Volume I Part 13 (1/2)
Professor Playfair was to pa.s.s through c.u.mberland. I begged that he would inquire of Mr Wright, at the Low-wood Inn, for those objects which he was to endeavour to procure for me, and to examine the limestone quarry in which I had found the specimen with entrochi. He went through another part of those primary mountains, and has found examples of this kind in the schisti; concerning which he has written me the following account.
”In a visit which I made to the Lakes of c.u.mberland in September 1791, in company with the Hon. Francis Charteris, I met with a limestone full of marine objects, though from its position it is certainly to be reckoned among the primary strata. The place where we found this stone was in the district of Lancas.h.i.+re, that is west of Windermere Lake, on the road from Ambleside to the north end of Coniston Lake, and not far from the point when you come in sight of the latter. Just about this spot we happened to meet with one of those people who serve as guides to travelers in those parts, and who told us, among other things, that stones with sh.e.l.ls in them were often found not far from where we were then walking. We immediately began to look about for specimens of that kind, and soon met with several; the most remarkable of which was in a rock that rose a little above the surface, about 300 or 400 yards to the right of the road. It was a part of a limestone stratum, nearly vertical, and was full of bivalves with the impressions as strong as in a common secondary limestone. The strata on both sides had the same inclination, and were decidedly primary, consisting of the ordinary micaceous schistus. This however I need not remark to you, who know so well from your own observations that the whole of the country I am now speaking of has every character of a primary one. I, only mention it, that it may not be supposed that the rock in question was some fragment of a secondary stratum that remained, after the rest was washed away, superinc.u.mbent on the primary.
”After I had seen this rock, I recollected that you had told me of something of the same kind that you saw in a quarry at Low-wood Inn; and it may be that both belonged to the same stratum or body of strata; for the direction of the strata, as nearly as I could observe, was from S.W.
to N.E.; and this also is nearly the bearing of Low-wood from the place where we now were. I send you a specimen, which you can compare with those you brought from the lime quarry at Low-wood.”
I have examined this specimen, and find it to be the common schistus of that country, only containing many bivalve sh.e.l.ls and fragments of entrochi and madrapore bodies, and mixed with pyrites.
I have already observed that one single example of a sh.e.l.l, or of its print, in a schistus, or in a stone stratified among those vertical or erected ma.s.ses, suffices to prove the origin of those bodies to have been, what I had maintained them to be, water formed strata erected from the bottom of the sea, like every other consolidated stratum of the earth. But now, I think, I may affirm, that there is not, or rarely, any considerable extent of country of that primary kind, in which some mark of this origin will not be found, upon careful examination; and now I will give my reason for this a.s.sertion. I have been examining the south alpine country of Scotland, occasionally, for more than forty years back, and I never could find any mark of an organised body in the schistus of those mountains. It is true that I know of only one place where limestone is found among the strata; this is upon Tweed-side near the Crook. This quarry I had carefully examined long ago, but could find no mark of any organised body in it. I suppose they now are working some other of the vertical strata near those which I had examined; for, in the summer 1792, I received a letter from Sir James Hall, which I shall now transcribe. It is dated at Moffat, June 2. 1792.
”As I was riding yesterday between n.o.ble-house and Crook, on the road to this place, I fell in with a quarry of alpine limestone; it consists of four or five strata, about three feet thick, one of them single, and the rest contiguous; they all stand between the strata of slate and schist that are at the place nearly vertical. In the neighbourhood, a slate quarry is worked of a pure blue slate; several of the strata of slate near the limestone are filled with fragments of limestone scattered about like the fragments of schist in the sandstone in the neighbourhood of the junction on our coast.[22]
[Note 22: This has a reference to very curious observations which we made upon the east coast where these mountains terminate, and which I am to describe in the course of this work.]
”Among the ma.s.ses of limestone lately broken off for use, and having the fractures fresh, I found the forms of c.o.c.kles quite distinct; and in great abundance.--I send you three pieces of this kind,” etc.
