Modern Geography
by Marion I. Newbigin · English · Gutenberg #40187 · 333,051 chars · public domain (US)
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Title: Modern Geography
Author: Marion I. Newbigin
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*** START OF THE PROJECT GUTENBERG EBOOK MODERN GEOGRAPHY ***
Transcriber's Note: Italic text is denoted by _underscores_ and bold
text by =equal signs=.
HOME UNIVERSITY LIBRARY
OF MODERN KNOWLEDGE
No. 7
_Editors:_
HERBERT FISHER, M.A., F.B.A.
PROF. GILBERT MURRAY, LITT.D.,
LL.D., F.B.A.
PROF. J. ARTHUR THOMSON, M.A.
PROF. WILLIAM T. BREWSTER, M.A.
_A complete classified list of the volumes of_ THE HOME UNIVERSITY
LIBRARY _already published will be found at the back of this book_.
MODERN
GEOGRAPHY
BY
MARION I. NEWBIGIN
D.SC. (LOND.)
EDITOR OF THE SCOTTISH GEOGRAPHICAL MAGAZINE
[Illustration]
NEW YORK
HENRY HOLT AND COMPANY
LONDON
WILLIAMS AND NORGATE
COPYRIGHT, 1911,
BY
HENRY HOLT AND COMPANY
CONTENTS
CHAP. PAGE
I THE BEGINNINGS OF MODERN GEOGRAPHY 7
II SURFACE-RELIEF AND THE PROCESS OF EROSION 19
III ICE AND ITS WORK 51
IV CLIMATE AND WEATHER 82
V THE PRINCIPLES OF PLANT GEOGRAPHY AND
THE CHIEF PLANT FORMATIONS OF EUROPE
AND NORTH AMERICA 112
VI THE DISTRIBUTION OF ANIMAL LIFE 143
VII CULTIVATED PLANTS AND DOMESTICATED ANIMALS 168
VIII THE RACES OF EUROPE AND THEIR ORIGIN 196
IX THE DISTRIBUTION OF MINERALS AND THE LOCALISATION
OF INDUSTRIES AND OF TOWNS 219
NOTES ON BOOKS 249
INDEX 251
MODERN GEOGRAPHY
CHAPTER I
THE BEGINNINGS OF MODERN GEOGRAPHY
In the year 1859 there occurred three events which, though not all
comparable to one another, yet make the year one of such importance that
we may take it as marking the beginning of the distinctively modern
period of geographical science. These three events were, first, the
deaths of Humboldt and Ritter, two great geographical pioneers who hewed
tracks through the tangled jungle of unsystematised geographical facts,
and second, the publication of the _Origin of Species_, by Charles
Darwin, a book which supplied the compass which has made further
road-making in that same jungle possible. In other words, as a result of
the life-work of the two great geographers named, and of the throwing by
Charles Darwin of a new ferment into the mass of contemporary thought,
what had been a mere collection of facts began to be a reasoned and
ordered science. Both Humboldt and Ritter lived to a great age, so that
at the time of their deaths not only was their work done, but there had
been time also for their influence to permeate the literature of the
subject.
Humboldt was, above all, a great traveller, but he was also a man of
science in the largest sense, interested not in one group of facts, but
in many. The extent of his knowledge and the breadth of his interests
enabled him to observe a vast number of phenomena while his particular
genius was manifest in the way in which he correlated these, and
considered them in their relation to each other. Though it is true that
his influence was most direct in the case of natural history, yet in
this respect also he pointed to the future, for the geographers of
to-day are indebted to the naturalists for some of their finest
generalisations.
Ritter was a great teacher, the prototype of those who alike by their
personal influence and by their books have enriched geographical science
within the last fifty years. He had not Humboldt's breadth of knowledge
and interest, but in the stress which he laid upon the earth as above
all interesting in that it is the field of the activity of man, he
emphasised an aspect of the subject in which perhaps the most
interesting modern developments have taken place.
Darwin had a twofold effect upon the progress of geography. In the first
place, in his detailed work, _e. g._ in connection with coral reefs, and
with the distribution of animals, and less directly in his investigation
of the part played by earthworms in the formation of soil, he himself
added to geographical knowledge. But he did much more than this. The
doctrine of evolution which he made common property has had and is
having an enormous effect upon geographical science, both directly and
indirectly.
As is well known, in connection with his own theory of the cause of
evolution, Darwin laid great stress upon the "Struggle for Existence."
But he himself expressly stated that he used the term in a "large and
metaphorical sense," a sense which in popular language it has tended to
lose. From the geographer's standpoint, therefore, it is better to say
that Darwin's work has added a new interest to the study of
interrelations. Humboldt, as we have indicated, was greatly interested
in such subjects as the connection between the climate of a region and
the vegetation, between the activities of man in a particular region and
the physical conditions, and so on. But Darwin added a new interest to
such studies. For example, it is a curious fact that desert plants have
often spiny leaves, long roots, and so forth, and it is interesting to
note how these peculiarities fit the plants for life in an arid climate.
But when Darwin showed that there was evidence that the physical
conditions of the desert gave rise to certain types of vegetation, it
became worth while to study both the physical conditions and the
characters of the plants in much greater detail than before.
If we simply lay it down as an axiom that, _e. g._ cactuses live in
deserts, the fact has only a moderate interest, but when we find that
almost any natural group of plants, if exposed through long ages to
gradually increasing conditions of drought, will produce "cactus" types,
then the whole subject acquires new importance. This illustration may
serve to suggest what Darwin has done for geography.
He showed that there is a delicately adjusted balance between organisms
and their surroundings, taken in their widest sense. But geology proves
that through the ages there have been constant, if slight, changes in
the physical conditions, and the effort of the organisms to readjust the
balance thus disturbed has led to evolution. Thus to some extent at
least the characters of organisms can be explained by the nature of
their surroundings. A further interest is added by the fact that in this
respect human societies and settlements can be shown to behave like
organisms. Therefore we can hope to explain at least partially the
manifold differences in man and his societies in different parts of the
globe by the minor differences in physical conditions. In other words,
the doctrine of evolution has added a unifying and co-ordinating
principle which has not only prevented geography from being crushed by
the enormous recent increase in known facts, but has also for the first
time raised it to the level of a science.
This addition of a co-ordinating principle may be said to be the direct
effect of the publication of the _Origin of Species_, but there has been
an indirect effect almost as important. The principles enunciated in
that book had a stimulating effect, not upon one science only but upon
every department of thought. Phenomena of no importance suddenly became
interesting, and the result of this interest was an enormous addition to
known facts. Not only has research been stimulated in every direction,
but as this research has been largely directed by the desire to discover
the interrelation of phenomena, we find that many of the old barriers
between the sciences are breaking down.
The botanists are no longer content to study the facts of plant
distribution; they now want to be able to give reasons for particular
distributions. Therefore they must seek the aid of the meteorologists to
explain differences of climate; of the physical geographer to make clear
the effects of relief, of differences of soil, and of drainage; of the
cartographer to represent the facts which emerge from their surveys, and
so on. The physician must now seek the assistance of the zoologist
before he can deal adequately with tropical disease, and the zoologist
must have the help of the physical geographer before he can give
adequate aid. The result is that in all directions geography is being
enriched by facts brought from the collateral sciences, while at the
same time its position as a central unifying science is becoming more
and more established; as a science which can deal with all these varied
facts, but deal with them from a standpoint peculiarly its own.
At the present time, geography may be compared to one of Rodin's statues
in which we see a beautiful figure as it were struggling to escape from
the marble in which it is imprisoned. So the geography of to-day is in
the act of escaping from the matrix of mere facts in which it has been
too long imprisoned. It is now displaying itself as a great unity in the
making of which all the sciences have played their part.
But even in this general survey of recent developments two other sets of
facts must be touched upon. We have given fifty years as the period
within which most of what is distinctively modern in geography has
developed. It must not be forgotten that within the same period there
has been a remarkable renewal of interest in geographical exploration.
Roughly speaking, within this period Africa has ceased to be an unknown
continent; the innermost recesses of Asia have been largely explored;
the Arctic and Antarctic areas have yielded many, though by no means the
whole, of their secrets; a great deal of exploration has been done in
America as a whole, as well as much detailed survey work in the United
States and Canada; the oceans have been investigated by successive
series of expeditions. Generally it may be said that in its broad
outlines our knowledge of the world has been completed, so that
geographical science is free to pass from the mere collection of raw
material to the higher task of arranging, classifying, and making
deductions, as well as to the more detailed surveys which are still
necessary.
The other point of interest is that the last fifty years have seen an
enormous increase in the facilities for travel, a fact which has led to
a great increase in the number of people to whom geography appeals. The
decade between 1830 and 1840 saw the beginning of two great series of
guide-books, Murray's _Handbooks_ and Baedeker's _Guides_, whose
importance for the travelling public can hardly be over-estimated. The
first "Baedeker" was a little guide to the Rhine, and since it was first
published this firm of publishers has not only extended its field of
operations over nearly the whole world, but has issued a constant stream
of new editions, which for the most frequented tourist regions are
practically annual. That great tourist agency whose name is now a
household word began operations in the early forties, and like the firm
of Baedeker has now taken the world as its sphere of action. We may say,
then, that during the course of the nineteenth century, travel,
previously a pastime of the rich, was brought within the reach of very
moderate purses. This democratisation of travel is still going on, and
in certain recent visits of British working men to Germany and elsewhere
we may perhaps see the beginning of a process which will eventually
bring some amount of journeying abroad within the reach of all.
As yet the effect upon geography of this increase in travelling has been
chiefly to enhance popular interest in the science, rather than to
enrich it, for the vast majority of "popular" travel books have added
little, if anything, to the sum total of knowledge. But this is partly
because geographical teaching has hitherto been badly organised, and the
greater number of travellers have started on their journeys without
having been taught what to observe or how to observe. There are already
indications that this condition of affairs is passing away, and that the
traveller of the future will start better equipped, and will demand in
his guide-books a new point of view. Starting from a higher level he
will bring back more from his travels.
Meantime it should be noted that some knowledge of the generalisations
laid down by geographers during the course of the last half century adds
enormously to the interest of travel, both at home and abroad, and that
for this reason, if for no other, geography is worth study by all.
In the following chapters we shall look, so far as possible, at those
aspects of the subject which make the widest appeal, and which are best
fitted to enable the ordinary man to understand his surroundings,
whatever they may be, and so aid him in that delicate task of adjustment
which, consciously or unconsciously, is the task of every living thing.
As limitations of space involve a similar limitation of subject-matter,
it has been thought best to lay most stress upon the conditions which
prevail in Europe and North America, the areas which have been most
thoroughly studied. Europe has the special interest that it has given
origin to the type of civilisation which has most profoundly modified
the earth's surface. This limitation cannot, however, be made rigid, for
it is of the essence of the modern standpoint that no area can be
understood without reference to the world at large. The geography of
Europe no less than of North America is determined by the position of
the respective continents on the surface of the globe, and cannot be
understood without a consideration of this position and its
implications. The standpoint adopted here is frankly anthropological,
that is, the world is considered as the home of man, its physical
peculiarities being regarded as interesting chiefly in their relation to
man and his activities.
Finally, we may note that the development of the subject within recent
years has been such that it is quite impossible, even within the
limitations already laid down, to give a complete survey of the subject.
All that will be attempted, therefore, is to suggest some of the lines
along which research is proceeding most actively at the present time,
special stress being laid upon those aspects of the subject which are
not as yet fully treated in the smaller text-books. The list of books of
reference at the end will, it is hoped, enable those interested to fill
in the blanks which such a scheme necessarily leaves.
CHAPTER II
SURFACE-RELIEF AND THE PROCESS OF EROSION
It is not necessary here to consider the various formal definitions of
geography which have been proposed in the last few years. As is only
natural with a developing subject, much discussion has taken place as to
the exact limits of its field of action, and many definitions have been
proposed with the object of setting forth these limits as clearly as
possible. But it is sufficient for our purpose to note that geography
deals with the surface-relief of the earth, and with the influence which
that relief exercises upon the distribution of other phenomena, and
especially upon the life of man. Before we proceed to study detailed
problems, then, it is obviously necessary to look at some general points
connected with the relief of the earth's surface and its causes.
In the words of the physical geographer, the earth's surface consists
of the solid crust, or lithosphere, of the mass of water forming the
seas and oceans and constituting the hydrosphere, and of that envelope
of gas which we call the atmosphere. Considered separately, each of
these is the concern of special sciences, and not of the geographer
proper. His business it is to take the facts furnished by the
meteorologists, the physicists, the geologists, and so forth, and with
these facts in hand to proceed to consider the effect of the interaction
of earth and water and air in a way which the separate sciences cannot
do. We must further note that it is the interactions of these three
which make the earth a possible home for life as we know it, and it is
these interactions therefore which influence the distribution of life on
the surface of the globe.
There may have been a period when the crust of the earth was clothed in
a uniform sheet of water, just as the globe is now enveloped in a
complete covering of air, but at present, as through the long ages of
geological time, the lithosphere consists of elevations and hollows, and
it is in the hollows that the water accumulates, so that we can
distinguish between the dry land and the ocean beds. Both chemically
and physically the fluid hydrosphere differs markedly from the solid
lithosphere, and it is, above all, the physical differences which are of
supreme importance to the geographer. Because of them sea and land
respond differently to the stream of solar energy which pours down upon
our globe, and it is this different response which is the predominating
factor in the production of the different climates, which again
determine in its main outlines the distribution of living organisms.
This being so, it is clear that it is of great importance to the
geographer to know exactly the distribution of land and water over the
surface of the earth. As the North Polar regions are still inadequately
known, and the South Polar regions hardly known at all, we cannot as yet
determine exactly this distribution, but any globe will show that land
and ocean are very unequally distributed. The great land masses cluster
round the North Pole, while the southern hemisphere consists largely of
water. We thus have a land hemisphere and a water one. According to
recent calculations the oceans occupy some 72 per cent. of the entire
surface of the globe, leaving only 28 per cent. of land. But while in
the northern hemisphere there is about one and a half times more water
than land, in the southern there is about six times more water, both
figures being liable to error, as indicated above, owing to our
uncertainty as to the land and water of the Polar zones.
This distribution is of great importance in connection with certain
theories as to the actual plan of the earth, but this is a difficult
subject which need not concern us here. It is discussed in Prof. J. W.
Gregory's volume on _The Making of the Earth_. More interesting is the
effect which the arrangement of land and water has had upon that part of
the life of the earth which was evolved in late geological time. Though
the geographer for convenience' sake recognizes three separate
continents in the Old World--Europe, Asia and Africa--yet these form
practically one land mass, which in its turn approaches America very
nearly at Bering Straits, and, less nearly, in the North Atlantic
through the intervention of the British Isles, the Faeroes, Iceland,
Greenland, etc. The centre of this land mass lies in Europe, a point not
without its importance.
In this great land mass of the northern hemisphere life has reached its
highest degree of development, both as regards animal form and as
regards human societies. It was in the northern hemisphere that the
highest mammals, the placentals, arose. There are many remarkable
resemblances between the faunas of Europe, of Asia and of Africa, and a
similar, if less marked, resemblance between those of North America on
the one hand and of Europe and temperate Asia on the other. On the other
hand, the two great land masses which occur in the southern hemisphere,
South America and Australia, show very marked differences in their
fauna, both from each other and from the northern land masses, and in
both cases the fauna has a primitive aspect, which is best marked in
Australia.
When we come to consider man, somewhat similar conditions present
themselves. The great civilisations developed in the land mass of the
Old World, though the waterless desert of the Sahara cut off much of
Africa from participation in them. America developed a relatively high
civilisation of its own, but as the icefields and ice-pack of the north
formed a greater barrier to the migrations of man than to those of the
northern animals, this American civilisation was for long cut off from
that of the Old World, and when free communication became possible, it
went down before that of the eastern world.
We must connect these facts directly with the peculiar distribution of
land and water in the northern hemisphere, which made free intercourse
possible, alike for the land animals and for man. The importance of this
intercourse may be suggested in a few words. When a group of organisms
is limited, from whatever cause, to a particular zone of the earth's
surface, the members of the group tend to acquire characters fitting
them for this restricted area. But if the area is open, constantly or
periodically, to incursions of organisms from adjacent areas, then, with
the widening of the environment, and the greater intensity of the
struggle for existence, evolution is quickened and new characters
appear. The men of the Eurasian continent learnt, on the fierce
battle-grounds of that continent, lessons which enabled them to conquer
without difficulty the more isolated human groups of the southern
hemisphere. The fact that they took south with them the mammals of the
north, who also have thriven at the expense of the native forms, shows
that the hold of the southern animals upon their habitat was no less
precarious than that of man himself.
One other point is worth notice in connection with the distribution of
land and water over the surface of the globe. We have seen that the
northern hemisphere is the region where organic evolution has been most
marked. It is, as it were, a great biological laboratory. On the other
hand, in the southern hemisphere, which has fewer land masses to
interfere with the circulation of the atmosphere, many physical
phenomena occur in a more marked and orderly fashion than to the north.
The westerly winds of the south blow with a force and a constancy which
makes it impossible to compare them with the more variable westerlies of
the north. Even the ocean currents of the south seem to show more
constancy than those of the north. If the northern hemisphere is a great
biological laboratory, the southern may be described as a physical one,
and one of the great interests of the further exploration of the
Antarctic is that it will probably cast light upon some important
meteorological problems. (See Dr. W. S. Bruce's volume on _Polar
Exploration_.)
The distribution of land and water, with all its effects on climate and
on the distribution of life, is, as we have seen, caused by the main
features of the relief of the earth, by the existence of vast
depressions in which the water accumulates, and of relative elevations
from which it flows. But the minor details of relief, hill and valley,
ocean depth and continental shelf, are also important, and exercise a
very marked effect upon distribution. They therefore demand in their
turn some consideration.
Taking first the prime distinction between land surface and ocean floor,
we note that the two differ from one another markedly, alike in their
characteristics and in the conditions to which they are exposed. The
land is subjected to constantly varying conditions: to the alternation
of day and night, and to the changes of the seasons, with corresponding
variations in temperature; to the fluctuations of the weather; to
running water, and so forth. In the great ocean depths at least, on the
other hand, the conditions are remarkably uniform. Neither diurnal nor
seasonal changes have here any effect; the temperature seems to
fluctuate but little; the water is almost still. This uniformity of
physical conditions is reflected in the uniformity of the surface over
wide areas. While the land surface shows marked irregularities, the
ocean floor has a monotonous character, with more gentle outlines.
In its most general form the characters of the sea bottom may be briefly
stated. Round the great land masses there is an area of relatively
shallow water, which is sometimes only a few miles wide, and at other
times extends outwards for hundreds of miles. This region is the
_Continental Shelf_, and its seaward boundary for convenience' sake is
taken at a depth of 100 fathoms, or 600 feet. Within this zone the
influence of the land is still felt, and some of the characters of land
surfaces appear. Thus we sometimes find that river valleys are prolonged
outwards over the Continental Shelf, giving a markedly irregular
appearance to the ocean floor. The British Islands lie upon a
Continental Shelf of this kind, and this is one of our reasons for
knowing that they are really only a part of the continent of Europe,
separated from it by a slight depression.
