CHAPTER VI.TRAP ROCKS.
We do not select the rocks which form the title of this chapter from mere arbitrary choice, or because they are geographically connected with the district under review, but because they are immediately the next in the chronological order of our course. The Sidlaws and Ochils have their position as precisely determined in relation to time as to space, for difficult often as it may be to fix the sequence of events within the historical era, there is generally no lack of evidence by which to ascertain, in the far remoter times,whenthe several strata and the igneous masses assumed their respective places on the surface of the globe. The proofs here are of a cumulative character, and irresistibly conclusive. The animate and inanimate things of earth, the living and the dead, are both admissible witnesses in the question, and their testimony is alike unexceptionable. The saurian seas had been disturbed upon the upheaval of their beds; these with their organic contents were elevated by the irruption of plutonic matter, and in their altered position gave a bolder contour and additional bulk to the primitive land. New accumulations were forming during the devonian period in the waters still mightily agitated along the lines of disturbance; new races of scale-enameled creatures occupied their depths, and huge crustaceans anchored among their rocky shallows. The interior regions again let loose their giant forces, and these chains of hills rose above the surface, disrupting and heaving into day the various deposits of the old red sandstone. Hence the formation of the one set of rocks preceded, in the order of time, the elevation of the other: not an islet appeared over all these parts while the sedimentary strata were accumulating beneath: plants and trees covered the flanks of the Grampians, algæand fuci abounded in the waters, and myriads of fishes sported amid their luxuriance; but as yet there was no basin of the Tay, no fertile Carse of Gowrie, no kingdom of Fife stored to repletion with its precious metals of iron, lime, and coal. The Sidlaws and Ochils, therefore, become invested with even a romantic interest, when we thus view them in their geological relations—their age precisely defined—and themselves, flinty and weather-stained, the memorials of the vast convulsions and changes of nature. They mark the outgoing of a period comparatively barren of vegetable life, and the incoming of the exuberant products of the carboniferous epoch.
I.The structureof the Sidlaw and Ochil ranges, from the amorphous character of the rocks, furnishes little or no room for geological description. These nearly parallel chains of hills, separated only by an interval of from two to five miles, and forming the lower water-shed of the basin of the Tay, consist of the various members of the trap family usually denominated whinstone, and whose structure is very different, upon a glance, from that of the sandstones and other sedimentary deposits we have been considering. This class of rocks have all a tendency, in mineralogical phraseology, to a spathose structure, and discover at least the rudiments of crystallization: there is no lamination in their internal texture, and the lines of stratification which they sometimes exhibit are assumed, or impressed by the previously consolidated strata among which they have been injected. They are not lavas, which are sub-aërial products, nor are they aqueous formations, whose materials have been deposited in water. These rocks are the results of igneous fusion deep under the crust of the earth, poured over the bottom of the sea, and protruded into the diversified dome-shaped forms which they generally present.
Trap-rock consists of several varieties, as porphyry, clinkstone, compact feldspar, amygdaloid, greenstone, and basalt. These all pass into each other by insensible gradations, often forming one continuous mass, for the most part composed of the same ingredients, and have in consequence been regarded by geologists as belonging to one group, produced under similar circumstances, and elevated at intervals about the same period. The porphyriticstructure prevails generally in both chains, and “porphyry has the peculiarity of being rarely found in any but the primary strata: it seems to be the whinstone of the Old World, or at least that which is of highest antiquity in the present.”[2]But not only are both ranges characterized by the same qualities and texture of rocks in hand-specimens, one hill answering to another; they also preserve the same general features of outline, and the same relations to the disrupted sandstones among which they have been injected. The highest point, for instance, in the eastern division of the Ochils, is Norman’s Law, attaining an elevation of nearly one thousand feet above the level of the sea: in its uprise the mass has brought along with it the lower beds of the gray sandstone, which flank its northern and eastern sides, within three hundred feet of the summit. To the north and west of Dundee the highest points of the Sidlaws are encompassed in like manner with their analogous beds of the gray rock. And so in every locality, whether along their base lines, or among the numerous ravines and valleys that intersect their cultivated slopes, the strata may be seen cropping out, bearing testimony to the convulsive movements to which they have been exposed, and the altered positions they have in consequence assumed.
