Theory of the Earth, Volume 1 (of 4)
by
James Hutton
Part 5 out of 6
those alpine strata. But then it is also necessary to include in this
character a general hardness and solidity in those vertical strata,
otherwise they would not have been properly alpine, or have resisted the
wearing and washing powers of the globe, so as to have remained higher
than the others; for, the vertical position, or great inclination of
those strata, should rather have disposed them the more to dissolution
and decay. Let us now see how far we shall be justified in that general
conclusion, by the examination of those bodies.
The fact is certain, that those alpine bodies are much harder, or less
subject to dissolution and decay, than the horizontal strata. But this
must be taken in the general, and will by no means apply to particular
cases which might be compared. Nothing, for example, more solid than the
lime-stones, or marbles, and iron-stones; nothing more hard or solid
than the chirt or flint; and all these are found among the horizontal
strata. But, while some strata among those horizontal beds are
thus perfectly solid, others are found with so slight degrees of
consolidation, that we should not be able to ascribe it to the proper
cause, without that gradation of the effect, which leads us to impute
the slightest degree of consolidation to the same operations that have
produced the complete solidity. While, therefore, the most perfect
solidity is found in certain strata, or occasionally among the
horizontal bodies, this forms no part of their character in general, or
cannot be considered as a distinctive mark, as it truly is with
regard to the alpine strata. These last have a general character of
consolidation and indissolubility, which is in a manner universal. We
are, therefore, now to inquire into the cause of this distinction, and
to form some hypothesis that may be tried by the actual state of things,
in being compared with natural appearances.
As the general cause of consolidation among mineral bodies, formed
originally of loose materials, has been found to consist in certain
degrees of fusion or cementation of those materials by means of heat;
and as, in the examination of the horizontal strata we actually
find very different degrees of consolidation in the several strata,
independent of their positions in relation to height or depth, we have
reason to believe that the heat, or consolidating operation, has not
been equally employed in relation to them all.
We are not now inquiring how an inferior stratum should have been heated
in a lesser degree, or not consolidated, while a superior stratum had
been consolidated in the most perfect manner; we are to reason upon a
fact, which is, that the horizontal strata in general appear not to have
been equally or universally consolidated; and this we must attribute to
an insufficient exertion of the consolidating cause. But, so far as the
erecting cause is considered as the same with that by which the elevated
bodies were consolidated, and so far as the vertical situation is a
proof of the great exertion of that subterraneous power, the strata
which are most erected, should in general be found most consolidated.
Nothing more certain than that there have been several repeated
operations of the mineralising power exerted upon the strata
in particular places; and all those mineral operations tend to
consolidation: Therefore, the more the operations have been repeated in
any place, the more we should find the strata consolidated, or changed
from their natural state. Vertical strata have every appearance from
whence we should be led to conclude, that much of the mineral power
had been exerted upon them, in changing their original constitution or
appearance. But the question now to be considered is this, How far
it may appear that these masses of matter, which now seem to be so
different from the ordinary strata of the globe, had been twice
subjected to the mineral operations, in having been first consolidated
and erected into the place of land, and afterwards sunk below the
bottom of the sea, in order a second time to undergo the process of
subterraneous heat, and again be elevated into the place where they now
are found.
It must be evident, here is a question that may not be easy to decide.
It is not to the degree of any change to which bodies may be subject,
that we are to appeal, in order to clear up the point in question,
but to a regular course of operations, which must appear to have been
successively transacted, and by which the different circumstances or
situations of those masses are to be discovered in their present state.
Now, though it does not concern the present theory that this question be
decided, as it is nothing but a repetition of the same operations that
we look for; nevertheless, it would be an interesting fact in the
natural history of this earth; and it would add great lustre to a theory
by which so great, so many operations were to be explained. I am far
from being sanguine in my expectations of giving all the satisfaction
in relation to this subject that I could wish; but it will be proper to
state what I have lately learned with regard to so curious a question,
that others, who shall have the opportunity, may be led to inquire, and
that thus the natural history of the earth may be enlarged, by a proper
investigation of its mineral operations.
With this view I have often considered our schistus mountains, both in
the north and south; but I never found any satisfactory appearance from
whence conclusions could be formed, whether for the question or against
it. The places I examined were those between the alpine countries and
the horizontal strata; here, indeed, I have frequently found a confused
mass, formed of the fragments of those alpine strata mixed with the
materials of the horizontal bodies; but not having seen the proper shape
and connection of those several deposits, I always suspended my judgment
with regard to the particular operations which might have been employed
in producing those appearances.
I had long looked for the immediate junction of the secondary or low
country strata with the alpine schistus, without finding it; the first
place in which I observed it was at the north end of the island of
Arran, at the mouth of Loch Ranza; it was upon the shore, where the
inclined strata appeared bare, being; washed by the sea. It was but a
very small part that I could see; but what appeared was most distinct.
Here the schistus and the sandstone strata both rise inclined at an
angle of about 45 deg.; but these primary and secondary strata were
inclined in almost opposite directions; and thus they met together like
the two sides of a _lambda_, or the rigging of a house, being a little
in disorder at the angle of their junction. From this situation of those
two different masses of strata, it is evidently impossible that either
of them could have been formed originally in that position; therefore, I
could not here learn in what state the schistus strata had been in when
those of the sand-stone, &c, had been superinduced.
Such was the state of my mind, in relation to that subject:, when at
Jedburgh upon a visit to a friend, after I had returned from Arran, and
wrote the history of that journey; I there considered myself as among
the horizontal strata which had first appeared after passing the Tweed,
and before arriving at the Tiviot. The strata there, as in Berwickshire,
which is their continuation to the east, are remarkably horizontal for
Scotland; and they consist of alternated beds of sand-stone and marl, or
argillaceous and micaceous strata. These horizontal strata are traversed
in places with small veins of whin-stone, as well as greater masses
forming rocks and hills of that material; but, except it be these, (of
which there are some curious examples), I thought there could be nothing
more of an interesting nature to observe. Chance, however, discovered to
me what I could not have expected or foreseen.
The river Tweed, below Melrose, discovers in its bed the vertical strata
of the schistus mountains, and though here these indurated bodies are
not veined with quartz as in many places of the mountains, I did not
hesitate to consider them as the same species, that is to say, the marly
materials indurated and consolidated in those operations by which they
had been so much changed in their place and natural position. Afterwards
in travelling south, and seeing the horizontal softer strata, I concluded
that I had got out of the alpine country, and supposed that no more of
the vertical strata were to be observed.
The river Tiviot has made a wide valley as might have been expected, in
running over thole horizontal strata of marly or decaying substances;
and the banks of this river declining gradually are covered with gravel
and soil, and show little of the solid strata of the country. This,
however, is not the case with the Jed, which is to the southward of the
Tiviot; that river, in many places, runs upon the horizontal strata, and
undermines steep banks, which falling shows high and beautiful sections
of the regular horizontal strata. The little rivulets also which fall
into the Jed have hollowed out deep gullies in the land, and show the
uniformity of the horizontal strata.
In this manner I was disposed to look for nothing more than what I had
seen among those mineral bodies, when one day, walking in the beautiful
valley above the town of Jedburgh, I was surprised with the appearance
of vertical strata in the bed of the river, where I was certain that
the banks were composed of horizontal strata. I was soon satisfied with
regard to this phenomenon, and rejoiced at my good fortune in stumbling
upon an object so interesting to the natural history of the earth, and
which I had been long looking for in vain.
Here the vertical strata, similar to those that are in the bed of
the Tweed, appear; and above those vertical strata, are placed the
horizontal beds, which extend along the whole country.
The question which we would wish to have solved is this; if the vertical
strata had been broken and erected under the superincumbent horizontal
strata; or if, after the vertical strata had been broken and erected,
the horizontal strata had been deposited upon the vertical strata,
then forming the bottom of the sea. That strata, which are regular and
horizontal in one place, should be found bended, broken, or disordered
at another, is not uncommon; it is always found more or less in all our
horizontal strata. Now, to what length this disordering operation might
have been carried, among strata under others, without disturbing the
order and continuity of those above, may perhaps be difficult to
determine; but here, in this present case, is the greatest disturbance
of the under strata, and a very great regularity among those above. Here
at least is the most difficult case of this kind to conceive, if we are
to suppose that the upper strata had been deposited before those below
had been broken and erected.
Let us now suppose that the under strata had been disordered at the
bottom of the sea, before the superincumbent bodies were deposited; it
is not to be well conceived, that the vertical strata should in that
case appear to be cut off abruptly, and present their regular edges
immediately under the uniformly deposited substances above. But, in the
case now under consideration, there appears the most uniform section
of the vertical strata, their ends go up regularly to the horizontal
deposited bodies. Now, in whatever state the vertical strata had been in
at the time of this event, we can hardly suppose that they could have
been so perfectly cut off, without any relict being left to trace that
operation. It is much more probable to suppose, that the sea had washed
away the relics of the broken and disordered strata, before those that
are now superincumbent had been begun to be deposited. But we cannot
suppose two such contrary operations in the same place, as that of
carrying away the relics of those broken strata, and the depositing of
sand and subtile earth in such a regular order. We are therefore led
to conclude, that the bottom of the sea, or surface of those erected
strata, had been in very different situations at those two periods, when
the relics of the disordered strata had been carried away, and when the
new materials had been deposited.
If this shall be admitted as a just view of the subject, it will be fair
to suppose, that the disordered strata had been raised more or less
above the surface of the ocean; that, by the effects of either rivers,
winds, or tides, the surface of the vertical strata had been washed
bare; and that this surface had been afterwards sunk below the influence
of those destructive operations, and thus placed in a situation proper
for the opposite effect, the accumulation of matter prepared and put in
motion by the destroying causes.
I will not pretend to say that this has all the evidence that should be
required, in order to constitute a physical truth, or principle from
whence we were to reason farther in our theory; but, as a simple fact,
there is more probability for the thing having happened in that manner
than in any other; and perhaps this is all that may be attained, though
not all that were to be wished on the occasion. Let us now see how
far any confirmation may be obtained from the examination of all the
attending circumstances in those operations.
I have already mentioned, that I had long observed great masses of
_debris_, or an extremely coarse species of pudding-stone, situated on
the south as well as north sides of those schistus mountains, where the
alpine strata terminate in our view, and where I had been looking for
the connection of those with the softer strata of the low country.
It has surely been such appearances as these which have often led
naturalists to see the formation of secondary and tertiary strata formed
by the simple congestion of _debris_ from the mountains, and to suppose
those masses consolidated by the operation of that very element by which
they had been torn off from one place and deposited in another. I never
before had data from whence to reason with regard to the natural history
of those masses of gravel and sand which always appeared to me in an
irregular shape, and not attended with such circumstances as might give
light into their natural history; but now I have found what I think
sufficient to explain those obscure appearances, and which at the same
time will in some respect illustrate or confirm the conjecture which
has now been formed with regard to the operations of the globe in those
regions.
In describing the vertical and horizontal strata of the Jed, no mention
has been made of a certain pudding-stone, which is interposed between
the two, lying immediately upon the one and under the other. This
puddingstone corresponds entirely to that which I had found along
the skirt of the schistus mountains upon the south side, in different
places, almost from one end to the other. It is a confused mass of
stones, gravel, and sand, with red marly earth; these are consolidated
or cemented in a considerable degree, and thus form a stratum extremely
unlike any thing which is to be found either above or below.
When we examine the stones and gravel of which it is composed, these
appear to have belonged to the vertical strata or schistus mountains.
They are in general the hard and solid parts of those indurated
strata, worn and rounded by attrition; particularly sand or marl-stone
consolidated and veined with quartz, and many fragments of quartz, all
rounded by attrition. In this pudding-stone of the Jed, I find also
rounded lumps of porphyry, but have not perceived any of granite.[32]
This however is not the case in the pudding-stone of the schistus
mountains, for, where there is granite in the neighbourhood, there is
also granite in the pudding-stone.
[Note 32: A view of this object is seen in plate 3d. It is from a
drawing taken by Mr Clerk of Eldin.]
From this it will appear, that the schistus mountains or the vertical
strata of indurated bodies had been formed, and had been wasted and worn
in the natural operations of the globe, before the horizontal strata
were begun to be deposited in those places; the gravel formed of those
indurated broken bodies worn round by attrition evince that fact. But
it also appears that the mineral operations of the globe, melting and
consolidating bodies, had been exerted upon those deposited strata above
the vertical bodies.
This appears evidently from the examination of our pudding-stone. The
vertical strata under it are much broken and injected with ferruginous
spar; and this same spar has greatly penetrated the pudding-stone above,
in which are found the various mineral appearances of that spar and iron
ore.