The Continental Shelf slopes away from the land gently, and is widest
where it fringes low continents, and narrowest where mountains approach
the coast. Over it is spread the waste of the land, the coarser lying
near the shore-line, the finer extending outwards to the steep seaward
slope. This rapid slope leads down to the more or less uniform ocean
plateau, whose surface is broken by the great ocean abysses, the
greatest of which has a depth of about six miles. Relative but not
absolute uniformity thus characterises all that part of the ocean floor
which lies below about 100 fathoms.
Again, though the ocean floor is doubtless being slowly raised by the
deposition upon it of the oceanic oozes, yet it is also true that as
compared with the land surface it displays great constancy. While the
land surface is constantly changing owing to the varying forces which
act upon it, the floor of the ocean can vary but little from age to age,
unless it is acted upon by the internal forces of the earth.
Turn now to the land. We note at once the two characters of marked
irregularity of surface, and of changeableness. The changeableness is
due to the forces of erosion which act upon the surface, and of these
forces the most important to the geographer is running water. It is
running water, aided by other agents, which carves the land into hill
and valley, which produces gorge and lake, only ultimately to fill up
the lake and plane away the gorge. It is running water which spreads out
on the lower ground the waste of the higher, and thus prepares the way
for the operations of man.
The result of the long-continued action of the varied forces of erosion
must necessarily be to reduce the surface to an almost level condition.
The denuding agents first produce irregularities and then finally remove
these, until the whole surface is once again almost level. The whole
globe would thus be reduced to the condition of a plain were it not for
the intervention of the internal forces which raise up the surface anew
into folds, or which produce volcanoes and outbursts of molten rock.
This constantly repeated series of changes may be said to be chiefly the
concern of the geologist, especially as it is a series which has
repeated itself in all time. But it is to be noted that at various parts
of the surface of the globe at the present time every stage in the
process occurs, and everywhere the question whether a particular land
area has been exposed for a relatively long or for a relatively short
period to the forces of erosion, has a profound influence upon life. It
is therefore important for the geographer to be able to recognise the
different stages. This he cannot hope to do without some detailed
knowledge of the effects of erosion.
Theoretically every land surface elevated above sea-level should pass
through what has been called a cycle of erosion. There should be a
period when the active forces are working upon a surface as yet but
little modified; this is the period called by analogy youth. At a later
stage the drainage has been well established, and the rivers run in
broad valleys, from which lakes and waterfalls have largely disappeared.
To this condition the term mature has been applied. At a still later
stage the land surface has been so worn by the eroding forces that the
whole process of erosion is slackened, and an uplift must occur before
the erosive forces regain their lost strength. This is the so-called
"cycle of normal erosion," but it is constantly liable to variations due
to local crust movements, to changes in climate, and to local
conditions, though at the same time the distinction of the various
stages has value for the geographer because of their varying effects
upon human life. It is necessary for us, therefore, to consider how the
different stages may be recognized, and how the forces of erosion act.
Let us begin our study of erosion by a general survey of the striking
features of the earth's surface at the present day. We know that at
various parts of the surface there rise lofty mountain chains, whose
summits are often permanently snow-clad, and which, from the sharpness
of their forms and from the masses of rock rubbish which are
accumulating round them, have obviously only been exposed for a
geologically short period to the action of the atmosphere and of running
water. When examined such mountain chains are all found to have the same
peculiarities of internal form, the rocks composing them being
elaborately folded and fractured. Careful investigation has convinced
geologists that all the existing great chains owe their origin to a
series of earth movements which occurred in the period called Tertiary,
that is, in the third of the great geological periods, the one
immediately preceding that in which we live.
These lofty mountain chains of Tertiary origin are most familiar in the
great series of folds which appear at the surface to form the Pyrenees,
the Alps, the Caucasus and the Himalayas, but the Atlas Mountains belong
to the same series, as does also that great mountain chain which, under
various names, runs down the western coast of the American continent.
[Illustration: Fig. 1.--The main points in regard to the structure of
Europe. The shaded areas (1) are regions of ancient rocks, much folded
and crumpled, which once formed mountain regions but are now mostly worn
down to uplands. The lines (2) show the regions affected by Tertiary
folding, largely occupied by mountain chains. The unshaded areas are
mostly plains and basins, only slightly affected by folding, and made up
of rocks which are often almost horizontal.]
As already indicated, these areas are recognised not only by the fact
that there appear at the surface a great number of peaks forming a
mountain chain, but also by the internal structure, the
characteristically complex folding of the rocks. Now outside of these
recently elevated areas in, for example, the continent of Europe, we
find two conditions. On the one hand, there are regions of upland type
but with rounded and smoothed forms, which are sometimes almost reduced
to the condition of a plain. Such regions occur in Ireland, in the west
of Great Britain generally, in Brittany, in the central plateau of
France, in the Ardennes, in Bohemia, in the central plateau of Spain, in
Scandinavia, and so forth. Between these relatively elevated areas we
have plains and low-lying river basins, such as the London basin, the
Paris basin, and so on. When the rocks are examined in both cases it is
found that in the basins and plains the rocks, as a general rule, are
only slightly inclined, while in the uplands and plateaux there are
obvious remnants of folding, and the rocks are of ancient types, not
relatively modern like those of the Alps, Himalayas, etc. (see fig. 1).
If, then, the existing mountain chains show complex folding in their
constituent rocks, and though geologically but of yesterday have been
already deeply affected by the denuding agents, must we not suppose that
the folded and contorted uplands of Europe and elsewhere are the last
remnants of very ancient mountain chains? It is they which form the
framework of the continents, and by their wear and tear the low grounds
have been formed, owing to the filling in of the great gulfs which ran
between the old mountain chains.
We may elaborate a little further this very interesting subject. Let us
first note that the geologists group the rocks composing the earth's
crust into three great divisions. We have, first, the Primary rocks,
which are the oldest, and include as their most generally interesting
member the Carboniferous rocks, with their coal-bearing beds, so
important in the modern industrial world. Second, we have the Secondary
beds, the most interesting members of which is the Chalk, so
well-developed in parts of England and France. Finally, the Tertiary
series includes the rocks of the period immediately preceding that in
which the first undoubted remains of man occur.
Each of these periods was of enormous length, and the labours of
successive generations of geologists have brought to light, at least in
broad outline, the general appearance of the globe in so far as affected
by the distribution of land and water, and the main earth movements, in
each separate period. Thus we know that during that long period of time
which is included in the Primary epoch, very extensive earth movements,
resulting in extensive folding and mountain formation, took place. The
geologists distinguish no less than three separate periods of folding in
Primary times. It is not necessary for us to consider these in detail;
their total result was to produce the mountain regions whose worn-down
stumps now form those uplands which we have described in Europe. But
they do not occur in Europe alone. That vast and relatively infertile
area in Eastern Canada which geologists call the Canadian Shield is a
region of very old rocks, once folded into a mountain region, but long
since worn down to an upland. In the eastern United States that long,
but interrupted, range of hills, which, under various names, runs from
the mouth of the St. Lawrence to Alabama and Georgia, and partially
shuts the seaboard off from the prairies and plains beyond, is a region
where the folding is still well marked, in spite of long denudation.
The Secondary period seems to have been one in which comparatively
little folding took place, while, as already indicated, the Tertiary was
one in which there was enormous folding in almost all parts of the
globe, the result being the appearance at the surface of the great
mountain chains of the present day. The structure of these chains makes
them relatively unstable, and the forces of erosion are now acting upon
them with extraordinary activity, beginning that process of wearing down
which has reduced their prototypes of the Primary period to mere
remnants of their former greatness.
Extensive as the Tertiary folding was, however, it left great areas
unaffected, or but slightly affected, and such areas form plains or
basins, where the rocks are but slightly tilted, or show a very simple
form of folding. In Europe such slightly modified rocks occur, _e. g._
in the Paris basin, and in the fertile plains of south-eastern England.
In the United States beds of a similar character occur right over the
great plains, filling what seems once to have been a great gulf between
the old highlands to the east and the towering modern mountain chains of
the west.
It must be realised that this is only a very summary and partial account
of a difficult and complicated problem; but from the standpoint of pure
geography it seems desirable to distinguish between those remnants of
ancient mountains which form the backbone of the continents, the
recently elevated mountain chains where enormously rapid erosion is
taking place, and the largely unmodified rocks which often form fertile
plains.
Let us next proceed to consider how the eroding agents act upon the
surface of the land as soon as it is exposed. We may begin with the
effect of running water upon a recently exposed surface, _e. g._ upon
land slowly emerging above sea-level, or even with the effect of heavy
rain upon sloping ground unprotected by a covering of vegetation. Alike
in the one case and in the other the first effect is the formation of a
number of shallow rills, which at first run parallel to one another.
Sooner or later, however, these parallel channels tend to converge, and
a torrent is formed such as may be seen in any mountain region.
[Illustration: Fig. 2.--An ideal profile of a mature river (AC), showing
the increase in the slope towards the source. The dotted line BC shows
an earlier stage, when there are smooth reaches and rapid reaches with
waterfalls, etc. Note that progressive erosion causes the source to
retreat (_i. e._ from B to A).]
[Illustration: Fig. 3.--An actual profile of the Loire. It will be noted
that the Loire is a mature river, its profile nearly coinciding with the
"ideal" condition. (After de Martonne.)]
Such a torrent consists of three often well-defined parts. First we have
the numerous tiny rills which collect together to form what the French
physiographers call a receiving basin (_bassin de réception_); then
there is the stream proper forming a canal which drains the basin, while
below, where the torrent debouches on the low ground, we find that it
spreads out fanwise and throws down its load of débris to form a cone
(_cône de déjection_). The torrent therefore already imitates a
full-grown river, with its threefold division into mountain track,
valley track, and plain track. It further illustrates the twofold work
of the river, that of erosion and deposition.
Observation on an unprotected surface after a heavy rainfall will
illustrate another point which is of much interest in connection with
the work of rivers. This is that the water has most excavating power,
not, as might be supposed, in the collecting basin, but in the valley
region, where the slope is still great, where the volume of the water is
at its maximum, and where it has acquired a load of débris by means of
which it carves out its bed. The excavation of the bed therefore
proceeds from below upwards towards the collecting basin. The result is
that the slope of the valley floor diminishes as we pass from the upper
region to the lower, owing to the levelling effect of erosion. The
process of levelling down cannot be carried beyond a certain point, the
so-called base level of erosion, which in a lateral stream is
determined by the point of junction with the main stream, and in a main
stream by the point which marks sea or lake level, for obviously no
point in the river valley can be worn down much below its mouth.
When the work of a river is completed, the line which marks the profile
of its bed should have a gentle and continuous slope downwards to base
level. The existence of irregularities, of breaks in the smoothness of
the slope, means that the work of excavation has not proceeded far, that
the river is young. But it is not necessary to proceed to the laborious
drawing of a profile in order to determine the extent to which the
process of excavation has been carried. The existence of rapids, of
waterfalls, the alternation of swift and slow-flowing reaches are all
proofs that it has not been carried far. In short, if a river is
navigable, the navigable reach at least is mature; if it is capable of
furnishing power, that region at least is youthful. If, as sometimes
happens, the middle course is navigable and slow-flowing, and the lower
course broken by rapids and falls, then the probability is that earth
movements have occurred, so that the two regions are of different age.
This is a condition which occurs relatively often in the case of large
rivers.
One other point is worth notice, because it illustrates another way in
which the analogy of youth and maturity holds good. The youthful river,
with its interrupted slope, its lakes and falls, does not permit the
water to flow off with the same regularity as the mature river with its
smoothed outlines. The mature river is thus a more perfect instrument of
drainage.
It is not necessary for our purpose to consider in detail the
characteristic forms of river erosion. It may be sufficient to notice
that rapids and waterfalls are due to the varying hardness of the rocks
forming the bed of the river, and that the normal course of events is
the transition from waterfall to rapid, and from rapid to stream flowing
quietly at the bottom of a rocky gorge. Long gorges or canyons tend to
occur in regions where river erosion is not greatly assisted by the
other eroding agents. As a general rule, as the river cuts its way down,
the other agents cut back the walls so exposed, so that a wide valley is
formed.
But a river does not only eat out its bed in its valley track. A
necessary consequence of this erosion is that it is also able to eat
back the slope on which it is rising, as a result of the smoothing out
of the curves of its bed, so that its source retreats further and
further into the mountain. In regions of abundant rainfall every slope
is abundantly supplied with streams, and therefore those streams which
cut back their region of origin most rapidly will necessarily encroach
upon their neighbours' territory. They therefore tend to tap some of the
tributaries of the other streams, a phenomenon which has sometimes
considerable human importance, and has been extensively studied of late
years under the name of river-capture.
Some examples may serve to make the phenomenon clear. Every one who has
travelled up the Rhone valley in Switzerland has noted the enormous
number of lateral streams, of all sizes, which tumble down the mountain
sides into the Rhone. These streams on, _e. g._, the south side, are,
roughly speaking, parallel to each other, and to a large extent enter
the main stream independently. That is, for the most part they are very
youthful streams. In some cases, however, _e. g._ in the case of the
Dranse and the Visp, the drainage is of a more advanced character, and
we find a large stream with tributaries of considerable size as
distinct from mere torrents. A glance at any great river system on the
map, _e. g._ the Mississippi, the Amazon, etc., will show that the
condition of a great stream with many tributaries is normal in a
district where the drainage is of the developed type. How are the two
conditions, that of numerous parallel mountain torrents and that of a
great river system, related to one another? There is no doubt that
capture, the encroachment of one stream upon the territory of another,
has played an important part in the process.
[Illustration: Fig. 4.--Sketch-map to illustrate river-capture.]
A very simple example of this widespread phenomenon may be taken in
illustration. The accompanying sketch-map, drawn by Mr. Lionel Hinxman,
shows part of the course of the River Feshie, one of the tributaries of
the Spey, and part of the Geldie Burn, one of the tributaries of the
Aberdeenshire Dee. It will be noted that the Feshie shows a very curious
bend, or elbow. Mr. Hinxman points out that this curious condition can
be explained on the supposition that the River Eidart, shown on the map
to the north of the bend, once formed the headwaters of the Feshie,
which cut its valley back until it captured the headwaters of the
Geldie, and thus brought water which formerly flowed into the Dee into
the Spey valley. The boundary between the two counties of Aberdeen and
Inverness is shown on the map by a dotted line, and it is seen that the
march follows the watershed, which between the present Geldie and the
bend on the Feshie is very low. Formerly, however, this watershed lay
much further to the west, and its shifting is due to the capture.
A careful study of large scale maps will show many examples of similar
river-capture, some old and some recent. A sharp bend, the so-called
elbow of capture, on a river in close proximity to another stream
affords in itself a certain presumption that capture has taken place,
though this presumption can only be verified by study on the spot.
It may be noted that before the capture is finally accomplished there
may be an intermediate stage when the water has the choice of two
channels, both of which may be utilised in a time of flood. A very
curious case is that of the Casiquiare, a river in South America which
connects together the two systems of the Amazon and the Orinoco, while
another is the connection recently discovered by Captain Lenfant, a
French explorer, between the systems of the Shari and the Niger in
Africa. Such conditions are obviously unstable, for one stream must
sooner or later predominate over the other, and deprive it even of flood
water.
Another example may help to explain the evolution of a complex river
system with many tributaries. A glance at the map of England (see
diagram) shows that while the rivers of Northumberland and Durham flow
independently into the sea, those of Yorkshire are united into a
characteristic bunch, and all reach the ocean by means of the Humber.
This estuary breaks through the high ground formed by the Wolds of
Yorkshire and Lincolnshire, which consists of hard rock. At one time it
is probable that the rivers of Yorkshire entered the sea separately,
while the other great factor of the Humber, the Trent, mingled its
waters with the present Witham. At this time the weathering of the land
surface had not reached its present stage so the land would lie higher.
In what is now the vale of York the rocks are much softer than where the
Wolds now stand, and the present Ouse, which was at first a longitudinal
tributary of a transverse stream, eating its way back through these soft
rocks, tapped successively the streams flowing eastwards from the
Pennines, and with the help of the abundant water so obtained was
enabled to cut out the wide estuary of the Humber.
[Illustration: Fig. 5.--Sketch-map of northern England, to show the
position of the Tyne and Aire Gaps, and the peculiar character of the
rivers of Yorkshire. The black areas are heights above 600 feet.]
One other important point in connection with river-capture has been
already suggested in the account given of the Feshie. In the little
sketch-map we see clearly the shift of the watershed to the east. The
ultimate cause of this shift is doubtless the fact that in Great
Britain the rainfall diminishes to the east, so that, generally
speaking, the westerly streams have more erosive power than the
easterly. But the special interest of the case is simply that it may
serve to suggest a fact not at first sight obvious, which is that
water-partings are excessively unstable features. One set of streams is
continually striving to encroach upon the others, and by capturing their
headwaters to reduce their erosive power. A very striking example of
capture on the large scale is seen in southern Patagonia, where the
water-parting does not lie near the summit of the chain of the Andes, as
might be expected, but considerably to the east, the western streams (or
glaciers) having captured all the headwaters of the eastern streams,
which lie in a region of much lower rainfall.
The net result is that running water not only scours valleys in the
sides of mountain chains, but also, sooner or later, wears away the
crest itself, and with the assistance of the other agents of denudation
tends to reduce the mountains to plains--or at least "peneplains." The
deduction is, of course, old enough, but the recent emphasis placed upon
river-capture helps us to realise it, showing us the actual "shift of
the divide," or, in other words, the wearing down of the summit levels.
This is a theoretical matter, but there is another point which has
practical significance. Referring once again to the sketch-map on p. 43,
we note that just at the sharp bend in the Feshie, that is, at the elbow
of capture, there is a narrow region, crossed by the boundary line,
which was once traversed by the headwaters of the Geldie, but is now a
dry valley. Such "gaps," as they are called, are present where recent
capture has occurred, and where they occur in hilly country they
sometimes form useful passes, permitting the construction of an easy
road across the hills. A good example is the Aire Gap (see fig. 5) in
the Pennine range of Great Britain, apparently connected with the fact
that the Ribble has captured the headwaters of the Aire. Another
interesting example is the so-called Tyne Gap, that breach in the
Pennines which occurs near the present head of the South Tyne; it was
traversed by the Roman wall, and is now crossed by the road and the
railway from Newcastle to Carlisle.
As we shall see, ice appears to have this power of cutting passes
through mountain chains to a much greater extent than running water; but
here, as in many other respects, there does not appear to be a sharp
breach between the action of the two.
CHAPTER III
ICE AND ITS WORK
In the last chapter we have spoken of the moulding of the surface of the
earth by means of running water and the agents summed up in the term
"weathering." The process is sometimes called "normal erosion," to
distinguish it from that other form of surface moulding in which ice and
frost play a prominent part. At the present time ice, in the form of
ice-sheets or glaciers, is confined to relatively small areas of the
globe, so that we are justified in regarding its action as exceptional
when compared with the work of running water. It is, however, well known
that this limitation of the field of action of ice is very recent, and
that during a period which geologically is only yesterday, a much
greater part of the surface than at present was ice-clad.
In point of fact, much of Europe, especially the northern parts and
those regions which lie close to the lofty mountain chains, much of
North America, and, probably, considerable parts of the southern
hemisphere, were subjected to the action of ice so recently that the
processes of normal erosion have not had time to obliterate, hardly even
to blur, the tracks which the ice left.