A remarkable bed of conglomerate or tufaceous trap intersects the chains at different, but generally corresponding, points of elevation, varying from two to four hundred feet above the sea-level. On the Ochil side this bed crosses the chain of hills from Letham school-house to Lindores Loch, where, along the line of the Edinburgh and Northern Railway, the out-crop may be observed at various places—very interestingly on the western slope of Clatchart—and again appearing at intervals toward Abernethy, whence it is traceable through the glen. In the ravines of the Sidlaws, behind Rossie Priory, in the den of Pitroddy, on the face of Kinnoul and Moncrieffe Hills, and across the ridge intersected by the Perth tunnel, indications of the same tufaceous bed can be traced, consisting, for the most part, of quartz rock, schist, and rounded masses of the different varieties of the trap, mixed not unfrequently with bowlders and smaller pieces of the gray and red sandstones.This formation has, doubtless, been produced on the bottom of a troubled sea, where the crust has been exposed to violent action—much of it comminuted and broken into fragments, rolled and fashioned into nodules, large portions of it torn up, but retaining their continuity for a space—when the molten flood has poured from below, and diffusing itself through the mass, the whole, after successive eruptions, has been lifted to its present elevation.
II. The amygdaloidal portion of these hills forms an interesting feature, and prevails very widely in both chains. This rock has a conglomerated stratified appearance in some places; but generally the matrix is very compact, rather porphyritic, of a dark brown or greenish hue, and when exposed to weathering, the innumerable small cavities or vesicular tissue by which it is laminated are prominently exposed. These cavities are filled with zeolites, carbonate of lime, chalcedony, prebnite, and various other crystalline silicious deposits. The green hue is derived from the decomposition, on the exposed surfaces, of the imbedded substances. This rock forms the true habitat of the richest and most beautiful specimens of the agate and jasper family, of the purest Scottish pebble, and of large sparkling geodes of amethystine crystals. The agates of Kinnoul and Moncrieffe are prized by lapidaries, as they are admired by amateurs, and no mineralogist should fail to visit the romantic pass of Glen Farg—illustrated by the classic pens of Galt, Lauder, and Scott—adorned and stored, in every niche of its serpentine course, with calc-spars, analcime, chabasie, stilbite, heulandite, konilite, and the entire family of the zeolites, presenting often fasciculi of crystals several inches in length, thin as silken threads, and rivaling frost-work in the transparency and brilliancy of their texture. The mass of rock constituting Bein Hill, and intersected by the turnpike for miles, appears as a simple agglutination of nodules of the size and color of garden peas, and consisting principally of analcime, zeolite, and chalcedonic pebbles.
What account is given of these curious formations—of their color, structure, and qualities—all so different from those of the surrounding matrix? Assuming the igneous origin of the trap family of rocks, and against which there can scarcely exist thepossibility of an argument, it is supposed that, when in the act of cooling, cavities would necessarily be produced in the heated molten mass by the expansive power of gases, and that upon their escape silicious and other deposits would be formed in the empty spaces. All the ingredients of the included crystals, of every genus, are plentifully diffused through nature, mixed up with the matter of every kind of rock; air and water are nowhere wanting, and substances sufficiently porous, for their transmission; a lamination or separation of coating, layer upon layer, is discernible in every agate; while the still partially existing hollows in some nodules, and the concentric nature of the bands of earthy matter which lines their surface, clearly demonstrate the deposition of the outer prior to that of the inner layer, and prove that at the very time when the crystallization had commenced, the cavities had assumed the form and shape which they now retain. Sometimes, too, the nodules have a compressed or flattened appearance; and the explanation in such cases is, that the cavities, if formed during the cooling of the beds, must have been altered in their shape by pressure either before the deposition of the silicious matter, or during the successive formation of the layers. Other, and indeed many, theories are broached, among which the most plausible is, that the cavities in which the agates are now found were caused by the “molecular aggregation of the silicious particles compelling the surrounding matter to yield in proportion to the attraction of these homogeneous particles.” The former explanation, however, is the most generally adopted, the most obvious in its conditions, and the most accordant with the existing processes of nature, the laws of heat, and the order of crystallization. The porosity and fibrous structure of agates, consisting of a congeries of minute radiating fibers at right angles to the rings or concentric layers, have also been established from microscopical examination, and hence the diversity of their colors, whether from vegetable matter or metallic oxides everywhere so abundant in the soils and crust of the globe.
