The History of the European Fauna
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Title: The History of the European Fauna
Author: R. F. Scharff
Release date: July 23, 2010 [eBook #33236]
Language: English
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_THE CONTEMPORARY SCIENCE SERIES._
Edited by HAVELOCK ELLIS.
THE HISTORY OF THE EUROPEAN FAUNA
THE HISTORY OF THE
EUROPEAN FAUNA
R. F. SCHARFF, B.Sc., Ph.D., F.Z.S.
_Keeper of the Natural History Collections, Science and Art Museum,
Dublin; Member of the Royal Irish Academy; Corresponding
Member of the Senckenbergische Naturforschende Gesellschaft._
WITH ILLUSTRATIONS.
LONDON
WALTER SCOTT, LIMITED
PATERNOSTER SQUARE
1899
CONTENTS.
PAGE
CHAPTER I.
INTRODUCTION 1-36
CHAPTER II.
PRELIMINARY CONSIDERATIONS 37-88
CHAPTER III.
THE FAUNA OF BRITAIN 89-131
CHAPTER IV.
THE ARCTIC FAUNA 132-188
CHAPTER V.
THE SIBERIAN MIGRATION 189-244
CHAPTER VI.
THE ORIENTAL MIGRATION 245-286
CHAPTER VII.
THE LUSITANIAN FAUNA 287-308
CHAPTER VIII.
THE ALPINE FAUNA 309-350
BIBLIOGRAPHY 351-354
INDEX 355-364
PREFACE.
Our knowledge of the present and past fauna of Europe is as yet
insufficient to indicate with precision the original homes of its
component elements, but I hope that the lines of research laid down
here, and the method of treatment adopted, will aid zoologists and
geologists in collecting materials for a more comprehensive study of the
history of our animals. I trust also that a fresh impulse will be given
by the publication of this book to the study of the Geographical
Distribution of Species. Collectors of Beetles, Butterflies, Shells, and
Fossils may derive some useful hints by its perusal and thus direct
their studies, so as to add, by accuracy in observation, to our
knowledge of the former geographical revolutions which have moulded our
islands and continents. To geographers, a survey of some of the more
important changes in the distribution of land and water in past
times--based upon the composition of our fauna--will be interesting. The
subject, however, is a complex one. I have ventured to indicate a
suitable method of treatment, and as such this attempt to elucidate the
history of the European fauna should be received.
This work was written as the outcome of a paper published in the
_Proceedings of the Royal Irish Academy_ (3rd series, vol. iv., 1897),
"On the Origin of the European Fauna." A summary of that paper appeared
in _Nature_ (vol. lvi., 1897), and fuller extracts of more important
parts, with some criticisms, in the _Geological Magazine_ (N.S., sec.
iv., vol. iv., 1897). I freely acknowledge the value of these
criticisms, which have largely assisted me to amplify and to improve
upon the ideas laid down in the paper.
I have found that it greatly facilitates comprehension of the arguments
used, to give a few maps indicating in a general way the extent of
former seas and continents. I may in this way, as Mr. Kendall has
pointed out, have submerged many square miles of land which had never
been covered by the sea,--at least not within recent geological
times,--but the maps were intended as illustrations of my views in a
broad spirit only.
Some zoologists may be surprised that, in some cases, I have not
followed the latest views in revised nomenclature. I felt that in a work
of this kind it was of supreme importance to employ names still current
in our leading text-books, such as _Lepus variabilis_ for the Mountain
Hare, instead of _Lepus timidus_. After each chapter I have endeavoured
to give a short summary of contents, while a bibliography of the
principal works and papers consulted will be found at the end. I should
also acknowledge the aid which I have received from such excellent
works of reference as the British Museum Catalogues of Birds, by Dr.
Bowdler Sharpe, and those of Reptiles, Amphibia, and Fishes, by Dr.
Guenther and Dr. Boulenger. The valuable works on Mammalia by Sir W.
Flower, Mr. Lydekker, Mr. Greve, and Dr. Trouessart, were indispensable
to me.
To Sir William Flower, Mr. Lydekker, Professor Sars, and Professor
Smitt, I am especially indebted for allowing me to reproduce drawings
from their works, and to my friend Mr. Welch for some beautiful
photographs. The Council of the Royal Irish Academy also kindly gave me
permission to reprint the maps used in illustration of my paper.
Professor Haddon first suggested my writing this book, and gave me many
useful hints; and great assistance was rendered me by my colleague, Mr.
G. H. Carpenter, in revising the proofs. To both of these kind friends I
desire to acknowledge my deep sense of gratitude.
R. F. SCHARFF.
THE HISTORY OF THE EUROPEAN FAUNA.
CHAPTER I.
INTRODUCTION.
Every student of natural history, whether he be interested in birds,
butterflies, or shells, contributes his share of facts which help to
show how the fauna of his country has originated. The capture of a
Swallow-tail or of a Marbled White Butterfly in England at once
furnishes material for reflection as to the reason of its absence from
Scotland and Ireland. Why should the Nightingale allow its beautiful
song to be heard in England, and never stray across the Channel to the
sister isle or cross the borders of North Britain? Lovers of bird-life
and sportsmen, who have observed the habits of the Ptarmigan in the wild
mountain recesses of Scotland, are aware that nowhere else in the
British Islands do we meet with this interesting member of the grouse
family, and many no doubt have allowed their minds to dwell upon the
causes of its singularly local distribution.
All these animals have a wide range in other parts of the world. In
past times, before man began to make observations on the geographical
distribution of birds and butterflies, or even before the appearance of
man in Northern Europe, they may have lived all over the British
Islands. For some reason or other they are perhaps dying out or
withdrawing towards their original home, which may either be northward,
or to the east or south. If we had some clue as to their former history
from fossil evidence--or, in other words, if their remains had been
preserved to us in geological deposits,--we should have less difficulty
in deciding this problem. But butterflies are scarcely ever preserved in
a fossil state, and birds very rarely. We know little or nothing,
therefore, of their past history from direct evidence, and are obliged
to trust to indirect methods of research which will be indicated later
on.
Mammals and Snails tell us their story more plainly. The bones of the
former and the shells of snails are easily preserved, and thus furnish
us with the necessary data as to their past history, for we find them
abundantly in most of the recent geological deposits. Among the mammals
of the British Islands there are some instances of distribution which
much resemble those I have quoted. Thus the Arctic Hare (_Lepus
variabilis_) is in the British Islands confined to Ireland and to the
mountains of Scotland; and if it were not for the fact that its bones
have been discovered in a cave in the south-west of England, we should
perhaps never have known that, formerly, it must have inhabited that
country as well. Of other mammals we possess fossil and also historical
evidence of their having once lived in these islands. Such are the Wolf
and the Wild Boar, both of which were abundant in Great Britain and
Ireland. The latter is a distinctly southern species. We assume this,
because its remains have never been found in high northern latitudes;
nor does it now occur in Northern Europe or Northern Asia, whilst all
its nearest relatives live in sub-tropical or tropical climates. The
Arctic Hare, on the contrary, has probably come to us from the north.
Its remains are unknown even in Southern Europe, and the more we
approach the Arctic Regions, the more abundant it becomes. Thus we have
here two instances of British mammals, one of which, the Wild Boar, has
died out--as it were in a southerly direction; whilst the other, the
Arctic Hare, is apparently retreating towards the north.
There are also some British mammals of which we have no fossil history,
at least of which no remains have as yet been found in these islands.
Such a one is the Harvest Mouse (_Mus minutus_). It has a somewhat
restricted range in England, and only just crosses the Scottish border
in the east. From the rest of Scotland and from the whole of Ireland it
is absent. To judge from this distribution, in connection with the fact
of its being unknown as a British fossil species, it is probably a late
immigrant to England, and has not had time to spread, throughout
Scotland at any rate. But it is also absent from Scandinavia, from the
Spanish peninsula, from almost the whole of Italy and the Alps, as also
from the Mediterranean Islands, whilst the little mouse occurs
abundantly right across Siberia. We shall learn more about centres of
dispersion later on; meanwhile I should mention that such a distribution
indicates that the Harvest Mouse has most likely originated in the east,
and has spread from there westward in recent geological times.
Conchologists have long ago been acquainted with the fact that many
molluscs, for example the so-called "Stone-cutter" Snail (_Helix
lapicida_) and the "Cheese Snail" (_Helix obvoluta_), have a very
restricted range in the British Islands. Both are entirely absent from
Scotland and Ireland, the Cheese Snail being confined to South-eastern
England. The Stone-cutter has rather a wider range, is even known from a
Welsh locality, and is met with as far north as Yorkshire. Their
distribution would indicate, therefore, that while both are recent
immigrants, the Cheese Snail is probably the last comer. This
supposition is in so far supported by fossil evidence, as the latter is
unknown in the fossil state, whilst the Stone-cutter has been described
by Messrs. Kennard and Woodward (p. 243)[1] as occurring in the cave
deposit known as the Ichtham fissure, and also from several English
pleistocene and holocene deposits. The Stone-cutter can scarcely be
looked upon as a very recent immigrant in the light of this evidence,
though we have no proof of its having ever had a much wider range in the
British Islands than it has to-day.
Among the lichens, which so abundantly cover the rocks and trees in
South-western Ireland, and which impart such a characteristic feature to
the scenery, we find a beautifully spotted slug (_Geomalacus
maculosus_).[2] It is a stranger to the rest of the British Islands, and
indeed occurs nowhere else in Northern Europe. We have to travel as far
as Northern Portugal before we again meet with it, and it is there also
that its nearest relations live.
