PRELIMINARY CONSIDERATIONS.
I intend to give in this chapter a general outline of the subject which
will be discussed in the subsequent ones. This will include a brief
history of the great events, in recent geological times, which have
modified the evolution of the European fauna by the influence which they
have exerted on the course of the successive streams of migration.
The composition of the European fauna is the first item which will have
to be taken into consideration. But not only must the existing species
of animals be dealt with: the extinct ones, too, at least those which
have lived in Europe during late Tertiary times, will be useful for our
inquiries. A knowledge of the past faunas is a most important factor in
tracing the original home of the European animals.
Where a species first originated, whether this was in one or several
places, or, in other words, where it first had its home, cannot be
determined with absolute certainty in the present state of our
knowledge, but as a rule it can be indicated approximately with a fair
amount of precision. In a few instances, species may possibly have had
a dual origin. The majority of naturalists doubt that there are any
such, but it seems to me that almost the same forces may have acted in
different localities on certain forms so as to produce, in very
exceptional circumstances, similar species. The vast majority of
animals, however, have no doubt originated in one locality; or, we might
say, almost all species have but one home.
We may assume that every animal gradually extends its range by
migration, as the result of the natural increase of the species
necessitating a search for fresh feeding grounds. Every species thus
tends to slowly take possession of all the habitable parts of the globe
to which it has access. They would all naturally spread from their
original homes in every direction, unless prevented by an impassable
barrier. We have already learned that to all land animals, the sea acts
as such a barrier. Mountains and rivers act also in a similar way, but
not to the same extent. It is not difficult to understand also that a
forest may be a formidable barrier to a typical inhabitant of the open
country and _vice versa_, whilst a desert is impassable to almost all
terrestrial organisms. Some species are scarcely affected by climate,
and flourish equally well in the tropics and in temperate or cold
countries; the majority, however, are greatly influenced by it. "No more
striking illustration," remarks Merriam (p. 38), "could be desired of
the potency of climate compared with the inefficiency of physical
barriers, than is presented by the almost total dissimilarity of the
North American Tropical and Sonoran Regions, though in direct contact,
contrasted with the great similarity of the Boreal Regions of North
America and Eurasia, now separated by broad oceans, though formerly
united, doubtless, in the region of Behring Sea."
To return to the composition of the European fauna, we now know
positively that a number of the mammals and birds inhabiting Central and
Eastern Europe are of Siberian origin. How they came, and when, will
form the subject for discussion in Chapter V. At present it will suffice
to mention that in the superficial deposits belonging to the Pleistocene
series of the North European plain have been discovered the remains of
many typical members of the Siberian Steppe-fauna. Some of these, such
as the Saiga-Antelope (_Saiga tartarica_), Fig. 2, still inhabit
portions of Eastern Europe, whilst others have retreated to their native
land. But it might be asked, how is it known that these species did not
originate in Europe, and thence migrate to Siberia? Because if they had
originated on our continent, they would have spread there. They would
have invaded Northern and Southern Europe, and they would probably have
left some remains in Spain, Italy, or Greece. They would also have left
some of their relations in Europe; but all their nearest allies, too,
are Asiatic. Moreover,--and this completes, I think, the proof of their
Siberian origin,--the Pleistocene remains of these animals in Europe
become less abundant, and the number of species likewise decreases, as
we proceed from east to west. With these remains of Steppe animals are
generally associated those of others, which we must also look upon as
Siberian emigrants, such as the Pikas or tailless Hares belonging to the
genus _Lagomys_, the pouched Marmots (_Spermophilus_), and others. Some
of them, as I have mentioned, still inhabit Central and Eastern Europe,
whilst others have a wider distribution on our continent.
[Illustration: Fig. 2.--The Saiga-Antelope (_Saiga tartarica_). (From
Lydekker's _Royal Natural History_, vol. ii. p. 298.)]
This migration must have been an unusually large one. It has been
suggested that the Glacial period had some connection with it, and there
can be little doubt, as we shall see later on, that a change of climate
probably brought about this great Siberian invasion of Europe. But other
causes might tend in the same direction, such as want of sufficient food
after a few years of great increase of any particular species. It is not
known to what we owe the periodic visits of the Central Asiatic
Sandgrouse (_Syrrhaptes paradoxus_), Fig. 3, but certain it is that
immense flocks of these birds invade Europe from time to time at the
present day, just as those mammals may have done in past ages.
[Illustration: Fig. 3.--Central Asiatic Sandgrouse (_Syrrhaptes
paradoxus_).]
The _Siberian_ migrations will be spoken of in the subsequent pages, as
the Siberian element of the European fauna. These migrations, however,
are not the only ones which reached Europe from Asia. The sixth chapter
deals with migrations which have influenced our fauna far more than the
Siberian. The latter did not last long, nor did they affect the whole of
Europe. But what I may call the _Oriental_ migrations spread to every
corner of Europe and certainly lasted throughout the whole of the
Tertiary Era. The Oriental element came probably from Central and
Southern Asia, and in its march to Northern Europe it was joined by
local European migrations. For on our continent, too, animals originated
and spread in all directions from their centres of dispersal. A separate
chapter has been given to the _Alpine_ fauna, and another to that of
South-western Europe, which will be known by the name of the
_Lusitanian_ element. Finally, animals have also reached us from the
north, and in the fourth chapter the history of that remarkable
migration will be fully discussed under the title of the _Arctic_
element of the European fauna.
It is generally believed that Africa played an important role in the
peopling of our continent, but this is quite a mistake. The eminent
Swiss palaeontologist Ruetimeyer was quite right in saying (p. 42) that it
is much more probable that Morocco, Algeria, and Tunis were stocked with
animals by way of Gibraltar, and perhaps also by Sicily and Malta, from
Europe, than the South of Europe from Africa.
I have already referred to what are known as "centres of dispersion" of
animals, but before continuing to explain the general outline of this
book, it will be necessary to make a few additional remarks on the
subject.
Since every animal naturally tends to spread in every direction from its
original home--that is to say, from the place of its origin--the latter
should correspond with the centre of its range. And in any particular
group of animals the maximum number of species should be formed in the
area or zone which is the centre of its distribution. In the great
majority of instances this is probably the case, in the higher animals
perhaps less so than in the lower; still the rule must hold good that
the original home of a species is generally indicated by the centre of
its geographical distribution.
Take for example our familiar Badger (_Meles taxus_). It inhabits
Europe and Northern Asia. It is absent apparently from many parts of
Central Asia, but it appears again farther south in Palestine, Syria,
Persia, Turkestan, and Tibet. West Central Asia would be about the
centre of its range. That this corresponds to its place of origin is
indicated by the fact that the only three other Badgers known--viz., _M.
anakuma_, _M. leucurus_, and _M. albogularis_--are confined to Asia. If
we examine the fossil history of the genus, we find that the two most
ancient instances of the existence of Badgers have been discovered in
Persia, where _M. Polaki_ and _M. maraghanus_ occur in miocene deposits.
