Theory of the Earth, Volume 1 (of 4)
by
James Hutton
Part 1 out of 6
THEORY OF THE EARTH, VOLUME I
With Proofs and Illustrations, in Four Parts
By
JAMES HUTTON, M.D. & F.R.S.E.
1795.
CONTENTS.
PART I.
THEORY OF THE EARTH; with the Examination of different Opinions on
that Subject.
CHAP. I.
THEORY OF THE EARTH; or an Investigation of the Laws observable in the
Composition, Dissolution, and Restoration of Land upon the Globe.
SECT. I.--Prospect of the Subject to be treated of.
SECT. II.--An Investigation of the Natural Operations employed in
consolidating the Strata of the Globe.
SECT. III.--Investigation of the Natural Operations employed in the
Production of Land above the Surface of the Sea.
SECT. IV.--System of Decay and Renovation observed in the Earth.
CHAP. II.
An Examination of Mr KIRWAN's Objections to the Igneous Origin of Stony
Substances.
CHAP. III.
Of Physical Systems, and Geological Theories, in general.
CHAP. IV.
The Supposition of Primitive Mountains refuted.
CHAP. V.
Concerning that which may be termed the Primary Part of the Present
Earth.
CHAP. VI.
The Theory of interchanging Sea and Land, illustrated by an
Investigation of the Primary and Secondary Strata 421.
SECT. I.--A distinct view of the Primary and Secondary Strata.
SECT. II.--The Theory confirmed from Observations made on purpose to
elucidate the Subject.
CHAP. VII.
Opinions examined with regard to Petrifaction, or Mineral Concretion.
CHAP. VIII.
The Nature of Mineral Coal, and the Formation of Bituminous Strata,
investigated.
SECT. I.--Purpose of this Inquiry.
SECT. II.--Natural History of Coal Strata, and Theory of this
Geological Operation.
SECT. III.--The Mineralogical Operations of the Earth illustrated from
the Theory of Fossil Coal.
PART I.
THEORY OF THE EARTH;
WITH THE
EXAMINATION
OF
DIFFERENT OPINIONS ON THAT SUBJECT.
IN EIGHT CHAPTERS.
CHAPTER I.
THEORY of the EARTH; or an Investigation of the Laws observable in the
Composition, Dissolution, and Restoration, of Land upon the Globe.
SECTION I.
Prospect of the Subject to be treated of.
When we trace the parts of which this terrestrial system is composed,
and when we view the general connection of those several parts, the
whole presents a machine of a peculiar construction by which it is
adapted to a certain end. We perceive a fabric, erected in wisdom, to
obtain a purpose worthy of the power that is apparent in the production
of it.
We know little of the earth's internal parts, or of the materials which
compose it at any considerable depth below the surface. But upon the
surface of this globe, the more inert matter is replenished with plants,
and with animal and intellectual beings.
Where so many living creatures are to ply their respective powers, in
pursuing the end for which they were intended, we are not to look for
nature in a quiescent state; matter itself must be in motion, and the
scenes of life a continued or repeated series of agitations and events.
This globe of the earth is a habitable world; and on its fitness for
this purpose, our sense of wisdom in its formation must depend. To judge
of this point, we must keep in view, not only the end, but the means
also by which that end is obtained. These are, the form of the whole,
the materials of which it is composed, and the several powers which
concur, counteract, or balance one another, in procuring the general
result.
The form and constitution of the mass are not more evidently calculated
for the purpose of this earth as a habitable world, than are the various
substances of which that complicated body is composed. Soft and hard
parts variously combine to form a medium consistence, adapted to the use
of plants and animals; wet and dry are properly mixed for nutrition,
or the support of those growing bodies; and hot and cold produce a
temperature or climate no less required than a soil: Insomuch, that
there is not any particular, respecting either the qualities of the
materials, or the construction of the machine, more obvious to
our perception, than are the presence and efficacy of design and
intelligence in the power that conducts the work.
In taking this view of things, where ends and means are made the object
of attention, we may hope to find a principle upon which the comparative
importance of parts in the system of nature may be estimated, and also
a rule for selecting the object of our inquiries. Under this direction,
science may find a fit subject of investigation in every particular,
whether of _form_, _quality_, or _active power_, that presents itself in
this system of motion and of life; and which, without a proper
attention to this character of the system, might appear anomalous and
incomprehensible.
It is not only by seeing those general operations of the globe which
depend upon its peculiar construction as a machine, but also by
perceiving how far the particulars, in the construction of that machine,
depend upon the general operations of the globe, that we are enabled to
understand the constitution of this earth as a thing formed by design.
We shall thus also be led to acknowledge an order, not unworthy of
Divine wisdom, in a subject which, in another view, has appeared as the
work of chance, or as absolute disorder and confusion.
To acquire a general or comprehensive view of this mechanism of the
globe, by which it is adapted to the purpose of being a habitable world,
it is necessary to distinguish three different bodies which compose the
whole. These are, a solid body of earth, an aqueous body of sea, and an
elastic fluid of air.
It is the proper shape and disposition of these three bodies that form
this globe into a habitable world; and it is the manner in which these
constituent bodies are adjusted to each other, and the laws of action
by which they are maintained in their proper qualities and respective
departments, that form the Theory of the machine which we are now to
examine.
Let us begin with some general sketch of the particulars now mentioned.
_1st_, There is a central body in the globe. This body supports those
parts which come to be more immediately exposed to our view, or which
may be examined by our sense and observation. This first part is
commonly supposed to be solid and inert; but such a conclusion is only
mere conjecture; and we shall afterwards find occasion, perhaps, to form
another judgment in relation to this subject, after we have examined
strictly, upon scientific principles, what appears upon the surface, and
have formed conclusions concerning that which must have been transacted
in some more central part.
_2dly_, We find a fluid body of water. This, by gravitation, is reduced
to a spherical form, and by the centrifugal force of the earth's
rotation, is become oblate. The purpose of this fluid body is essential
in the constitution of the world; for, besides affording the means of
life and motion to a multifarious race of animals, it is the source of
growth and circulation to the organized bodies of this earth, in being
the receptacle of the rivers, and the fountain of our vapours.
_3dly_, We have an irregular body of land raised above the level of the
ocean. This, no doubt, is the smallest portion of the globe; but it is
the part to us by far most interesting. It is upon the surface of this
part that plants are made to grow; consequently, it is by virtue of
this land that animal life, as well as vegetation, is sustained in this
world.
_Lastly_, We have a surrounding body of atmosphere, which completes the
globe. This vital fluid is no less necessary, in the constitution of the
world, than are the other parts; for there is hardly an operation upon
the surface of the earth, that is not conducted or promoted by its
means. It is a necessary condition for the sustenance of fire; it is the
breath of life to animals; it is at least an instrument in vegetation;
and, while it contributes to give fertility and health to things that
grow, it is employed in preventing noxious effects from such as go into
corruption. In short, it is the proper means of circulation for the
matter of this world, by raising up the water of the ocean, and pouring
it forth upon the surface of the earth.
Such is the mechanism of the globe: Let us now mention some of those
powers by which motion is produced, and activity procured to the mere
machine.
First, There is the progressive force, or moving power, by which this
planetary body, if solely actuated, would depart continually from the
path which it now pursues, and thus be for ever removed from its end,
whether as a planetary body, or as a globe sustaining plants and
animals, which may be termed a living world.
But this moving body is also actuated by gravitation, which inclines
it directly to the central body of the sun. Thus it is made to revolve
about that luminary, and to preserve its path.
It is also upon the same principles, that each particular part upon the
surface of this globe, is alternately exposed to the influence of light
and darkness, in the diurnal rotation of the earth, as well as in its
annual revolution. In this manner are produced the vicissitudes of night
and day, so variable in the different latitudes from the equator to the
pole, and so beautifully calculated to equalise the benefits of light,
so variously distributed in the different regions of the globe.
Gravitation, and the _vis infita_ of matter, thus form the first two
powers distinguishable in the operations of our system, and wisely
adapted to the purpose for which they are employed.
We next observe the influence of light and heat, of cold and
condensation. It is by means of these two powers that the various
operations of this living world are more immediately transacted;
although the other powers are no less required, in order to produce or
modify these great agents in the economy of life, and system of our
changing things.
We do not now inquire into the nature of those powers, or investigate
the laws of light and heat, of cold and condemnation, by which the
various purposes of this world are accomplished; we are only to mention
those effects which are made sensible to the common understanding of
mankind, and which necessarily imply a power that is employed. Thus,
it is by the operation of those powers that the varieties of season
in spring and autumn are obtained, that we are blessed with the
vicissitudes of summer's heat and winter's cold, and that we possess the
benefit of artificial light and culinary fire.
We are thus bountifully provided with the necessaries of life; we are
supplied with things conducive to the growth and preservation of our
animal nature, and with fit subjects to employ and to nourish our
intellectual powers.
There are other actuating powers employed in the operations of this
globe, which we are little more than able to enumerate; such are those
of electricity, magnetism, and subterraneous heat or mineral fire.
Powers of such magnitude or force, are not to be supposed useless in a
machine contrived surely not without wisdom; but they are mentioned here
chiefly on account of their general effect; and it is sufficient to have
named powers, of which the actual existence is well known, but of which
the proper use in the constitution of the world is still obscure.
The laws of electricity and magnetism have been well examined by
philosophers; but the purposes of those powers in the economy of the
globe have not been discovered. Subterraneous fire, again, although the
most conspicuous in the operations of this world, and often examined by
philosophers, is a power which has been still less understood, whether
with regard to its efficient or final cause. It has hitherto appeared
more like the accident of natural things, than the inherent property of
the mineral region. It is in this last light, however, that I wish to
exhibit it, as a great power acting a material part in the operations of
the globe, and as an essential part in the constitution of this world.
We have thus surveyed the machine in general, with those moving powers,
by which its operations, diversified almost _ad infinitum_, are
performed. Let us now confine our view, more particularly, to that part
of the machine on which we dwell, that so we may consider the natural
consequences of those operations which, being within our view, we are
better qualified to examine.
This subject is important to the human race, to the possessor of this
world, to the intelligent being Man, who foresees events to come, and
who, in contemplating his future interest, is led to inquire concerning
causes, in order that he may judge of events which otherwise he could
not know.
If, in pursuing this object, we employ our skill in research, not in
forming vain conjectures; and if _data_ are to be found, on which
Science may form just conclusions, we should not long remain in
ignorance with respect to the natural history of this earth, a subject
on which hitherto opinion only, and not evidence, has decided: For in no
subject, perhaps, is there naturally less defect of evidence, although
philosophers, led by prejudice, or misguided by false theory, may have
neglected to employ that light by which they should have seen the system
of this world.
