NATURE AND STRUCTURE OF THE GRAMPIANS. PRIMARY ROCKS.
In beginning a description of the earth, every one is prepared for the
information, that it must have existed in some form or other antecedent
to the development of life upon its surface. Revelation asserts a
succession in the objects created, as well as in all the cosmical
arrangements connected with the early history of our planet. Things
were not perfected at once, and brought simultaneously into adaptation
and form; a preparation and a fitting up, as it were, of the inorganic
preceded the introduction of the organic structures of creation; and,
accordingly, the solid framework of the globe gives corroborative
evidence of this anterior condition of its history. The rocks of the
period are, from this circumstance, denominated PRIMARY, because they not
merely denote the absence, but are assumed to have been formed before the
existence, of any types of organic matter, vegetable or animal.
Nowhere can this first lesson in geology be more forcibly taught than by
an examination of the sterile rocks and rapidly decomposing precipices
of this bleak and hoary region. Once through the glens, and fairly
commencing the ascent of the center mountain, every symptom of existing
life has disappeared; and amid the huge, tabular masses that accompany
you in the upward journey, there is no trace of organic forms in these
vestiges of the past. The nucleus of the whole group is granite, one
dense aggregation of crystals; now rent and furrowed by a thousand seams,
the heart and penetralia bared and open, a convulsed sea of molten matter
still and motionless as the grave! The associated rocks, all of the
primary class, are gneiss, mica-slate, quartz-rock, chlorite-slate, and
limestone; and these inclose no relic of a living thing. Geology thus
ascends the stream of Time; but it gives no farther tidings of a scene
like this, save that it arose from the depth beneath at the Creator’s
bidding.
THE STRUCTURE OF THE DISTRICT.—The mountain of Ben-Mac-Dhui, according to
recent measurements, is 4,418 feet in height, and covers a superficial
area of nearly forty miles in extent. It occupies a central position
in the Grampian range, being about equidistant betwixt Aberdeen on the
German Sea and the western coast, so ribbed and indented by the Atlantic.
Ranges of granitoid rocks, of the primary class, diverge for nearly forty
miles south and north of Ben-Mac-Dhui, thereby giving this mountain a
prominence in position possessed by no other within the boundaries of the
island.
The valleys by which this monarch is surrounded, open in every direction,
and run toward every point of the compass. Two great rivers, the Don and
Dee, take their rise in some of the deep gullies of the mountain, while
the Spey is fed by the innumerable streams that issue from its sides.
These rivers have each an easterly direction, which, by their water-shed,
give shape and character to the whole district. A hundred lateral glens,
with their tributary streams, and all their tarn-head or loch, debouch
upon the three principal straths, whereby their deepest solitudes are
reached, and the very foundations of their loftiest peaks bared and
laid open. There, remote from human habitation, the geologist sees as
it were two conditions of the world,—the one, the shattered framework
and fragments of its early convulsions, huge mountains prostrate and
crumbling beneath his feet,—and the other, the spring-heads of renewed
vitality collecting in countless dripping rills, each to sustain its
own little plot of pasturage and flowerets, not the less welcome that
they are all so rare and alpine, and looking in their freshness as if
they were there purposely to cicatrize and heal up the deep scars in the
rugged precipices around.
Loch-na-gar on the south-east, and Ben-y-gloe on the south-west, have
also their separate congeries of lofty hills and precipitous defiles,
inclosing tarns, lochs, and rivers; likewise their own peculiar grouping
of glens and straths, whose inner recesses are all most speedily attained
through the velvet pathways of their moss and crow-berry. From the poetic
peak the prospect is worthy of its fame. All around is a vast rolling
surface of mountains, with steep mural precipices, and separated by deep
ravines, while immediately underneath a cliff of 1,300 feet lies the
lake, contracted to a span, and rendered even darker in its gloom by the
snowy glaciers that sparkle here and there on the overhanging rocks.