The latter had migrated as far west as Greece in miocene times; no other
trace of the Badger, however, is known from Europe until we come to the
pleistocene beds. There are a good many cases known among mammals where
the centre of dispersion would indicate to us a similar origin. On the
other hand, there may be no fossil evidence of the occurrence of a
species, or of its ancestors, in Asia, whilst such has been discovered
in Europe. I think, however, that the present range of a species forms a
safer criterion for the determination of its original home, as the
Asiatic continent is still practically unworked from a palaeontological
point of view. In a letter which I received from Professor Charles
Deperet, he advocates the view that the wild Boar (_Sus scrofa_) is
probably of European, and not, as I maintained (_c_, p. 455), of Asiatic
origin; because there seemed to be a direct descent from Hyotherium of
the middle miocene of Europe, through the upper miocene Pig of the
Mount Leberon (_Sus major_) and of Eppelsheim (_Sus antiquus_), and the
pliocene Pigs of Montpellier (_Sus provincialis_) and of the Auvergne
(_Sus arvernensis_). No doubt this appears rather a strong case in
favour of the European origin of the wild Boar, but although the
Tertiary strata of Asia, as I remarked, are as yet little known, a
number of fossil pigs are known from India, Persia, and China, the
oldest being the upper miocene Persian Pig (_Sus maraghanus_). Pigs are
therefore as old in Asia as in Europe, and as a direct intercourse
between the two continents probably never ceased since miocene times, it
is not surprising that this genus should occur in both. Even if the
genus had its origin in Europe, it is quite possible that in later
Tertiary times, the active centre of origin was shifted to the
neighbouring continent, and that henceforth many new species issued
forth from Asia, some of which may subsequently have been modified on
reaching our continent. The wild Boar (_Sus scrofa_), however, to judge
from its general range, I must look upon as merely an immigrant in
Europe. I have no doubt that it originated somewhere in Asia, probably
in the south.
The view I take of the origin of our European Boar is also supported by
Dr. Forsyth Major's recent researches. He was led to a re-investigation
of the history of the Pig while examining a large number of fossil
skulls in the Museum at Florence, and came to the conclusion that only
three or four species of recent wild pigs can be clearly distinguished
(_b_, p. 298). One of these, viz., _Sus vittatus_, he thinks, is
traceable in slight modifications from Sardinia to New Guinea and from
Japan to South Africa. The centre of distribution of this species lies
in Southern Asia. Of the three remaining species, two, viz., _Sus
verrucosus_ and _S. barbarus_, are entirely confined to the great
islands which form part of the Malay Archipelago. Finally, _Sus scrofa_,
our Central European wild Boar, is so closely related to _S. vittatus_
that the Sardinian Boar might be looked upon as a variety of either the
one or the other. At any rate, Dr. Major recognises clearly in _Sus
vittatus_ the representative of the ancestral stock of which _Sus
scrofa_ is a somewhat modified offshoot.
The fauna of Europe consists, as I have mentioned, to a large extent of
immigrants from the neighbouring continents. This is especially
noticeable among the higher animals. When we come to the lower, such as
the amphibia, we find a larger percentage, and among the land mollusca
the great majority, to be of European origin. The foreigners are, as we
learned, called Orientals, Siberians, and Arctics. For the sake of
convenience, only two of the great European centres of origin have a
chapter devoted to themselves, namely, the Alpine and the Lusitanian
centres. There is another, however, of almost equal importance which
lies in the east.
In the British Islands there is only an exceedingly small and
insignificant group of species which are peculiar, and which we may
consider to have had their origin there. Almost the whole of the British
fauna is composed of streams of migrants which came from the north,
south, and east, though many of these immigrant species have since their
arrival been more or less distinctly modified into varieties or local
races.
The eminent French conchologist Bourguignat (_a_, p. 352) was of opinion
that, as far as terrestrial mollusca were concerned, there are in Europe
three principal centres of creation or dispersion--all situated in
mountainous countries and not in the plains. He distinguished the
Spanish, Alpine, and Tauric centres, and believed that almost all
species known from Europe had originated in one of these three, and that
each of them possessed quite a distinct type of its own. This theory
seems to agree very well with the facts of distribution. Let us take,
for instance, the genus _Clausilia_, a pretty turret-shaped snail, which
abounds on old ruined walls. Only two species, viz., _Cl. laminata_ and
_Cl. bidentata_, are met with in Ireland. In England we find the same
species with the addition of two others, _Cl. biplicata_ and _Cl.
Rolphii_. Crossing over the Channel to Belgium, these four species occur
again, and also several others not known in England. In Germany the list
of _Clausiliae_ mounts up to twenty-five species, including all those
found in the British Islands. As we proceed eastward the number of
species of this genus increases steadily, and when we reach the Caucasus
or the Balkan Peninsula the conchologist is able to make a collection
of several hundred different kinds, whilst farther east again they
diminish. This clearly indicates there is in South-Eastern Europe a
powerful centre of creation of _Clausiliae_, from which the species have
spread all over Europe. But it is by no means certain that this centre
was always in our continent, for in South-Eastern Asia and the Malay
Archipelago _Clausiliae_ increase once more. It is interesting to note,
however, that almost all these eastern forms belong to the sub-genus
_Phaedusa_ (_vide_ Boettger), which had only been known as a fossil genus
from a few species in the Eocene and Oligocene of Southern Europe. The
first centre of origin, therefore, may possibly have been in Southern
Asia, and in these early Tertiary times a second centre may have become
established in Southern Europe from which the sub-genus _Garnieria_ went
eastward, _Macroptychia_ southward, and _Nenia_ westward across the
Atlantic to South America. Only a few remnants of these primitive
_Clausiliae_ are now left in Europe, such as the interesting _Cl.
(Laminifera) Pauli_.
As an example of a genus which has its centre of distribution in
South-Western Europe we might take that to which our common brown garden
slug belongs, viz., _Arion_. Dr. Simroth, who was the first to point out
that the species of _Arion_ had spread over our continent from
South-Western Europe (p. 5), is inclined to the belief that the
_Arionidae_ had originated on the old land-bridge between Europe and
North America, which is generally known by the name of "Atlantis." From
this a branch went westward to the New World and another eastward as far
as Southern Asia, but _Arion_ and a number of other genera are more or
less confined to South-Western Europe. Only a few species of _Arion_
have a wide range in Europe, one of them, _A. subfuscus_, crossing the
borders of our continent into Siberia. In the British Islands and in
Western Germany, which are about equi-distant from the supposed creative
centre of the genus, there are found five species. In France six or
seven species are met with, and in Spain and Portugal about ten. Towards
the east, _Arions_ diminish in number. This genus, therefore, forms part
of a migration which I have designated as "Lusitanian" from _Lusitania_,
the name applied by the Romans to what we now call Portugal. Another
genus of slugs, _Geomalacus_, is interesting from the fact that one
species occurs in the British Islands, being otherwise confined to the
Lusitanian province. Parmacella, a slug-like animal bearing a tiny shell
at the extremity of its tail, has probably likewise had its origin in
this part of Europe. All this, however, will be more fully referred to
in the seventh chapter, which deals with the Lusitanian fauna.
As regards the Alpine centre of origin, Dr. Kobelt considers three
groups of mollusca as especially characteristic of the Alps, viz., the
sub-genus _Campylaea_ of the great and widely-spread genus _Helix_, and
the genera _Pomatias_ and _Zonites_. The latter, which is not to be
confounded with our British _Hyalinia_ (formerly united with _Zonites_),
does not extend very far south or north of the Alps. There may be others
too, which owe their origin to these mountains, but most of the
terrestrial mollusca are exceedingly ancient, and many genera have
existed long before the Alps had made their appearance above the surface
of the early Tertiary seas. It should be remembered that _Hyalinia_ and
_Pupa_, both British genera, are known from carboniferous deposits in
forms which closely approach those living at the present day, and in
these and a great number of other instances, it is quite impossible to
determine the original home of the genus.
This little digression on centres of dispersion will help us to
understand in what manner the indigenous element of the European fauna
joined in with the alien members as they arrived in our continent. The
species confined to South-Eastern England need not necessarily have come
to us from Eastern Europe or Siberia. Alpine species spread northward
probably at the same time as the Siberian animals went westward. An
Alpine form may therefore have joined a batch of the latter and entered
England with them. Even a Lusitanian animal may have mingled with these
migrants, so that all three elements may occur together in one locality.