The same law or mode of formation applies to crystallized minerals generally, and has continued to operate from primitive times to our own in their production. The sparkling topazes of Cairngorm and gigantic crystals of the Alps—the semi-opal ofIceland and the heliotrope of Kinnoul—the dazzling emeralds of Brazil and Ethiopia—the stupendous garnets of Fahlun—the delicately-colored fluors and calc-spars of Derbyshire and Cumberland—the gorgeous rubies and sapphires of India and Ceylon—the beautiful prismatic idocrase of Vesuvius and Etna—the splendid amethystine geodes of Oberstein, Siberia, and Spain, little grottoes lined with polished geometrical figures, all declare a common birth as they all nestle in rocks of a common origin. The diamond, the richest as it is the rarest of all, belongs to a totally different class of crystallized bodies, and owes its formation to the agency of entirely different causes.
III.The dykes or veinsform another striking feature among the geological phenomena of these hills, and seem as if nature intended them for lacings or bands to give greater cohesion and stability to its parts. They consist of long narrow strips of rock, which have made their way through the previously consolidated strata, intersecting the planes of their several beds at nearly right angles, and constituting among themselves a system of parallel and vertical partitions in the rock. Once observed in any district, these dykes are of too marked a character not to excite inquiries as to their uses and mode of formation; and occurring, as they do, in every region and among all classes, from the oldest primary to the newest tertiary deposits, they are obviously designed for some great purpose in the plan of Creation.
Veins may be described as tabular masses that penetrate the earth’s crust to an unknown depth, and almost invariably consist of different materials from the rocks they traverse. They are supposed to have all been in a state of fusion, and either themselves to have produced rents and fissures in their pressure upward, or to have filled with their molten ingredients such as from other causes were already existing. When detected in sandstone or other stratified formations, they are readily distinguished, and acknowledged to be of foreign origin as well as of posterior date. The matter of them consists generally, among the secondary formations, of basalt or greenstone; more frequently of porphyry and feldspar among the older and crystalline rocks. In their passage through whinstone the sides of the veins are usually smoothed andpolished as if by the action of another body rubbing against them; the sandstones and other sedimentary rocks are indurated, or discoloration may be traced for a considerable space inward from the walls of the vein. There is no mixing up of the materials of the dyke, nor any approach to incorporation with those of the including mass. After exposure on the surface to atmospheric influences, the basalt or greenstone splits up into large tabular blocks, which become extremely friable, and scale off in thin layers, leaving a central ball, which exfoliates in like manner, and gradually molders into dust. These dykes are very numerous in the Grampians, occurring everywhere, and diverging in every direction through the primary rocks. They traverse the lower district on the south of the range, five or six crossing the Tay, and running nearly parallel in a north-westerly course. They rise above the sandstone in various places of Strathearn, forming mural ridges, furrowed into broad jointed masses, or piled loosely above each other. The outgoing of some of these remarkable concretions can be traced into the German ocean. From St. Andrews westward, their line of bearing may be detected, both among the trap-hills and the sandstones which flank them, and like well-run stags, after debouching from the Ochills and Sidlaws, converging upon the forest of Glenartney. Doubling, winding, and dragging out and in among the passes from Crieff to Comrie, two of them may be descried on the steep face of Aberuchill, fairly scaling its lofty summits; and driving onward, may others be observed on the south of the Ruchle, to the far heights of Uam-Var.
