Theory of the Earth Volume I Part 19

"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 quant.i.te suffisante d'eau. Or pour rendre cette union plus constante, il faut que la terre alcaline s'a.s.simile intimement a l'acide, ce qui ne se sera jamais sans un intermedeliant, qui h.o.m.ogene les parties de ce nouveau corps, et pour que cela ce fa.s.se 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 const.i.tuent la terre alcaline, qu'apres cela cette liqueur savonneuse ayant l'entree libre s'a.s.simile 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 h.o.m.ogenees 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, acc.u.mulated, 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, a.s.sert, 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 a.s.sez, 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, subst.i.tuted 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 creva.s.ses, 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 ma.s.se dense-liquide, les dissout, meme en partie, et forme, dans cet etat, des veines et de ma.s.ses 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 ma.s.ses 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 pa.s.se cette operation. Les nuance du pa.s.sage d'une pierre a l'autre deviennent plus visibles, les veines et ma.s.ses 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 ma.s.se.

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 ma.s.se 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 fa.s.se 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 pet.i.ts 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 pet.i.tes 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 surpa.s.sant, a bien des egards, le grais, fauss.e.m.e.nt 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 trans.m.u.tation 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 a.n.a.logy 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 trans.m.u.tation 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 a.n.a.logous 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, pa.s.ser, 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 princ.i.p.al 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 const.i.tuantes 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 a.s.semblage 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 ais.e.m.e.nt concevoir qu'a la faveur de ce fluide, il regne, dans les parties les plus intimes des corps souterrains, une circulation qui fait continuellement changer de place aux elemens de la matiere, jusqu'a ce que reunis par la force des affinites, les corpuscules similaires prennent la forme que la nature leur a a.s.signee."

Those nodular bodies or figured parts which are here inclosed in the rock, are evidently what may be called calcedony agates. M. Patrin is persuaded, from the examination of them, that they had not been formed in the manner of German agates, which he supposes is by mean of infiltration; and he has endeavoured to conceive another manner of operating, still however by means of water, which I suppose, according to this hypothesis, is to dissolve substances in one part, and deposits them in another, There must certainly be some great _desideratum_ in that mineral philosophy which is obliged to have recourse to such violent suppositions. First, water is not an universal solvent, as it would require to be, upon this supposition; secondly, were water allowed to be an universal menstruum, here is to be established a circulation that does not naturally arise from the mixture of water and earth; and, lastly, were this circulation to be allowed, it would not explain the variety which is found in the consolidation and concretion of mineral bodies.

So long, therefore, as we are to explain natural appearances by reasoning from known principles, and not by ascribing those effects to preternatural causes, we cannot allow of this regular operation which M. Patrin alleges to be acting in the interior parts of the most solid bodies. This is indeed evident, that there has been a cause operating in the internal parts of the most solid bodies, a cause by which the elements, or const.i.tuent parts of those solid bodies, have been moved and regularly disposed, as this author very well observes must have been the case in our agates or eyed stones; but to ascribe to water this effect, or to employ either an ineffectual or an unknown cause, is not to reason philosophically with regard to the history of nature; it is to reason phantastically, and to imagine fable.

M. Monnet has imagined a petrifying power in water very different from any that has. .h.i.therto been conceived, I believe, by natural philosophers, and I also believe, altogether inconsistent with experience or matter of fact; but as it is not without good reason that this naturalist has been induced to look out for a petrifying cause different from any hitherto supposed, and as he has endeavoured very properly to refute the systems of petrification hitherto received, I would beg leave to transcribe his reasoning upon the subject in corroboration of the present theory of consolidation by the means of fusion.

It is upon occasion of describing one of the species of alpine stone or schistus which contains quartzy particles. _Nouveau voyage mineralogique, etc._ Journal de Physique Aoust 1784.

"Il y a loin de cette pierre, que je regarde comme une variete de roches ardoisees, aux veritable ardoises. La composition de toutes ces pierres est due aux terres quartzeuses et argileuses, et a la terre talqueuse, que je demontrerai un jour etre une espece particuliere et distincte des autres, qui const.i.tue les bonnes ardoises, et fait, ainsi que le quartz, qu'elles resistent aux injures de l'air, sans s'effleurir, comme je ferai voir que cette terre, qu'on designera sous la denomination de terre talqueuse, si l'on veut, resiste au grand feu sans se fondre. Les differences de toutes ces pierres, quoique composees des memes matieres, mais dans des proportions differentes, sont frappantes, et pourroient faire croire qu'elles n'appartiennent pas a ce genre. Mais qui ne voit ici que toutes ces differences, ou ces varietes, ne sont dues qu'aux modifications de la matiere premiere, qu'elle a eprouvees, soit en se melant avec des matieres heterogenes, prevenantes du debris des etres qui ont existe, comme l'argile, par exemple, qui, de l'aveu de presque tous les naturalistes, est le produit de l'organization des plantes, ou soit en se melant avec de la matiere deja solidifiee depuis long-temps?