But those injecting operations reach no farther up among the marl strata
in this place; and then would appear to have been confined to the
pudding-stone. But in another place, about half a mile farther up the
river, where a very deep section of the strata is discovered, there
are two injections from below; the one is a thin vein of whin-stone or
basaltes, full of round particles of steatites impregnated with copper;
it is but a few inches wide, and proceeds in a kind of zigzag. The other
appears to have been calcareous spar, but the greatest part of it is now
dissolved out. The strata here descend to the bottom of the river, which
is above the place of the pudding-stone and vertical strata. Neither are
these last discoverable below the town of Jedburgh, at least so far as
I have seen; and the line of division, or plane of junction of the
vertical and horizontal strata, appears to decline more than the bed of
the river.
But it may be asked, how the horizontal strata above, among which are
many very strong beds, have been consolidated. The answer to this
question is plain. Those strata have been indurated or consolidated
in no other manner than the general strata of the earth; these being
actually the common strata of the globe; while the vertical or schistus
strata are the ordinary strata still farther manufactured, (if we may be
allowed the expression) in the vicissitude of things, and by the mineral
operations of the globe. That those operations have been performed by
subterraneous heat has been already proved; but I would now mention some
particular appearances which are common or general to those strata, and
which can only be explained upon that principle.
The red marly earth is prevalent among those strata; and it is with this
red ferruginous substance that many of the sand-stone strata are tinged.
It is plain that there had been an uniform, deposits of that sand and
tinging earth; and that, however different matter might be successively
deposited, yet that each individual stratum should be nearly of the same
colour or appearance, so far as it had been formed uniformly of the same
subsiding matter. But, in the most uniform strata of red sand-stone,
the fracture of the stone presents us with circular spots of a white or
bluish colour; those little spheres are in all respects the same with
the rest of the stone, they only want the tinging matter; and now it may
be inquired how this has come about.
To say that sphericles of white sand should have been formed by
subsiding along with the red sand and earth which composed the uniform
stratum whether of sand-stone or marl, (for it happens equally in both,)
is plainly impossible, according to our notion of that operation in
which there is nothing mysterious. Those foliated strata, which are of
the most uniform nature, must have been gradually accumulated from the
subsiding sand and earth; and the white or colourless places must have
had their colour destroyed in the subsequent cementing operations. It
is often apparent, that the discharging operation had proceeded from a
centre, as some small matter may be perceived in that place. I know not
what species of substance this has been, whether saline or phlogistic,
but it must have had the power of either volatilising or changing the
ferruginous or red tinging substance so as to make it lose its colour.
I have only mentioned spherical spots for distinctness sake; but this
discharging operation is found diversifying those strata in various
ways, but always referable to the same or similar causes. Thus, in many
of the veins or natural cracks of those strata, we find the colour
discharged for a certain space within the strata; and we often see
several of those spots united, each of them having proceeded from its
own centre, and uniting where they approached. In the two veins above
mentioned, of whin-stone and spar traversing the strata, the colour of
the strata is, discharged more or less in the places contiguous with the
veins.
I am now to mention another appearance of a different kind. Those strata
of marl are in general not much consolidated; but among, them there
are sometimes found thin calcareous strata extremely consolidated,
consequently much divided by veins. It is in the solid parts of those
strata, perfectly disconnected from the veins, that there are frequent
cavities curiously lined with crystals of different sorts, generally
calcareous, sometimes containing also those that are siliceous, and
often accompanied with pyrites. I am persuaded that the origin of those
cavities may have been some hollow shells, such as _echini_ or some
marine object; but that calcareous body has been so changed, that it is
not now distinguishable; therefore, at present, I hold this opinion only
as conjecture.
Having, in my return to Edinburgh, traveled up the Tiviot, with a view
to investigate this subject of primary and secondary operations of the
earth, I found the vertical strata, or alpine schistus, in the bed of
the river about two miles below Hawick. This was the third time I had
seen those vertical bodies after leaving the mountains of Lauderdale.
The first place was the bed of the river Tweed, at the new bridge below
Melrose; but here no other covering is to be seen above those vertical
strata besides the soil or traveled earth which conceals every thing
except the rock in the bed of the river. The second place was Jedburgh,
where I found the vertical strata covered with the horizontal sandstone
and marl, as has been now described. The third place was the Tiviot, and
this is that which now remains to be considered.
Seeing the vertical strata in the bed of the river, I was desirous to
know if those were immediately covered with the horizontal strata. This
could not be discovered in the bed of the river where the rock was
covered upon the banks with travelled earth. I therefore left the river,
and followed the course of a brook which comes from the south side. I
had not gone far up the bank, or former boundary of the Tiviot, when
I had the satisfaction to find the vertical strata covered with the
pudding-stone and marly beds as in the valley of the Jed.
It will now be reasonable to suppose that all the schistus which we
perceive, whether in the mountains or in the valleys, exposed to our
view had been once covered with those horizontal strata which are
observed in Berwickshire and Tiviotdale; and that, below all those
horizontal strata in the level country, there is at present a body or
basis of vertical or inclined schistus, on which the horizontal strata
of a secondary order had been deposited. This is the conclusion that I
had formed at Jedburgh, before I had seen the confirmation of it in the
Tiviot; it is the only one that can be formed according to this view of
things; and it must remain in the present state until more evidence be
found by which the probability may be either increased or diminished.
Since writing this, I have read, in the Esprit de Journaux, an abstract
of a memoir of M. Voigt, upon the same subject, which I shall now
transcribe.
"La mer a commence par miner les montagnes primitives dont les debris se
sont precipites au fond. Ces debris forment la premiere couche qui est
posee immediatement sur les montagnes primitives. D'apres l'ancien
langage de mineurs, nous avons jusqu'aujourd'hui appelle cette couche
_le sol mort rouge_, parce qu'il y a beaucoup de rouge dans son melange,
qu'elle forme le sol ou la base d'autres couches, et peut-etre de
toutes, qu'elle est entierement inutile et, en quelque facon, morte pour
l'exploitation des mines. Plusieurs se sont efforces de lui donner un
nom harmonieux; mais ils ne l'ont pu sans occasionner des equivoques.
Les mots _Breche Puddinstone Conglomerations_, &_c_. designent toujours
des substances autres que cette espece de pierre.
"Il est tres agreable de l'examiner dans les endroits ou elle forme des
montagnes entieres. Cette couche est composee d'une quantite prodigieuse
de pierres arrondies, agglutinees ensemble par une substance argileuse
rouge et meme grise, et le toute a acquis assez de durete. On ne trouve
dans sa composition aucune espece de pierre qui, a en juger par les
meilleures observations, puisse avoir ete formee plus tard qu'elle;
on n'y voit par-tout que des parties et des produit des montagnes
primitives principalement de celles qui abondent le plus dans ces
contrees. Le sol mort, par exemple, qui compose les montagnes des
environs de Walbourg, pres d'Eisenach, contient une quantite de gros
morceaux de granit et de schiste micace; c'est vraisemblablement parce
que les montagnes primitives les plus voisines de Rhula, etc. sont,
pour la plus part, formees de ces deux especes de pierres. Pres de
Goldlauter, le sol mort consiste presque tout en porphyre, substance
dont sont formees les montagnes primitives qui y dominent; et le
Kiffauserberg dans la Thuringe a probablement recu ces morceaux arrondis
de schiste argileux des montagnes voisine du Hartz. Vous trouverez
ici que le schiste argileux existoit deja lorsque la mer a jette les
premiers fondemens de nos montagnes stratifiees. Je serois fort etonne
que quelqu'un me montrat un sol mort qui contint un morceaux de gypse,
de marne, de pierre puante et autres. Quoiqu'il en soit il n'est pas
aise d'expliquer pourquoi on ne trouve point de corps marins petrifies
dans cette espece de pierre. C'est peut-etre que, par l'immense quantite
de pierres dures roulees dans le fond de la mer, ils ont ete brises
avant qu'ils aient commence de s'agglutiner ensemble. Mais on rencontre
sur-tout au Kiffhauserberg des troncs d'arbres entiers petrifies; preuve
qu'il y avoit deja ou de la vegetation avant que l'ocean destructeur se
fut empare de ces cantons, ou du moins que quelques isles avoient existe
au-dessus de la surface."
Here we find the same observations in the mountains of Germany that
I have been making with regard to those of Scotland. I have formerly
observed masses of the same kind in the west of England, to the east of
the Severn; but I could not discover any proper connection of that mass
with the regular strata. I have also long observed it in many parts of
Scotland, without being able to attain a sufficiently satisfactory idea
with regard to those particulars by which the alternation of land and
water, of the superficial and internal mineral operations of the globe,
might be investigated.
It will be very remarkable if similar appearances are always found upon
the junction of the alpine with the level countries. Such an appearance,
I am inclined to think, may be found in the Val d'Aoste, near Yvree. M.
de Saussure describes such a stone as having been employed in building
the triumphal arch erected in honour of Augustus. "Cet arc qui etoit
anciennement revetu de marbre, est construit de grands quartiers d'une
espece assez singuliere de poudingue ou de gres a gros grains. C'est une
assemblage de fragmens, presque touts angulaires, de toutes sortes de
roches primitives feuilletees, quartzeuses, micacees; les plus gros de
ces fragmens n'atteignent pas le volume, d'une noisette. La plupart des
edifices antiques de la cite l'Aoste et de ses environs, sont construits
de cette matiere; et les gens du pays sont persuades que c'est une
composition; mais j'en ai trouve des rochers en place dans les montagnes
au nord et au-dessus de la route d'Yvree."
We may now come to this general conclusion, that, in this example of
horizontal and posterior strata placed upon the vertical _schisti_ which
are prior in relation to the former, we obtain a further view into the
natural history of this earth, more than what appears in the simple
succession of one stratum above another. We know, in general, that all
the solid parts of this earth, which come to our view, have either
been formed originally by subsidence at the bottom of the sea, or been
transfused in a melted state from the mineral regions among those solid
bodies; but here we further learn, that the indurated and erected
strata, after being broken and washed by the moving waters, had again
been sunk below the sea, and had served as a bottom or basis on which to
form a new structure of strata; and also, that those new or posterior
strata had been indurated or cemented by the consolidating operations
of the mineral region, and elevated from the bottom of the sea into the
place of land, or considerably above the general surface of the waters.
It is thus that we may investigate particular operations in the general
progress of nature, which has for object to renovate the surface of the
earth necessarily wasted in the operation of a world sustaining plants
and animals.
It is necessary to compare together every thing of this kind which
occurs; it is first necessary to ascertain the fact of their being a
prior and posterior formation of strata, with the mineral operations
for consolidating those bodies formed by collection of the moveable
materials; and, secondly, it is interesting to acquire all the data we
can in order to form a distinct judgment of that progress of nature in
which the solid body of our land is alternately removed from the bottom
of the sea into the atmosphere, and sunk again at the bottom of the sea.
I shall now transcribe what M. Schreiber has wrote in relation to
this subject. It is in a memoir concerning the gold mine of Gardette,
published in the Journal de Physique.
"Avant de quitter la montagne de la Gardette qu'il me soit permis de
rapporter une observation qui peut-etre n'est pas denuee de tout
interet pour les naturalistes; je l'ai faite dans une galerie a environ
cinquante-trois toises a l'ouest du principal puit laquelle a ete
poussee sur la ligne de reunion de la pierre calcaire, et du granit
feuillete ou gneiss pour fonder le filon dans cet endroit. Ce filon
a six pouces d'epaisseur, et consiste en quartz entre-mele d'ochre
martiale, de pyrite cuivreuse et galene. Cette derniere est souvent
recouverte de chaux de plomb grise, et de petits cristaux de mine de
plomb jaune donnant dans l'analyse un indice d'or. Ce filon finit a la
reunion de la pierre calcaire au gneiss. Cette reunion se fait ici dans
la direction d'une heure 6/8 de la boussole de raineur, et sous un
inclinaison, occidentale de 26 degres.
"Mais ce qu'il y a de remarquable, c'est que le gneis ne participe en
rien de la pierre calcaire quoiqu'il n'en soit separe que par une couche
d'une pouce d'epaisseur de terre argileuse et calcaire, tandis que le
rocher calcaire renferme beaucoup de fragmens de granit et de gneis,
dans le voisinage de cette reunion.
"Cette observation prouve incontestablement que le granit et le gneis
avoient deja acquis une durete capable de resister aux infiltration
des parties calcaire, et qu'ils existoient a-peu-pres tels qu'ils sont
aujourd'hui lorsque la pierre calcaire commenca a se former; autrement
elle n'auroit pu saisir et envelopper des morceaux detaches de ces
rochers auxquels on donne avec raison l'epithete de primitif ou de
premiere formation."
