Transcriber's Note
Text emphasis is displayed as _Italics_ and =Bold= respectively.
Superscript characters are denoted with the carat character (i.e., 8^e).
Whole and fractional parts are displayed as 5-1/2.
FRAGMENTS
OF
EARTH LORE
[Illustration: PLATE I
OROGRAPHIC MAP OF
SCOTLAND]
FRAGMENTS
OF
EARTH LORE
SKETCHES & ADDRESSES
Geological and Geographical
BY
JAMES GEIKIE, D.C.L., LL.D., F.R.S., &c.
MURCHISON-PROFESSOR OF GEOLOGY AND MINERALOGY IN THE
UNIVERSITY OF EDINBURGH
FORMERLY OF H.M. GEOLOGICAL SURVEY OF SCOTLAND
WITH MAPS AND ILLUSTRATIONS
EDINBURGH
JOHN BARTHOLOMEW & CO.
LONDON: SIMPKIN, MARSHALL, HAMILTON, KENT & Co., Ltd.
1893
PREFACE.
The articles in this volume deal chiefly with the history of Glacial
times and the origin of surface-features. As they were not written with
any view to their subsequent appearance in a collected form, each is so
far independent and complete in itself. Under these circumstances some
repetition was unavoidable, if the articles were not to be recast, and
I did not think it advisable to make such radical alteration. With the
exception of verbal changes and some excisions, therefore, the papers
remain substantially in their original state. Here and there a footnote
has been added to indicate where the views expressed in the text have
since been modified; but I have not been careful to insert such notes
throughout. Geologists, like other folk, live and learn, and the reader
will probably discover that the opinions set forth in some of the
later articles are occasionally in advance of those maintained in the
writer's earlier days.
I have to thank the Publishers of _Good Words_ for allowing me to
republish the articles on the Cheviot Hills and the Outer Hebrides. My
acknowledgments are also due to Mr. Bartholomew for the excellent maps
with which the volume is so well illustrated.
Edinburgh, _April 5th, 1893_.
LIST OF MAPS.
Plate I. PHYSICAL FEATURES OF SCOTLAND _Frontispiece_
" II. STRUCTURE OF MOUNTAINS 60
" III. PAST AND PRESENT GLACIATION OF THE WORLD 193
" IV. ICE AGE IN NORTHERN EUROPE 324
" V. THE GEOGRAPHICAL EVOLUTION OF CONTINENTS 348
" VI. BATHY-HYPSOMETRICAL MAP, ILLUSTRATING
DEVELOPMENT OF COAST-LINES 428
CONTENTS.
CHAP. PAGE
I. GEOGRAPHY AND GEOLOGY 1
II. THE PHYSICAL FEATURES OF SCOTLAND 14
III. MOUNTAINS: THEIR ORIGIN, GROWTH, AND DECAY 36
IV. THE CHEVIOT HILLS 62
V. THE LONG ISLAND, OR OUTER HEBRIDES 125
VI. THE ICE AGE IN EUROPE AND NORTH AMERICA 160
VII. THE INTERCROSSING OF ERRATICS IN GLACIAL
DEPOSITS 194
VIII. RECENT RESEARCHES IN THE GLACIAL GEOLOGY
OF THE CONTINENT 220
IX. THE GLACIAL PERIOD AND THE EARTH-MOVEMENT
HYPOTHESIS 248
X. THE GLACIAL SUCCESSION IN EUROPE 288
XI. THE GEOGRAPHICAL EVOLUTION OF EUROPE 326
XII. THE EVOLUTION OF CLIMATE 349
XIII. THE SCIENTIFIC RESULTS OF DR. NANSSEN'S
EXPEDITION 382
XIV. THE GEOGRAPHICAL DEVELOPMENT OF COAST-LINES 393
I.
Geography and Geology.[A]
[A] Portion of a lecture given in 1886 to the Class of Geology in the
University of Edinburgh.
The teaching of Geography naturally occupies a prominent place in
every school curriculum. It is rightly considered essential that we
should from an early age begin to know something of our own and other
countries. I am not sure, however, that Geography is always taught in
the most interesting and effective manner. Indeed, according to some
geographers, who are well qualified to express an opinion, the manner
in which their subject is presented in many of our schools leaves much
to be desired. But a decided advance has been made in recent years,
and with the multiplication of excellent text-books, maps, and other
appliances, I have no doubt that this improvement will continue. When
I attended school the text-books used by my teachers were about as
repellent as they could be. Our most important lesson was to commit to
memory a multitude of place-names, and the maps which were supposed
to illustrate the text-books were, if possible, less interesting and
instructive. Nowadays, however, teachers have a number of more or less
excellent manuals at their service, and the educational maps issued by
our cartographers show in many cases a very great advance on the bald
and misleading caricatures which did duty in my young days as pictures
of the earth's surface.
During the progress of some war we often remark that the task of
following the military operations compels us to brush up our Geography.