Or nous ne craignons pas de dire, ce que nous avons dit plusieurs fois quand l'occasion s'en est presentee, que cette matiere unique, que se modifie selon les occasions et les circonstances, et qui prend un caractere a.n.a.logue au matieres qu'elle rencontre, est l'eau, que beaucoup de naturalistes cherchent vainement ailleurs. Ils ne peuvent comprendre, malgre les exemples frappans qui pourroient les porter a adopter cette opinion, que ce fluide general soit l'element des corps solides du regne mineral, comme il est de ceux du regne vegetal et du regne animal. L'on cherche serieus.e.m.e.nt, par des experiences chimiques, a decouvrir si l'eau est susceptible de se convertir en terre comme si la nature n'avoit pas d'autre moyen que nous de la faire pa.s.ser de l'etat fluide a l'etat solide. Voyez le spath calcaire et le quartz transparens; est il a presumer qu'ils ne sont que le resultat du depot des matieres terreuses fait par les eaux? Mais, dans ce ca-la encore, il faut supposer que l'eau qui est restee entre ces partie s'est solidifiee; car, qu'est-elle donc devenue, et quel est donc le lien qui a uni ces parties et leur a fait prendre une forme reguliere? Il est vrai qu'on nous parle d'un suc lapidifique; mais c'est-la un etre de raison, dont il seroit bien plus difficile d'etablir l'existence, que de croire a la solidification de l'eau. On nous donne cependant comme un principe certain que l'eau charie d'un lieu a un autre les matieres qu'il a dissoutes, et qu'elle les depose a la maniere des sels. Mais c'est supposer une chose dementie par l'experience; savoir, que l'eau ait la propriete de dissoudre les matieres terreuses, telles que la quartzeuse. A la verite, M. Auchard de Berlin y joint de l'air fixe; mais cet air fixe ne sauroit tenir en dissolution un atome de quartz dans l'eau; et quelle qu'ait ete l'exact.i.tude de ceux qui ont repete les experiences de M. Auchard, on n'a pu reussir a imiter la nature, c'est-a-dire, a former des cristaux quartzeux, comme il a annonce. Que l'eau ait la faculte de tenir en dissolution quelques pet.i.tes parties de terre calcaire, au moyen de cet air fixe, il n'en faut pas conclure qu'elle puisse former de cette maniere tous les cristaux calcaires, sans que l'eau elle-meme y concoure pour sa part; car ce seroit conclure quelque fois que la partie seroit egale au tout. Voyez ces geodes calcaire et argileuses, qui renferment des cristaux nombreux de quartz ou de spath calcaire; ne sont ils que le resultat du depot de l'eau qui y a ete renfermee, ou que la cristallization pure et simple des molecules que vous supposez avoir ete tenues en dissolution par cette eau? Il naitroit de cette opinion une foule d'objections qu'il seroit impossible de resoudre. Cependant M. Guettard, dans la mineralogie du Dauphine, qui vient de paroitre, ouvrage tres-estimable a beaucoup d'egards, explique, selon cette maniere de penser, la formation de cristallizations quartzeuses qu'on trouve dans certaines geodes de cette province, et celle des mines de cristal des hautes montagnes. En supposant meme comme vraie l'explication qu'il en donne, on trouveroit en cela un des plus grands probleme, et des plus difficiles a resoudre qu'il y ait en mineralogie; car d'abord il faudroit expliquer comment un si pet.i.te quant.i.te d'eau que celle qui a ete renfermee dans les geodes, et celle qui est parvenue dans les fentes des rochers, ont pu fournir un si grande quant.i.te de matiere que celle qui const.i.tue ces cristallisations, et ce qui n'est pas le moins difficile a concevoir, comment l'eau a pu charrier cette matiere a travers tant de matieres differentes, et la conserver precis.e.m.e.nt pour cette destination; comment, par exemple, l'eau est venue deposer de la terre quartzeuse dans les ma.s.ses enormes de pierres calcaires, qui forment la cote qui domine le village de Champigny, a quatre lieues de Paris, au dela de Saint-maur; car s'il nous faut citer un exemple frappant de cette singularite, et a portee d'etre vue des naturalistes qui sont dans la capitale, je ne puis mieux faire que de citer cette cote, une des plus curieuses de la France, et que je me propose de fair connoitre en detail dans la troisieme partie de la mineralogie de la France. On verra, dis-je, dans cette bonne pierre a chaux, et une de plus pure des environs de Paris, de tres-abondantes cristallisations de quartz transparent, et quelque fois de belle eau, que les ouvriers sont forces de separer de la partie calcaire, a laquelle elles adherent fortement.