But these are exceptions. The migrations have, as a rule, not joined to
any great extent; indeed, all those naturalists who have carefully
examined the problem of the origin of the European fauna, have felt
that it was composed of elements which arrived at different times.
The great Russian naturalist, the late Professor Brandt, distinguished
five phases in the history of the Eurasian mammalian fauna (pp.
249-254). During the first phase--an uncertain period of long
duration--the mammals held intact their position in the northern half of
Asia. The Mammoth, the Hairy Rhinoceros, Bison, Musk Ox, Wild Sheep,
Reindeer, and perhaps Tigers, Hyaenas, etc., lived then, with numerous
peculiar Rodents, under such climatic conditions, according to Brandt,
that they were able to extend their range along with tree vegetation to
the extreme north of the Asiatic continent. This, he thinks, seems to
have been the case especially with the Reindeer, Mammoth, Rhinoceros,
and Musk Ox. The second phase was characterised by the dispersion of the
Northern Asiatic mammalian fauna towards Central, Southern, and Western
Europe, and this period lasted until the complete extermination of the
Mammoth. The third phase dates from the time when the Mammoth and the
Hairy Rhinoceros had become extinct, whilst the fourth commenced with
the disappearance of the Reindeer in Europe, and terminated when the
Wild Ox in the feral state had become unknown. Finally, the last phase
constitutes the present time. Lartet held similar views, and also
believed that Europe was peopled by successive migrations from Asia.
Botanists have worked at the problem of the European flora much more
systematically, and our knowledge of the origin of that flora has been
greatly increased within the last twenty years, chiefly by the
researches of Professor Engler. More recently, detailed studies have
been made in Scandinavia by Professor Blytt, in the Alps by Dr. Christ
and Mr. Ball, in Germany by Professor Drude, Dr. Schulz, and many
others. Dr. Schulz (p. 1) is of opinion that the great majority of the
European plants have either migrated to or have originated in our
continent since the beginning of the Pliocene epoch, and that the
original home of the immigrants must be looked for in Asia and in Arctic
America. From the latter an almost uninterrupted migration must have
taken place during the greater part of Tertiary times up to the
commencement of the Pliocene epoch, partly over a direct land-connection
with Europe by way of Greenland, Iceland, and the Faroes, and also _via_
Spitsbergen, Franz Josef Land and Novaya Zemlya, and partly by an
indirect one across the Behring Straits between Alaska and Kamtchatka.
A good deal of work still requires to be done before zoologists have
acquired the same intimacy with the European fauna as botanists have
with the flora. However, the view that our animals all come from Asia,
as was long ago believed, has been abandoned for some time. The first to
bring under the notice of naturalists the hypothesis, that there must
have been two distinct migrations of northern animals to Central
Europe--one from the north, and another from the east--was the late Mr.
Bogdanov. The Arctic species, of which remains have been discovered in
the Pyrenees--namely, the Reindeer, Arctic Hare, Willow Grouse, etc., he
thought had nothing to do with those which invaded Europe from Siberia
during the Glacial period. He maintained that the former had quite a
distinct origin, and came from Scandinavia (p. 26).
As I shall deal with this problem more fully in a subsequent chapter, I
need only mention that I fully agree with the view expressed by Mr.
Bogdanov that two distinct migrations of northern species to Central
Europe can be traced.
No one, I think, has done more in fostering a careful study of the
migrations of animals than our distinguished geologist Professor Boyd
Dawkins. He did not follow Bogdanov in distinguishing two Arctic
migrations; however, he did more in constructing a very ingenious chart
(_a_, p. 111) representing the geography of Europe during the last and
most recent geological epoch--the Pleistocene--and indicating on it the
probable extent, during that time, of an eastern and a southern
migration of mammals. The map is very instructive, and is the first ever
published giving a clear idea of a southern and an eastern migration to
Europe. He believed that the migration of the southern mammals
northward, took place conjunctly with the westward movement of the
eastern species. Having once reached Europe, the southern species are
supposed to have passed northward in summer time, whilst the eastern
forms (he calls them northern) would swing southwards. The two
migrations would thus occupy, at different times of the year, the same
tract of ground (_a_, p. 113). From the mingling of the remains of the
Hyaena with those of the Reindeer and Hippopotamus in the Kirkdale
Cavern, he infers that the former preyed upon the Reindeer at one time
of the year, and on the Hippopotamus at another. He argues that in such
a manner might be explained the curious mixture of northern and southern
types which we find in the British pleistocene and in cave deposits.
Besides mammals, the only European animals which have received some
attention with a view to a study of their origin, are the Butterflies
and the Land-Snails. The entomologists who have taken up the problem
have in so far scarcely produced satisfactory results, as they all
seemed to be bound down to the hypothesis that practically all the
butterflies had been destroyed in Europe during the Glacial period.
Hofman, in his interesting little work, comes to the conclusion (p. 50),
that only in Greece and Spain could a small remnant of the butterflies
have survived the extreme rigours of climate. Greece was at that time
connected with Asia Minor, and Spain with North Africa; and the author
supposes that the semi-alien fauna inhabiting these tracts was mainly
responsible for the re-stocking of Southern Europe, but that the main
mass of our butterflies are post-glacial Siberian immigrants.
The work published by Messrs. Speyer deals only with the origin of the
Central European Butterflies. The period during which our European
species originated is not specified, but the authors believe that they
had their home either in Southern Russia or Central Asia. The fact that
the number of butterflies decreases very considerably as we proceed
north-westward in Europe appears to them to substantiate these views.
The apparent dislike evinced by butterflies to the damp Atlantic Coast
climate, they think, clearly indicates that they had originated in a dry
and more continental climate. The history of the North European
Butterflies and Moths has been carefully described by Mr. Petersen. He
adopts Hofman's theory as to the almost total extinction of the
Lepidoptera in Europe during the Glacial period. The chief immigration
to Europe after that period is, he thinks, Siberian.
At first there appeared species which belonged to a cold climate, and
which now live in elevated regions; then came forms suited to a milder
climate, which established themselves on the north-easterly slopes of
the Alps. The most recent addition which our continent has received from
Siberia is, according to Mr. Petersen, the present Scandinavian fauna.
Scandinavia has obtained a larger number of species than the European
plain, because to this last migration were added such as prefer a
northern or Alpine climate.
As a contribution to the history and composition of the European fauna,
by far the most important work ever published is that of Dr. Kobelt, the
eminent German conchologist. Whilst the researches into the origin of
the Lepidoptera, above described, have been marred by the prevalent
prejudice as to the deleterious effects of a glacial climate on the
butterflies, the present author boldly works out the problem on
independent lines. He shuns theories and speculations almost altogether.
His great work, as yet practically unknown, the result of a lifetime of
the most painstaking labour, ranks among the most important
contributions to zoogeography. I shall have frequent occasion to refer
to it throughout these pages. Meanwhile some of his more remarkable
conclusions may be mentioned. "Comparing all classes of animals as to
their zoogeographical importance, the highest rank must undoubtedly be
accorded to the land-snails" (i., p. 7). "The Pleistocene, and with it
the land and fresh-water molluscan fauna of the present day has been
gradually evolved from the Tertiary one, and its roots can be traced
through the Cretaceous to the Jurassic epoch. During the whole of that
time no sudden appearance of a new fauna can be demonstrated. Quite
slowly, step by step, the Cretaceous is succeeded by the Tertiary fauna,
and one after the other of the characteristic palaearctic genera
appear--first the fresh-water, then the land forms" (p. 141). "The
division of the North Alpine from the South Alpine fauna must be older
than the Glacial period; and the present Central European fauna had
already become developed from the Pliocene _in all its details of form
and distribution_ before the commencement of the Ice Age" (p. 162). "We
must draw the conclusion from the preceding remarks, that the present
(palaearctic) molluscan fauna in its distribution is older than the
Glacial period, and that the latter produced merely a retreat of the
fauna from the most inhospitable regions of Europe with a subsequent
re-immigration, but did not cause its destruction" (i., p. 169).
