin.
The form of mountains is also very different: some form chains whose height is nearly equal in a long extent of soil, others are divided by deep vallies; some are regular, and others as irregular as possible; and sometimes in the middle of a valley or plain, we find a little mountain. There are also two sorts of plains, the one in the low lands, the other in mountains. The first are generally divided by some large river: the others, though of a very considerable extent, are dry, and at farthest have only a small rivulet. These plains on mountains are often very high, and difficult of access; they form countries above other countries, as in Auvergne, Savoy, and many other high places: the soil is firm, and produces much grass, and odoriferous plants, which render these plains the best pasture in the world.
The summits of high mountains are composed of rocks of different heights, which resemble from a distance the waves of the sea. It is not on this observation alone we can rely that the mountains have been formed by the waves, I only relate it because it accords with the rest: but that which evidently proves that the sea once covered and formed mountains, are the shells and other marine productions found throughout in such great quantities, that it is not possible for them to have been transported by the sea into such remote continents, and deposited to such considerable depths; to this may be added, the horizontal and parallel strata every where met with, and which can only have been formed by the waters. The composition even of the hardest matters, as stone and marble, prove they had been reduced into fine powder before their formation, and precipitated to the bottom of the water in form of a sediment: it is also proved by the exactness with which fossil-shells are moulded in those matters in which they are found; the inside of these shells are absolutely filled with the same matters as that in which they are enclosed; the corresponding angles of mountains and hills, which no other cause than the currents of the sea could have been able to form; the equality in the height of opposite hills, and beds of different matters, formed at the same levels, and, in short, the direction of mountains, whose chains extend in length in the same direction as the waves of the sea extend, incontestibly demonstrate the fact.
With respect to the depths on the surface of the earth, the greatest, without contradiction, are the depths of the sea; but as they do not present themselves to our sight, and as we can only judge of them by the plumb line, we shall only speak of those which appear on dry land, such as the deep vallies between mountains, the precipices between rocks, the abysses perceived from the tops of mountains, as the abyss of Mount Ararat, the precipices of the Alps, the vallies of the Pyrennees, &c. These depths are a natural consequence of the elevation of mountains; they receive the waters and the earth which flow from the mountains, and the soil is generally very fertile, and are fully inhabited.
The precipices which are between rocks are frequently formed by the sinking of one side, the base of which sometimes gives way more on one side than the other, by the action of the air and frost, which splits and divides them, or by the impetuous violence of torrents. But these abysses, or vast and enormous precipices, found at the summits of mountains, and to the bottom of which it is not possible sometimes to descend, although they are above a mile, or a mile and a half round, have been formed by the fire. These were formerly the funnels of volcanos, and all the matter which is there deficient has been ejected by the action and explosion of these fires, which are since extinguished through a defect of combustible matter. The abyss of Mount Ararat, of which M. Tournefort gives a description in his voyage to the Levant, is surrounded with black and burnt rocks, as one day the abysses of Etna, Vesuvius, and other volcanos, will be, when they have consumed all the combustible matters they include.
In Plots' Natural History of Staffordshire, in England, a kind of gulph is spoken of which has been sounded to the depth of 2600 perpendicular feet without meeting with any water, or the bottom being found, as the rope was not of sufficient length to reach it.
Greatest cavities and deepest mines are generally in mountains, and they never descend to a level with the plains, therefore by these cavities we are only acquainted with the inside of a mountain, and not with the internal part of the globe itself.
Besides, these depths are not very considerable. Ray asserts that the deepest mines are not above half a mile deep. The mine of Cotteberg, which in the time of Agricola passed for the deepest of all known mines, was only 2500 feet perpendicular. It is evident there are holes in certain places, as that in Staffordshire, or Pool's Hole, in Derbyshire, the depth of which is perhaps greater; but all this is nothing in comparison with the thickness of the globe.
If the kings of Egypt, instead of having erected pyramids, and raised such sumptuous monuments of their riches and vanity, had been at the same expence to sound the earth, and make a deep excavation to the depth of a league, they, perhaps, might have found substances which would have amply recompensed the trouble, labour, and expence, or at least we should have received information on the matters of which the internal part of the globe is composed, which might have been very useful, and which we at present have not.
