The theory which has been developed, and which considers the earth as an
extinct sun, as a star cooled down from its original heated condition,
as a nebula, or luminous cloud, which has passed from the gaseous to the
solid state--this fine conception, which unites so brilliantly the
kindred sciences of astronomy and geology, belongs to the French
mathematician, Laplace, the immortal author of the “Mécanique Céleste.”
The hypothesis of Laplace assigns to the sun, and to all bodies which
gravitate in what Descartes calls his _tourbillon_, a common origin. “In
the primitive state in which we must suppose the sun to be,” he says,
“it resembles one of those nebulæ which the telescope reveals to us,
consisting of a more or less brilliant central _nucleus_, surrounded by
luminous clouds, which clouds, condensing at the surface, become
transformed into a star.”
It has been calculated that the centre of the earth has a temperature of
about 195,000° Cent., a degree of heat which surpasses all that the
imagination can conceive. We can have no difficulty in admitting that,
at a heat so excessive, all the substances which now enter into the
composition of the globe would be reduced to the state of gas or vapour.
Our planet, then, must have been originally an aggregation of aëriform
fluids--a mass of matter entirely gaseous; and if we reflect that
substances in their gaseous state occupy a volume eighteen hundred times
larger than when solid, we shall have some conception of the enormous
volume of this gaseous mass. It would be as large as the sun, which is
fourteen hundred thousand times larger than the terrestrial sphere. In
Fig. 12 we have attempted to give an idea of the vast difference of
volume between the earth in its present solid state and in its primitive
gaseous condition. One of the globes, A, represents the former, B the
latter. It is simply a comparison of size, which is made the more
strikingly apparent by means of these geometrical figures--one the
twentieth part of an inch in diameter, the other two inches and three
quarters.
[Illustration: VI.--The Earth circulating in space in the state of a
gaseous star.]
[Illustration: Fig. 12.--Comparative volume of the earth in the gaseous
and solid state.]
At this excessive temperature the gaseous mass, which we have described,
would shine in space as the sun does at the present day; and with the
same brilliancy as that with which, to our eyes, the fixed stars and
planets shine in the serenity of night, as represented on the opposite
page (PLATE VI.). Circulating round the sun in obedience to the laws of
universal gravitation, this incandescent gaseous mass was necessarily
regulated by the laws which govern other material substances. As it got
cooler it gradually transferred part of its warmth to the glacial
regions of the inter-planetary spaces, in the midst of which it traced
the line of its flaming orbit. Consequent on its continual cooling (but
at the end of a period of time of which it would be impossible, even
approximately, to fix the duration), the star, originally gaseous, would
attain a liquid state. It would then be considerably diminished in
volume.
The laws of mechanics teach us that liquid bodies, when in a state of
rotation, assume a spherical form; it is one of the laws of their being,
emanating from the Creator, and is due to the force of attraction. Thus
the Earth takes the spheroidal form, belonging to it, in common with the
greater number of the celestial bodies.
The Earth is subject to two distinct movements; namely, a movement of
translation round the sun, and a movement of rotation on its own
axis--the latter a uniform movement, which produces the regular
alternations of days and nights. Mechanics have also established the
fact, which is confirmed by experiment, that a fluid mass in motion
produces (as the result of the variation of the centrifugal force on its
different diameters), a swelling towards the equatorial diameter of the
sphere, and a flattening at the poles or extremities of its axis. It is
in consequence of this law, that the Earth, when it was in a liquid
state, became swollen at the equator, and depressed at its two poles;
and that it has passed from its primitive spherical form to the
spheroidal--that is, has become flattened at each of its polar
extremities, and has assumed its present shape of an oblate spheroid.
This bulging at the equator and flattening towards the poles afford the
most direct proofs, that can be adduced, of the original liquid state of
our planet. A solid and non-elastic sphere--a stone ball, for
example--might turn for ages upon its axis, and its form would sustain
no change; but a fluid ball, or one of a pasty consistence, would swell
out towards the middle, and, in the same proportion, become flattened at
the extremities of its axis. It was upon this principle, namely, by
admitting the primitive fluidity of the globe, that Newton announced _à
priori_ the bulging of the globe at the equator and its flattening at
the poles; and he even calculated the amount of this depression. The
actual measurement, both of this expansion and flattening, by
Maupertuis, Clairaut, Camus, and Lemonnier, in 1736, proved how exact
the calculations of the great geometrican were. Those gentlemen,
together with the Abbé Outhier, were sent into Lapland by the Academy of
Sciences; the Swedish astronomer, Celsius, accompanied them, and
furnished them with the best instruments for measuring and surveying. At
the same time the Academy sent Bouguer and Condamine to the equatorial
regions of South America. The measurements taken in both these regions
established the existence of the equatorial expansion and the polar
depression, as Newton had estimated it to be in his calculations.