But to proceed in pursuing a little farther our general or preparatory
ideas. A solid body of land could not have answered the purpose of a
habitable world; for, a soil is necessary to the growth of plants; and a
soil is nothing but the materials collected from the destruction of the
solid land. Therefore, the surface of this land, inhabited by man,
and covered with plants and animals, is made by nature to decay, in
dissolving from that hard and, compact state in which it is found below
the soil; and this soil is necessarily washed away, by the continual
circulation of the water, running from the summits of the mountains
towards the general receptacle of that fluid. The heights of our land
are thus levelled with the shores; our fertile plains are formed from the
ruins of the mountains; and those travelling materials are still pursued
by the moving water, and propelled along the inclined surface of the
earth[1] These moveable materials, delivered into the sea, cannot, for
a long continuance, rest upon the shore; for, by the agitation of the
winds, the tides and currents, every moveable thing is carried
farther and farther along the shelving bottom of the sea, towards the
unfathomable regions of the ocean.
[Note 1: M. de Luc, in his second letter to me, published in the Monthly
Review for 1790, says, "You ought to have proved that both gravel and
sand are carried from our continents to the sea; which, on the contrary,
I shall prove not to be the case." He then endeavours to prove his
assertion, by observing, that, in certain places where there is not
either sufficient declivity in the surface, or force in the running
water, gravel and sand are made to rest, and do not travel to the sea.
This surely is a fact to which I most readily assent; but, on the other
hand, I hope he will acknowledge, that, where there is sufficient
declivity in the surface, or force in the running water, sand, gravel,
and stones, are travelled upon the land, and are thus carried into the
sea--at last. This is all that my theory requires, and this is what I
believe will be admitted, without any farther proof on my part.]
If the vegetable soil is thus constantly removed from the surface of the
land, and if its place is thus to be supplied from the dissolution of
the solid earth, as here represented, we may perceive an end to this
beautiful machine; an end, arising from no error in its constitution as
a world, but from that destructibility of its land which is so necessary
in the system of the globe, in the economy of life and vegetation.
The immense time necessarily required for this total destruction of
the land, must not be opposed to that view of future events, which is
indicated by the surest facts, and most approved principles. Time, which
measures every thing in our idea, and is often deficient to our schemes,
is to nature endless and as nothing; it cannot limit that by which alone
it had existence; and, as the natural course of time, which to us seems
infinite, cannot be bounded by any operation that may have an end, the
progress of things upon this globe, that is, the course of nature,
cannot be limited by time, which must proceed in a continual succession.
We are, therefore, to consider as inevitable the deduction of our land,
so far as effected by those operations which are necessary in the
purpose of the globe, considered as a habitable world; and, so far as
we have not examined any other part of the economy of nature, in which
other operations and a different intention might appear.
We have now considered the globe of this earth as a machine, constructed
upon chemical as well as mechanical principles, by which its different
parts are all adapted, in form, in quality, and in quantity, to a
certain end; an end attained with certainty or success; and an end from
which we may perceive wisdom, in contemplating the means employed.
But is this world to be considered thus merely as a machine, to last no
longer than its parts retain their present position, their proper forms
and qualities? Or may it not be also considered as an organized body?
such as has a constitution in which the necessary decay of the machine
is naturally repaired, in the exertion of those productive powers by
which it had been formed.
This is the view in which we are now to examine the globe; to see if
there be, in the constitution of this world, a reproductive operation,
by which a ruined constitution may be again repaired, and a duration or
stability thus procured to the machine, considered as a world sustaining
plants and animals.
If no such reproductive power, or reforming operation, after due
inquiry, is to be found in the constitution of this world, we should
have reason to conclude, that the system of this earth has either been
intentionally made imperfect, or has not been the work of infinite power
and wisdom.
Here is an important question, therefore, with regard to the
constitution of this globe; a question which, perhaps, it is in
the power of man's sagacity to resolve; and a question which, if
satisfactorily resolved, might add some lustre to science and the human
intellect.
Animated with this great, this interesting view, let us strictly examine
our principles, in order to avoid fallacy in our reasoning; and let us
endeavour to support our attention, in developing a subject that is
vast in its extent, as well as intricate in the relation of parts to be
stated.
The globe of this earth is evidently made for man. He alone, of all the
beings which have life upon this body, enjoys the whole and every part;
he alone is capable of knowing the nature of this world, which he thus
possesses in virtue of his proper right; and he alone can make the
knowledge of this system a source of pleasure, and the means of
happiness.
Man alone, of all the animated beings which enjoy the benefits of this
earth, employs the knowledge which he there receives, in leading him to
judge of the intention of things, as well as of the means by which they
are brought about; and he alone is thus made to enjoy, in contemplation
as well as sensual pleasure, all the good that may be observed in the
constitution of this world; he, therefore, should be made the first
subject of inquiry.
Now, if we are to take the written history of man for the rule by which
we should judge of the time when the species first began, that period
would be but little removed from the present state of things. The Mosaic
history places this beginning of man at no great distance; and there
has not been found, in natural history, any document by which a high
antiquity might be attributed to the human race. But this is not the
case with regard to the inferior species of animals, particularly those
which inhabit the ocean and its shores. We find, in natural history,
monuments which prove that those animals had long existed; and we thus
procure a measure for the computation of a period of time extremely
remote, though far from being precisely ascertained.
In examining things present, we have data from which to reason with
regard to what has been; and, from what has actually been, we have
data for concluding with regard to that which is to happen hereafter.
Therefore, upon the supposition that the operations of nature are
equable and steady, we find, in natural appearances, means for
concluding a certain portion of time to have necessarily elapsed, in the
production of those events of which we see the effects.
It is thus that, in finding the relics of sea-animals of every kind
in the solid body of our earth, a natural history of those animals
is formed, which includes a certain portion of time; and, for the
ascertaining this portion of time, we must again have recourse to the
regular operations of this world. We shall thus arrive at facts which
indicate a period to which no other species of chronology is able to
remount.
In what follows, therefore, we are to examine the construction of the
present earth, in order to understand the natural operations of time
past; to acquire principles, by which we may conclude with regard to the
future course of things, or judge of those operations, by which a world,
so wisely ordered, goes into decay; and to learn, by what means such a
decayed world may be renovated, or the waste of habitable land upon the
globe repaired.
This, therefore, is the object which we are to have in view during this
physical investigation; this is the end to which are to be directed all
the steps in our cosmological pursuit.
The solid parts of the globe are, in general, composed of sand, of
gravel, of argillaceous and calcareous strata, or of the various
compositions of these with some other substances, which it is not
necessary now to mention. Sand is separated and sized by streams and
currents; gravel is formed by the mutual attrition of stones agitated
in water; and marly, or argillaceous strata, have been collected, by
subsiding in water with which those earthy substances had been floated.
Thus, so far as the earth is formed of these materials, that solid body
would appear to have been the production of water, winds, and tides.
But that which renders the original of our land clear and evident,
is the immense quantities of calcareous bodies which had belonged
to animals, and the intimate connection of these masses of animal
production with the other strata of the land. For it is to be proved,
that all these calcareous bodies, from the collection of which the
strata were formed, have belonged to the sea, and were produced in it.
We find the marks of marine animals in the most solid parts of the
earth; consequently, those solid parts have been formed after the ocean
was inhabited by those animals which are proper to that fluid medium.
If, therefore, we knew the natural history of those solid parts, and
could trace the operations of the globe, by which they had been formed,
we would have some means for computing the time through which those
species of animals have continued to live. But how shall we describe a
process which nobody has seen performed, and of which no written
history gives any account? This is only to be investigated, _first_, in
examining the nature of those solid bodies, the history of which we want
to know; and, 2_dly_, In examining the natural operations of the globe,
in order to see if there now actually exist such operations, as, from
the nature of the solid bodies, appear to have been necessary to their
formation.
But, before entering more particularly into those points of discussion,
by which the question is to be resolved, let us take a general view of
the subject, in order to see what it is which science and observation
must decide.
In all the regions of the globe, immense masses are found, which, though
at present in the most solid state, appear to have been formed by the
collection of the calcareous _exuviae_ of marine animals. The question
at present is not, in what manner those collections of calcareous relics
have become a perfect solid body, and have been changed from an animal
to a mineral substance; for this is a subject that will be afterwards
considered; we are now only inquiring, if such is truly the origin of
those mineral masses.
That all the masses of marble or limestone are composed of the
calcareous matter of marine bodies, may be concluded from the following
facts:
1_st_, There are few beds of marble or limestone, in which may not be
found some of those objects which indicate the marine origin of the
mass. If, for example, in a mass of marble, taken from a quarry upon the
top of the Alps or Andes[2], there shall be found one cockle-shell, or
piece of coral, it must be concluded, that this bed of stone had been
originally formed at the bottom of the sea, as much as another bed which
is evidently composed almost altogether of cockle-shells and coral. If
one bed of limestone is thus found to have been of a marine origin,
every concomitant bed of the same kind must be also concluded to have
been formed in the same Manner.
[Note 2: "Cette sommite elevee de 984 toises au dessus de notre lac, et
par consequent de 1172 au dessus de la mer, est remarquable en ce que
l'on y voit des fragmens d'huitres petrifies.--Cette montagne est
dominee par un rocher escarpe, qui s'il n'est pas inaccessible, est du
moins d'un bien difficile acces; il paroit presqu'entierement compose
de coquillages petrifies, renfermes dans un roc calcaire, ou marbre
grossier noiratre. Les fragmens qui s'en detachent, et que l'on
rencontre en montant a la Croix de fer, sont remplis de _turbinites_ de
differentes especes." M. DE SAUSSURE, _Voyage dans les Alpes_, p. 394.]
We thus shall find the greatest part of the calcareous masses upon this
globe to have originated from marine calcareous bodies; for whether
we examine marbles, limestones, or such solid masses as are perfectly
changed from the state of earth, and are become compact and hard, or
whether we examine the soft, earthy, chalky or marly strata, of which so
much of this earth is composed, we still find evident proofs, that those
beds had their origin from materials deposited at the bottom of the sea;
and that they have the calcareous substance which they contain, from the
same source as the marbles or the limestones.
2_dly_, In those calcareous strata, which are evidently of marine
origin, there are many parts that are of a sparry structure, that is
to say, the original texture of those beds, in such places, has been
dissolved, and a new structure has been assumed, which is peculiar to
a certain state of the calcareous earth. This change is produced by
crystallisation, in consequence of a previous state of fluidity, which
has so disposed the concreting parts, as to allow them to assume a
regular shape and structure proper to that substance. A body, whose
external form has been modified by this process, is called a _crystal_;
one whose internal arrangement of parts is determined by it, is said to
be of a _sparry structure_; and this is known from its fracture.
