since the formation of the secondary strata, and have, perhaps,
given rise to, or at least have partaken of, some of those changes
which these strata themselves have experienced. There are actually
considerable portions of the primitive formations uncovered, although
placed in lower situations than many of the secondary formations;
and we cannot conceive how it should have so happened, unless the
primitive strata in those places had forced themselves into view,
after the secondary strata had been formed. In certain countries, we
find numerous large blocks of primitive substances scattered over
the surface of secondary formations, and separated by deep valleys,
or even by arms of the sea, from the peaks or ridges from which they
must have been derived. We must necessarily conclude, therefore,
either that these blocks have been ejected by eruptions, or that the
valleys (which must have stopped their course) did not exist at the
time of their being transported; or, lastly, that the motions of the
waters by which they were transported, exceeded in violence any thing
that we can imagine at the present day[6].
Here, therefore, we have a collection of facts, a series of epochs,
anterior to the present time, of which the successive steps may
be perfectly ascertained, although the duration of their intervals
cannot be defined with precision. They are so many fixed points,
which serve to regulate and direct our inquiries respecting this
ancient chronology.
_Examination of the Causes which act at present on the surface of the
Globe._
Let us now examine those changes which are taking place at the
present day upon the globe, investigating the causes which still act
in its surface, and endeavouring to determine the possible extent
of their effects. This portion of the history of the Earth is so
much the more important, that it has long been considered possible
to explain the more ancient revolutions on its surface by means of
these still existing causes; in the same manner as it is found easy
to explain past events in political history, by an acquaintance
with the passions and intrigues of the present day. But we shall
presently see, that unfortunately the case is different in physical
history:--the thread of operations is here broken; the march of
Nature is changed; and none of the agents which she now employs,
would have been sufficient for the production of her ancient works.
There still exist, however, four causes in full activity, which
contribute to alter the surface of our continents. These are, rains
and thaws, which waste down the steep mountains, and precipitate the
fragments to their bottoms; running waters, which carry off these
fragments, and deposit them in places where their current is abated;
the sea, which undermines the foundations of elevated coasts, forming
steep cliffs, and which throws up great banks of sand upon the low
coasts; and, lastly, volcanoes, which pierce through the solid strata
from below, elevate these strata, or spread over the surface vast
quantities of ejected matter[7].
_Of Slips, or Falling down of the Materials of Mountains._
In every place where the broken strata present their edges on abrupt
surfaces, there fall down to their base, every spring, and even after
every storm, fragments of their materials, which are rounded by
rolling upon each other. These collected heaps gradually assume an
inclination determined by the laws of cohesion, and thus form, at the
bottom of the cliff, taluses, of greater or less elevation, according
as the fragments which have fallen are more or less abundant.
These taluses constitute the sides of the valleys in all elevated,
mountainous regions, and are covered with a rich vegetation, whenever
the fragments from the upper parts begin to fall less abundantly;
but their want of solidity subjects themselves also to slips, when
they are undermined by rivulets. On these occasions, towns, and rich
and populous districts, are sometimes buried under the ruins of a
mountain; the courses of rivers are interrupted, and lakes are formed
in places which were before the abodes of fertility and cheerfulness.
Fortunately these great slips happen but seldom, and the principal
use of those hills of debris, is to furnish materials for the ravages
of torrents.
_Alluvial Formations[8]._
The rains which fall, the vapours which are condensed, and the
snows which are melted, upon the ridges and summits of mountains,
descend, by an infinite number of rills, along their slopes, carrying
with them some portions of the materials of which these slopes are
composed, and tracing slight furrows by their passage. These rills
soon unite in the deeper gutters with which the surface is marked,
run off by the deep valleys which intersect their bottom, and thus
form streams and rivers, which carry back to the sea the waters it
had formerly supplied to the atmosphere. On the melting of the snows,
or when a storm takes place, these mountain torrents become suddenly
swollen, and rush down the declivities with a velocity proportioned
to their steepness. They dash violently against the bases of those
taluses of fallen fragments which cover the sides of all the high
valleys, carrying off the already rounded fragments of which they are
composed, and which thus become smoothed, and still farther polished,
by attrition. But in proportion as they reach the more level valleys,
where their violence is diminished, or when they arrive at more
expanded basins, where their waters are permitted to spread, they
throw out upon their banks the largest of those stones which they had
rolled down. The smaller fragments are deposited still lower; and
nothing reaches the great canal of the river excepting the minutest
particles, or the most impalpable mud. It often happens, also, that
before these streams unite to form great rivers, they have to pass
through large and deep lakes, in which their mud is deposited, and
from which their waters come forth limpid.