I am uncharitable enough to suspect that it would frequently be
truer to say that, before these campaigns commenced, we had no such
knowledge to brush up. The countries involved in the commotion were
probably mere names to many of us. We had no immediate interest in
them or their inhabitants, and had we been asked, before the outbreak
of hostilities, to indicate the precise positions of the places upon a
map, some of us perhaps might have been sorely puzzled to do so. Nor
is such ignorance always discreditable. One cannot know everything;
the land-surface of the globe contains upwards of 50 millions of
square miles, and one may surely be excused for not having a detailed
knowledge of this vast area. I have referred to the subject simply
because I think it gives us a hint as to how the teaching of Political
Geography might be made most instructive and interesting. Historical
narrative might often be interwoven with the subject in such a way
as to fix geographical features indelibly on the memory. Striking
and picturesque incidents, eventful wars, the rise and progress of
particular trades, the routes followed by commerce, the immigration
and emigration of races, the gradual development of the existing
political divisions of the Old World, the story of Columbus and the
early voyagers, the geographical discoveries of later times--all these,
and such as these, might be introduced into our lessons in Political
Geography. The wanderings of a Mungo Park, a Bruce, a Livingstone, a
Stanley, traced on a good map, could not fail to arrest the attention
of the youthful student of African geography. In like manner, the
campaigns of the great Napoleon might be made to do good service
in illustrating the geographical features of large portions of our
own continent. Then, as regards Britain, what a world of poetry and
romantic story clings to every portion of its surface--why, the very
place-names themselves might suggest to any intelligent teacher themes
and incidents, the deft treatment of which would make the acquisition
of Geography a delightful task to the dullest boy or girl.
The intimate relation that obtains between Political Geography and
History has indeed long been recognised, and is in fact self-evident.
And we are all well aware that in our school manuals of Geography it
has been usual for very many years to note the scenes of remarkable
events. Such notes, however, are of necessity extremely brief; and it
need hardly be said that to fully incorporate history in a text-book of
general Geography would be quite impracticable. It might be done to a
certain extent for our own and a few of the more important countries;
but similar detail need not be attempted in regard to regions which are
of less consequence from the political point of view. Indeed, I should
be inclined to leave the proper application of historical knowledge in
the teaching of Geography very much to the teacher himself, who would
naturally select such themes and incidents as seemed best adapted to
attract the attention of his pupils. Be that, however, as it may,
it is enough for my present purpose if I insist upon the fact that
the proper study of Political Geography involves the acquisition of
some historical knowledge. One can hardly conceive the possibility
of an intelligent student taking pains to become acquainted with the
political geography of a country without at the same time endeavouring
to learn something of its history--otherwise, his geographical
attainments would hardly surpass those of a commercial traveller, whose
geographical studies have been confined to the maps and tables of his
Bradshaw.
But if it be impossible to ignore History in the teaching of Political
Geography, it is just as impossible to exclude from our attention
great physical features and characteristics. Surface-configuration,
climate, and natural products all claim our attention. It is obvious,
in fact, that the proper study of Political Geography must give us
at least a general notion of the configuration, the river-systems,
and climatic conditions of many different lands. For has not the
political development of races depended most largely on the physical
conditions and natural resources of the countries occupied by them?
So far, then, as these have sensibly influenced the progress of
peoples, they come naturally under the consideration of Political
Geography. Thus, if Political Geography be closely connected and
interwoven, as it were, with History, not less intimate are its
relations to Physical Geography. It does not embrace all Physical
Geography, but it introduces us to many facts and phenomena, the
causes and mutual relations of which we cannot understand without
first mastering the teachings of Physical Geography. In the study of
this latter science we come more closely into contact with Nature;
we cease to think of the surface of the earth as parcelled out into
so many lots by its human occupants--we no longer contemplate that
surface from the limited point of view of the political geographer--we
are now not merely members of one particular community, but have
become true citizens of the world. To us north and south, east and
west are of equal interest and importance. Our desire now is to
understand, if haply we may, the complex system of which we ourselves
form a part. The distribution of land and water--the configuration of
continental areas and oceanic basins--the circulation of oceanic and
terrestrial waters--earth-movements and volcanoes--ice-formations--the
atmosphere--climatology--the geographical distribution of plants
and animals--in a word, _the world as one organic whole_ now forms
the subject of our contemplation. Such being the scope of Physical
Geography, it is satisfactory to know that its importance as a subject
of study in our schools has been fully recognised. This being admitted,
I shall now proceed to show that Physical Geography, although, like
Political Geography, it is a separate and distinct subject, yet, just
as the study of the latter involves some knowledge of History, so