The results of the great extension of ice action in that period which
geologists call Pleistocene were twofold. In the first place, as the
result of the presence of the ice-sheet, we have vast accumulations of
débris spread over the lower grounds. These accumulations sometimes form
great sheets of boulder clay; sometimes they are collected into the
curious sandy and gravelly mounds called kames which in parts of,
_e. g._ Scotland, have a great extension; sometimes they have formed
great heaps of material at the entrances of valleys. Again, these
deposits have sometimes blocked valleys and so formed lakes, and they
have supplied the post-glacial rivers with a vast amount of material
which has been used to scour out the river-beds, and has been often
re-sorted and re-arranged by running water.
Secondly, the fact that the northern region and the high grounds
further south, in both Europe and North America, have been recently clad
in ice is associated with many peculiarities of surface form, some of
which have exercised a marked influence on human settlements and ways of
communication.
These peculiarities of surface moulding have been the object of
singularly detailed study in late years, and from this detailed study
many interesting facts have emerged. It may be well to state at once
that this study has been largely stimulated by the fact that there is at
present a great want of unanimity of opinion as to the exact cause of
these peculiarities of form. According to one school ice is a more
powerful eroding agent than water; according to another its action is
largely conservative, and its power of erosion is slight as compared
with that of water.
The beginnings of a possible solution of the problem are perhaps to be
seen in the suggestions of those who seek the causes of the peculiar
features of glaciated regions in the way in which running water works
when it is controlled and modified by the existence of ice; but we must
admit that, on the whole, the conflict is still hot and many members of
the opposing schools will have no compromise.
To the geographer, however, the very fierceness of the controversy has
been useful. The question as to the exact part played respectively by
water and by ice in surface moulding is really a question for the
geologist. It is, however, of great importance to the geographer that
recently glaciated surfaces should be studied from every point of view,
for from this detailed study are emerging many important
generalisations. We shall, therefore, in this chapter only touch very
lightly upon the actual points in dispute, but shall lay stress upon the
interesting facts admitted by both parties.
When the conception of a just-vanished period of great glaciation was
being established by the labours of many geologists, stress was
naturally laid upon the obvious resemblances between parts of, _e. g._
Scotland and Wales, and those parts of the Alps which have been exposed
by the retreat of the existing glaciers. Thus we find that most of the
text-books emphasise the occurrence of perched blocks, of erratics,
_i. e._ of blocks of rock which must have been carried from a distance,
of the phenomenon of crag and tail, of giants' kettles, and so on. All
these are of more geological than geographical importance; they do not
in themselves greatly affect the distribution of other phenomena over
the surface. We shall not, therefore, stop to consider them in detail.
It is otherwise with those indications of recent glaciation which have
been studied within the last few years, and they demand the geographer's
most careful consideration.
The most active discussion has taken place in regard to the peculiar
features of the valleys in recently-glaciated districts, and we shall
discuss especially this point.
We have already described the general features presented by valleys
which owe their origin to running water. In such valleys, as we have
seen, the longer the forces work the more nearly is the valley floor
reduced to an even slope, whose angle decreases in passing from the
mountain to the plain track. In the ordinary river valley the shape of
the valley approximates to that of a V, that is, the valley narrows
downwards, the river occupying the narrowest region.
Again, as a general rule there is no great difference of level between
the tributary valleys--at least at their extremities--and the main
valley, that is, there is no sharp discordance between the two. While,
however, the "mature" river valley shows a gentle, continuous slope, we
usually find that "young" rivers, at least in their mountain track, show
an alternation of plain and gorge, which is very easily observed in any
hilly region.
In other words, we find that, owing to the inclination of the rocks, or
to their varying hardness, or to other causes, particular reaches are
less easily eroded than others. These form waterfalls, which ultimately,
as we have seen, give place to gorges. Beyond the waterfall the
diminishing slope checks the rapidity of flow, and the stream tends to
widen out, and also to throw down its load of débris, so that an
alluvial plain may be formed.
One other character of an ordinary river valley may be noted. It heads,
as we have seen, in a collecting basin, which receives the surface
runnels and the outflows of the springs which form the beginning of the
river.
Let us now turn to the valleys in a recently glaciated country. We omit
any description of existing glaciers; these will be found described in
the volume on the Alps, and further, photography and the picture
postcard have rendered the main features of a glacier familiar to every
one. Almost every large railway station now shows fine coloured
photographs of some of the important Swiss glaciers.
Taking, then, a valley known to have been occupied by a Pleistocene
glacier, we find the following features. As contrasted with an ordinary
river valley, the glacial valley is usually flat-bottomed, a condition
described as U-shaped to point the contrast with the river valley.
Examples in Great Britain and elsewhere are frequent, but some of the
Alpine valleys show the phenomenon in a very striking form. Two good
examples are the Aar valley at Meiringen, and the Lauterbrunnen valley
at the village of the same name. Both have been rendered more or less
familiar by constant photographing (see fig. 7).
The reason why they have been so much photographed leads us to consider
another peculiarity of the glaciated valley. In both the cases named a
steep cliff wall rises from either side of the broad, flat valley
floor, and from the summit of this cliff the lateral streams leap into
the main valley by often superb waterfalls. This is a very important
feature of glaciated valleys--the fact that their tributaries are
markedly _discordant_, that is, that there is marked difference of level
between the beds of the side and main streams.
Because the side valleys lie high above the main they are said to
"hang," and are called hanging valleys, while the main valley is said to
be over-deepened. The rocky height over which the water springs may be
called the junction step, as an attempt to translate the French term
_gradin de confluence_ which is applied to it.
Incidentally we may note that in the Alps the junction step is of great
human importance. Its presence gives the water the power which is used
in lighting the Alpine villages with electricity, and in driving the
trains which often carry the tourist to those villages. In the French
and Italian Alps especially, the power is being more and more used to
supply the motive force for various minor manufactures, notably for the
production of nitrogenous manure from the air.
[Illustration: Fig. 6.--A diagrammatic cross-section of a recently
glaciated valley. AB, the mountain slope which rose above the ancient
glacier and has therefore retained the sharp, unrounded forms due to
ordinary weathering. BC, the shelf or shoulder, formerly covered by the
ice, and therefore strewn with glacial débris. It now usually forms a
pasture or alp. The dotted line connecting CC shows the probable form of
the pre-glacial valley; CD, the rocky wall of the existing U-shaped
valley on whose floor the river now flows.]
Associated with the hanging valleys of Alpine regions is the presence
of a curious shelf, shoulder, or "bench," which frequently lies on the
top of the cliff from which the lateral streams spring (see figs. 6 and
7). Any one who has done some walking in the Alps, must have noticed a
peculiar and often trying feature of any walk which leads up the side of
the valley. This is that the walk begins with a very steep ascent,
where the road or track zig-zags to and fro. After this steep and trying
climb the walker reaches a broad shelf (BC in figs. 6 and 7), where the
slope is much less, and where the extent of relatively level ground
gives room for the erection of a huge hotel, or perhaps only of a group
of chalets. This shelf is covered with fine herbage, destined to be
cropped by the cows of the community.
[Illustration: Fig. 7.--An actual cross-section of the Lauterbrunnen
valley. The vertical and horizontal scales are the same. B marks the
edge of the cliff wall over which the streams leap in cascades. A is the
position of the stream at the bottom of the U-shaped valley. BC marks
the position of the shelf, largely occupied by the pastures or alps.
Above them are rocky, unsmoothed slopes.]
If the traveller continue his walk he will find that above this pasture
ground or _alp_ the slopes are again steep up to the mountain summits.
Possibly, however, his walk has been to see a famous waterfall from
above, and he will find that the streams which flow with relative
slowness over the comparatively gentle slopes of the alp or shelf, will
at some point tumble over the region up which he climbed, probably in a
series of leaps or cascades.
The U-shaped valley, the "hanging" tributaries, the shelf or shoulder
running along the upper part of the cliff wall which bounds the main
valley, all these are striking features of glaciated regions. We shall
not here discuss the probable causes of this striking "break of slope,"
so different from the characteristically continuous slopes of an
ordinary mature river valley. As has been indicated, it is here that
active controversy rages. It is, however, important to note that the
shoulder or bench of which we have spoken was almost certainly once
covered by the ice, its gentle slope indicating the original valley
floor, before over-deepening took place.
The reason why pasture now grows upon it is that it is covered with fine
glacial débris, which makes fertile soil. The fertile soil, which is
often irrigated by milky water from existing glaciers, combined with the
effect of altitude upon the plants, produces rich pasturage, and makes
cattle-rearing an important alpine industry.
The next interesting feature of glaciated regions is the occurrence of
those curious mountain forms which have special names in nearly every
recently-glaciated region. Those gigantic arm-chair-shaped notches, high
up on the mountain sides, which the Welsh call cwms, the Scotch corries,
the French cirques, and the Germans kare, are very widespread in the
Highlands of Scotland, in the mountains of Wales, in the Tyrol, and in
other parts of the Alps (though they are not common in the Central
region), and in North America as well as elsewhere.
A cirque (fig. 8) is shaped something like an office arm-chair. The
floor has only a gentle downward slope, and often lodges a lake; or in
other cases it is marshy, showing that a lake was once present. The back
and sides are steep and precipitous. In some instances, if several
cirques occur near together, the side walls may be eroded through, so
that a shelf is produced, as one might produce a bench by putting two
chairs side by side, and cutting away the contiguous arms. Very often,
as one may easily see in the Highlands of Scotland, a series of cirques
occur, one above the other, so that a climber proceeding from the valley
floor upwards has a succession of steep "pitches," to use a
mountaineering term, alternating with easy if wet walks across the
floors of the successive cirques.
[Illustration: Fig. 8.--Diagram showing two glacial cirques.]
It quite often happens in the case of high mountains in the Alps that
the topmost of such a series of cirques still retains a glacier, what is
called a dead glacier, that is, one which has practically ceased to
move.
In other cases, again, we may find that what should be the flat floor
of the cirque has been largely eaten away, as it were, by a huge rounded
trough, which occupies what would be the extreme front of the seat of
the arm-chair. In this trough a stream runs, and the trough has the
characteristic U-shaped rounding characteristic of glacial forms.
Further, at the top of the wall of the trough a bench or shelf exists,
which is obviously the remains of the old cirque floor. In the case of
all characteristic glacial cirques, however, the special feature is that
the flat bottom of the cirque is discontinuous with the valley below;
they are not parts of the same system of drainage. What we may call an
unconformity appears between the two regions, more or less marked
according as running water has or has not had time to begin the work of
the removal of the unconformity.
The immediate human importance of these corries or cirques is not so
apparent as in the case of hanging valleys, but they must be mentioned,
if only because of their extraordinary abundance in glaciated regions,
and especially in Great Britain. There are two views as to their origin,
and we shall indicate both here without making any attempt to decide
which is the correct one. A very full and clear statement of one
position will be found in an article by Prof. Garwood in the
_Geographical Journal_ for September 1910, while previous articles by
Prof. Davis and others in this journal formulate the opposed view.
To the first school the corrie is simply in origin the collecting basin
of a pre-glacial stream, such a basin tending to acquire, roughly
speaking, a flattish bottom and somewhat steep sides. With the onset of
the ice the floor of the basin was protected by the ice from further
erosion, while the frost ate back the wall and so steepened it, and the
glacier carried away all débris as it formed. At a later stage the lower
part of the glacier disappeared and only the cirque glacier was left. It
continued its protective action, while below the powerful torrents
hollowed out a trough. This process was perhaps repeated several times,
with the final result that the protected cirque was left as a
much-modified remnant of pre-glacial conditions, while the valley below
was powerfully eroded by the glacial torrents. Thus a cirque lying above
an existing valley is to be regarded as the beheaded end of an old
valley, preserved by its ice covering, while below the old valley has
been fundamentally modified by the scour of the glacial torrents. On
this view the sharp distinction between the two angles of slope marks
the distinction between the work of ice (protective) and the work of
water (erosive). A series of cirques means a succession of glacial and
interglacial periods.
According to the other school, for whom ice is a more powerful eroding
agent than water, the cirque was produced by the ice, its presence or
absence, in _e. g._ the Alps, being determined by the shape of the
pre-glacial mountains. Cirques are believed to have been produced by the
ice wherever the form of the mountains conduced to the accumulation of
snow, and the occurrence of a series of cirques, and of the troughs
which seem sometimes to eat into their floors, is ascribed to the
successive retreat of the great ice-plough, _i. e._ to the action of the
retreating ice itself, and not to the water which flows from beneath it.
* * * * *
Another striking feature of many glacial valleys is a very marked want
of continuity in the slope of the main valley. Not only do the side
valleys "hang" over the main valleys, but, further, this main valley
itself often consists of relatively level reaches alternating with rocky
bars, through which the river has sometimes later cut a gorge. Examples
of this are very frequent. The famous gorge of the Aar above Meiringen
is a river gorge cut through a rocky bar of this kind.
The Pyrenees are somewhat less familiar, both to tourists and in the
form of pictures, but there, also, the same thing occurs. Above the
health resort of Cauterets lies the little Lac de Gaube, whose mouth is
blocked by a rocky bar through which the little torrent is cutting a
tiny gorge. If the tourist crosses the lake in a boat and begins to walk
up the valley above it, he will find that it has the form of a
staircase, the huge steps being separated from one another by broad
plateaux, which are flat and swampy, and have obviously been occupied by
lakes not long ago. Above each plateau there is a rocky wall, almost
precipitous, down which the stream flows in cascades. In other parts of
the Pyrenees the same phenomenon occurs, and the lakes sometimes
persist, lying one above the other in a series.
[Illustration: Fig. 9.--Profile of the Maderaner thal in Switzerland, to
show the staircase arrangement peculiar to recently glaciated valleys.
(From Garwood.)]
The phenomenon is so common that it markedly affects human life in the
Alps. The "landings," as the French call them, usually afford good
pasture ground, while those which lie at no great elevation can be
cultivated. Further, as the ground is level there is room for houses or
even for a considerable village. The intervening region or step is too
rocky to give level ground for human habitations or for pasture and
cultivation. Where the river has had time to cut a gorge, the road must
leave the stream, and can often be constructed only with difficulty. The
result is that an Alpine valley often consists of a chain of villages,
linked together by a difficult mule track or path. The abundant
water-power, however, makes mechanical traction relatively easy, and we
have sometimes the curious condition that a mule track is replaced by a
railway, without the intervention of a road fit for wheeled traffic.
We need not stop to discuss the probable cause of this step and stair
arrangement, which presents much the same problem as the series of
cirques at the head of the valley. It is enough to indicate that
according to one group of physical geographers the flat landings are due
to the way in which the gradually decreasing glacier protected its bed
from erosion, while the torrent which issued from it eroded very rapidly
below; according to another school the landings are due to direct
glacial erosion. There are other observers, again, who lay especial
stress upon the modifications of the erosive powers of running water,
due to the presence of the ice. For us it is of interest to notice that,
as has been already indicated, the staircase effect occurs also, though
on a smaller scale, in the case of mountain streams generally, some of
which must be post-glacial in origin. In other words, there seems to be
fundamental similarity between the work of ice and of water, the
differences being differences of degree rather than of kind, and due
largely to the varying fluidity of the two.
There is still one other feature of glaciated regions to which reference
must be made. This is the occurrence of peculiarly open passes in
considerable numbers across mountain regions which have been recently
glaciated. In the geography books and in some maps, the Alps, for
example, are represented as a great barrier, shutting off the fertile
plains of Italy from the countries of Central Europe. But history shows
that they have never been such a barrier, and the phrase of "splendid
traitor" has been applied to the whole mountain range, in order to
emphasise its total inadequacy as a barrier, either to armed or to
peaceful invasion.
Since the time of Napoleon I public attention has been focussed upon a
few great Alpine passes, notably the Mont Cenis, the Simplon and the St.
Gothard, which are crossed by great carriage roads, now functionally
replaced by railway tunnels beneath. But we must not forget that in
addition to these and the other great passes there are almost
innumerable ways of crossing the Alps on foot, and the presence either
of Hospices or of small inns on many of the smaller passes shows that
they are constantly used at the present time, in spite of railway
tunnels and carriage roads elsewhere. Even a pass relatively so
difficult as the Théodule, was used by very large numbers of Italian
peasants during the time when work on the Simplon railway made great
demands on Italian labour.
Any one of the passes, great or small, shows in outline the same
characters. There is a steep ascent, often steeper on the Italian than
on the other side, then a broad, windswept, open summit, sometimes
almost level, below which the rapid descent begins. Not infrequently a
lake, or lakes, may be found near the summit.
On a smaller scale the same phenomenon occurs in such glaciated regions
as Scotland, the relatively low connections between one valley system
and another greatly facilitating communication, and usually carrying
both road and railway, where the latter exists. Such connections between
two drainage systems (that is, the existence of a very low divide
between the two) only exist on a small scale outside glaciated regions,
so that they, with all their effects upon communications, must be
largely ascribed to ice-action. We shall describe one case in a little
detail, with the proviso that while no one denies the frequency of such
passes in glaciated regions, some authorities believe that their
production was due more to glacial torrents than to the erosive action
of ice itself.
A very pretty example is the picturesque pass known as the Gemmi, which
is traversed only by a mule path, and connects Kandersteg, and thus the
lake of Thun and the town of Berne, with the Rhone valley, which the
path enters at the village of Leuk. The walk proper is, however, over at
the Baths of Leuk, a small health resort lying at the foot of the great
Gemmiwand, a wall of rock over 1,600 feet in height on the summit of
which is the Gemmi pass. Readers of Mark Twain's _A Tramp Abroad_ will
remember his interesting description of the crossing of the pass, which
is part of the regulation tour in Switzerland.
The excursion may be very briefly described. The traveller starts from
the village of Kandersteg, and almost immediately begins a steep climb,
which after a rise of over 2,000 feet leads him over a ridge to a
pasture, once swept by an avalanche. Another short but steep rise (note
the staircase arrangement) leads him to the lonely Daubensee, a little
lake which is frozen for more than half the year and has no outlet. It
is itself fed by a glacier lying to the traveller's right, the Laemmern
glacier, which is shrinking and exposing more and more of its old bed.
Even to the most inexperienced traveller it is obvious that this present
day shrinkage is, as it were, the last remnant of a shrinkage which has
been going on for a prolonged period, so that the route by which the
traveller ascended from Kandersteg is but a remnant of the bed of the
old glacier. The point of special interest, however, is that at the end
of the Daubensee the traveller leaves the glacial valley by which he has
ascended, and passing through a great notch or gateway in a wall of
rock, begins the almost precipitous descent to Leukerbad, which lies at
his feet, 1,600 feet below. It is this notch which makes the pass, and
it is fundamentally a breach in the mountain wall which separates the
drainage of the Rhine from that of the Rhone. Comparing small things
with great we may note that this gateway presents some resemblance to
the Tyne and Aire Gaps in the Pennines, already mentioned, which may
also have been modified by ice-action.