The lower rivers, and all the streams which descend from the less
elevated mountains and hills, also produce effects, upon the
districts through which they flow, more or less analogous to those of
the torrents from the higher mountains. When these rivers are swollen
by great rains, they attack the base of the earthy or sandy hills
which they meet with in their course, and carry their fragments to be
deposited upon the lower grounds, and which are thus, in some degree,
raised by each succeeding inundation. Finally, when the rivers reach
great lakes or the sea, and when that rapidity, which carried off
and kept in suspension the particles of mud comes to cease entirely,
these particles are deposited at the sides of their mouths, where
they form low grounds, by which the shores are prolonged. And if
these shores are such, that the sea also throws up sand upon them,
and thus contributes to their increase; there are created, as it
were, provinces, and even entire kingdoms, which usually become the
most fertile, and speedily the richest, in the world, if their rulers
permit human industry to exert itself in peace.
_Formation of Downs._[9]
The effects which the sea produces, without the co-operation of
rivers, are much less beneficial. When the coast is low, and the
bottom sandy, the waves push the sand toward the shore, where, at
every reflux of the tide, it becomes partially dried; and the wind,
which almost always blows from the sea, drifts it upon the beach.
Thus are formed those hillocks of sand, named Downs, which, if the
industry of man does not fix them by suitable plants, move slowly,
but invariably, toward the interior of the country, and overwhelm
fields and dwellings, because the same wind that raises the sand of
the beach upon the down, throws that of its summit in the opposite
direction from the sea. When the nature of the sand, and that of the
water which is raised with it, are such as to form a durable cement,
the shells and bones, thrown upon the beach, become incrusted with
it. Pieces of wood, trunks of trees, and plants growing near the
sea, are enveloped in these aggregates; and thus are produced what
might be denominated _indurated downs_, such as we see upon the
coasts of New Holland, and of which a precise idea may be formed from
the description given of them by Peron[10].
_Formation of Cliffs or Steep Shores._
On the other hand, when the coast is high, the sea, which is thus
prevented from throwing up any thing, exercises a destructive
action upon it. Its waves, by sapping the foundation, cause the
superincumbent portion of the face of the cliff, thus deprived of
support, to be incessantly falling down in fragments. These fragments
are tumbled about by the billows, until the softer and more divided
parts disappear. The harder portions, from being rolled in contrary
directions, assume the form of boulders and pebbles; and these, at
length, accumulate in sufficient quantity to form a rampart, by which
the bottom of the cliff is protected against farther depredations.
* * * * *
Such is the action of water upon the solid land; and we see, that
it consists almost entirely in reducing it to lower levels, but
not indefinitely. The fragments of the great mountain ridges are
carried down into the valleys; their finer particles, together with
those of the lower hills and plains, are borne to the sea; alluvial
depositions extend the coasts at the expence of the high grounds.
These are limited effects, to which vegetation in general puts a
stop, and which, besides, presuppose the existence of mountains,
valleys, and plains, in short, all the inequalities of the globe; and
which, therefore, cannot have given rise to these inequalities. The
formation of downs is a phenomenon still more limited, both in regard
to height and horizontal extent; and has no relation whatever to that
of those enormous masses into the origin of which it is the object of
geology to inquire.[11]
_Depositions formed in Water._
Although we cannot obtain a precise knowledge of the action exerted
by water within its own bosom, it is yet possible to determine its
limits to a certain degree.
Lakes, pools, marshes, and sea-ports, into which rivulets discharge
their waters, more especially when these descend from near and steep
hills, deposit large quantities of mud, which would at length fill
them up entirely, if care were not taken to clean them out. The sea
also throws quantities of slime and sediment into harbours and
creeks; into all places, in short, where its waters are more tranquil
than ordinary. The currents also heap up at their meeting, or throw
out at their sides, the sand which they are continually raising from
the bottom of the sea, forming it into banks and shallows.
_Stalactites._
Certain waters, after dissolving calcareous substances by means of
the superabundant carbonic acid with which they are impregnated,
allow these substances to crystallize after the acid has evaporated;
and, in this manner, form stalactites, and other concretions. There
are strata, confusedly crystallized in fresh water, which are
sufficiently extensive to be compared with some of those which have
been deposited by the ancient sea. The famous Travertine quarries
of the neighbourhood of Rome, and the rocks of the same substance,
which are formed, and continually varied in figure, by the river
of Teverona, are generally known. These two modes of action may be
combined; the deposits accumulated by the sea may be solidified by
stalactite. Thus, when springs abounding in calcareous matter, or
containing some other substance in solution, happen to fall into
places where these deposits are formed, we then find aggregates in
which marine and fresh-water productions may be blended. Of this
description are the banks in the island of Guadeloupe, which, along
with human skeletons, present land and sea shells mingled together.
Of the same nature also is the quarry described by Saussure, in the
neighbourhood of Messina, in which the sandstone is seen forming by
the consolidation of the sand thrown up by the sea.