Many more similar examples might be quoted, but enough, I think, has
been said to show that the British fauna is made up of several elements
whose original homes may lie widely apart and in different directions.
We have fossil evidence that some of the northern species, and also a
few of the southern ones, have become extinct within comparatively
recent times; others are apparently on the verge of extinction, whilst
many not only maintain their position in the constant struggle for
existence, but are even extending their range.
The problem of tracing the origin of the British fauna, or at least that
of some of the more characteristic members of every section or element,
appears at first a somewhat difficult task. Indeed, the means of
dispersal of the various groups of animals are so different that it
occurred to me it might be better to deal with the mammals, the birds,
the reptiles, and so forth, all separately. This idea I have attempted
to follow to some extent, with most satisfactory results. The British
fauna of the present day is no doubt complex, but no more so than the
fauna of the most recent of our geological deposits--the Pleistocene.
However, when we go back still further and look at the earlier Tertiary
remains, we find the fauna becoming less complex. Northern species
disappear, and the strata are entirely filled with the remains of
southern animals and plants. Geologists indeed are quite unanimous in
their belief, that the fauna of the British Islands during the earlier
epochs of the Tertiary Era was a southern one; that it then gradually
became more temperate, until at last, in more recent times, decidedly
northern forms invaded the country. These seem to have driven out--to
some extent at least--the southern species; but more recently again, the
southerners, reinforced by an eastern contingent, appear to have gained
territory and are advancing into the area held by the northerners. The
eastern invasion does not seem to have affected Ireland at all, and we
find the country there divided between the southern and northern
animals. We can thus roughly construct a map as I have done here,
showing, by means of horizontal and sloping lines, the principal areas
inhabited at the present time by the species of northern, southern, and
eastern origin (Fig. 1).
[Illustration: Fig. 1.--Map of the British Islands, indicating
approximately the areas inhabited by the northern, southern, and eastern
animals. The horizontal lines represent the areas of northern species,
the sloping lines those of southern and eastern ones.]
In the problems which are being discussed in this work I have often
found it of advantage, in order to facilitate the comprehension of the
arguments used, to give maps. Some of these represent the geographical
conditions at the particular epoch referred to in the text, but they
merely claim to give a general idea. There was never any intention to
make them correspond with all the data of which we have geological
evidence. They are what I might call "diagrammatic." In comparing them
with reconstructions of former physical geography such as have been
attempted from time to time, I hope geologists will therefore deal
leniently with the faults I may have committed, and remember that the
maps are "impressions," or "diagrams," and not faithful representations
of all the geographical revolutions witnessed by some of our remote
forefathers at any particular period.
The knowledge we gain from a study of the British Tertiary deposits
enables us to affirm positively that both the eastern and the northern
species arrived in these islands comparatively recently, but that the
southern forms must have migrated northward from the Continent long ages
ago. Since the northern and the eastern migrations--that is to say,
those coming from the north and east--were the last to arrive in
Northern Europe, the remains of the animals contained in the most recent
deposits of that portion of our continent will furnish us with a clue as
to the extent of the area inhabited by them. This is not all, however.
It is also possible to discover from these remains the direction which
the animals that they belonged to came from. As we shall learn later
on, a migration on a vast scale entered Europe during the Pleistocene
epoch--the most recent of the geological epochs, during which great
extensions of glaciers occurred in the mountainous regions of Europe.
The latter period is known to us as the Ice Age or Glacial period. This
will be described more fully in Chapter II., meanwhile I may mention
that we presume that this migration came from the east, because no
remains of the members of that particular fauna are known from Spain,
Southern Italy, Scandinavia, Ireland, or from the Balkan peninsula. The
number of species evidently belonging to this same migration, moreover,
become fewer as we proceed westward, and a large proportion of them
still inhabit Northern Asia, though most of them are now extinct in
Europe. After having thoroughly studied such a recent geological
migration, we learn to understand others better, though the more ancient
they are, the fewer are the traces and the more difficult are they to
follow.
Then again we have to take into consideration the fact, that whilst
mammals, particularly the larger herbivores, are forced to migrate
frequently owing to scarcity of food or temporary changes of climate,
many of the invertebrates remain practically unaffected by either. Most
of our land mollusca, for instance, are satisfied with meagre provender,
and stand extremes of climate well, as long as there is sufficient
moisture. As a result of their peculiar disposition, many of them, no
doubt, have survived through several geological epochs, and have
witnessed vast geographical revolutions in their immediate surroundings,
whilst mammals are comparatively short-lived. Being driven from one
country to another, and exposed to innumerable enemies, new types appear
and old ones rapidly vanish; in fact, there are almost constant changes
in the mammalian fauna as we pass from one epoch to another.
I have until now referred more particularly to the British fauna and the
North European in general, because the history of our own animals
interests us all more than those of any other European area. It is,
moreover, preferable to commence our investigations into the origin of
the European fauna by the study of a small district. This should, if
possible, be an island. If we took a slice of the continent like France
or Germany, we should find the problem more complex. Instead of choosing
the British Islands, we might, however, take an island like Corsica or
Sardinia. In either of these we should discover peculiarities in the
composition of their fauna precisely similar to those which I have
indicated to be present in the British fauna. We should find probably a
more striking endemic[3] element, which with us is so meagre that it
can almost be left unnoticed; the main features, however, remain nearly
the same. The fauna of both of these islands is composed of a strong
southern element, of an eastern and a northern one, and in addition we
have here species whose ancestors lived in Western Europe.
Before investigating more minutely the problems suggested by the
composition of the faunas of these insular and also of some continental
areas, it is necessary that we should thoroughly understand all about
the migrations of animals. One of the principal objects of this work is
to show how the autochthonous animals of Europe, _i.e._, those which
have originated there, may be distinguished from the immigrants, and to
trace the latter to the home of their ancestors. But in doing so, it is
necessary to refer to the many important geographical changes which have
occurred in Europe during the latest geological epochs. The study of the
geographical distribution of the European fauna, as expounded in this
work, will in many instances confirm the theories as to geographical
changes based upon geological foundations. But in every case the views
herein advocated are founded upon the geographical distribution of
living and extinct organisms alone.
A terrestrial mammal like the deer can, under ordinary circumstances,
only reach one part of a country from another by walking or running to
it; but a beetle, such as the cockchafer, has two different modes of
progression. It may walk or fly. In both, however, there is a third mode
of transport--an involuntary one. The deer may be suddenly seized by a
flood whilst crossing a river, and carried far away without necessarily
coming to grief. The beetle in a similar manner could be transported to
a distant country, or it might be caught in a whirlwind and blown
hundreds of miles off.
We may thus distinguish between the natural or active and the accidental
or passive means of distribution of animals. The active mode of
dispersal again may be only migratory, as in most animals, or periodic
and migratory, as in some birds and fishes. It is of course the tendency
of every species to spread in all directions from its original home,
provided it does not encounter obstacles, such as want of food,
unsuitability of climate or soil, or barriers such as mountains, rivers,
or the sea. Birds might be thought to be little interfered with by any
of these barriers, but, as Dr. Wallace has shown, they are almost as
much affected by them in their distribution as mammals are.
This then is the ordinary migratory distribution. Periodic distribution
obtains with migratory birds and fishes. The annual flight of swallows
to their northern summer residence comes under the heading of periodic
migration or distribution, but apart from this, the swallow must seek to
extend its range by the ordinary method, like every other animal.
Similarly, the herring migrates periodically into shallow water to
spawn, only to return again to its deeper home, where, as its numbers
increase, there must be a tendency to spread. We have in these cases,
therefore, both a periodic and an ordinary movement of migration.
Now, in studying the composition of a fauna, and especially its origin,
it is of the utmost importance to be able to determine approximately the
percentage of accidental arrivals and of the ordinary migrants--that is
to say, of those which have reached the country owing to accidental
distribution, and of animals which have adopted the usual course of
migration. It is of all the more import to review this subject of
accidental, or, as Darwin called it, "the occasional means" of
distribution, as both he and Dr. Wallace have, I venture to think,
somewhat over-estimated its significance. No one doubts that accidental
transportal takes place, but the question is whether the accidentally
transported animals arrive living and reach a spot where suitable food
is procurable, and whether they are able to propagate their own species
in the new locality. For it must be clear to anybody that the accidental
transportal of a beetle or of a snail to a new country cannot affect its
fauna or add one permanent member to it unless all these conditions are
fulfilled. As a matter of fact, only exceedingly few instances are on
record of man having witnessed, for example, the accidental transportal
across the sea to an island of a live animal.
To mention an example, Colonel Feilden informs us (_Zoologist_, 1888)
that, when living on the island of Barbadoes, an alligator arrived one
day on the shore, and at the same time a tree measuring 40 feet in
length, which was recognised as a Demerara species, was likewise
stranded. He thinks that there can be no doubt that the alligator, which
was alive when it reached Barbadoes, was transported by the tree, thus
covering a distance of 250 miles from the nearest land. Numerous
observations on the accidental transportal of seeds and tree-trunks from
one island to another, and from a continent to an island, have been
recorded, and even on our own shores we may witness the occasional
arrival of such vegetable products from a far distant land. On the west
coast of Ireland it not unfrequently happens that large West Indian
beans are stranded, and in this as well as in many other similar cases
the seeds have often proved none the worse for their prolonged immersion
in sea-water. That locusts are sometimes blown to great distances from
the land is not so surprising, since their power of steering through the
air is very limited. Darwin mentions (p. 327) having caught one 370
miles from the coast of Africa, and that swarms of them sometimes
visited Madeira. Sir Charles Lyell relates that green rafts composed of
canes and brush-wood are occasionally carried down the Parana River in
South America by inundations, bearing on them the tiger, cayman,
squirrels, and other quadrupeds.
