If, in examining our land, we shall find a mass of matter which had been evidently formed originally in the ordinary manner of stratification, but which is now extremely distorted in its structure, and displaced in its position,—which is also extremely consolidated in its mass, and variously changed in its composition,—which therefore has the marks of its original or marine composition extremely obliterated, and many subsequent veins of melted mineral matter interjected; we should then reason to suppose that here were masses of matter which, though not different in their origin from those that are gradually deposited at the bottom of the ocean, have been more acted upon by subterranean heat and the expanding power, that is to say, have been changed in a greater degree by the operations of the mineral region. If this conclusion shall be thought reasonable, then here is an explanation of all the peculiar appearances of the alpine schistus masses of our land, those parts which have been erroneously considered as primitive in the constitution of the earth.
We are thus led to suppose, that some parts of our earth may have undergone the vicissitudes of sea and land more than once, having been changed from the summit of a continent to the bottom of the sea, and again erected, with the rest of that bottom, into the place of land. In that case, appearances might be found to induce natural philosophers to conclude that there were in our land primary parts, which had not the marine origin which is generally to be acknowledged in the structure of this earth; and, by finding other masses, of marine origin, superincumbent upon those primary mountains, they might make strange suppositions in order to explain those natural appearances.
Let us now see what has been advanced by those philosophers who, though they term these parts of the earth primordial, and not primitive, at the same time appear to deny to those parts an origin analogous to that of their secondary mountains, or strata that are aquiform in their construction.
M. de Luc, after having long believed that the strata of the Alps had been formed like those of the low countries, at the bottom of the sea, gives an account of the occasion by which he was first confirmed in the opposite opinion.[26] Like a true philosopher, he gives us the reason of this change.
Footnote 26:[ (return) ] Lettres Physique et Morales sur l'Histoire de la Terre, tom. 2. pag. 206.
"Ce fut une espèce de montagne très commune, et que j'avois souvent examinée qui dessilla mes yeux. La pierre qui la compose est de la classe appellée schiste; son caractère générique est d'être feuilletée; elle renferme l'ardoise dont on couvre les toits. Ces feuillets minces, qu'on peut prendre pour des couches, et qui le font en effet dans quelques pierres de ce genre, rappelloient toujours l'idée vague de dépôts des eaux. Mais il y a des masses dont la composition est plutôt par fibres que par feuillets, et dont le moëllon ressemble aux copeaux de bois d'un chantier. Le plus souvent aussi les feuillets sont situés en toute suite de sens dans une même montagne, et quelquefois même verticalement, Enfin il s'en trouve de si tortillés, qu'il est impossible de les regarder comme des dépôts de l'eau.
"Ce fut donc cette espèce de montagne qui me persuada la première que toutes les montagnes n'avoient pas une même origine. Le lieu où j'abjurai mon erreur, étoit un de ces grands chantiers pétrifiés, qui, par la variété du tortillement, et des zig-zags des fibres du moëllon qui le composoit, attira singulièrement mon attention. C'étoit un sort grand talus qui venoit d'une face escarpée; j'y montai pour m'approcher du rocher, et je remarquai, avec étonnement, des multitudes de paquets enchevêtrés les uns dans les autres, sans ordre ni direction fixe; les uns presqu'en rouleaux; les autres en zig-zag; et même ce qui, séparé de la montagne, eût peu être pris pour des couches, le trouvoit incliné de toute manière dans cette même face de rocher. Non, me dis-je alors à moi-même; non, l'eau n'a pu faire cette montagne.... Ni celle-là donc, ajoutai-je en regardant ailleurs.... Et pourquoi mieux celle-là? Pourquoi toutes les montagnes devroient-elles être le produit des eaux, seulement parce qu'il y en a quelques-unes qui annoncent cette origine? En effet, puis qu'on n'a songé aux eaux, comme cause des montagnes, que par les preuves évidentes que quelques-unes offroient de cette formation; pourquoi étendre cette conséquence à toutes, s'il y en a beaucoup qui manquent de ces caractères? C'est comme le dit Mr. d'Alembert, qu'on généralise ses premières remarques l'instant d'apres qu'on ne remarquoit rien."
Science is indebted to this author for giving us so clear a picture of natural appearances, and of his own reasoning upon those facts, in forming his opinion; he thus leads astray no person of sound judgment, although he may be in error. The disposition of things in the present case are such, that, reasoning from his principles, this author could not see the truth; because he had not been persuaded, that aquiform strata could have been so changed by the chemical power of fusion, and the mechanical force of bending while in a certain state of softness.
But though, in this case, the reasoning of this philosopher is to be justified, so far as he proceeded upon principles which could not lead him to the truth, his conduct is not so irreproachable in applying them to cases by which their fallacy might have been detected. This author acknowledges calcareous strata to be aquiform in their original; but, in those mountains which he has so much examined, he will find those aquiform bodies have undergone the same species of changes, which made him conclude that those schistus mountains had not been truly aquiform, as he at first had thought them. This would have led him to reason back upon his principles, and to say, If one species of strata may be thus changed in its texture, and its shape, may not another be equally so? Therefore, may not the origin of both be similar?
But least I should do injustice to this author, to whom we are indebted for many valuable observations in natural history, I shall transcribe what he has said upon the subject, being persuaded that my readers will not think this improper in me, or impertinent to the argument.