_Lithophytes._
In the torrid zone, where lithophytes of many species abound, and are
propagated with great rapidity, their strong trunks are interwoven
and accumulated so as to form rocks and reefs; and rising even to
the surface of the water, shut up the entrance of harbours, and lay
frightful snares for navigators. The sea, throwing up sand and mud
upon the tops of these shoals, sometimes raises their surface above
its own level, and forms islands, which are soon covered with a rich
vegetation.
_Incrustation._
It is also possible, that, in particular places, large quantities
of the animals inhabiting shells, leave their stony coverings when
they die, and that these, cemented together by slime of greater or
less consistence, or by other cementing substances, form extensive
deposits or shell banks. But we have no evidence that the sea can now
incrust those shells with a paste as compact as that of the marbles,
the sandstones, or even the coarse limestone (calcaire grossier) in
which we see the shells of our strata enveloped. Still less do we any
where find the sea depositing those more solid and more siliceous
strata which have preceded the formation of the shelly strata.
In short, all these causes united, would not change, in an
appreciable degree, the level of the sea; nor raise a single stratum
above its surface; and still less would they produce the smallest
hillock upon the surface of the earth.
It has been asserted that the sea has undergone a general diminution
of level; and proofs of this are said to have been discovered in some
parts of the shores of the Baltic.[12] But whatever may be the causes
of these appearances, we are certain that they are not general in
their operation; and that, in the greater number of harbours, where
any alteration of the level would be a matter of so much interest,
and where fixed and ancient works afford so many means of measuring
its variations, the mean level of the sea is constant. There
has, therefore, never been a universal lowering, nor a universal
encroachment, of the waters of the ocean. In some places, indeed,
such as Scotland, and various parts of the Mediterranean, evidence
has been thought to have been found, that the sea has risen, and that
it now covers shores which were formerly above its level[13].
_Volcanoes._
The action of volcanoes is still more limited, and more local, than
any of those which have yet been mentioned. Although we have no
precise idea of the means by which nature keeps up these violent
fires at such great depths, we can judge decidedly, by their effects,
of the changes which they may have produced at the surface of the
globe. After a volcano has announced itself, by some shocks of an
earthquake, it forms for itself an opening. Stones and ashes are
thrown to a great distance, and lava is vomited forth. The more fluid
part of the lava flows in long streams, while the less fluid portion
stops at the edges of the opening, raises its margins all round, and
forms a cone, terminated by a crater. Thus volcanoes accumulate upon
the surface matters which were previously buried in the bowels of
the earth, after modifying their nature, and raise themselves into
mountains. By these means, they have formerly covered some parts of
our continent, and have also suddenly produced islands in the middle
of the sea. But these mountains and islands have always been composed
of lava, and all their materials have undergone the action of fire:
they are disposed as matters should be, which have flowed from an
elevated point. Volcanoes, therefore, neither raise nor overturn the
strata through which their apertures pass; and if some causes acting
from those depths have contributed, in certain cases, to raise up
large mountains, they cannot have been volcanic agents of the same
nature as those which exist at the present day.
* * * * *
Thus, we repeat, it is in vain that we search, among the powers
which now act at the surface of the earth, for causes sufficient
to produce the revolutions and catastrophes, the traces of which
are exhibited by its crust: And if we have recourse to the constant
external forces with which we are as yet acquainted, we shall have no
greater success.
_Constant Astronomical Causes._
The pole of the earth moves in a circle around the pole of the
ecliptic, and its axis is more or less inclined to the plane of
the ecliptic; but these two motions, the causes of which are now
ascertained, are much too limited for the production of effects like
those whose magnitude we have just been stating. At any rate, their
excessive slowness would render them altogether inadequate to account
for catastrophes which, as we have shewn, must have been sudden.
The same reasoning applies to all other slow motions which have been
conceived as causes of the revolutions in question, chosen doubtless
in the hope that their existence could not be denied, because it
might always be easy to hold out that their very slowness rendered
them imperceptible. But whether they be true or not is of little
importance, for they explain nothing, as no cause acting slowly could
have produced sudden effects.
Admitting that there has been a gradual diminution of the waters;
that the sea has transported solid matters in all directions;
that the temperature of the globe is either diminishing or
increasing;--none of these causes could have overturned our strata;
enveloped in ice large animals, with their flesh and skin; laid dry
marine testacea, the shells of which are, at the present day, as
well preserved as if they had been drawn up alive from the sea; and,
lastly, destroyed numerous species, and even entire genera.