But though actual observations of such abnormal instances of the
dispersal of animals are few, many experiments have been made to
demonstrate the possibility of a passive transportal of species over
wide distances. It was especially Darwin who gave a great stimulus by
setting the example to those interested in natural history in the
conduct of such researches. He was struck by the fact that, though
land-shells and their eggs are easily killed by sea-water, almost all
oceanic islands, even the smallest and most isolated, are inhabited by
them, and felt that there must be some unknown but occasionally
efficient means for their transportal (p. 353). To quote his words: "It
occurred to me that land-shells, when hibernating and having a
membranous diaphragm over the mouth of the shell, might be floated in
chinks of drifted timber across moderately wide arms of the sea. And I
find that several species in this state withstand uninjured an immersion
in sea-water during seven days: one shell, the _Helix pomatia_, after
having been thus treated and again hibernating, was put into sea-water
for twenty days, and perfectly recovered. During this length of time the
shell might have been carried by a marine current of average swiftness
to a distance of 660 geographical miles. As this _Helix_ has a thick
calcareous operculum, I removed it, and when it had formed a new
membranous one, I again immersed it for fourteen days in sea-water, and
again it recovered and crawled away. Baron Aucapitaine has since tried
similar experiments: he placed one hundred land-shells, belonging to ten
species, in a box pierced with holes, and immersed it for a fortnight
in the sea. Out of the hundred shells, twenty-seven recovered. The
presence of an operculum seems to have been of importance, as out of
twelve specimens of _Cyclostoma elegans_ which it thus furnished, eleven
revived. It is remarkable, seeing how well the _Helix pomatia_ resisted
with me the salt-water, that not one of fifty-four specimens belonging
to four other species of _Helix_ tried by Aucapitaine, recovered. It is,
however, not at all probable that land-shells have often been thus
transported; the feet of birds offer a more probable method."
We have here positive evidence that such shells as _Helix pomatia_ and
_Cyclostoma elegans_ might easily be transported to an island from the
mainland. The former occurs in France, Holland, and England, and the
latter all along western continental Europe and England. And yet neither
of these species inhabits the Canary Islands, Madeira, or Ireland, none
of which are at too great a distance from Europe to be within easy reach
for a floating object. The fact that _Cyclostoma elegans_ does not live
in Ireland is of particular interest in connection with the
floating-theory just quoted, as on all sides of Ireland dead specimens
have been picked up on the shore, showing that marine currents carry
specimens and have thus transported them for countless centuries.
Nevertheless the species has not established itself in Ireland. If such
a fate meets a land-shell of the type of _Cyclostoma elegans_, it may be
asked, with some justification, what chance slugs or the smaller
non-operculated species would have to reach an island like Ireland
alive from the mainland, and to colonise it successfully.
Both slugs and their eggs are killed by a short immersion in sea-water,
as I have proved experimentally. I have also subjected slugs, in the act
of crawling on twigs, to an artificial spray of sea-water. This seemed
to irritate their tender skins to such an extent that they curled
themselves up, released their hold on the twig and let themselves drop
to the ground. If we supposed, therefore, that a slug had successfully
reached the sea, transported on a tree-trunk, the moisture would tend to
lure it forth from its hiding-place under the bark, whilst the mere
spray would prove fatal to its existence. Those species of snails and
slugs which lead an underground existence, rarely venturing above
ground, such as _Testacella_ and _Coecilianella_, would have even less
chance of being accidentally carried to some distant island.
The suggestion advanced by Darwin (p. 353), that young snails just
hatched might sometimes adhere to the feet of birds roosting on the
ground and thus be transported, appears to me so extremely improbable as
to be scarcely worth serious consideration. Indeed, as Darwin himself
acknowledged later on, it does not help us very much to suggest possible
modes of transport. What we require is direct evidence. How far we are,
however, from obtaining it, may be inferred from Mr. Kew's remark (p.
119), that "we have little or no actual evidence of precise modes of
dispersal even for short distances on land."
A very curious statement was made by a well-known French conchologist,
the late M. Bourguignat, with regard to introductions of mollusca.
Whether he had any actual facts collected in support of it, I cannot
say, but he maintained that species accidentally transported, with the
exception of those under maritime influence, can only be acclimatised
from north to south, and not from south to north--from east to west, but
not from west to east (p. 353).
The whole theory of the accidental or abnormal dispersal of mollusca
appears to have been originated by Darwin, in order to account for their
presence on so-called _Oceanic islands_. His views were strongly
supported by Wallace, who defines these islands (p. 243) as those which
are of volcanic or coralline formation usually far from continents,
entirely without indigenous land mammals or amphibians, but with a fair
number of birds and insects, and usually with some reptiles.
I do not wish it to be understood that I am in any way undervaluing the
great works of these distinguished naturalists. Darwin's views have had
more influence in advancing Zoology than those of any man, and his fame
is unassailable. Nevertheless, I feel that his theories regarding the
origin of the faunas of oceanic islands require revision.
The formerly prevalent belief of the permanence of ocean basins has been
shaken by the utterances of some of the greatest geologists of our day,
whilst many positively assert that what is now deep sea of more than
1000 fathoms was dry land within comparatively recent geological epochs.
Thus the Azores are classed by Darwin and Wallace among the oceanic
islands--that is to say, among such as have received their fauna and
flora by flotsam and jetsam. But Professor Neumayr believes, on
geological grounds, that the Old and New Worlds were connected by a
land-bridge during Tertiary times right across the Atlantic, and that
the Canary Islands, Madeira, and Azores (p. 547) are the last remnants
of this continent. This meets with the entire approbation of Dr. von
Ihering, who has recently re-investigated the subject from a faunistic
point of view (p. 135). Take another instance of one of Wallace's most
typical oceanic islands, the Galapagos Group. Their fauna and flora have
recently been most thoroughly re-explored by an American expedition, the
result of which, according to Dr. Baur, goes to show that these islands
must have formed part of the mainland of South America at no distant
date. The fauna and flora are therefore to be regarded as having reached
them in the normal mode, viz., by migration on land. According to Mr.
Beddard (p. 138), it is difficult to see how earthworms could be
transported across the sea. Floating tree-trunks have been observed far
out at sea, but unless the water remained absolutely calm during the
long period necessary for the drifting by currents so that no splashing
occurred, the worms would probably be killed. Yet earthworms do occur
on oceanic islands. It is indeed quite possible that our views with
regard to the origin of the remainder of the Pacific Islands may change
very materially, and once more revert to what Dr. Gould expressed nearly
fifty years ago in the following words: "From a consideration of the
land-shells on the Pacific Islands, it seems possible to draw some fair
inferences as to the relations of the lands which once occupied the area
of the Pacific Ocean, and whose mountain peaks evidently now indicate or
constitute the islands with which it is now studded." Indeed Dr. von
Ihering goes so far as to positively state that in his opinion the
Polynesian Islands are not volcanic eruptions of the sea floor, which
being without life were successively peopled from Australia and the
neighbouring islands, but the remains of a great Pacific continent,
which was in early mesozoic times connected with other continental land
masses (_a_, p. 425).
Before coming to a decision on the part played by flotsam and jetsam in
the constitution of an island fauna, those who have studied the problem
on the spot should, however, have a voice in the matter. And though,
from my experience in northern latitudes, I feel sure that island faunas
there are but slightly affected by occasional dispersal of species, Mr.
Hedley, who has made the fauna of the Pacific Islands his special study,
assures me that drift migration plays an important _role_ in that
region. I hope we may soon have a more detailed account of his
particular observation bearing on this interesting subject.
On the other hand, Mr. Simpson, who has gained considerable experience
of oceanic dispersal in the West Indian region, though he acknowledges
having often noticed bamboo rafts, which would be suitable in the
transportal of invertebrates, nevertheless does not attach much
importance to this means of distribution. "The fact," he remarks, "that
the operculates (operculate land-shells) form so large a proportion of
the Antillean land-snail fauna, that a majority of the genera are found
on two or more of the islands and the mainland, while nearly every
species is absolutely restricted to a single island, appears to me to be
very strong testimony in favour of a former general land connection" (p.
428).
Amphibians are affected in the same manner by sea-water as slugs are.
The accidental transportal of an amphibian from the mainland to an
island is therefore almost inconceivable. And the presence of frogs,
toads, and newts in the British Islands, in Corsica and Sardinia,
indicates, if nothing else did, that all these islands were at no
distant date united with the continent of Europe.
As regards the terrestrial reptiles, the case is somewhat different.
Many of them readily take to the sea, and, as probably all snakes and
some lizards are able to swim, it is possible that sometimes, though
very rarely, they might reach islands if not too far from a continent.
Instances of accidental transportal of land-reptiles to islands have
actually been observed. But the fact of the occurrence of such instances
by no means proves that reptiles thus conveyed are able to establish
themselves permanently in their new home. Sir Charles Lyell records in
his _Principles of Geology_ that a large boa-constrictor was once seen
floating to the island of St. Vincent, twisted round the trunk of a
tree. It appeared so little injured by its long voyage from South
America, that it captured some sheep before it was killed.
