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, _when_ the 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, algæ and
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 STRUCTURE of 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 porphyritic structure 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 the possibility 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 of Iceland 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 VEINS form 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
and polished 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 term _Ochil_, 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 the _Ochil_ range, near Devon. The
Gælic word _ochain_, or _ochail_, 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
the series 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 its _being_ alone, 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
God can 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 as _unshapen_.
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 the most 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 beautiful diversity 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 gentleness of 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 the WHOLE as 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 of FINAL CAUSES we 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. The SCHEME of
creation, in all its parts and relations, we may never know; its course
and order we can distinctly trace through many of its arrangements.
[Illustration: Relative Positions of Trap.]