The etymology of the termOchil, would seem to be connected in some way with these geological phenomena. A tradition exists that, from time immemorial, the earthquakes of Comrie were cotemporaneous with subterranean movements or noises in theOchilrange, near Devon. The Gælic wordochain, orochail, signifies, according to Armstrong, “moaning, wailing, howling;” and hence it is inferred that the name of the “Moaning Hills” may have been given to the range, from the sounds so frequently heard in the district. There can be no question as to the probability of a subterranean sympathy betwixt the two localities, through the instrumentality of these dykes, or otherwise; and, though theseries of events referred to above belong to an anterior age—far remote, indeed, from the human and all its traditions—a plausible origin is thus given to the name, in connection with an analogous series of events that did happen within the human period.
IV. A vast historical interest, therefore, is to be attached to these hills, and their phenomena of veins, connected as they are with the first elevatory movements of the globe, and when form and outline were being given to its massive fullness. The hand of the Creator is clearly seen in raising them up from the depths below. Not a particle of the entire volume is in its original position, or that which it would of itself statically assume. God formed everything for use, while beauty and agreeableness of shape are inseparably combined. When viewed in the light of causation, it is not enough merely to say, and there to stop short, that we see in the outward face of nature the impress of power, wisdom, and goodness—that none of these things made themselves—that the rocks and mountains are an image of Jehovah’s greatness—the streams, plains, trees, corns, animals, the effect of His love and care. All this they unquestionably are, but they are more. Their arrangement and disposition, beside their mere existence, evince a continued superintendence—a purpose and a will to maintain an order and construction of elements which would otherwise separate and dissolve—a keeping together, and as one, each after their own kind, the inorganic and organic parts of creation. The philosophy, as well as theology, of these arrangements have been thus beautifully recorded: Thou coveredst the earth with the deep as with a garment, the waters stood above the mountains; at thy rebuke they fled, at the voice of thy thunder they hastened away into the place thou hast prepared for them. Thou hast set a bound that they may not pass over; that they turn not again to cover the earth.—It is demonstrable that, were all the rocks which compose our mountain ranges and dry land to be dissolved and carried into the sea, the waters of the globe are sufficient again to cover and conceal from view their vast and multiform materials, and to replace them in those depths whence they originally arose.
Dr. Chalmers, in his work on natural theology,[3]has not, we think, correctly apprehended the bearings of the argument for the existence of a God drawn from the fact of the existence of a material world. “We do not perceive,” he says, “how, on the observation of an unshapen mass, there can from itsbeingalone, be drawn any clear or strong inference in favor of its non-eternity: or that simply because it now is, a time must have been when it was not. We cannot thus read in the entity of matter, a prior non-entity, or an original commencement for it: and something more must be affirmed of matter than merely that it is, ere we can discern that either an artist’s mind or an artist’s hand has at all been concerned with it.” Is this either sound reasoning or good philosophy? The fact of the entity of matter does, necessarily and directly, lead to the inference that it had a beginning. It could not originate itself, and just the more as it is viewed in its mere materiality, so much the stronger and irresistible the conclusion that there was no potentiality inherent in itself to cause it to begin to exist. Strip these hills of all their verdure—remove from the mind all consideration of their beauty, variety, and softness of outline—divest that landscape of its ebb and flow of tide—of all that constitutes the scene one of the most charming on the face of the earth, and in its desolation and sterility you would still in idea revert to a period when it was not. These shapeless, inert, barren masses of rock, and soil, and sand, did not place themselves there by any power of their own. Whether on Mount Horeb or Bencleugh, the mind will learn, from its own inner voice, that the traces of Jehovah are there—a Power, beyond and above, that called these rude piles into being—the absence of all form and vitality in themselves the proof and the witness of the Creator’s mind and the Creator’s hand. Death cannot originate anything into life. Matter, as matter, cannot constitute nor begin of itself to be. A scene like this could not now commence its own being, and at no period in the past did it possess a single property of self-existence. The entity and eternity of matter are, therefore, two physically impossible things, as nothing but the one supreme intelligent Godcan be at once self-existent and eternal, and that which is God cannot be material.