Mammals might be accidentally conveyed to islands on such rafts as have
been described by Sir Charles Lyell, and there are instances on record
of their having crossed short distances of sea by swimming. Elephants
and also deer and pigs are good swimmers, the former having been known
to swim for six hours at a stretch. "But," remarks Mr. Lydekker (p. 13),
"it may be assumed that about twenty miles is the utmost limit which
mammals are likely to cross by swimming, even when favoured by currents.
Such passages as these must, however, be of very rare occurrence, for a
terrestrial mammal is not likely to take it into its head to swim
straight out to sea in an unknown direction. Moreover, supposing a
mammal, near to a particular island, to have arrived there by swimming,
unless it happen to be a pregnant female, or unless another individual
of the same species but of the opposite sex should arrive soon after (a
most unlikely event), it would in due course die without being able to
propagate its kind."
All zoologists, indeed, are quite in accord with Dr. Wallace's view as
expressed in _Island Life_ (p. 74). "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." As all the European islands come under this
category, their mammals exhibiting distinct relationship with those on
the European continent, they all have been connected with it formerly.
Perhaps the most powerful of all agents in the transportal of species by
accidental means is man. But his actions may be accidental as well as
intentional. We have therefore to distinguish between the animals
disseminated all over the world by pure chance, and those which have
been introduced into new countries purposely. Invertebrates, such as
snails, centipedes, woodlice, beetles, and cockroaches, are constantly
being unintentionally carried with vegetables, fruit, trees, and with
timber from one country to another. Earthworms are sometimes transported
in the balls of earth in which the roots of trees are enveloped. As
regards molluscs, Mr. Kew believes (p. 178) that during the last three
centuries at least, human agency has influenced their disposal more than
all other causes taken together. A large number of species of
invertebrates in America are said to owe their existence in that country
to accidental introduction by man. In most cases, however, no
particular reason can be assigned why they should have been thus
introduced, and as a matter of fact there are always individual
differences of opinion as to the precise number of such. Certain it is,
that though the number of supposed introductions from Europe to America
is very large, those which have been carried from America to Europe is
exceedingly small. In fact, I remember only two instances of accidental
animal importations from America which have firmly established
themselves in Europe, viz., a small fresh-water mollusc, _Planorbis
dilatatus_, and the much-dreaded vine-pest, _Phylloxera vastatrix_.
As a rule the animals die out very shortly after their arrival on
foreign soil. Many instances, nevertheless, are on record, especially in
the case of molluscs, where snails thus transported have not only
survived but are apparently in a flourishing condition and spreading.
_Helix aspersa_, for example, our large garden snail, has been
naturalised in many foreign countries by French and Portuguese sailors,
who had taken them on board their ships as food.
It certainly cannot be denied that a number of species among almost all
groups of invertebrates have been unintentionally conveyed by man from
Europe into foreign countries. It has been proposed by Dr. von Ihering
to apply the term "cenocosmic" to those species which have become spread
all over the world through artificial means, and thus to distinguish
them from cosmopolitan ones which have attained a similar range
naturally. The latter he calls "palincosmic" species (_a_, p. 422). Many
so-called cenocosmic ants are believed by Dr. von Ihering to be
palincosmic. We are altogether too apt to regard cosmopolitan as
synonymous with introduced, and we should hesitate before concluding
that because one of our common European species occurs in Australia or
South America, it must have been transported there recently by human
agency. Some of our widely-distributed forms are probably of very great
antiquity, and may have spread to distant lands in early Tertiary times,
when a different state of the geographical conditions enabled them to do
so.
I cannot quote a more appropriate instance than the molluscan fauna of
Madeira. No less than thirteen of the Madeiran snails are looked upon as
having been introduced from Europe by human agency, on the sole evidence
that these happen to be common European species. Yet the correctness of
this supposition must be questioned in face of the interesting
observation made by Darwin (p. 357), "that Madeira and the adjoining
islet of Porto Santo possess many distinct but representative species of
land-shells, some of which live in crevices of stone; and although large
quantities of stone are annually transported from Porto Santo to
Madeira, yet this latter island has not become colonised by the Porto
Santo species. Nevertheless, both islands have been colonised by
European land-shells, which no doubt had some advantage over the
indigenous species." Darwin, therefore, meets the evident anomaly by
suggesting that the European species are supposed to possess some
advantages as colonisers. But the true explanation appears to me to lie
in the supposition that the European land-shells found in the Madeiran
Islands are all, or for the greater part, ancient forms which survived
both there and on the continent, whilst the remainder of the forms
inhabiting these islands are either such as are now extinct in Europe,
or have become modified since their arrival there from the continent at
a time when extensive land-connections allowed a free migration by land.
The theory of accidental introductions is an extremely popular one. It
allows free scope to a host of speculations, and once the idea has taken
firm root that a certain species is introduced, especially among the
class of naturalists who by way of experiment are wont to create new
centres of dispersion in their own neighbourhood, evidence to the
contrary must be of the most convincing nature to shake the popular
belief. Thus, it is almost regarded as an established fact by
conchologists and others, that the fresh-water mussel (_Dreyssensia
polymorpha_) was introduced into England at the beginning of this
century. Though it has been proved that this species is quite unable to
live in pure sea-water, yet the view that it has been carried from the
Black Sea ports to this country attached to the bottom of ships is
maintained by many, whilst others incline to the theory that the shell
came with timber. But _Dreyssensia polymorpha_ was by no means always
confined to the Caspian and Black Sea areas; it occurs abundantly in the
lower continental boulder-clay (see p. 230), and no doubt it had at one
time a much wider geographical distribution. It appears to me possible,
that it was able to maintain itself in certain fresh-water lakes and
slow-flowing rivers in Northern Europe, from which it might have spread
since the introduction of canals into Europe at the beginning of the
century. As the larva of this fresh-water mussel is free-swimming, its
propagation is much favoured by canals. Quickly-flowing rivers are fatal
to its existence, since the delicate larvae are swept out to sea and
perish. Such an hypothesis as this is strengthened by the fact of its
recent discovery in a sandy layer fifteen feet below the present surface
under the streets of London in a deposit which probably, as Mr. Woodward
remarks (p. 8), was accumulated in the early days of the city's
existence. In spite of Mr. Woodward's interesting find, and Dr.
Jeffreys' opinion, who always maintained that this shell was indigenous
to England, popular belief still clings tenaciously to the introduction
theory.
Among man's intentional introductions into a new country, no instance is
better known than that of the rabbit to Australia. Rabbits are entirely
confined to Europe. In their transplantation to Australia they were
carried to a country with a different climate and among new
surroundings. Yet the rabbits flourished, and within comparatively few
years increased to such an extent as to become a burden and pest to the
country. It may be remembered though, that, owing to the complete
absence of small carnivores, which act with us as a check upon the too
rapid increase of this rodent, the speed with which it established
itself in the new surroundings is not so very surprising.
Many of the English settlers in the New World felt that America lacked
the presence of our familiar birds. The homely sparrow was therefore
brought over, with the result that the Agricultural Department of the
United States is now devising means for its destruction, so rapid has
been its increase.
Similarly, the inhabitants of Jamaica, annoyed by the great profusion of
rats in their island, sent over to India for a number of mongoose. These
have decimated the rats since their arrival, but they have multiplied to
such an extent as to be a serious menace to the native fauna.
To give an instance nearer home, the Capercaillie (_Tetrao urogallus_)
was successfully introduced into Scotland in 1837. From its different
centres of distribution it is spreading in all directions where
sufficient cover is obtainable. But this case differs from the others
very materially, in so far as this bird was formerly a native of
Scotland, and only became extinct during the last century.
However, although there are many examples of undoubtedly successful
introductions by human agency, quite as many, or perhaps more,
unsuccessful ones might be quoted. In fact, it is by no means easy to
establish a species in any new locality. Frequently it happens that the
species seems to be on the increase at first, but then there is a
decline, and after a few years the new plantation has entirely vanished.
In other cases, the species disappears immediately after the
introduction takes place, or lingers on for many years if it receives
special and uninterrupted protection.
It may not be generally known that the English Hare (_Lepus Europaeus_)
is not found in Ireland, where the Mountain Hare (_Lepus variabilis_)
alone occurs. Attempts to acclimatise the English species have been made
in a number of places in Ireland, but many of them have been failures,
and not one of them has been a signal success.[4] Similarly, the
endeavour to introduce the French or Red-legged Partridge (_Caccabis
rufa_) into Ireland has met with a like result. According to Dr. Day, it
was tried during the summer of 1869 to naturalise the Sterlet
(_Acipenser ruthenus_) from Russian waters into the Duke of Sutherland's
River Fleet by importing artificially impregnated ova. From one hundred
and fifty to two hundred lively young sterlets are said to have been
turned out, but nevertheless the experiment met with no success. Several
fortunately abortive efforts were also made in British rivers to
establish _Silurus glanis_, a hideous monster of a fish, and quite
unpalatable.
The Natterjack Toad (_Bufo calamita_) has a very local distribution in
the British Islands. In Ireland it is found only along the coast of
Dingle Bay in County Kerry, where it is known among the peasantry as the
Black Frog. There is no doubt about its being indigenous there, and
though it has not spread beyond the very limited area of its habitat,
the Irish climate cannot be said to be unsuited to its existence. Yet it
seems to be extremely difficult to acclimatise it elsewhere, for though
no less than sixty specimens were turned out in Phoenix Park, Dublin,
about forty years ago, none of them were ever seen afterwards. They were
placed in the vicinity of one of the lakes, so as to give them ample
scope for breeding and developing the young, and in surroundings which
were considered eminently suitable at the time.