A few attempts have also been made by naturalists to trace the origin of
the fauna of some smaller European areas. Thus Ruetimeyer, in dealing
with the mammalian fauna of Switzerland, remarks (p. 31) "that it seems
certain that, in spite of many local disturbances, the continuity of
generations was never interrupted throughout the whole of the Tertiary
period until the present day."
An even more interesting memoir is that of Mr. Koeppen on the origin of
the Crimean fauna. It is only recently, according to this author, that
this peninsula has become connected with Southern Russia. And it is for
this reason that the Squirrel and a number of other animals, and also
plants, present in Russia, are absent from the Crimea. Originally the
latter probably formed a westward continuation of the Caucasus, and at
that time it was surrounded by the sea on all other sides. "Much later,"
he continues, "after and in consequence of a local subsidence, the
country between the Caucasus and the Crimea became interrupted. The
latter existed for a long time as an island, and only much later, in
recent geological times, did it become united with Southern Russia by
means of the isthmus of Perekop."
There is, on the whole, a great diversity of opinion as to how the
European fauna has originated; however, except in Dr. Kobelt's work, no
attempt has hitherto been made to collect together all the available
information, and to include in the inquiry more than one class of
animals. The little work which I venture to bring before the public will
not by any means exhaust the subject, nor is our knowledge of the
European fauna sufficient to give more than a mere sketch of many of the
animal groups mentioned. As we have learned in the introduction,
different classes of animals are not all of equal importance in
indicating the changes which have taken place in the distribution of
land and water. While Dr. Kobelt is of opinion that the land-snails are
by far the most important in such an inquiry, Mr. Lydekker believes that
mammals afford the safest and truest indications of such changes. Mr.
Beddard puts in a claim for earthworms, as even a narrow strait of
sea-water forms an insuperable barrier to their dispersion. Dr. Wallace
agrees with Mr. Lydekker, and goes so far as to say (p. 74) that
"whenever we find that a considerable number of the mammals of two
countries exhibit distinct marks of relationship, we may be sure that an
actual land-connection, or at all events an approach to within a very
few miles of each other, has at one time existed." Besides the groups
referred to, I claim that particular attention should be devoted to
Amphibia, which, contrary to Wallace, I hold do not possess special
facilities for dispersal; and also to spiders and to all wingless
animals leading a subterranean life, such as some of the wood-lice,
planarian worms and apterous beetles.
A thorough knowledge of the changes in the distribution of land and
water is desirable in order to appreciate the extent and variations of
former migrations. A study of the British fauna, for example, teaches us
that the British Islands were once connected with one another and with
the continent of Europe between England and France. It was Professor
James Geikie, I believe, who first pointed out, many years ago, that the
area now covered by the Irish Sea was formerly in all probability a
fresh-water lake. This had its outlet at the southern extremity in the
form of a stream into which most likely flowed the smaller rivers from
the south-east of Ireland, and which was joined from the east by the
Severn, and finally debouched into the Atlantic (Fig. 4). The range in
the British Islands of those species which have migrated to them from
the south, indicates that whilst the Atlantic Ocean had gradually crept
up and flooded the area between Ireland and Wales, and had turned the
fresh-water lake into a bay, communication between Scotland and Ireland
was still possible. The occurrence of many Scandinavian species in
Scotland which are absent on the continent of Europe, indicates that
these two countries also were united formerly. Most geologists hold that
such a connection, if it existed, must have broken down in Pliocene
times. Professor Judd, however, has expressed his belief (p. 1008) that
it still existed until after the appearance of man in Northern Europe,
and that our forefathers might have been able to walk dry foot from
Scotland to Norway.
[Illustration: Fig. 4.--Map of the British Islands and surrounding area
at a time when the earlier members of the southern migration reached
England. (Only some of the rivers have been indicated. The shaded parts
represent water, the light land.)]
I shall also show on distributional evidence, in the fourth chapter,
that until recent geological times Scandinavia was continued northward,
by way of Bear Island, with Spitsbergen and probably Franz Josef Land,
which islands again were joined with North Greenland and Arctic North
America, and that the polar fauna and flora were able to spread on this
land-connection to both America and Europe.
That Gibraltar was connected with Morocco, and Sicily with Southern
Italy and Greece on the one hand, and with Tunis on the other, is more
generally recognised; whilst Professor Suess has shown (vol. i., p.
442), on purely geological grounds, that the Egean Sea was dry land up
till quite recently--certainly, he thinks, till after the appearance of
man. This supposition enables us to understand, as will be more fully
discussed in the sixth chapter, how the Oriental fauna entered Europe.
Such minor zoogeographical problems as the occurrence of the Wild Goat
of Asia Minor (_Capra aegagrus_) on the islands of Crete and on some of
the Cyclades now almost explain themselves. The Sea of Marmora is
probably a modern formation, so that Asia Minor extended not long ago
beyond the Turkish capital, but Dr. Kobelt believes that an arm of the
Black Sea communicated up till recent times along the lower course of
the Maritza with the Gulf of Saros. It can be shown also that Sardinia
and Corsica formed part of the continent of Europe, and that their
present fauna and flora reached them by migration on land.
The Russian naturalists, Brandt and Koeppen, believed that at no very
distant date a sea extended right across Eastern Russia from the Caspian
to the Arctic Ocean, whilst Professor Boyd Dawkins expressed himself in
very similar language as follows (_c_, p. 35): "Before the lowering of
the temperature in Central Europe the sea had already rolled through the
low country of Russia, from the Caspian to the White Sea and the Baltic,
and formed a barrier to western migration to the Arctic mammals of
Asia." These naturalists based their opinions on distributional
evidence, but additional facts will be brought forward in the fifth
chapter to substantiate these views.
These are some of the more important geographical events which will be
dealt with in detail in the subsequent chapters in connection with the
history of the migrations of the European fauna.
A separate chapter has been devoted to the British fauna and its origin,
since it plays a very important part in the evolution of that of our
continent. So essential is a thorough knowledge of this fauna, that I
think it would be difficult to understand, without it, the main
features of the great migrations; and I have before now expressed the
opinion that the British fauna forms the key to the solution of the
problem of the origin of European animals. We know that our British
species came to us by land--at least the bulk of them. But we want to
know what direction they came from, and at what time they arrived. When
Ireland became disconnected from Great Britain, and the latter from
Scandinavia and France, is another interesting problem. Professor Boyd
Dawkins has indicated to us a method of the special line of research to
meet such inquiries. "The absence," he says (_b_, p. xxix), "of the
beaver and the dormouse from Ireland must be due to the existence of
some barrier to their westward migration from the adjacent mainland, and
the fact that the Alpine hare is indigenous, while the common hare is
absent, implies that, so far as relates to the former animal, the
barrier did not exist."