These considerations have struck most naturalists; and among those
who have endeavoured to explain the present state of the globe,
hardly any one has attributed it entirely to the agency of slow
causes, still less to causes operating under our eyes. The necessity
to which they are thus reduced, of seeking for causes different
from those which we see acting at the present day, is the very
circumstance that has forced them to make so many extraordinary
suppositions, and to lose themselves in so many erroneous and
contradictory speculations, that the very name of their science, as
I have elsewhere remarked, has long been a subject of ridicule to
prejudiced persons, who have only looked to the systems which it
has been the means of hatching, and have forgotten the extensive
and important series of authentic facts which it has brought to
light[14].
_Older Systems of Geologists._
During a long time, two events or epochs only, the Creation and
the Deluge, were admitted as comprehending the changes which have
been operated upon the globe; and all the efforts of geologists
were directed to account for the present existing state of things,
by imagining a certain original state, afterwards modified by the
deluge, of which also, as to its causes, its operations, and its
effects, each entertained his own theory.
Thus, according to one[15], the earth was at first invested with
an uniform light crust, which covered the abyss of the sea; and
which being broken up for the production of the deluge, formed the
mountains by its fragments. According to another[16], the deluge was
occasioned by a momentary suspension of cohesion among the particles
of mineral bodies; the whole mass of the globe was dissolved, and
the paste thus formed became penetrated with shells. According to a
third[17], God raised up the mountains for the purpose of allowing
the waters, which had produced the deluge, to run off; and selected
those places in which there was the greatest quantity of rocks,
without which the mountains could not have supported themselves. A
fourth[18] created the earth from the atmosphere of one comet, and
deluged it by the tail of another: The heat which it retained from
its origin, was what, in his opinion, excited the whole of the living
beings upon it to sin; for which they were all drowned, excepting the
fishes, whose passions were apparently less vehement.
It is evident, that, even while confined within the limits prescribed
by the Book of Genesis, naturalists might still have a pretty wide
range: they soon found themselves, however, in too narrow bounds; and
when they had succeeded in converting the six days of creation into
so many indefinite periods, the lapse of ages no longer forming an
obstacle to their views, their systems took a flight proportioned to
the periods which they could then dispose of at pleasure.
Even the great Leibnitz amused himself, like Descartes, by conceiving
the earth to be an extinguished sun[19], a vitrified globe, upon
which the vapours falling down again, after it had cooled, formed
seas, which afterwards deposited the limestone formations.
By Demaillet the whole globe was conceived to have been covered
with water for many thousands of years. He supposed this water
had gradually retired; that all the land animals were originally
inhabitants of the sea; that man himself commenced his career as a
fish; and he asserts, that it is not uncommon, even now, to meet with
fishes in the ocean, which are still only half converted into men,
but whose descendants will in time become perfect human beings[20].
The system of Buffon is merely an extension of that of Leibnitz, with
the addition only of a comet, which, by a violent blow, struck off
from the sun the liquefied mass of the earth, together with those of
all the other planets at the same instant. From this supposition,
he was enabled to assume positive dates, as, from the present
temperature of the earth, it could be calculated how long it had
taken to cool down so far; and, as all the other planets had come
from the sun at the same time, it could also be calculated how many
ages are still required for cooling the greater ones, and to what
degree the smaller are already frozen[21].
_More recent Systems._
In our own times, men of still bolder imaginations have exercised
their minds upon this great subject. Some writers have revived
and greatly extended the ideas of Demaillet. They suppose that
every thing was originally fluid; that this fluid gave existence
to animals, which were at first of the most simple kind, such as
the monads and other infusory and microscopic species; that, in
process of time, and by assuming different habits, the races of
animals became complicated, and assumed that diversity of nature
and character in which they now appear. By means of those various
races of animals, part of the waters of the sea have gradually been
converted into calcareous earth; while the vegetables, concerning the
origin and metamorphoses of which these writers are totally silent,
have, on their part, converted a portion of the same water into clay:
These two earths, on being stripped of the characters which life had
impressed upon them, are resolved, by a final analysis, into silex;
and hence the reason that the oldest mountains are more siliceous
than the rest. All the solid parts of the earth, therefore, owe
their existence to life, and, without life, the globe would still be
entirely liquid[22].
Other writers have preferred the ideas of Kepler, and, like that
great astronomer, have considered the globe itself as possessed of
vital faculties. According to them a vital fluid circulates in it;
a process of assimilation goes on in it, as well as in animated
bodies; every particle of it is alive; it possesses instinct and
volition, even to the most elementary molecules, which attract and
repel each other according to sympathies and antipathies. Each kind
of mineral has the power of converting immense masses into its own
nature, as we convert our food into flesh and blood. The mountains
are the respiratory organs of the globe, and the schists its organs
of secretion; it is by these latter that it decomposes the water of
the sea, in order to produce the matters ejected by volcanoes. The
veins are carious sores, abscesses of the mineral kingdom; and the
metals are products of rottenness and disease, which is the reason
that almost all of them have so bad a smell[23].