It has occasionally happened, too, that animals are introduced by
kindly-disposed persons with the view of adding a species to their
fauna, in complete ignorance of their previous existence in the country
where they wished to naturalise them. Thus we are told that in the year
1699 one of the Fellows of Trinity College, Dublin, procured Frog's
spawn from England in order to add that amphibian to the Irish fauna. It
was placed in a ditch in the College Park, whence the species is
supposed to have gradually spread all over the island. This story is
quoted by many writers as the true history of the Frog in Ireland, and
is given as an example of the rapidity with which animals spread.
Unfortunately the would-be introducer seemed unaware that, according to
Stuart's _History of Armagh_, the first Frog which was ever seen in
Ireland made its appearance in a pasture field near Waterford about the
year 1630, that is to say, seventy years before its introduction in
Dublin.[5] But even Stuart was mistaken in supposing that no Frog had
ever been seen in Ireland before, since Giraldus Cambrensis, in his
_Topography of Ireland_, mentions that a Frog was found in a meadow near
Waterford in the year 1187.
Certain British species of vertebrates are generally looked upon as
introduced species, though we cannot trace any record of their first
establishment, and it is quite possible that, though there was local
extinction and subsequent local re-introduction, they are truly
indigenous and may never have become totally extinct. Such are, for
instance, the Rabbit (_Lepus cuniculus_) and the Pheasant (_Phasianus
colchicus_). The latter certainly had become naturalised in England
before the Norman invasion.
But cases of introduction such as those above referred to are by no
means confined to the vertebrates, similar instances among invertebrates
being numerous enough. I am sure every naturalist is personally
acquainted with a good number, and it is hardly necessary that I should
quote in any detail after what has been said on the subject generally.
The two species of snails, _Helix pomatia_ and _Cyclostoma elegans_,
both of which occur in England, and which I had occasion to mention
among those experimented on by Darwin, were turned out in several
suitable localities in Ireland by Thompson, but failed to establish
themselves. The former, according to Mr. Kew, was also introduced into
Scotland and Norway, whilst fifty or sixty specimens were brought to
Petersfield in England, but none of these trials at acclimatisation were
successful. As among vertebrates, a large number of the so-called
successful introductions rest upon insufficient evidence.
When we once more carefully review the evidence as to the undoubted
difficulty attendant on intentional introduction of animals by human
agency, placed as they often were in most suitable localities, we must
feel that accidental introduction cannot play an important role in the
making of the fauna of any country. Especially is this the case with an
island fauna. Vertebrates are almost altogether excluded, and
invertebrates must arrive singly as a rule, often stranded on an
inhospitable and unsuitable shore. Their chances of surviving a passage
by sea, of finding suitable food and shelter and a mate in order to
procreate their species, appear to me infinitesimally small. Yet there
may be some such cases. However, I quite agree with Mr. Andrew Murray--a
high authority on geographical distribution--that "colonisation or
occasional dispersal is insufficient to account for the character of
the faunas and floras of oceanic islands; and I believe that the normal
mode in which islands have been peopled, has been by direct continuity
with the land at some former period, or by contiguity so close as to be
equivalent to junction" (p. 15). "That a slight intermixture," he
continues, "due to Mr. Darwin's colonisation, occurs in many (probably
in all) I am ready to admit; and from instances to be afterwards
noticed, I am disposed to reckon the proportions of such intermixtures
in the flora, in the most favourable circumstances, at not more than two
per cent. In the fauna I think it must be much less."
Mr. Murray's views, though they relate only to oceanic islands, are
likewise applicable to continental islands such as our own. I think we
might take the admixture in the British fauna due to occasional,
including human introduction, as amounting to five per cent. It is
better to take a high estimate, so as to include all the species about
whose native land there might be some reasonable doubt. Now of what
importance, after all, is this five per cent.? The remaining ninety-five
per cent. of the species of animals belonging to the British fauna
undoubtedly migrated to these islands in the normal way by land.
It is of great importance, in dealing with the question of the origin of
the British fauna, to thoroughly grasp this conclusion--_that
ninety-five per cent. of the animals have reached us by land_. We can
afford in fact to ignore the five per cent. altogether. It is an
insignificant factor. As regards the botanical aspect of the question,
botanists are quite in accord with the zoologists, and entirely share
their views in the belief of a former land-continuity between the
British Islands and the Continent. "It cannot be denied," says Professor
Blytt (p. 32), "that a plant of one or another species may, in an
exceptional case, migrate, without human assistance, all at once, across
large tracts of land and sea, and that such migration, if operating
during geological periods, might introduce a number of species even into
distant oceanic islands; but when the question is of whole communities
of plants, such as the above enumerated elements in our flora, then such
an accidental and sudden transport across large tracts can only be
conceived to be at all probable in the case of Arctic plants carried by
drifting ice to a bare country without native flora; as to the other
species, we must imagine that the _migration during the gradual change
of climate has proceeded slowly and step by step across connected tracts
of country_. In that manner we may assume that our country has in the
course of time obtained its present covering of plants. Each of the
above-named elements in our flora has doubtless its corresponding
element in our fauna. The fauna and flora of a region stand in relation
of complicated dependence to each other. The animals live on the plants.
The fecundation of the plants takes place in a great degree by means of
insects; their seeds are often scattered by resident birds and
quadrupeds. Everything indicates that _conveyance to small distances is
the rule_, and that sudden and long migration is the exception."
The conviction which has been gained by zoologists and botanists, that
the British Islands once formed part of the Continent, is based on the
present British fauna and flora. The remains, however, of animals which
used formerly to live in these countries, such as the Mammoth, the Irish
Elk, the Cave Bear, and many others, tell us the same tale. They could
not have peopled England by swimming across the Channel, or even by
walking across solid ice, as has once been suggested. Nothing but a
land-connection induced them to explore this country more closely, and
finally to decide on settling there.
The origin of the British fauna will be discussed more in detail in the
third chapter. The methods of investigation adopted, along with a
general scheme of this book, will be found in the next.
The manner in which the origin of the fauna of any particular
continental area can be traced is very similar to that adopted in the
case of an island. Portions of the continent of Europe can be shown to
have been islands in former times. Thus the Crimea, now a peninsula
united to the mainland by the narrow isthmus of Perekop, must have been
an island in comparatively recent times. The absence of a number of
striking and familiar South Russian species of mammals and reptiles
proves this to have been the case. It was probably long after the
appearance of man, though before historic times, that these changes
took place.
We shall learn in the subsequent chapters, that by a careful study of
the fauna and flora the fact can be established, not only of the former
connection of an island with a continent, but also whether such union
existed (geologically speaking) within recent or more remote times. The
better the fauna is known, both recent and fossil, the more precisely
can the period of connection be indicated, and its duration determined.
FOOTNOTES:
[1] The numbers in brackets throughout this work refer to the
page-number in the Bibliography at the end.
[2] A map giving its exact distribution in Ireland will be found on p.
300, and a figure of the slug on p. 298.
[3] The term _endemic_ will be employed throughout this work as applied
to species peculiar to a country and not found elsewhere.
_Autochthonous_ will be used in speaking of a species which has
originated in a country to which, however, it is not peculiar; _e.g._,
the Chamois is an autochthonous Alpine species, but occurs also in the
Pyrenees and Caucasus. An _indigenous_ species is one native to a
country, as opposed to the term "introduced," and is applicable to all
species which have reached it by ordinary migration.
[4] I might refer any one more specially interested in these
introductions to an article on this subject in the _Irish Naturalist_ of
March 1898, by Mr. Barrett-Hamilton.
[5] I should recommend those who are particularly interested in the full
history of the Irish frog to read the notes on this subject contained in
vol. ii. of the _Irish Naturalist_.
CHAPTER II.
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.
CHAPTER III.
THE FAUNA OF BRITAIN.
The British Islands are, as I have remarked, very suitable as a
starting-point for our investigations. Their fauna and flora are fairly
well known, and the distribution of the large animals at any rate, which
are of course of much importance in these researches, has been as much
studied as that of any other area in Europe. We possess in England an
abundance of the remains of past animal life, and a combination of the
data furnished by both of these important factors will enable us to draw
up a history of the origin of the present British fauna.
In the first chapter I indicated that in the fauna of the British
Islands three divisions or elements are recognisable--a northern, a
southern, and an eastern. These elements correspond to migrations which
can be proved to have arrived in this country at different periods in
past times. When we investigate these migrations more closely, the
eastern is found to be composed partly of European and partly of
Siberian species. The southern is made up of European and of Central and
Southern Asiatic species. To make matters still more complex, the
southern and eastern migrations insensibly merge into one another, so
that it is often very difficult to determine to which of them an animal
may belong. The European species spread principally from three centres
over Europe--viz., from the Lusitanian, Alpine, and the Balkan centres.
The southern element of the British fauna is therefore composed of
animals which have originated in these three centres, and in Central and
Southern Asia. The Balkan species have been included with those coming
from the latter centre under the term "Oriental" migration. The sixth
chapter is devoted to it, whilst the Lusitanian and Alpine migrations
have each a chapter to themselves.