M. Schreiber continues his reasoning upon those mineral appearances, in
adducing another argument, which I do not think equally conclusive. He
says, "Le filon de la Gardette devoit pareillement exister avant la
montagne calcaire, car s'il s'etoit forme apres, je ne voit pas la
raison pour laquelle il s'y seroit arrete court, et pourquoi il ne se
seroit pas prolonge dans cette espece de rocher." It is not necessary,
in the formation of a vein, that it should proceed in traversing all the
strata which then are superincumbent; it is reasonable to suppose, and
consistent with observation to find them stop short in proceeding from
one stratum to another. Had M. Schreiber found any pieces of the vein
contained in the calcareous rock, he would have had good reason for
that assertion; but, to conclude that fact from grounds which do not
necessarily imply it, is not to be permitted in sound reasoning, if
certainty is the object, and not mere probability.
SECT. II.--The Theory confirmed from Observations made on purpose to
elucidate the subject.
Having got a distinct view of the primary and secondary mineral bodies
or strata of the globe, and having thus acquired a particular object to
inquire after, with a view to investigate or illustrate this piece of
natural history, I was considering where we might most probably succeed
in finding the junction of the low country strata and alpine schistus.
I inquired of Mr Hall of Whitehall, who had frequent opportunities of
traversing those mountains which lie between his house in the Merse and
Edinburgh; and I particularly entreated him to examine the bed of the
Whittater, which he executed to my satisfaction.
Mr Hall having had occasion to examine the Pease and Tour burns, in
planning and superintending the great improvement of the post road upon
Sir James Hall's estate while Sir James was abroad, he informed me that
the junction of the schistus and sand-stone strata was to be found in
the Tour burn. Professor Playfair and I had been intending a visit to
Sir James Hall at Dunglass; and this was a motive, not so much to hasten
our visit, as to chose the most proper time for a mineral expedition
both upon the hills and along the sea shore.
It was late in the spring 1788 when Sir James left town, and Mr Playfair
and I went to Dunglass about the beginning of June. We had exceeding
favourable weather during the most part of our expedition; and I now
propose to give an account of the result of our observations.
Dunglass burn is the boundary between the counties of East Lothian and
Berwickshire; and it is almost the boundary between the vertical and
horizontal strata. To the north-west of this burn and beautiful dean are
situated the coal, lime-stone, marl, and sand-stone strata; they are
found stretching away along the shore in a very horizontal direction
for some time, but become more and more inclined as they approach the
schistus of which the hills of Lammermuir to the south are composed.
Though the boundary between the two things here in question be easily
perceivable from the nature of the country at the first inspection, by
the rising of the hills, yet this does not lead one precisely to the
junction; and in the extensive common boundary of those two things, the
junction itself is only to be perceived in few places, where the rock is
washed bare by the rivers or the sea, and where this junction is exposed
naked to our view. The sea is here wearing away the coast; and the bank,
about 200 feet high, is gradually falling down, making in some places a
steep declivity, in others a perpendicular cliff. St Abb's Head and Fast
Castle are head lands projecting into the sea, and are the bulwarks of
this shore, which is embayed to the westward, where the sea preys upon
the horizontal strata. The solid strata are every where exposed either
in the cliff or on the shore; we were therefore certain of meeting with
the junction in going from Dunglass to Fast Castle, which is upon the
schistus. But this journey can only be made by sea; and we first set out
to examine the junction in the Tour and Pease burns, where we had been
informed it was to be found.
In the bottom of those rivulets the sand-stone and marly strata appear
pretty much inclined, rising towards the schistus country. The two burns
unite before they come to the shore; and it is about midway between this
junction and the bridges which are thrown over those two hollows, that
the junction is to be found.
The schistus strata here approach towards vertical; and the sand-stone
strata are greatly inclined. But this inclination of those two different
strata are in opposite directions; neither does the horizontal section
of those two different strata run parallel to the junction; that is to
say, the intersection of those two different strata is a line inclined
to the horizon.
At Jedburgh the schistus was vertical, and the strata horizontal; and
there was interposed a compound bed of pudding-stone, formed of various
water-worn bodies, the gravel of the schistus strata, and porphyries.
Here again, though we have not a regular pudding-stone, we have
that which corresponds to it, as having been the effect of similar
circumstances. These are the fracture and detritus of the schistus,
while the strata were deposited upon the broken ends of the schistus at
the bottom of the sea. Most of the fragments of the schistus have their
angles sharp; consequently, they had not travelled far, or been much
worn by attrition. But more or less does not alter the nature of an
operation; and the pudding-stone, which at Jedburgh is interposed
between the vertical schistus and horizontal strata, is here properly
represented by the included fragments of schistus in the inclined
strata.
The line of this junction running, on the one hand, towards Fast Castle
eastward, and, on the other, towards the head of Dunglass burn
westward, our business was to pursue this object in those two different
directions. But it was chiefly in the sea coast that was placed our
expectations, having recollection of the great banks of gravel under
which the strata are buried about Oldhamstocks, near which, from all
appearances, the junction was to be expected.
Having taken boat at Dunglass burn, we set out to explore the coast;
and, we observed the horizontal sand-stone turn up near the Pease burn,
lifting towards the schistus. We found the junction of that schistus
with the red sand-stone and marly strata on the shore and sea bank, at
St. Helens, corresponding in general with what we had observed in the
burns to the westward. But, at Siccar Point, we found a beautiful
picture of this junction washed bare by the sea. The sand-stone strata
are partly washed away, and partly remaining upon the ends of the
vertical schistus; and, in many places, points of the schistus strata
are seen standing up through among the sand-stone, the greatest part of
which is worn away. Behind this again we have a natural section of those
sand-stone strata, containing fragments of the schistus.
After this nothing appears but the schistus rocks, until sand-stone and
marl again are found at Red-heugh above the vertical strata. From that
bay to Fast Castle we had nothing to observe but the schistus, which is
continued without interruption to St Abb's Head. Beyond this, indeed,
there appears to be something above the schistus; and great blocks of a
red whin-stone or basaltes come down from the height and lie upon the
shore; but we could not perceive distinctly how the upper mass is
connected with the vertical schistus which is continued below.
Our attention was now directed to what we could observe with respect
to the schisti, of which we had most beautiful views and most perfect
sections. Here are two objects to be held in view, in making those
observations; the original formation or stratification of the schisti,
and the posterior operations by which the present state of things has
been procured. We had remarkable examples for the illustration of both
those subjects.
With regard to the first, we have every where among the rocks many
surfaces of the erected strata laid bare, in being separated. Here we
found the most distinct marks of strata of sand modified by moving
water. It is no other than that which we every day observe upon the
sands of our own shore, when the sea has ebbed and left them in a waved
figure, which cannot be mistaken. Such figures as these are extremely
common in our sand-stone strata; but this is an object which I never had
distinctly observed in the alpine schisti; although, considering that
the original of those schisti was strata of sand, and formed in water,
there was no reason to doubt of such a thing being found. But here the
examples are so many and so distinct, that it could not fail to give us
great satisfaction.
We were no less gratified in our views with respect to the other object,
the mineral operations by which soft strata, regularly formed in
horizontal planes at the bottom of the sea, had been hardened and
displaced. Fig. 4. represents one of those examples; it was drawn by Sir
James Hall from a perfect section in the perpendicular cliff at Lumesden
burn. Here is not only a fine example of the bendings of the strata, but
also of a horizontal shift or hitch of those erected strata.
St Abb's Head is a promontory which, at a distance, one would naturally
conclude to be composed of the schisti, as is all the shore to that
place; but, as we approached it, there was some difference to be
perceived in the external appearance, it having a more rounded and
irregular aspect. Accordingly, upon our arrival, we found this head-land
composed of a different substance. It is a great mass of red whin-stone,
of a very irregular structure and composition. Some of it is full of
small pebbles of calcareous spar, surrounded with a coat of a coloured
substance, different both from the whin-stone ground and the inclosed
pebble. Here ended our expedition by water.
Having thus found the junction of the sand-stone with the schistus
or alpine strata to run in a line directed from Fast Castle to
Oldhamstocks, or the heads of Dunglass burn, we set out to trace this
burn, not only with a view to observe the junction, if it should there
appear, but particularly to discover the source of many blocks of
whin-stone, of all sizes, with which the bed of this burn abounds.
The sand-stone and coal strata, which are nearly horizontal at the mouth
of this burn, or on the coast, become inclined as we go up the course of
the rivulet; and of this we have fine sections in the bank. The Dean of
Dunglass is formed of precipitous and perpendicular rocks, through which
the running water has worn its way more than a hundred feet deep; above
this Dean the banks are steep and very high, but covered with
soil, which here is a deep gravel. The burn runs all the way up to
Oldhamstocks upon the sand-stone strata; but there, these are traversed
by a high whin-stone dyke, which crosses the burn obliquely, as we found
it on both banks though not in the bed of the burn; it is in the south
bank below the village, and on the north above it. Here is the source
of the whin-stone which we were looking for; it is the common blue
basaltes, of the same nature with the Giant's Causeway, but with no
regular columner appearance.
Above Oldhamstocks we again found the sand-stone in the bank, but it
soon disappeared under a deep cover of gravel, and the burn then divided
into several rivulets which come from the hills. We traced the one which
led most directly up to the mountains, in expectation of meeting with
the schistus, at least, if not the junction of it with the sandstone.
But in this we were disappointed. We did not however lose our labour;
for, though the junction which we pursued be not here visible, we met
with what made it sufficiently evident, and was at the same time an
object far more interesting in our eyes.
I have already quoted Mr Voigt's description of the _sol mort rouge_; he
says, that in places it forms entire mountains; here we have a perfect
example of the same thing; and the moment we saw it, we said, here is
the _sol mort rouge_. We ascended to the top of the mountain through
a gully of solid pudding-stone going into decay, and furnishing the
country below with that great covering of gravel, soil, and water worn
stones. We were now well acquainted with the pudding-stone, which is
interposed between the horizontal and alpine strata; but from what we
had seen to the eastward, we never should have dreamed of meeting with
what we now perceived. What we had hitherto seen of this pudding-stone
was but a few fragments of the schistus in the lower beds of sand-stone;
here a mountain of water-worn schisti, imbedded in a red earth and
consolidated, presented itself to our view. It was evident that the
schisti mountains, from whence those fragments had come, had been prior
to this secondary mass; but here is a secondary mountain equal in height
to the primary, or schisti mountains, at the basis of which we had seen
the strata superinduced on the shore. Still, however, every thing here
is formed upon the same principle, and nothing here is altered except
the scale on which the operation had been performed.
Upon the coast, we have but a specimen of the pudding-stone; most of
the fragments had their angles entire; and few of them are rounded by
attrition. Here, on the contrary, the mountain is one pudding-stone;
and most of the fragments are stones much rounded by attrition. But the
difference is only in degree, and not in kind; the stones are the same,
and the nature of the composition similar. Had we seen the mass of which
this mountain is only a relict, (having been degraded by the hands of
time), we should have found this pudding-stone at the bottom of
our sand-stone strata; could we have penetrated below this mass of
pudding-stone, we should have found our schistus which we left on the
shore at St. Helens and in the Tour burn. In Tiviotdale the vertical
schisti are covered with a bed of pudding-stone, the gravel of which had
been much worn by attrition, but the thickness of that bed is small;
here again the wearing operation has been great, and the quantity of
those materials even more than in proportion to those operations. We
returned perfectly satisfied; and Sir James Hall is to pursue this
subject farther when he shall be in those mountains shooting muir game.
We had now only one object more to pursue; this was to examine the south
side of those mountains of Lammermuir upon the sea shore, in order
to see the junction of the primary schistus with the coal strata
of Berwickshire. Mr Hall was to meet us at the Press, and we were
afterwards to go with him to Whitehall. We met accordingly; but the
weather was rainy; and we went directly to Whitehall. I had often seen
the pudding-stone in great masse; in the banks of the Whiteader, as
it comes out of the mountains, but then I had not seen its connection
neither, on the one hand, with the schisti, nor, on the other, with the
sand-stone strata. We knew that at Lammerton upon the sea coast there
was coal, and consequently the sand-stone strata; and reasoning upon
those data we were sure that our proper course of investigation was to
trace the river Ey to the shore, and then go south the coast in search
of the junction of the schistus with the horizontal strata. This we
executed as well as the weather would permit; but had it to regret,
that the rainy season was not so favourable for our views, as it was
agreeable to the country which had been suffering with the drought.
It is needless now to enlarge upon this subject. I shall only mention
that we found the red marly strata above the pudding-stone in the bed of
the Ey and its branches; we then traced the schistus down the Ey, and
found a mass of the most consolidated pudding-stone upon the coast to
the north of the harbour of Eymouth. But this mass did not rest on the
schistus; it is immediately upon a mass of whin-stone; and the schistus
is in the harbour, so that this whin-stone mass seems to be here
interposed between the pudding-stone and schistus. We then pursued
the coast southwards until we found the junction of the schistus and
sand-stone strata about two miles from Eymouth; but here the junction
was not attended with any pudding-stone that we could perceive.