But, if the reasoning here is bad, the philosophy is still worse. It is not philosophy at all to speak of anything in nature asunshapen. Matter is never presented to us in its simple elements. What we see of the visible, material world, is something in combination with something else, substance united with substance, and the union and combination are not accidental or chancework. There are law, order, and definite proportion in every compound body. Things go together by determinate arrangement. When first summoned into being, the elements of the universe had each separately their own communicated properties; they took their places in the mass, each according to their natures; and now the little and the great, the bowlder on the heath and the orbs on high, the concrete rock and our whole planetary system, are modeled upon a plan, and all subservient to a purpose. In decomposition none of them waste or decay. Resolved into their primary atoms, they unite in new arrangements, and collect into new bodies; and in the putrid corrupting mass, the law of order, symmetry, and beauty, reigns in active operation, eliminating new structures and establishing new harmonies.
Men have long been acquainted with the fact, that in all combinations of two or more substances, there are certain proportions which obtain among the different ingredients, and that the best mixtures are those which are regulated according to a scale. The arts have flourished, and improved in one age above those in another, just in proportion as this principle has been attended to, and the degree in which the properties of compounds have been ascertained. We hence learn to imitate the crystal in its clearness, and to rival the colors of gems and flowers. The metals are thus tempered for the use and benefit of society. The acids are neutralized, and salts are formed, and the health of man is restored or preserved. Dalton discovered the law of combination in definite and multiple proportions to be constant in the thin air we breathe—that water, in all conditions and situations, consists of the two ingredients oxygen and hydrogen, and that these in weight are always as eight of the former to one of the latter—that even themost elastic gases are composed of particles of real, ponderable, definable matter—and that through all substances, palpable or impalpable, gross or ethereal, the principle of aggregation, according to the atomic theory, is universal. Science has not, indeed, as yet determined what is the law of connection between the chemical composition and the crystalline forms of bodies; although Sir David Brewster has clearly established that there is an exact correspondence between their optical properties and their crystalline forms,—the law of the transmission of light through specific substances. Sir Isaac Newton had long before cone to the conclusion—and from the heavens brought down a philosophy to explain the theory of the earth—that “All things considered, it seems probable that God, in the beginning, formed matter in solid, massy, hard, impenetrable particles, of such sizes, figures, and with such other properties, and in such proportion to space, as most conduced to the end for which he formed them; and that these primitive particles, being solids, are incomparably harder than any porous bodies compounded of them; even so very hard as never to wear or break to pieces, no ordinary power being able to divide what God made one in the first creation.” Philosophy such as this, verified, much of it, by an induction of rigid experiments, discovers a universe of matter worthy of its author, and like him—a God, not of confusion, but of order; things framed, every one of them, according to rule and method, and all stamped with the indelible impress of utility, design and loveliness. The “unshapen” has no place in the physical world.
“It is not,” continues Dr. Chalmers, “from some matter being harder than others, that we infer a God; but when we behold the harder placed where it is obviously the most effective for a beneficial end, as in the nails, and claws, and teeth of animals, in this we see evidence of a God.”
Now, this is precisely what has been done in the construction and disposition of the several parts of our planet. The hardest matter is placed where it can subserve a beneficial end, on the bottom of the sea, the shores of a continent, the hills that border the valleys of a country. The framework of the globe is in itself of the most durable materials, and these materials have been all so arranged as to render the earth solid, fertile, and beautifuldiversity of climate, combined with diversity of soil, moisture, and shelter. These rocks may have been molten in the depths beneath; but no innate powers of nature raised them unto mountains, and separated the hard from the soft, lifting the heavier substance into the highest places, and scooping out the hollows for the lighter. These are acts, all of them, of divine might, directed to a purpose, and what alone could render this world a fitting abode for living things. Wonderfully made are all the creatures of our earth,—every bone, sinew, and muscle in its appropriate place—and so constructed as best to perform their respective functions. But equally wonderful the adjustment and adaptation, through all its parts, of that earth on which they are domiciled, and which ministers so admirably to the various wants and requirements of its diversified tribes of plants and animals. Not more significant of design, nor more effective for a beneficial end, the bony heads and enameled scales of the finny inhabitants of the period, the cephalaspes and holoptychii of the stratified rocks, than the indurated texture of the traps as a solid casement in which their waters were to be retained, and a storehouse of well-assorted materials, whence substance and nutriment were to be extracted for the land. The argument, in short, so far as fitness and utility are concerned, is one and the same in both classes of objects—the house and its inmates alike illustrative of contrivance and skill—equally eloquent in praise of the artist’s mind or the artist’s hand.
