Theory of the Earth Volume I Part 7

The immediate question now before us is not, If the subterraneous fire, or elevating power, which we perceive sometimes as operating with such energy, be the consolidating cause of strata formed at the bottom of the sea; nor, if that power be the means of making land appear above the general surface of the water? for, though this be the end we want to arrive at ultimately, the question at present in agitation respects the laws of nature, or the generality of particular appearances.

Has the globe within it such an active power as fits it for the renovation of that part of its const.i.tution which may be subject to decay? Are those powerful operations of fire, or subterraneous heat, which so often have filled us with terror and astonishment, to be considered as having always been? Are they to be concluded as proper to every part upon the globe, and as continual in the system of this earth?

If these points in question shall be decided in the affirmative, we can be at no loss in ascertaining the power which has consolidated strata, nor in explaining the present situation of those bodies, which had their origin at the bottom of the sea. This, therefore, should be the object of our pursuit; and in order to have demonstration in a case of physical inquiry, we must again have recourse to the book of nature.

The general tendency of heat is to produce fluidity and softness; as that of cold is, on the contrary, to harden soft and fluid bodies. But this softening power of heat is not uniform in its nature; it is made to act with very different effect, according to the nature of the substance to which it is applied. We are but limited in the art of increasing the heat or the cold of bodies; we find, however, extreme difference in their substances with respect to fusibility.

A fusible substance, or mineral composition in a fluid state, is emitted from those places of the earth at which subterraneous fire and expansive force are manifested in those eruptive operations. In examining these emitted bodies, men of science find a character for such productions, in generalising the substance, and understanding the natural const.i.tution of those bodies. It is in this manner that such a person, finding a piece of lava in any place of the earth, says with certainty, Here is a stone which had congealed from a melted state.

Having thus found a distinguishing character for those fused substances called, in general, Lavas, and having the most visible marks for that which had been actually a volcano, naturalists, in examining different countries, have discovered the most undoubted proofs of many ancient volcanos, which had not been before suspected. Thus, volcanos will appear to be not a matter of accident, or as only happening in a particular place, they are general to the globe, so far as there is no place upon the earth that may not have an eruption of this kind; although it is by no means necessary for every place to have had those eruptions.

Volcanos are natural to the globe, as general operations; but we are not to consider nature as having a burning mountain for an end in her intention, or as a princ.i.p.al purpose in the general system of this world. The end of nature in placing an internal fire or power of heat, and a force of irresistible expansion, in the body of this earth, is to consolidate the sediment collected at the bottom of the sea, and to form thereof a ma.s.s of permanent land above the level of the ocean, for the purpose of maintaining plants and animals. The power appointed for this purpose is, as on all other occasions, where the operation is important, and where there is any danger of a shortcoming, wisely provided in abundance; and there are contrived means for disposing of the redundancy. These, in the present case, are our volcanos.

A volcano is not made on purpose to frighten superst.i.tious people into fits of piety and devotion, nor to overwhelm devoted cities with destruction; a volcano should be considered as a spiracle to the subterranean furnace, in order to prevent the unnecessary elevation of land, and fatal effects of earthquakes; and we may rest a.s.sured, that they, in general, wisely answer the end of their intention, without being in themselves an end, for which nature had exerted such amazing power and excellent contrivance.

Let us take a view of the most elevated places of the earth; if the present theory is just, it is there that we should find volcanos. But is not this the case? There are volcanos in the Andes; and round the Alps we find many volcanos, which are in France upon the one side, and in Germany upon the other, as well as upon the Italian side, where Vesuvius still continues to exhibit violent eruptions.

It is not meant to allege, that it is only upon the summit of a continent volcanos should appear. Subterraneous fire has sometimes made its appearance in bursting from the bottom of the sea. But, even in this last case, land was raised from the bottom of the sea, before the eruption made its exit into the atmosphere. It must also be evident, that, in this case of the new island near Santorini, had the expansive power been retained, instead of being discharged, much more land might have been raised above the level of the ocean.