From Loch-na-gar eastward to Craigdarroch and the more distant Morven,
and through the great forests of Balloch-bowie, Glentanner, and Glenesk,
granite is the prevailing rock. Around Balmoral, immediately under “these
steep frowning glories,” the granite rises into a number of smaller and
beautifully dome-shaped hills. Cloch-na-bein and Mount Battock, washed
by the Feugh and the Dye, are likewise composed of granite. Gneiss,
mica-schist, quartz-rock, and clay-slate hang on the southern slopes,
training down into the plains of Kincardine and Forfarshire. To the west
of Loch-na-gar, and intermediate betwixt that range and the granitoid
masses which cluster round Ben-Mac-Dhui, the same alternating series of
stratified rocks occur. From Castleton to the head of Loch Callater, and
along by Glen-clunie to the junction with Glen-beg, where the counties
of Aberdeen and Perth meet, the strike of these rocks is again passed
over in a walk of a few miles; the beds penetrated and tilted up by
veins of granite and feldspar. Several dykes of the latter mineral, of
an extremely deep-red color and glassy crystalline texture, traverse
the district, extending over a vast range of country, penetrating
indifferently the granites and schists, and always forming attractive
objects in the beds of the rivers.
In the immediate vicinity of Castleton and Invercauld, the geological
phenomena of the district are very accessible as well as instructive, in
consequence of the comparative smallness of the mountains, and isolated
position into which they are thrown. A magnificent amphitheater of hill
and plain is spread out before the traveler, through which the Dee,
after a course of upward of twenty miles from its wells—mysterious as
the fountains of the Nile—rolls its waters, now joined by the Quioch,
Clunie, Candlie, and all the tributaries of the surrounding peaks.
Some of the hills present bare precipitous cliffs, as Craig Koynach and
the Lion’s Face, where the granite, schistose, and calcareous rocks
are finely exposed to view. Their strike is continued westward, when
they are severally crossed in the easy ascent of Morne, half of whose
dome-shaped top is covered with quartz-rock, which here, as in most of
the neighboring heights, attains to an enormous thickness, and shows
in weathering the yellow granular texture of sandstone. So remarkably
like are some specimens we picked up by the roadside, that for a time
we imagined ourselves to be approaching a region of secondary deposits.
Internally, however, the bright crystalline structure is uninvaded by
decay. Ben-Beck, Cairn-a-drochel, and Ben-Viach behind Mar Lodge, are
chiefly composed of gneiss, passing into a slaty micaceous schist. The
same character of rock continues upward through Glen-lui until its
junction with Glen-lui-beg and Glen-derry, where the granite maintains
its sovereignty over all that primitive lofty region.
The geologist, in penetrating these primeval wilds, has but little
choice left him as to the comforts of his pathway. Arrived at the top of
Glen-lui, the two diverging passes, right and left, are equally desolate,
savage, and grand. He may make his selection as the feeling of the moment
prompts, but he will not be able to congratulate himself as the traveler
in a different field—
Hic locus est, partes ubi se via fundit in ambas:
_Dextera_, quæ ditis magni sub mænia tendit;
Hac iter Elysium nobis: ut _læva_ malorum
Exercet pænas, et ad impia Tartara mittit.
No “fiends,” indeed, as Dryden renders it, are here, unless the belated
traveler may allow his fancy to shape these gnarled withered stumps of
the old forest, as it well may, into grisly living forms; or the red deer
breaking from their coverts, and gazing in wild amazement from the crags,
startle him from his propriety. Still Loch Avon, black as pitch, and
imbosomed in horrid rocks, is not an unfitting emblem of the Tartarean
lake.
Pursuing his route to Strathspey, either through the desolate openings
of Ben-Avon, or by the wild passes of Brae-Riach and Cairn-gorm,
the geologist again drops down among the gneiss, schists, limestone,
and quartz. These types of rock line the trough of the Spey, on both
sides, as far as the granite district of Ericht and Laggan, presenting
the usual phenomena of granitic and feldspathic dykes, and in some
places, as at Loch-an-Eilan, remarkable twistings and flexures in the
mica-schist around this eagle-haunted lake. Glen Tilt, on the south-west,
is distinguished by a singular display of granitic veins, appearing
to radiate from a common center—the well-known phenomena which the
philosophers of the Hutton and Playfair school pressed so keenly and
successfully into the service of their theory. The gneiss is generally to
be observed in the form of low ridges, interstratified with quartz-rock,
and approaching in mineral qualities to the mica-slate.