the prosecution of Physical Geography compels us to make a certain
acquaintance with Geology. We cannot, in fact, learn much about the
atmosphere, about rain and rivers, glaciers and icebergs, earthquakes
and volcanoes, and the causes of climate, without at the same time
becoming more or less familiar with the groundwork on which geological
investigations are based. And just as a knowledge of history enables
us better to understand the facts of Political Geography, so some
acquaintance with the results of geological inquiry are necessary
before we can hope to comprehend many of the phenomena of which
Physical Geography treats. Let me try to make this plain. The physical
geographer, we shall suppose, is considering the subject of terrestrial
waters. He tells us what is meant by the drainage-system of a country,
points out how the various minor water-courses or brooks and streams
unite to form a river, describes for us the shape of the valley through
which a typical river makes its way--how the valley-slope diminishes
from the mountains onwards to the sea-coast--how, at first, in its
upper or mountain-track, the flow of the river is torrential--how,
as the slope of the valley decreases, the river begins to wind about
more freely, until it reaches the head of its plain-track or delta,
when, no longer receiving affluents, it begins to divide, and enters
the sea at last by many mouths. He tells us further what proportion of
the rainfall of the country passes seawards in our river, and he can
measure for us the quantity of water which is actually discharged. All
this is purely Physical Geography; but when we come to ask why some
rivers flow in deep cañons, like those of the Colorado--why valleys
should widen out in one part and contract, as it were, elsewhere--why
the courses of some rivers are interrupted by waterfalls and rapids,
and many other similar questions, the physical geographer must know
something of Geology before he can give an answer. He can describe
the actual existing conditions; without the aid of Geology, he can
tell us nothing of their origin and cause. So the political geographer
can map out for us the present limits of the various countries of
Europe, but History must be invoked if we would know how those
boundaries came to be determined. The moment, therefore, the physical
geographer begins to inquire into the origin of any particular
physical feature, he enters upon the domains of the geologist. And as
he cannot possibly avoid doing so, it is quite common now to find a
good deal of the subject-matter of Geology treated of in text-books
of Physical Geography. I state this merely to show how very closely
the two sciences are interlocked. Take, for example, the configuration
of river valleys just referred to. The physical geographer recognises
the fact that a river performs work; by means of the sediment which
it carries in suspension and rolls along its course, it erodes its
bed in many places, and undermines its banks, and thus its channel is
deepened and widened. He can measure the amount of sediment which it
carries down to the sea, and the quantity of saline matters which its
waters hold in solution: and knowing that all these substances have
been abstracted from the land, he is able to estimate approximately
the amount of material which is annually transferred from the surface
of the drainage-area involved. He discovers this to be so relatively
enormous that he has no difficulty in believing that the valleys
in which rivers flow might have been hollowed out by the rivers
themselves. But, without trespassing further into the geologist's
domains, he cannot go beyond this: and you will at once perceive that
something more is required to prove that any particular valley owes its
origin to the erosive action of running water. Suppose someone were
to suggest to him that his river-valley might be a minor wrinkle in
the earth's crust caused by earth-movements, or that it might indicate
the line of a fissure or dislocation, due to some comparatively recent
convulsion--how could his computation of the amount of material at
present carried seawards by the river prove such suggestions to be
erroneous? And what light could it throw upon the origin of the
varied configuration of the river-valley--how would it explain the
presence or absence of cascades and rapids, of narrow gorges and open
expanses? None of these phenomena can be interpreted and accounted
for without the aid of the geologist: without some knowledge of rocks
and rock-structures, the origin of the earth's surface-features
is quite inexplicable. To give an adequate explanation of all the
surface-features of a country in detail would of course require a
profound study of Geology; but a general acquaintance only with its
elementary facts is quite sufficient to enable us to form a reasonable
and intelligent view of the cause and origin of the main features
of the land as a whole. Thus a few lessons in elementary Geology
would make clear to any child how rivers have excavated valleys, why
cataracts and gorges occur here, and open valleys with gently-flowing
waters elsewhere.
Let me select yet another example to show how dependent Physical
Geography is upon Geology. The physical geographer, in describing the
features of the land, tells us how the great continental areas are
traversed in various directions by what he calls mountain-chains. Thus,
in speaking of America, he tells us that it may be taken as a type
of the continental structure--namely a vast expanse of land, low or
basin-like in the interior, and flanked along the maritime regions by
elevated mountain borders--the highest border facing the deepest ocean.
He points out further that the great continental areas are crossed from
west to east by well-marked depressions, to a large extent occupied
by water. Thus Europe is separated from Africa by the Mediterranean,
a depression which is continued eastward through the Black Sea into
the Aralo-Caspian area. South America is all but cut away from North
America, while Australia is separated from Asia by the East India Seas.