Now, the eruption of that elastic force through the bottom of the sea, may be considered as a waste of power in the operations of the globe, where the elevation of indurated strata is an object in the exertion of that power; whereas, in the centre of a continent sufficiently elevated above the level of the sea, the eruption of that fiery vapour calculated to elevate the land, while it may occasionally destroy the habitations of a few, provides for the security and quiet possession of the many.

In order to see the wisdom of this contrivance, let us consider the two extreme places at which this eruption of ignited matter may be performed. These are, on the one hand, within a continent of land, and, on the other, at the bottom of the ocean. In the one case, the free eruption of the expanding power should be permitted; because the purpose for which it had been calculated to exist has been accomplished. In the other, again, the free eruption of that powerful matter should be repressed; because there is reserved for that power much of another operation in that place. But, according to the wise const.i.tution of things, this must necessarily happen. The eruption of the fiery vapour from volcanos on the continent or land, is interrupted only occasionally, by the melted bodies flowing in the subterraneous chimney; whereas, at the bottom of the ocean, the contact of the water necessarily tends to close the orifice, by acc.u.mulating condensed matter upon the weakest place.

If this be a just theory of the natural operations of the globe, we shall have reason to expect, that great quant.i.ties of this melted matter, or fusible substance, may be found in form of lava, among the strata of the earth, where there are no visible marks of any volcano, or burning mountain, having existed. Here, therefore, is an important point to be determined; for, if it shall appear that much of this melted matter, a.n.a.logous to lava, has been forced to flow among the strata which had been formed at the bottom of the sea, and now are found forming dry land above its surface, it will be allowed, that we have discovered the secret operations of nature concocting future land, as well as those by which the present habitable earth had been produced from the bottom of the abyss. Here, therefore, we shall at present rest the argument, with endeavouring to show that such is actually the case.

It appears from Cronstedt's Mineralogy, that the rock-stone, called trap by the Swedes, the amygdaloides and the schwarts-stein of the Germans, are the same with the whin-stone of this country. This is also fully confirmed by specimens from Sweden, sent me by my friend Dr Gahn.

Whatever, therefore, shall be ascertained with regard to our whin-stone, may be so far generalized or extended to the countries of Norway, Sweden, and Germany.

The whin-stone of Scotland is also the same with the toad-stone of Derbyshire, which is of the amygdaloides species; it is also the same with the flagstone of the south of Staffordshire, which is a simple whin-stone, or perfect trap. England, therefore, must be included in this great s.p.a.ce of land, the mineral operations of which we explore; and also Ireland, of which the Giant's Causeway, and many others, are sufficient proof.

In the south of Scotland, there is a ridge of hills, which extends from the west side of the island in Galloway to the east side in Berwickshire, composed of granite, of schistus, and of siliceous strata.

The Grampians on the north, again, form another range of mountains of the same kind; and between these two great fields of broken, tumbled, and distorted strata, there lies a field of lesser hardness and consolidation, in general; but a field in which there is a great manifestation of subterraneous fire, and of exerted force.

The strata in this s.p.a.ce consist, in general, of sand-stone, coal, lime-stone or marble, iron-stone, and marl or argillaceous strata, with strata of a.n.a.logous bodies, and the various compositions of these. But what is to the present purpose is this, that, through all this s.p.a.ce, there are interspersed immense quant.i.ties of whinstone; a body which is to be distinguished as very different from lava; and now the disposition of this whin-stone is to be considered.

Sometimes it is found in an irregular ma.s.s or mountain, as Mr Cronstedt has properly observed; but he has also said, that this is not the case in general. His words are: "It is oftener found in form of veins in mountains of another kind, running commonly in a serpentine manner, contrary or across to the direction of the rock itself."

The origin of this form, in which the trap or whin-stone appears, is most evident to inspection, when we consider that this solid body had been in a fluid state, and introduced, in that state, among strata, which preserved their proper form. The strata appear to have been broken, and the two correspondent parts of those strata are separated to admit the flowing ma.s.s of whin-stone.