3_dly_, There are, in all the regions of the earth, huge masses of
calcareous matter, in that crystalline form of sparry state, in
which perhaps no vestige can be found of any organised body, nor any
indication that such calcareous matter had belonged to animals; but
as, in other masses, this sparry structure, or crystalline state, is
evidently assumed by the marine calcareous substances, in operations
which are natural to the globe, and which are necessary to the
consolidation of the strata, it does not appear, that the sparry masses,
in which no figured body is formed, have been originally different from
other masses, which, being only crystallised in part, and in part still
retaining their original form, leave ample evidence of their marine
origin[3].
[Note 3: M. de Saussure, describing the marble of Aigle, says, "Les
tables polies de ce marbre presentent frequemment des coquillages, dont
la plupart sont des peignes stries, et de tres-beaux madrepores. Tous
ces corps marins on pris entierement la nature et le grain meme
du marbre, on n'y voit presque jamais la coquille sous sa forme
originaire."]
We are led, in this manner, to conclude, that all the strata of the
earth, not only those consisting of such calcareous masses, but others
superincumbent upon these, have had their origin at the bottom of the
sea, by the collection of sand and gravel, of shells, of coralline
and crustaceous bodies, and of earths and clays, variously mixed,
or separated and accumulated. Here is a general conclusion, well
authenticated in the appearances of nature, and highly important in the
natural history of the earth.
The general amount of our reasoning is this, that nine-tenths, perhaps,
or ninety-nine hundredths of this earth, so far as we see, have
been formed by natural operations of the globe, in collecting loose
materials, and depositing them at the bottom of the sea; consolidating
those collections in various degrees, and either elevating those
consolidated masses above the level on which they were formed, or
lowering the level of that sea.
There is a part of the solid earth which we may at present neglect, not
as being persuaded that this part may not also be found to come under
the general rule of formation with the rest, but as considering this
part to be of no consequence in forming a general rule, which shall
comprehend almost the whole, without doing it absolutely. This excluded
part consists of certain mountains and masses of granite. These are
thought to be still older in their formation, and are said never to
be found superincumbent on strata which must be acknowledged as the
productions of the sea.
Having thus found the greater part, if not the whole, of the solid land
to have been originally composed at the bottom of the sea, we may now,
in order to form a proper idea of these operations, suppose the whole of
this seaborn land to be again dispersed along the bottom of the ocean,
the surface of which would rise proportionally over the globe. We would
thus have a spheroid of water, with granite rocks and islands scattered
here and there. But this would not be the world which we inhabit;
therefore, the question now is, how such continents, as we actually have
upon the globe, could be erected above the level of the sea.
It must be evident, that no motion of the sea, caused by this earth
revolving in the solar system, could bring about that end; for let us
suppose the axis of the earth to be changed from the present poles, and
placed in the equinoctial line, the consequence of this might, indeed,
be the formation of a continent of land about each new pole, from whence
the sea would run towards the new equator; but all the rest of the globe
would remain an ocean. Some new points might be discovered, and others,
which before appeared above the surface of the sea, would be sunk by
the rising of the water; but, on the whole, land could only be gained
substantially at the poles. Such a supposition, as this, if applied to
the present state of things, would be destitute of every support, as
being incapable of explaining what appears.
But even allowing that, by the changed axis of the earth, or any other
operation of the globe, as a planetary body revolving in the solar
system, great continents of land could have been erected from the place
of their formation, the bottom of the sea, and placed in a higher
elevation, compared with the surface of that water, yet such a continent
as this could not have continued stationary for many thousand years; nor
could a continent of this kind have presented to us, every where within
its body, masses of consolidated marble, and other mineral substances,
in a state as different as possible from that in which they were, when
originally collected together in the sea.
Consequently, besides an operation, by which the earth at the bottom of
the sea should be converted into an elevated land, or placed high above
the level of the ocean, there is required, in the operations of the
globe, a consolidating power, by which the loose materials that had
subsided from water, should be formed into masses of the most perfect
solidity, having neither water nor vacuity between their various
constituent parts, nor in the pores of those constituent parts
themselves.
Here is an operation of the globe, whether chemical or mechanical, which
is necessarily connected with the formation of our present continents:
Therefore, had we a proper understanding of this secret operation, we
might thereby be enabled to form an opinion, with regard to the nature
of that unknown power, by which the continents have been placed above
the surface of that water wherein they had their birth.
If this consolidating operation be performed at the bottom of the
ocean, or under great depths of the earth, of which our continents are
composed, we cannot be witnesses to this mineral process, or acquire the
knowledge of natural causes, by immediately observing the changes which
they produce; but though we have not this immediate observation of those
changes of bodies, we have, in science, the means of reasoning from
distant events; consequently, of discovering, in the general powers of
nature, causes for those events of which we see the effects.
That the consolidating operation, in general, lies out of the reach of
our immediate observation, will appear from the following truth: All the
consolidated masses, of which we now inquire into the cause, are, upon
the surface of the earth, in a state of general decay, although the
various natures of those bodies admit of that dissolution in very
different degrees[4]
From every view of the subject, therefore, we are directed to look into
those consolidated masses themselves, in order to find principles from
whence to judge of those operations by which they had attained their
hardness or consolidated state.
It must be evident, that nothing but the most general acquaintance with
the laws of acting substances, and with those of bodies changing by the
powers of nature, can enable us to set about this undertaking with any
reasonable prospect of success; and here the science of Chemistry must
be brought particularly to our aid; for this science, having for its
object the changes produced upon the sensible qualities, as they are
called, of bodies, by its means we may be enabled to judge of that which
is possible according to the laws of nature, and of that which, in like
manner, we must consider as impossible.
[Note 4: Stalactical and certain ferruginous concretions may seem
to form an exception to the generality of this proposition. But an
objection of this kind could only arise from a partial view of things;
for the concretion here is only temporary; it is in consequence of a
solution, and it is to be followed by a dissolution, which will be
treated of in its proper place.]
Whatever conclusions, therefore, by means of this science, shall be
attained, in just reasoning from natural appearances, this must be held
as evidence, where more immediate proof cannot be obtained; and, in
a physical subject, where things actual are concerned, and not the
imaginations of the human mind, this proof will be considered as
amounting to a demonstration.
SECTION II.
An Investigation of the Natural Operations employed in consolidating
the Strata of the Globe.
We are now about to investigate those mineral operations of the globe by
which the qualities of hardness and solidity, consequently of strength
and durability, are procured to great bodies of this earth.
That those qualities are not original to such bodies, but actually
superinduced in the natural operations of the earth, will appear from
the examination of some of the hardest and most solid of those mineral
bodies. In such masses, (for example of flint and agate,) we find
included shells and coralline bodies. Consequently, there must be a
natural operation in the globe for consolidating and hardening its soft
and loose materials. It is concerning the nature of this consolidating
operation that we are now to inquire.
There are just two ways in which porous or spongy bodies can be
consolidated, and by which substances may be formed into masses of
a natural shape and regular structure; the one of these is simple
_congelation_ from a fluid state, by means of cold; the other is
_accretion_; and this includes a separatory operation, as well as that
by which the solid body is to be produced. But in whichever of these
ways solidity shall be procured, it must be brought about by first
inducing fluidity, either immediately by the action of heat, or
mediately with the assistance of a solvent, that is, by the operation
of solution. Therefore, fire and water may be considered as the general
agents in this operation, which we would explore.
Heat has been already mentioned as a general power, and as acting in all
the different parts of the globe; I would now wish more particularly to
call the attention of the reader to subterraneous fire, or heat, as
a powerful agent in the mineral regions, and as a cause necessarily
belonging to the internal constitution of this earth.
It is not our purpose at present to inquire into the particular nature
of this power of subterraneous heat, or to trace the proper connection
and analogy of the internal fire with that which is so necessary to our
life, and which acts so great a part upon the surface of the earth, this
being reserved for the last part. Our intention in here mentioning it,
is only to dispose the mind to look for active powers or efficient
causes, in that part of the earth which has been commonly considered as
passive and inert, but which will be found extremely active, and the
source of mighty revolutions in the fate of land.
There may, indeed, be some difficulty in conceiving all the
modifications of this mineral power; but as, on the one hand, we are not
arbitrarily to assume an agent, for the purpose of explaining events, or
certain appearances which are not understood; so, on the other, we must
not refuse to admit the action of a known power, when this is properly
suggested in the appearances of things; and, though we may not
understand all the modifications, or the whole capacity and regulation
of this power in bodies, we are not to neglect the appropriating to it,
as a cause, those effects which are natural to it, and which, so far as
we know, cannot belong to any other. On all occasions, we are to judge
from what we know; and, we are only to avoid concluding from our
suppositions, in cases where evidence or real information is necessarily
required. The subject now considered, subterraneous fire, will afford an
example of that truth; and, a general view of this great natural power
will here find a proper place, before the application of it for the
explanation of natural appearances.
No event is more the object of our notice, or more interesting as a
subject for our study, than is the burning of a fire: But, the more that
philosophers have studied this subject, the more they seem to differ
as to the manner in which that conspicuous event is to be explained.
Therefore, being so ignorant with regard to that fire of which we see
the origin as well as the more immediate effects, how cautious should
we be in judging the nature of subterraneous fire from the burning of
bodies, a subject which we so little understand.
But, though the cause of fire in general, or the operations of that
power in its extreme degrees, be for us a subject involved in much
obscurity, this is not the case with regard to the more common effects
of heat; and, tho' the actual existence of subterraneous fire, as the
cause of light and heat, might be a thing altogether problematical in
our opinion; yet, as to other effects, there are some of these from
which the action of that liquefying power may be certainly concluded as
having taken place within the mineral region, although the cause should
be in every other respect a thing to us unknown. In that case, where the
operation or effect is evident, and cannot be disputed, to refuse to
admit the power in question, merely because we had not seen it act, or
because we know not every rule which it may observe in acting, would
be only to found an argument upon our ignorance; it would be to
misunderstand the nature of investigating physical truths, which must
proceed by reasoning from effect to cause.
Our knowledge is extremely limited with regard to the effects of heat in
bodies, while acting under different conditions, and in various degrees.
But though our knowledge in these respects is limited, our judgment with
regard to the efficacy of this power of heat is in its nature positive,
and contains not any thing that is doubtful or uncertain. All mankind,
who have the opportunity, know that the hard substance of ice is by heat
converted into water, wherein no hardness remains; and the profound
philosophy of Dr Black, in relation to the subject of _latent heat_, as
that of Sir Isaac Newton, in relation to the weight of bodies, is not
necessary to convince the world that in the one case ice will melt, and
in the other, that heavy bodies will move when unsupported.
But though, in the abstract doctrine of _latent heat_, the ingenuity
of man has discovered a certain measure for the quantity of those
commutable effects which are perceived; and though this be a progress of
science far above the apprehension of the vulgar, yet still, that solid
bodies are changed into fluids, by the power of heat, is the same
unalterable judgment, which the savage forms as well as the philosopher.