The Arctic Hare is, as I have already mentioned, one of the mammals of
the northern element of the British fauna. It is now confined to the
mountains of Scotland and the plain and mountains of Ireland. But in
former times it had a wider range in the British Islands. The Stoat is
another distinctly northern mammal. It occurs with us, as Messrs. Thomas
and Barrett-Hamilton have pointed out, in two distinct varieties or
species, the one being confined to Great Britain, the other to Ireland.
As I shall explain more fully later on (p. 135), I have reasons to
believe that the Irish Stoat came from the Arctic Regions as a northern
migrant, but that the English Stoat, on the other hand, reached England
with the Siberian fauna from the east. A third northern animal, now
extinct in the British Islands, is the Reindeer. It is supposed to have
died out in these countries not very many centuries ago, and records
have been handed down to us that it still inhabited Scotland as late as
the thirteenth century. Like the Stoat, it occurred in two well-known
varieties, distinguished from one another by the shape and form of the
antlers. In the English pleistocene deposits the remains of both kinds
are met with mingled together, whilst in Ireland only one of them has
been found. The explanation of this case is similar to that of the two
stoats. One of the varieties, which we may call the northern one, came
to us from the Arctic Regions; the second wandered to the British
Islands at a later period, when Ireland had probably become separated
from England. It was therefore unable to penetrate so far west.
One of the most familiar examples of a northern British bird is the Red
Grouse (_Lagopus scoticus_). By most authorities it is looked upon as a
species distinct from the Scandinavian Willow Grouse (_Lagopus albus_),
but except in colour it is indistinguishable from it, and the eggs are
identical. The whole genus _Lagopus_ is a distinctly Arctic one, and
there can be no doubt that the British Grouse belongs to the northern
migration, just like the Arctic Hare. The Ptarmigan (_Lagopus mutus_)
and the Snow Bunting are also migrants from the north. Though as
resident British birds they are quite confined to Scotland, the remains
of the former have been found in a cave in the south of Ireland, showing
that its range in the British Islands was formerly more extensive.
Another bird which probably came to our shores with this same migration,
though it is now unfortunately extinct, is the Great Auk (_Alca
impennis_), of which some specimens have luckily been preserved in our
museums. From the occurrence of its remains in kitchen-middens and other
recent deposits, the Great Auk is known to have inhabited the coasts of
Scotland, Ireland, and Scandinavia, as well as those of Newfoundland.
Mr. Ussher recently found the bones of this bird near Waterford, which,
I believe, is the most southern locality known. The manner of their
occurrence leaves no doubt that the bird had been used as food by the
early races of man. In all probability it originated in the Arctic
Regions, and subsequently spread south on either side of the Atlantic.
We need not here refer to the many winter visitants,--northern birds
which appear regularly, or at more or less long intervals, in these
islands,--although in most of the ornithological works they are included
under the term "British Birds."
All the British reptiles and amphibia appear to have reached us from the
south or east, but among the fishes there are a good many northern
forms. The whole salmon family--the _Salmonidae_--are typical northern
immigrants. The Stickleback (_Gasterosteus aculeatus_), too, has
undoubtedly come to us from the north. The genus _Cottus_, like
_Gasterosteus_, is certainly Arctic in origin. Originally freshwater
forms, many species are now found between tide-marks, and of these a
few have migrated southward along the coasts of the great continents.
Thus we meet with various species of _Cottus_ as far south as California
and Japan, on the American and Asiatic coasts of the Pacific
respectively. In Europe, two species, viz., _C. scorpio_ and _C.
bubalis_, range as far south as the French coast. Our freshwater
_Cottus_, the Miller's thumb (_Cottus gobio_), has migrated to us from
the north with the Arctic species. All the freshwater forms, indeed, of
this genus are typically Arctic.
A large number of land and freshwater invertebrates too have no doubt
reached us from the north. Some of them may have originated in
Scandinavia or within the Arctic Circle, but others probably came still
farther, either from America or even from Asia, and used the Arctic
land-connection _via_ Greenland in their migration to Europe. As I shall
give a number of additional instances of such migrants in the succeeding
chapters, I need not, perhaps, dwell upon them now any longer, except to
mention a few of the more typical ones. _Vertigo alpestris_, a minute
snail with an amber-coloured shell, and our freshwater pearl-mussel,
_Unio (Margaritana) margaritifer_, belong to this migration. Then among
butterflies we may cite the Marsh-ringlet (_Coenonympha typhon_), and
among beetles, _Pelophila borealis_ and _Blethisa multipunctata_. There
are a number of northern spiders, among which a few certainly indicate
an Arctic origin, or at any rate, that they have wandered to Europe
across Greenland and the old Arctic land-connections. _Bathyphantes
nigrinus_, _Linyphia insignis_, and _Drapetisca socialis_, for instance,
are three British species whose range indicates a northern origin, and
which also occur, according to Mr. Carpenter, in North America. Mr.
Carpenter also tells me that the Collembolan, _Isotoma littoralis_, is a
typical northern migrant. He has recently discovered it in the west of
Ireland, its only station in the British Islands.
Among the crustacea, the genus _Apus_ forms an exceedingly interesting
illustration of the northern migration, _Apus glacialis_ having been
discovered in a Scottish pleistocene freshwater deposit, whilst it is
now almost confined to the Arctic regions.
To the same group of animals also belong the three remarkable species of
freshwater sponges, _Ephydatia crateriformis_, _Heteromeyenia Ryderi_,
and _Tubella pensylvanica_, which Dr. Hanitsch has described from some
lakes in Western Ireland. None of these are known from Great Britain or
from the continent of Europe. A few North American plants grow wild in
the same district. That any of these should owe their existence in
Ireland to accidental introduction appears to me exceedingly improbable.
In a former contribution to this subject (_a_, p. 475) I assumed that
these American plants and animals had migrated to Europe at the same
time as the other northern forms referred to. My friend Mr. Carpenter,
however, takes exception to this (p. 383), and I quite recognise the
force of his argument. "Their very restricted and discontinuous
ranges," he says, "along the extreme western margin of Europe mark them
as decidedly older than those northern animals and plants which have a
circumpolar distribution." We have indeed quite similar examples in the
Oriental migration, of which part is very ancient, surviving here and
there and exhibiting discontinuous distribution. We may therefore look
upon these American immigrants as among the oldest members of that
northern stock which have survived in our islands--probably a mere
remnant of a once luxuriant flora and fauna.
In order to show the importance of the Eastern or Siberian element in
the English, or, we might say with Dr. Sclater, the Anglo-Scotian
mammalian fauna, I herewith give a list of the species of mammals which
probably migrated to Great Britain from Siberia. I have marked with an
asterisk those which still exist in this country (not in Ireland), or
have become extinct within historic times.
Canis lagopus.
Gulo luscus.
* Mustela erminea.
* " putorius.
* " vulgaris.
* Sorex vulgaris.
Lagomys pusillus.
* Castor fiber.
Spermophilus Eversmanni.
" erythrogenoides.
* Mus minutus.
* Arvicola agrestis.
* " amphibius.
" arvalis.
* " glareolus.
" gregalis.
" ratticeps.
Equus caballus.
Saiga tartarica.
Ovibos moschatus.
Cricetus songarus.
Myodes lemmus.
Cuniculus torquatus.
Alces latifrons.
" machlis.
Rangifer tarandus.
We have evidence that most of these twenty-six species of mammals came
from Eastern Europe, but there is no reason to suppose that they
originated there. On the contrary, it is highly probable, as I said
before, that their native home is Siberia, and that they entered Europe
to the north of the Caspian. Along with these, vast numbers of other
forms of life, and also plants, swarmed into our continent, and as we
advance eastward from England we meet with them in increasing numbers to
the present day. But not only on the Continent do we find these
survivals of the great Siberian migration, which has been so ably
described by Professor Nehring; no less than nine species still inhabit
Great Britain (if we include the recently extinct Beaver). On the other
hand, not more than three have been found fossil in Ireland, and of
these only one still survives. This very significant fact will be
referred to again more fully on p. 153. Meanwhile it should be
remembered that these three species, viz., _Mustela erminea_, _Equus
caballus_, and _Rangifer tarandus_, occur in Ireland in varieties
distinct from those found in Central Europe. It is upon this, and many
other circumstances, that I founded my belief that Ireland was already
separated from England at the time of the arrival of the Siberian
emigrants in the latter country. As we shall see, the Irish Stoat,
Horse, and Reindeer probably came by a different route from that taken
by the English representatives of the same species.
Very few of the lower animals of Siberian origin have reached the
British Islands. Most of those which were formerly thought to be
Siberian are either of East European or of Central and South Asiatic
origin, though they probably joined the Siberian migration on their way
to England. The Arctic migration brought a greater variety of species to
this country than the Siberian, but neither the one nor the other has
contributed more than a small percentage to the British fauna. The bulk
of that fauna is derived from the various European centres of dispersal,
and especially from Central and Southern Asia.
Those animals which have their home in the latter area, I have named
Orientals, though it must be remembered that they need not necessarily
have come from what is known among zoologists as the "Oriental Region."