It may perhaps be alleged that those mountains of c.u.mberland and Tweedale are not the primary mountains, but composed of the secondary schistus, which is every where known to contain those objects belonging to a former earth. Naturalists who have not the opportunity of convincing themselves by their proper examination, must judge with regard to that geological fact by the description of others. Now it is most fortunate for natural history, that it has been in this range of mountains that we have discovered those marks of a marine origin; for, I shall afterwards have occasion to give the clearest light into this subject, from observations made in other parts of those same mountains of schist, by which it will be proved that they are the primary strata; and thus no manner of doubt will then remain in the minds of naturalists, who might otherwise suspect that we were deceiving ourselves, by mistaking the secondary for the primitive schistus.
I have only farther to observe, that those schisti mountains of Wales, of c.u.mberland, and of the south alpine part of Scotland, where these marine objects have been found, consist, of that species of stone which in some places makes the most admirable slate for covering houses; and, in other parts, it breaks into blocks that so much resemble wood in appearance, that, without narrow inspection, it might pa.s.s for petrified wood.
We are therefore to conclude that the marks of organised bodies in those primary mountains are certainly found; at the same time the general observation of naturalists has some foundation, so far as the marks of organised bodies are both rarely to be met with in those ma.s.ses, and not easily distinguished as such when they are found.
But this scarcity of marine objects is not confined to those primary mountains, as they are called; for among the most horizontal strata, or those of the latest production, there are many in which, it is commonly thought, no marine calcareous objects are to be found; and this is a subject that deserves to be more particularly considered, as the theory may thus receive some ill.u.s.tration.
Sandstone, coal, and their accompanying strata, are thought to be dest.i.tute of calcareous marine productions, although many vestiges of plants or vegetable productions are there perceived. But this general opinion is neither accurate nor true; for though it be true that in the coal and sandstone strata it is most common to find marks of vegetable production, and rarely those calcareous bodies which are so frequent in the limestone, yet it is not unusual for coal to be accompanied with limestone formed of sh.e.l.ls and corals, and also with ironstone containing many of those marine objects as well as wood. Besides, sandstone frequently contains objects which have been organised bodies, but which do not belong to the vegetable kingdom, at least to no plant which grows upon the land, but would seem to have been some species of zoophite perhaps unknown.
I have also frequently seen the vestige of sh.e.l.ls in sandstone, although in these strata the calcareous bodies are in general not perceived.
The reason of this is evident. When there is a small proportion of the calcareous matter in the ma.s.s of sand which is pervious to steam and to the percolation of water, the calcareous bodies may be easily dissolved, and either carried away or dispersed in the ma.s.s; or even without being thus dispersed by means of solution, the calcareous matter may be absorbed by the siliceous substance of the stratum by means of fusion, or by heat and cementation. The fact is, that I have seen in sandstone the empty mould of marine sh.e.l.ls with some siliceous crystallization, so far as I remember, which corresponded perfectly with that idea. The place I saw this was in a fine white sandstone accompanying the coal, upon the sea side at Brora in Sutherland.
Mineralogy is much indebted to Mr Pallas for the valuable observations which he has given of countries so distant from the habitations of learned men. The physiology of the globe has also been enriched with some interesting observations from the labours of this learned traveller.
But besides giving us facts, Mr Pallas has also reasoned upon the subject, and thus entered deep into the science of Cosmogeny; here it is that I am afraid he has introduced some confusion into the natural history of the earth, in not properly distinguis.h.i.+ng the mineral operations of the globe, and those again which belong entirely to the surface of the earth; perhaps also in confounding the natural effects of water upon the surface of the earth, with those convulsions of the sea which may be properly considered as the accidental operations of the globe. This subject being strictly connected with the opinions of that philosopher with regard to primitive mountains, I am obliged to examine in this place matters which otherwise might have come more properly to be considered in another.