But let us return to the mountains; the highest are in the southern countries, and the nearer we approach the equator, the more inequalities we find on the surface of the globe. This is easy to prove, by a short enumeration of the mountains and islands.
In America, the chain of the Cordeliers, the highest mountains of the earth, is exactly under the equator, and extends on the two sides far beyond the tropic circles.
In Africa, the highest mountains of the Moon, and Monomotapa, the great and the little Atlas, are under the equator, or not far from it.
In Asia, Mount Caucasus, the chain of which extends under different names as far as the mountains of China, is nearer the equator than the poles.
In Europe, the Pyrennees, the Alps, and mountains of Greece, which are only the same chain, are still less distant from the equator than the poles.
Now these mountains which we have enumerated, are all higher, more considerable and extended in length and breadth than the mountains of the northern countries.
With respect to their direction, the Alps form a chain which crosses the whole continent from Spain to China. These mountains begin at the sea coast of Galicia, reach to the Pyrennees, cross France, by Vivares, and Auvergne, pass through Italy and extend into Germany, beyond Dalmatia, as far as Macedonia; from thence they join with the mountains of Armenia, Caucasus, Taurus, Imaus, and extend as far as the Tartarian sea. So likewise Mount Atlas traverses the whole continent of Africa, from west to east, from the kingdom of Fez to the Straits of the Red Sea; and the mountains of the Moon have the same direction.
But in America, the direction is quite contrary, and the chains of the Cordeliers and other mountains extend from south to north more than from east to west.
What we have now said on the great eminences of the earth, may also be observed on the greatest depths of the sea. The vast and highest seas are nearer the equator than the poles; and there results from this observation, that the greatest inequalities of the globe are in the southern climate. These irregularities on the surface of the earth, are the causes of an infinity of extraordinary effects: for example, between the Indus and the Ganges, there is a large peninsula, which is divided through its middle, by a chain of high mountains called the Gate, and which extends from north to south, from the extremities of Mount Caucasus to Cape Comorin; on one is the coast of Malabar, and the other Coromandel; on the side of Malabar, between this chain of mountains and the sea, the summer season lasts from September to April, during which the sky is serene and dry; on the other side the Coromandel the above period is their winter, and it rains every day plentifully and from the month of April to the month of September is their summer, whereas it is winter in Malabar; insomuch, that in many places, which are scarcely 20 miles distant, we may, by crossing the mountains, change seasons. It is said that the same thing takes place at Razalgat in Arabia, and at Jamaica, which is divided through its middle by a chain of mountains, whose direction is from east to west, and that the plantations to the south of these mountains feel the summer heat, at the time those to the north endure the rigor of winter.
Peru, which is situated under the line, and extends about a thousand leagues to the south, is divided into three long and narrow parts; these the natives call Lanos, Sierras, and Andes. The Lanos, which comprehends the plains, extends along the coast of the South Sea: the Sierras are hills with some vallies, and the Andes are the famous Cordeliers, the highest mountains that are known. The Lanos is about ten leagues in breadth; in many places the Sierras are twenty leagues broad, and the Andes in some places more and in some less. The breadth is from east to west, and the length from north to south. This part of the world is remarkable for the following particulars: first, in the Lanos the wind almost constantly blows from the south-west, which is contrary to what happens in the torrid zone: secondly, it never rains nor thunders in the Lanos, although there is plenty of dew: thirdly, it almost continually rains in the Andes: fourthly, in the Sierras, between the Lanos and the Andes, it rains from September to April.
It was for a long time supposed, that the chains of the high mountains run from west to east, till the contrary was found in America. But no person before M. Bourguet discovered the surprising regularity of the structure of those great masses: he found (after having crossed the Alps thirty times in fourteen different parts of it, twice over the Apennine mountains, and made divers tours in the environs of these mountains, and of Mount Jura) that all mountains are formed nearly after the manner of works of a fortification. When the body of the mountain runs from east to west, it forms prominences, which face the north and south; this wonderful regularity is so striking in vallies, that we seem to walk in a very regular covered way; if, for example, we travel in a valley from north to south, we perceive that the mountain on the right forms projections which front the east, and those of the mountain on the left front the west, so that the saliant angles of one side reciprocally answer the returning angles of the other, which are always alternatively opposed to them. The angles which mountains form in great vallies are less acute, because the direction is less steep, and they are farther distant from each other. In plains they are not so perceptible, except by the banks of rivers, which are generally in the middle of them, and whose natural windings answer the most advanced angles or striking projections of the mountains. It is astonishing so visible a thing was so long unobserved, for when in a valley the inclination of one of the mountains which border it is less steep than that of the other, the river takes its course much nearer the steepest mountain, and does not flow through its middle.