The explanation given is as follows:--At the time when the glaciation
reached its maximum height the mass of ice in what is now the Laemmern
glacier was so great that it could not be contained within its own
valley. The ice was piled up so high that it over-rode the watershed,
rose up beyond the containing wall of its own valley, and pushed a long
arm over the valley wall, down into the Rhone valley. This tongue of
ice, either by its own erosive power, or because of the glacial and
sub-glacial streams which it produced, wore out a notch in the wall as
it crossed, and it is this notch which makes the pass. As the glacier
gradually shrank, it could no longer send this tributary over the wall
into the valley below, and was constrained to send all its drainage into
its own valley, that is ultimately into the Rhine. But the Gemmi pass
persists as a proof of its former magnitude, of the fact that once part
of the Laemmern drainage reached the Mediterranean instead of the North
Sea, that there was once a communication between the Rhine and the Rhone
drainage systems.
Many at least of the great Alpine passes are believed to have been
produced in this way, and therefore we must add to the peculiarities of
recently-glaciated countries, the fact that passes are likely to be
frequent across their hills and valleys, owing to the power which ice
possesses, when enormously developed, of rising above valley walls, and
streaming down into another valley system. Some of the great Alpine
passes, perhaps, arose in other ways, but this brief description may be
of interest as suggesting one, probably common, mode of origin.
If we sum up what has been said as to the special features of glaciated
regions, we may note that their valleys tend to be U-shaped, and to be
discontinuous with their tributary valleys, which "hang" over them. On
the top of the cliff from which these tributary streams leap is a shelf,
which is clearly a portion of the floor of the pre-glacial valley and is
covered by glacial débris. At the heads of the valleys there are often
cirques or plateaux, which again are markedly discordant, hanging high
above the valley below. In the main valley itself there are similar
discordances, giving rise to a staircase arrangement. Finally, different
valley systems often communicate with each other by passes, natural
highways which hang high above both valley systems alike.
Obviously, however, we might replace this detailed summary by the simple
statement that whereas in a region subjected only to the action of
running water, there is a marked tendency to continuity of slopes
throughout, a tendency more and more marked the longer the water acts,
in glaciated regions there is an equally obvious discordance, a
discontinuity of slope, most marked where water has not had time to
begin its smoothing action. As every glaciated valley which we can study
in detail has been subjected to the action both of ice and of water, it
is a simple deduction that the discontinuity is due to the differential
action of the two. This is the point of geographical importance, and to
the geographer it is of minor importance to know whether it is the
passive resistance of the ice which has caused the discontinuity, or
whether it is the water which has been unable to keep pace with the
activity of the ice.
* * * * *
There is one other point which must be alluded to even in this very
brief consideration of the effect of the ice age upon the physical
geography of the glaciated regions. This is the fact that it greatly
modified the numbers and distribution of plants and animals throughout
the areas affected. Obviously the covering of ice must have rendered a
large part of Europe uninhabitable both for man and for the vast
majority of animals and plants. In Europe, therefore, as also in North
America, there must have been a southward sweep of all living organisms,
driven from their original habitat by the onset of the cold period. But
the conditions in the two continents differed greatly.
In North America, especially in the east, there are no transverse chains
of mountains, there is no southern sea until the Gulf of Mexico is
reached in lat. 30°, and even here Florida almost touches the tropic,
and Mexico extends far beyond it. In this continent, therefore, the
plants and animals, though driven far to the south, still found room to
live and multiply, and had no great obstacle to cross either in their
southward journey, or when they strove to re-annex their old territory
as the cold conditions passed away again.
It is a curious fact that the forest trees of eastern Asia and of
eastern North America show a remarkable resemblance to one another, and
both regions are very rich in species and in genera. It is believed that
this rich North American flora is a remnant of pre-glacial conditions,
and that its persistence is due to the ease with which the trees
obtained an asylum to the south during the period when the climate was
most severe.
In Europe, in spite of the fact that the winter climate is much milder
than in corresponding latitudes in North America, the number of kinds of
forest trees is much less, there is little resemblance to those of Asia
and the eastern United States, and the trees have generally a less
southern aspect. This is the more remarkable in that trees of southern
facies introduced from China and Japan and from the United States thrive
admirably in Europe, showing that there is no climatic obstacle to their
presence there. To mention only a few examples, the Tree of Heaven
(_Ailanthus glandulosa_), so very common, even as a wild tree in many
parts of the continent of Europe, was introduced from China, while the
beautiful _Sophora japonica_, so frequently planted in towns, comes, as
its name indicates, from Japan, and the various species of those
beautiful flowering trees known as Catalpa are either American or
Asiatic. The western plane (_Platanus occidentalis_), another favourite
town tree, comes from the United States, and other American trees which
are found very abundantly in towns in the warmer parts of Europe are the
black walnut and the honey locust (_Gleditschia tricanthos_). Perhaps
more striking than any of these is the case of the so-called false
acacia (_Robinia pseudacacia_), which is as common over a great part of
the continent of Europe as hawthorn bushes or wild roses are with us,
and yet is a North American species, introduced less than three hundred
years ago. Generally, we may say that all the more beautiful trees now
growing in the warmer parts of Europe come either from eastern Asia or
from the United States. In other words, the Ice Age seems to have
greatly impoverished the flora of Europe. To a less extent this is also
true of western North America, which has fewer species of trees than the
east.
Why had the ice this impoverishing effect upon Europe? The topography of
the continent supplies the answer. In the first place, in Europe there
are numerous transverse chains of mountains. The Pyrenees, the Alps, the
Caucasus, each with its load of ice, each with glaciers deploying on the
low ground at its feet, must have been obstacles in the way of the
southern migration alike of plants and of animals. Again, even if these
obstacles were passed or turned, the great inland sea formed another
barrier further south. In consequence of this difficulty in finding
asylums the pre-glacial plants and animals must have perished in
considerable numbers, and thus a general impoverishment took place. One
must not of course exaggerate. A proportion of the pre-glacial forms did
succeed in living through the period of stress, but many must have been,
as it were, squeezed out of Europe or out of existence by the
unfavourable climatic conditions.
As the climate improved the lands swept bare once again became
inhabitable, and there was a recolonisation by movements from the south
and from the east. We shall indicate later how man himself came from
the south and the east to colonise the west and north, but his movements
were only part of a great series which included also those of plants and
animals.
CHAPTER IV
CLIMATE AND WEATHER
To the superficial observer those daily variations in the atmospheric
conditions in any one locality which we sum up under the term weather,
may appear to occur without order or regularity, but detailed quantitive
study soon shows that even British weather displays constancy in its
irregularity. The existence of such basal constancy, indeed, lies at the
root of all intelligent utilisation of the soil. The irresponsible
amateur gardener may lightheartedly assume that a particular spring will
be "early," but the professional is not easily induced to abandon his
rule that such and such operations must not be undertaken before certain
fixed dates. The farmer, if he is to avoid bankruptcy, must know within
what limits the first autumn frost is likely to make its appearance,
and when the last spring one may be expected.
Collective experience, then, whether expressed in the meteorologist's
figures or in a less accurate form, leads us to the conclusion that for
every locality on the earth's surface there is a certain fixed average
succession of weather, which we sum up in the term _climate_.
In the case of both climate and weather our knowledge may be summed up
in such general terms as "wet" or "dry," "warm" or "cold," and so forth,
or we may borrow the meteorologist's notations, and express the facts in
degrees of temperature, inches of rainfall and of pressure, percentages
of humidity, and so on. But it should be understood that such figures
can be used by the geographer with justification only when he is himself
aware, and can assume that his audience is aware, of the significance of
the figures in connection with the processes of erosion and the
phenomena of life. To say that the mean January temperature of a
particular place is 30° F., is only a convenient shorthand way of saying
that in this place in winter plant life is arrested, water is ice-bound,
and most animals sleep or migrate. In other words, the use of the
figures assumes a certain knowledge of biology and of physics on the
part of the audience.
We do not propose here to treat either climate or weather with any
fullness, for there is a volume in the series specially devoted to these
and kindred subjects. All that will be attempted, therefore, is to
discuss one or two important climates with the object of considering
later their respective effects on the distribution of other phenomena on
the surface of the globe. This is the more worth doing in that the
subject is one which has had a great deal of attention devoted to it in
recent years.
Certain points in regard to climate, _e. g._ the fact that the regions
of the earth near the equator get more solar heat than those nearer the
poles, and that parts of the globe are subjected to variable winds, as
contrasted with those regions where the extraordinarily regular winds
called "trades" blow, have of course been known for long enough. But not
till the latter half of the nineteenth century did the civilised nations
begin regular meteorological observations, and these observations are
still scanty for the uncivilised and partially civilised regions. The
meteorological raw material necessary for the exact study of climates
has thus only been available for a comparatively short period, and is
still incomplete.
We may begin with that type of climate which has so profoundly
influenced the civilisation of western Europe, and therefore also the
new civilisations of America, Australia, South Africa, and so on. This
is the type called Mediterranean, because it reaches its best
development and has been most studied round the Mediterranean area. But
it also occurs in California, in parts of Chile, in South Africa round
Cape Colony, and in south and south-western Australia. Generally, it is
characteristic of lands lying on the western side of continents, in the
latitudes between tropical and temperate, and is therefore sometimes
called the maritime sub-tropical climate. The term maritime is applied
because, as we shall see, for some part of the year oceanic influences
prevail, sub-tropical indicates the position in latitude.
A very curious illustration of the similarity of climate in the
different regions named is to be found in the fact that in parts of the
Mediterranean area two introduced American plants, the agave and the
prickly pear, are more obvious and abundant than most native plants;
while in California, Cape Colony and southern Australia the cultivated
plants are chiefly of Mediterranean origin.
The main features of the Mediterranean climate may be briefly
summarised. The most important character, next to the mild temperature,
is the fact that no rain (or very little) falls in summer, the growing
season further north, which is here largely a period of cessation of
plant growth. The rain, which tends to be scanty or even absent in the
interior of land masses, _e. g._ in Spain and Asia Minor, and also to
the south, _e. g._ in the Desert of Sahara, in the Mediterranean region
proper falls in the winter months. It is this winter rainfall and the
summer drought which define the Mediterranean type of climate.
The reason for this seasonal distribution of rainfall is as interesting
as the fact itself, and to understand it we must turn to the circulation
of air on the surface of the globe.
In the following description we shall restrict ourselves, for the sake
of clearness, to the Mediterranean region itself, the region where the
Mediterranean type of climate is developed over the largest area, and
where, for many reasons, it is most important. But it must be noted that
the conditions which give rise to the Mediterranean type of climate are
the same wherever it occurs, though in the Mediterranean area they are
greatly modified by the great inland sea of that name, which carries
oceanic conditions far into the land.
We must note, first, that at all seasons those regions of the earth
which are directly beneath the vertical rays of the sun are heated most
intensely. Therefore the air over these regions, being rendered light by
heating, rises, and a belt of low pressure is thus formed. Only at the
equinoxes does this belt of high temperature, low pressure, and light
winds or calms, coincide with the equator. In the northern summer it
moves north with the sun; in the northern winter it travels south with
the sun, being always over what is called the _heat equator_. Into this
belt of low pressure air from north and south, where the pressure is
greater, tends to rush in, and we have thus formed the constant or
"trade" winds, which, owing to the deflection produced by the earth's
rotation, appear as the north-east trades in the northern hemisphere and
the south-east in the south. These winds are dry winds, because they
blow from colder to warmer latitudes, and they accompany the equatorial
low-pressure belt in its north and south movements.
In the northern summer the trade winds may extend northward to lat. 35°
or even 40°, while in winter their northern limit is 10° to 15° further
south. A glance at the map, then, will show that in summer the
Mediterranean area is within or near the sphere of action of the dry
trade winds, which are continental, sweeping into the region after
having blown over land surfaces.
We must next consider the atmospheric movements in the region to the
north of the trade wind belt. An area of more or less permanent low
pressure, best marked in winter, exists in the North Atlantic, in about
60° N. lat., and draws the air into it in the direction known as
counterclockwise, that is, in the direction opposite to that of the
hands of the clock. The result is the production of the winds which
appear off the coast of western Europe as the warm south-westerly winds
of winter, while they appear off the coast of North America as cold
northerly winds. In the southern hemisphere, where, as we have seen,
there is less land to interfere with the development of the atmospheric
circulation, these winds form the prevailing westerlies.
In the Atlantic these south-westerly winds obviously blow in a direction
opposite to the north-east trades, whence the name of anti-trades often
given to them. As they blow across the broad Atlantic they arrive off
Europe saturated with moisture. As they come from lower latitudes they
are warmth bringing. In winter these winds reach the Mediterranean area
owing to the southern shift of the trades, and bring moisture with them;
while in summer they lie more to the north, and though their moisture
affects the coast of Portugal it does not reach the greater part of the
Mediterranean area.
Within that area the northern limit of the rainless summer may be said,
in a rough sense, to correspond with about the 40th parallel of
latitude, though it varies according to local conditions in the
different peninsulas. To the north of this line, therefore, the climate
is more or less affected even in summer by the anti-trades.
It must not be supposed that the region of the trade winds and of the
anti-trades lie side by side. Between the two there is a zone of
variable winds, but in general terms we can explain the peculiarities of
the Mediterranean rainfall by saying that the region lies within or
just at the edge of the dry trades in summer, and within the zone of the
moist anti-trades in winter.
Let us next consider how the area is demarcated from the surrounding
regions. There is of course no hard and fast line, but we can indicate
in broad outline the meteorological limits. To take the absolutely
rainless summer as the limit would cut out, as we have suggested above,
the greater part of the northern shore of the Mediterranean, except the
southern halves of all the great peninsulas. Quite generally, however,
we may say that the northern limit of the Mediterranean region, in its
western half, is defined by the occurrence of considerable summer rain.
That is, it is bounded to the north by a region which is within reach of
the rain-bringing anti-trades in summer as well as in winter, and which
has a lower temperature than the Mediterranean region proper. To the
east the region is limited by deserts, for the westerlies of winter can
only carry their moisture a certain distance inwards, and though they
are greatly assisted by the long, eastward-stretching, inland sea, yet
there comes a time when all their load of moisture is lost, and desert
conditions supervene.
To the south the desert again forms the boundary, though here for a
different cause. North Africa behind the Atlas is permanently within the
trade-wind belt, that is, it is permanently subjected to the action of
drying winds, and its rainfall is therefore small or nil. Similarly in
California the southern limit of the Mediterranean zone of climate is
the desert region of Arizona, Mexico, and the north of Lower California.
A similar band of desert separates the Mediterranean zone from the
tropical region of summer rain in the other places where the
Mediterranean type occurs.
This may be summed up as follows:--Defining the Mediterranean climate
only by its rainfall, we may say that it prevails over lands both to the
north and south of that sea, and these have all or most of their
rainfall in winter, when the winds, though typically westerly, are often
stormy and rendered variable by local conditions. In the summer there
may be no rain at all, or, to the north, small amounts. To the north the
region passes gradually into that colder zone where rain occurs
abundantly both in summer and winter, while to the east and south the
rainfall diminishes greatly, and there is a gradual transition to desert
conditions. To the west the boundary of the region is theoretically the
ocean, but the western coastline owes to its peculiar position a more
abundant precipitation, which makes the vegetation of, _e. g._, Portugal
present quite a different appearance from that of southern Italy or
Algiers. These peculiarities of rainfall the region owes to its position
between two great wind systems, of which one gains the mastery in winter
and the other in summer.
So far in this discussion we have spoken only of the distribution of the
rainfall throughout the year, but there are other features of the
Mediterranean climate which are almost as important in considering the
effects of the climate on the life of the region. These are the amount
of the rainfall, and the temperature.
Beginning with general points, it is very important to notice that the
rainfall throughout the area as a whole is relatively scanty, except
where special conditions, _e. g._ great elevation, or local
rain-bringing winds, increase it. Translated into terms of plant life
this means that continuous forests of the type so characteristic of the
greater part of Europe till man interfered, are relatively rare within
the limits of the Mediterranean region. Looking at the same fact from
the human standpoint we may say that the rainfall is often so scanty
that irrigation is necessary before man can prosper. These two facts,
that Mediterranean man had not to clear forests before he planted and
sowed, as the Teutons were obliged to do, and that he had often to bring
water artificially before his crops would grow, have been of supreme
importance in the evolution of Mediterranean civilisation. Even at this
stage it is interesting to note that France in this, as in many other
respects, has shared in two civilisations, for her territory to the
south shows Mediterranean characters, and elsewhere resembles the cool
temperate zone of Europe.
The next general point of importance is that of temperature. As was to
be expected from its latitude the basin of the Mediterranean is a
relatively warm region. Local conditions, and especially the presence of
a great mass of water, make the winter exceptionally mild, while the
summers, though not excessively hot they are considerably cooler than
those of similar latitudes in Asia, are yet warm and sunny. The result
is that, given water artificially supplied, or given crops which can
take water from the deeper layers of the soil, the region is productive,
the destructive frost of the north not being a menace. This relative
easiness of life in the more favoured parts of the region has been of
great importance in its history.
We may give next some actual figures to illustrate what has been said
about temperature and rainfall. Let us begin with rainfall, and in order
to have a basis of comparison we may first note that Edinburgh has a
mean annual rainfall of about 28 inches, and London one of about 25
inches. In other words, when the total amount of rain which falls in any
one year is estimated for many years in either of these places, these
totals added together and divided by the number of years of observation,
the quotient is the figure given. The figures show that the rainfall in
London is less than that in Edinburgh, while in Paris it is less than in
either.
Passing now to consider the Mediterranean area we find that, speaking
generally, the rainfall diminishes, for the reasons already explained,
in passing from west to east, and in passing from north to south. Thus
Gibraltar, at one end of the basin has a fall of 32" per annum, as
compared with one of 15" at Athens near the other extremity. Genoa in
the north has the heavy fall of 51", while Biskra in Algiers has only
8".
There are many local variations, due to local causes, and in comparing
the falls with those of Edinburgh and London we must remember that the
higher temperatures mean much greater evaporation. Sunny Naples has
about 4" more rain in the year than Edinburgh, and has 7" more than
foggy London, but yet has not a wet climate.
For temperatures a few figures may suffice. In London the mean January
temperature is 39° F., while it is only 36° F. at Paris. In Nice the
mean January temperature is 45°, which is about the same as that of
Athens, and rather less than that of Naples. In January, then, the
temperature of Nice is only 6° higher than that of London. In July the
mean temperature at London is 62°, as against 73° at Nice and over 80°
at Athens. In other words, owing to our mild winters and cool summers,
there is far more difference between British and Mediterranean
temperatures in summer than in winter. In the Mediterranean region
itself the difference between the temperatures of summer and winter
increases as we pass eastwards, so that it is especially to the west
that characteristically Mediterranean conditions occur, _i. e._ mild,
frost-free winters, and summers which for the latitude are not
excessively hot. This feature also has been of importance in the
development of the Mediterranean civilisations.
We have treated the climate of the Mediterranean area in some detail, as
an example of the methods and results of modern climatology. We may note
much more briefly the characteristics of one or two other climatic
provinces.
Mediterranean influences, expressed in winter rains, are continued
eastward into Mesopotamia and even into Persia, the rain always becoming
scantier, and desert conditions tending to supervene. Still further
east, however, we come to a region where the rainfall is abundant, and
where the population is once more dense. These are the monsoon
countries, including India and China, where the usually plentiful
rainfall again permits the land to nourish man abundantly.
Excluding Africa south of the Sahara from consideration, we may indeed
say that the Old World has two regions of abundant rainfall and dense
population, the one to the west and the other to the south-east,
separated from each other by warm and cold deserts. Each of these two
regions has given rise to its own civilisation, each has produced its
own types of cultivated plants and domestic animals, and the root
differences between the two must be regarded as largely the result of
climatic conditions.