M. Pallas in his _Observations sur la formation des montagnes_, (page 48) makes the following observations.
”J'ai deja dit que _la bande de montagnes primitives schisteuses_ heterogenes, qui, par toute la terre, accompagne les chaines granitiques, et comprend les roches quartzeuses et talceuses mixtes, trapezodes, serpentines, le schiste corne, les roches spathiques et cornees, les grais purs, le porphyre et le jaspre, tous rocs feles en couches, ou presque perpendiculaires, ou du moins tres-rapidement inclinees, (les plus favorables a la filtration des eaux), semble aussi-bien que le granit, anterieure a la creation organisee. Une raison tres-forte pour appuyer cette supposition, c'est que la plupart de ces roches, quoique lamelleuse en facon d'ardoise, n'a jamais produit aux curieux la moindre trace de petrifactions ou empreintes de corps organises. S'il s'en est trouve, c'est apparemment dans des fentes de ces roches ou ces corps ont ete apportes par un deluge, et encastrees apres dans une matiere infiltree, de meme qu'on a trouve des restes d'Elephans dans le filon de la mine d'argent du Schlangenberg.[23] Les caracteres par lesquels plusieurs de ces roches semblent avoir souffert des effets d'un feu-tres-violent, les puissantes veines et amas des mineraux les plus riches qui se trouvent princ.i.p.alement dans la bande qui en est composee, leur position immediate sur le granit, et meme le pa.s.sage, par lequel on voit souvent en grand, changer le granit en une des autres especes; tout cela indique une origine bien plus ancienne, et des causes bien differentes de celles qui ont produit les montagnes secondaires.”
[Note 23: This is a very natural way of reasoning when a philosopher finds a fact, related by some naturalists, that does not correspond with his theory or systematic view of things. Here our author follows the general opinion in concluding that no organised body should be found in their primitive strata; when, therefore, such an object is said to have been observed, it is supposed that there may have been some mistake with regard to the case, and that all the circ.u.mstances may not have been considered. This caution with regard to the inaccurate representation of facts, in natural history, is certainly extremely necessary; the relicts of an elephant found in a mineral vein, is certainly a fact of that kind, which should not be given as an example in geology without the most accurate scientifical examination of the subject.]
Here M. Pallas gives his reason for supposing those mountains primitive or anterior to the operations of this globe as a living world; _first_, because they have not, in general, marks of animals or plants; and that it is doubtful if they ever properly contain those marks of organised bodies; _secondly_, because many of those rocks have the appearance of having suffered the effects of the most violent fire. Now, What are those effects? Is it in their having been brought into a fluid state of fusion. In that case, no doubt, they may have been much changed from the original state of their formation; but this is a very good reason why, in this changed state, the marks of organised bodies, which may have been in their original const.i.tution, should be now effaced.
The _third_ reason for supposing those mountains primitive, is taken from the metallic veins, which are found so plentifully in these ma.s.ses.
Now, had these ma.s.ses been the only bodies in this earth in which those mineral veins were found, there might be some species of reason for drawing the conclusion, which is here formed by our philosopher. But nothing is so common (at least in England) as mineral veins in the strata of the latest formation, and in those which are princ.i.p.ally formed of marine productions; consequently so far from serving the purpose for which this argument was employed, the mineral veins in the primitive mountains tend to destroy their originality, by a.s.similating them in some respect with every other ma.s.s of strata or mountain upon the globe.
_Lastly_, M. Pallas here employs an argument taken from an appearance for which we are particularly indebted to him, and by which the arguments which have been already employed in denying the originality of granite is abundantly confirmed. It has been already alleged, that granite, porphyry, and whinstone, or trap, graduate into each other; but here M. Pallas informs us that he has found the granite not only changed into porphyry, but also into the other alpine compositions. How an argument for the originality of these mountains can be established upon those facts, I am not a little at a loss to conceive.
The general mineralogical view of the Russian dominions, which we have, in this treatise, may now be considered with regard to that distinction made by naturalists, of primitive, secondary, and tertiary mountains, in order to see how far the observations of this well informed naturalist shall be found to confirm the theory of the earth which has been already given, or not.
The Oural mountains form a very long chain, which makes the natural division betwixt Europe and Asia, to the north of the Caspian. If in this ridge, as a centre of elevation, and of mineral operations, we shall find the greatest manifestation of the violent exertion of subterraneous fire, or of consolidating and elevating operations; and if we shall perceive a regular appearance of diminution in the violence or magnitude of those operations, as the places gradually recede from this centre of active force; we may find some explanation of those appearances, without having recourse to conjectures which carry no scientific meaning, and which are more calculated to confound our acquired knowledge, than to form any valuable distinction of things. Let us consult M. Pallas how far this is the case, or not.
After having told us that all those various alpine schisti, jaspers, porphyries, serpentines, etc. in those mountains, are found mutually convertible with granite, or graduating into each other, our author thus continues, (p. 50).