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By HENRY M. CADELL, OF GRANGE, late H.M. Geological
Survey.
To the eye of the ordinary tourist, and to the eye of
many who call themselves artists, mountains seem to be all tolerably alike
in architecture and external form. Judging from the majority of the pictures
in our art galleries there seems to be but one great rock formation out of
which all mountains, with perhaps the exception of volcanos, have been
formed. When, however, we turn to Nature herself, and look more closely into
her face, with the help of a little elementary geology to guide us, we soon
begin to perceive that there are mountains and mountains, that some
mountains are knotty and others smooth, some are terraced and some are
scarred, some have jagged, saw-like crests, and others have smooth summits
covered with loose debris. There are, moreover, many varieties in the nature
of mountain sides. The sides of some are entirely composed of bare, rugged
rock without a patch of soil or a blade of vegetation to relieve their weird
grandeur. Such rock masses are usually steep and almost inaccessible. Other
mountain sides again consist of long straight "screes" or talus slopes of
debris inclined at an angle of about 350 to the horizon, with perhaps a
ridge or knob of rock protruding at the top. The face of Salisbury Crags is
an excellent example of a hillside of this kind. Many mountains again,
especially in Scotland, have neither conspicuous "screes" nor many
protruding crags along their slopes. Their sides are smooth and grassy, and
are covered with a thin skin of stiff stony boulder clay which looks as if
it had been plastered against the rock with a huge trowel at some remote
period in the past.
Underlying all these and many other phases of mountain
scenery, there is some hidden cause which it is a work of no small interest
to investigate. To consider all the varied types of mountain scenery even in
Scotland, would lead us far beyond the limits of the present paper, but we
may confine out attention at present to the mountains in the North-west
Highlands, as there is perhaps no other region in Britain where so many
distinct types of scenery are found in close association.
It is almost superfluous to remark at the outset that
each kind of scenery depends on the geological structure of the district
seen. It depends not less on the composition of the rocks than on their
curvature and arrangement relatively to one another. Geologically, for
purposes of classification, the rocks of the earth's crust are arranged not
according to their lithological composition, but according to the fossils
with which they may be associated. Thus there are various formations or
systems characterised by the presence of certain forms of plant and animal
life which flourished at sonic particular period in the earth's history; but
not necessarily characterised by any particular kind of rock. There may, for
example, be sandstone or limestone in the oldest or youngest of the
stratified systems, and indeed there are few formations in which one or both
of these rocks are not present.
This classification on chronological lines is,
however, of little importance to our present inquiry if it does not coincide
with a classification based on the physical characters of the rocks as well,
for the scenery of a country depends not on the age but on the kind of rock
in question. In Sutherland and Ross this happens to be the case, each of the
great formations is distinguished more by the physical nature of the rocks
than by the fossils they contain, as out of five distinct formations only
one has in this district yielded undeniable organic remains. The five
formations of Sutherland are-
5. Old red sandstone conglomerate.
4. Eastern
schists.
3. Silurian quartzite and limestone.
2. Cambrian sandstone.
1. Archaan gneiss.
Each of these gives rise to a distinct type of
scenery, and in the intrusive granite of Ben Laoghal a sixth class of
mountain structure may be observed.
The archean gneiss is the great foundation on which
all the newer rocks have been deposited, and hence it is only visible where
the latter have been denuded away. The tracts of country where the gneiss
predominates are generally wild and rugged in the extreme. The rock spreads
out in a vast sea of billowy knobs and ridges, or rises into majestic
mountains whose dark and knotty summits are sometimes over 3,000 feet in
altitude. All the west coast of Sutherland southwards from Loch Inchard is
composed of the old gneiss, and a more rugged piece of country than the
Ceathramli Garb/i, or "rough quarter," situated between Loch Inchard and
Loch Stack could scarcely be imagined. It is a tract of gneiss ridges and
hummocks without soil and almost destitute of vegetation, where nothing but
naked rock is to be seen for several miles at a time, and where it takes
about twenty acres to feed a single sheep. For several miles inland the
knolls and ridges of the Ceathramh Garbh do not rise to heights of over 500
feet above sea-level, and resemble the swelling billows of an angry ocean
which have suddenly become petrified ere they broke. As we recede from the
coast, however, the gneiss rises into a line of grim mountains dark and
forbidding in aspect. The best example perhaps of these is Ben Stack, a
mountain which when seen from the west resembles on a small scale the
Matterhorn. It has from this point of view a steep and rugged pyramidal
outline, and forming as it does one of a row of majestic summits that
surround the rough gneiss tract below, its importance to the landscape is
great indeed, and its well-marked individuality is not likely to be soon
forgotten by the attentive spectator.
The scenery of the Cambrian rocks is widely different
from that of the underlying gneiss. The gneiss is a tough gnarled
unstratified mass of crystalline rock, traversed indeed by bands of
variegated mineral matter and by veins of coarse pink granite or "pegmatite"
as it is called by geologists, but destitute of any planes of bedding such
as characterise all sedimentary formations. The red and chocolate coloured
Cambrian rocks are, on the other hand, well bedded, and although they form
the oldest stratified formation known to the geologists, they are as fresh
and unaltered by the vicissitudes of time as many quite recent sandstones.
The Cambrian scenery is at places—as in the Parph
between Cape Wrath and Loch Inchard—rather dull and uninteresting, but
southwards in the Assynt district the red sandstone rises into a series of
magnificent Bens, which, like the gneiss mountains farther north, tower
majestically over the rugged pavement of archaan rock that stretches away
from their bases to the rockbound shore. The best known of the Cambrian
mountains of Assynt are Suilven, Canisp, and Quinaig, which form parts of a
line sweeping southwards to Coigach and Loch Broom, and including such
important summits as Coul Beg, Coul More, Stack Polly, and Ben More Coigach.