The monsoon countries are so named because of the regular seasonal
reversal of the winds, which blow from land to sea in winter and from
sea to land in summer, affording an example of a land and sea breeze on
the gigantic scale. The result is that, subject to local modifications,
the summer winds are moisture-bringing, and the winter winds are dry.
Whereas, then, in the Mediterranean the heat of summer is largely
wasted, from the agriculturist's point of view, on account of the
scarcity of the water necessary for growth, in monsoon regions, unless
the rain fail, as it sometimes does, the hot season is the moist season,
and, therefore, other things being equal, growth must be faster here
than in the Mediterranean area. The monsoon countries extend over a
great stretch of latitude, and therefore temperature conditions vary
greatly, while the great variety of surface-relief produces here
abnormally heavy rainfall, and there desert conditions. The essential
contrast with the Mediterranean type is, however, the summer rainfall.
Taking the globe as a whole we find that summer rainfall is more common
than winter, and in addition to occurring in monsoon regions, it tends
to occur in tropical regions generally. As we approach the equator from
the tropics we find that the total fall increases, and tends to show two
maxima, which occur when the sun is overhead, _i. e._ at the equinoxes.
For our particular purpose, however, the climatic conditions in tropical
and equatorial regions generally, though of great importance to the
climatologist, are not of great interest, for except in monsoon
countries the hot parts of the earth do not show the most highly
developed human societies.
Let us turn next to that part of Europe which is outside the reach of
Mediterranean influences. Here we find that the rain is distributed
throughout the year, and is usually abundant, though it decreases in
passing eastwards from the seaboard. Temperatures are naturally lower
than in the Mediterranean basin, and winter frost plays an important
part in determining the choice of cultivated plants. As the figures
which we have already quoted for London and Paris suggest, the winter
cold increases on passing eastward. Paris is colder in winter than
London, though it lies south of it. Vienna is again colder than Paris.
But the increase in winter cold is compensated for by an increase in the
summer heat. In other words, as the distance from the sea increases in
Europe the climate becomes drier and more extreme.
This observation naturally leads up to a consideration of the effect of
the proximity of the sea upon climate. Water heats more slowly than
land, but also cools more slowly, and therefore the proximity of large
masses of water has, speaking generally, a moderating influence upon
climate, producing the so-called maritime climate. In the case of the
British Isles this effect is very marked, because the ocean to the west
of us is unusually warm, and the circulation of the atmosphere is such
that the prevailing winds of winter blow towards us from the warmer
parts of this ocean, while the fact that the summer winds often have a
northerly component helps to keep the summer temperatures down.
The peculiar conditions of the British Islands illustrate the fact that
climate does not depend upon latitude alone, but may be greatly modified
by local conditions, especially by the distribution of land and water,
and the direction of the wind.
Let us now sum up what has been said in regard to the main types of
climate found in Europe. Round the Mediterranean basin we have an area
with mild winters and warm summers, where the rain tends to fall during
the winter season, making summer a period of drought. This climate
extends beyond the limits of Europe into Northern Africa and Western
Asia, and is separated from the regions of tropical climate, which have
no winter and have rains at the hottest season, by a belt of desert.
The western seaboard of Europe has a maritime climate, the sea tempering
the winter, but diminishing the summer heat. The prevailing winds are
westerly, and the rainfall is typically abundant and distributed
throughout the year. On passing inwards this type of climate changes
into the continental type, with cold winters and hot summers, and
diminishing rainfall. Though precipitation occurs at all seasons of the
year, it tends to be greatest in summer, giving, _e. g._ in parts of the
Balkan States, a type eminently suited to the cereal maize, which needs
more summer rain than wheat.
If we bear in mind that North America is a large continent, and Europe a
very small one, and that while Europe has no eastern seaboard, it is the
eastern seaboard of America which faces Europe, we may realise that the
climates of North America show a remarkable analogy to the European. On
the western side we have in British Columbia and California respectively
the same two types of maritime climate which occur in Europe, that is,
British Columbia has a mild equable climate with abundant and equally
distributed rainfall, and California has a Mediterranean climate.
At the eastern side the conditions are a little different, and show us
that the mere presence of the sea is not sufficient to produce a
"maritime" climate. The prevailing winds in eastern North America are
off the shore; they cannot therefore carry oceanic influences landwards.
To the north the winds tend to have a northerly component, and cold
currents of water also stream out of the Arctic and chill eastern North
America. The result is that we find that Labrador, though lying in the
latitude of Great Britain, has a very severe climate. Further south the
conditions are of the "continental" character even on the seaboard, the
winters being very cold and the summers hot. Rainfall is equally
distributed throughout the year, but on passing inland it diminishes in
amount and tends to be limited to the warm season. The diminution would
be much more obvious than it actually is were it not that the existence
of the large Gulf of Mexico, and also the size of the North American
continent, give rise in the south to a monsoon effect, which greatly
increases the rainfall of the south-eastern corner of the States.
Further to the west, in the lee of the great barrier of the Rocky
Mountains, the rainfall is slight.
Incidentally, we may notice that the eastern seaboard of the great
Eurasian continent also has a more extreme climate than the western,
offering in this respect an analogy to the conditions which prevail on
the eastern and western halves of temperate North America. The cause in
both cases is the same--the direction of the prevailing winds.
We cannot close this chapter without some reference to weather, a
subject of more geographical importance than is generally realised. In
speaking of climate we have used figures which were invariably _means_,
_i. e._ have been obtained by averaging a great number of observations.
But where a great number of mean figures are used in a discussion, it is
always found that the different averages are based upon varying numbers
of observations, and are therefore not strictly comparable with one
another. There is always a risk that such figures may mask facts of real
geographical importance. No doubt some of the difficulties will
disappear with the progress of meteorological science, which will enable
the geographer only to select figures which are strictly comparable.
Meantime, however, observations for long periods are rare, and the
meteorologist must be content to take the figures which are available.
For this reason as well as for others, it is advisable to add to the
somewhat abstract study of means, that is, of climate, some note upon
the actual conditions, that is, upon weather.
[Illustration: Fig. 10.--Diagram to illustrate a cyclone travelling
towards the east. The two concentric circles represent isobars, that is,
they are lines drawn through points where the barometer registers the
same (low) pressure. Into the area of low pressure so formed the winds
blow strongly in the direction known as counterclockwise, and are
represented by the arrows whose double barbs signify their strength. It
will be noted that in the rear of the cyclone the winds are northerly.
They thus chill the air here, and by chilling it _raise_ the pressure.
The winds to the front of the cyclone are warm because southerly, they
therefore tend to _lower_ the pressure here by warming the air, and the
result is that the isobars tend to be displaced towards the east, and at
the same time become deformed. In other words, the cyclone moves to the
east.]
We may take British weather, which has become a proverb on account of
its variableness, as a text for a brief discussion of the subject.
The daily variations in our weather, as all who have read weather
reports know, are chiefly determined by the movements of areas of low
pressure or cyclones, which mostly come to us from the Atlantic, and
continue eastwards past us, often towards the Baltic. We have already
noted the occurrence of what we have called a permanent area of low
pressure in the North Atlantic, but this "permanent area" in point of
fact is due chiefly to the constant passage here of cyclones, or moving
areas of low pressure.
The causes of the eastward displacement of these depressions are
interesting. One cause is the general eastward movement of the
atmosphere in this region, produced in the fashion already described.
This movement necessarily raises the pressure to the west of the
depression, owing to the influx of fresh air, while the onward movement
of the air in front of the depression lowers the pressure there, and so
produces displacement. Again, the air is sucked into a depression in the
direction opposite to the hands of a clock, and a moment's reflection
will show that this means that the winds to the east of the depression
are southerly and those to the west of it northerly. The warm southerly
winds in front tend to lower the pressure by warming the air, while the
cold northerly winds behind it raise the pressure by cooling the air.
This again produces a displacement of the depression towards the east
(see fig. 10).
The fact just described has an interesting practical result. If after a
day or night of storm and rain, the temperature falls, we know that the
depression causing the storm has passed us, and that we are feeling the
effects of the colder winds in its rear. If the thermometer suddenly
rises again, then a new depression is approaching, and we are feeling
its warm breath before its winds reach us. The clearness and chilliness
of the air after a stormy or windy period gives us one of our commonest
meteorological sensations, and produces a marked psychical effect,
reflected in much of our literature.
One other reason for the eastward motion of the cyclones with us is that
they seem to prefer damp air, and so tend to follow the North Sea and
pass towards the Baltic, where they often die away.
In the British area, though the depressions move faster in winter than
in summer, they have only a mean speed of about 16 miles an hour, while
in the United States their mean speed is 25 miles per hour, and their
effects are often disastrous except when discounted by the warnings of
the Weather Bureau.
In the case of the British Isles cyclones are most frequent and best
marked in winter, and they are of great importance in producing our mild
and windy winters. In summer they travel further northwards, and as a
rule affect our climate less. When, however, from causes still
inadequately known, they are better marked in summer than usual, we have
a "bad" summer, that is, one which is wet and relatively windy.
The fact that the English Channel is one of the favourite tracks of
cyclones has been an important element in protecting the British Islands
from foreign invasion, while we all know that it is also a factor in
diminishing free intercourse with the Continent.
[Illustration: Fig. 11.--Diagram showing the changes in temperature,
pressure and wind due to a cyclone passing to the north of a point of
observation A. The passage of the cyclone figured occupied a period of
six days. It will be noted that as it approaches A the wind is southerly
and light (arrows with single barbs) and the temperature high. As it
passes the winds become violent (arrows with double barbs), and shift to
the south-west, and the barometer falls rapidly. As it disappears the
pressure rises, the temperature falls, and the wind veers to the
north-west, while remaining violent. The fall of the wind and its
shifting to a south-westerly direction mark the return to the normal
condition of affairs, the influence of the cyclone being past.]
The second point of importance about our weather is the periodic
occurrence at some part of our area of anticyclones, or areas of high
pressure, out of which the winds stream gently in the same direction as
the hands of the clock. These areas of high pressure do not display
the same tendency to move as do the cyclones, and are most frequently
merely displaced by advancing cyclones. For reasons into which space
does not permit us to go fully here, anticyclones have a very different
effect in summer and in winter. In winter they may bring to us the
continental cold, and make our weather abnormally severe, though often
bright and fine. On the other hand, in summer they bring to us
continental warmth, so that "good" summers are those in which
anticyclonic conditions are most frequent, while "severe" winters are
due to the same cause. Anticyclones also sometimes induce a curious form
of inversion, in that places to the north of a given spot may have
temporarily a higher temperature than places to the south. It is such
facts which are entirely masked by "mean" figures.
We do not as yet understand the causes which make cyclones sometimes
more numerous or better marked than usual, which cause them sometimes to
cross our area, and at other times to travel too far north or too far
south to influence our weather. It is possible that further
investigation in the future may unravel this problem; it is practically
certain that a freer use of wireless telegraphy, and the establishing of
meteorological stations in northern seas, would give weather forecasting
a definiteness and accuracy which it does not yet possess.
[Illustration: Fig. 12.--British weather map for Nov. 29, 1910. A
cyclone lies over the south of Scandinavia, and into it the winds are
sweeping strongly in a counterclockwise direction. An anticyclone lies
over Iceland, and from it the winds are streaming gently in a clockwise
direction.]
We cannot follow this interesting subject further here, but we have
said enough to illustrate its geographical significance. As a science or
sub-science by itself it will form the subject of a special volume in
this series. It may be enough to point out that the _Daily Weather
Report_, published by the Meteorological Office at a cost of one penny,
and reproduced in some daily newspapers, is a document well worth the
careful study of those with any interest in geography.
CHAPTER V
THE PRINCIPLES OF PLANT GEOGRAPHY AND THE CHIEF PLANT FORMATIONS OF
EUROPE AND NORTH AMERICA
We have now taken a general survey of the earth's surface, have noted
its mountain heights and its ocean depths, watched the formation of
hills and valleys which is due to the joint action of atmospheric
agents, running water and ice, and considered briefly some of the points
of interest about climate. We next pass to that most characteristic
feature of the surface, its clothing of plants. Except where the surface
of the ground has been artificially sterilised by man, or is rendered
unproductive by ice, by lava, by a total lack of water, or by the
existence of poisonous salts, it is clothed with vegetation, and it is
the presence of this vegetation which is its most obvious character.
Here, however, as in other regions of thought, the geographical
standpoint has only been reached slowly. Man's habit of analysis made
him study grasses and trees for long generations before he got back to
the forest and to the grassland as they occur in nature. Plants as
individuals are the province of the botanist, but those plant groups
which are the expression of the interaction of climatic factors, soil,
and surface relief, are the concern of the geographer.
When we take a general survey of the face of the earth from the point of
view of plant geography, we note three main conditions. In certain
regions, alike in the tropics and in temperate zones, we find that
plants reach their maximum size, combined with great differentiation of
structure, and the formation of woody stems which offer great resistance
to varying conditions of climate and weather. Such highly-organised
plants form forests, which still dominate over a large part of the
earth's surface.
Man's nearest allies, the anthropoid apes and the monkeys, are for the
most part forest animals, and the lowest races of men are still forest
dwellers. Where man is a forest dweller he seems not to reach his full
size, as we see in the case of the pigmies of the Congo forest, and the
negritos of the Philippines, and he suffers from a chronic insufficiency
of food, which acts as a check both to his mental and physical
development. There has, therefore, always been war between evolving man
and the giants of the plant world, a war which has swept the forests
away from many of the more civilised parts of the globe, and which still
continues, though man's victory is now so complete that he can afford to
be generous, and give protection to the remnants of his former foe.
But over parts of the globe the climate, and especially the amount or
distribution of the rainfall, makes it difficult or impossible for
forests to grow naturally. Here other types of plants, lower in stature,
and evading rather than facing the problems of winter cold or summer
drought, flourish and form what we call the grasslands. The grasslands
favour man in several respects. They feed the animals upon which he
depends for food, for clothing, and for the conveyance of his person or
property, and they offer much less resistance than the forest to his
agricultural operations. Even the large herbivorous mammals which in
their wild state haunt the forests, usually leave these at night to
feed upon the grasslands, so that it is the grasslands which have
largely fed man at every stage of civilisation. The atmospheric
conditions within the woodlands also, the deficient sunlight, the
humidity, and so forth, seem unfavourable to human development.
Where the conditions are especially unfavourable to plant life, we find
that even the grassland plants are unable to keep up the struggle, and
diminish in number, losing their power of forming a complete covering
for the soil, and thus the grassland passes into desert, whether the hot
waterless desert of low latitudes, or the cold frozen desert of northern
ones.
In the most general sense, then, we may say that these three formations,
woodland, grassland and desert, divide the surface of the land among
them, and between them there is constant conflict. The grasslands are
for ever attempting to encroach upon the woodlands, and in this attempt
they have been assisted, sometimes to too great an extent, by the
operations of man. Similarly the desert is always striving to encroach
upon the grassland, and in this endeavour it has been sometimes
involuntarily aided by man, who has also done much voluntarily to
reclaim the desert land for the grasses.
Let us note next the particular conditions which favour woodland,
grassland and desert respectively. The distribution of plants over the
surface of the earth at large is determined by a number of factors, by
the amount of heat, by the amount and distribution of precipitation, by
the nature and strength of the winds, by the characters of the soil, and
so on. But forests occur under the equator and also far to the north; we
have cold deserts as well as hot ones; there are extensive grasslands in
the Sudan as well as in the Canadian Far West. This proves that the
varying amounts of heat may be neglected in considering the cause of the
distribution of the three great plant formations.
Again, the soil is of minor importance, for different types of forest
and of grassland occur on different types of soils. We are thus led to
the conclusion that it is the precipitation and the wind which determine
the distribution. To understand the reason for this we must consider the
needs of different types of plants in the matter of water.
Plants can only take in the mineral constituents of their food in the
form of a solution, and this solution must be weak, or it has a
poisonous effect. For example, sulphate of ammonia is a valuable manure,
but if a considerable amount be dissolved in water and applied to the
roots of a growing plant, death may very likely take place.
It is a necessary consequence of the fact that plants can only absorb
weak solutions of their food salts, that their roots take in more water
than is actually needed by the plant. _One_ of the functions of the
leaves is therefore to get rid of surplus water, the process being
called transpiration. Transpiration takes place faster in a tall plant
like a tree, which grows up into dry layers of the air, than in a low
plant like a grass. It takes place faster in windy weather than in calm.
Other things being equal it takes place faster in warm weather than in
cold, and the larger the plant and the more numerous its leaves the more
water is given off, that is, the more water is returned to the air from
the soil.
The result of all this is that forest trees require far more water than
grassland. It has been calculated that a beech wood aged 50 to 60 years
gives off during the growing season 354 tons of water per acre, which
illustrates the drying effect of the presence of the wood. Similarly,
the effect of tree-planting in the marshy regions of France and Italy,
where the soil as a consequence has dried and the marshes disappeared,
shows how great a demand upon ground water trees make, as compared with
grasses and low growing herbs.
On the other hand, although trees take an enormous amount of water from
the soil, they can draw their supplies from a large area. It is the
extremities of the fine branches of the roots which take in the water,
and these pass deep down into the soil, and spread out over a vast area.
In other words, trees avail themselves of the water in the deeper layers
of the soil, and can tolerate relatively long periods of drought, if the
surface drying of the soil does not extend to the deeper layers. In hot
summer weather grasslands brown and wither long before the trees show
any signs of water-famine.
In consequence, we may say that as long as the total rainfall of a
region is sufficient to ensure a constant supply of moisture in the
subsoil during the growing season, trees can thrive, even if little or
no rain falls during this season. On the other hand, drying winds are
very hurtful to trees, especially if they occur at a period when the
tree is unable, either because of the coldness of the subsoil, or
because of its dryness, to take in fresh water to replace that which is
lost. The hurtfulness of late frosts is largely due to the cold suddenly
checking root absorption at a time when the growing parts, acted upon by
the spring winds, are giving out water freely.
Grasses transpire less freely than trees, but their root system is much
shallower and less well-developed. They depend upon the water in the
upper layers of soil, and must have frequent, even if gentle, showers
during their growing season, while they are quite indifferent to drought
and even to cutting winds during their resting period.
A little reflection will show that it results from these facts that
woodland, grassland and desert do not form a continuous series. It may
quite well be that woodland passes through scrub into desert without the
intervention of grassland. Right across Europe there is (or was) a broad
belt of forest. Southward towards the Mediterranean this thins out into
a characteristic form of scrub, called maquis, whose characters we
shall describe later, and this scrub passes in all directions into
desert land. Here no belt of grassland intervenes, for the rainless
Mediterranean summer makes the growth of grass virtually impossible,
except where special conditions, _e. g._ hills, introduce modifications.
Contrasted with this we have the conditions in North America where,
_e. g._ in Canada, the western coast is densely forest-clad, as is also
the eastern region. In journeying eastward after crossing the Rocky
Mountains the forest dies away into grassland, and the same thing
happens, though more slowly, in a westward journey. The reason is that
in this case there is a steady diminution of precipitation on passing to
the interior, but what precipitation remains is, as we have seen,
largely, though not wholly, summer rain, and is, therefore, sufficient
to determine the growth of grass, though not of trees.