We find, in fact, all over the world that well-marked natural features
are constantly being repeated. Not only do the great land-masses
of the globe bear certain resemblances to each other, but even in
their detailed structure similar parallelisms recur. The physical
geographer notes all these remarkable phenomena, but he can give us
no clue to their meaning. He may describe with admirable skill the
characteristic features of plains and plateaux, of volcanic mountains
and mountain-chains, but he cannot tell us why plains should occur
here and mountains there; nor can he explain why some mountains, such
as those of Scotland or Norway, differ so much in configuration from
the Alps and the Pyrenees. The answer to all these questions can only
be given by Geology. It is from this science we learn how continental
areas and oceanic basins have been evolved. The patient study of the
rocks has revealed the origin of the present configuration of the
land. There is not a hill or valley, not a plateau or mountain-region,
which does not reveal its own history. The geologist can tell you why
continents are bordered by coast-ranges, and why their interiors are
generally comparatively low and basin-shaped. The oceanic basins and
continental areas, we learn, are primeval wrinkles in the earth's
crust, caused by its irregular subsidence upon the gradually cooling
and contracting nucleus. The continents are immense plateau-like areas
rising more or less abruptly above those stupendous depressions
of the earth's crust which are occupied by the ocean. While those
depressions are in progress the maritime borders of the land-areas are
subjected to enormous squeezing and crushing, and coast-ranges are the
result--the elevation of those ranges necessarily holding some relation
to the depth of the contiguous ocean. For, the deeper the ocean the
greater has been the depression under the sea, and, consequently,
the more intense the upheaval along the continental borders. It is
for the same reason that destructive earthquakes are most likely to
occur in the vicinity of coast-ranges which are of comparatively
recent geological age. These, and indeed all, mountains of elevation
are lines of weakness along which earth-movements may continue from
time to time to take place. But all mountains are not mountains of
elevation; many elevated regions owe their mountainous character simply
to the erosive action of sub-aërial agents, such as rain, frost, ice,
and running water, the forms assumed by the mountains being due to
their petrological character and geological structure. There are,
for example, no true mountains of elevation in Scotland; hence to
write of the _chain of the Grampians_ or the _range of the Lowthers_
is incorrect and actually misleading. Without the aid of Geology the
geographer cannot, in fact, discriminate between mountains of elevation
and mountains of denudation; hence geographical terms so constantly in
use as _mountain-range_ and _mountain-chain_ are very often applied by
writers, ignorant of geological structure, to elevated regions which
have no claim to be described either as _chains_ or _ranges_. Some
knowledge of Geology, therefore, is essential to us if we would have
correct views of many of the grandest features of the globe. But it
will be said that, after all, the physical geographer deals with the
earth as we now find it; he does not need to trouble himself with the
origin of the phenomena he describes. Well, as I have just shown, he
cannot, even if he would, escape trenching on Geology; and if he could,
his subject would be shorn of much of its interest. He recognises that
the world he studies has in it the elements of change--the forces of
Nature are everywhere modifying the earth's surface--considerable
changes are sometimes brought about even in one's lifetime, while
within the course of historical ages still greater mutations have
taken place--he becomes conscious, in short, that the existing state
of things is but the latest phase of an interminable series of changes
stretching back into the illimitable past, and destined to be prolonged
into the indefinite future. Thus he gladly welcomes the labours of the
geologist, whose researches into the past have thrown such a flood of
light upon the present. In fact, he can no more divorce his attention
from the results of geological inquiry than the political geographer
can shut his eyes to the facts of History.
Let me, in conclusion, give one further illustration of the close
inter-dependence of the two sciences of which I am speaking. One of the
subjects treated of by Physical Geography is the present geographical
distribution of plants and animals. The land-surface of the globe has
been mapped out into so many biological regions, each of which is
characterised by its special fauna and flora. The greatest changes in
the flora and fauna of a continent are met with as we pass from south
to north, or _vice versa_. Proceeding in the direction of the latitude,
the changes encountered are much less striking. Now, these facts are
readily explained by the physical geographer, who points out that
the distribution is due chiefly to climatic conditions--a conclusion
which is obvious enough. But when we go into details we find that mere
latitude will not account for all the phenomena. Take, for example,
the case of the Scandinavian flora of our own Continent. It is true
that this flora is largely confined to northern latitudes; but isolated
colonies occur in our own mountains and in the mountains of middle
and southern Europe. How are these to be accounted for? The physical
geographer says that the plants grow there simply because they obtain
at high levels in low latitudes the favourable climatic conditions
underneath which they flourish at low levels in high latitudes. He
therefore concludes that the distribution of life-forms is due to
varying climatic and physical conditions. But if we ask him how those
curious colonies of foreigners come to be planted on our mountains,
he cannot tell. To get our answer we must come to the geologist; and
he will explain that they are, as it were, living fossils--monuments
of former great physical and climatic changes. He will prove to us
that the climate of Europe was at a recent geological period so cold
that the Scandinavian flora spread south into middle Europe, where it
occupied the low grounds. When the climate became milder, then the
northern invaders gradually retired--the main body migrating back
to the north--while some stragglers, retreating before the stronger
Germanic flora, took shelter in the mountains, whither the latter could
not or would not follow, and so there our Scandinavians remain, the
silent witnesses of a stupendous climatic revolution. Now, all the
world over, plants and animals have similar wonderful tales to tell of
former geographical changes. The flora and fauna of our country, for
example, prove that the British Islands formed part of the Continent at
a very recent geological period; and so, from similar evidence, we know
that not long ago Europe was joined on to Africa. On the other hand,
the facts connected with the present distribution of life demonstrate
that some areas, such as Australia, have been separated from the
nearest continental land for vastly prolonged periods of time.