A fine example of this kind may be seen upon the south side of the Earn, on the road to Crief. It is twenty-four yards wide, stands perpendicular, and appears many feet above the surface of the ground. It runs from that eastward, and would seem to be the same with that which crosses the river Tay, in forming Campsy-lin above Stanley, as a lesser one of the same kind does below it. I have seen it at Lednoc upon the Ammon, where it forms a cascade in that river, about five or six miles west of Campsy-lin. It appears to run from the Tay east through Strathmore, so that it may be considered as having been traced for twenty or thirty miles, and westwards to Drummond castle, perhaps much farther.

Two small veins of the same kind, only two or three feet wide, may be seen in the bed of the Water of Leith, traversing the horizontal strata, the one is above St Bernard's well, the other immediately below it. But, more particularly, in the shire of Ayr, to the north of Irvine, there are to be seen upon the coast, between that and Scarmorly, in the s.p.a.ce of about twenty miles, more than twenty or thirty such d.y.k.es (as they are called) of whin-stone. Some of them are of a great thickness; and, in some places, there is perceived a short one, running at right angles, and communicating with other two that run parallel.

There is in this country, and in Derbyshire[14], another regular appearance of this stone, which Cronstedt has not mentioned. In this case, the strata are not broken in order to have the whin-stone introduced, they are separated, and the whin-stone is interjected in form of strata, having various degrees of regularity, and being of different thickness. On the south side of Edinburgh, I have seen, in little more than the s.p.a.ce of a mile from east to west, nine or ten ma.s.ses of whin-stone interjected among the strata. These ma.s.ses of whin-stone are from three or four to an hundred feet thick, running parallel in planes inclined to the horizon, and forming with it an angle of about twenty or thirty degrees, as may be seen at all times in the hill of Salisbury Craggs.

[Note 14: See Mr Whitehurst's Theory of the Earth.]

Having thus described these ma.s.ses, which have flowed by means of heat among the strata of the globe, strata which had been formed by subsidence at the bottom of the sea, it will now be proper to examine the difference that subsists between these subterraneous lavas, as they may be termed, and the a.n.a.logous bodies which are proper lavas, in having issued out of a volcano.[15]

[Note 15: The Chevalier de Dolomieu, in his accurate examination of Aetna and the Lipari islands, has very well observed the distinction of these two different species of lavas; but without seeming to know the principle upon which this essential difference depends. No bias of system, therefore, can here be supposed as perverting the Chevalier's view, in taking those observations; and these are interesting to the present theory, as corresponding perfectly with the facts from whence it has been formed. It will be proper to give the account of these in his own words.

La zeolite est tres-commune dans certains laves de l'Ethna; il seroit peut-etre possible d'y en rencontrer des morceaux aussi gros que ceux que fournit l'isle de Ferroe. Quoique cette substance semble ici appartenir aux laves, je ne dirai cependant point que toutes les zeolites soient volcaniques, ou unies a des matieres volcaniques; celles que l'on trouve en Allemagne sont, dit-on, dans des circonstances differentes; mais je doit annoncer que je n'ai trouve cette substance en Sicile, que dans les seules laves qui evidemment ont coule dans la mer, et qui out ete recouvertes par ses eaux. La zeolite des laves n'est point une dejection volcanique, ni une production du feu, ni meme un matiere que les laves aient enveloppee lorsqu'elles etoient fluides; elle est le resultat d'une operation et d'une combinaison posterieure, auxquelles les eaux de la mer ont concouru. Les laves qui n'ont pas ete submergees, n'en contiennent jamais. J'ai trouve ces observations si constantes, que par-tout ou je rencontrois de la zeolite, j'etois sur de trouver d'autres preuves de submersion, et partout ou je voyois des laves recouvertes des depots de l'eau, j'etois sur de trouver de la zeolite, et un de ces faits m'a toujours indique l'autre. Je me suis servi avec succes de cette observation pour diriger mes recherches, et pour connoitre l'antiquite des laves. _Mineralogie de Volcans, par M. Faujas de Saint-Fond_. Here would appear to be the distinction of subterraneous lava, in which zeolite and calcareous spar may be found, and that which has flowed from a volcano, in which neither of these are ever observed.]