Again, in North Africa the forests of the Atlas Mountains pass directly,
without intervening grassland, into the Sahara desert, but to the south
of the desert the grassy and park-like Sudan separates the desert from
the luxuriant tropical forest. In the latter case, however, it is
possible that man's influence has counted for something.
On mountains, in whatever latitude, the conditions are much more
uniform, partly because it is wind, assisted by temperature variations,
which is the dominating factor. Moisture is usually abundant, but high
up what is called physiological drought occurs; that is, the temperature
is too low for the plants to be able to absorb the abundant water.
In ascending any mountain, the following are the chief changes which
occur. The lower slopes will probably be cultivated. As we ascend the
precipitation increases, and forests appear. First we have probably a
belt of deciduous trees, passing above into the more resistant conifers.
This belt usually ascends higher on the south than on the north side,
and higher on mountains which occur in a group than on isolated peaks.
As the wind is more and more felt, and increases the dangerous
transpiration of winter the trees become more and more dwarfed to escape
its force. There may be a belt of prostrate mountain pines above,
marking the tree limit; in any case the trees are gradually replaced by
dwarfed shrubs. Then comes the zone of Alpine plants, the grasses
making a complete sward, but being accompanied by many other plants.
Gradually, as the soil becomes scantier, and the surface more rocky and
exposed, the continuous sward disappears, and the conditions of a cold
desert appear. A few scattered plants occur, ceasing near the snow-line,
the highest being usually plants of simple structure like mosses and
lichens.
As we have already indicated, in the case of the mountains of Europe
there are often glacial shelves at considerable elevations, whose
covering of fine débris determines the growth of peculiarly fine grass.
The economic value of this grassland has in many cases in the Alps
induced man to destroy the forest in order to increase pasture land. The
result has often been disastrous, for once the trees are cut down the
forest soil is rapidly destroyed by weathering, especially on slopes,
the courses of streams are altered by the more rapid run-off, and
widespread flooding and destruction of pastures have sometimes resulted.
In North America, similarly, man's attempt to increase pasture land or
arable land at the expense of woodland has often led to disastrous
consequences.
We have already spoken of the special features of the Mediterranean
climate, and indicated that its peculiarities are reflected in its
vegetation; we must now consider this vegetation in a little more
detail. The fact that the region is chiefly visited by the inhabitants
of more northern climates in spring gives rise to a somewhat erroneous
impression in regard to the plants. In spring the Mediterranean
vegetation is at its best. The mild winters permit the plants which
further north die down or cease to grow, to go on blooming. The rains so
moisten the soil that the first warm days cause very rapid growth in
those plants which finish their activities before the hot, dry summer
begins. They must flower and seed in spring, and die down till the rains
of autumn awaken them again.
In our own country we have a few plants which hurry through their
activities in this way. The lesser celandine, the wood anemone and a few
others strive to flower and fruit before the forest trees are thickly
clad with leaves. The snowdrop, even the wild hyacinth, though it is
much later, similarly limit their active life to a short period in
spring. This phenomenon, only suggested in our climate, is very marked
in the Mediterranean area.
That region is especially characterised by its richness in bulbous and
tuberous plants. These, as all who have grown hyacinths or narcissuses
know, demand relatively large amounts of water during their short
growing period. In spring, therefore, the shores of the Mediterranean
are bright with many kinds of anemones, with narcissus, asphodel, bell
hyacinth, Allium, tulips, and so on, all awakened by the spring warmth
and the spring rains. Accompanying them are many bright-coloured
annuals, also in a hurry to race through their life-history before the
terrible drought of summer. Now also the grass grows, and the
autumn-sown corn becomes tall. As the weather grows hotter and drier,
the plants with bulbous and tuberous roots die down to the ground, the
annuals die altogether, leaving their seeds to wait till the autumn
rains before they sprout. The grasses turn brown, and the peculiar
parched appearance of the Mediterranean summer spreads over the land.
To a northern visitor at this season it is not luxuriance but desolation
which is the prevailing note. Except on the hill slopes there are no
masses of broad-leafed foliage trees--there is not the deep bright green
characteristic of the summer woods further north. The trees do not reach
a great size; the leaves are usually small, and the fact that they
strive to avoid the sun by arranging themselves with the edge upwards
instead of the flat surface, makes them appear smaller than they are.
They are often needle-shaped, sometimes shining and coated with resin,
sometimes silvery owing to a coating of hairs on the under surface. Many
plants have spines or thorns, and succulent plants like agave, aloe and
prickly pear are common. The absence of a complete covering of
vegetation causes the surface soil to dry completely, and so form clouds
of dust which adds to the generally desolate appearance. Indeed, the
brown powdery appearance of the soil is one of the points which
especially strikes the stranger, accustomed to the darker, moister soil
of the north, always covered with vegetation, except where man has
interfered.
Here and there, however, are indications that even this parched brown
earth holds wealth for man. The vines, if dusty and far less luxuriant
than one expects, are loaded with ripening fruit. The gorgeous scarlet
flowers of the double pomegranate gleam amid the dark foliage; the
gnarled and twisted olives show on close inspection masses of small
green fruits; the oleander bushes are covered with pink flowers; there
are great round balls on the orange and lemon trees, and many other
fruit trees are loaded with produce.
Let us sum up first what man gains from the plants of the Mediterranean,
and then look at some points in regard to the wild plants. In the first
place, we see that man takes advantage of the rapid growth of annuals in
the early part of the year. The annuals most useful to him, here as
elsewhere, are, of course, the cereals, especially wheat, which, if sown
in autumn, is nourished by the winter rains, and grows rapidly with the
warmth of spring to ripen in May, June or July, according to the
locality.
In the second place, certain trees or shrubs, by reason of their
resistance to drought, and their elaborate root system, which enables
them to gather water from the deeper layers of the soil, will produce
succulent fruits without needing artificial supplies of water. The most
important of these, throughout the whole Mediterranean area, are the
vine and the olive. The olive supplies the oil which is all the more
necessary in that the absence of grass makes pastoral industries, and
therefore the production of cheese and butter difficult or impossible
except in the high grounds, while the vine supplies the wine which with
bread and oil form the essential parts of the diet of Mediterranean man.
The olive tree, which is indigenous, may be regarded as one of the most
characteristic trees of the area, and it is interesting to note that the
novice not infrequently confuses it with another tree, almost as
characteristic the evergreen or holm oak. The two are not nearly
related, the olive belonging to the same family as the lilac and privet,
while the evergreen oak is a true oak. Both trees, however, show similar
adaptations to summer drought, and their resemblance to one another is a
good example of convergence due to a similar environment. Both have
small evergreen leaves; small that they may not lose too much water in
summer, evergreen that they may assimilate even during the winter. Both
have their leaves silvery beneath, which again prevents loss of water;
both have gnarled trunks, branching low down, in order that the leaves
may avoid the dry upper layers of the air. Adaptations of this kind are
present to a greater or less degree in all the trees which are tolerant
of Mediterranean conditions, and many of these trees yield useful
fruits.
In addition to the cultivated plants mentioned, a great number of others
are grown within the area, as we shall see later, but the point of
interest is that the plants which have been of importance in the history
of the region have been either annuals which ripened early, or
fruit-bearing trees with special adaptations to resist drought.
Apart from the annuals and the bulbous and tuberous plants already
described, the wild plants are chiefly shrubs or stunted trees with
similar drought-resisting characters. During the long ages he has
inhabited the Mediterranean, man has doubtless contributed largely to
the destruction of the forests which are now, as we have seen,
represented by the stunted scrub or maquis. But on climatic grounds we
cannot suppose that the Mediterranean forests had ever the luxuriance of
those further north, or of the tropical forests of the south.
Where there is sufficient rain chestnut woods occur, but this is only
on the hill slopes. Above the chestnut, beech may occur, as in Sicily.
The maritime pine and the Corsican pine form open woods in the damper
places, and the picturesque stone pine, with its rounded head, is very
characteristic. We have already mentioned the evergreen or holm oak as
common, and the cork oak occurs abundantly in some places. These trees,
with the cypress, must have formed the primitive forests, and they still
constitute the most important forest trees of the area. The occurrence
of a native palm (_Chamærops_) is interesting as suggesting the warmth
of the climate, and even on the European shores the date palm is
extensively planted, though its true home is the margin of the African
and Arabian deserts.
Of the characteristic shrubs the most striking are perhaps the many
species of Cistus, with large almost rose-like flowers, and leaves which
attempt to adapt themselves to the climate by many different devices.
Sometimes they are stiff and leathery, sometimes resinous, sometimes
hairy. Many plants in the area have a coating of resin on their leaves.
This, no doubt, preserves them against loss of water, but also probably
protects against grazing animals. Goats thrive in the Mediterranean
partly because of the catholicity of their taste in vegetation, and in
consequence the plants have had to protect themselves against their
appetite as well as against drought. Only those with some disagreeable
quality, hairs, spines, resin, strong flavour, etc., could hope to
protect themselves in the dry season, when grass is virtually absent. It
is in consequence common to find aromatic or strongly-flavoured plants
with glandular leaves; lavender, rosemary, myrtle, etc., are examples.
Other shrubby plants associated with the Mediterranean are oleander, the
noble laurel, the tree heath, arbutus, many kinds of broom, and
generally evergreen shrubs specially adapted to resist drought.
Let us turn from this picture to the appearance presented by Central and
Northern Europe. As we have seen, the forest which once covered most of
the area, except the steppe region of southern Russia, has largely
disappeared, but enough remains to enable us to reconstruct the picture
of the original forest.
As contrasted with the (chiefly) evergreen woodland of the
Mediterranean, the forests of the low grounds are here deciduous. In
summer clothed in magnificent foliage, well adapted to give off enormous
quantities of water, in winter the trees stand tall and bare, exposing
nothing but their branches to the winter blasts. While the buds of
Mediterranean plants have no special means of protection, the typical
forest trees of Central Europe have their buds carefully sheathed in
scales, clothed in hairs, or coated with resin, to keep out alike the
cold and the damp of the northern winter. While the leaves of
Mediterranean plants are usually small, often coated with hairs beneath,
often resinous, and so on, the forest trees further north have large
leaves of delicate texture, with no special protection against drought.
Again, while the luxuriant forest of the tropics includes many different
species of trees, the deciduous forests of cool temperate regions
contain few species, and are often pure woods, that is, consist of one
dominant species, forming beech woods or oak woods, and so on. The dense
shade of the beech makes undergrowth difficult or impossible, but the
other woods have a complicated undergrowth of many different kinds of
plants, especially pronounced in spring before the leaves appear on the
trees. But this undergrowth never reaches the luxuriance that it does in
the tropical forest, and creepers and climbing plants are few.
As we ascend from the low ground to the higher, or as we travel
northwards to high latitudes, the broad-leafed deciduous forests are
replaced by coniferous ones. European conifers, with the exception of
the larch, are evergreen, and all are more tolerant of cold and wind
than deciduous trees. Pines, spruce, fir, larch, and silver fir are the
most important kinds. Both at high altitudes and in high latitudes these
conifers are often accompanied by birch, which is not a cone-bearing
tree, but is very tolerant of cold and wind.
To the north there comes sooner or later a limit beyond which the cold
and winds make further tree growth impossible. Here we come to a tundra
region, where the place of trees is taken by low-growing shrubs, with
small leaves and other adaptations to ensure against excessive loss of
water. It is, as it were, the reappearance of the Mediterranean type,
but here the cause is, not the absence of water, but the fact that the
cold makes it impossible for the roots to absorb it. A condition of
physiological drought results, and only plants well adapted to prevent
undue loss of water can resist such conditions of life.
A somewhat similar type of vegetation occurs over vast areas in the more
northern parts of Europe, forming the moors and heaths of much of
Scotland, of parts of England and Ireland, of parts of Germany, and so
on. Here the presence of peat produces conditions very unfavourable to
plant life, except to certain shrubby plants such as heather and other
plants of the heather family, juniper, bog myrtle, and so on, and some
grasses and sedges, etc., all of which have special adaptations to life
in a peaty soil. Over the large areas, therefore, covered by these
heaths, trees are absent, or few, and this stunted shrubby vegetation
takes their place.
Large areas of natural grassland, except for the tracts of pasture land
already described in the mountain regions, are infrequent in Europe.
They occur in Southern Russia and in the Hungarian plain, and form part
of that great series of steppes and plains which stretches into Asia,
and passes into a region of deserts.
The conditions favourable to the growth of grass here, instead of
trees, seem to be purely climatic. Very important is the prevalence of
strong cold winds during winter, which is a period of drought. The
scanty rains come in early summer, which suits grasses admirably, while
the total precipitation is too slight for trees. The summers are hot,
and the rains cease early and give place to a period of drought, very
injurious to trees, while it injures the grasses little, owing to the
fact that they have had time to make their growth.
The abundant natural growth of grass makes these steppe regions well
suited to the pastoral industries, which tend, as civilisation
progresses, to give place to agriculture.
To sum up, we have seen that looking at Europe as a whole three great
plant formations are represented. We have, first, the cool temperate
forest, which once extended over the greater part of the continent,
wherever the conditions were suitable. This has now largely given place
to arable land. Next, we find round the Mediterranean sea, and in those
great peninsulas and islands which are bathed by it, a zone of modified
woodland passing into scrub, remarkable for the rapid growth of annuals
in the early part of the year, and for the abundance of trees bearing
useful fruits. Finally, linking Europe to temperate Asia, we have belts
of steppe land, characterised by a luxuriant growth of grass in the
early summer, and fitted by nature for pastoral industries, which do not
thrive near the Mediterranean. Another way of putting the same facts
would be to say that Europe proper is a region of temperate forest,
linked to Africa by scrub land passing into desert, and to Asia by
steppe land passing into desert.
* * * * *
The flora of North America, owing to the size of the continent, offers
more resemblance to that of Asia than to Europe.
Bearing in mind what has been already said about the structure of North
America--with its western mountain range and eastern uplands enclosing
between them a region of moderate relief--and also what has been said in
regard to its climates and to the influence of climate upon vegetation,
it is relatively easy to deduce the main points in regard to the flora.
To the far north there is a treeless tundra region, quite comparable to
that which occurs over vast areas in North Asia, and on a reduced scale
in the northern part of the continent of Europe. Next we have a wide
band of predominantly coniferous forest, which, although its species are
different, yet in broad outline is entirely homologous with the
coniferous forest found in northern Asia, south of the tundra region. In
Canada this forest consists of spruces and larches, the species being
peculiar to the continent. Mingled with the conifers are smaller numbers
of the hardier deciduous trees, such as birches, poplars, and willows.
What we have already said as to the climatic differences between the
eastern and western sides of continents will at once suggest that this
band of forest is not likely to run directly across the continent from
east to west. In point of fact it stretches from Labrador in a
north-westerly direction to Alaska, leaving almost the whole of the
western seaboard to be occupied by another type. This type is the
extraordinarily luxuriant and beautiful western forest, consisting for
the most part of conifers. It is largely these conifers which have
enriched European parks and gardens within recent years, and although it
is perhaps the great _Sequoia_ (_Wellingtonia_) _gigantea_ which has
most impressed popular imagination, it must be remembered that size and
luxuriance are characteristic of many species. This western forest
stretches down the western seaboard to the State of California, and,
indeed, persists until increasing aridity makes forest growth
impossible. Its great luxuriance, compared with the scantier forests of
the Mediterranean region in Europe, is partly to be ascribed to a
greater rainfall, and doubtless partly to man's interference, for the
original forests of the Mediterranean must have been largely destroyed,
as the western American forests are in process of being. One must
remember also that the proximity of mountain ranges to the seaboard in
western North America gives a heavy rainfall, and suitable places for
forest growth. The fact that the trees are predominantly coniferous
gives them great resistance to the summer drought. In front of the
mountain ranges the coastal plain is occupied by an evergreen scrub
vegetation comparable to that of the lowlands of the Mediterranean
basin.
In British Columbia, where the Cascade Range lies at no great distance
from the Rocky Mountains, the western coniferous forest practically
clothes the whole area from the coast to the main range, but further
south, where the Cascade Range and its continuation the Sierra Nevada
are widely separated from the main range, a dry and semi-desert region
occurs, between the two, which bears a desert type of vegetation,
including especially a plant related to our wormwood, called sagebrush,
with cactuses in the warmer parts. Another area which is too arid to
carry trees, except where local conditions raise the rainfall, extends
from Texas northwards to about the latitude of Edmonton or Battleford,
and lies in the "rain shadow" of the Rocky Mountains. This is the region
of the Great Plains, mostly too arid to carry anything but herds of
cattle, and mostly forming natural pasture, being thus analogous to the
steppes of Asia.
Eastward the rainfall increases, and we pass from the area of
unreclaimed pasture to the prairies, now largely laid down to wheat and
other food plants. Southward the Great Plains pass into the deserts of
Mexico, but northwards they are separated from the northern coniferous
forest by a belt of aspen, and it is in this region that the Canadians
are steadily pushing the cultivation of wheat into the plains, wherever
the local rainfall makes this possible.
So far we have left south-eastern Canada and the whole of the eastern
and south-eastern States out of consideration. Speaking very broadly, we
may say that all this area is clothed by a forest of mixed coniferous
and broad-leaved trees which is comparable to the forest which covers
the greater part of temperate Europe. But it is not to be expected that
a forest which extends from the northern shores of the Gulf of St.
Lawrence to the extremity of the peninsula of Florida, that is, through
about 25 degrees of latitude, should be uniform throughout. In point of
fact, botanists distinguish three separate zones. In south-eastern
Canada and the New England states the Weymouth pine (_Pinus strobus_)
predominates, being accompanied by limes, ashes, maples, oaks, elms,
chestnuts, and so forth. Further south, and especially further west,
extending to the Mississippi plains, there is a deciduous forest
extraordinarily rich in species. Practically all our common genera of
forest trees are represented, sometimes by very fine species, but in
addition there are many genera with no European representatives. Very
striking is the abundance of magnolias (whence the name of magnolia
forest sometimes given to this type), and species of the laurel family,
as well as of liquidambar. The magnolias and liquidambar are especially
interesting, because they once occurred in Europe, their disappearance
there being probably caused by the glacial period as explained on p. 78.
We have emphasised above (p. 137) the luxuriance of the forests of the
west coast of the States, but it should be noticed that luxuriant as its
conifers are, there is a remarkable poverty in broad-leaved forms, as
compared with these eastern forests, and this even in the warmer parts
of the west coast. The reason is probably the same as in the
Mediterranean region in Europe. The existence of a belt of desert to the
south of the present "Mediterranean" region of western America made it
difficult for the trees to migrate southwards at the onset of cold
conditions in the glacial period, and thus many forms, which are known
to have existed in California in Tertiary times, have now completely
disappeared from the region, while they persist in the eastern forests
to this day.
The third type of forest which occurs in the eastern half of North
America is the "rain forest" of Florida and parts of the adjacent
states. Here the rainfall is abundant all the year round, with a summer
maximum, and the temperature is high. There is thus no need to economise
water, and where the soil permits there is a luxuriant type of forest,
which recalls that of the tropics, although it is poorer. Where soil
conditions are unfavourable we have pine woods, conifers throughout the
eastern United States always taking advantage of conditions relatively
unfavourable to the broad-leafed trees.