It does not follow, as a consequence of the partial cooling down of the
terrestrial mass, that all the gaseous substances composing it should
pass into a liquid state; some of these might remain in the state of gas
or vapour, and form round the terrestrial spheroid an outer envelope or
_atmosphere_ (from the Greek words ατμος, _vapour_, and σφαιρα,
_sphere_). But we should form a very inexact idea of the atmosphere
which surrounded the globe, at this remote period, if we compared it
with that which surrounds it now. The extent of the gaseous matter which
enveloped the primitive earth must have been immense; it doubtless
extended to the moon. It included, in short, in the state of vapour, the
enormous body of water which, as such, now constitutes our existing
seas, added to all the other substances which preserve their gaseous
state at the temperature then exhibited by the incandescent earth; and
it is certainly no exaggeration to place this temperature at 2,000°
Centigrade. The atmosphere would participate in this temperature; and
acted on by such excessive heat, the pressure that it would exert on the
Earth would be infinitely greater than that which it exercises at the
present time. To the gases which form the component parts of the present
atmospheric air--namely, nitrogen, oxygen, and carbonic acid--to
enormous masses of watery vapour, must be added vast quantities of
mineral substances, metallic or earthy, reduced to a gaseous state, and
maintained in that state by the temperature of this gigantic furnace.
The metals, the chlorides--metallic, alkaline, and earthy--sulphur, the
sulphides, and even the silicates of alumina and lime; all, at this
temperature, would exist in a vaporous form in the atmosphere
surrounding the primitive globe.
It is to be inferred that, under these circumstances, the different
substances composing this atmosphere would be ranged round the globe in
the order of their respective densities; the first layer--that nearest
to the surface of the globe--being formed of the heavier vapours, such
as those of the metals, of iron, platinum, and copper, mixed doubtless
with clouds of fine metallic dust produced by the partial condensation
of their vapours. This first and heaviest zone, and the thickest also,
would be quite opaque, although the surface of the earth was still at a
red heat. Above it would come the more vaporisable substances, such as
the metallic and alkaline chlorides, particularly the chloride of sodium
or common salt, sulphur and phosphorus, with all the volatile
combinations of these substances. The upper zone would contain matter
still more easily converted into vapour, such as water (steam), together
with others naturally gaseous, as oxygen, nitrogen, and carbonic acid.
This order of superposition, however, would not always be preserved. In
spite of their differences of density, these three atmospheric layers
would often become mixed, producing formidable storms and violent
ebullitions; frequently throwing down, rending, upheaving, and
confounding these incandescent zones.
As to the globe itself, without being so much agitated as its hot and
shifting atmosphere, it would be no less subject to perpetual tempests,
occasioned by the thousand chemical actions which took place in its
molten mass. On the other hand, the electricity resulting from these
powerful chemical actions, operating on such a vast scale, would induce
frightful electric detonations, thunder adding to the horror of this
primitive scene, which no imagination, no human pencil could trace, and
which constitutes that gloomy and disastrous chaos of which the
legendary history of every ancient race has transmitted the tradition.
In this manner would our globe circulate in space, carrying in its train
the flaming streaks of its multiple atmosphere, unfitted, as yet, for
living beings, and impenetrable to the rays of the sun, around which it
described its vast orbit.
The temperature of the planetary regions is infinitely low; according to
Laplace it cannot be estimated at less than 100° below zero. The glacial
regions traversed in its course by the incandescent globe would
necessarily cool it, at first superficially, when it would assume a
pasty consistence. It must not be forgotten that the earth, on account
of its liquid state, would be obedient in all its mass to the action of
flux and reflux, which proceeds from the attraction of the sun and moon,
but to which the sea alone is now subject. This action, to which all its
liquid and movable particles were subject, would singularly accelerate
the commencement of the solidification of the terrestrial mass. It would
thus gradually assume that sort of consistence which iron attains, when
it is first withdrawn from the furnace, in the process of puddling.