And in this way it is, that the story of our earth should be read, and the course of creation should be traced. In the first ordering of things, we see the interposition of a great First Cause; and the farther back we go in our geological researches, the more closely do we discern the chain that connects our globe, and all that is in it, with the throne of the Eternal. The everlasting hills, we are constantly reminded in Scripture, are the witnesses of his power. They are appealed to as the evidences of his ever-active, ever-sustaining presence. What wonderful manifestations of his might and wisdom have they been called to testify! Mount Ararat, the symbol of his saving interposition—Mount Sinai, for the giving of the law, and surrounded with the thunder and terror of his great name—Horeb, proclaiming his mercy and the gentlenessof his love—Gilboa, drenched in the blood of his swift vengeance—Hermon, a token of the minuteness of his care and the sweetness of his grace—Tabor, Olivet, and Calvary! scenes of the mystery of incarnation and awful purity of inflexible justice.—And these very hills and mountains around, standing memorials through all ages and their revolutions, that at his bidding they arose, and by his sustaining agency they are still upheld and preserved on high.
We regard as utterly untenable the doctrine, therefore, that from the “entity” of matter we cannot infer the existence of a God. Matter, as mere matter, we do not see, and know nothing of. All the matter that is brought under our notice, is either organized or elaborated into arrangement and disposition of parts, as nicely harmonized and adjusted as organic shape and form.—The organic and inorganic structure may differ, but the difference is one of degree, as much as of kind. The argument, from the existence and composition of the atmosphere, the salubrious mixture of gases in the formation of water, the capacity and adaptation of soils for the germination of seeds and the growth of plants, is equally pointed as to the proof of design and beneficial end, as that which is derived from the fleece of the sheep, the feathers of the bird, and the silicious coating of the wheat-stalk. The uses of these things are obvious, and seen and appreciated at once.—But so is every molecule of matter and aggregation of rock, in the largest amorphous mass as in the polished crystallized gem, assimilated by law and indurated for use. And when we see the structure of the entire globe so directly conducive to the well being of its numerously diversified families, we have the argument the same in thewholeas in the parts, in the lumpish mass as in the order and symmetry of the bones, muscles, and organs of the animal frame. But for these hills the rain would fall perniciously, and the dews distill in vain. Of what use the return of the seasons, with no variety of climate? and while the ocean encompassed the globe, where would be the courses of the rivers, the mists and exhalations of the valleys? We may often mistake the uses of things, the end and purpose of particular arrangements; but the doctrine ofFinal Causeswe ought never to leave out of our calculations. They pervade all nature. They permeate all bodies.The world as constituted, the creation which we contemplate and admire, is in all its parts and dispositions a system of means and ends, a combination of instruments end skillfully-balanced agencies, a bright ever-discoursing record of the Eternal Mind, which yet shrouds itself in light inaccessible and utterly unfathomable to the comprehension of all created, finite intelligences, whether human or angelic.
Thus geology takes us up to the beginnings of creation—shows us the ingredients and arrangements of matter—lays bare the foundations of our earthly dwelling, the divisions and conveniences of its apartments—and seeing wisdom in adaptation, design in endurance and suitability, we infer, upon equally irresistible grounds, that the earth is of God, and manifests in everything the perfections of its Author. Theschemeof creation, in all its parts and relations, we may never know; its course and order we can distinctly trace through many of its arrangements.
Relative Positions of Trap.
Relative Positions of Trap.
Relative Positions of Trap.