Here, therefore, are evident effects, which mankind in general attribute
to the power of heat; and it is from those known effects that we are to
investigate subterraneous fire, or to generalise the power of heat, as
acting in the interior parts, as well as on the surface of this earth.
If, indeed, there were any other cause for fluidity besides the
operation of fire or the power of heat, in that case the most evident
proof, with regard to the flowing, or former fluidity, of mineral
bodies, would draw to no conclusion in proving the existence of mineral
fire; but when we have not the smallest reason for conjecturing any
other cause, or the least doubt with regard to that which, in the
doctrine of latent heat, has been properly investigated, the proofs
which we shall bring, of fusion in all the minerals of this earth,
must be held as proofs of mineral fire, in like manner as the proof of
subterraneous fire would necessarily imply mineral fusion as its natural
effect.
Thus we have, in our physical investigation, several points in view.
First, from the present state of things, to infer a former state of
fusion among mineral bodies. Secondly, from that former fusion, to infer
the actual existence of mineral fire in the system of the earth. And,
lastly, from the acknowledged fact of subterraneous fire as a cause, to
reason with regard to the effects of that power in mineral bodies.
But besides the power or effect of subterraneous heat in bodies which
are unorganised, and without system, in the construction of their
different parts, we have to investigate the proper purpose of this great
agent in the system of this world, which may be considered as a species
of organised body. Here, therefore, final causes are to be brought into
view, as well as those which are efficient. Now, in a subject involved
with so much obscurity, as must be for us the internal regions of the
globe, the consideration of efficient and final causes may contribute
mutually to each others evidence, when separately the investigation of
either might be thought unsatisfactory or insufficient.
So far it seemed necessary to premise with regard to the great mineral
power which we are to employ as an agent in the system of this earth;
and it may be now observed, that it is in the proper relation of this
power of heat and the fluidity or softness of bodies, as cause and
effect, that we are to find a physical principle or argument for
detecting those false theories of the earth that have been only
imagined, and not properly founded on fact or observation. It is also by
means of this principle, that we shall be enabled to form a true theory
of the mineral region, in generalising particular effects to a common
cause.
Let us now proceed in endeavouring to decide this important question,
viz. By what active principle is it, that the present state of things,
which we observe in the strata of the earth, a state so very different
from that in which those bodies had been formed originally, has been
brought about?
Two causes have been now proposed for the consolidating of loose
materials which had been in an incoherent state; these are, on the one
hand, fire; or, on the other, water, as the means of bringing about that
event. We are, therefore, to consider well, what may be the consequences
of consolidation by the one or other of those agents; and what may be
the respective powers of those agents with respect to this operation.
If we are not informed in this branch of science, we may gaze without
instruction upon the most convincing proofs of what we want to attain.
If our knowledge is imperfect, we may form erroneous principles, and
deceive ourselves in reasoning with regard to those works of nature,
which are wisely calculated for our instruction.
The strata, formed at the bottom of the sea, are to be considered
as having been consolidated, either by aqueous solution and
crystallization, or by the effect of heat and fusion. If it is in the
first of these two ways that the solid strata of the globe have attained
to their present state, there will be a certain uniformity observable
in the effects; and there will be general laws, by which this operation
must have been conducted. Therefore, knowing those general laws, and
making just observations with regard to the natural appearances of those
consolidated masses, a philosopher, in his closet, should be able to
determine, what may, and what may not have been transacted in the bowels
of the earth, or below the bottom of the ocean.
Let us now endeavour to ascertain what may have been the power of water,
acting under fixed circumstances, operating upon known substances, and
conducting to a certain end.
The action of water upon all different substances is an operation
with which we are familiar. We have it in our power to apply water in
different degrees of heat for the solution of bodies, and under various
degrees of compression; consequently, there is no reason to conclude
any thing mysterious in the operations of the globe, which are to be
performed by means of water, unless an immense compressing power should
alter the nature of those operations. But compression alters the
relation of evaporation only with regard to heat, or it changes the
degree of heat which water may be made to sustain; consequently, we are
to look for no occult quality in water acting upon bodies at the bottom
of the deepest ocean, more than what can be observed in experiments
which we have it in our power to try.
With regard again to the effect of time: Though the continuance of time
may do much in those operations which are extremely slow, where no
change, to our observation, had appeared to take place, yet, where it
is not in the nature of things to produce the change in question, the
unlimited course of time would be no more effectual, than the moment by
which we measure events in our observations.
Water being the general medium in which bodies collected at the bottom
of the sea are always contained, if those masses of collected matter are
to be consolidated by solution, it must be by the dissolution of
those bodies in that water as a menstruum, and by the concretion or
crystallization of this dissolved matter, that the spaces, first
occupied by water in those masses, are afterwards to be filled with a
hard and solid substance; but without some other power, by which the
water contained in those cavities and endless labyrinths of the strata,
should be separated in proportion as it had performed its task, it is
inconceivable how those masses, however changed from the state of their
first subsidence, should be absolutely consolidated, without any visible
or fluid water in their composition.
Besides this difficulty of having the water separated from the porous
masses which are to be consolidated, there is another with which, upon
this supposition, we have to struggle. This is, From whence should come
the matter with which the numberless cavities in those masses are to be
filled?
The water in the cavities and interstices of those bodies composing
strata, must be in a stagnating state; consequently, it can only act
upon the surfaces of those cavities which are to be filled up. But
with what are they to be filled? Not with water; they are full of that
already: Not with the substance of the bodies which contain that water;
this would be only to make one cavity in order to fill up another.
If, therefore, the cavities of the strata are to be filled with solid
matter, by means of water, there must be made to pass through those
porous masses, water impregnated with some other substances in a
dissolved state; and the aqueous menstruum must be made to separate
from the dissolved substance, and to deposit the same in those cavities
through which the solution moves.
By such a supposition as this, we might perhaps explain a partial
consolidation of those strata; but this is a supposition, of which the
case under consideration does not admit; for in the present case, which
is that of materials accumulated at the bottom of the ocean, there is
not proper means for separating the dissolved matter from the water
included in those enormous masses; nor are there any means by which a
circulation in those masses may be formed. In this case, therefore,
where the means are not naturally in the supposition, a philosopher, who
is to explain the phenomenon by the natural operation of water in this
situation, must not have recourse to another agent, still more powerful,
to assist his supposition which cannot be admitted.
Thus, it will appear, that, to consolidate strata formed at the bottom
of the sea, in the manner now considered, operations are required
unnatural to this place; consequently, not to be supposed, in order to
support a hypothesis.
But now, instead of inquiring how far water may be supposed instrumental
in the consolidation of strata which were originally of a loose
texture, we are to consider how far there may be appearances in those
consolidated bodies, by which it might be concluded, whether or not the
present state of their consolidation has been actually brought about by
means of that agent.
If water had been the menstruum by which the consolidating matter was
introduced into the interstices of strata, masses of those bodies could
only be found consolidated with such substances as water is capable of
dissolving; and these substances would be found only in such a state as
the simple separation of the solvent water might produce.
In this case, the consolidation of strata would be extremely limited;
for we cannot allow more power to water than we find it has in nature;
nor are we to imagine to ourselves unlimited powers in bodies, on
purpose to explain those appearances by which we should be made to know
the powers of nature. Let us, therefore, attend, with every possible
circumspection, to the appearances of those bodies, by means of which we
are to investigate the principles of mineralogy, and know the laws of
nature.
The question now before us concerns the consolidating substances of
strata. Are these such as will correspond to the dissolving power of
water, and to the state in which these substances might be left by the
separation of their menstruum? No; far, far from this supposition is the
conclusion that necessarily follows from natural appearances.
We have strata consolidated by calcareous spar, a thing perfectly
distinguishable from the stalactical concretion of calcareous earth,
in consequence of aqueous solution. We have strata made solid by the
formation of fluor, a substance not soluble, so far as we know, by
water. We have strata consolidated with sulphureous and bituminous
substances, which do not correspond to the solution of water. We have
strata consolidated with siliceous matter, in a state different from
that under which it has been observed, on certain occasions, to be
deposited by water. We have strata consolidated by feld-spar, a
substance insoluble in water. We have strata consolidated by almost all
the various metallic substances, with their almost endless mixtures
and sulphureous compositions; that is to say, we find, perhaps, every
different substance introduced into the interstices of strata which had
been formed by subsidence at the bottom of the sea.
If it is by means of water that those interstices have been filled with
those materials, water must be, like fire, an universal solvent, or
cause of fluidity, and we must change entirely our opinion of water in
relation to its chemical character. But there is no necessity thus to
violate our chemical principles, in order to explain certain natural
appearances; more especially if those appearances may be explained in
another manner, consistently with the known laws of nature.
If, again, it is by means of heat and fusion that the loose and porous
structure of strata shall be supposed to have been consolidated, then
every difficulty which had occurred in reasoning upon the power or
agency of water is at once removed. The loose and discontinuous body of
a stratum may be closed by means of softness and compression; the porous
structure of the materials may be consolidated, in a similar manner, by
the fusion of their substance; and foreign matter may be introduced into
the open structure of strata, in form of steam or exhalation, as well as
in the fluid state of fusion; consequently, heat is an agent competent
for the consolidation of strata, which water alone is not. If,
therefore, such an agent could be found acting in the natural place of
strata, we must pronounce it proper to bring about that end.
The examination of nature gives countenance to this supposition, so far
as strata are found consolidated by every species of substance,
and almost every possible mixture of those different substances;
consequently, however difficult it may appear to have this application
of heat, for the purpose of consolidating strata formed at the bottom of
the ocean, we cannot, from natural appearances, suppose any other cause,
as having actually produced the effects which are now examined.
This question, with regard to the means of consolidating the strata of
the globe, is, to natural history, of the greatest importance; and it is
essential in the theory now proposed to be given of the mineral system.
It would, therefore, require to be discussed with some degree of
precision in examining the particulars; but of these, there is so great
a field, and the subject is so complicated in its nature, that volumes
might be written upon particular branches only, without exhausting what
might be laid upon the subject; because the evidence, though strong in
many particulars, is chiefly to be enforced by a multitude of facts,
conspiring, in a diversity of ways, to point out one truth, and by the
impossibility of reconciling all these facts, except by means of one
supposition.
But, as it is necessary to give some proof of that which is to be
a principle in our reasoning afterwards, I shall now endeavour to
generalise the subject as much as possible, in order to answer that end,
and, at the same time, to point out the particular method of inquiry.
There are to be found, among the various strata of the globe, bodies
formed of two different kinds of substances, _siliceous_ bodies, and
those which may be termed _sulphureous_ or _phlogistic_. With one or
other, or both of those we substances, every different consolidated
stratum of the globe will be found so intimately mixed, or closely
connected, that it must be concluded, by whatever cause those bodies
of siliceous and sulphureous matter had been changed from a fluid to a
concreted state, the strata must have been similarly affected by the
same cause.