Having found the same or similar appearances from the one end to the
other, and on both sides of that range of mountains which run from sea
to sea in the south of Scotland, we may now extend our view of this
mineral operation in comprehending every thing of the same kind which we
meet with in our island or any other distant country.
Thus perhaps the pudding-stone of the south of England will be
considered in the same light as having been formed of the _debri_ and
_detritus_ of the flinty bodies.
In the island of Arran, there is also a pudding-stone, even in some
of the summits of the island, exactly upon the border of the schistus
district, as will be described in the natural history of that island.
This pudding-stone is composed of gravel formed of the hardest parts
of the schistus and granite or porphyry mountains. That compound
parasitical stone has been also again cemented by heat and fusion; I
have a specimen in which there is a clear demonstration of that fact.
One of the water-worn stones which had been rounded by attrition, has in
this pudding-stone been broken and shifted, the one half slipping over
the other, three quarters of an inch, besides other smaller slips in
the same stone. But the two pieces are again cemented; or they had been
shifted when the stone was in that soft state, by which the two pieces
are made perfectly to cohere. Those shifts and veins, in this species of
stone, are extremely instructive, illustrating the mineral operations of
the globe.
In like manner to the north of the Grampians, along the south side of
Loch Ness, there are mountains formed of the debris of schistus and
granite mountains, first manufactured into sand and gravel, and then
consolidated into a pudding-stone, which is always formed upon the same
principle. The same is also found upon the south side of those mountains
in the shire of Angus.
I may also give for example the African _Brechia_, which is a
pudding-stone of the same nature. This stone is composed of granites or
porphyries, serpentines and schisti, extremely indurated and perfectly
consolidated. It is also demonstrable from the appearance in this stone
that it has been in a softened state, from the shape and application
of its constituent parts; and in a specimen of it which I have in my
cabinet, there is also a demonstration of calcareous spar flowing among
the gravel of the consolidated rock.
This fact therefore of pudding-stone mountains, is a general fact, so
far as it is founded upon observations that are made in Africa, Germany,
and Britain. We may now reason upon this general fact, in order to see
how far it countenances the idea of primitive mountains, on the one
hand, or on the other supports the present theory, which admits of
nothing primitive in the visible or examinable parts of the earth.
To a person who examines accurately the composition of our mountains,
which occupy the south of Scotland, no argument needs be used to
persuade him that the bodies in question are not primitive; the thing
is evident from inspection, as much as would be the ruins of an ancient
city, although there were no record of its history. The visible
materials, which compose for the most part the strata of our south
alpine schisti, are so distinctly the _debris_ and _detritus_ of a
former earth, and so similar in their nature with those which for the
most part compose the strata on all hands acknowledged as secondary,
that there can remain no question upon that head. The consolidation,
again, of those strata, and the erection of them from their original
position, and from the place in which they had been formed, is another
question.
But the acknowledging strata, which had been formed in the sea of loose
materials, to be consolidated and raised into the place of land, is
plainly giving up the idea of primitive mountains. The only question,
therefore, which remains to be solved, must respect the order of things,
in comparing the alpine schisti with the secondary strata; and this
indeed forms a curious subject of investigation.
It is plain that the schisti had been indurated, elevated, broken, and
worn by attrition in water, before the secondary strata, which form the
most fertile parts of our earth, had existed. It is also certain that
the tops of our schistus mountains had been in the bottom of the sea
at the time when our secondary strata had begun to be formed; for the
pudding-stone on the top of our Lammermuir mountains, as well as the
secondary strata upon the vertical schisti of the Alps and German
mountains, affords the most irrefragable evidence of that fact.
It is further to be affirmed, that this whole mass of water-formed
materials, as well as the basis on which it rested, had been subjected
to the mineral operations of the globe, operations by which the loose
and incoherent materials are consolidated, and that which was the bottom
of the sea made to occupy the station of land, and serve the purpose for
which it is destined in the world. This also will appear evident, when
it is considered that it has been from the appearances in this very
land, independent of those of the alpine schisti, that the present
theory has been established.
By thus admitting a primary and secondary in the formation of our land,
the present theory will be confirmed in all its parts. For, nothing but
those vicissitudes, in which the old is worn and destroyed, and new
land formed to supply its place, can explain that order which is to be
perceived in all the works of nature; or give us any satisfactory
idea with regard to that apparent disorder and confusion, which would
disgrace an agent possessed of wisdom and working with design.
CHAP. VII.
Opinions examined with regard to Petrifaction, or Mineral Concretion.
The ideas of naturalists with regard to petrifaction are so vague and
indistinct, that no proper answer can be given to them. They in general
suppose water to be the solvent of bodies, and the vehicle of petrifying
substances; but they neither say whether water be an universal
menstruum, nor do they show in what manner a solid body has been formed
in the bowels of the earth, from that solution. It may now be proper to
examine this subject, not with a view to explain all those petrifactions
of bodies which is performed in the mineral regions of the earth, those
regions that are inaccessible to man, but to show that what has been
wrote by naturalists, upon this subject, has only a tendency to corrupt
science, by admitting the grossest supposition in place of just
principle or truth, and to darken natural history by introducing an ill
conceived theory in place of matter of fact.
M. le Comte de Buffon has attempted to explain the crystallization
of bodies, or production of mineral forms, by the accretion or
juxtaposition of elementary bodies, which have only form in two
dimensions, length and breadth; that is to say, that mineral concretions
are composed of surfaces alone, and not of bodies. This however is only
an attempt to explain, what we do not understand, by a proposition which
is either evidently contradictory, or plainly inconceivable. It is
true that this eloquent and ingenious author endeavours to correct the
palpable absurdity of the proposition, by representing the constituent
parts of the mineral bodies as "_de lames infiniment minces_;" but who
is it does not see, that these infinitely thin plates are no other than
bodies of three dimensions, contrary to the supposition; for, infinitely
thin, means a certain thickness; but the smallest possible or assignable
thickness differs as much from a perfect superficies as the greatest.
M. de Luc has given us his ideas of petrifaction with sufficient
precision of term and clearness of expression; his opinion, therefore,
deserves to be examined; and, as his theory of petrifaction is equally
applicable to every species of substance, it is necessary again to
examine this subject, notwithstanding of what has been already said,
in the first part of this work, concerning consolidation and mineral
concretion from the fluid state of fusion.
This author has perhaps properly exposed Woodward's Theory of
Petrification in saying[33], "Son erreur a cet egard vient de ce qu'il
n'a point reflechi sur la maniere dont se fait la _petrifaction_. Il
ramollit d'abord les _pierres_ pour y faire entrer les coquilles, sans
bien connoitre l'agent qu'il y employe; et il les duroit ensuite, sans
reflechir au comment." To avoid this error or defect, M. de Luc, in his
Theory of Petrifaction, sets out with the acknowledged principle of
cohesion; and, in order to consolidate strata of a porous texture, he
supposes water carrying minute bodies of all shapes and sizes, and
depositing them in such close contact as to produce solidity and
concretion. Now, if Dr Woodward softened stones without a proper
cause, M. de Luc, in employing the specious principle of cohesion, has
consolidated them upon no better grounds; for, the application of this
principle is as foreign to his purpose, as is that of magnetism. Bodies,
it is true, cohere when their surfaces are closely applied to each
other; But how apply this principle to consolidation?--only by supposing
all the separate bodies, of which the solid is to be composed, to be
in perfect contact in all their surfaces. But this, in other words,
is supposing the body to be solid; and, to suppose the agent, water,
capable of thus making hard bodies solid, is no other than having
recourse to the fortuitous concourse of atoms to make a world; a thought
which this author would surely hold in great contempt.
[Note 33: Lettres Physiques et Morales.]
He then illustrates this operation of nature by those of art, in
building walls which certainly become hard, and which, as our author
seems to think, become solid. But this is only an imperfect or erroneous
representation of this subject; for, mortar does not become hard upon
the principle of petrification adopted by our author. Mortar, made of
clay, instead of lime, will not acquire a stony hardness, nor ever, by
means of water, will it be more indurated than by simply drying; neither
will the most subtile powder of chalk, with water and sand, form any
solid body, or a proper mortar. The induration of mortar arises from the
solution of a stony substance, and the subsequent concretion of that
dissolved matter, operations purely chemical. Now, if this philosopher,
in his Theory of Petrifaction, means only to explain a chemical
operation upon mechanical principles, why have recourse, for an example
in this subject, to mineral bodies, the origin of which is questioned?
Why does he not rather explain, upon this principle, the known
concretion of some body, from a fluid state, or, conversely, the
known solution of some concreted body? If again he means to explain
petrifaction in the usual way, by a chemical operation, in that case,
the application of his polished surfaces, so as to cohere, cannot take
place until the dissolved body be separated from the fluid, by means of
which it is transported from place to place in the mineral regions. But
it is in this preliminary step that lies all the difficulty; for, could
we see how every different substance might be dissolved, and every
dissolved substance separated from its solvent at our pleasure, we
should find no difficulty in admitting the cohesion of hard bodies,
whether by means of this doctrine of polished surfaces, or by the
principle of general attraction, a principle which surely comprehends
this particular, termed a cohesive power.
It must not be alleged, that seeing we know not how water dissolves
saline bodies, therefore, this fluid, for any thing that we know, may
also dissolve crystal; and, if water thus dissolves a mineral substance
in a manner unknown to us, it may in like manner deposit it, although
we may not be able to imagine how. This kind of reasoning is only
calculated to keep us in ignorance; at the same time, the reasoning of
philosophers, concerning petrifaction, does not in general appear to be
founded on any principle that is more sound. That water dissolves salt
is a fact. That water dissolves crystal is not a fact; therefore, those
two propositions, with regard to the power of water, are infinitely
removed, and cannot be assimilated in sound physical reasoning. It is
no more a truth that water is able to dissolve salt, than that we never
have been able to detect the smallest disposition in water to dissolve
crystal, flint, quartz, or metals. Therefore, to allege the possibility
of water being capable of dissolving those bodies in the mineral
regions, and of thus changing the substance of one body into another, as
naturalists have supposed, contrary to their knowledge, or in order to
explain appearances, is so far from tending to increase our science,
that it is abandoning the human intellect to be bewildered in an error;
it is the vain attempt of lulling to sleep the scientific conscience,
and making the soul of man insensible to the natural distress of
conscious ignorance.
But besides that negative argument concerning the insolubility of
crystal, by which the erroneous suppositions of naturalists are to
be rejected, crystal in general is found regularly concreted in the
cavities of the most solid rock, in the heart of the closest agate, and
in the midst of granite mountains. But these masses of granite were
formed by fusion; I hope that I shall give the most satisfactory proof
of that truth: Consequently, here at least there is no occasion for the
action of water in dissolving siliceous substances in one place, in
order to concrete and crystallise it in another.
In these cavities of the solid granite rock, where crystal is found
regularly shooting from a basis which is the internal surface of the
cavity, we find the other constituent substances of the granite also
crystallised. I have those small cavities, in this rock, from the island
of Arran, containing crystal, felt-spar, and mica, all crystallised in
the same cavity[34]. But this is nothing to the _druzen_ or crystalline
concretions, which are found in a similar manner among metallic and
mineral substances in the veins and mines; there, every species of
mineral and metallic substance, with every variety of mixture and
composition, are found both concreted and crystallised together in every
imaginable shape and situation.
[Note 34: The Chevalier Dolomieu makes the following observation.
Journal de Physique, Juillet 1791.
"J'ai ete etonne de trouver au centre d'un enorme massif de granit, que
l'on avoit ouvert avec la poudre pour pratiquer un chemin, des
morceaux, gros comme le poing et au dessous, de spath calcaire blanc,
tres-effervescent, en grandes ecailles, ou lames entrecroisees. Il
n'occupoit point des cavites particulieres, il n'y paroissoit le
produit d'une infiltration qui auroit rempli des cavites, mais il etoit
incorpore avec les feld-spath, le mica, et le quartz, faissoit masse
avec eux, et ne pouvoit se rompre sans les entrainer avec lui."
This great naturalist is convinced that the spar had not been here
introduced by infiltration, although that is the very method which he
employs to form concretions, not only of spar but of crystal, zeolite,
and pyrites, in the closest cavities of the most solid rocks of
basaltes. These four substances in this stone were so mixed together
that nothing but the fusion of the whole mass could explain the state in
which they appeared; but, thinking that such a supposition could not
be allowed, this naturalist, like a man of science when his data fail,
leaves the matter without any interpretation of his own. This however is
what he has not done in the case of basaltes, or that which he mistakes
for proper lavas, as I shall have occasion to show.]