The bearing of all these stratified rocks is, on the main, sufficiently
indicated by the outline of the Grampian range. The quartz, mica, and
chlorite slates, are nearly continuous along the chain, traversing in a
S. W. by N. E. direction the breadth of the island, from sea to sea. The
line of strike, however, is often interrupted, either by the eruptive
veins above mentioned, or by the upheaval of the central axis, which,
as it rose with greater violence, or was parted into higher and unequal
ridges, would necessarily occasion corresponding changes in the lie and
direction of their coverings. This principle in geological dynamics has
been satisfactorily established by Mr. Hopkins of Cambridge, who has
shown, that in the production of any great line of elevatory disturbance,
whether affecting straight, curvilinear, or ellipsoidal masses, the
strata would frequently be broken by fissures at various angles to the
chief line of strain or elevation. Hence these interminable glens,
transverse straths, cul-de-sacs, and countless depressions, forming tarns
and lochs, all inosculating into each other, and which give such variety
and grandeur to this alpine region. The pent up ebullient matter beneath
the crust would thereby force its way to the surface—now in the form
of veins—now in long narrow ridges—and in other quarters assuming the
contour of broad mountain domes. The dip, in like manner, corresponding
to these partial strikes, as well as great axis of the chain, is often
various—as at the Linn of Dee, and along the braes of Corry Mulzie, the
beds being almost horizontal, while generally they are so highly inclined
as to be nearly vertical.
There are also numerous examples where the crystalline strata dip inward
toward the granite ridges, and in this manner form an acute angle with
the base, instead of being infolded over and welded to them. The only
admissible explanation in these instances of the dip is, that the ends
of the strata adjacent to the eruptive masses have sunk into depressions
occasioned by the evolution of igneous matter, while their upper edges
have been tilted backward. Hence the schists often rise into independent
elevated crests all along the chain, and even where no granite appears
at the surface. The rocks in Glen-Beg and Glen-Clunie afford examples
of this kind, where, as in Cairn-na-well, and the other mountains here,
they are highly inclined, and plunge in the direction of the principal
range. Geology, viewed in this light, becomes an auxiliary to physical
geography, explains many anomalous appearances on the earth’s surface,
and successfully accounts for all the flexures, breaks, undulations, and
inequalities, that constitute such marked features in the primary strata.
Until very recently, the doctrine maintained was, that nearly all the
inequalities on the earth’s surface were produced by the erosive and
denuding effects of water; that not merely the small lateral valleys and
branches of rivers, but likewise all their main trunks, were caused by
the slow and gradual working of the stream, cutting the most solid and
massive rocks in the same way and almost with the same instrument by
which the lapidary divides a block of marble or granite. Nay, with such a
ready agent, acting through incalculably remote and indefinite periods of
time, the conclusion was arrived at, that “on our continents there is no
spot on which a river may not formerly have run.” A sounder philosophy,
and one far more accordant with the facts, is now beginning to prevail,
namely, that nearly all transverse gorges, by which rivers escape across
ridges from one water basin to another, are nothing more than ancient
apertures in the crust of the earth, which have resulted from the former
disruption and denudation of the rocks: and that rivers, properly so
called, have never cut sections through chains, but simply flow in
chasms prepared for them.
NATURE AND QUALITIES OF THE ROCKS.—The granite is the most prevailing,
as well as the most striking in its appearance and texture, in the whole
range. Mineralogically considered, every specimen is a gem. Granite
is a compound, aggregate rock, here of a lively flesh or rose color,
consisting of perfectly formed crystals of quartz, feldspar, mica,
and in some instances hornblende, when it merges into what is termed
syenite. The sparkling film is mica. It is not metallic; but it shines
with metallic luster; and in some places of the chain, as at Rothes on
the Spey side, it is found in plates so large as to become a substitute
for glass. The component parts of mica are silex, alumine, potash, iron,
manganese, and traces of other substances. The colors of the mineral are
various, according to the proportions of some of the ingredients. The
laminæ are divisible into plates no thicker than 1/300,000th part of an
inch. Entering into the composition of almost every rock from the oldest
to the newest, it abounds chiefly in granite and schist, but also occurs
in sandstones, and the slaty shales of the coal formation.
I never look at a piece of granite, fragments of which are strewed on
every heath, without being reminded of Paley’s inaccurate and disparaging
comparison betwixt “the stone” and “the watch,” in his celebrated
argument for the existence of Deity. Take a specimen fresh and living
from the rock, or from any bowlder that meets you on the way. There is
not a stain in all that composite mass: how bright every ingredient! No
workmanship of man can rival it in its closeness of texture, beauty of
color, distinctness and delicacy of shading and outline. What chemistry
elaborated these particles as they separated and united? What scales
weighed their impalpable elements? What hands constructed their nicely
harmonizing proportions? Whence derived their principle of cohesion as
they cooled and inosculated in the burning crucible? As that fragment of
rock, so is the whole interior of the mighty range—the whole basis of the
continents of the world—countless myriads of sparkling gems wrought into
symmetry and form; the foundations of our earthly habitation literally
“garnished with all manner of precious stones.”