These two species of bodies, therefore, the siliceous and the
sulphureous, may now be examined, in relation to the causes of their
concretion, with a view to determine, what has been the general
concreting or consolidating power, which has operated universally in the
globe; and particularly to show, it has not been by means of any fluid
solution, that strata in general have been consolidated, or that those
particular substances have been crystallized and concreted.
Siliceous matter, physically speaking, is not soluble in water; that is
to say, in no manner of way have we been enabled to learn, that water
has the power of dissolving this matter.
Many other substances, which are so little soluble in water, that their
solubility could not be otherwise detected of themselves, are made to
appear soluble by means of siliceous matter; such is feld-spar, one of
the component parts of rock-granite.
Feld-spar is a compound of siliceous, argillaceous, and calcareous
earth, intimately united together. This compound siliceous body
being, for ages, exposed to the weather, the calcareous part of it is
dissolved, and the siliceous part is left in form of a soft white earth.
But whether this dissolution is performed by pure water, or by means
also of an acid, may perhaps be questioned. This, however, is certain,
that we must consider siliceous substances as insoluble in water.
The water of Glezer in Iceland undoubtedly contains this substance in
solution; but there is no reason to believe, that it is here dissolved
by any other than the natural means; that is, an alkaline substance, by
which siliceous bodies may be rendered soluble in water[5].
[Note 5: This conjecture, which I had thus formed, has been fully
confirmed by the accurate analysis of those waters. See vol. 3d. of the
Phil. Trans. of Edin.]
It may be, therefore, asserted, that no siliceous body having the
hardness of flint, nor any crystallization of that substance, has ever
been formed, except by fusion. If, by any art, this substance shall be
dissolved in simple water, or made to crystallise from any solution, in
that case, the assertion which has been here made may be denied.
But where there is not the vestige of any proof, to authorise the
supposition of flinty matter being dissolved by water, or crystallized
from that solution, such an hypothesis cannot be admitted, in opposition
to general and evident appearances[6].
[Note 6: The Chevalier de Dolomieu has imagined an ingenious theory for
the solution of siliceous substances in water [Journal de Physique, Mai
1792.]. This theory has not been taken up merely at a venture, but
is founded upon very accurate and interesting chemical experiments.
Hitherto, however, the nature of the siliceous substance is not
sufficiently known, to enable us to found, upon chemical principles, the
mineral operations of nature. That siliceous substance may be dissolved,
or rendered soluble in water, by means of alkaline salt, and that it may
be also volatilised by means of the fluor acid, is almost all that we
know upon the subject. But this is saying no more in relation to the
mineral operations employed upon the siliceous substance, than it would
be, in relation to those upon gold, to say that this metal is dissolved
by aqua regia.
It is to be admitted, that every simple substance may have its
menstruum, by means of which it may be retained with water in a
dissolved state; but from this it does not follow, that it is by the
means of aqueous solutions of all those mineral bodies, that nature
operates the consolidation of bodies, which we find actually
accomplished with all those different substances. It is the business of
this work to show, that from all appearances in the mineral regions, as
well as those upon the surface in the atmosphere, the supposition, of
that manner of consolidating bodies by solution, is inconsistent both
with natural appearances, and also with chemical principles.
Our ingenious author, who has, with, great diligence as well as an
enlightened mind, observed the operations of nature upon the surface
of the earth, here says, "ce n'est pas sans etonnement que je remarque
depuis long-temps que jamais aucune eau qui coule a la surface de la
terre n'attaque le quartz, aucune n'en tient en dissolution, pendant que
celles qui circulent interieurement le corrodent aussi souvent qu'elles
le deposent."--How dangerous it is in science for ingenious men to allow
themselves to form conclusions, which the principles on which they
reason do not strictly warrant, we have a remarkable example in the
present case.
M. de Dolomieu sees no corrosion of quartz, or solution of that
substance, upon the surface of the earth; from this, then, he concludes,
that siliceous substance is not dissolved in that situation of things.
On the other hand, he finds siliceous bodies variously concreted among
the solid strata of the earth; and, from this he concludes, that
siliceous substance has been both dissolved by water in the strata, and
also there again concreted and crystallised in having been separated
from the water. This is certainly what we all perceive; but we do not
all allow ourselves to draw such inconclusive inferences from our
premises. Notwithstanding the greatest accuracy of our observations,
quartz may be dissolvable in a minute degree by water, upon the surface
of this earth; and, all the appearances of siliceous bodies, in the
mineral regions, where we cannot immediately see the operation, may be
better explained by fusion than by aqueous solution.
But, from his chemical experiments, our author has conjectured that
there may be a phlogistic substance, by means of which the siliceous
earth is dissolved when in darkness; and that this solvent loses its
power, if exposed to the light of day. I have one observation to oppose
to this ingenious theory. Under deep black mosses, through which no ray
of light can penetrate, every condition for dissolving siliceous bodies
should be found, according to the supposition in question; neither will
sufficient time be found wanting, in those deep mosses, upon the summits
of our mountains; yet, examine the matter of fact? not the smallest
solution is to be perceived in the siliceous parts of the stones which
are found under those mosses, but every particle of iron is dissolved,
so that the surface of every stone is white, and nothing but the
siliceous earth of the feld-spar, and perhaps the argillaceous, is left.
Here we have in this author an instructive example: No person, in my
opinion, has made such enlightened or scientific experiments, or such
judicious observations with regard to the nature of siliceous substance,
as a compound thing; no person reasons more distinctly in general, or
sees more clearly the importance of his principles; yet, with regard to
mineral concretions, how often has he been drawn thus inadvertently
into improper generalization! I appeal to the analogy which, in this
treatise, he has formed, between the stalactical concretions upon
the surface of the earth, and the mineral concretions of siliceous
substance. As an example of the great lights, and penetrating genius, of
this assiduous studier of nature, I refer to the judicious observations
which he has made upon the subject of aluminous earth, in this
dissertation.
I am surprised to find this enlightened naturalist seeking, in the
origin of this globe of our earth, a general principle of fluidity or
solution in water, like the alkahest of the alchymists, by means of
which the different substances in the chemical constitution of precious
stones might have been united as well as crystallised. One would
have thought, that a philosopher, so conversant in the operations of
subterraneous fire, would have perceived, that there is but one general
principle of fluidity or dissolution, and that this is heat.]
Besides this proof for the fusion of siliceous bodies, which is
indirect, arising from the in dissolubility of that substance in water,
there is another, which is more direct, being founded upon appearances
which are plainly inconsistent with any other supposition, except that
of simple fluidity induced by heat. The proof I mean is, the penetration
of many bodies with a flinty substance, which, according to every
collateral circumstance, must have been performed by the flinty matter
in a simply fluid state, and not in a state of dissolution by a solvent.
These are flinty bodies perfectly insulated in strata both of chalk and
sand. It requires but inspection to be convinced. It is not possible
that flinty matter could be conveyed into the middle of those strata, by
a menstruum in which it was dissolved, and thus deposited in that place,
without the smallest trace of deposition in the surrounding parts.
But, besides this argument taken from what does not appear, the actual
form in which those flinty masses are found, demonstrates, _first_,
That they have been introduced among those strata in a fluid state, by
injection from some other place. 2_dly_, That they have been dispersed
in a variety of ways among those strata, then deeply immersed at the
bottom of the sea; and, _lastly_, That they have been there congealed
from the state of fusion, and have remained in that situation, while
those strata have been removed from the bottom of the ocean to the
surface of the present land.
To describe those particular appearances would draw this paper beyond
the bounds of an essay. We must, therefore, refer those who would
inquire more minutely into the subject, to examine the chalk-countries
of France and England, in which the flint is found variously formed; the
land-hills interspersed among those chalk-countries, which have been
also injected by melted flint; and the pudding-stone of England, which
I have not seen in its natural situation. More particularly, I would
recommend an examination of the insulated masses of stone, found in
the sand-hills by the city of Brussels; a stone which is formed by an
injection of flint among sand, similar to that which, in a body of
gravel, had formed the pudding-stone of England[7].
[Note 7: Accurate descriptions of those appearances, with drawings,
would be, to natural history, a valuable acquisition.]
All these examples would require to be examined upon the spot, as a
great part of the proof for the fusion of the flinty substance, arises,
in my opinion, from the form in which those bodies are found, and the
state of the surrounding parts. But there are specimens brought from
many different places, which contain, in themselves, the most evident
marks of this injection of the flinty substance in a fluid state. These
are pieces of fossil wood, penetrated with a siliceous substance, which
are brought from England, Germany, and Lochneagh in Ireland.
It appears from these specimens, that there has sometimes been a prior
penetration of the body of wood, either with irony matter, or calcareous
substance. Sometimes, again, which is the case with that of Lochneagh,
there does not seem to have been any penetration of those two
substances. The injected flint appears to have penetrated the body
of this wood, immersed at the bottom of the sea, under an immense
compression of water. This appears from the wood being penetrated
partially, some parts not being penetrated at all.
Now, in the limits between those two parts, we have the most convincing
proofs, that it had been flint in a simple fluid state which had
penetrated the wood, and not in a state of solution.
_First_, Because, however little of the wood is left unpenetrated, the
division is always distinct between the injected part and that which is
not penetrated by the fluid flint. In this case, the flinty matter has
proceeded a certain length, which is marked, and no farther; and, beyond
this boundary, there is no partial impregnation, nor a gradation of the
flintifying operation, as must have been the case if siliceous matter
had been deposited from a solution. 2_dly_, The termination of the
flinty impregnation has assumed such a form, precisely, as would
naturally happen from a fluid flint penetrating that body.
In other specimens of this mineralising operation, fossil wood,
penetrated, more or less, with ferruginous and calcareous substances,
has been afterwards penetrated with a flinty substance. In this case,
with whatever different substances the woody body shall be supposed
to have been penetrated in a state of solution by water, the regular
structure of the plant would still have remained, with its vacuities,
variously filled with the petrifying substances, separated from the
aqueous menstruum, and deposited in the vascular structure of the wood.
There cannot be a doubt with regard to the truth of this proposition;
for, as it is, we frequently find parts of the consolidated wood, with
the vascular structure remaining perfectly in its natural shape and
situation; but if it had been by aqueous solution that the wood had been
penetrated and consolidated, all the parts of that body would be found
in the same natural shape and situation.
This, however, is far from being the case; for while, in some parts, the
vascular structure is preserved entire, it is also evident, that, in
general, the woody structure is variously broken and dissolved by the
fusion and crystallization of the flint. There are so many and such
various convincing examples of this, that, to attempt to describe them,
would be to exceed the bounds prescribed for this dissertation; but such
specimens are in my possession, ready for the inspection of any person
who may desire to study the subject.