Thus if we follow the eastern seaboard of the United States from
Labrador to Florida we pass through the following floral regions:--
(1) Coniferous forest, with relatively few species, (2) mixed coniferous
and deciduous forest with chiefly the harder types of deciduous trees,
(3) predominantly deciduous forest with many of the larger-leafed and
more delicate forms, and finally (4) forest of the sub-tropical rainy
type, intermixed with coniferous woods on the barren sandy soil and in
the swamps.
The western coast shows more uniformity, the western type of coniferous
forest stretching from Alaska to California, though it is richer, and
more luxuriant in the warmer regions when moisture is still obtainable.
As the moisture diminishes the forest dies away and desert or
semi-desert conditions supervene.
CHAPTER VI
THE DISTRIBUTION OF ANIMAL LIFE
In the last chapter we looked at a few of the interesting
generalisations which have emerged of late years from the study of plant
distribution. An enormous amount of detailed investigation had been done
before these generalisations were arrived at, and though still much
remains to be done, yet the broad lines of a science of plant
distribution may now be said to be established. The scientific study of
animal distribution has not yet reached a corresponding stage of
advancement, partly no doubt because the dependence of the more highly
organised and active animal upon the physical conditions is less close
than that of the stationary plant, so that the subject is more
difficult. Facts are accumulating on all sides, but the subject is still
rather at the level of collecting information than at that of laying
down broad generalisations. There are, however, indications of progress
in many directions, and an attempt will be made here to suggest some of
the lines along which research is especially busy at the present time.
In speaking of plants we confined our attention exclusively to land
plants, for the reason that aquatic plants are usually small in size,
relatively simple in structure, of somewhat limited vertical
distribution, owing to their dependence upon light, and of little direct
importance to man. In considering animals, on the other hand, we cannot
exclude the aquatic forms, which are often of great human importance. In
many regions man depends largely, sometimes even exclusively, on the
animals of the sea for his food. We shall, then, begin with some account
of aquatic animals, considering the subject, as before, especially from
the point of view of the inhabitants of Europe and North America.
Beginning with the sea we find that the scientific study of marine
animals received an enormous impetus from the work of the _Challenger_
expedition. The results of that expedition appeared in many large
volumes, which form a conspicuous feature in any complete scientific
library and contain a mass of useful material. The _Challenger_
expedition was followed by many others, European and American, and the
result is that we now know a great deal about marine animals and their
distribution. Further, the Fishery Boards of various Governments carry
on continuous observations on the conditions of life in the seas near
their coasts, which have added and are adding enormously to our
knowledge.
We cannot here consider in detail the various facts brought to light by
these means. Only a few general points can be touched upon. One
interesting generalisation is that the life of the ocean can be divided
into three groups: the life of the littoral or shore zone, the life of
the open ocean (pelagic fauna), and the life of the great ocean depths
(abyssal fauna). The last, though of great zoological interest, is so
remote from human life that we need not consider it. The pelagic forms
include both the small delicate organisms which float passively with the
ocean currents, and also powerful swimmers like many fish, and aquatic
mammals such as whales and seals. The littoral forms live in the region
which is within the reach of land influences, that is, from low-tide
mark to the edge of the Continental Shelf (cf. p. 27). Among forms
directly important to man they include many fish; crustaceans such as
crabs and lobsters; shell-fish such as oysters, mussels, clams, etc.;
less important forms such as sea-urchins, which are extensively eaten in
the Mediterranean; sponges, an important article of commerce; the
various corals, especially the precious coral, and so on.
Of the useful marine animals, those which are most readily captured are
the littoral forms, many of which, on shores where the tides are well
marked, are exposed, or at least brought within easy reach, by the daily
ebb and flow of the tide, and can be obtained with the minimum of
apparatus. The extensive shell-mounds found on many shores, _e. g._ on
those of Denmark, show at how early a date man availed himself of the
abundant food supply to be obtained on the shore rocks. All edible
animals found in the sea are "fish" to maritime populations, but fish in
the restricted sense are usually more active, and require more skill for
their capture than the less intelligent molluscs or crustaceans, and
were probably not used at so early a date. They are by no means equally
distributed in all seas, and their distribution shows many points of
interest.
We must notice, in the first instance, that the waste of the land is of
great importance in feeding marine forms, whether directly or
indirectly. Marine animals, therefore, occur most abundantly over the
Continental Shelf, where they are within reach of the food brought down
by the rivers from the land. Again, many fish, or the organisms upon
which fish feed, depend largely upon those minute plants called diatoms
which float in the upper layers of the waters of the ocean. These are
especially abundant in the colder seas, which doubtless helps to explain
the abundance of fish in high latitudes. These diatoms, like many other
small organisms in the sea, are swept about by the ocean currents, whose
course greatly influences the movements of fish.
We saw in the case of forests that hot climates conduce to a great
variety of species, while in colder climates the species are few, but
the number of individuals very great. Something of the same sort seems
to occur with fishes. In warm seas the number of species is very great,
while in colder seas there are fewer species, but those which do occur
are sometimes found in vast numbers. Fortunately for man these prolific
northern species are often edible, whereas in warm seas poisonous or
inedible forms are common. The valuable cod family is found chiefly in
high latitudes.
The consequence of the facts just described is that valuable fisheries
tend to occur in cool or cold climates rather than hot ones, and because
of the dependence of so many forms on the Continental Shelf, they occur
in the northern or land hemisphere rather than in the southern or
oceanic one.
The most valuable fisheries in the world seem to be those off
Newfoundland, where the broad Continental Shelf, forming the so-called
"banks," feeds myriads of cod. The mingling of the waters brought by the
cold Labrador currents with those brought by the warm Gulf Stream
perhaps influences this marvellous abundance of fish, as does also the
waste brought by the icebergs.
Next to the banks of Newfoundland the most valuable fishing ground is
the shallow North Sea, which, as we have seen, lies on the surface of
the Continental Shelf. Fish are much more abundant here than on the
narrower shelf on the western coast of Britain, and the wealth of the
North Sea has been an important factor in the development of the
countries bordering it.
The warm, salt, relatively deep, and tide-less Mediterranean is not
nearly so rich in food fishes as the more northerly seas, a fact
reflected in the large importation of dried fish alike from Newfoundland
and from the region of the North Sea. But this is an economic and not a
zoological statement, for the Mediterranean is in reality richer in fish
species than the North Sea, in this respect, as in some others,
approaching tropical regions. Among the economically important fish are
the tunny, a very large form allied to the mackerel, which is dried, and
sardines and anchovies, which are preserved in oil. Otherwise the fish
are eaten fresh, and do not enter into general trade.
Fresh-water fish are abundant all over Europe, but with some exceptions
they are not greatly prized in those countries where the
better-flavoured marine fish can be obtained. Elsewhere, as in Russia,
Germany, and parts of France, they become important.
Much more valuable than fresh-water fish in the strict sense are the
various kinds of salmon, which come up the rivers to breed, but spend
much time also in salt water. In the rivers of Scotland and Scandinavia
salmon are still very important, but the fisheries in both cases are
insignificant when compared with those of western North America. Salmon
are inhabitants of temperate waters, and in North America do not extend
further south than the rivers flowing into the north of the Gulf of
California. Off the coast of Alaska and British Columbia, especially the
former, they are enormously abundant, and being caught in quantities
which far exceed the local demand are largely canned for export.
It is interesting to note that in regard to fresh-water fish, as with
marine forms, the northern part of the world is especially rich in
edible species, as compared alike with the southern hemisphere and with
the tropics. The salmon family is confined to the northern hemisphere,
and the carp family, though not peculiar, is largely represented in the
north. To it belong the whitefish, which form important food fish in
many parts of America. Sturgeon, which are important in Russia, occur in
the great rivers of eastern Europe, and in parts of Asia, and also on
the eastern coast of North America, and off California.
Turning next to the distribution of land animals within the European
area, the first point is to note that for the globe at large zoologists
employ zoogeographical divisions based chiefly upon the distribution of
the land _mammals_. The reasons for this are manifold.
In the first place, mammals are of relatively recent origin, and in
taking account of their spread over the globe, we may assume that in
broad outline the continents, or at least the deep oceans, were much the
same when the existing mammals were evolved as at present. This
naturally simplifies the problem, for if we divided the globe into
regions on the basis of the distribution of reptiles, for example, we
should find it necessary to take account of many differences between the
world in which the first reptiles arose and the world as it is at
present.
Again, the chances of land mammals passing from one region to another,
except by the crossing of land surfaces, are small. Thus the occurrence
of similar land mammals in two regions now widely separated is almost
certain proof of a former land connection between the two regions. The
difficulty which most land mammals find in crossing mountain chains, or
deserts, or considerable extents of water, makes it easy to define
zoogeographical regions separated from one another by the existence of
such "barriers to distribution" as they are called. Finally, mammals are
highly organised animals of relatively large size, and their
distribution is more easily studied than that of insects, for instance.
Without going into the zoogeographical regions in detail, we may note
that there is, as already stated, considerable resemblance between the
mammals of Europe, Asia, Africa and North America, that is, of the land
hemisphere, while South America, which was for long isolated from North
America, has a peculiar and relatively primitive fauna, and Australia,
whose isolation has lasted longer, has an even more peculiar and a much
more primitive fauna.
When we look at the fauna of the great land mass formed by the
continents of Europe, Asia, Africa and North America, sometimes called
by zoogeographers the _Arctogæic_ realm, we find that North America
differs from the eastern land mass as regards its land mammals in
several respects. Though long separated from South America it has been
connected long enough for some of the southern forms to find their way
northwards, so that we find skunks, raccoons, and other mammals
strikingly different from analogous forms found in the Old World. Again,
it is relatively so long since there was any free communication between
the eastern and western hemispheres that the two faunas have had time to
diverge without destroying the fundamental resemblance.
Beginning with the fauna of the Old World, we find that no effective
barrier of any sort separates the animals of Europe, even of western
Europe, from the animals of temperate Asia, even of eastern Asia. Right
across from the British Isles to Japan, through about a hundred and
fifty degrees of longitude, there is great general similarity in the
land animals. To the south, on the other hand, the Atlas mountains and
the African desert cut off the greater part of the continent of Africa,
and eastwards the transverse mountain chains, no less than the
difference of climate and the cold, barren nature of the uplands of
central Asia, cut off the rich fauna of the peninsula of India with
Further India, etc., from the habitable regions of temperate Asia, with
their scantier fauna.
We are thus left with the conception of a very large and tolerably
uniform zoological region, stretching right across Europe and temperate
and northern Asia. This is the Palæarctic region of zoogeographers.
The European section of it is somewhat impoverished as compared with the
Asiatic section, partly perhaps because of the effects of the ice, and
certainly also because for long ages Europe has been densely populated,
and the larger wild animals have thus been exterminated. Asia, with its
northern forests and its more southerly steppes, has always been a great
reservoir of life, which has periodically overflowed into Europe. Some
of these overflowing animals, like the black and the brown rats,
succeeded in establishing themselves very firmly; others, like the saiga
antelope, died out rapidly except in the extreme east of the European
area.
It is possible that further investigation will show that not the mammals
only, but land animals in general can be grouped according to their
habitat like plants, but so far the attempts made in this direction have
been tentative only. Generally, we may say that the mammals of Central
Europe are of the woodland type, but no detailed classification into
steppe and woodland animals exists. It may be useful, therefore, to
indicate the chief kinds of mammals found in the European area, grouped
according to affinity, in the absence of a geographical classification.
Mammals, apart from the egg-laying monotremes, and the marsupials of
Australia, are divided into nine orders, and of these, one, that
including the anteaters, etc., of South America, Africa and India, is
entirely unrepresented in Europe. Another, the Cetaceans, or whales, has
no land representatives; and the same is true of the aberrant sea-cows,
though their ancestors lived on land and occurred in Egypt.
Excluding these orders we are left with six which have European
representatives. These are the following:--
Primates, or monkeys and apes.
Insectivores, or insect-eating mammals, such as moles, shrews and
hedgehogs.
Chiroptera, or bats.
Ungulates, or hoofed animals, including horses, cattle, sheep, deer,
pigs, etc.
Carnivores, or flesh-eaters, including lions, cats, foxes, dogs, etc.
Rodents, or gnawing animals, among which are rats, mice, squirrels, etc.
The _Primates_ are represented by one form only, the Barbary ape, found
in Gibraltar. _Bats_ are numerous, but are of less geographical
interest than land forms. The remaining four orders are all important.
The _Ungulates_ include the largest land mammals, and their size and
conspicuous nature have led to the gradual replacement of the wild forms
by domesticated ones. Only a very few, such as deer, wild goats (ibex),
the wild boar, the wild sheep (moufflon) of Corsica, manage to survive,
and that mostly by aid of special protection. The presence of the large
wild forms is incompatible with almost any form of agriculture as is
often proved disastrously in Africa, hence man's ruthless warfare upon
them.
But if man has destroyed the large ungulates he has found himself unable
even to reduce the numbers of the _Rodents_, who gain in many ways by
civilisation. The destruction of their rivals, the grass-eating
ungulates, increases their natural food-supply. In South America, where
there were very few ungulates till the white man brought his flocks and
herds, the rodents were very numerous and reached a great size. Again,
the operations of agriculture give the rodents enormous artificial
sources of food-supply, and the number of man's domesticated or
semi-domesticated animals makes him wage a bitter war against the small
carnivores, the natural enemies of the rodents. Protected from their
enemies, abundantly fed by man's providence, it is no wonder that these
small animals have multiplied greatly.
Their multiplication has been assisted by the fact that they inherit
from their early days, when the struggle was keen, an enormous
fertility. Many of the rodents are steppe animals, and share with steppe
organisms in general the power of periodic multiplication in enormous
numbers.
The steppe is a region where the rainfall is normally just enough to
ensure a free growth of grass at certain seasons. Variations in
rainfall, which perhaps occur in great cycles, may at one time produce a
luxuriance of growth which increases the food-supply all round, and at
another give rise to semi-desert conditions with a resulting enormous
death-rate. The steppe organisms, then, must be very fertile because of
the risks of their environment, and the Asiatic overflow is possibly
determined by successions of years of abundant rainfall, which increase
the number of individuals, followed by a series of years of scanty rain,
which make it necessary for the overflow of population to migrate.
Among examples of European rodents we may mention the very destructive
rats, mice and voles, which practically feed everywhere at man's
expense; and the hamster, an Asiatic form which reaches as far west as
the Rhine, and stores large quantities of corn and other food in an
elaborately made burrow. The hamster has the rodent power of rapid
multiplication, and is often terribly destructive to cultivated crops.
Rabbits are similarly very destructive where special precautions are not
taken. Even the porcupine of southern Europe is capable of doing
considerable damage. Less serious enemies of man are such forms as the
following:--lemmings; marmots, of which there are two forms, an Alpine
and an Asiatic, the latter extending like the other steppe animals into
the plains of central Europe; beavers; squirrels; dormice; etc. These
examples may be sufficient to illustrate the important points in regard
to the rodents--their destructiveness, their fertility, and the fact
that many were originally inhabitants of steppes and open plains, but
tend, as man clears the forest-land for his own purposes, to extend
their range to the cleared land, and to appropriate the new and
extensive food-supply furnished by man's industry.
While the ungulates, because of the nature of their food, must almost
necessarily be rather large animals, the carnivores occur both in large
and small forms. The tendency is for the large forms to be killed out
with the progress of civilisation; thus the lion has wholly disappeared
from Europe, wolf and bear are almost gone, but a considerable number of
smaller forms still remain, such as badger, genet, wolverene, lynx, wild
cat, stoat, marten, weasel, etc. The last order to be mentioned, that of
the _Insectivores_, includes small mammals, such as moles, shrews, and
hedgehogs, which feed largely on insects, but may be partially
vegetarians.
As was to be expected from the climate and from the peculiar flora, the
Mediterranean region possesses a richer fauna than central Europe, both
as regards mammals and lower forms. Even the European portion shows
considerable African influence.
A few words must be said about other land animals apart from mammals. In
regard to birds it is noticeable that the habit of migration, and the
fact that the greater part of the continent of Europe lies on the
direct line between the northern breeding grounds of many species and
the southern winter quarters, gives Europe a very rich bird fauna. The
British Islands owe to their peculiarly mild climate a rich bird fauna
at all seasons, for while the summer climate attracts many forms for
nesting purposes, the mild winter brings many migrants flying from the
cold of continental Europe.
In regard to birds as well as to other animals, the Mediterranean owes
to its warm climate a richer fauna than countries farther north. Some
interesting southern forms, such as pelican, flamingo and ibis, reach
this region, though not extending into central Europe, except as
stragglers.
The climate of Europe is not hot enough anywhere to lead to the presence
of a rich reptilian fauna, but there is, again, a marked increase to the
south. It is stated that there are only twenty-one species of reptiles
in central Europe, while there are fifty-nine in southern Europe, and no
less than a hundred and forty in the Mediterranean region taken in the
large sense. Poisonous forms are few, and do not, as in hotter
countries, constitute a serious menace to man. Very interesting is the
presence of the chameleon in southern Spain, as in north Africa.
Perhaps the most important human aspect of the European reptiles is the
presence of numbers of insect-eating forms. In the warmer parts of
Europe every wall or patch of rock seems alive with lizards in the
summer sunshine, and these must play a not inconsiderable part in the
keeping down of noxious insects.
Omitting a great number of other groups, we may say something about
insects, which are of enormous importance in human life, both directly
and indirectly.
It has been shown of late years that many insects are the sole means by
which certain very deadly diseases are transmitted from man to man, or
from one animal to another. Almost every few months a new announcement
of an insect-carried disease is made, but the most important forms are
the following:--Mosquitoes and gnats transmit such diseases as malaria,
yellow fever, and more horrible diseases still, due to the presence in
the blood of small parasitic worms. Tsetse flies carry sleeping
sickness, and also transmit the very fatal fly disease of domesticated
animals, a fact which has been and is of great importance in the
settlement of Africa. In the case of most diseases there seems to be a
close connection between one particular species of insect and a
particular disease.
Mosquitoes and gnats are very abundant in many parts of Europe, and the
forms belonging to the genus Anopheles, which carry the germ of malaria,
are widely distributed. In parts of the Mediterranean area their
presence is associated with the prevalence of malaria, which has existed
there for a prolonged period, and is believed by some to have had an
important bearing upon the fates of the ancient civilisations of the
Mediterranean basin.
The regions in Europe affected, or seriously affected, by malaria are
diminishing yearly. This is now due to conscious efforts, but a similar
process has been going on probably for a long period, for many obscure
diseases, notably "ague," seem to have been forms of malaria. Their
disappearance seems to be due to drainage, which diminishes the breeding
places of the mosquitoes, and also to the progress of agriculture, for
ponds which form on rich, well-manured land are apparently unsuited to
mosquito larvæ. The subject is of great geographical importance, for
the spread of man over the surface of the globe, and the progress of
civilisation must have been influenced in all time by the prevalence of
fly-borne disease. Such diseases have hitherto been the greatest
obstacle in the way of the civilisation of Africa.
In Uganda extensive tracts of fertile wooded land have had to be
abandoned on account of the presence there of the tsetse fly, while,
prior to this abandonment, there were districts in which every living
soul had been destroyed by the deadly sleeping sickness transmitted by
this fly. We can hardly suppose that such facts are without a parallel
in human history; and man's distribution over the surface of the globe,
and in detail the distribution of his settlements within a country, have
doubtless been greatly influenced by the distribution even of such
insignificant creatures as the various kinds of flies.