To these observations we may join other particular ones, which confirm them; for example, the mountains of Switzerland are much more steep, and their direction much greater on the south side than on the north, and on the west side than on the east. This may be perceived in the mountains of Gemmi, Brisa, and almost every other mountain in this country. The highest are those which separate Valesia and the Grisons from Savoy, Piedmont, and Tirol. These countries are only a continuation of these mountains, the chain of which extends to the Mediterranean, and continues even pretty far under the sea. The Pyrennees are also only a continuation of that vast mountain which begins in Upper Valesia, and whose branches extend very far to the west and south, preserving throughout the same great height; whereas on the side of the north and of the east these mountains grow lower by degrees, till they become plains; as we see by the large tract which the Rhine and Danube water before they reach their mouths, whereas the Rhone descends with rapidity towards the south into the Mediterranean. The same observation is found to hold good in the mountains of England and Norway; but the part of the world where this is most evidently seen is at Peru and Chili; the Cordeliers are cut very sharply on the western side, the length of the Pacific Ocean, whereas on the eastern side they lower by degrees into large plains, watered by the greatest rivers of the world.32
M. Bourguet, to whom we owe this great discovery of the correspondence of the angles of mountains, terms it "The Key of the Theory of the Earth;" nevertheless, it appears to me, that if he had conceived all the importance of it, he would more successfully have made use of it, by connecting it with suitable facts, and would have given a more probable theory of the earth; whereas in his treatise he presents only the skeleton of an hypothetical system, most of the conclusions of which are false or precarious. The theory we have given turns on four principal facts, which cannot be doubted, after the proofs have been examined on which they are founded. The first is, that the earth is every where, and to considerable depths, composed of parallel strata, and matters which have formerly been in a state of softness: the second, that the sea has for ages covered the earth which we now inhabit; the third, that the tides and other motions of the waters produce inequalities at the bottom of the sea; and the fourth, that the mountains have taken their form and the correspondent direction from the currents of the sea.
After having read the proofs which the following articles contain, it may be determined, whether I was wrong to assert, that these circumstances solidly established also ascertains the truth of the theory of the earth. What I have said on the formation of mountains has no need of a more ample explanation; but as it might be objected that I do not assign a reason for the formation of the peaks or points of mountains, no more than for some other particular circumstances, shall add the observations and reflections which I have made on this subject.
I have endeavoured to form a clear and general idea of the manner in which the different matters that compose the earth are arranged, and it appears to me they may be reduced into two general classes; the first includes all the matters we find placed in strata, or beds horizontally or regularly inclined; and the second comprehends all matters formed in masses, or in veins, either perpendicular or irregularly inclined. In the first class are included sands, clays, granite, flints, free-stone, coals, slates, marls, chalks, calcinable stones, marbles, &c. In the second I rank metals, minerals, crystals, precious stones and small flints: these two classes generally comprehend all the known materials of the earth. The first owe their origin to the sediments carried away and deposited by the sea, and should be distinguished into those which being assayed in the fire, calcine and are reduced into lime, and those which fuse and are convertible into glass. The materials of the second class are all vitrifiable excepting those which the fire entirely consumes by inflammation.
In the first class we distinguish two kinds of sands; the one, which is more abundant than any other matter of the globe, is vitrifiable, or rather is only fragments of actual glass; the other, whose quantity is much less, is calcinable, and must be looked upon as the powder of stone, and which differs only from gravel by the size of the grains. The vitrifiable sand is, in general, deposited in beds, which are often interrupted by masses of free-stone, granite, and flint; and sometimes these matters are also in banks of great extent.