It would be a very easy matter to adduce many further illustrations to
show how close is the connection between the studies of the physical
geographer and the geologist. I do not indeed exaggerate when I say
that no one can hope to become a geologist who is not well versed in
Physical Geography; nor, on the other hand, can the physical geographer
possibly dispense with the aid of Geology. The two subjects are as
closely related and interwoven, the one with the other, as History is
with Political Geography. I do not see therefore how educationists who
have admitted the great importance of Physical Geography as a branch
of general education, can logically exclude Geology as a subject of
instruction in schools. Already, indeed, it has been introduced by many
teachers, and I am confident that ere long it will be as generally
taught as Physical Geography. I would not, however, present the subject
to young people as a lesson to be learned from books. A good teacher
should be able to dispense with these helps, or rather hindrances--for
such they really are to a young beginner. His pupils ought to have
previously studied the subject of Physical Geography, and if they have
been well taught they ought to have already acquired no mean store of
geological knowledge. They ought, in fact, to have learned a good deal
about the great forces which are continually modifying the surface of
the globe, and what they have now to do is to study more particularly
the results which have followed from the constant operation of
those forces. We shall suppose, for example, that the teacher has
described how rivers erode their channels, and waves tend to cut back
a coast-line, and how the products of erosion, consisting of gravel,
sand, and mud, are distributed along river-valleys and accumulated in
lakes and seas. He now exhibits to his class good-sized fragments of
conglomerate, sandstone, and shale, and points out how each of these
rocks is of essentially the same character, and must therefore have
had the same origin, as modern sedimentary accumulations. His pupils
should be encouraged to examine the rocks of their own neighbourhood,
whether exhibited in natural sections or artificial exposures, and to
compare these with the products of modern geological action. One hour's
instruction in the field is, in fact, worth twenty hours of reading
or listening to lectures. Knowledge at first hand is what is wanted.
There are many excellent popular or elementary treatises dealing with
Historical Geology, and these have their uses, and may be read with
profit as well as pleasure. But the mere reading of such books, it is
needless to say, will never make us geologists. They help no doubt to
store the mind with interesting and entertaining knowledge, but they do
not cultivate the faculties of observation and reasoning. And unless
geology is so taught as to accomplish this result, I do not see why it
should enter into any school curriculum. Further, I would remark that,
however interesting a geological treatise may be, it cannot possibly
stimulate the imagination as the practical study of the science
is bound to do. One may put into the hands of a youth a clear and
well-written description of some particular fossiliferous limestone,
and he may by dint of slavish toil be able to repeat verbatim all
that he has read. That is how a good deal of book-knowledge of science
is acquired. Only think, however, of the drudgery it involves--the
absolute waste of time and energy. But let us illustrate our lesson
by means of a lump of the limestone itself; let us show him the
character of the rock and the nature of its fossil contents, and his
difficulties disappear. Better still--let us take him, if we can, into
a limestone quarry, and he will be a dull boy indeed if he fails fully
to understand what limestone is, or to realise the fact that the rock
he is looking at accumulated slowly, like existing oceanic formations,
at the bottom of a sea that teemed with animal life. It is unnecessary,
however, that I should illustrate this subject further. I would only
repeat that the beginner should be taught from the very first to use
his own eyes, and to draw logical conclusions from the facts which
he observes. Trained after this manner, he would acquire, not only a
precise and definite knowledge of what geological data really are,
but he would learn also how to interpret those data. He would become
familiar, in fact, with the guiding principles of geological inquiry.
How much or how little of Historical Geology should be given in schools
will depend upon circumstances. Great care, however, should be taken to
avoid wearying the youthful student with strings of mere names. What
good is gained by learning to repeat the names of fifty or a hundred
fossils, if you cannot recognise any one of these when it is put into
your hand? With young beginners I should not attempt anything of that
kind. If the neighbourhood chanced to be rich in fossils, I should
take my pupils out on Saturday to the sections where they were found,
and let them ply their hammers and collect specimens for themselves. I
should describe no fossils which they had not seen and handled. Of the
more remarkable forms of extinct animals and plants, which are often
represented by only fragmentary remains, I should exhibit drawings
showing the creatures as they have been restored by the labours of
comparative anatomists. Such restorations and ideal views of geological
scenes like those given by Heer, Dana, Saporta, and others, convey far
more vivid impressions of the life of a geological period than the
most elaborate description. In fine, the story of our earth should be
told much in the same manner as Scott wrote the history of Scotland
for his grandson. There is no more reason for requiring the juvenile
student to drudge through minute geological data before introducing him
to the grand results of geological investigation, than there is for
compelling him to study the manuscripts in our Record Offices before
allowing him to read the history which has been drawn from these and
similar sources of information. It is enough if at the beginning of
his studies he has already learned the general nature of geological
evidence and the method of its interpretation. Provided with such a
stock of geological knowledge as I have indicated, our youth would
leave school with some intelligent appreciation of existing physical
conditions, and a not inadequate conception of world-history.