There can be no doubt that these two different species of bodies have had the same origin, and that they are composed of the same materials nearly; but from the different circ.u.mstances Of their production, there is formed a character to these bodies, by which, they may be perfectly distinguished. The difference of those circ.u.mstances consists in this; the one has been emitted to the atmosphere in its fluid state the other only came to be exposed to the light in a long course of time, after it had congealed under the compression of an immense load of earth, and after certain operations, proper to the mineral regions, had been exercised upon the indurated ma.s.s. This is the cause of the difference between those erupted lavas, and our whin-stone, toad-stone, and the Swedish trap, which may be termed subterraneous lava. The visible effects of those different operations may now be mentioned.

In the erupted lavas, those substances which are subject to calcine and vitrify in our fires, suffer similar changes, when delivered from a compression which had rendered them fixed, though in an extremely heated state. Thus, a lava in which there is much calcareous spar, when it comes to be exposed to the atmosphere, or delivered from the compressing force of its confinement, effervesces by the explosion of its fixed air; the calcareous earth, at the same time, vitrifies with the other substances. Hence such violent ebullition in volcanos, and hence the emission of so much pumice-stone and ashes, which are of the same nature.

In the body of our whin-stone, on the contrary, there is no mark of calcination or vitrification. We frequently find in it much calcareous spar, or the _terra calcarea aerata_, which had been in a melted state by heat, and had been crystallized by congelation into a sparry form.

Such is the _lapis amygdaloides_, and many of our whin-stone rocks, which contain pebbles crystallized and variously figured, both calcareous, siliceous, and of a mixture in which both these substances form distinct parts. The specimens of this kind, which I have from the whin-stone or porphyry rock of the Calton-hill, exhibit every species of mineral operation, in forming jasper, figured agate, and marble; and they demonstrate, that this had been performed by heat or fusion.

I do not mean to say, that this demonstration is direct; it is conditional, and proceeds upon the supposition, that the basaltic or porphyry rock, in which those specimens are found, is a body which had been in a melted state. Now, this is a supposition for which I have abundance of evidence, were it required; but naturalists are now sufficiently disposed to admit that proposition; they even draw conclusions from this fact, which, I think, they are not sufficiently warranted in doing; that is, from this appearance, they infer the former existence of volcanos in those places. For my part, though I have made the most strict examination, I never saw any vestige of such an event.

That there are, in other countries, evident marks of volcanos which have been long extinguished, is unquestionably true; but naturalists, imagining that there are no other marks of subterraneous fire and fusion, except in the production of a lava, attribute to a volcano, as a cause, these effects, which only indicate the exertion of that power which might have been the cause of a volcano.

If the theory now given be just, a rock of marble is no less a mark of subterraneous fire and fusion, than that of the basaltes; and the flowing of basaltic streams among strata broken and displaced, affords the most satisfactory evidence of those operations by which the body of our land had been elevated above the surface of the sea; but it gives no proof that the eruptive force of mineral vapours had been discharged in a burning mountain. Now, this discharge is essential in the proper idea of a volcano.

Besides this internal mark of an unerupted lava in the substance of the stone or body of the flowing ma.s.s, there are others which belong to it in common with all other mineral strata, consolidated by subterraneous fire, and changed from the place of their original formation; this is, the being broken and dislocated, and having veins of foreign matter formed in their separations and contractions.