We may now proceed to consider sulphureous substances, with regard to
their solubility in water, and to the part which these bodies have acted
in consolidating the strata of the globe.
The sulphureous substances here meant to be considered, are substances
not soluble in, water, so far as we know, but fusible by heat, and
inflammable or combustible by means of heat and vital air. These
substances are of two kinds; the one more simple, the other more
compound.
The most simple kind is composed of two different substances, viz.
phlogiston, with certain specific substances; from which result, on the
one hand, sulphur, and, on the other, proper coal and metals. The more
compound sort, again, is oily matter, produced by vegetables, and
forming bituminous bodies.
The _first_ of these is found naturally combined with almost all
metallic substances, which are then said to be mineralised with sulphur.
Now, it is well known, that this mineralising operation is performed by
means of heat or fusion; and there is no person skilled in chemistry
that will pretend to say, this may be done by aqueous solution. The
combination of iron and sulphur, for example, may easily be performed by
fusion; but, by aqueous solution, this particular combination is again
resolved, and forms an acido-metallic, that is, a vitriolic substance,
after the phlogiston (by means of which it is insoluble in water) has
been separated from the composition, by the assistance of vital air.
The variety of these sulphureo-metallic substances, in point of
composition, is almost indefinite; but, unless they were all soluble in
water, this could not have happened by the action of that solvent. If we
shall allow any one of those bodies to have been formed by the fluidity
of heat, they must all have been formed in the same manner; for there is
such a chain of connection among those bodies in the mineral regions,
that they must all have been composed, either, on the one hand, by
aqueous solution, or, on the other, by means of heat and fusion.
Here, for example, are crystallised together in one mass, 1_st,
Pyrites_, containing sulphur, iron, copper; 2_dly, Blend_, a composition
of iron, sulphur, and calamine; 3_dly, Galena_, consisting of lead
and sulphur; 4_thly, Marmor metallicum_, being the terra ponderosa,
saturated with the vitriolic acid; a substance insoluble in water;
5_thly, Fluor_, a saturation of calcareous earth, with a peculiar acid,
called the _acid of spar_, also insoluble in water; 6_thly, Calcareous
spar_, of different kinds, being calcareous earth saturated with fixed
air, and something besides, which forms a variety in this substance;
_lastly, Siliceous substance_, or _Quartz crystals_. All these bodies,
each possessing its proper shape, are mixed in such a manner as it would
be endless to describe, but which may be expressed in general by saying,
that they are mutually contained in, and contain each other.
Unless, therefore; every one of these different substances may be
dissolved in water, and crystallised from it, it is in vain to look for
the explanation of these appearances in the operations of nature, by the
means of aqueous solution.
On the other hand, heat being capable of rendering all these substances
fluid, they may be, with the greatest simplicity, transported from one
place to another; and they may be made to concrete altogether at
the same time, and distinctly separate in any place. Hence, for the
explanation of those natural appearances, which are so general, no
further conditions are required, than the supposition of a sufficient
intensity of subterraneous fire or heat, and a sufficient degree of
compression upon those bodies, which are to be subjected to that violent
heat, without calcination or change. But, so far as this supposition is
not gratuitous, the appearances of nature will be thus explained.
I shall only mention one specimen, which must appear most decisive
of the question. It is, I believe, from an Hungarian mine. In this
specimen, petro-silex, pyrites, and cinnabar, are so mixed together, and
crystallised upon each other, that it is impossible to conceive any one
of those bodies to have had its fluidity and concretion from a cause
which had not affected the other two. Now, let those who would deny the
fusion of this siliceous body explain how water could dissolve these
three different bodies, and deposit them in their present shape. If,
on the contrary, they have not the least shadow of reason for such a
gratuitous supposition, the present argument must be admitted in its
full force.
Sulphur and metals are commonly found combined in the mineral regions.
But this rule is not universal; for they are also frequently in a
separate state. There is not, perhaps, a metal, among the great number
which are now discovered, that may not be found native, as they are
called, or in their metallic state.
Metallic substances are also thus found in some proportion to the
disposition of the particular metals, to resist the mineralising
operations, and to their facility of being metallised by fire and
fusion. Gold, which refuses to be mineralised with sulphur, is found
generally in its native state. Iron, again, which is so easily
mineralised and scorified, is seldom found in its malleable state. The
other metals are all found more or less mineralised, though some of them
but rarely in the native state.
Besides being found with circumstances thus corresponding to the natural
facility, or to the impediments attending the metallization of those
different calces, the native metals are also found in such a shape, and
with such marks, as can only agree with the fusion of those bodies;
that is to say, those appearances are perfectly irreconcilable with any
manner of solution and precipitation.
For the truth of this assertion, among a thousand other examples, I
appeal to that famous mass of native iron discovered by Mr Pallas in
Siberia. This mass being so well known to all the mineralists of Europe,
any comment upon its shape and structure will be unnecessary[8].
[Note 8: Since this Dissertation was written, M. de la Peyrouse has
discovered a native manganese. The circumstances of this mineral are so
well adapted for illustrating the present doctrine, and so well related
by M. de la Peyrouse, that I should be wanting to the interest of
mineral knowledge, were I not to give here that part of his Memoir.
"Lorsque je fis inserer dans le journal de physique de l'annee 1780, au
mois de Janvier, une Dissertation contenant la classification des mines
de manganese, je ne connoissois point, a cette epoque, la mine de
manganese native. Elle a la couleur de son regule: Elle salit les doigts
de la meme teinte. Son tissu parait aussi lamelleux, et les lames
semblent affecter une sorte de divergence. Elle a ainsi que lui, l'eclat
metallique; comme lui elle se laisse aplatir sous le marteau, et
s'exfolie si l'on redouble les coups; mais une circonstance qui est trop
frappante pour que je l'omette, c'est la figure de la manganese native,
si prodigieusement conforme a celle du regule, qu'on s'y laisseroit
tromper, si la mine n'etoit encore dans sa gangue: Figure
tres-essentielle a observer ici, parce qu'elle est due a la nature meme
de la manganese. En effet, pour reduire toutes les mines en general, il
faut employer divers flux appropries. Pour la reduction de la manganese,
bien loin d'user de ce moyen, il faut, au contraire, eloigner tout flux,
produire la fusion, par la seule violence et la promptitude du feu. Et
telle est la propension naturelle et prodigieuse de la manganese a la
vitrification, qu'on n'a pu parvenir encore a reduire son regule en un
seul culot; on trouve dans le creuset plusieurs petits boutons, qui
forment autant de culots separes. Dans la mine de manganese native, elle
n'est point en une seule masse; elle est disposee egalement en plusieurs
culots separes, et un peu aplatis, comme ceux que l'art produit;
beaucoup plus gros, a la verite, parce que les agens de la nature
doivent avoir une autre energie, que ceux de nos laboratoires; et cette
ressemblance si exacte, semble devoir vous faire penser que la mine
native a ete produite par le feu, tout comme son regule. La presence
de la chaux argentee de la manganese, me permettroit de croire que la
nature n'a fait que reduire cette chaux. Du reste, cette mine native
est tres-pure, et ne contient aucune partie attirable a l'aimant. Cette
mine, unique jusqu'a ce moment, vient, tout comme les autres manganese
que j'ai decrites, des mines de fer de _Sem_, dans la vallee de
_Viedersos_, en Comte de Foix."--_Journal de Physique, Janvier 1786_.]
We come now to the _second_ species of inflammable bodies called oily or
bituminous. These substances are also found variously mixed with mineral
bodies, as well as forming strata of themselves; they are, therefore, a
proper subject for a particular examination.
In the process of vegetation, there are produced oily and resinous
substances; and, from the collection of these substances at the bottom
of the ocean, there are formed strata, which have afterwards undergone
various degrees of beat, and have been variously changed, in consequence
of the effects of that heat, according as the distillation of the more
volatile parts of those bodies has been suffered to proceed.
In order to understand this, it must be considered, that, while immersed
in water, and under insuperable compression, the vegetable, oily, and
resinous substances, would appear to be unalterable by heat; and it is
only in proportion as certain chemical separations take place, that
these inflammable bodies are changed in their substance by the
application of heat. Now, the most general change of this kind is in
consequence of evaporation, or the distillation of their more volatile
parts, by which oily substances become bituminous, and bituminous
substances become coaly.
There is here a gradation which may be best understood, by comparing the
extremes.
On the one hand, we know by experiment, that oily and bituminous
substances can be melted and partly changed into vapour by heat, and
that they become harder and denser, in proportion as the more volatile
parts have evaporated from them. On the other hand, coaly substances are
destitute of fusibility and volatility, in proportion as they have
been exposed to greater degrees of heat, and to other circumstances
favourable to the dissipation of their more volatile and fluid parts.
If, therefore, in mineral bodies, we find the two extreme states of this
combustible substance, and also the intermediate states, we must either
conclude, that this particular operation of heat has been thus actually
employed in nature, or we must explain those appearances by some other
means, in as satisfactory a manner, and so as shall be consistent with
other appearances.
In this case, it will avail nothing to have recourse to the false
analogy of water dissolving and crystallising salts, which has been so
much employed for the explanation of other mineral appearances. The
operation here in question is of a different nature, and necessarily
requires both the powers of heat and proper conditions for evaporation.
Therefore, in order to decide the point, with regard to what is the
power in nature by which mineral bodies have become solid, we have
but to find bituminous substance in the most complete state of coal,
intimately connected with some other substance, which is more generally
found consolidating the strata, and assisting in the concretion of
mineral substances. But I have in my possession the most undoubted proof
of this kind. It is a mineral vein, or cavity, in which are blended
together coal of the most fixed kind, quartz and marmor metallicum. Nor
is this all; for the specimen now referred to is contained in a rock
of this kind, which every naturalist now-a-days will allow to have
congealed from a fluid state of fusion. I have also similar specimens
from the same place, in which the coal is not of that fixed and
infusible kind which burns without flame or smoke, but is bituminous or
inflammable coal.
We have hitherto been resting the argument upon a single point, for the
sake of simplicity or clearness, not for want of those circumstances
which shall be found to corroborate the theory. The strata of fossil
coal are found in almost every intermediate state, as well as in those
of bitumen and charcoal. Of the one kind is that fossil coal which melts
or becomes fluid upon receiving heat; of the other, is that species of
coal, found both in Wales and Scotland, which is perfectly infusible in
the fire, and burns like coals, without flame or smoke. The one species
abounds in oily matter, the other has been distilled by heat, until it
has become a _caput mortuum_, or perfect coal.
The more volatile parts of these bituminous bodies are found in their
separate state on some occasions. There is a stratum of limestone in
Fifeshire, near Raith, which, though but slightly tinged with a black
colour, contains bituminous matter, like pitch, in many cavities, which
are lined with calcareous spar crystallised. I have a specimen of such
a cavity, in which the bitumen is in sphericles, or rounded drops,
immersed in the calcareous spar.