By examining these vitrifiable matters, we find only a few sea shells there, and those not placed in beds, but dispersed about as if thrown there by chance. For example, I have never seen them in free-stone; that stone which is very plenty in certain places, is only composed of sandy parts, which are re-united, and are only met with in sandy soils; and the quarries of it are generally in peaked hills and in divided eminences. We may work these quarries in all directions, and if they are in large beds, they are much farther from each other than in quarries of calcinable stone or marble. Blocks of free-stone may be cut of all dimensions and in all directions, although it is difficult to work, it nevertheless has but a degree of hardness sufficient to resist powerful strokes without splitting; for friction easily reduces it into sand, excepting certain black pieces found therein, and which are so very hard, that the best files cannot touch them. Rock is vitrifiable as free-stone, and of the same nature, only it is harder and the parts more connected. This also contains many hard pieces, as may easily be remarked on the summits of high mountains, which cut and tear the shoes of travellers. This rocky stone, which is found at the top of high mountains, and which I look upon as a kind of granite, contains a great quantity of talky leaves, and is so hard as not to be worked but by an infinite deal of labour.
I have narrowly examined these sharp pieces which are found in free-stone and rock, and have discovered it to be a metallic matter, melted and calcined by a very violent fire, and which perfectly resembles certain substances thrown out by the volcanos, of which I saw a great quantity when I was in Italy, where the people called them Schiarri. They are very heavy black masses, on which neither water nor the file can make any impression, and the matter of which is different from that of the lava; for this is a kind of glass, whereas the other appears to be more metallic than vitreous. The sharp pieces in free-stone, and rock, resemble greatly the first matter, which seems still to prove that all these matters have been formerly liquified by fire.
We sometimes see on the upper parts of mountains, a prodigious quantity of blocks of this mixed rock; their position is so irregular that they appear to have been thrown there by chance, and it might be thought they had fallen from some neighbouring height, if the places where they are found were not raised above the other parts. But their vitrifiable nature, and their angular and square figures, like those of free-stone, discover them to be of one common origin. Thus in the great beds of vitrifiable sand, blocks of free-stone and rock are formed, whose figures and situations do not exactly follow the horizontal position of these strata. The rain, by degrees, carried away from the summits of the hills and mountains the sand which at first covered them, and then began to furrow and cut those hills into the spaces which are found between the nucleus in free-stone, as the hills of Fontainbleau are intersected. Each hilly point answers to a nucleus in a quarry of free-stone, and each interval has been excavated and loosened by the rain, which has caused the sand, they at first contained, to flow into the vallies; so likewise the highest mountains, whose summits are composed of rocks, and terminated by these angular blocks of granite, have formerly been covered with vitrifiable sand, and the rain having carried away the sand which covered them, they remained on the tops of the mountains in the position they were formed. These blocks generally present points; they increase in size in proportion as they descend; one block often rests upon another, the second upon a third, and so on, leaving irregular intervals between them: and as in time the rain washed away all the sand which covered these different parts on the top of the high mountains, they would remain naked, forming larger or lesser points; and this is the origin of the peaks or horns of mountains.
For supposing, as it is easy to prove by the marine productions we find there, that the chain of the Alps was formerly covered by the sea, and that above this chain there was a great thickness of vitrifiable sand, which rendered the whole mountains a flat and level country. In this depth of sand, there would necessarily be formed granite, free-stone, flint, and all matters which take their origin and figure in sand, nearly in a similar manner to that of the crystallisation of salts. These blocks once formed would support their original positions, after the rains and torrents had carried away the sand which surrounded them, and being left bare formed all those peaks or pointed eminences we see in so many places. This is also the origin of those high and detached rocks found in China and other countries, as in Ireland, where they are called the Devil's stones, and whose formation as well as that of the peaks of mountains, had hitherto appeared so difficult to explain; nevertheless the explanation which I have given is so natural, that it directly presents itself to the mind of those who examine these objects, and I must here quote what Father Tatre says, "From Yanchu-in-yen, we came to Hoytcheou, and on the road met with something particular, rocks of an extraordinary height, of the shape of a large square tower, and situate in the midst of vast plains: I cannot account for it, unless by supposing they were formerly mountains, from which the rain having washed away the earth that surrounded them, thus left the rocks entirely bare. What strengthens this conjecture is, that we saw some which, towards the base, are still covered with earth to a considerable height."