The terms "Oriental animals" and "Oriental migration" are used here in a
wider sense, and include even those species which reached Central and
Northern Europe from South-Eastern Europe. It is astonishing, what a
vast number of both vertebrate and invertebrate animals can be traced
back to this Oriental migration. Great tracts of Europe were repeatedly
submerged beneath the sea during Tertiary times, and on their
re-appearance were formed into green fields and pastures new for the
rich Asiatic fauna, which was ever ready to flood the neighbouring
continent. This went on, and not for a comparatively short space of
time, as in the case of the Siberian invasion; the immeasurable ages
which passed, whilst several of the Tertiary epochs dawned upon Europe,
witnessed an almost constant stream of Asiatic immigrants pouring in
upon us. Europe returned her own products in exchange, but they must
have been scanty in comparison to the enormous number of species which
have undoubtedly originated in Central and Southern Asia. Very many of
the widely distributed forms in the British Islands are of Oriental
origin. Among these are also the cosmopolitan species, such as the Barn
Owl (_Strix flammea_) and the Painted Lady Butterfly (_Vanessa cardui_).
A great number of our British Mammals, Birds, Butterflies, and Beetles
have come to us with the Oriental migration. But, as I shall explain in
the special chapter devoted to it, the earlier migrants from the
south-east found their northward progress barred by a great sea which
stretched through Central Europe from west to east. The Mediterranean
was then divided into two smaller basins. On their arrival in Greece,
which was then connected with Asia Minor and Southern Italy, the
Oriental migrants seem to have turned westward, skirting the shores of
the Mediterranean. When they finally reached Spain, many then changed
their course northward (see Fig. 5, p. 117) and wandered to the British
Islands with the Lusitanian animals which came from South-Western
Europe.
Dr. Wallace makes mention of a fairly large number of species and
varieties of Lepidoptera, Coleoptera, and land and freshwater Mollusca,
supposed to be _peculiar to the British Islands_. Even if these were all
found to be of British origin, most of their nearest relatives are
continental species. Many, however, must be looked upon as mere races or
sub-species of familiar continental forms. But others, such as
_Geomalacus maculosus_ and _Asiminea Grayana_, are by no means confined
to the British Islands. Some of the so-called varieties enumerated by
Dr. Wallace are merely slight individual variations in form and colour,
which, only by the extraordinary tendency of the variety-monger to
advertise himself, have received a distinct Latin denomination. The
number of the remaining species, after weeding out the unworthy ones,
will be found to be insignificant.
Similarly, the list of seventy-five species and varieties of flowering
plants included by Dr. Wallace among the forms peculiar to the British
Islands (p. 360) is reduced by Sir Joseph Hooker to twenty. The
remainder are to be considered as varietal forms of a very trifling
departure from the type, or as hybrids.
Just as we distinguish in the British Islands the parts inhabited by
Englishmen, Scotchmen, and Irishmen, so we can recognise three divisions
in the animal world, and these roughly correspond to the boundaries of
England, Scotland, and Ireland. Most of the eastern species inhabit
England, most of the northern ones are confined to Scotland, whilst
Ireland is occupied chiefly by southern animals. This, however, is only
a very rough-and-ready method of sub-dividing the British Islands into
their component parts according to the origin of their faunas. On closer
study such a division is found to be unsatisfactory. The eastern species
do not really stop at the Scottish frontier, they range far into
Scotland. Nor are the northern forms confined to the latter country.
Many of them range into Ireland, and also into England. I have
constructed a map of the British Islands showing approximately the
boundaries of the northern, eastern, and southern species (p. 7), but
even this may not altogether meet with the views of an ornithologist or
conchologist. For every group of animals the boundaries would probably
require to be marked differently. There is also a good deal of
overlapping, so that the attempt to define the limits of the various
elements meets with great difficulties. But the map represents, I think,
fairly well the general impression one receives as to the disposition of
its component elements, after a careful study of the British fauna as a
whole.
The distribution of the British plants has been worked out much more
thoroughly than that of the animals. It need not surprise us, therefore,
that the first attempt to separate the British Islands into natural
divisions was made by a botanist--the late Mr. Watson. As he himself
pointed out, in making these divisions he did not take into
consideration the origin of the British species. They represent merely
groups of assemblages of plants of different types of vegetation. Edward
Forbes, on the other hand, founded his districts on the origin of
plants. His work is not only the first of the kind, but it is a
classical essay, and remains one of the most remarkable contributions to
the literature on the geographical distribution of living organisms
known to science. The vegetation of the British Islands, he informs us
(p. 4), presents a union of five well-marked floras, four of which are
restricted to definite provinces, whilst the fifth, besides exclusively
claiming a great part of the area, overspreads and commingles with all
the others. These are--
I. Mountainous districts of South-west }
and West of Ireland. } Lusitanian type.
II. South-west of England, and }
South-east of Ireland. } Gallican type.
III. South-east of England.
IV. Mountains of Scotland, Cumberland, }
and Wales. } Scandinavian type.
V. General Flora. Germanic type.
Professor Forbes points out, in connection with the plants of the
Germanic type, that the fauna accompanying this flora presents the same
peculiarities and diminishes westward and to the north. This type
includes, therefore, almost all the species which can be shown to have
come to us directly from the east, few if any of which have penetrated
to Ireland.
On a previous occasion, the same author had divided the British Islands
into ten districts, according to the distribution of their molluscan
fauna. These are--
I. The Channel Isles.
II. South-east of England (including Cambridgeshire).
III. South-west of England.
IV. North-east of England.
V. North-west of England (including Isle of Man).
VI. North of Ireland.
VII. South of Ireland.
VIII. South of Scotland.
IX. North of Scotland.
X. Shetland Isles.
In a short paper on this subject (_b_, p. 5), I have shown that some of
these districts are founded on erroneous data, whilst, with the
knowledge now at our disposal, others can no longer be maintained as
distinct. I thought then that the molluscan fauna warranted a division
of the British Islands into the following two provinces:--
I. England and Wales (except the South-west).
II. South-west of England and Wales and the whole of Ireland and
Scotland.
The second district contains some species of molluscs which are almost
entirely absent from the first, such as _Geomalacus maculosus_,
_Testacella Maugei_, _Helix pisana_, _Helix revelata_, _Helix acuta_,
and _Pupa ringens_. These are all of Lusitanian origin, and do not occur
in Central Europe. Scotland alone cannot be classed as a separate
province, since it does not contain a single species peculiar to itself.
But, along with Ireland and the South-west of England and Wales, it is
distinguished from the remainder of these countries by the almost total
absence of what have been called Germanic types.
A French conchologist, the late Dr. Fischer, dealt with the British
molluscan fauna in a somewhat similar spirit (p. 57). He divided the
British area into two districts, but these differ from mine in so far as
the South-west of England and Wales and the West of Ireland form one;
the remainder of England and Ireland as well as the whole of Scotland
the other. His classification is of particular interest, since the first
district represents part of a larger Atlantic province, the second a
portion of the Germanic province of the European sub-region. The latter
he looks upon as one of the sub-regions of the great Palaearctic Region.
Attention is thus drawn to the intimate relationship existing between
the western parts of the British Islands and the Spanish peninsula on
the one hand, and between the eastern portions and Central Europe on the
other.
Mr. Jordan's North-Sea-and-Baltic district includes Scotland and the
North of Ireland, whilst England joined with the West and South of
Ireland forms part of his Celtic province. Both of these districts or
provinces belong to Mr. Jordan's greater Germanic Region (p. 302).
In the collection illustrating the geographical distribution of animals
in the Dublin Museum, the British species have been grouped into three
divisions. One contains those with a wide range over the British
Islands, another the characteristic forms of the south-east and lowland
districts of Great Britain, and the third the Irish and the western and
highland Anglo-Scotian species. Mr. Carpenter has named the last two
divisions the "_Teutonic_" and the "_Celtic_." More recently, he has
recognised that this last division contains two distinct groups; one
including animals of northern, the other those of southern origin. He
acknowledges indeed, just as I do, three distinct faunas in the British
Islands, with the addition of the group of generally distributed species
of undetermined origin.
Many other naturalists have worked in the direction I have
indicated--namely, in grouping the British animals into several distinct
assemblages, without, however, taking their foreign range into
consideration, or their origin. I have already referred to the useful
work done by botanists, who have been the pioneers in the science of the
geographical distribution of living organisms. Among the British
naturalists who have applied the principles of Watson to zoology, A. G.
More deserves to be specially mentioned. He was the first to make a
serious study of the British fauna on the lines laid down by that
distinguished botanist. In conjunction with E. Boyd, he published a
valuable essay on the "Distribution of Butterflies in Great Britain,"
and later on the birds were similarly dealt with. All the more
important groups of animals are now being studied with a view to
determining their exact range in these islands. Mr. Harvie-Brown, Mr. J.
W. Taylor, Mr. Eagle Clarke, Mr. Miller Christy, Mr. Ussher, Mr.
Barrington, and a number of others have considerably advanced our
knowledge in this direction in recent years.
Any such contributions are to be welcomed as furnishing us with the
necessary data to solve the problem of the origin of the British fauna.
Meanwhile we know enough to enable us to assert positively that the
latter has reached us by land-connections from various parts of Europe
(cf. p. 35). This statement of course refers to the bulk of the British
fauna. The small proportion of indigenous species, or such as have been
introduced accidentally, may be left out of consideration when dealing
with the great mass of animals which have evidently migrated to the
British Islands on land now sunk beneath the sea (see Fig. 4, p. 60).