As the earth cooled, beds of concrete substances would necessarily be
formed, which, floating at first in isolated masses on the surface of
the semi-fluid matter, would in course of time come together,
consolidate, and form continuous banks; just as we see with the ice of
the present Polar Seas, which, when brought in contact by the agitation
of the waves, coalesces and forms icebergs, more or less movable. By
extending this phenomenon to the whole surface of the globe, the
solidification of its entire surface would be produced. A solid, but
still thin and fragile crust, would thus envelop the whole earth,
enclosing entirely its still fluid interior. The entire consolidation
would necessarily be a much slower process--one which, according to the
received hypothesis, is very far from being completed at the present
time; for it is estimated that the actual thickness of the earth’s crust
does not exceed thirty miles, while the mean radius or distance from the
centre of the terrestrial sphere, approaches 4,000 miles, the mean
diameter being 7,912·409 miles; so that the portion of our planet,
supposed to be solidified, represents only a very small fraction of its
total mass.
[Illustration: Fig. 13.--Relative volumes of the solid crust and liquid
mass of the globe.]
We say thirty miles, for such is the ordinary estimated thickness of the
earth’s crust, usually admitted by savants; and the following is the
process by which this result has been obtained.
We know that the temperature of the earth increases one degree
Centigrade for every hundred feet of descent. This result has been
borne out by a great number of measurements, made in many of the mines
of France, in the tin mines of Cornwall, in the mines of the Erzgeberge,
of the Ural, of Scotland, and, above all, in the soundings effected in
the Artesian wells of Grenelle and Passy, near Paris, of St. André de
Iregny, and at a great number of other points.
The greatest depth to which miners have hitherto penetrated is about 973
yards, which has been reached in a boring executed in Monderf, in the
Grand Duchy of Luxembourg. At Neusalzwerk, near Minden, in Prussia,
another boring has been carried to the depth of 760 yards. In the
coal-mines of Monkwearmouth the pits have been sunk 525 yards, and at
Dukinfield 717 yards. The mean of the thermometic observations made, at
all these points, leads to the conclusion that the temperature increases
about one degree Fahrenheit for every sixty feet (English) of descent
after the first hundred.
In admitting that this law of temperature exists for all depths of the
earth’s crust, we arrive at the conclusion that, at a depth of from
twenty-five to thirty-five miles--which is only about five times the
height of the highest mountains--the most refractory matter would be in
a state of fusion. According to M. Mitscherlich, the flame of hydrogen,
burning in free air, acquires a temperature of 1,560° Centigrade. In
this flame platinum would be in a state of fusion. Granite melts at a
lower temperature than soft iron, that is at about 1,300°; while silver
melts at 1,023°. In imagining an increase of temperature equal to one
degree for every hundred feet of descent, the temperature at twenty-five
miles will be 1,420° C. or 2,925° F.; thirty miles below the surface
there will be a probable temperature of 1,584° C. or 3,630° F.; it
follows, if these arguments be admitted, and the calculation correct,
that the thickness of the solid crust of the globe does not much exceed
thirty miles.
This result, which gives to the terrestrial crust a thickness equal to
1/190 of the earth’s diameter, has nothing, it is true, of absolute
certainty.
Prof. W. Hopkins, F.R.S., an eminent mathematician, has much insisted
upon the fact, that the conductibility of granite rocks, for heat, is
much greater than that of sedimentary rocks; and he argues that in the
lower stratum of the earth the temperature increases much more slowly
than it does nearer the surface. This consideration has led Mr. Hopkins
to estimate the probable thickness of the earth’s solid crust at a
minimum of 200 miles.
In support of this estimate Mr. Hopkins puts forward another argument,
based upon the precession of the equinoxes. We know that the terrestrial
axis, instead of always preserving the same direction in space,
revolves in a cone round the pole of the ecliptic. Our globe, it is
calculated, will accomplish its revolution in about 25,000 years. In
about this period it will return to its original position. This
balancing, which has been compared to that of a top when about to cease
spinning, produces the movement known as the _precession of the
equinoxes_. It is due to the attraction which the sun and moon exercise
upon the swelling equatorial of the globe. This attraction would act
very differently upon a globe entirely solid, and upon one with a liquid
interior, covered by a comparatively thin crust. Mr. Hopkins subjected
this curious problem to mathematical analysis, and he calculated that
the precession of the equinoxes, observed by astronomers, could only be
explained by admitting that the solid shell of the earth could not be
less than from about 800 to 1,000 miles in thickness.