Paley, forgetful of every law or purpose so conspicuously developed in
the whole of these beautiful arrangements, thus commences his great work
on Natural Theology:—“In crossing a heath, suppose I pitched my foot
against a _stone_, and were asked how the stone came to be there, I might
possibly answer, that, for anything I knew to the contrary, it had lain
there forever: nor would it perhaps be very easy to show the absurdity of
this answer. But, suppose I had found a _watch_ upon the ground, and it
should be inquired how the watch happened to be in that place, I should
hardly think of the answer which I had before given, that for anything I
knew, the watch might have always been there.”
How many fallacies are there in this statement so far as mention is made
of the stone? The science of geognosie, not so far advanced in Paley’s
time, now clearly establishes the “absurdity” of supposing its having
lain from “eternity” in the place where it is found. The relative ages of
mountains, and therefore their succession in Time, are now demonstrable
and well understood. Then, the component parts of the mineral are as well
defined, as accurately proportioned, and arranged in manner and order as
precisely, as the several parts of the watch. The mica, the quartz, the
feldspar, have each their law or order of structure, as well as their
principle of aggregation; and they have taken their respective forms and
no other, and have assumed their compound structure and no other, in
obedience to chemical affinities and an atomic adjustment, as certain and
unalterable as are the conditions and requirements of dynamics.
Nay, more, the parent rock, from which that stone was taken, has its own
place in the system; its position, amidst the upheaved disrupted strata
around, has been assumed for a purpose; and the very size, form, and
outline of the giant mass, are all shaped to an end. Rocks are as easily
distinguished as trees or animals, which have not risen up by accident,
but have been constructed out of certain materials, and arranged each
according to its own class. Their internal characters, and even outward
shape, are marked and defined. The gnarled oak in fiber and texture
differs not more from the soft, pendulous, graceful willow, than are
the differences of rocks and minerals in their normal arrangement of
particles; in their diversity of fracture, cleavage, luster, and density.
We see at once the mechanism of the watch, the growth and expansion of
plants and animals. But so, upon gaining the least knowledge of its
frame-work and structure, we cannot open our eyes upon any part of the
external world, without being impressed with the conviction, that all
which we see and admire, must be the work of a higher power. Design
is stamped upon everything. Will, order, and might are everywhere
visible.—Geology, discovering harmony amidst apparent confusion,
renovation in decay, shows that every rock is fitted to its place;
that systems and series of formations are arranged upon a principle
of utility; and so thoroughly calculated to exercise their assigned
functions have all the parts been formed, that the most elaborate
machinery of man’s contrivance falls infinitely short of the beauty and
perfection everywhere displayed in the material creation. Lain forever!
No; such a scene of mountain, valley, river, plain, and ocean—all related
to each other—does not exist by chance, is not conserved nor arranged by
accident.
THEORY OF FORMATION.—When we examine a piece of granite, nothing appears
less likely, to a common observer, than that it was once in a molten
state through the action of fire, and that its crystalline structure was
assumed in process of cooling. Now, the fact of its crystallization,
the beautiful and perfect arrangement of its parts, the impress of the
one crystal upon the other reciprocally communicating their respective
shapes to each other, and the compact, agglutinated state of the whole,
is regarded as the strongest proof of the igneous origin of this
remarkable rock. Granite is not a mere congeries of parts, which, after
being separately formed, was somehow brought together and united; but
it is certain that the quartz, at least, was fluid when it was molded
on the feldspar. In some granites, the impressions of the substances
on one another are observed in a different order, and the quartz gives
its form to the feldspar. The ingredients of granite were therefore
fluid when mixed; and this fluidity was not the effect of solution in a
menstruum, as in that case one kind of crystal does not impress another,
but each retains its own peculiar shape; and the conclusion is, that
they crystallized from a state of simple fluidity, such as, of all known
causes, heat alone is able to produce.