Many members of the great Siberian invasion reached England, but Ireland
remained entirely free from these migrants. The assumption therefore
seems not unreasonable, that the latter country at the time of their
arrival was no longer joined to England. The great bulk of the Irish
fauna is composed of Lusitanian, Alpine, and Oriental immigrants, and
there is besides a distinctly Arctic or North American element. All
these, of course, must have established themselves in Ireland before
the Siberian fauna set foot in England, since it has been shown that a
continuous land-surface was necessary for their migration. Owing to the
perfect preservation of the remains of the Siberian migrants in recent
continental deposits, the history of that migration can be clearly
followed, and it is possible even to determine the date of its arrival
in England--in geological language at any rate. The time of the
colonisation of Ireland can be thus approximately fixed as having taken
place at a period prior to the arrival of the Siberian migrants in
England.
All those who have seriously studied the problems presented by our
British fauna--notably the late Professor Forbes, and more recently Mr.
Carpenter and myself--are agreed that the Lusitanian element is the
oldest, and that the newest is that which has come to us from the east.
The sequence of events in the British Islands was probably as
follows:--The first comers were the members of that fauna which issued
from South-western Europe; then came the Alpine, and at the same time
probably the Arctic and the Oriental; and finally the Eastern or
Siberian. The migrations of all but the last continued, uninterruptedly,
for very long periods.
The study of these migrations has convinced me that, though climate was
a powerful factor in the evolution or history of the European fauna, the
geographical changes which took place on our continent in later Tertiary
times exerted a yet stronger influence. The principal climatic
disturbance is generally supposed to have been the so-called "Ice Age."
So firmly rooted is the conviction, among naturalists of the present
day, of the enormous destruction which this period produced on our
European fauna, so that all animal life practically disappeared from
large areas of our continent, that it is desirable that we should now
shortly review the history of that remarkable period in order to
ascertain in how far these views are corroborated by facts. Frequent
reference, moreover, will be made throughout this work to the theories
connected with the Glacial period.
It has been stated by an eminent geologist that during part of the
Glacial period the climate was such that neither plants nor animals
could have existed in the British Islands. If that had been so, it is
evident that very few organisms could have even survived in France,
though a number of Arctic species might have dragged on an existence in
Southern Europe. At any rate, on the return of more genial conditions,
the Arctic species would undoubtedly have been the first to gain
admission to the British Islands, to re-people the arid wastes. Our
supposition that the Lusitanian element in the British fauna is the
oldest would therefore be wrong. From early Tertiary times onward, the
climate of Europe, which was then semi-tropical, gradually became more
and more temperate; until finally the Ice Age or Glacial period arrived,
during which, according to Professor J. Geikie--one of our highest
authorities on this subject--a great part of Northern Europe became
practically uninhabitable owing to the severity of the climate.
To enable us to judge better of the true value of the many hypotheses
which have been advanced to account for this supposed extraordinary fall
of temperature during the "Ice Age," we must compare the views of other
authorities with the one just quoted. I do not propose to discuss the
causes which have led to the production of the Glacial period--those
interested in these questions should consult the writings of Dr. Croll,
Professor J. Geikie, Professor Bonney, Mr. Falsan, and others--but
merely to give the climatic aspects from a physical, zoological, and
botanical point of view.
According to Professor Penck (_a_, p. 12), the nature of the glacial
climate can be determined by comparing the snow-line of the Glacial
period with that of the present day. The position of the snow-line is
dependent on two climatic factors--viz., precipitation and temperature.
We know the height at which snow must have lain permanently during the
Glacial period, or during the maximum phase of glaciation. If the Ice
Age had been produced solely by an increase of snowfall, as has been
suggested, Professor Penck tells us that then it must have snowed three
or four times as much as it does now. But he does not adopt the view
that the Ice Age is due to an increase of snowfall alone. His
calculations, based upon the height of the snow-line, tend to show that
a general decrease of temperature to the extent of from 4-5 degrees
Centigrade (all other atmospheric conditions remaining the same as now)
would be sufficient to give us back the Glacial period.
Professor Neumayr (p. 619) adopted a similar principle in determining
the temperature which prevailed in Europe during the Glacial period.
Snow now lies in the Pyrenees 1000 metres higher than it did then, 1,200
metres higher in the Alps, and 800 metres higher in the Tatra mountains.
Since the temperature in Central Europe decreases by half a degree
Centigrade for every 100 metres of elevation, it follows that if the
glacial phenomena had only been brought about by a decrease of
temperature without an increase of moisture, we should have had a
reduction of temperature during the Glacial period of six degrees
Centigrade in the Pyrenees, of seven degrees in the Alps, and of four in
the Tatra mountains. The general lowering of the temperature of Europe,
says Professor Neumayr, could not have amounted to more than six degrees
Centigrade. Moreover, he is of opinion that the very low snow-line in
the British Islands proves that even during the Ice Age a comparatively
mild climate prevailed there, and that the climatic conditions
generally, in the different parts of Europe, were relatively about the
same as they are now.
Professor J. Geikie does not give us his views as to the temperature of
the Glacial period, but he maintains that a lowering of the temperature
is evinced not only by the widespread phenomena of glaciation, but by
the former presence in our temperate latitudes of a northern fauna and
flora.
Mr. Charles Martins, who based his calculations on the temperature
during the Glacial period on the glaciers of Chamounix, concluded that
it only needed a lowering of the temperature to the extent of four
degrees Centigrade to bring the glaciers down to the plain of Geneva,
and in fact give us back the Glacial period. It need not surprise us,
therefore, that the French geologist, Mr. Falsan, the author of _La
periode glaciere_, is of opinion (p. 230) that the mean annual
temperature of France during the Glacial period was approximately from
6-9 degrees Centigrade, perhaps more. Close to the immense glaciers of
the Rhone, it might have been about six degrees. This is the actual mean
annual temperature of the South-west of Sweden and Norway, or the North
of Scotland.
Although all these investigations tend to show that the climate of
Europe during the Glacial period was by no means so severe as we are
often led to believe, yet there exists also a school of geologists who
maintain there was actually a higher temperature than at present. The
inconsistency of mentioning heat in connection with ice and snow is more
apparent, however, than real, for we must remember Tyndall's original
remark on this subject. It is the snow, he says, which feeds the
glaciers. But the snow comes from the clouds, and these again originate
from the vapours which the sun causes to be absorbed from the ocean.
Without the sun's heat, we should have no water vapour in the
atmosphere; without vapour, no clouds; without clouds, no snow; without
snow, no glaciers. The ice of glaciers, therefore, owes its origin
indirectly to the sun's heat. It has been supposed that if the sun's
heat diminished, larger glaciers would form than those existing to-day,
but the diminution of the solar heat would infallibly reduce the amount
of water vapour in the air, and would thus stop the very source of
glaciers.
Mr. Falsan even admits that without a change of the mean annual
temperature (p. 201) of Europe, the central portions of our continent
might at this period have enjoyed an insular climate. This more equable
and humid climate could, within certain limits, favour the development
of the ancient glaciers by increasing the snowfall and slackening the
summer rate of melting.
It seems evident then, according to these views, that with a
comparatively slight change of the atmospheric conditions in the British
Islands, we might have glaciers back again on all our highest mountain
ranges in England, Scotland, and Ireland. But a widespread belief seems
to prevail that the presence of glaciers implies a very low temperature.
Snow and ice, however, are formed as soon as the temperature falls below
freezing point; it does not matter whether there be 1 or 20 degrees of
cold. Winters with a few degrees of frost will be just as favourable for
the growth of glaciers as winters with the most severe cold.