All these are distinguished by their warm red or
purple tint, and by their lines of stratification, which can be detected
miles away. The strata are often very thick, and are intersected by
well-marked vertical joints or planes of weakness, along which the rock
tends to split when exposed to the weather. The sides of the Cambrian
mountains are thus often step-like in profile, each of the steps being the
edge of a horizontal bed which has not crumbled away, but has been abruptly
cut off by a joint face, from which a slice of the rock has been rent by the
frost and has rolled away en masse to the foot of the slope. There is in
this way a talus of debris at the bottom of each steep part of the hillside,
and the foundation of the mountain is, as a rule, completely covered by a
long talus such as conceals the lower part of Salisbury Crags near
Edinburgh. Talus slopes, or "screes," are not as a rule observable, or at
least so conspicuous round the mountains of archaan gneiss in this region.
The Cambrian mountains are remarkably grand and
striking, and possess a singularly well-marked individuality, which,
however, the ordinary artist very often completely fails to observe. To him
they appear as often as not to be members of the universal "putty formation"
out of which most of the protuberances on Mother Earth would appear to have
been moulded. Suilven, "The Sugar Loaf," is perhaps the most striking of the
red sandstone Bens, rising as it does all alone in the midst of a desolate
tract of ice-worn hummocks of gneiss, like a solitary sentinel posted in the
rear of a great army, the main body of which has marched off to the east and
left it standing alone in the wilderness.
The Silurian quartzite, which rests on both the gneiss
and the sandstone, has an individuality quite as distinct as either of these
formations. It is nearly white or light pink in colour, and does not in its
undisturbed state occur in very thick beds, but lies like a cake on the tops
of mountains whose lower parts are formed of the older and darker rocks. The
great gneiss ridge. between Loch Eriboll and the Kyle of Durness is partly
capped on its eastern slope with white quartzite. From the west the edge of
the light rock is seen capping the crests of Ben Spionnu and Cran Stacach
which separate the Loch Eriboll valley from Strath Dionard, and on the west
side of the Dionard the huge gneiss ridge of Foinaven is likewise tipped
with whitish quartzite. As we go southwards, however, we reach an area of
great geological disturbance, and the quartzite suddenly becomes enormously
thick and prominent among the scenic features of the region. It has been so
packed and thrust together that instead of occupying a subordinate place it
monopolises our attention by virtue of its great bulk and peculiar style of
weathering. As quartzite is simply a very hard sandstone composed almost
wholly of quartz, it has hardly any of the ingredients that form a good soil
for vegetation. The quartzite slopes are hence barren and bleak in the
extreme. The rock, moreover, does not split along great vertical joints like
the red sandstone, but breaks up into angular blocks and splinters, which
roll down the slopes and produce splendid screes which are more than
anything else a characteristic feature of this formation. A dark mass of
gneiss capped by quartzite crumbling away and shedding long streams of
fragments over the more sombre rock below, such as is well seen in Ben Arklc
and parts of Foinaven, resembles to my mind the head of a venerable
patriarch whose long white locks flow down from his smooth bald head and
spread out over his rounded back and shoulders.
I happened quite lately to visit a large exhibition of
water colours in London by well-known artists, and among many pictures of
great merit I came across a painting of a Sutherland deer forest. I soon
recognised the place as one almost every yard of which I had carefully
examined geologically a few years before. In this picture, the painting of
which was excellent, the artist had altogether failed to bring out the very
characters of which I have just been speaking.
Eastward from Loch Eriboll the country is mainly a
dreary plateau of the so-called "Eastern Schists." These rocks rise here and
there into important and grand mountains such as Ben Hope and Clibreck.
Although not so well marked in point of scenic characters as the older
formations to the west, yet the eastern schists have some distinctive
features of their own. The tops of the schist mountains are generally smooth
and rounded, and covered with great slabs of the rock which peels off in
flat tabular cakes. Seen from a distance the colour of these hill tops and
slopes is light slaty grey, and there is a thin growth of light green moss
and grass, which takes away from the formation the forbidding desolation of
the quartzite. The western side of Ben Hope is a magnificent precipice, is
gashed by gullies between which the rock forms huge buttresses that seem to
prop up the mighty mass above. Seen from Hope Lodge and the main road, Ben
Hope is truly a grand and striking mountain, rising as it does like a huge
pyramid over the smooth, dreary plateau of peat and purple bent that sweeps
away between Loch Eriboll and the Kyle of Tongue. Generally speaking,
however, the eastern schist mountains are notable for nothing but their
ugliness. Ben Hope, when seen from the south, is merely a rounded mass, and
Ben Armine is as shapeless and stupid looking a mountain as is to be found
anywhere.
The old red sandstone is not important in Sutherland,
but its great conglomerates form in Ben Griam More and Ben Griam Beg huge
terraced pyramids that rise steeply from a brown waste of peat and heather,
which are conspicuous landmarks from all the low country along the
north-east corner of the county.
By far the most beautiful of the mountains in the east
of Sutherland is the granitic mass of Ben Laoghal (Ben Loyal), the jagged
crests of which rise in striking contrast to the smooth and flowing uplands
over which they tower. There are few spots in Sutherland better adapted for
the artist than the neighbourhood of Tongue, where the beauties of Ben
Laoghal can be studied from all points of view, and where the woodlands and
rocky or sandy shore of the Kyle give charming pieces of foreground not
easily obtainable in other parts of the district.
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