Now, it is to be observed, that, if the cavity in the solid limestone or
marble, which is lined with calcareous crystals containing pyrites, had
been thus encrusted by means of the filtration of water, this water must
have dissolved calcareous spar, pyrites, and bitumen. But these natural
appearances would not even be explained by this dissolution and supposed
filtration of those substances. There is also required, _first_, A
cause for the separation of those different substances from the aqueous
menstruum in which they had been dissolved; _2dly_, An explanation of
the way in which a dissolved bitumen should be formed into round hard
bodies of the most solid structure; and, _lastly_, Some probable means
for this complicated operation being performed, below the bottom of the
ocean, in the close cavity of a marble stratum.
Thus, the additional proof, from the facts relating to the bituminous
substances, conspiring with that from the phenomena of other bodies,
affords the strongest corroboration of this opinion, that the various
concretions found in the internal parts of strata have not been
occasioned by means of aqueous solution, but by the power of heat and
operation of simple fusion, preparing those different substances to
concrete and crystallise in cooling.
The arguments which have been now employed for proving that strata have
been consolidated by the power of heat, or by the means of fusion, have
been drawn chiefly from the insoluble nature of those consolidating
substances in relation to water, which is the only general menstruum
that can be allowed for the mineral regions. But there are found, in
the mineral kingdom, many solid masses of saltgem, which is a soluble
substance. It may be now inquired, How far these masses, which are not
infrequent in the earth, tend either to confirm the present theory, or,
on the contrary, to give countenance to that which supposes water the
chief instrument in consolidating strata.
The formation of salt at the bottom of the sea, without the assistance
of subterranean fire, is not a thing unsupposable, as at first sight
it might appear. Let us but suppose a rock placed across the gut
of Gibraltar, (a case nowise unnatural), and the bottom of the
Mediterranean would be certainly filled with salt, because the
evaporation from the surface of that sea exceeds the measure of its
supply.
But strata of salt, formed in this manner at the bottom of the sea, are
as far from being consolidated by means of aqueous solution, as a bed of
sand in the same situation; and we cannot explain the consolidation of
such a stratum of salt by means of water, without supposing subterranean
heat employed, to evaporate the brine which would successively occupy
the interstices of the saline crystals. But this, it may be observed, is
equally departing from the natural operation of water, as the means for
consolidating the sediment of the ocean, as if we were to suppose
the same thing done by heat and fusion. For the question is not,
If subterranean heat be of sufficient intensity for the purpose of
consolidating strata by the fusion of their substances; the question is,
Whether it be by means of this agent, subterranean heat, or by water
alone, without the operation of a melting heat, that those materials
have been variously consolidated.
The example now under consideration, consolidated mineral salt, will
serve to throw some light upon the subject; for, as it is to be shown,
that this body of salt had been consolidated by perfect fusion, and
not by means of aqueous solution, the consolidation of strata of
indissoluble substances, by the operation of a melting heat, will meet
with all that confirmation which the consistency of natural appearances
can give.
The salt rock in Cheshire lies in strata of red marl. It is horizontal
in its direction. I do not know its thickness, but it is dug thirty or
forty feet deep. The body of this rock is perfectly solid, and the salt,
in many places, pure, colourless, and transparent, breaking with a
sparry cubical structure. But the greatest part is tinged by the
admixture of the marl, and that in various degrees, from the slightest
tinge of red, to the most perfect opacity. Thus, the rock appears as if
it had been a mass of fluid salt, in which had been floating a quantity
of marly substance, not uniformly mixed, but every where separating and
subsiding from the pure saline substance.
There is also to be observed a certain regularity in this separation of
the tinging from the colourless substance, which, at a proper distance,
gives to the perpendicular section of the rock a distinguishable figure
in its structure. When looking at this appearance near the bottom of
the rock, it, at first, presented me with the figure of regular
stratification; but, upon examining the whole mass of rock, I found,
that it was only towards the bottom that this stratified appearance took
place; and that, at the top of the rock, the most beautiful and regular
figure was to be observed; but a figure the most opposite to that of
stratification. It was all composed of concentric circles; and these
appeared to be the section of a mass, composed altogether of concentric
spheres, like those beautiful systems of configuration which agates so
frequently present us with in miniature. In about eight or ten feet from
the top, the circles growing large, were blended together, and gradually
lost their regular appearance, until, at a greater depth, they again
appeared in resemblance of a stratification.
This regular arrangement of the floating marly substance in the body
of salt, which is that of the structure of a coated pebble, or that
of concentric spheres, is altogether inexplicable upon any other
supposition, than the perfect fluidity or fusion of the salt, and the
attractions and repulsions of the contained substances. It is in vain
to look, in the operations of solution and evaporation, for that which
nothing but perfect fluidity or fusion can explain.
This example of a mineral salt congealed from a melted state, may be
confirmed from another which I have from Dr Black, who suggested it to
me. It is an alkaline salt, found in a mineral state, and described in
the Philosophical Transactions, _anno_ 1771. But to understand this
specimen, something must be premised with regard to the nature of fossil
alkali.
The fossil alkali crystallises from a dissolved state, in combining
itself with a large portion of the water, in the manner of alum; and,
in this case, the water is essential to the constitution of that
transparent crystalline body; for, upon the evaporation of the water,
the transparent salt loses its solidity, and becomes a white powder. If,
instead of being gently dried, the crystalline salt is suddenly exposed
to a sufficient degree of heat, that is, somewhat more than boiling
water, it enters into the state of aqueous fusion, and it boils, in
emitting the water by means of which it had been crystallised in the
cold, and rendered fluid in that heated state. It is not possible to
crystallise this alkaline salt from a dissolved state, without the
combination of that quantity of water, nor to separate that water
without destroying its crystalline state.
But in this mineral specimen, we have a solid crystalline salt, with
a structure which, upon fracture, appears to be sparry and radiated,
something resembling that of zeolite. It contains no water in its
crystallization, but melts in a sufficient heat, without any aqueous
fusion. Therefore, this salt must have been in a fluid state of fusion,
immediately before its congelation and crystallization.
It would be endless to give examples of particular facts, so many are
the different natural appearances that occur, attended with a variety of
different circumstances.
There is one, however, which is peculiarly distinct, admits of
sufficiently accurate description, and contains circumstances from which
conclusions may be drawn with clearness. This is the ironstone, which
is commonly found among the argillaceous strata, attendant upon fossil
coal, both in Scotland and in England.
This stone is generally found among the bituminous schistus, or black
argillaceous strata, either in separate masses of various shapes and
sizes, or forming of itself strata which are more or less continuous in
their direction among the schistous or argillaceous beds.
This mineral contains, in general, from 40 to 50 _per cent._ of iron,
and it loses near one third of its weight in calcination. Before
calcination it is of a grey colour, is not penetrable by water, and
takes a polish. In this state, therefore, it is perfectly solid; but
being calcined, it becomes red, porous, and tender.
The fact to be proved with regard to these iron-stones is this, That
they have acquired their solid state from fusion, and not in concreting
from any aqueous solution.
To abridge this disquisition, no argument is to be taken from contingent
circumstances, (which, however, are often found here as well as in the
case of marbles); such only are to be employed as are general to the
subject, and arise necessarily from the nature of the operation.
It will be proper to describe a species of these stones, which is
remarkably regular in its form. It is that found at Aberlady, in East
Lothian.
The form of these iron-stones is that of an oblate or much compressed
sphere, and the size from two or three inches diameter to more than
a foot. In the circular or horizontal section, they present the most
elegant septarium[9]; and, from the examination of this particular
structure, the following conclusions may be drawn.
_First_, That, the septa have been formed by the uniform contraction
of the internal parts of the stone, the volume of the central parts
diminishing more than that of the circumference; by this means, the
separations of the stone diminish, in a progression from the center
towards the circumference.
_2d_, That there are only two ways in which the septa must have received
the spar or spatthose ore with which they are filled, more or less,
either, _first_ By insinuation into the cavity of the septa after these
were formed; or, _2dly_, By separation from the substance of the stone,
at the same time that the septa were forming.
[Note 9: Plate I.]
Were the first supposition true, appearances would be observable,
showing that the sparry substance had been admitted, either through the
porous structure of the stone, or through proper apertures communicating
from without. Now, if either one or other of these had been the case,
and that the stone had been consolidated from no other cause than
concretion from a dissolved state, that particular structure of the
stone, by means of which the spar had been admitted, must appear at
present upon an accurate examination.
This, however, is not the case, and we may rest the argument here. The
septa reach not the circumference; the surface of the stone is solid and
uniform in every part; and there is not any appearance of the spar in
the argillaceous bed around the stone.
It, therefore, necessarily follows, that the contraction of the
iron-stone, in order to form septa, and the filling of these cavities
with spar, had proceeded _pari passu_; and that this operation must have
been brought about by means of fusion, or by congelation from a state of
simple fluidity and expansion.
It is only further to be observed, that all the arguments which have
been already employed, concerning mineral concretions from a simply
fluid state, or that of fusion, here take place. I have septaria of this
kind, in which, besides pyrites, iron-ore, calcareous spar, and another
that is ferruginous and compound, there is contained siliceous
crystals; a case which is not so common. I have them also attended with
circumstances of concretion and crystallization, which, besides being
extremely rare, are equally curious and interesting.
There is one fact more which is well worth our attention, being one
of those which are so general in the mineral regions. It is the
crystallizations which are found in close cavities of the most solid
bodies.
Nothing is more common than this appearance. Cavities are every where
found closely lined with crystallizations, of every different substance
which may be supposed in those places. These concretions are well known
to naturalists, and form part of the beautiful specimens which
are preserved in the cabinets of collectors, and which the German
mineralists have termed _Drusen_. I shall only particularise one
species, which may be described upon principle, and therefore may be
a proper subject on which to reason, for ascertaining the order of
production in certain bodies. This body, which we are now to examine, is
of the agate species.
We have now been considering the means employed by nature in
consolidating strata which were originally of an open structure; but in
perfectly solid strata we find bodies of agate, which have evidently
been formed in that place where they now are found. This fact, however,
is not still that of which we are now particularly to inquire; for this,
of which we are to treat, concerns only a cavity within this agate; now,
whatever may have been the origin of the agate itself, we are to show,
from what appears within its cavity, that the crystallizations which are
found in this place had arisen from a simply fluid state, and not from
that of any manner of solution.
The agates now in question are those of the coated kind, so frequent in
this country, called pebbles. Many of these are filled with a siliceous
crystallization, which evidently proceeds from the circumference
towards the centre. Many of them, again, are hollow. Those cavities are
variously lined with crystallized substances; and these are the object
of the present examination.