Let us now see what the fauna and flora, as far as we know it, tell us
of the climate of the Glacial period. At the very outset of our inquiry
we are confronted with one very serious difficulty in the problem, and
that is the supposed occurrence of inter-glacial mild phases alternating
with colder ones during the Ice Age. At first, when traces of a
temperate flora and fauna were discovered intercalated between two
layers of boulder clay, their presence was explained by the supposition
of a mild inter-glacial period. The famous Forest-bed on the east coast
of England was also pronounced to be an inter-glacial deposit, though
not coming precisely under this definition. In a few places one such bed
was found, in some two or more, and in others none at all. Professor
James Geikie discovered the evidences of no less than five of such
inter-glacial epochs (p. 612) in Europe. Lest a reader of that author's
remarkable work on the Ice Age might carry with him the idea that his
hypotheses had met with general acceptance, a few quotations from almost
equally high authorities on glacial matters will be useful. "That the
glaciers," remarks Professor Bonney (p. 245), "were liable to important
oscillations seems to be proved, but whether the evidence suffices to
establish inter-glacial epochs, in the usual sense of the words, is more
doubtful. When the snow-fields, as in the Alps, were much more
extensive than they are at present, the glaciers which radiated from
them would be more sensitive to minor climatal change. Even now they
oscillate considerably. But during a Glacial epoch, an inch, either more
or less, of precipitation might mean a considerable advance or retreat
of the ice in the lowlands." French geologists look with even less
favour on Professor Geikie's theories. Mr. Falsan (p. 212) says that he
agrees with Messrs. Favre, de Saporta, Lory, de Mortillet, Desor, de
Lapparent, Lortet, Chantre, Benoit, Fontannes, Deperet, and many other
geologists, that there was only a single Glacial period, which,
according to each particular region, might be divided into several
phases, or into their equivalents--viz., one or more extensions of the
ancient glaciers. But, on the whole, the view that there was at least
one inter-glacial phase in the Glacial period meets with more general
acceptance among geologists, I think, though the other opinion agrees
much better with the nature of the fauna and flora as it has been
revealed to us from the pleistocene deposits.
The occurrence of the remains of such arctic species of mammals as the
Musk-Ox, Arctic Fox, Glutton, Lemming, and many others in these
deposits, is frequently held up to us by geologists as a proof of the
prevalence of an arctic climate while these beds were laid down. And
indeed this appears at first a most satisfactory explanation of the
phenomenon. But we must not judge the climate of Europe by their
presence alone. As I shall explain more fully in Chapter V., these
species invaded Europe owing to two circumstances. Firstly, because the
climate of Siberia was becoming colder, necessitating a southward
movement, with a consequent over-population in a reduced area; secondly,
because a new short route to Europe had been opened up for them about
the same time (see p. 221). An invasion of Europe therefore took place
from east to west. Similar invasions occur even at the present day,
though not caused by a change in our climate, for every now and then
immense flocks of the Siberian Sandgrouse emigrate to our continent. The
mammalian migrants referred to are not to be looked upon as constituting
the whole of our fauna at that time. Europe had a fauna of its own, and
these invaders merely mingled with our animals. There was, no doubt, a
keen struggle for existence, as the result of which the weaker in many
cases succumbed. The hypothesis, however, that these Siberian migrants
occupied an empty continent, forsaken by its pre-glacial inhabitants, is
not supported by any facts.
All those who have investigated the pleistocene fauna have been struck
by the extraordinary mixture of northern and southern types of animals.
Professor Dawkins attempted to explain these facts by the supposition
(p. 113) that "in the summer time the southern species would pass
northwards, and in the winter time the northern would sway southwards,
and thus occupy at different times of the year the same tract of ground,
as is now the case with the elks and reindeer." "In some of the
caverns," he continues (p. 114), "such as that of Kirkdale, the hyaena
preyed upon the reindeer at one time of the year, and the hippopotamus
at another."
A similar mingling of northern and southern faunas has also been
observed in France. Mr. Falsan tells us (p. 236), that the remains of
the mammals gathered and determined by Lartet and Gaudry belong partly
to species which have been wrongly regarded as indications of a severe
climate, and partly to such as are accustomed to a relatively mild
temperature. In several localities in France, viz., at Levallois, St.
Acheul, and Arcy, the remains of the Hippopotamus have occurred together
with those of the Reindeer; whilst, according to Sir H. Howorth, the
Lion has been found together with northern Voles at Bicetre, near Paris.
It is stated by the same authority (p. 115) that much the same
conditions exist in Germany. "The lion and the spotted hyaena, the
mammoth and rhinoceros, were found with the marmot, the suslik, the
lemming, the pica, and the reindeer." At another locality near Thiede,
remains of the Mammoth, woolly Rhinoceros, Horse, Ox, Reindeer, Arctic
Fox, Lemming, and Pica are met with in the same deposit. In quoting the
presence of these northern animals in Europe as evidence of an arctic
climate, we commit a fatal mistake. Indeed, breeders of animals and
those acquainted with zoological gardens know perfectly well that it is
much easier to keep a northern species in a southern climate, than a
southern species in a northern one. If in a Central European deposit
occur a mixture of northern and southern forms of animals, the presence
of the latter is more remarkable than that of the former. Logically, we
should look upon the occurrence of southern species in the north,
therefore, as supporting the view that a mild climate had induced them
to travel northward. The only indication, indeed, of the presence of a
Monkey in the British Isles in former times comes to us from the very
same strata which have also yielded the remains of the Siberian mammals.
Before I conclude the consideration of the pleistocene fauna, it may be
of interest to hear what Mr. Lydekker, one of our highest authorities on
fossil mammals, has to say on this subject. "The most remarkable feature
connected with this fauna is the apparently contradictory evidence which
it affords as to the nature of the climate then prevalent. The Glutton,
Reindeer, Arctic Fox, and Musk-Ox are strongly indicative of a more or
less arctic climate; many of the Voles (_Microtus_), Picas (_Lagomys_),
and Susliks (_Spermophilus_), together with the Saiga Antelope, appear
to point equally strongly to the prevalence of a Steppe-like condition;
while the Hippopotamus and Spotted Hyaena seem as much in favour of a
sub-tropical state of things. Many attempts have been made to reconcile
these apparently contradictory circumstances; one of the older views
being that while the tropical types of animals lived during a warm
interlude, they migrated southwards with the incoming of colder
conditions to the arctic type of fauna. Since, however, it has now been
ascertained that the remains of both tropical and arctic forms have been
found lying side by side in the same bed, it is perfectly certain that
such an explanation will not meet the exigencies of the case" (p. 300).
In Germany the remains of the Siberian mammals occur to a large extent
in a pleistocene deposit known as "loess," and the theory has of late
years gained ground that the latter is the fine dust-like sand
accumulated during an intensely arctic dry climate. That many of the
mammals discovered in the "loess" now inhabit the dry steppes of Eastern
Europe and North-Western Asia seems to lend support to this supposition;
but besides the mammals there are also land and freshwater shells in
this deposit. The molluscan fauna certainly indicates no
steppe-character, according to Dr. Kobelt (_b_, i. p. 166).
The attempt to utilise the Siberian migrants to Europe as indicators of
a severe climate there, certainly fails to establish conviction. But it
may be asked, surely the remains of the Alpine and Arctic plants which
have been found in pleistocene deposits must decide this question in
favour of one or the other hypothesis? Let us test it.