Mais c'est trop nous arreter a combattre une opinion qui doit son origine aux premieres idees qu'ont eues les premiers observateurs en mineralogie, qui se detruira d'elle meme comme tant d'autres dont il nous reste a peine le souvenir."

We find here an accurate naturalist, and a diligent observer, who, in conformity with what my sentiments are upon the subject, thinks it impossible that the crystallizations in close cavities, and concretions of different solid substances within each other, which so frequently occur in the mineral regions, could have been produced, by means of solution and crystallization, from a fluid vehicle. But what has he now subst.i.tuted in place of this solution, in order to explain appearances?--a mere supposition, viz. that nature may have the power of converting water, in those secret places, into some other thing; or rather that the substance of water is here converted into every other thing; for, though he has only mentioned quartz and calcareous spar, what mineral substance is there that may not be found in those close cavities? They are actually almost all, not even excepting gold; for, small grains of gold are inclosed within the cavities of a porous stone, in the Siberian mine. Now, for what purpose should nature, (to the power of which we are not to set a limit) have such an object in view as to convert water into every thing, unless it were to confound human understanding? For, so far as human experience has been as yet able to reach, there would appear to be certain elementary substances; and among these is water, or the principles of that fluid[43]. But because water is so generally found in bodies, and so necessarily in most of the operations of this world, why convert it into every other thing? Surely, for no better reason than that there has not occurred to this mineralist any other way of explaining certain natural appearances which aqueous solution could not produce. Here is no dispute about a matter of fact; it is on all hands allowed, that in certain cavities, inaccessible to any thing but heat and cold, we find mineral concretions, which contain no water, and which, according to the known operations of nature, water could not have produced; must we therefore have recourse to water acting according to no known principle, that is to say, are we to explain nature by a preternatural cause?

[Note 43: Water is now considered by men of science, as a compound substance; this doctrine, which seems to follow so necessarily from the experiments of the French philosophers, must be tried by the growing light of chemical science. In the oxygenating operation of inflammable and combustible bodies when burning, those ingenious chemists overlooked the operation of _phlogistic matter_, which has no weight, and which escapes on that occasion, as I have had occasion to show in a dissertation upon phlogiston, and in the Philosophy of Light, Heat, and Fire. How far this view, which I have given of those interesting experiments, may lead to the explanation of other collateral phenomena, such as that of the water produced, I will not pretend to conjecture.

One thing is evident, that if the weight of the water, procured in burning inflammable and vital air, be equal to that of those two ga.s.ses, we would then have reason to conclude, either that water were a compound substance, or that vital air, and inflammable vapour were compounds of water and the matter of light, or solar substance.]

I dare say that this is not the view that M. Monnet takes of the subject, when he thinks to explain to himself the concretion of those different substances by means of water; but, according to my apprehension of the matter, his theory, when sifted to the bottom, will bear no other construction; and, unless he shall consider water like the matter of heat, as capable of producing the fluidity of fusion, and of being also again abstracted from the fluid, by pervading the most solid body, which would then be a substance different from water, he must employ this aqueous substance as a menstruum or solvent for solid bodies, in the same manner as has been done by those naturalists whom he he justly censure, and conform to those erroneous ideas which first observations, or inaccurate knowledge of minerals, may have suggested to former naturalists.

It is the dissolution and concretion of siliceous substance, no doubt, that gives such difficulty to our naturalists in explaining petrifaction: they have, however, something apparently in their favour, which it may be proper now to mention.

In the _first_ place, although siliceous substance is not soluble, so far as we know, by simple water, it is soluble by means of alkaline substance; consequently, it is possible that it may be dissolved in the earth.

_Secondly_, The water of Giezer in Iceland, actually petrifies bodies which are alternately imbibed with that hot water and exposed to the air. This water, therefore, not only contains siliceous substance in a dissolved state, but deposits this again, either by means of cooling, or being aerated, or of evaporating. Consequently, without knowing the principle upon which it proceeds, we here perceive a natural operation by which siliceous petrifaction may be performed.