But before describing what is found within, it is necessary to attend to
this particular circumstance, that the cavity is perfectly inclosed with
many solid coats, impervious to air or water, but particularly with
the external cortical part, which is extremely hard, takes the highest
polish, and is of the most perfect solidity, admitting the passage of
nothing but light and heat.
Within these cavities, we find, _1st_, The coat of crystals with which
this cavity is always lined; and this is general to all substances
concreting, in similar circumstances, from a state of fusion; for when
thus at liberty they naturally crystallise. _2dly_, We have frequently
a subsequent crystallization, resting on the first, and more or less
immersed in it. _3dly_, There is also sometimes a third crystallization,
superincumbent on the second, in like manner as the second was on the
first. I shall mention some particulars.
I have one specimen, in which the primary crystals are siliceous, the
secondary thin foliaceous crystals of deep red but transparent iron-ore,
forming elegant figures, that have the form of roses. The tertiary
crystallization is a frosting of small siliceous crystals upon the edges
of the foliaceous crystals.
In other specimens, there is first a lining of colourless siliceous
crystals, then another lining of amethystine crystals, and sometimes
within that, fuliginous crystals. Upon these fuliginous and amethystine
crystals are many sphericles or hemispheres of red compact iron-ore,
like haematites.
In others, again, the primary crystals are siliceous, and the secondary
calcareous. Of this kind, I have one which has, upon the calcareous
crystals, beautiful transparent siliceous crystals, and iron sphericles
both upon all these crystals, and within them.
_Lastly_, I have an agate formed of various red and white coats, and
beautifully figured. The cavity within the coated part of the pebble is
filled up without vacuity, first, with colourless siliceous crystals;
secondly, with fuliginous crystals; and, lastly, with white or
colourless calcareous spar. But between the spar and crystals there are
many sphericles, seemingly of iron, half sunk into each of these two
different substances.
From these facts, I may now be allowed to draw the following
conclusions:
1_st_, That concretion had proceeded from the surface of the agate body
inwards. This necessarily follows from the nature of those figured
bodies, the figures of the external coats always determining the shape
of those within, and never, contrarily, those within affecting those
without.
2_dly_, That when the agate was formed, the cavity then contained every
thing which now is found within it, and nothing more.
3_dly_, That the contained substances must have been in a fluid state,
in order to their crystallizing.
_Lastly_, That as this fluid state had not been the effect of solution
in a menstruum, it must have been fluidity from heat and fusion.
Let us now make one general observation and argument with regard to
the formation of those various coated, concreted, crystallized, and
configured bodies. Were the crystallization and configuration found
to proceed from a central body, and to be directed from that centre
outwards, then, without inquiring into collateral appearances, and other
proofs with regard to the natural concretion of those substances, we
might suppose that these concretions might have proceeded from that
central body gradually by accretion, and that the concreting and
crystallizing substances might have been supplied from a fluid which had
before retained the concreting substance in solution; in like manner as
the crystallizations of sugar, which are formed in the solution of
that saccharine substance, and are termed candies, are formed upon the
threads which are extended in the crystallizing vessel for that purpose.
But if, on the contrary, we are to consider those mineral bodies as
spheres of alternate coats, composed of agate, crystal, spars, etc.; and
if all those crystallizations have their _bases_ upon the uncrystallized
coat which is immediately external to it, and their _apices_ turned
inwards into the next internal solid coat, it is not possible to
conceive that a structure of this kind could have been formed in
any manner from a solution. But this last manner is the way without
exception in which those mineral bodies are found; therefore we are to
conclude, that the concretion of those bodies had proceeded immediately
from a state of fusion or simple fluidity.
In granite these cavities are commonly lined with the crystal
corresponding to the constituent substances of the stone, viz. quartz,
feld-spar, and mica or talk. M. de Saussure, (Voyages dans les Alpes,
tom. ii. sec. 722.), says, "On trouve frequemment des amas considerables
de spath calcaire, crystallise dans les grottes ou se forme le crystal de
roche; quoique ces grottes soient renfermees dans le coeur des montagnes
d'un granit vif, & qu'on ne voie aucun roc calcaire au dessus de ces
montagnes."
So accurate an observer, and so complete a naturalist, must have
observed how the extraneous substance had been introduced into this
cavity, had they not been formed together the cavity and the calcareous
crystals. That M. de Saussure perceived no means for that introduction,
will appear from what immediately follows in that paragraph. "Ces rocs
auroient-ils ete detruits, ou bien ce spath n'est il que le produit
d'une secretion des parties calcaires que l'on fait etres dispersees
entre les divers elemens du granit?"
Had M. de Saussure allowed himself to suppose all those substances in
fusion, of which there cannot be a doubt, he would soon have resolved
both this difficulty, and also that of finding molybdena crystallized
along with feld-spar, in a cavity of this kind. sec. 718.
To this argument, taken from the close cavities in our agates, I am now
to add another demonstration. It is the case of the calcedony agate,
containing a body of calcareous spar; here it is to be shown, that,
while the calcareous body was altogether inclosed within the calcedony
nodular body, these two substances had been perfectly soft, and had
mutually affected each others shape, in concreting from a fluid state.
In order to see this, we are to consider that both those substances have
specific shapes in which they concrete from the third state; the
sparry structure of the one is well known; the spherical or mammelated
crystallization of the calcedony, is no less conspicuous; this last
is, in the present case, spherical figures, which are some of
them hemispheres, or even more. The figures which we have now in
contemplation are so distinctly different as cannot be mistaken; the
one is a rhombic figure bounded by planes; the other is a most perfect
spherical form; and both these are specific figures, belonging
respectively to the crystallization of those two substances.
The argument now to be employed for proving that those two bodies had
concreted from the fluid state of fusion, and not from any manner of
solution, is this: That, were the one of those bodies to be found
impressing the other with its specific figure, we must conclude that the
impressing body had concreted or crystallized while the impressed body
was in a soft or fluid state; and that, if they are both found mutually
impressing and impressed by each other, they must have both been in
the fluid and concreting state together. Now the fact is, that the
calcareous body is perfectly inclosed within the solid calcedony, and
that they are mutually impressed by each others specific figure, the
sparry structure of the calcareous body impressing the calcedony with
its type of planes and angles, at the same time that, in other parts,
the spherical figures of the calcedony enter the solid body of the
spar, and thus impress their mammelated figures into that part which is
contiguous. It is therefore inconceivable, that these appearances
could have been produced in any other manner than by those two bodies
concreting from a simply fluid state.
There are in jaspers and agates many other appearances, from whence the
fusion of those substances may be concluded with great certainty and
precision; but it is hoped, that what has been now given may suffice for
establishing that proposition without any doubt.
It must not be here objected, That there are frequently found siliceous
crystals and amethysts containing water; and that it is impossible
to confine water even in melted glass. It is true, that here, at the
surface of the earth, melted glass cannot, in ordinary circumstances, be
made to receive and inclose condensed water; but let us only suppose a
sufficient degree of compression in the body of melted glass, and we
can easily imagine it to receive and confine water as well as any
other substance. But if, even in our operations, water, by means of
compression, may be made to endure the heat of red hot iron without
being converted into vapour, what may not the power of nature be able to
perform? The place of mineral operations is not on the surface of the
earth; and we are not to limit nature with our imbecility, or estimate
the powers of nature by the measure of our own.[10]
[Note 10: This is so material a principle in the theory of consolidating
the strata of the earth by the fusion of mineral substances, that I beg
the particular attention of the reader to that subject. The effect of
compression upon compound substances, submitted to increased degrees of
heat, is not a matter of supposition, it is an established principle
in natural philosophy. This, like every other physical principle, is
founded upon matter of fact or experience; we find, that many compound
substances may with heat be easily changed, by having their more
volatile parts separated when under a small compression; but these
substances are preserved without change when sufficiently compressed.
Our experiments of this kind are necessarily extremely limited; they
are not, however, for that reason, the less conclusive. The effects of
increasing degrees of heat are certainly prevented by increasing degrees
of compression; but the rate at which the different effects of those
powers proceed, or the measure of those different degrees of increase
that may be made without changing the constitution of the compound
substance, are not known; nor is there any limit to be set to that
operation, so far as we know. Consequently, it is a physical principle,
That the evaporation of volatile substances by heat, or the reparation
of them from a compound substance, consequently the effect of fire in
changing that compound substance, may be absolutely prevented by means
of compression.
It now remains to be considered, how far there is reason to conclude
that there had been sufficient degrees of compression in the mineral
regions, for the purpose of melting the various substances with which we
find strata consolidated, without changing the chemical constitution of
those compound substances.
Had I, in reasoning _a priori_, asserted, That all mineral bodies might
have been melted without change, when under sufficient compression,
there might have arisen, in the minds of reasoning men, some doubt with
regard to the certainty of that proposition, however probable it were to
be esteemed: But when, in reasoning _a posteriori_, it is found that all
mineral bodies have been actually melted, then, all that is required to
establish the proposition on which I have founded my theory, is to
see that there must have been immense degrees of compression upon the
subjects in question; for we neither know the degree of heat which had
been employed, nor that of compression by which the effect of the heat
must have been modified.
Now, in order to see that there had been immense compression, we have
but to consider that the formation of the strata, which are to be
consolidated, was at the bottom of the ocean, and that this place is to
us unfathomable. If it be farther necessary to show that it had been at
such unfathomable depth strata were consolidated, it will be sufficient
to observe, it is not upon the surface of the earth, or above the level
of the sea, that this mineral operation can take place; for, it is there
that those consolidated bodies are redissolved, or necessarily going
into decay, which is the opposite to that operation which we are now
inquiring after; therefore, if they were consolidated in any other place
than at the bottom of the sea, it must have been between that place of
their formation and the surface of the sea; but that is a supposition
which we have not any reason to make; therefore, we must conclude that
it was at the bottom of the ocean those stratified bodies had been
consolidated.]
To conclude this long chemico-mineral disquisition, I have specimens in
which the mixture of calcareous, siliceous, and metallic substances,
in almost every species of concretion which is to be found in mineral
bodies, may be observed, and in which there is exhibited, in miniature,
almost every species of mineral transaction, which, in nature, is found
upon a scale of grandeur and magnificence. They are nodules contained in
the whin-stone, porphyry, or basaltes of the Calton-hill, by Edinburgh;
a body which is to be afterwards examined, when it will be found to have
flowed, and to have been in fusion, by the operation of subterraneous
heat.
This evidence, though most conclusive with regard to the application of
subterraneous heat, as the means employed in bringing into fusion all
the different substances with which strata may be found consolidated, is
not directly a proof that strata had been consolidated by the fusion of
their proper substance. It was necessary to see the general nature of
the evidence, for the universal application of subterraneous heat, in
the fusion of every kind of mineral body. Now, that this has been done,
we may give examples of strata consolidated without the introduction
of foreign matter, merely by the softening or fusion of their own
materials.
Back to Full Books
|