Here is an infinite operation, but an operation which is easily
performed by the natural arrangement of substances acting freely in
a fluid state, and concreting together, each substance, whether more
simple or more compound, directing itself by its internal principle of
attraction, and affecting mechanically those that are concreting around
it.
We see the very same thing happen under our eye, and precisely in the
same manner. When a fluid mass of any mineral or metallic substance is
made to congeal by sudden cooling on the outside, while the mass within
is fluid, a cavity is thus sometimes formed by the contraction of the
contained fluid; and in this cavity are found artificial _druzen_, as
they may be called, being crystallizations similar to those which the
mineral cavities exhibit in such beauty and perfection.
Petrification and consolidation, in some degree, may doubtless be
performed, in certain circumstances, by means of the solution of
calcareous earth; but the examples given by M. de Luc, of those bodies
of lime-stone and agate petrified in the middle of strata of loose or
sandy materials, are certainly inexplicable upon any other principle
except the fusion of those substances with which the bodies are
petrified[35].
[Note 35: Vid. Lettre 28 et Lettre 103. Lettres Physiques et Morales.]
This subject deserves the strictest attention; I propose it as a
touchstone for every theory of petrification or perfect consolidation.
First, There are found, among argillaceous strata, insulated bodies of
iron-stone, perfectly consolidated; secondly, There are found, in strata
of chalk and lime-stone, masses of insulated flints; thirdly, There
are found, in strata of sea sand, masses of that sand cemented by a
siliceous substance; fourthly, In the midst of blocks of sand-stone,
there are found masses of loose or pure sand inclosed in crystallised
cavities; and in this sand are found insulated masses of crystallised
spar, including within them the sand, but without having the sparry
or calcareous crystallization disturbed by it. There are also other
globular masses of the same kind, where the sparry crystallization is
either not to be observed, or appears only partially[36]: And now,
lastly, In strata of shell-sand, there are found masses of consolidated
lime-stone or marble. In all those cases, the consolidated bodies are
perfectly insulated in the middle of strata, in which they must of
necessity have been petrified or consolidated; the stratum around the
bodies has not been affected by the petrifying substance, as there
is not any vestige of it there; and here are examples of different
substances, all conspiring to prove one uniform truth. Therefore, a
general theory of petrification or consolidation of mineral bodies must
explain this distinct fact, and not suffer it any longer to remain a
_lusus naturae_.
[Note 36: Mem. de l'Academie Royale des Sciences, an. 1775.]
Let us now consider what it is that we have to explain, upon the
supposition of those concretions being formed from a solution. We have,
first, To understand what sort of a solution had been employed for the
introducing of those various substances; secondly, How those concretions
had been formed from such solutions within those bodies of strata; and,
lastly, How such concretions could have been formed, without any vestige
appearing of the same substance, or of the same operation, in the
surrounding part of the stratum. Whatever may be the difficulty
of explaining those particular appearances by means of fusion and
mechanical force, it is plainly impossible to conceive those bodies
formed in those places by infiltration, or any manner of concretion from
a state of solution.
Naturalists, in explaining the formation of stones, often use a chemical
language which either has no proper meaning, or which will not apply to
the subject of mineral operations. We know the chemical process by which
one or two stony concretions may be formed among bodies passing from
one state to another. When, therefore, a change from a former state of
things in mineral bodies is judged by naturalists to have happened, the
present state is commonly explained, or the change is supposed to have
been made by means of a similar process, without inquiring if this had
truly been the case or not. Thus their knowledge of chemistry has led
naturalists to reason erroneously, in explaining things upon false
principles. It would be needless to give an example of any one
particular author in this respect; for, so far as I have seen, it
appears to be almost general, every one copying the language of another,
and no one understanding that language which has been employed.
These naturalists suppose every thing done by means of solution in the
mineral kingdom, and yet they are ignorant of those solvents. They
conceive or they imagine concretions and crystallizations to be formed
of every different substance, and in every place within the solid body
of the earth, without considering how far the thing is possible which
they suppose. They are constantly talking of operations which could only
take place in the cavities of the earth above the level of the sea, and
where the influence of the atmosphere were felt; and yet this is the
very place which we have it in our power to examine, and where, besides
the stalactite, and one or two more of the same kind, or formed on the
same principle, they have never been able to discover one of the many
which, according to their theory, ought always to be in action or
effect. So far from knowing that general consolidating operation, which
they suppose to be exerted in filling up the veins and cavities of the
earth by means of the infiltrating water of the surface, they do not
seem fully to understand the only operation of this kind which they see.
The concretion of calcareous matter upon the surface of the earth is
perhaps the only example upon which their theory is founded; and
yet nothing can be more against it than the general history of this
transaction.
Calcareous matter, the great _vinculum_ of many mineral bodies, is in
a perpetual state of dissolution and decay, in every place where the
influences of air and water may pervade. The general tendency of this
is to dissolve calcareous matter out of the earth, and deliver that
solution into the sea. Were it possible to deny that truth, the
very formation of stalactite, that operation which has bewildered
naturalists, would prove it; for it is upon the general solubility of
calcareous matter exposed to water that those cavities are formed, in
which may be found such collections of stalactical concretion; and the
general tendency of those operations is to waste the calcareous bodies
through which water percolates. But how is the general petrifaction or
consolidation of strata, below the surface of the sea, to be explained
by the general dissolution of that consolidating substance in the
earth above that level? Instead of finding a general petrifying or
consolidating operation in the part of the earth which we are able to
examine, we find the contrary operation, so far at least as relates to
calcareous spar, and many other mineral bodies which are decomposed and
dissolved upon the surface of the earth.
Thus in the surface of the earth, above the level of the sea, no
petrifying operation of a durable nature is found; and, were such an
operation there found, it could not be general, as affecting every kind
of substance. But, even suppose that such a general operation were found
to take place in the earth above the level of the sea, where there might
be a circulation of air and percolation of water, How could the strata
of the earth below the level of the sea be petrified? This is a question
that does not seem to have entered into the heads of our naturalists
who attempt to explain petrifaction or mineral concretion from aqueous
solutions. But the consolidation of loose and incoherent things,
gathered together at the bottom of the sea, and afterwards raised
into rocks of various sorts, forms by far the greatest example of
petrification or mineral operation of this globe. It is this that must
be explained in a mineral theory; and it is this great process of
petrifaction to which the doctrine of infiltration, whether for the
mechanical purpose of applying cohesive surfaces, or the chemical one of
forming crystallizations and concretions, will not by any means apply.
Nothing shows more how little true science has been employed for the
explanation of phenomena, than the language of modern naturalists, who
attribute, to stalactical and stalagmical operations, every superficial
or distant resemblance to those calcareous bodies, the origin of which
we know so well. It is not a mere resemblance that should homologate
different things; there should be a specific character in every thing
that is to be generalised. It will be our business to show that, in the
false stalactites, there is not the distinctive character of those water
formed bodies to be found.
In the formation of stalactical concretions, besides the incrustation as
well as crystallization of the stony substance from the aqueous vehicle
by which it had been carried in the dissolved state, we have the other
necessary accompanyments of the operation, or collateral circumstances
of the case. Such, for example, is that tubular construction of the
stalactite, first formed by the concretion of the calcareous substance
upon the outside of the pendant gut of water exposed to the evaporation
of the atmosphere; we then see the gradual filling up of that pervious
tube through which the petrifying water had passed for a certain time;
and, lastly, we see the continual accretion which this conducting body
had received from the water running successively over every part of
it. But among the infinite number of siliceous concretions and
crystallizations, as well as those of an almost indefinite variety of
other substances, all of which are attributed to solution, there is not
the least vestige of any collateral operation, by which the nature of
that concretion might be ascertained in the same manner. In all
those cases, we see nothing but the concreted substances or their
crystallizations; but, no mark of any solvent or incrusting process is
to be perceived. On the contrary, almost all, or the greatest part
of them, are so situated, and attended with such circumstances, as
demonstrate the physical impossibility of that being the manner in which
they had been concreted; for, they are situated within close cavities,
through which nothing can pervade but heat, electricity, magnetism,
etc.; and they fill those cavities more or less, from the thinnest
incrustation of crystals to the full content of those cavities with
various substances, all regularly concreted or crystallised according to
an order which cannot apply to the concretion of any manner of solution.
That there is, in the mineral system, an operation of water which may
with great propriety be termed _infiltration_, I make no doubt. But this
operation of water, that may be employed in consolidating the strata
in the mineral regions, is essentially different from that which is
inconsiderately employed or supposed by mineralists when they talk
of infiltration; these two operations have nothing in common except
employing the water of the surface of the earth to percolate a porous
body. Now, the percolation of water may increase the porousness of that
body which it pervades, but never can thus change it from a porous to a
perfect solid body. But even the percolation of water through the strata
deposited at the bottom of the sea, necessarily required, according to
the supposition of naturalists, must be refused; for, the interstices of
those strata are, from the supposition of the case, already filled with
water; consequently, without first removing that stagnant water, it is
in vain to propose the infiltration of any fluid from the surface.
This is a difficulty which does not occur in our theory, where the
strata, deposited at the bottom of the sea, are to be afterwards heated
by the internal fires of the earth. The natural consequence of those
heating operations may be considered as the converting of the water
contained in the strata into steam, and the expulsion of steam or
vapour, by raising it up against the power of gravity, to be delivered
upon the surface of the earth and again condensed to the state of water.
Let us now conceive the strata, which had been deposited at the bottom
of the sea, as exhausted of their water, and as communicating with the
surface of the earth impregnated with water. Here again we have the
power of gravity to operate in carrying down water to that place which
had been before exhausted by the power of heat; and in this manner, by
alternately employing those two great physical agents, we cannot doubt
that nature may convey soluble substances from above, and deposit them
below for the purpose of consolidating porous bodies, or of filling with
saline and earthy matter those interstices which had been originally
filled with water, when the strata were deposited at the bottom of the
sea. How far any marks of this operation may be perceived, by carefully
examining our mines and minerals, I know not; I can only say that, on
the contrary, whenever those examined objects were clear and distinct,
with the concomitant circumstances, so as to be understood, I have
always found the most certain marks of the solid bodies having concreted
from the fluid state of fusion. This, however, does not exclude the case
of infiltration having been previously employed; and I would intreat
mineralists, who have the opportunity of examining the solid parts of
the earth, to attend particularly to this distinction. But do not let
them suppose that infiltration can be made to fill either the pores or
veins of strata without the operation of mineral heat, or some such
process by which the aqueous vehicle may be discharged.
Not only are mineral philosophers so inconsiderate, in forming
geological theories upon a mere supposition or false analogy, they
have even proceeded, upon that erroneous theory, to form a geological
supposition for explaining the appearances of strata and other stony
masses in employing a particular physical operation, which is, that
of _crystallization_[37]. Now crystallization may be considered as a
species of elective concretion, by which every particular substance, in
passing from a fluid to a solid state, may assume a certain peculiar
external shape and internal arrangement of its parts, by which it is
often distinguished. But, to suppose the solid mineral structure of the
earth explained, like an enigma, by the word _crystallization_, is to
misunderstand the science by which we would explain the subject of
research; and, to form a general mineral theory thus upon that term,
is an attempt to generalise without a reason. For, when it were even
admitted that every solid body is crystallised, we thus know no more of
the geology of this earth, or understand as little of the general theory
of mineral concretion, as we did before;--we cannot, from that, say
whether it be by the operation of solution or of fusion which had
produced the perceived effect.
[Note 37: Journal de Physique; Avril 1753.]
M. de Carosi has wrote a treatise upon certain petrifactions[38]. In the
doctrine of this treatise there is something new or extraordinary. It
will therefore be proper to make some observations on it.
[Note 38: Sur la Generation du Silex et du Quartz en partie.
Observations faites en Pologne 1783, a Cracovie.]
The object of this treatise is to describe the generation of silex and
quartz, with their modifications or compositions, formed within mineral
bodies of a different substance. The natural history contained in this
little treatise is well described and sufficiently interesting. But It
is chiefly in order to examine the means which, according to the theory
of this treatise, are employed in petrifying bodies, that I consider it
in this place.
The first section of this treatise has for title, _Generation du Caillou
et du Quartz de la terre calcaire pure_. It may be worth while to
compare the natural history of this part of the earth with the flint and
chert found in our chalk and lime-stone countries. I shall therefore
transcribe what is worth observing upon that subject (p. 5.).