Even apart from their power of transmitting disease, the blood-sucking
flies must have influenced man in his choice of localities for
settlements, and must have been an important factor in the process of
adjustment to his surroundings. The naturalist Brehm gives an appalling
picture of the number and blood-thirstiness of the mosquitoes of the
Siberian tundra, which render life almost intolerable there for both man
and beast in summer. Even within the British Islands the uncultivated
and undrained regions are often badly infested with small blood-sucking
flies, and their numbers must have been vastly greater in the old days
before drainage and intensive cultivation had reduced them. It is quite
possible that some of the anomalies in regard to the spread of
particular races of men over the surface can be explained by the varying
susceptibility of different races to insect attack, and there can be no
doubt that the blood-sucking insects must have had some effect in
determining the rapidity or slowness with which particular tracts were
colonised by man.
Apart from the blood-sucking flies, there are many other interesting
points about the insects of Europe, notably the wealth of beautiful and
striking forms which occur round the Mediterranean basin. One of these,
which extends northwards and westwards to northern France, is the
curious Praying Mantis, a predatory insect belonging to the same order
as the locust. It is an eastern form, which, like so many others, has
taken advantage of the mild climate of western Europe to extend its
range far beyond what we must regard as its natural limits. In France it
shows the effect of relatively unfavourable conditions in the fact that
it takes some nine to ten months for the eggs to hatch, whereas in
hotter countries the process may take place in a few weeks.
In the warmer parts of Europe a very striking feature is the number and
large size of the members of the locust and grasshopper families, whose
shrill noise is so characteristic a sound in, for example, the pastures
of Switzerland in summer-time. Among the locusts there occur, in many
parts of Europe, those migratory forms which possess that power of
periodic enormous multiplication which we have already noted so
frequently among grassland animals. The migratory instinct only seems to
develop when the numbers have greatly increased in any given locality,
and in Europe generally the climate does not permit this to take place.
It does, however, occur in the south-east of the Mediterranean basin,
notably in the island of Cyprus, in Syria, and also in Northern Africa,
where locusts sometimes reach the dimensions of a plague.
We may add to this account of land animals a few details on the land
mammals of North America. The great point of contrast here is that
Europe, from the beginning of the historic period, has always been a
relatively well-peopled region, while in America, prior to the advent of
the white man, the population was scanty. There was thus far more room
in North America than in Europe for great flocks of large mammals. Thus
the plains and prairies carried great herds of bison, while to the north
there were other herds of reindeer, which were never tamed by the
inhabitants of North America as they were in the Old World by the Lapps
and others. The musk-ox is another interesting animal found in the north
of America. It once also lived in Europe, but died out long ago. Just as
the coniferous forest and tundra in Asia produce many small fur-bearing
animals, so do the forest and tundra of North America. Deer are present
as in the Old World, though they are of different types, and there is a
curious animal known as the prong-buck which is peculiar. Wild sheep
occur as they do in Europe, but no wild horse nor ass roams the plains
of America as they roam to-day the wastes of Asia. Without going into
further detail, we may say generally that as regards wild animals, no
less than as regards wild plants, North America shows a closer
resemblance to Asia than to that favoured peninsula of Asia which the
geographers call Europe.
CHAPTER VII
CULTIVATED PLANTS AND DOMESTICATED ANIMALS
Before proceeding to discuss the chief races of men in Europe, something
must be said of its cultivated plants and animals. Originally,
doubtless, the various human groups which have mingled in Europe had
each their own type of culture, based upon the possession and
cultivation of particular animals and plants. The lapse of time has
caused so complete an intermixture that it is only possible to a very
small extent to disentangle the different elements which have gone to
the making of present day civilisation. Nevertheless, as climatic
differences remain and still determine minor differences, it seems worth
while to consider briefly the distribution of cultivated plants and
domesticated animals at the present day.
Europe has been so strongly influenced by the neighbouring land-masses
of which it forms a part, that we must begin with a few words about
them.
The great continent of Asia, of which Europe, as we have seen, is but a
peninsula, can be divided into a series of zones, distinguished alike by
climate and by vegetation. To the north we have the cold tundra region,
passing to the south into the forest region. The Asiatic forest region
is continuous with that of Europe, but while the European forest extends
southward till Mediterranean conditions intervene, close to the sea of
that name, the Asiatic forest has its southern limit in about the
latitude of London. To the south of the Asiatic forest stretches a zone
of steppes passing into desert, and even into tundra in the elevated
regions of Central Asia. The steppe region, as we have already
indicated, enters Europe by way of Russia and pushes a long arm up the
Danube into Hungary.
South of the Asiatic steppes and deserts comes an interrupted band of
warm temperate or tropical forest, luxuriant to the east where there are
summer rains, scanty and scrub-like to the west, where Asia meets the
Mediterranean.
The steppes and desert of Asia are populated, scantily enough, with
wandering pastoral nomads, who constantly tend to overflow from their
own region into those of the surrounding agricultural populations. These
agricultural populations are concentrated in three areas, all specially
favoured by nature. To the east the summer rains, the luxuriant
indigenous flora, and the presence of great river valleys, that is, of
naturally fertile regions, led to the early establishment of
agricultural populations in China and India. Further to the west, the
fertile valleys of the Tigris and Euphrates early saw the founding of a
great civilisation. This region, the Mesopotamia of geographers, is very
near the third area, the Mediterranean, though far enough removed to
have a very scanty rainfall, which made irrigation a necessity for
agriculture. Its inter-relations with the Mediterranean must have begun
early, and, remembering that part of the Mediterranean itself is in
Asia, we need not stop to discuss the vexed question as to whether the
Mediterranean civilisation was largely indigenous, or originated in the
continent of Asia. It is often difficult to ascertain whether plants
which have long been grown in the Mediterranean area, and are
well-fitted to it, are really indigenous there, or were brought to it
from the Mesopotamian countries. There is much similarity of climatic
conditions, and for our purpose it is sufficient to note that the
cultivated plants of the Mediterranean basin fall into three main
categories. There are, first, the plants specially adapted to its
climate; these are either native or were introduced from the countries
close at hand. Second, there are many plants, much less perfectly
adapted to conditions of drought, and therefore often demanding
irrigation in summer, which were introduced from the Far East, after
they had been cultivated there for long periods. Thirdly, and much fewer
in number, there are the plants introduced, at a relatively late date,
from America.
Of the first group the most important are the cereals barley and wheat,
and the olive and the vine. These four have been known in the area from
the earliest times, and they still form the basis of the diet of
Mediterranean peoples. Bread, olive oil to replace the butter used by
pastoral peoples, wine as a beverage, with fresh grapes and the dried
forms of raisins and currants, these early made life possible in the
Mediterranean area.
Barley is older than wheat, and is more productive but less valuable. It
is now largely grown in the basin of the Mediterranean as a food for
horses, instead of oats which, like rye, is a cereal not well suited to
the Mediterranean climate. As a bread plant it was early replaced in the
Mediterranean by wheat, but it is still used to make bread in some other
parts of Europe, _e. g._ in Scandinavia, and is also of importance
outside the Mediterranean as the origin of fermented beverages.
Wheat is the most valuable bread plant which exists, both on account of
its proteid content and on account of its digestibility. It demands a
warm dry period for ripening, with much sunshine, and is well adapted to
Mediterranean conditions. Here it is sown in the autumn, to enable it to
take advantage of the "early and the latter rain," _i. e._ the autumn
and spring rains, and ripens early before the excessive drought of
summer sets in. Like barley it has always been associated with plough
culture, the animal used being the ox. According to most authorities
plough culture originated in Mesopotamia.
The vine and olive are apparently both indigenous to the Mediterranean,
and both are well adapted to withstand drought. In regard to the vine
there are several interesting points. To the traveller from the north it
is most familiar in France or Germany, where it is grown on sunny
slopes, usually terraced to prevent stagnant water from lying. In the
Mediterranean, on the other hand, it is planted in hollows, or low-lying
ground, which permits of the collection of water, for it will receive no
summer rain. The vintage is more secure than further north, and the
resistance to the attacks of parasites is greater, yet, curiously
enough, the Mediterranean countries do not produce the finest wines.
This seems to be partly because the climate does not permit of the long
storage necessary for maturing to take place. The cool cellars, so
important in the wine industry further north, are here absent.
To the four plants which we have mentioned we must add such forms as the
fig, which if not indigenous was of very early introduction; garlic,
greatly valued as a flavouring matter; various kinds of pulse; sesame;
millet, once widely grown though no longer important, and flax, known
from remote antiquity.
The second group, that comprising plants introduced from the Far East,
includes many valuable fruit trees, which in the region of the
absolutely rainless summer mostly require irrigation. The peach came
from China in the time of Alexander the Great; the various citrus
fruits, lemon, orange, lime, citron, etc., now so characteristic a
feature, were introduced from China or India. India also gave rice,
extensively cultivated during long ages, and still extensively consumed,
though the facility with which communication with the East is now
effected makes it relatively little grown, except in the plain of
Lombardy, which is easily irrigated. China sent the white mulberry, and
with it the cultivation of the silkworm, so important in many regions.
From the Far East also came the sugar-cane, very important till the
recent development of the sugar beet industry. Cotton also was probably
introduced from the Far East, which thus supplied many cultivated plants
and has enormously enriched life for Mediterranean man.
Of the American plants of late introduction the most interesting is
maize, which fed the somewhat limited indigenous civilisation of North
America. Maize requires a warm climate with much sunshine, but needs
much moisture during its short growing season. It is not a very
valuable cereal, but it is enormously productive and therefore cheap.
Generally it may be said to be used as food by man only when necessity
compels its use. It is thus employed by subject races, _e. g._ negroes,
and by the poor in the warmer parts of Europe. In the Mediterranean it
is not sufficiently valuable to be grown on irrigated land, and it will
not grow without irrigation where the summer is rainless. Where there
are summer rains, however, as in North Italy, or where mountain slopes
increase the rainfall, as in parts of Greece, or where the land is
rendered valueless for wheat by winter flooding, there maize is grown.
Generally it occurs within the Mediterranean area wherever the necessary
water occurs naturally or can be supplied cheaply. It forms a very
important part of the food of the poor in North Italy, for example, but
not in the south, where water is too costly.
Two other important plants of American origin are tobacco and the
potato. The latter plant is little grown in the Mediterranean, but a
considerable amount of tobacco is produced. Another American plant, the
prickly pear, besides furnishing an edible fruit, is important as a
hedge plant within the area.
Cereals in the Mediterranean are grown, as we have seen, on ploughed
land, as elsewhere. A more characteristic form of cultivation is
garden-culture, practised where water can be obtained for irrigation.
Such gardens consist primarily of fruit trees, all the citrus fruits,
peaches, apricots, pomegranates, pistachio, almonds, and many other
forms of nuts, plums, even apples and pears, being grown in this way. So
productive is the ground once water is supplied, that plants are grown
in association in a fashion hardly suggested in the north. Thus among
the fruit trees many different kinds of vegetables, such as garlic,
cucumbers, leeks, salad plants, many sorts of melons, tomatoes,
egg-plants, beans, and peas, etc., are grown. Elsewhere one may see corn
sown beneath the olive trees, and the vine sharing the same ground with
them.
The picture of Mediterranean life may be completed by adding a few words
about the domesticated animals. These are naturally in essence the same
as those further north, but their relative numbers and the uses to which
they are put are different.
The dog and cat both occur, but the former has little importance in the
pastoral industries, and is largely a watch animal, insufficiently fed,
and therefore important as a sanitary agent in that it devours garbage.
Among the ungulates or hoofed animals, the ass was domesticated in the
region long before the horse, and it and the mule are still more
important than the horse, partly, no doubt, because both are hardier,
and the problem of food is a difficulty in the largely pastureless
Mediterranean region.
Few camels now occur in Europe, where they have been always closely
associated with Mahometans, appearing and disappearing with them.
The pasturage difficulty greatly reduces the importance of cattle, which
are draught animals rather than a source of food. As draught animals
cattle go back to the dawn of history, but their numbers are small and
the use of either their flesh or their milk as food is insignificant.
Philippson in his book on the Mediterranean gives some striking figures
to illustrate the difference in numbers between the cattle of the
Mediterranean countries and those of Central Europe. Spain has only 2.1
million cattle, and yet it is scarcely smaller than Germany, which has
19 millions; Switzerland has 1,340,000 head of cattle, and Greece, which
is about half as large again, has only 360,000. It is to be noted,
however, that the irrigated plains of North Italy now support a
considerable amount of cattle, whose milk gives rise to a considerable
cheese industry; but, then, the olive will not grow in North Italy,
which is therefore not strictly within the Mediterranean area.
The Arabs introduced the Indian buffalo which has spread considerably,
and is now found in South Italy and the Balkan peninsula. The pig has
been banished from parts of the region on religious grounds, but
elsewhere it chiefly thrives where oak forests grow, the acorn being an
important part of its food. The really important ungulates, however, are
sheep and goats, which are often very numerous, and which, apart from
birds and fish, furnish the most important part of the animal food of
the inhabitants. The milk furnishes cheese, which is an important
element of diet, while leather, wool and hair are also important
products.
The goats chiefly feed upon the young shoots of shrubs, and frequent the
denser thickets, while the sheep browse upon the grasses and herbs to
be found in the more open forms of maquis. The climate permits the
animals to remain in the open during the whole year, and this prevents
the collection of the manure for the arable lands. Further, the summer
drought makes it difficult for even these hardy animals to obtain food,
and necessitates in many regions a curious form of nomadism, to which
the name of transhumance is given. Transhumance, still well developed in
Spain, is the periodic and alternating displacement of flocks and herds
between two regions of different climate.
As we have had frequent reason to remark, the rainlessness of the
Mediterranean summer is locally modified by many causes, notably by
elevation. Mountains may receive frequent showers, while the plains are
parched and brown, and therefore there may be pasture on the mountains
while there is none in the plains. On lofty mountains also the winter
snow lingers long enough to promote the growth of summer pasture. While
there are considerable herds of sheep and goats, then, it may be
necessary for the flocks and their keepers to travel to the mountains in
summer and back to the plains in winter. In Spain these periodic
migrations, now largely made by means of the railway, formerly took
place by well-defined routes, along which the immense army of sheep,
accompanied by a smaller army of attendants, passed twice a year,
causing enormous destruction to the cultivated lands through which they
passed. Everywhere the conflict between shepherd and husbandman is more
or less acute, but it seems to have been especially acute in Spain,
which is in some respects a link between Africa and Europe. Its constant
liability to Arab invasion made agriculture especially difficult, while
frequent wars favoured the pastoral industry; for flocks may be removed
to a place of safety on an alarm, but agriculture must have some
security before it can develop. In the semi-desert regions of North
Africa some form of pastoral nomadism, with the social polity which
comes from pastoral nomadism, was the natural result of the physical and
climatic conditions, and Spain, like the lands of the eastern part of
Europe, has been constantly liable to have its nascent agriculture
destroyed by incursions of such pastoral nomads. In both cases the slow
victory of the agriculturists, marked by many temporary reverses,
affords an extraordinarily interesting chapter in human history. A
stable civilisation must always be based upon agriculture, but every
disturbance of an old and stable civilisation has temporarily encouraged
the pastoral as contrasted with the agricultural industries.
In regard to the other animals of the Mediterranean, mention need only
be made of the domesticated birds. The fowl has long been known; it is
believed to have been introduced from the East eight centuries B.C. Both
the eggs and the flesh are of great importance as a source of food. In
spite of Roman history, geese are relatively unimportant, as are also
ducks, but the turkey, late introduction from America, is well suited to
the climate and has become important. Pigeons are everywhere abundant,
sometimes so much so that their manure is extensively used as a
fertiliser. We have already mentioned silkworms, and students of
classical history know that bees have long been kept.
* * * * *
If we sum up what has been said about Mediterranean cultivated plants,
we may note that these have been derived partly from native plants,
partly from plants native to the warm forest country of eastern Asia,
and partly from American plants. Regarding for a moment the Eurasiatic
continent as a whole, we may say that the old civilisations, both to the
east and to the west, arose in the forest regions--in the monsoon
forests to the east, in the drought-resisting forest or scrub of the
west. The temperate forest of Asia has produced no great civilisation,
and the civilisation of the temperate forest zone of Europe has owed
much to the earlier civilisation of the Mediterranean, with which it has
always had free communication.
This free communication has taken place chiefly by means of the
Mediterranean seaboard of France, especially by means of the great Rhone
valley, which forms a natural highway to the north. France, with both an
Atlantic and a Mediterranean seaboard, has been the natural intermediary
between the Mediterranean scrub land, with its characteristic
civilisation, and the temperate forest region, with its colder climate,
and its greater rainfall, which produce a corresponding difference in
the cultivated plants.
We have seen that wheat is the great bread plant of the Mediterranean,
and it is interesting to note that in this respect France is almost
purely Mediterranean. It is, above all, the country of white bread,
which plays a very important part in the dietary of the people. In
ordinary years the country produces nearly as much wheat as it consumes.
In addition to this large use of wheat as a bread plant, France shows
strong Mediterranean influence in the part which wine plays in the
dietary of the people, in the variety of vegetables, especially kinds of
pulse, which are grown; in the fact that fowls and pork form a large
part of the animal food consumed, and in that flax has been grown in
considerable amounts for long ages, so that linen is an important part
of household wealth. The Midi is of course definitely Mediterranean in
culture, but just as the vine extends far to the north and west so also
do Mediterranean influences extend far beyond the region of
Mediterranean climate and Mediterranean flora.
But fertile as much of France is, it must not be regarded as consisting
of nothing but fields of waving wheat. To complete and correct the
picture we must add that, as in Russia, considerable amounts of
buckwheat are grown for use as human food. Buckwheat, the "black wheat"
of the French, perhaps introduced by the Arabs, is not a true cereal,
but a relative of the knot-grass of British fields. It is very easily
grown, even on poor land, and in France replaces wheat where the
conditions are unfavourable, or where agriculture is backward. It is not
without interest to note that while its use in France as human food is
an indication of extreme poverty, in the United States buckwheat cakes
take a place as a luxury. Oatcakes in lowland Scotland, "black bread" in
well-to-do households in Germany, are other similar instances of the
reappearance of a despised food-stuff as a luxury. Such foods become
luxuries when they can be used to supplement, not to replace, white
bread. Most of the buckwheat of France, however, is now grown as food
for domesticated animals.
Again, fruit trees are extensively grown in France as in the
Mediterranean region, with a gradual increase in the forms which require
more moisture and less heat as we travel northwards. The typically
Mediterranean forms early disappear, while many kinds of plums, pears
and apples increase in numbers and in value. As we travel northwards
also, the various forms of berries, scarcely represented in the south,
increase in importance. The strawberries of Brittany form a good
example, but throughout Europe generally this change takes place,
culminating in the enormous wealth of wild berries--cranberries,
whortleberries, and so on, which is a characteristic feature of the
Scandinavian uplands in late summer.
As we travel to the north-west also, with the increase in the rainfall
and the consequent increase in pasturage, the number of cattle
increases, and with them the increased use of beef as food, and the
increas
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