Plants being more directly affected than animals by changes of
temperature and rainfall, remarks Mr. Clement Reid (p. 185), give
evidence of the highest value when we inquire into former climatic
conditions. The severity of the climate during the Glacial period is
often assumed from the occurrence in pleistocene strata of such plants
as _Dryas octopetala_, some species of willow, the dwarf birch, and
others, which are now found in high latitudes and in the Alps, but are,
as a rule, absent from the plain of Northern Europe. Professor J. Geikie
goes so far as to state (p. 398) that it was unlikely that southern
England during the climax of the glacial cold had much if any vegetation
to boast of, and continues, "It is certain, however, that it was clothed
and peopled by an Arctic flora and fauna when the climatic conditions
were somewhat less severe, relics of that flora having been detected at
Bovey Tracey." He believes, therefore, that an Arctic flora took
possession of England as soon as the climate enabled it to live in the
country. Arctic plants, according to this explanation of the sequence of
events, were the first immigrants to reconquer the dreary, plantless
wastes and make them habitable for mammals.
Fortunately these views do not at all agree with those of many of our
leading European botanists and others entitled to have a voice in the
matter. Professor Warming is of opinion that the main mass of the
present flora of Greenland survived the Glacial period in that country
(p. 403); whilst Professor Drude has shown (p. 288) that all plant life
could not possibly have been destroyed in northern countries. He
maintains that the greater part of the Arctic floral elements which
unite Greenland and Scandinavia must have survived the Glacial period in
these countries in sheltered localities. Indeed, he justly remarks,
where at the present moment do we find such plantless wastes? Greenland,
Franz-Josef Land, and Grinnell Land, situated in high Arctic latitudes,
all have a flora composed of flowering plants and cryptograms. "I cannot
understand," he continues (p. 286), "why a flora, possibly mixed with
northern forms but in the main points agreeing with our present floral
elements, should not have persisted throughout the Ice Age even in the
heart of Germany." "To my mind," says Col. Feilden, the well-known
Arctic traveller (_b_, p. 51), "it seems indisputable that several
plants now confined to the polar area must have originated there, and
have outlived the period of greatest ice-development in that region."
The theory in favour of a survival of the pre-glacial flora has been
especially strengthened by the late Mr. Ball (than whom probably no
botanist possessed a better knowledge of Alpine plants), who was
strongly in favour of this view as far as the Alps are concerned. "Is it
credible," he says (p. 576), "that in the short interval since the close
of the Glacial period hundreds of very distinct species and several
genera have been developed on the Alps, and, what is no less hard to
conceive, that several of these non-Arctic species and genera should
still more recently have been distributed at wide intervals throughout a
discontinuous mountain chain some 1,500 miles in length, from the
Pyrenees to the Eastern Carpathians?" Mr. Ball's remarks, indeed, just
touch upon a very important characteristic of all the so-called _Alpine
plants_. In Europe they chiefly occur in Scandinavia and the central and
southern mountain ranges, whilst they are mostly absent from the
intervening lowlands. Again, we find a large number of species in the
mountains of Central Asia and in some of the North American mountains.
Almost all species of Alpine plants, in fact, are examples of
discontinuous distribution; and this, as every naturalist knows, is
always, in both animals and plants, a proof of antiquity.
The glacial or Alpine flora is very old, and must have originated long
before the Ice Age. But it might be urged, why should these plants be
now almost confined to the Arctic regions and the higher mountain
ranges, where the temperature undoubtedly is very low, if they had
originated during a pre-glacial period probably much milder than the
present? The answer can be given by those who have made Alpine plants
their special study, and who have attempted to grow them by
administering to them a temperature and such climatic conditions as to
be most conducive to good health. We should all expect these plants to
be very robust, and especially to be able to stand extremely low
temperatures. But, strange to say, the very opposite is the case.
Professor Blytt tells us (p. 19) that "Arctic and Alpine species in the
Christiania Botanic Gardens endure the strongest summer heat without
injury, while they are often destroyed when not sufficiently covered
during winter." The English climate then, one would think, ought to suit
these plants, since the winters are not too cold; but we find that at
Kew Gardens the large collection of Alpine plants have to be wintered in
frames under glass in order to keep them in good health; and Professor
Dyer, the Director of the Gardens, thinks they are mostly intolerant of
very low temperatures (compare also pp. 161-164).
Such being the constitution of Alpine plants, how could they possibly
have originated during the Glacial period and wandered from the
mountains into the plains, across numbers of formidable barriers, often
exposed to icy winds, for thousands of miles? As a matter of fact,
Alpine plants have survived in the high North and in the Alps because
they are there permanently protected during winter by a covering of snow
from very low temperatures, and they are at the same time prevented from
drying up. If they are given sufficient moisture and a constant, mild
temperature they seem to do very well. Such conditions are afforded them
in many parts of the British Islands, and we find indeed the Mountain
Avens (_Dryas octopetala_), one of the most typically Arctic plants,
growing wild in profusion on the coast of Galway, in Ireland, at
sea-level. The winter temperature of that part of Ireland resembles
that of southern Europe, being no less than 12 deg. Fahr. above freezing
point. This fact appears to strengthen the view not only that the Alpine
flora is of pre-glacial origin, but that the climate of Europe during
the Glacial period was mild.
Having now shortly reviewed the state of our knowledge with regard to
the former presence in our temperate latitudes of Arctic animals and
plants, it still remains for me to give a succinct statement of the
light thrown by this fauna and flora on the widespread phenomena of
glaciation. It is necessary to do so, because, though the greater
development of glaciers on the mountains of Europe in former times does
not presuppose the prevalence of an Arctic climate, the survival through
the Ice Age of a fauna and flora could not possibly have taken place in
northern Europe if the theories of glaciation now so much in vogue are
really true. Professor Geikie reminds us, in speaking of his native
country (p. 67), that "we must believe that all the hills and valleys
were once swathed in snow and ice; that the whole of Scotland was at
some distant date buried underneath one immense _mer de glace_, through
which peered only the higher mountain tops." That under such conditions
no fauna or flora to speak of could have survived in Scotland is
evident. Then again he argues (p. 426) that because in the great plain
of Europe we meet occasionally with striated rock-surfaces and _roches
moutonnees_ very similar to those produced by the glaciers of
Switzerland, it must have been traversed by "inland ice" flowing from
Scandinavia and the Baltic southward. The boulder clay of Germany is
supposed to have accumulated underneath this vast "_mer de glace_," as
he calls it. There is no question here of a simple local development of
glaciers, such as could have existed under a mild and moist climate;
practically all the plants and animals would have been annihilated in
northern Europe under such conditions, as there were no areas free from
ice. A more vivid idea of the state of Europe during the epoch of
maximum glaciation will be obtained by looking at Professor Geikie's map
(p. 437). The whole of Scandinavia, Iceland, Scotland, Ireland, and
Switzerland is there represented as having been completely enveloped in
ice, and also the greater part of Russia, Germany, and England. In
speaking of Scandinavia (p. 424) he remarks that "the whole country has
been moulded and rubbed and polished by one immense sheet of ice, which
in its deeper portions could hardly have been less than 5000 feet or
even 6000 feet thick." The greater portion of the area indicated as
having been underneath a sheet of ice is thickly covered with
superficial accumulations of gravel, sand, and clay. The latter is
generally spoken of as "boulder clay," and, with the associated sand and
gravel, it may be observed equally well in Russia or Germany, in England
or Ireland. As a rule these stony clays thicken out as they are traced
from the high-lying tracts to the low grounds; and especially near the
mountains the rock-surfaces are often polished and striated. "For many
years it was believed," continues Professor Geikie (p. 432), "that all
those superficial deposits were of iceberg origin. The low grounds of
Northern Europe were supposed to have been submerged at a time when
numerous icebergs, detached from glaciers in Scandinavia and Finland,
sailed across the drowned countries, dropping rock-rubbish on the way.