II.
The Physical Features of Scotland.[B]
[B] _Scottish Geographical Magazine_, vol. i., 1885.
Scotland, like "all Gaul," is divided into three parts, namely, the
Highlands, the Central Lowlands, and the Southern Uplands. These, as a
correctly drawn map will show, are natural divisions, for they are in
accordance not only with the actual configuration of the surface, but
with the geological structure of the country. The boundaries of these
principal districts are well defined. Thus, an approximately straight
or gently undulating line taken from Stonehaven, in a south-west
direction, along the northern outskirts of Strathmore to Glen Artney,
and thence through the lower reaches of Loch Lomond to the Firth of
Clyde at Kilcreggan, marks out with precision the southern limits of
the Highland area and the northern boundary of the Central Lowlands.
The line that separates the Central Lowlands from the Southern Uplands
is hardly so prominently marked throughout its entire course, but it
follows precisely the same north-east and south-west trend, and may
be traced from Dunbar along the base of the Lammermoor and Moorfoot
Hills, the Lowthers, and the hills of Galloway and Carrick, to Girvan.
In each of the two mountain-tracts--the Highlands and the Southern
Uplands--areas of low-lying land occur, while in the intermediate
Central Lowlands isolated prominences and certain well-defined belts
of hilly ground make their appearance. The statement, so frequently
repeated in class-books and manuals of geography, that the mountains of
Scotland consist of three (some writers say five) "ranges" is erroneous
and misleading. The original author of this strange statement probably
derived his ignorance of the physical features of the country from
a study of those antiquated maps upon which the mountains of poor
Scotland are represented as sprawling and wriggling about like so many
inebriated centipedes and convulsed caterpillars. Properly speaking,
there is not a true mountain-range in the country. If we take this
term, which has been very loosely used, to signify a linear belt of
mountains--that is, an elevated ridge notched by cols or "passes"
and traversed by transverse valleys--then in place of "three" or
"five" such ranges we might just as well enumerate fifty or sixty, or
more, in the Highlands and Southern Uplands. Or, should any number
of such dominant ridges be included under the term "mountain-range,"
there seems no reason why all the mountains of the country should
not be massed under one head and styled the "Scottish Range." A
mountain-range, properly so called, is a belt of high ground which has
been ridged up by earth-movements. It is a fold, pucker, or wrinkle
in the earth's crust, and its general external form coincides more or
less closely with the structure or arrangement of the rock-masses of
which it is composed. A mountain-range of this characteristic type,
however, seldom occurs singly, but is usually associated with other
parallel ranges of the same kind--the whole forming together what
is called a "mountain-chain," of which the Alps may be taken as an
example. That chain consists of a vast succession of various kinds of
rocks, which at one time were disposed in horizontal layers or strata.
But during subsequent earth-movements those horizontal beds were
compressed laterally, squeezed, crumpled, contorted, and thrown, as it
were, into gigantic undulations and sharper folds and plications. And,
notwithstanding the enormous erosion or denudation to which the long
parallel ridges or ranges have been subjected, we can yet see that the
general contour of these corresponds in large measure to the plications
or foldings of the strata. This is well shown in the Jura, the parallel
ranges and intermediate hollows of which are formed by undulations of
the folded strata--the tops of the long hills coinciding more or less
closely with the arches, and the intervening hollows with the troughs.
Now folded, crumpled, and contorted rock-masses are common enough in
the mountainous parts of Scotland, but the configuration of the surface
rarely or never coincides with the inclination of the underlying
strata. The mountain-crests, so far from being formed by the tops of
great folds of the strata, frequently show precisely the opposite kind
of structure. In other words, the rocks, instead of being inclined away
from the hill-tops like the roof of a house from its central ridge,
often dip into the mountains. When they do so on opposite sides the
strata of which the mountains are built up seem arranged like a pile of
saucers, one within another.
There is yet another feature which brings out clearly the fact that the
slopes of the surface have not been determined by the inclination of
the strata. The main water-parting that separates the drainage-system
of the west from that of the east of Scotland does not coincide with
any axis of elevation. It is not formed by an anticlinal fold or
"saddleback." In point of fact it traverses the strata at all angles
to their inclination. But this would not have been the case had the
Scottish mountains consisted of a chain of true mountain-ranges. Our
mountains, therefore, are merely monuments of denudation, they are
the relics of elevated plateaux which have been deeply furrowed and
trenched by running water and other agents of erosion. A short sketch
of the leading features presented by the three divisions of the country
will serve to make this plain.