"Nous rencontrons chez nous dans les parties le plus montagneuses, et
les moins couvertes de terreau, ou tout-au plus de sable, entre de purs
rochers calcaires une quantite incroyable de cailloux (silex) tant en
boules, que veines, couches, et debris. Au premier coup d'oeil l'on
s'imagine que ce font des debris de montagnes eloignees, qui y furent
amenes par les eaux, mais, en examinant la chose de plus pres, on est
convaincu, que ce sont tout au contraire, des parties detachees des
montagnes de la contree. Car il y a sur presque toute l'etendue de nos
montagnes calcaires une couche, ou pour mieux dire, un banc compose
de plusieurs couches de base calcaire, mais qui ou sont parsemees
irregulierement de boules, de rognons, de veines, et de petits filons
de silex, ou qui contiennent cette pierre en filon, veines, et couches
paralleles, et regulierement disposees. Les boules et rognons de silex
y font depuis moins de la grandeur d'une petite noisette, jusqu'au
diametre de plus de six pouces de notre mesure. La plupart de ces boules
tant qu'elles sont dans l'interieur cache de la roche vive, et qu'elles
n'ont rien souffert de l'impression de l'air, ont, pour l'ordinaire, une
croute de spath calcaire, au moyen de la quelle elles sont accrues a
la roche mere; ou pour mieux dire la croute spatheuse fait l'intermede
entre le silex, et la roche calcaire, par ou se fait le passage de l'une
a l'autre. Mais ceci ne vaut que de boules de silex entierement formees.
C'est dont on peut meme se convaincre a la vue, par beaucoup de pierres
dont le pave de la ville de Cracovie est compose. Mais la, ou le silex
n'est pas encore entierement acheve, la croute spatheuse manque, en
revanche on y voit evidemment le passage par degres successifs de la
roche calcaire au silex qui y est contenu, et les nuances de ce passage
sont souvent si peu marquees que meme les acides mineraux ne suffisent
pas a les determiner, ce n'est que le briquet, qui nous aide a les
decouvrir. On voit bien ou la pierre calcaire s'enfonce en couleur, l'on
s'appercoit, ou sa durete, ses cassures changent, mais, comme elle y
souffre encore quelque impression des acides, l'on ne sauroit determiner
au juste le point, ou elle a deja plus de la nature du silex, que de
celle de la chaux, qu'en la frappant du briquet.
"Tels sont les cailloux en boules et rognons avant leur etat de
perfection, il y aura meme au milieu une partie de pierre calcaire non
changee.
"Ceux au contraire, ou la nature a acheve son ouvrage, ont une croute de
chaux endurcie, et sont purement du silex fini, mais de toutes couleurs,
d'un grain et d'une texture plus ou moins fine, qui passe assez souvent
par degres dans les differentes varietes du noble silex. Ils ont, pour
l'ordinaire, dans leur interieur une cavite, mais pas toujours au
centre, et qui vient apparemment de la consommation de cette partie
calcaire qui y resta la derniere, et n'en fut changee ou dissolute et
separee, que lorsque le reste du silex etoit deja entierement fini. Ces
cavites sont toujours, ou enduites de calcedoine en couche concentriques
recouverte de petits cristaux fort brillans et durs de quartz, ou bien
seulement de ces derniers-ci. Par-fois il y a aussi du spath calcaire
crystallise, mais cela est extremement rare. Quelque-fois enfin ces
cavites sont remplies d'une noix de calcedoine. Je n'ai reussi qu'une
seule fois en cassant un pareil silex en boule d'y trouver encore le
reste de l'eau de crystallisation."
The only remark that I would here make is this, that, if the
crystallization of those close cavities in the _silex_ had at any time
required water of solution, it must always have required it. But, if
there had been water of solution contained in those close cavities, for
the crystallization of the various things which are often found within
them, How comes it that this water is almost never found? I have good
reason to believe that water contained within a solid flint will not
make its escape, as does that contained in the _anhydrites_ of Mount
_Berico_, which are composed of a porous calcedony. But the siliceous
crystallizations within close cavities is a curious subject, which we
shall have occasion to examine more particularly in treating of agates.
We now proceed to the next section, which is the generation of silex and
quartz in marl, (p. 19.)
"Il y a des contrees, chez nous, qui out des etendus assez considerables
en long et en large, de montagnes de pierre de marne calcaire, dans
lesquelles on rencontre le meme phenomene que dans celles de chaux pure;
c. a. d. nous y trouvons du silex de differentes varietes, et dans tous
les degres successifs de leur formation, et de leur perfection. Outre
cela, nous y voyons encore quelque chose, qui semble nous conduire a
la decouverte des moyens, dont se sort la nature pour effecteur cette
operation, et qui nous etoit cache dans les montagnes de chaux pure: ces
bancs de pierre marnesilicieuse, contiennent une partie considerable de
pyrites sulfureuses, qui non seulement y forment une grande quantite
de petits sillons, mais toute la masse de la montagne est rempli de
parcelles souvent presqu'imperceptibles de ce mineral. Ces pyrites sont
evidemment des productions du phlogistique et de l'acide contenu dans la
montagne.
"L'eau, qui s'y trouve ordinairement en assez grande abondance, en
detacha, extraha d'un et l'autre, et les combina apres tous les deux
ensemble. Cette meme eau les dissout derechef, et en fait de nouvelles
combinaisons. C'est ce qu'on voit evidemment la, ou la nature, ayant
commence ses operations, il n'y est reste de la pyrite, qu'une portion
de la partie inflammable liee a une base terrestre. Dans ces endroits
la marne n'est que fort peu sensible aux acides, et de blanche qu'elle
etoit, sa couleur est devenue presque noire. C'est la qu'on observe les
differens degres du changement de la marne en silex, contenant, meme
encore, par fois, de parties pyriteiques non detruites dans son
interieur. Et comme la nature forme ici, de meme, que dans la chaux pure
les silex, la plupart en boules ou rognons; comme les different degres
de metamorphoses de la marne en silex, sont ici beaucoup plus nombreuses
que la, de sorte qu'il y a des bandes entieres, qui meriteroient plutot
d'etre appelles bandes silicieuses, que marneuses; comme il y a, enfin,
une grande quantite de pyrites, qu'ailleurs, il est tres probable
qu'elle se serve la du meme moyen qu'ici pour operer la metamorphose en
question.
"Ne nous precipitons, cependant, pas a en tirer plus de consequences;
poursuivons plutot le fil de notre recit.
"Le silex, qui se trouve ici, est non seulement de differents degres de
perfection, il est de plus d'une espece. Il y a de la pierre a feu, 2 de
la calcedoine, 3 des agathes, et 4 differentes nuances et passages des
especes ordinaires aux fines du silex.
"La pierre a feu, est, ordinairement dans son etat de perfection d'un
grain assez fin, d'une couleur grise plus ou moins foncee, et meme
donnant, dans le noiratre, plus ou moins diaphane; ses cassures sont
concentriques ou coquillees, et sa masse est assez compacte. Outre sa
conformation ordinaire en boules et rognons, elle fait presque toujours
la noix de ursins marins, qui y font en grand nombre, et dont la
coquille est le plus souvent, et presque toujours de spath calcaire,
meme au milieu d'une boule de silex parfait.
"Les calcedoines et agathes de ces couches sont toujours (au moins, je
ne les ai pas encore vues autrement) de coraux et autres corps marins
petrifies. Donc, il faut que les couches de pierres roulees, d'ou j'ai
tire ma collection citee plus haut, soyent des debris de montagne"
detruites de cette espece. Il y en a qui sont tres parfaites comme
celles qui composent ma collection, d'autres meritent plutot d'etre
rangees parmi les passages du silex ordinaire, et ses especes plus
fines; d'autres encore sont, en effet, de vraies agathes, mais qui
renferment dans leur interieur plus ou moins de parties non parfaites
presque calcaires, qui s'annoncent d'abord par leur couleur blanche,
par leur gros grains relativement au reste, par leur opacite, par leur
mollesse respective, et souvent meme par leur sensibilite pour les
acides mineraux. Mais celles, qui sont finies, quoiqu'elles ayent, pour
la plupart, une couleur presque noire, ne laissent, cependant, pas
d'avoir aussi des teintes plus claires comme brunatres, verdatres,
rougeatres, jaunatres, bleuatres, tachetees, veinees, etc. Leur clarte
n'est pas moins variable, que leur couleur, il y en a de presqu'opaques,
comme aussi de presque transparentes, sur tout la, ou la calcedoine
predomine.
"Le quartz s'y trouve comme dans les pierres de la premiere section, c,
a, d, crystallise, en groupes dans de petites cavites; quelquefois aussi
en veines. La calcedoine y est de meme, ou bien en mamelons, ou bien en
stalactites, lorsqu'elle a de la place pour s'y deposer.
"Un phenomene encore plus curieux que cela est cette belle pyrite
sulphureuse jaune, comme de l'or, qui est quelquefois parsemee par tout
la substance de petrifications agathisees, et qui apparemment y fut
deposee apres la dite metamorphose a la faveur des petits pores, qui y
etoient restes ouverts."
I would beg that mineralists, who use such language as this, would
consider if it contains a distinct idea of the operation which they
would thereby describe, or if it does not contain either a contradiction
or an inconceivable proposition. It supposes a calcareous body to be
metamorphosed, somehow by means of the mountain acid, into a siliceous
body. But, finding many bodies of pyrites contained within that solid
flint, it is said, that, when the calcareous body was flintified, there
were left in it cavities which were afterwards filled with pyrites. Let
us reflect a moment upon this doctrine. These cavities were first open
to the outside of the flinty body; but now the pyrites with which they
had been filled is insulated in the solid flint. Here three things are
required; first, The calcareous body is to be flintified, at the same
time leaving the body full of small cavities open to the outside;
secondly, These cavities are to be filled with pyrites; lastly, These
mineral bodies are to be so inclosed within the flint, as to leave no
vestige of the former processes. This marly mountain itself, which had
been formed of loose materials gathered together at the bottom of the
sea, was first to be filled with pyrites, in various shapes, by means of
the phlogistic and the acid of the mountain. Here is proposed to us an
operation which is totally unknown, or of which we have no kind of
idea. But, let us suppose pyrites formed in this mountain, (of whatever
chemical substances), by means of water; Why should water again undo
that pyrites, in order to form other concretions? And, Why should the
flint be formed first with cavities, and then made solid, after pyrites
had been introduced into those cavities of the agate, and, as our author
expresses it, _parsemee pour toute la substance?_ Here are suppositions
which are not only perfectly gratuitous, but are also inconsistent with
any thing that we understand. This is not explaining nature; it is only
feigning causes[39].
[Note 39: The description of those insulated siliceous bodies,
containing in their closed cavities all the usual concretions of
calcedony and crystals, as well as full of small pyrites floating in the
solid flint, are extremely interesting to a mineral system, or such a
geological theory as should explain the present state of things in those
strata that had been formed by deposits of known materials at the bottom
of the sea; they are indeed such appearances as may be found, more or
less, in all consolidated strata. But it is this author's explanation of
that petrifaction which is our present object to consider; and, as he is
so particular in giving us his theory upon the subject, it is easy to
detect the error of his reasoning. Were those naturalists who explain
things only in general, by saying that water is the agent, and
infiltration the means employed by nature;--were these naturalists, I
say, to give us as particular a description of their process, it would
appear as inconsistent with the nature of things as that which we have
from this author, who examines nature very minutely, and who sees
distinctly that the infiltrating theory is inapplicable for the
explanation of those petrifactions.]
The third section has for title, "_Generation du Silex et Quartz de la
Pierre Puante_." Here we find an example worthy of being recorded,
as contributing to throw great light upon those mineral operations;
however, the opinion of our author and mine, upon this subject, differ
widely. He proceeds thus:
"Cette pierre n'est, comme chacun le scait, qu'une pierre calcaire
contenant du bitume.
"Nos montagnes n'en contiennent seulement pas de simples couches, mais
il y en a meme de grandes bancs fort epais.
"Le caillou, ou silex qui s'y genere, forme, tantot de gros blocs
informes, qui occupent des cavites dans l'interieure des montagnes,
tantot, enfin, en forme de filons.
"J'ai remarque cette metamorphose sur trois endroits differens, dans
chacun des quels la nature a autrement opere.
"Sur l'un, la pierre puante fait un banc horizontal dans une montagne de
pierre calcaire crystalline, ou d'une espece de marbre, qui contient
des couches et filons de metal. Ce banc de pierre puante y fait le toit
d'une couche de galene de plomb et de pierre calaminaire, et dans ses
cavites et fentes il y a non seulement des blocs de grandeur differente,
mais aussi des veines et petites bandes courtes de silex, tant
ordinaire, que noble c, a, d, de la pierre a feu, de calcedoine,
d'agathes, et meme d'une espece de cornaline jaune et rouge pale. Je ne
m'arreterai pas a en detailler les varietes, parce qu'elles sont trop
accidentelles. Je ne les connois pas meme toutes, il s'en faut de
beaucoup, parce qu'elles se trouvent dans des anciennes mines negligees,
peut etre depuis plus d'un siecle, et par consequent peu accessibles. Je
ne doute, cependant pas, que, si l'on pouvoit mieux sonder le terrain,
on y trouveroit bien plus encore du peu que j'ai cite. Parmi ce silex,
il y a aussi de petites groupes et de petites veines de quartz solide et
crystallise.