Such was thought to have been the origin of the erratics, stony clay,
and other superficial accumulations, and hence they came to be known as
the 'great northern drift formation.'" "But," he adds (p. 433), "when
the phenomena came to be studied in greater detail and over a wider
area, this explanation did not prove satisfactory. The facts described
in the preceding paragraphs--the occurrence of striated surfaces and
_roches moutonnees_, the disturbed appearances associated with the till,
and the not infrequent presence of giants' kettles--convinced geologists
that all the vast regions over which boulder-clay is distributed were
formerly occupied by the 'inland ice' of Scandinavia."
I think Professor Geikie over-estimates the value of the evidences which
appear to be in favour of his theory. His treatise on the Ice Age leaves
one under the impression that the older view of the marine origin of the
boulder-clay is not only done with for good and all, but that no
geologists nowadays believe in it. If a more careful study of the
glacial phenomena has led most geologists to abandon what I might call
the "marine view" in favour of the terrestrial one, a more careful study
of the fauna and flora will, I venture to think, have the opposite
effect. However, it appears that even from a purely geological point of
view more can be said in favour of the old theory than Professor Geikie
and his school are ready to admit. Thus we are told by Professor Bonney
(p. 280), in referring to the boulder-clay, that "the singular mixture
and apparent crossing of the paths of boulders are less difficult to
explain on the hypothesis of distribution by floating ice than on that
of transport by land-ice, because, in the former case, though the drift
of winds and currents would be generally in one direction, both might be
varied at particular seasons. So far as concerns the distribution and
thickness of the glacial deposits, there is not much to choose between
either hypothesis; but on that of land-ice it is extremely difficult to
explain the intercalation of perfectly stratified sands and gravel and
of boulder-clay, as well as the not infrequent signs of bedding in the
latter." "Anything," writes Professor Cole (p. 239), "that keeps open
the position maintained by Lyell and others, that extensive glaciation
is compatible with mild and sheltered nooks and corners, and that much
of the distribution of boulder-clay was performed in seas and not on
land, may be welcomed by rationalists, at any rate until further
research has been carried on among the Arctic glaciers. At present every
year brings evidence of modern marine boulder-clays in high latitudes,
and removes us farther and farther from belief in a _moraine profonde_."
That foraminifera are occasionally found in boulder-clay has been known
for a long time, but it is only within recent years that these marine
organisms have been shown to occur in so many localities, that Mr.
Wright, who examined a large number of samples, says (p. 269), "I am
forced to the conclusion that the Scottish as well as the Irish
boulder-clay is a true marine sedimentary deposit."
In the fourth and fifth chapters I shall return to this subject again,
and mention a number of facts of distribution which appear to me much
easier of explanation by means of the marine than by the land-ice
theory. But I do not propose to go into further geological details in
this volume, as I think I have clearly conveyed my position in this
controversy.
Before concluding this short review of the glacial problem, so far as it
affects the origin of the European fauna, I should like to refer to the
opinion of one who has devoted years to the study of the glacial
phenomena in the Arctic Regions, viz., Col. Feilden. "To a certain
extent," he says (_a_, p. 57), "all boulder clays at home are
fragmentary when compared with the boulder-bearing beds of Kolguev,
which we may safely assume are 50 miles in length by 40 in width, with a
thickness of not less than 250 feet, probably far more, all lying in one
undisturbed mass. It is suggestive that all the glacial deposits which I
have met with in Arctic and Polar lands, with the exception of the
terminal moraines now forming above sea-level in areas so widely
separated as Smith's Sound, Grinnell Land, North Greenland, Spitsbergen,
Novaya Zemlya, and Arctic Norway, should be glacio-marine beds.
Throughout this broad expanse of the Arctic Regions I have come across
no beds that could be satisfactorily assigned to the direct action of
land-ice; that is to say, beds formed _in situ_ by the grinding force
and pressure of an ice-sheet. On the contrary, so far as I can judge,
the glacial beds which I have traced over the extensive area mentioned
above have all been deposited subaqueously and re-elevated."
One of the strongest arguments that can be used against the view of the
marine origin of the glacial phenomena in Northern Europe seems to me
the fact that we find polished rock-surfaces far removed from the source
of glaciers, and so exactly resembling those produced at the present day
by our Alpine glaciers as to appear identical to the experienced eye.
Most of such striated and polished rocks occurring in the higher
mountain ranges of Scandinavia, and also of the British Islands, have no
doubt been actually produced by glaciers, whilst those in the plain,
sometimes hundreds of miles away from the mountains, must have
originated in a similar manner; that is to say, by a heavy mass of
material containing stones being slowly dragged over the rock-surfaces.
The weight which causes the stones to polish the latter is generally
ice, but it is quite conceivable that any other substance, especially if
it is in a semi-solid state, must act and operate in much the same way.
All polished rock-surfaces are carved by glaciers, because we can see
them done by glaciers every day, is the argument commonly used nowadays.
It was not so formerly. But Mr. Mallet and his views are almost
forgotten now; his name does not even appear in our great modern works
on the Ice Age. His argument was that as the land rose out of the
glacial sea, the mud which had accumulated round the shore slipped
downward in a direction determined by the contour of the surrounding
valleys and mountains. The moment the land rose above water-level, the
large mass of gravel and mud lying upon it slipped downward. During a
steady rising of the land there would therefore be produced a continuous
sliding down of this mud-glacier, which would groove and polish the rock
underneath it, in the same manner as the ice-glaciers do in the Alps (p.
47). Professors Sedgwick and Haughton became strong adherents of Mr.
Mallet's theory at the time, but it seems later on to have fallen into
disfavour with geologists, who may not even be thankful to have it
brought to light again.
SUMMARY OF CHAPTER II.
I have endeavoured to show in this chapter how we can determine
approximately the original home of an animal. By this means we are able
to study the component elements of the European fauna, which is found to
consist to a large extent of migrants from the neighbouring continents.
There is a Siberian, an Oriental, and an Arctic element in it. The
remainder of the fauna is derived from local centres of dispersal. What
was formerly believed to have been one great northern migration now
resolves itself, on closer study, into two very distinct ones--the
Siberian and the Arctic. The mammals have received most attention
hitherto, because their remains are so frequently met with, thus
enabling us more easily to investigate their past history; but
butterflies and snails have not been neglected, and at least one very
remarkable work on the latter has been published dealing with their
origin in Europe and in the remainder of the Palaearctic region.
The former distribution of land and water is intimately connected with
the origin of the European fauna, and the changes which have taken place
in this respect may be best traced by the present distribution of
mammals, snails, and earthworms. In this manner the British Islands may
be shown to have been connected with one another and with the Continent;
Spain with Morocco across the Straits of Gibraltar; Greece with Asia
Minor, and so forth.
The British fauna has played such an important part in the evolution of
the European fauna, that it forms the key to the solution of the wider
problem. In it five elements are recognisable, of which the Lusitanian
element is the oldest, and the Siberian the most recent. It has been
deemed advisable to conclude this chapter with a short review of the
history of the Glacial period in its climatic effects on the animals and
plants of Europe. A number of writers are quoted who have conducted
special researches in determining the temperature of our continent at
the time. The fauna of Europe is frequently described as having been of
an Arctic nature, but as a matter of fact there existed during the Ice
Age a striking and most remarkable mingling of a northern and a southern
fauna. The presence of Siberian mammals in Europe is said to have been
due to the prevalence of a dry steppe climate, but this view is not
supported by other evidence. The Alpine flora in a wide sense is
probably pre-glacial in origin, and appears to have survived the Ice Age
where it is now known to exist. A few words on the phenomena of
glaciation are added before bringing the chapter to a close.