* * * * *
The Highlands.--The southern boundary of this, the most extensive of
the three divisions, has already been defined. The straightness of
that boundary is due to the fact that it coincides with a great line
of fracture of the earth's crust--on the north or Highland side of
which occur slates, schists, and various other hard and tough rocks,
while on the south side the prevailing strata are sandstones, etc.,
which are not of so durable a character. The latter, in consequence
of the comparative ease with which they yield to the attacks of the
eroding agents--rain and rivers, frost and ice--have been worn away to
a greater extent than the former, and hence the Highlands, along their
southern margin, abut more or less abruptly upon the Lowlands. Looking
across Strathmore from the Sidlaws or the Ochils, the mountains seem
to spring suddenly from the low grounds at their base, and to extend
north-east and south-west, as a great wall-like rampart. The whole area
north and west of this line may be said to be mountainous, its average
elevation being probably not less than 1500 feet above the sea.
A glance at the contoured or the shaded sheets of the Ordnance Survey's
map of Scotland will show better than any verbal description the
manner in which our Highland mountains are grouped. It will be at once
seen that to apply the term "range" to any particular area of those
high grounds is simply a misuse of terms. Not only are the mountains
not formed by plications and folds, but they do not even trend in
linear directions. It is true that a well-trained eye can detect
certain differences in the form and often in the colouring of the
mountains when these are traversed from south-east to north-west. Such
differences correspond to changes in the composition and structure of
the rock-masses, which are disposed or arranged in a series of broad
belts and narrower bands, running from south-west to north-east across
the whole breadth of the Highlands. Each particular kind of rock gives
rise to a special configuration, or to certain characteristic features.
Thus, the mountains that occur within a belt of slate, often show a
sharply cut outline, with more or less pointed peaks and somewhat
serrated ridges--the Aberuchill Hills, near Comrie, are an example. In
regions of gneiss and granite the mountains are usually rounded and
lumpy in form. Amongst the schists, again, the outlines are generally
more angular. Quartz-rock often shows peaked and jagged outlines;
while each variety of rock has its own particular colour, and this in
certain states of the atmosphere is very marked. The mode in which the
various rocks yield to the "weather"--the forms of their cliffs and
corries--these and many other features strike a geologist at once; and
therefore, if we are to subdivide the Highland mountains into "ranges,"
a geological classification seems the only natural arrangement that can
be followed. Unfortunately, however, our geological lines, separating
one belt or "range" from another, often run across the very heart
of great mountain-masses. Our "ranges" are distinguished from each
other simply by superficial differences of feature and structure. No
long parallel hollows separate a "range" of schist-mountains from
the succeeding "ranges" of quartz-rock, gneiss, or granite. And no
degree of careful contouring could succeed in expressing the niceties
of configuration just referred to, unless the maps were on a very
large scale indeed. A geological classification or grouping of the
mountains into linear belts cannot therefore be shown upon any ordinary
orographical map. Such a map can present only the relative heights
and disposition of the mountain-masses, and these last, in the case
of the Highlands, as we have seen, cannot be called "ranges" without
straining the use of that term. Any wide tract of the Highlands, when
viewed from a commanding position, looks like a tumbled ocean in
which the waves appear to be moving in all directions. One is also
impressed with the fact that the undulations of the surface, however
interrupted they may be, are broad--the mountains, however they may
vary in detail according to the character of the rocks, are massive,
and generally round-shouldered and often somewhat flat-topped, while
there is no great disparity of height amongst the dominant points of
any individual group. Let us take, for example, the knot of mountains
between Loch Maree and Loch Torridon. There we have a cluster of eight
pyramidal mountain-masses, the summits of which do not differ much in
elevation. Thus in Liathach two points reach 3358 feet and 3486 feet;
in Beinn Alligin there are also two points reaching 3021 feet and
3232 feet respectively; in Beinn Dearg we have a height of 2995 feet;
in Beinn Eighe are three dominant points--3188 feet, 3217 feet, and
3309 feet. The four pyramids to the north are somewhat lower--their
elevations being 2860 feet, 2801 feet, 2370 feet, and 2892 feet. The
mountains of Lochaber and the Monadhliath Mountains exhibit similar
relationships; and the same holds good with all the mountain-masses of
the Highlands. No geologist can doubt that such relationship is the
result of denudation. The mountains are monuments of erosion--they
are the wreck of an old table-land--the upper surface and original
inclination of which are approximately indicated by the summits of the
various mountain-masses and the direction of the principal water-flows.
If we in imagination fill up the valleys with the rock-material which
formerly occupied their place, we shall in some measure restore the
general aspect of the Highland area before its mountains began to be
shaped out by Nature's saws and chisels.