If these are mineral operations, proper to the lower regions of the earth, and exerted upon bodies under immense compression, such things will be sometimes found in the unerupted lavas, as well as in the contiguous bodies with which they are a.s.sociated. If, on the contrary, these are operations proper to the surface of the earth, where the dissolving power of water and air take place, and where certain stalactical and ferruginous concretions are produced by these means; then, in erupted lavas, we should find mineral concretions, which concretions should be denied to bodies which had been consolidated at the bottom of the sea; that is to say, where, without the operation of subterraneous fire, no changes of that kind could have taken place, as has already been observed. But in the unerupted species of lava, that is to say, in our whin-stone, every species of mineral appearance is occasionally to be found. Let those who have the opportunity to examine, say, what arc to be found in proper lavas, that is, those of the erupted kind. Sir William Hamilton informed me, when I showed him those mineral veins and spars in our whin-stone, that he had never observed the like, in lavas We have now formed some conclusions with regard to the nature and production of those parts of the land of this globe which we have had the means of examining perfectly; but; from the accounts of travellers, and from, the specimens which are brought to us from distant parts, we have reason to believe, that all the rest of the earth is of the same nature with that which has been now considered. The great ma.s.ses of the earth are the same every where; and all the different species of earths, of rocks or stone, which have as yet appeared, are to be found in the little s.p.a.ce of this our island.

It is true, that there are peculiar productions in the mineral kingdom which are rare, as being found only in few places; but these things are merely accidental in relation to the land, for they belong in property to those parts of the mineral region which we never see. Such are, the diamond of the east, the platina of the west, and the tin of Cornwall, Germany, and Sumatra. Gold and silver, though found in many countries, do not appear to be immediately necessary in the production of a habitable country. Iron, again, is universal in the operations of the globe, and is found often in that profusion which equals its utility.

Between these two extremes, we find all other minerals, that is to say, here and there in moderate quant.i.ty, and apparently in some proportion to their use. But all these substances are to be considered as the vapours of the mineral regions, condensed occasionally in the crevices of the land; and it is only the rocks and strata (in which those mineral veins are found) that are now examined with regard to their original composition, at the bottom of the sea, as well as to that, operation by which those bodies had been indurated in their substance, and elevated from the place in which they had been formed.

Thus, we have sufficient reason to believe, that, in knowing the construction of the land in Europe, we know the const.i.tution of the land in every part of the globe. Therefore, we may proceed to form general conclusions, from the knowledge of the mineral region, thus acquired in studying those parts which are seen.

Having thus found, _first_, That the consolidated and indurated ma.s.ses of our strata had suffered the effects of violent heat and fusion; _2dly_, That those strata, which had been formed in a regular manner at the bottom of the sea, have been violently bended, broken, and removed from their original place and situation; and, _lastly_, Having now found the most indubitable proof, that the melting, breaking, and removing power of subterraneous fire, has been actually exerted upon this land which we examine, we cannot hesitate in ascribing these operations as a cause to those effects which are exposed to our view. Now, these may be considered as consisting in the solid state and present situation of those stratified bodies, originally formed by subsidence in the ocean; appearances which cannot, in reason, be ascribed to any other cause, and which, upon this principle, are perfectly explained.

It is not meant to specify every particular in the means employed by nature for the elevation of our land. It is sufficient to have shown, that there is, in nature, means employed for the consolidating of strata, formed originally of loose and incoherent materials; and that those same means have also been employed in changing the place and situation of those strata. But how describe an operation which man cannot have any opportunity of perceiving? Or how imagine that, for which, perhaps, there are not proper data to be found? We only know, that the land is raised by a power which has for principle subterraneous heat; but, how that land is preserved in its elevated station, is a subject in which we have not even the means to form conjecture; at least, we ought to be cautious how we indulge conjecture in a subject where no means occur for trying that which is but supposition.

We now proceed, from the facts which have been properly established, to reason with regard to the duration of this globe, or the general view of its operations, as a living world, maintaining plants and animals.

SECTION IV.

System of Decay and Renovation observed in the Earth.

