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.[279:A]
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.