In his researches on the _rigidity of the earth_, Sir William Thomson
finds that the phenomena of precession and nutation require that the
earth, if not solid to the core, must be nearly so; and that no
continuous liquid vesicle at all approaching 6,000 miles in diameter can
possibly exist in the earth’s interior, without rendering the phenomena
in question very sensibly different from what they are.
The calculations of Mr. Hennessey are in direct opposition to those of
Sir William Thomson, and show that the earth’s crust cannot be less than
eighteen miles, or more than 600 miles in thickness.
Admitting, for the present, that the terrestrial crust is only thirty
miles in thickness, we can express in a familiar, but very intelligible
fashion, the actual relation between the dimensions of the liquid
nucleus and the solid crust of the earth. If we imagine the earth to be
an orange, a tolerably thick sheet of paper applied to its surface will
then represent, approximately, the thickness of the solid crust which
now envelopes the globe. Fig. 13 will enable us to appreciate this fact
still more correctly. The terrestrial sphere having a mean diameter of
7,912 miles, or a mean radius of 3,956 miles, and a solid crust about
thirty miles thick, which is 1/260 of the diameter, or 1/130 of the
radius, the engraving may be presumed to represent these proportions
with sufficient accuracy.
To determine, even approximately, the time such a vast body would take
in cooling, so as to permit of the formation of a solid crust, or to fix
the duration of the transformations which we are describing, would be an
impossible task.
[Illustration: Fig. 14.--Formation of primitive granitic mountains.]
The first terrestrial crust formed, as indicated, would be incapable of
resisting the waves of the ocean of internal fire, which would be
depressed and raised up at its daily flux and reflux in obedience to
the attraction of the sun and moon. Who can trace, even in imagination,
the fearful rendings, the gigantic inundations, which would result from
these movements! Who would dare to paint the sublime horrors of these
first mysterious convulsions of the globe! Amid torrents of molten
matter, mixed with gases, upheaving and piercing the scarcely
consolidated crust, large crevices would be opened, and through these
gaping cracks waves of liquid granite would be ejected, and then left to
cool and consolidate on the surface. Fig. 14 represents the formation of
a primitive granitic mountain, by the eruption of the internal granitic
matter which forces its way to the surface through a fracture in the
crust. In some of these mountains, Ben Nevis for example, three
different stages of the eruption can be traced. “Ben Nevis, now the
undoubted monarch of the Scottish mountains,” says Nicol, “shows well
the diverse age and relations of igneous rocks. The Great Moor from
Inverlochy and Fort William to the foot of the hill is gneiss. Breaking
through, and partly resting on the gneiss is granite, forming the lower
two-thirds of the mountain up to the small tarn on the shoulder of the
hill. Higher still is the huge prism of porphyry, rising steep and
rugged all around.” In this manner would the first mountains be formed.
In this way, also, might some metallic veins be ejected through the
smaller openings, true injections of eruptive matter produced from the
interior of the globe, traversing the primitive rocks and constituting
the precious depository of metals, such as copper, zinc, antimony, and
lead. Fig. 15 represents the internal structure of some of these
metallic veins. In this case the fracture is only a fissure in the rock,
which soon became filled with injected matter, often of different kinds,
which in crystallising would completely fill the hollow of this cleft,
or crack; but sometimes forming cavities or geodes as a result of the
contraction of the mass.
[Illustration: Fig. 15.--Metallic veins.]
But some eruptions of granitic and other substances, ejected from the
interior, never reach the surface at all. In such cases the clefts and
crevices--longitudinal or oblique--are filled, but the fissures in the
crust do not themselves extend to the surface. Fig. 16 represents an
eruption of granite through a mass of sedimentary rock--the granite
ejected from the centre fills all the clefts and fractures, but it has
not been sufficiently powerful to force its way to the surface.
[Illustration: Fig. 16.--Eruption of granite.]
On the surface of the earth, then, which would be at first smooth and
unbroken, there were formed, from the very beginning, swelling
eminences, hollows, foldings, corrugations, and crevices, which would
materially alter its original aspect; its arid and burning surface
bristled with rugged protuberances, or was traversed by enormous
fissures and cracks. Nevertheless, as the globe continued to cool, a
time arrived when its temperature became insufficient to maintain, in a
state of vapour, the vast masses of water which floated in the
atmosphere. These vapours would pass into the liquid state, and then the
first rain fell upon the earth. Let us here remark that these were
veritable rains of boiling water; for in consequence of the very
considerable pressure of the atmosphere, water would be condensed and
become liquid at a temperature much above 100° Centigrade (212° Fahr.)