Philosophers observing an apparent disorder and confusion in the solid parts of this globe, have been led to conclude, that there formerly existed a more regular and uniform state, in the const.i.tution of this earth; that there had happened some destructive change; and that the original structure of the earth had been broken and disturbed by some violent operation, whether natural, or from a super-natural cause. Now, all these appearances, from which conclusions of this kind have been formed, find the most perfect explanation in the theory which we have been endeavouring to establish; for they are the facts from whence we have reasoned, in discovering the nature and const.i.tution of this earth: Therefore, there is no occasion for having recourse to any unnatural supposition of evil, to any destructive accident in nature, or to the agency of any preternatural cause, in explaining that which actually appears.

It is necessary for a living or inhabited world, that this should consist of land and water. It is also necessary, that the land should be solid and stable, refilling, with great power, the violent efforts of the ocean; and, at the same time, that this solid land should be resolved by the influence of the sun and atmosphere, so as to decay, and thus become a soil for vegetation. But these general intentions are perfectly fulfilled in the const.i.tution of our earth, which has been now investigated. This great body being formed of different mixed ma.s.ses, having various degrees of hardness and solubility, proper soil for plants is supplied from the gradual resolution of the solid parts; fertility in those soils arises from the mixture of different elementary substances; and stability is procured to that vegetable world, by the induration of certain bodies, those rocks and stones, which protect the softer ma.s.ses of clay and soil.

In this manner, also, will easily be explained those natural appearances which diversify the surface of the earth for the use of plants and animals, and those objects which beautify the face of nature for the contemplation of mankind. Such are, the distinctions of mountains and valleys, of lakes and rivers, of dry barren deserts and rich watered plains, of rocks which stand apparently unimpaired by the lapse of time, and sands which fluctuate with the winds and tides. All these are the effects of steady causes; each of these has its proper purpose in the system of the earth; and in that system is contained another, which is that of living growing bodies, and of animated beings.

But, besides this, man, the intellectual being, has, in this subject of the mineral kingdom, the means of gratifying the desire of knowledge, a faculty by which he is distinguished from the animal, and by which he improves his mind in knowing causes. Man is not satisfied, like the brute, in seeing things which are; he seeks to know how things have been, and what they are to be. It is with pleasure that he observes order and regularity in the works of nature, instead of being disgusted with disorder and confusion; and he is made happy from the appearance of wisdom and benevolence in the design, instead of being left to suspect in the Author of nature, any of that imperfection which he finds in himself.

Let us now take a view of that system of mineral economy, in which may be perceived every mark of order and design, of provident wisdom and benevolence.

We have been endeavouring to prove, that all the continents and islands of this globe had been raised above the surface of the ocean; we have also aimed at pointing out the cause of this translation of matter, as well as of the general solidity of that which is raised to our view; but however this theory shall be received, no person of observation can entertain a doubt, that all, or almost all we see of this earth, had been originally formed at the bottom of the sea. We have now another object in our view; this is to investigate the operations of the globe, at the time that the foundation of this land was laying in the waters of the ocean, and to trace the existence and the nature of things, before the present land appeared above the surface of the waters. We should thus acquire some knowledge of the system according to which this world is ruled, both in its preservation and production; and we might be thus enabled to judge, how far the mineral system of the world shall appear to be contrived with all the wisdom, which is so manifest in what are termed the animal and vegetable kingdoms.

It must not be imagined that this undertaking is a thing unreasonable in its nature; or that it is a work necessarily beset with any unsurmountable difficulty; for, however imperfectly we may fulfill this end proposed, yet, so far as it is to natural causes that are to be ascribed the operations of former time, and so far as, from the present state of things, or knowledge of natural history, we have it in our power to reason from effect to cause, there are, in the const.i.tution of the world, which we now examine, certain means to read the annals of a former earth.

The object of inquiry being the operations of the globe, during the time that the present earth was forming at the bottom of the sea, we are now to take a very general view of nature, without descending into those particulars which so often occupy the speculations of naturalists, about the present state of things. We are not at present to enter into any discussion with regard to what are the primary and secondary mountains of the earth; we are not to consider what is the first, and what the last, in those things which now are seen; whatever is most ancient in the strata which we now examine, is supposed to be collecting at the bottom of the sea, during the period concerning which we are now to inquire.