This is the account given in the Huttonian theory, as expressed nearly
in the words of Playfair, which, along with the position of veins, the
disruption of superincumbent strata, and other phenomena, has resulted
in the universally received admission of the Plutonic character of this
class of rocks. Dr. Macculloch has extended the principle, and has
satisfactorily proved, that granite is but one term in the series of
igneous products, the passages from which are distinctly traceable into
granitoid syenite, and syenitic greenstone, and thence into greenstone,
basalt, and lava. Professor Forchhammer considers granite, when melted,
as one simple compound, and which only on cooling becomes separated into
the different minerals that compose it.
Granite, wherever it is found, is inferior to every other rock; and as it
composes many of the greatest mountain chains, it has the pre-eminence
of being elevated the highest into the atmosphere and sunk the deepest
under the surface, of all the mineral constituents of the globe to which
our researches extend. The associated primary rocks in this upland region
overlie the granite, and possess a distinctly stratified structure.
They are not now in their original position. They have been tilted up,
traversed, and interlaced by the granite while in fusion, and have been
altered greatly in their texture and qualities by their contact with the
heated mass. Hence they are called METAMORPHIC ROCKS, because of the
change to which they have been subjected.
The rocks that immediately overlie the granite are gneiss, mica-slate,
quartz-rock, and limestone. They all partake of the crystalline
structure, and all, except the last, possess the same ingredients,
and assume interchangeably the same aspect. Of gneiss there are three
varieties, each composed of feldspar, quartz, and mica, and distinguished
by the size and form of the crystals that constitute the mass. This rock,
consisting in all cases of thin lenticular plates, has a ribbon-like
appearance, and, according to the predominance of one of the parts,
becomes glandular, slaty, or aggregate. Mica-slate consists of quartz
and mica—the latter predominating—and feldspar frequently entering as
an adjunct. Quartz-rock, as the term implies, is formed of the pure
siliceous matter, nearly homogeneous in many instances—but scales of
mica are often present—and feldspar not always absent. The limestone,
again, differs from all the above in the excess of the calcareous
element, while, along with talc, steatite, actynolite, asbestus, and
other simple minerals, mica, quartz, and feldspar are likewise to be
numbered among the imbedded crystals. These rocks, over the entire
surface of the globe, are of one family, and generally associated. They
are always the lowest of the stratified series, and follow in the order
now described. They are essentially one and the same in their constituent
mineral qualities—different in the form and proportions in which they
are aggregated—and geographically connected with the granite in their
distribution. Thus these crystalline rocks not only constitute the floor
of our earth, but have in all probability supplied the materials under
whose plutonic agency, when fused and molten, the massive pavement was
raised above the waters and tempered into its present consistency.
Granite, the derivative rock, is found, accordingly, in every region of
the globe—the lowest as well as the most universally distributed—the
basis as well as the apex of every great mountain chain. No true Highland
scenery is anywhere to be found that does not embrace granite as the
most prominent feature in the picture. Not a hill in Scotland, two
thousand feet high, but incloses a portion of this rock. The beauties
of the English lake country are all derived from this source. The lofty
serrated peaks of Wales have been raised upon its crystal foundations.
The north-west and central portions of France, the Swiss and Tyrolese
Alps, the vast expanse betwixt Dresden and Vienna, the Caucasus, great
part of the Himalayan, Uralian, and Altai mountains, and large elevated
districts in China, are all less or more of granite formation. Through
Northern Russia and Scandinavia the granite may be regarded as merely
a continuation of our Scottish range—one great stony girdle, which
forms the primary mineral boundary of Northern Europe. America, Africa,
Australia, possess not a single ridge of celebrity through which the
same fundamental rock is not traceable in every district. How simple,
uniform, universal the component elements of the globe! One and the same
atmosphere surrounds it, one ocean washes it, one system of massive
pillars supports it, one sun enlightens it. How direct and irresistible
the inference, that one intelligent, all-powerful Being fashioned and
framed it!
The separation of the dry land from the waters was, doubtless, effected
through the instrumentality of means. The igneous theory of granite, and
other amorphous rocks, is in accordance with this supposition, which
thereby imparts a sacred and peculiar interest to all our investigations
respecting the origin and elevation of mountains. The range of geological
investigation is thus wide as the circumference of the globe—deep as the
foundations of the earth—and sublime thoughts are everywhere awakened of
Him—
Whose dwelling is the light of setting suns,
And the round ocean, and the living air,
And the blue sky, and in the mind of man:
A motion and a spirit that impels
All thinking things, all objects of all thought,
And rolls through all things!