[Illustration: VII.--Condensation and rainfall on the primitive globe.]
The first drop of water, which fell upon the still heated terrestrial
sphere, marked a new period in its evolution--a period the mechanical
and chemical effects of which it is important to analyse. The contact of
the condensed water with the consolidated surface of the globe opens up
a series of modifications of which science may undertake the examination
with a degree of confidence, or at least with more positive elements of
appreciation than any we possess for the period of chaos; some of the
features of which we have attempted to represent, leaving of necessity
much to the imagination, and for the reader to interpret after his own
fashion.
The first water which fell, in the liquid state, upon the slightly
cooled surface of the earth would be rapidly converted into steam by the
elevation of its temperature. Thus, rendered much lighter than the
surrounding atmosphere, these vapours would rise to the utmost limits of
the atmosphere, where they would become condensed afresh, in consequence
of their radiation towards the glacial regions of space; condensing
again, they would re-descend to the earth in a liquid state, to
re-ascend as vapour and fall in a state of condensation. But all these
changes, in the physical condition of the water, could only be
maintained by withdrawing a very considerable amount of heat from the
surface of the globe, whose cooling would be greatly hastened by these
continual alternations of heat and cold; its heat would thus become
gradually dissipated and lost in the regions of celestial space.
This phenomenon extending itself by degrees to the whole mass of watery
vapour existing in the atmosphere, the waters covered the earth in
increasing quantities; and as the conversion of all liquids into vapour
is provocative of a notable disengagement of electricity, a vast
quantity of electric fluid necessarily resulted from the conversion of
such large masses of water into vapour. Bursts of thunder, and bright
flashes of lightning were the necessary accompaniments of this
extraordinary struggle of the elements--a state of things which M.
Maurando has attempted to represent on the opposite page (PLATE VII.).
How long did this struggle for supremacy between fire and water, with
the incessant noise of thunder, continue? All that can be said in reply
is, that a time came when water was triumphant. After having covered
vast areas on the surface of the earth, it finally occupied and entirely
covered the whole surface; for there is good reason to believe that at a
certain epoch, at the commencement, so to speak, of its evolution; the
earth was covered by water over its whole extent. The ocean was
universal. From this moment our globe entered on a regular series of
revolutions, interrupted only by the outbreaks of the internal fires
which were concealed beneath its still imperfectly consolidated crust.
“At the early periods in which the materials of the ancient crystalline
schists were accumulated, it cannot be doubted that the chemical
processes which generated silicates were much more active than in more
recent times. The heat of the earth’s crust was probably then far
greater than at present, while a high temperature prevailed at
comparatively small depths, and thermal waters abounded. A denser
atmosphere, charged with carbonic acid gas, must also have contributed
to maintain, at the earth’s surface, a greater degree of heat, though
one not incompatible with the existence of organic life.
“These conditions must have favoured many chemical processes, which in
later times have nearly ceased to operate. Hence we find that
subsequently to the eozoic times, silicated rocks of clearly marked
chemical origin are comparatively rare.”[32]
[32] “Address to the American Association for the Advancement of
Science,” by Thomas Sterry Hunt, LL.D., p. 56. 1871.
In order to comprehend the complex action, now mechanical, now chemical,
which the waters, still in a heated state, exercised on the solid crust,
let us consider what were the components of this crust. The rocks which
formed its first _stratum_--the framework of the earth, the foundation
upon which all others repose--may be presumed to have been a compound
which, in varying proportions, forms granite and gneiss, and has
latterly been designated by geologists Laurentian.
What is this gneiss, this granite, speaking of it with reference to its
mineralogical character? It is a combination of silicates, with a base
of alumina, potash, soda, and sometimes lime--_quartz_, _felspar_, and
_mica_ form, by their simple aggregation, _granite_--it is thus a
ternary combination, or composed of three minerals.
_Quartz_, the most abundant of all minerals, is silica more or less pure
and often crystallised. _Felspar_ is a crystalline or crystallised
mineral, composed of _silicate_ of alumina, potash, soda, or lime;
potash-felspar is called _orthoclase_, soda-felspar _albite_,
lime-felspar _anorthite_. _Mica_ is a silicate of alumina and potash,
containing magnesia and oxide of iron; it takes its name from the Latin
_micare_, to shine or glitter.