"Au second endroit la pierre puante fait un filon, ou si l'on veut,
une couche ou bande verticale, qui partage la montagne en deux parties
presqu'egales de l'epaisseur de trois aunes a peu pres. La montagne,
ou cela se voit est aussi une ancienne mine de cuivre et de plomb,
consistant en plusieurs varietes de marbre, different en couleur et en
grain, deposees par couches les unes sur les autres. Le filon de silex
est forme de feuilles alternatives de pierre puante et de silex, tous
les deux de couleur brun de bois a peu pres; mais le silex est plus
fonce que sa compagne. Ces feuilles alternatives, consistent d'autres
bien plus minces encore, qui souvent n'ont pas l'epaisseur d'une ligne,
mais ce qu'il y a de plus curieux, c'est que la meme feuille est d'un
but de pierre porque, qui, vers le milieu, passe successivement en
silex, qui, a son tour, vers l'autre but, qui etoit expose a l'air
repasse par les memes gradations en une espece de tuffe calcaire. Ce qui
nous fait voir evidemment la generation et la destruction du silex, meme
avec une partie des moyens par lesquels elle s'opere. Comme l'endroit de
cette decouverte n'est accessible qu'a la superficie, je ne saurois dire
s'il y a d'autres varietes de silex outre la dite. Il l'est a supposer
autant par analogie, que par quelques morceaux qui ont de petites veines
transversales d'une espece de calcedoine, et qui sont, meme, sur leur
fentes, garnis de petits cristaux de roche. Mais ce qu'il y a de sur
c'est que ce filon, parvenu a une certaine profondeur, s'ennoblit et
contient du metal, c. a. d. de la galene de plomb, et de la pyrite
cuivreuse, j'y en ai trouves de morceaux, qui en font de preuves
incontestables. Le caillou d'ici est un grain fin d'une texture forte,
peu transparent, donne beaucoup d'etincelles au briquet, mais ses
cassures sont ecailleuses.
"La montagne calcaire du troisieme lieu a une couche de pierre puante
epaisse de plusieurs aunes, qui, derechef contient de petites couches
irregulieres et des bandes transversales de silex, qui ont jusques a
six pouces passes d'epaisseur. La pierre puante est d'une couleur
gris-brune, d'un grain assez fin, et d'un tissu assez dur; ses cassures
sont irregulieres, mais plus la pierre s'approche du silex, plus elles
donnent dans le coquille. Le silex ordinaire est d'un brun de bois, d'un
grain assez fin, et d'un tissu resistant, et ses cassures sont egales a
la pierre porque. Ce n'est pas la la seule variete, il y a, aussi, de la
calcedoine et des agathes de couleurs differentes. Meme la pierre a
feu est assez souvent traversee de veines de calcedoine, de quartz
crystallise, et de spath calcaire blanc en feuilles et en crystaux. Il
arrive que la meme veine est composee de ces trois especes de pierres a
la fois, de sorte que l'une semble passer dans l'autre, parce que les
limites reciproques sont, souvent, assez indistinctes. Il est evident,
que le silex est forme de la pierre puante, parce qu'on remarque ici
les memes phenomenes dont j'ai parle plus haut, c. a. d. les passages
successifs de l'une dans l'autre pierre, tant en montant qu'en
descendant."
There is nothing particular in the siliceous mixture in this species of
lime-stone, except the vein of that substance. It is evident that this
vein, traversing the mountain, had been introduced in the fluid state
of fusion. I do not mean to say, that, in this particular case now
described, the evidence of that truth peculiarly appears; but that, from
the general nature of mineral veins breaking and traversing the solid
strata of the globe, no other conclusion can be formed; and that in
the particulars of this example there is nothing that could lead us to
suppose any other origin to the petrifactions contained in this vein
of stinking lime-stone. It is plain, that our author has imagined to
himself an unknown manner of executing his mineral metamorphoses. He
sees plainly that the common notion of infiltration will not at all
explain the evident confusion of those calcareous and siliceous bodies
which appear to him to be metamorphosing into each other. Nothing,
indeed, can explain those phenomena but a general cause of fluidity; and
there is no such general cause besides that of heat or fusion.
But to show how mineralists of great merit, gentlemen who have examined
systematically and with some accuracy, may impose upon themselves in
reasoning for the explanation of mineral appearances from limited
notions of things, and from the supposition of these having been formed
where they now are found, that is, upon the surface of the earth, I
would beg leave to transcribe what this author has said upon this
species of petrifaction. It is not that he is ignorant of what
mineralists have already said upon the subject; it is because he sees
the incompetency of their explanations in those particular cases; and
that he would employ some other more effectual means. (p. 50.)
"Toute terre calcaire a changer dans une autre doit, avant toute chose,
etre rendue refractaire ce qui ne peut se faire qu'en la saturant avec
un acide. Mais une terre simplement, saturee d'un acide, est d'une
reduction fort aisee, vu que l'acide n'y tient pas trop fort, d'ailleurs
ce n'est qu'un sel neutre terreux fort facile a dissoudre dans une
quantite suffisante d'eau. Or pour rendre cette union plus constante, il
faut que la terre alcaline s'assimile intimement a l'acide, ce qui ne
se sera jamais sans un intermedeliant, qui homogene les parties de ce
nouveau corps, et pour que cela ce fasse il est indispensable, qu'il
s'opere une dissolution fonciere des parties terrestres de la chaux, qui
facilite l'ingress a l'acide, et a l'intermede pour qu'ils s'y lie bien
fortement. Supposons qu'il se forme une liqueur savonneuse de l'acide et
du phlogistique, que l'air fixe, mis en liberte, ouvre les interstices
des parties qui constituent la terre alcaline, qu'apres cela cette
liqueur savonneuse ayant l'entree libre s'assimile a la terre en
proportion requise, que l'eau, qui servoit de vehicule dans cette
operation, s'evapore successivement, et emporte le superflu des
ingrediens, pour qu'il se puisse operer le rapprochement le plus exacte
des parcelles ou molecules homogenees de nouveau corps qu'enfin les
molecules les plus pures et les mieux affinees soyent reunies en forme
liquide dans des cavites, et que par l'evaporation et separation de
l'eau, ou elles nageoient, il s'en forme des crystaux n'aurons-nous
pas une boule de silex, avec de crystaux de quartz dans ses creux
interieurs."
The supposed case is this; a calcareous body is to be metamorphosed
into a siliceous nodule, having a cavity within it lined with quartz,
crystals, etc. M. de Carosi means to inform us how this may be done.
Now, as this process requires no other conditions than those that may
be found upon the surface of this earth, the proper way to prove this
hypothetical theory, would be to exhibit such a mineral body produced
by those means. But, even supposing that such a process were to be
exhibited, still it would remain to be explained, how this process,
which requires conditions certainly not be found at the bottom of the
sea, could be accomplished in that place, where the strata of the earth
had been deposited, accumulated, consolidated, and metamorphosed.
This mineral process, which has been now described, will no doubt revolt
the opinions of many of our chemists as well as naturalists; and I
should not have thought of transcribing it, but as an example of that
inconclusive reasoning which prevails in mineralogical writings upon
this subject.
But this is not all. We have, upon this occasion, a most remarkable
example of the fallaceous views that may be taken of things; and of the
danger to science when men of sense and observation form suppositions
for the explanation of appearances without that strict conformity with
the principles of natural philosophy which is requited on all occasions.
Both M. de Carosi, and also M. Macquart[40], to whom our author
communicated his ideas and proper specimens, assert, that from their
accurate experience, they find calcedony growing daily, not only in the
solid body of gypsum, etc. while in the mine, but also in the solid
stone when taktn out of the mine, and preserved in their cabinet.
[Note 40: Vid. Essais de Mineralogie par M. Macquart.]
What answer can be made to this positive testimony of these gentlemen,
by a person who has not seen any such a thing, and who has not the
opportunity of examining the cases in which those naturalists may have
perhaps been led into some delusion? Were I however to conjecture upon a
subject in which I have not any positive information, I should suppose
that some part of the calcedony, like the _oculus mundi_ when dipped in
water, may be so transparent, while containing some portion of humidity,
that it is not easily distinguishable from the gypsum in which it is
concreted; but that in having the humidity evaporated, by being taken
out of the mine and exposed to the dry air, those portions of calcedony,
which did not before appear, may be perceived by becoming more
opaque[41].
[Note 41: From the description given in this treatise, and from the
drawings both of M. de Carosi and M. Macquart, I find a very valuable
inference to be made, so much the more interesting, as I have not found
any example of the like before. This arises from the intimate connection
which is here to be perceived between agate and gypsum. Now, upon this
principle, that the agate-calcedony had been formed by fusion, a truth
which, from the general testimony of minerals, I must presume, it is
plain, that those nodules of gypsum had been in the fluid state of
fusion among those marly strata, and that the gypseous bodies had been
penetrated variously with the siliceous substance of the calcedony.
The description of those siliceous penetrations of gypsum is followed by
this conclusion: "En voila assez, je crois pour faire voir que le silex
ci-decrit est effectivement une emanation du gypse, et non pas une
matiere heterogene amenee d'autre part et deposee, ou nous la voyons."
In this instance our author had convinced himself that the calcedony
concretions had not been formed, as he and other mineralists had before
supposed, by means of infiltration; he has not, however, substituted
any thing more intelligible in its stead. I do not pretend that we
understand mineral fusion; but only that such mineral fusion is a thing
demonstrable upon a thousand occasions; and that thus is to be explained
the petrification and consolidation of the porous and naturally
incoherent strata of the earth.]
There is, however, a subject in which I can more freely accuse this
author of being deceived. This naturalist says, that calcareous stones
become silex by a certain chemical operation; and that those flinty
bodies, in being exposed upon the surface of the earth, out of their
natural bed, are again, by a contrary chemical operation, changed from
flint to a calcareous substance. I will give it in his own words, (p.
56.)
"Cela dit, venons au fait. Tout silex progenere de chaux, detache de son
lieu natal, et expose aux changemens de saisons, s'amollit, recoit de
crevasses, perd sa transparence, devient, enfin, tout-a-fait opaque, le
phlogistique s'en evapore, l'acide en est detache, lave, et de
terre vitrescible, qu'il etoit, il redevient chaux, comme il etoit
auparavant."
Here is no question with regard to mere opinion, but to matter of fact;
and, in this case, nothing is more evident, than that upon the surface
of this earth, that is, in the examinable parts above the level of the
sea, there is no transition either of calcareous bodies into flint,
nor of flinty bodies into calcareous substance. Calcareous matter is
constantly dissolved by water, when it is exposed to the washing of
that fluid; and it is even dissolved out of the most perfect union or
combination with siliceous substance, and the most solid composition of
an insoluble body, as may be perceived in the decaying of feld-spar. A
superficial view of flints, which have come out of a body of chalk, may
have created such an opinion, which will not either bear the light of
chemical or mineral investigation. The subject of these chalk flints
will be minutely examined in its proper place.
Our author has carefully examined the subject of flintification; and the
country where he makes his observations would seem to be well disposed
for such a research. He has had great opportunity and inclination to
examine the subject which he writes upon; and he has given a distinct
account of what be has seen. His description of the flintification of
sand-stone is extremely interesting. I will therefore transcribe it,
both as a valuable portion of natural history, and also in order to
contrast this author's opinion, with regard to the means employed by
nature in petrifying bodies, and that which I maintain to be the general
consolidating operation of the globe. It is Section V. _Generation du
Caillou du Silex du Gres, ou Pierre Sablonneuse_.
"Tout gres est susceptible de cette metamorphose quant au grain et quant
a la couleur; depuis la breccia quartzeuse jusqu'a la pierre a rasoir;
et depuis le gres blanc jusqu'au brun et presque noiratre, tient ou non
tient, dur, ou presque friable, c'est indifferent, toutes ces varietes
donnent du silex, et surtout de la calcedoine, de la cornaline, et des
agathes. Quant au ciment je l'y ai toujours remarque calcaire et faisant
effervescence avec les acides dans les endroits de la pierre qui
n'etoient point encore changes; et jamais je n'ai vu ce changement dans
du gres dont le ciment fut ou quartzeux ou argileux et refractaire.
Ainsi le ciment entre pour quelque chose dans ce changement.