It will be observed that while streams descend from the various
mountains to every point in the compass, their courses having often
been determined by geological structure, etc., their waters yet tend
eventually to collect and flow as large rivers in certain definite
directions. These large rivers flow in the direction of the average
slope of the ancient table-land, while the main water-partings that
separate the more extensive drainage-areas of the country mark out,
in like manner, the dominant portions of the same old land-surface.
The water-parting of the North-west Highlands runs nearly north and
south, keeping quite close to the western shore, so that nearly all the
drainage of that region flows inland. The general inclination of the
North-west Highlands is therefore easterly towards Glenmore and the
Moray Firth. In the region lying east of Glenmore the average slopes of
the land are indicated by the directions of the rivers Spey, Don, and
Tay. These two regions--the North-west and South-east Highlands--are
clearly separated by the remarkable depression of Glenmore, which
extends through Loch Linnhe, Loch Lochy, and Loch Ness, and the further
extension of which towards the north-east is indicated by the straight
coast-line of the Moray Firth as far as Tarbat Ness. Now, this long
depression marks a line of fracture and displacement of very great
geological antiquity. The old plateau of the Highlands was fissured and
split in two--that portion which lay to the north-west sinking along
the line of fissure to a great but at present unascertained depth. Thus
the waters that flowed down the slopes of the north-west portion of the
broken plateau were dammed by the long wall of rock on the "up-cast,"
or south-east side of the fissure, and compelled to flow off to
north-east and south-west along the line of breakage. The erosion thus
induced sufficed in the course of time to hollow out Glenmore and all
the mountain-valleys that open upon it from the west.
The inclination of that portion of the fissured plateau which lay to
the south-east is indicated, as already remarked, by the trend of
the principal rivers. It was north-east in the Spey district, nearly
due east in the area drained by the Don, east and south-east in that
traversed by the Tay and its affluents, westerly and south-westerly in
the district lying east of Loch Linnhe.[C] Thus, a line drawn from Ben
Nevis through the Cairngorm and Ben Muich Dhui Mountains to Kinnaird
Point passes through the highest land in the South-east Highlands, and
probably indicates approximately the dominant portion of the ancient
plateau. North of that line the drainage is towards the Moray Firth;
east of it the rivers discharge to the North Sea; while an irregular
winding line, drawn from Ben Nevis eastward through the Moor of Rannoch
and southward to Ben Lomond, forms the water-parting between the North
Sea and the Atlantic, and doubtless marks another dominant area of the
old table-land.
[C] The geological reader hardly requires to be reminded that many
of the minor streams would have their courses determined, or greatly
modified, by the geological structure of the ground. Thus, such
streams often flow along the "strike" and other "lines of weakness,"
and similar causes, doubtless, influenced the main rivers during the
gradual excavation of their valleys.
That the valleys which discharge their water-flow north and east
to the Moray Firth and the North Sea have been excavated by rivers
and the allied agents of erosion, is sufficiently evident. All the
large rivers of that wide region are typical. They show the orthodox
three courses--namely, a torrential or mountain-track, a middle or
valley-track, and a lower or plain-track. The same is the case with
some of the rivers that flow east from the great north-and-south
water-parting of the North-west Highlands, as, for example, those that
enter the heads of Beauly Firth, Cromarty Firth, and Dornoch Firth.
Those, however, which descend to Loch Lochy and Loch Linnhe, and the
sea-lochs of Argyllshire, have no lower or plain-track. When we
cross the north-and-south water-parting of the North-west Highlands,
we find that many of the streams are destitute of even a middle or
valley-track. The majority are mere mountain-torrents when they reach
the sea. Again, on the eastern watershed of the same region, a large
number of the valleys contain lakes in their upper and middle reaches,
and this is the case also with not a few of the valleys that open upon
the Atlantic. More frequently, however, the waters flowing west pass
through no lakes, but enter the sea at the heads of long sea-lochs or
fiords. This striking contrast between the east and west is not due to
any difference in the origin of the valleys. The western valleys are as
much the result of erosion as those of the east. The present contrast,
in fact, is more apparent than real, and arises from the fact that
the land area on the Atlantic side has been greatly reduced in extent
by subsidence. The western fiords are merely submerged land-valleys.
Formerly the Inner and Outer Hebrides were united to themselves and the
mainland, the country of which they formed a part stretching west into
the Atlantic, as far probably as the present 100 fathoms line. Were
that drowned land to be re-elevated, each of the great sea-lochs would
appear as a deep mountain-valley containing one or more lake-basins of
precisely the same character as those that occur in so many valleys
on the eastern watershed. Thus we must consider all the islands lying
off the west coast of the Highlands, including the major portions of
Arran and Bute, as forming part and parcel of the Highland division of
Scotland. The presence of the sea is a mere accident; the old lands
now submerged were above its level during a very recent geological
period--a period well within the lifetime of the existing fauna and
flora.