_Granite_ (from the Italian _grano_, being granular in its structure)
is, then, a compound rock, formed of felspar, quartz, and mica, and the
three constituent minerals are more or less crystalline. _Gneiss_ is a
schistose variety of granite, and composed of the same minerals; the
only difference between the two rocks (whatever may be their difference
of origin) being that the constituent minerals, instead of being
confusedly aggregated, as in granite, assume a foliated texture in
gneiss. This foliated structure leads sometimes to gneiss being called
_stratified granite_. “The term gneiss originated with the Freiberg
miners, who from ancient times have used it to designate the rock in
which their veins of silver-ore were found.”[33]
[33] Cotta’s “Rocks Classified and Described,” by P. H. Lawrence, p.
232.
The felspar, which enters into the composition of granite, is a mineral
that is easily decomposed by water, either cold or boiling, or by the
water of springs rich in carbonic acid. The chemical action of carbonic
acid and water, and the action (at once chemical and mechanical) of the
hot water in the primitive seas, powerfully modified the granitic rocks
which lay beneath them. The warm rains which fell upon the
mountain-peaks and granitic pinnacles, the torrents of rain which fell
upon the slopes or in the valleys, dissolved the several alkaline
silicates which constitute felspar and mica, and swept them away to form
elsewhere strata of clay and sand; thus were the first modifications in
the primitive rocks produced by the united action of air and water, and
thus were the first sedimentary rocks deposited from the oceanic waters.
The argillaceous deposits produced by this decomposition of the
felspathic and micaceous rocks would participate in the still heated
temperature of the globe--would be again subjected to long continued
heat; and when they became cool again, they would assume, by a kind of
semi-crystallisation, that parallel structure which is called foliation.
All foliated rocks, then, are metamorphic, and the result of a
metamorphic action to which sedimentary strata (and even some eruptive
rocks) have been subjected subsequently to their deposition and
consolidation, and which has produced a re-arrangement of their
component mineral particles, and frequently, if not always, of their
chemical elements also.
In this manner would the first beds of crystalline _schist_, such as
mica-schist, be formed, probably out of sandy and clayey muds, or
arenaceous and argillaceous shales.
At the end of this first phase of its existence, the terrestrial globe
was, then, covered, over nearly its whole surface, with hot and muddy
water, forming extensive but shallow seas. A few islands, raising their
granitic peaks here and there, would form a sort of archipelago,
surrounded by seas filled with earthy matter in suspension. During a
long series of ages the solid crust of the globe went on increasing in
thickness, as the process of solidification of the underlying liquid
matter nearest to the surface proceeded. This state of tranquillity
could not last long. The solid portion of the globe had not yet attained
sufficient consistency to resist the pressure of the gases and boiling
liquids which it covered and compressed with its elastic crust. The
waves of this internal sea triumphed, more than once, over the feeble
resistances which were opposed to it, making enormous dislocations and
breaches in the ground--immense upheavals of the solid crust raising the
beds of the seas far above their previous levels--and thus mountains
arose out of the ocean, not now exclusively granitic, but composed,
besides, of those schistose rocks which have been deposited under water,
after long suspension in the muddy seas.
On the other hand the Earth, as it continued to cool, would also
contract; and this process of contraction, as we have already explained,
was another cause of dislocation at the surface, producing either
considerable ruptures or simple fissures in the continuity of the crust.
These fissures would be filled, at a subsequent period, by jets of the
molten matter occupying the interior of the globe--by _eruptive
granite_, that is to say--or by various mineral compounds; they also
opened a passage to those torrents of heated water charged with mineral
salts, with silica, the bicarbonates of lime and magnesia, which,
mingling with the waters of the vast primitive ocean, were deposited at
the bottom of the seas, thus helping to increase the mass of the mineral
substances composing the solid portion of the globe.
These eruptions of granitic or metallic matter--these vast discharges of
mineral waters through the fractured surface--would be of frequent
occurrence during the primitive epoch we are contemplating. It should
not, therefore, be a matter for surprise to find the more ancient rocks
almost always fractured, reduced in dimensions by faults and
contortions, and often traversed by veins containing metals or their
oxides, such as the oxides of copper and tin; or their sulphides, such
as those of lead, of antimony, or of iron--which are now the object of
the miner’s art.