"Le commencement de cette metamorphose paroit (autant que j'ai pu
l'observer dans mes debris roules) se faire par le ciment, qui dissout
la, ou les agens eurent l'acces libre, rend les grains en quartz
mobiles, les emporte, les mele avec sa masse dense-liquide, les dissout,
meme en partie, et forme, dans cet etat, des veines et de masses
calcedonieuse, carneoliques, ou d'une autre espece de silex, au milieu
du gres peu, ou pas du tout, change. Car autant que je puis voir, ce
n'est pas par couches ou veines qu'elle s'opere, mais par boules et
masses rond-oblongues. Au commencement ces veines et taches sont fort
minces, et le reste du gres n'est point du tout, ou a peine sensiblement
change hormis qu'il gagne, plus de consistence, a proportion du
changement souffert. Mais a mesure que le silex y augmente et se
perfectionne, on y appercoit les degres par lesquels a passe cette
operation. Les nuance du passage d'une pierre a l'autre deviennent plus
visibles, les veines et masses de silex grandissent au point, meme,
qu'il y a jusqu'aux trois quart du gres change en silex clair comme de
l'eau n'ayant que fort peu de grains de sable nageants dans sa masse.
Des morceaux de cette espece sont rares a la verite, mais j'en ai,
cependant, trouve quelques uns. Ordinairement, dans les beaux morceaux,
le silex fait la base, et le sable y est, comme nageant tantot en grains
separes tantot en parties et flocons. Dans les pieces moins belles, le
sable fait la base, et le silex sert a la fois de ciment, et forme aussi
plus ou moins de veines, qui traversent la masse en maintes et maintes
directions. Mais si c'est un gres a gros grains, ou de la breccia, alors
le reste prend la nature silicieuse mele de sable fin, et les gros
grains de quartz restent tels, qu'ils etoient, sans changer. J'ai
deja remarque que cette metamorphose semble s'operer, comme celle des
cailloux d'origine calcaire en forme approchans la spherique, il faut
encore y a jouter, que j'ai lieu de croire, qu'elle se fasse aussi du
dedans en dehors, tout, comme la decomposition se fait du dehors au
dedans.
"Il arrive dans cette pierre, comme dans toute autre, qu'il se forme
des crystallisations dans les cavites. Lorsqu'elles sont de silex, leur
figure est toujours mamelonnee, mais leur eau ou purete, leur grandeur
et leur couleur n'est pas par tout egale. Il y en a qui sont grands, et
de la plus pure calcedoine, d'autres sont petits et chaque goutte ou
mamelon contient un grain de sable, de facon que cela a l'air d'un gres
crystallise en mamelons ou stalagmitique. D'autres encore sont, de
calcedoine, mais recouverts d'une croute, tantot blanche qui fait
effervescence avec l'acide mineral, et qui est, par consequent, de
nature calcaire; tantot cette croute est bleue foncee nuancee de
bleu-celeste; tantot, enfin, elle est noire, mais toutes les deux
refractaires. Outre ces crystallisations silicieuses, il y en a, quoique
rarement, de quartzeuses, qui ou forment de petites veines de crystal,
ou bien des groupes de crystaux quartzeux, ou qui enfin, enduisent les
mamelons de silex."
Our author then makes a specification of the different varieties; after
which he continues, p. 69.
"Apres tout ceci, l'on conviendra j'espere, que notre grais est une
pierre bien singuliere, et surpassant, a bien des egards, le grais,
faussement dit crystallise, de Fontainebleau. La raison de la figure du
grais Francois est fort evidente, c'est le spath calcaire, qui lui
sert de ciment, qui la lui fit prendre; mais qu'est-ce qui opere les
metamorphoses racontees dans notre grais siliceux? Seroit-ce son ciment
calcaire ou marneux par les memes raisons, qui font changer la marne en
silex? La chose est tres-probable, et je n'en saurois pas meme, deviner
d'autre. En ce cas la nature auroit un moyen d'operer par la voie
humide, ce que nous faisons dans nos laboratoires en quelque facon, par
la voie seche, c, a, d, de fondre et liquefier la terre vitrescible, au
moyen des alcalis; secret que nous lui avons deja arrache en partie, en
faisant la liqueur silicieuse."
"Je n'ose, cependant, decider pas meme hypothetiquement, sur cette
matiere, pour n'avoir pu observer la nature dans ses ateliers, et parce
que je ne possede que des pieces, qui detachees de leur lieu natal,
depuis un tres long-tems, furent exposees aux intemperies des saisons,
ou elles peuvent avoir souffert bien de changemens."
There cannot be a more fair exposition of facts; and it is only our
author's opinion of this mineral transmutation that I would controvert.
I do not pretend to understand the manner of operating that our author
here supposes nature to take. I only maintain, that here, as every where
in general, the loose and incoherent strata of the globe have been
petrified, that is, consolidated, by means of the fusion of their
substances; and this I think is confirmed from the accurate description
here given of the flintification of sand-stone. Here is described very
distinctly an appearance which is very common or general on those
occasions; this is the parts or particles of stone floating in the fluid
siliceous substance, and there dissolving more or less.
M. de Carosi describes very systematically the generation of silex,
calcedony, onyx, and quartz, in calcareous earth, marl, gypsum,
sand-stone, and also what he terms _terre glaise, ou de l'Argile_. It is
in this last that we find a perfect analogy with what is so frequent in
this country of Scotland. These are the agates, calcedonies, calcareous
and zeolite nodules, which are found produced in our whin-stone
or subterraneous lavas, that is, the amygdaloides of Crondstedt.
Naturalists explain the formation of those nodular bodies differently.
The Chevalier de Dolomieu supposes these rocks to have been erupted
lavas, originally containing cavities; and that these cavities in the
solid rock had been afterwards filled and crystallised, by means of
infiltration, with the different substances which are found variously
concreted and crystallised within the solid rocks. Our author, on the
contrary, supposes these formed by a species of chemical transmutation
of calcareous and argillaceous earths, which, if not altogether
incomprehensible, is at least not in any degree, so far as I know, a
thing to be understood.
This is not the place where that subject of these particular rocks,
which is extremely interesting, is to be examined. We shall afterwards
have occasion to treat of that matter at large. It is sufficient here to
observe, that our author finds occasion to generalise the formation of
those petrifactions with the flintifications in calcareous and gypseous
bodies. When, therefore, the formation of any of them shall be
demonstrated, as having taken its origin in the fusion of those
substances, this mode of operation, which is generalised in the
consolidation of strata, will be properly inferred in all the rest.
Petrifaction is a subject in which mineralogists have perhaps wandered
more widely from the truth than in any other part of natural history;
and the reason is plain. The mineral operations of nature lie in a part
of the globe which is necessarily inaccessible to man, and where the
powers of nature act under very different conditions from those which we
find take place in the only situation where we can live. Naturalists,
therefore, finding in stalactical incrustation a cause for the formation
of stone, in many respects analogous to what is found in the strata of
the earth, and which had come from the mineral region in a consolidated
state, have, without due consideration, attributed to this cause all the
appearances of petrifaction or mineral concretion. It has been one of
the objects of this work to show that this operation of incrustation,
or petrifaction by means of solution, is altogether ineffectual for
producing mineral concretions; and that, even were it capable of forming
those mineral bodies, yet that, in the solid parts of this earth, formed
by a deposit of travelled materials at the bottom of the sea, the
conditions necessary to this incrustating process do not take place.
Those enlightened naturalists who have of late been employed in
carefully examining the evidences of mineral operations, are often
staggered in finding appearances inconsistent with the received doctrine
of infiltration; they then have recourse to ingenious suppositions, in
order to explain that enigma. In giving examples of this kind. I have in
view both to represent the natural history these mineralists furnish
us with, which is extremely interesting, and also to show the various
shapes in which error will proceed, when ingenious men are obliged to
reason without some necessary principle in their science. We have just
now had an example in Europe; I will next present the reader with one
from Asia.
M. Patrin, in his _Notice Mineralogique de la Daourie_, (Journal de
Physique, Mars 1791) gives us a very distinct account of what he met
with in that region. Describing the country of Doutchersk upon the river
Argun, in Siberia, he proceeds thus:
"Ces colines sont formees d'un hornstein gris qui paroit se convertir en
pierre calcaire par l'action des meteores; car tout celui qu'on prend
hors du contact de l'air donne les plus vives etincelles, et ne fait pas
la moindre effervescence avec les acides, meme apres avoir ete calcine;
et l'on observe celui qui est a decouvert, passer, par nuances
insensibles, jusqu'a l'etat de pierre calcaire parfaite de couleur
blanchatre."
Here M. Patrin has persuaded himself, probably from an imperfect
examination of the subject, that there takes place a mineral
metamorphosis, which certainly is not found in any other part of the
earth, and for which he does not find any particular cause. The natural
effect of the meteors, in other parts of the earth, is to dissolve the
calcareous substance out of bodies exposed to those agents; and the
gradation from the one of those two things to the other, which seems to
be the data on which he had proceeded in forming his conclusion, is not
sufficient to prove the metamorphosis, even were there not so strong a
physical objection to it; for, it is by no means unusual for mineral
bodies to graduate thus from one substance to another. However that be,
this is not the principal object of the example[42].
[Note 42: Here we have well informed naturalists reasoning with all the
light of our present mineralogy, and maintaining, on the one hand, that
gypsum is transformed into calcedony, by the operation of the meteors,
or some such cause; and, on the other, that a siliceous substance is by
the same means converted into lime-stone. What should we now conclude
from this?--That calcareous and siliceous substances were mutually
convertible. But then this is only in certain districts of Poland and
Siberia. Every where, indeed, we find strange mixtures of calcareous and
siliceous bodies; but neither mineralists nor chemists have, from these
examples, ventured to affirm a metamorphosis, which might have spared
them much difficulty in explaining those appearances.
This is a subject that may be taken in very different lights. In one
view, no doubt, there would appear to be absurdity in the doctrine of
metamorphosis, as there is now a days acknowledged to be in that of
_lusus naturae_; and those reasoning mineralists might thus, in the
opinion of some philosophers, expose their theory to contempt and
ridicule. This is not the light in which I view the subject. I give
those gentlemen credit for diligently observing nature; and I applaud
them for having the merit to reason for themselves, which would seem to
be the case with few of the many naturalists who now speak and write
upon the subject.
Let us now draw an inference, with regard to this, in judging of the
different theories. Either the received system concerning mineral
operations is just, in which case those gentlemen, who employ a secret
metamorphosis, may be to blame in laying it aside; or it is erroneous
and deficient; and, in that case, they have the merit of distinguishing
the error or deficiency of the prevailing system. How far they have seen
the system of nature, in those examples which they have described,
is another question. In the mean time, I am to avail myself of the
testimony of those gentlemen of observation, by which the insufficiency
at least of the received mineral system is acknowledged.]
After speculating upon the effect of the ancient ocean upon the
mountains of that country, he proceeds as follows:
"Je laisse ces conjectures pour remarquer un fait singulier: la colline,
qui est au nord de l'eglise de la fonderie, a son arrete composee de ce
hornstein qui se decompose en pierre calcaire; mais ici, les parties,
qui sont ainsi decomposees, offrent une substance calcedonieuse
disposees par zones concentriques, comme on l'observe dans les agates
d'oberstein; mais ce ne sont point ici des corps parasites formes par
infiltration dans des cavites pre-existantes comme les agates; on voit
que ce sont les parties constituantes de la roche qui, _par un
travail interne_, et par une sorte de crystallisation, out pris cette
disposition reguliere (que ce mot de _crystallisation_ ne revolte point,
j'appelle ainsi toute tendance a prendre une forme constante, polyedre
ou non polyedre.) Les couches les plus voisine du centre sont nettes et
distinctes; peu-a-peu elles le sont moins, et enfin elles s'evanouissent
et se confondent avec le fond de la roche. Chaque assemblage de ces
zones a une forme ronde ou ovale plus ou moins reguliere de sept a huit
pouces de diametre.
"Cela ressemble en grand a ce qu'on observe dans les pierres oeillees,
et la cause est vraisemblablement la meme. Je le repete, je regarde
cette disposition reguliere comme une veritable cristallisation, qui
peut s'operer et qui s'opere en effet dans l'interieur des corp les plus
solide, tant qu'ils sont fournis a l'action des agens de la nature.
"Tous ceux qui visitent l'interieur de la terre savent que les roches
memes le plus compactes y sont intimement penetrees d'humidite, et ce
fluide n'est certainement pas l'eau pure; c'est l'agent qui opere toutes
les agregations, toutes les cristallisations, tous les travaux de la
nature dans le regne mineral. On peut donc aisement concevoir qu'a la
faveur de ce fluide, il regne, dans les parties les plus intimes des
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