Opinions of zoologists, botanists, and geologists are practically
unanimous on this subject; yet there are two other theories, which have
from time to time been advanced to account for the origin of the British
fauna. Only the first of these, however, can claim the serious attention
of those interested in the problem. Its chief contention lies in the
oft-asserted dictum of the "_imperfection of geological record_." It has
been suggested, in fact, that the British fauna, instead of having
migrated to our islands, might have originated there, but that, owing
to the fragmentary nature of our Tertiary deposits, all trace of their
early history had disappeared. "The origin of European species," remarks
Professor Cole (p. 238), "within the area of the British Isles, and
their migration outwards when local conditions became less favourable
for their multiplication, are possibilities that seem too often
disregarded. Yet the geologist must see in the western borderland of
modern Europe a diminished continent from which land-animals must have
again and again moved eastward." "Hence geologists may fairly be
unwilling to look on our isles as barren lands waiting to be peopled in
pliocene or later times. Far rather has the breaking up of a broad
land-area along the present continental edge sent our land-fauna to the
new steppes that opened eastward, leaving us a mere diminished remnant
to struggle with the glacial period."
There are in Professor Cole's views many points with which I readily
agree. In the first place, he acknowledges that migration has taken
place on land, so that we have our land-connection between Great Britain
and the Continent whatever theory we accept as to the direction taken by
the migrants. That the western borderland of Europe has given rise to
many important assemblages of animals in past times, seems to me also
exceedingly probable, nor do I look upon the British Islands as "barren
lands waiting to be peopled in pliocene or later times." On the
contrary, I believe an almost uninterrupted stream of migrants poured
into the British Isles before pliocene times from the south. But what I
thoroughly disagree with, is the remark that our British land-fauna has
been sent to the new steppes that opened eastward. These are the more or
less arid portions of Eastern Europe. Professor Cole no doubt has in
mind those species of mammals which I have included in what I called the
Siberian migration, and of which we have fossil evidence in the late
Tertiary deposits of Europe. It would be impossible here to discuss this
subject fully, especially as I have done so in the subsequent chapters;
but, even if we had no geological record whatsoever, the present range
of the species in question and their nearest relatives must convince us
that they could not have originated in Western Europe. However, on the
strength of the geological evidence, Professor Nehring--the only one who
has made this fauna his special study--remarks (p. 228), that there
seems scarcely any doubt that this steppe-fauna just referred to had
come to us from the east. Professors Boyd Dawkins, Brandt, and Lartet
held similar views.
The theory that an ice-sheet stretched across a narrow sea might be the
means of aiding a fauna across from the mainland to an island, is
particularly inapplicable to the British Islands. Neither Mr. Kinahan
nor Mr. Lamplugh, the two supporters of this view, have, however, taken
the trouble to apply it to more than one species of the British fauna.
An ice-bridge, thinks Mr. Kinahan, "could easily have connected Scotland
and Ireland, thus giving a land causeway for migration" (p. 3). Mr.
Lamplugh throws more light on this interesting speculation by giving us
the name of an animal which he believes crossed a narrow sea on a bridge
of ice. This animal unfortunately happens to be one whose remains have
never been found in high northern latitudes, viz., the Irish elk
(_Cervus giganteus_). And because he is of opinion that this species of
extinct deer found its way to the Isle of Man from the mainland on a
waning ice-sheet, he sees no reason why certain elements of the Irish
fauna should not have been similarly introduced.
It seems of no advantage to begin the discussion on the origin of the
British fauna by assuming the former existence of ice-bridges, and the
possibility of a migration across them of some of its members. If a
glacier connected Scotland and Ireland, the climate of both countries
(since they were highlands and acted as the feeders of the ice-sheet)
must have been uncomfortable to the majority of the British species.
What were the inducements that could have prompted those which had
braved the discomforts of Scotland to emigrate to Ireland at such a
time? What light does it throw on the origin of the Irish fauna as a
whole, to advance the extremely improbable hypothesis that certain
elements of it may have reached Ireland by an ice-bridge? If any
species came to that country in such an unusual manner, surely they must
have been Arctic or northern forms. But what about the southern species,
which form the bulk of the Irish fauna and also the flora? Even the
Arctic element of the British fauna, which probably includes, besides
the Reindeer, many hundreds of species, could not, I think, have
migrated to these islands on an ice-bridge. Indeed, I agree with most of
the writers who have dealt with the subject, in asserting that the
northern as well as all the other elements of our fauna utilised for
their migration the old land-bridges which connected these islands with
one another and with the Continent.
There is a greater diversity of opinion as to the age during which the
British fauna arrived in these islands. This is naturally a much more
complicated problem, but it is one which I am convinced will ultimately
be solved mainly by means of a study of the geographical distribution of
animals and plants. If we can settle the relative ages of the various
migrations, we thereby supply an important link in our attempt to
reconstruct the past geographical features of the British Islands. The
range of the British species will give us an idea of the nature of the
land-connections and their gradual changes in course of time. Geological
data are exceedingly valuable in these inquiries, but it is a fatal
mistake to build our geographical theories and the origin of the British
fauna as a whole entirely on the assumptions of a certain school of
geologists. Unfortunately, Dr. White's very interesting remarks on the
British fauna for this reason lose much of the value which they might
otherwise possess.
In his remarkable essay the late Edward Forbes affirms that the flora
peculiar to the west of Ireland, of which the strawberry tree (_Arbutus
unedo_) is the most striking example, and which exhibits such strong
southern affinities, is not only much the most ancient of our island
floras, but that it is actually of miocene age. It migrated to Ireland
from Spain at a very remote period, during which he supposed that a
direct land-connection existed between the two countries. The
destruction of this old land-bridge, he thinks, must have taken place
before the commencement of the Glacial period. Climatal changes during
that time destroyed the mass of the southern flora which had thus
reached Ireland, the survivors being species such as were most hardy
(saxifrages, heaths, etc.), which he considers to be the only relics of
this most ancient portion of our flora.
The northern or Arctic fauna and flora, according to the same author,
established themselves in the British Isles during the Glacial
period--at a time when these were groups of islands in the midst of an
ice-bound sea. Finally, the great mass of our animals and plants
migrated from the Continent to England after the Glacial period. "The
migration of the species," he says, "less speedy of diffusion, which are
now peculiar to England was arrested by the breaking up of the
land-connection between England and Ireland, and thence the famous
deficiencies of the sister isle, as, for instance, its freedom from
reptiles" (p. 10). He is also of opinion, that the separation between
England and the Continent took place at a later date than that between
England and Ireland.
According to Dr. A. R. Wallace (p. 338), we possessed just before and
during the Glacial period "a fauna almost or quite identical with that
of adjacent parts of the Continent, and equally rich in species." But
the submersion, he thinks, which is supposed to have occurred during the
latter part of the Glacial period, destroyed the greater part of the
life of our country. When England again became continental, continues
Dr. Wallace, this fauna was succeeded by an assemblage of animals from
Central Europe. "But sufficient time does not seem to have elapsed for
the migration to have been completed before subsidence again occurred,
cutting off the further influx of purely terrestrial animals, and
leaving us without the number of species which our favourable climate
and varied surface entitle us to." The comparative zoological poverty of
Ireland he attributes to the fact that "the depth of the Irish Sea being
somewhat greater than that of the German Ocean, the connecting land
would there probably be of small extent and of less duration, thus
offering an additional barrier to migration."
Dr. Wallace's explanation of the origin of the British fauna is
disappointing after Forbes's careful study and critical inquiry into
its component elements. So great an authority on geographical
distribution might have given us more lucid statements of his views on a
variety of topics connected with this subject.
In speaking of the fauna of Ireland, Professor Leith Adams, Professor
Dawkins, and Mr. Alston are evidently only thinking of the mammals,
which form but a very small proportion of it. The first-mentioned
palaeontologist held that there was a land-communication between Scotland
and Ireland at the close of the Glacial period, by which the greater
portion of the mammals that had found their way to the former country
crossed to the latter (p. 100). And, he continues, the severance between
the two countries must have taken place before the slow-travelling Mole,
the Beaver, the forest-haunting Elk and the Roebuck had time to arrive.
Much in the same spirit are Mr. Alston's remarks on this subject (p. 5).
"The absence from the known fossil fauna of Scotland and Ireland of most
of the characteristic post-pliocene English animals, shows that the
northward migration of these forms was slow, gradually advancing as the
glacial conditions of the northern parts of our islands decreased in
intensity. Thus it is not difficult to suppose that the Hedgehog,
Ermine, Badger, Squirrel, and Mountain Hare may have found their way
through southern Scotland into Ireland long before they were able to
penetrate into the still sub-arctic regions of the Highlands.
Subsequently, when the improvement of the climate had continued, the
Shrews and Voles may well have found their way northward along the
comparatively genial coasts, before the larger beasts of prey could find
a sufficient stock of game."
That the Bear, Wolf, Stag, Horse, Mammoth, and Reindeer lived in Ireland
before the Glacial period is considered highly probable by Professor
Boyd Dawkins (_a_, p. 152).
Only the Butterflies are dealt with in Dr. Buchanan White's clever
little essay on distribution. And, as I remarked before, his conclusions
are somewhat marred by the unwarrantable assumption that our islands at
no distant date were totally destitute of all plant-life, and were
therefore uninhabitable by animals. But his paper differs in so far from
most of the others, that he has made a thorough study of the one group
he deals with. In some respects it may serve as a model to future
students in its general treatment of the problem he has set himself to
work out. He adopts the principle, even for butterflies, that though it
is possible for them to be blown over from the Continent, they have
probably migrated with the rest of our indigenous fauna and flora across
the dry bed of the German Ocean. His conclusions are that Britain
derived its butterfly fauna from continental Europe in post-glacial
times, that the Arctic and Alpine species were the first arrivals, and
that one part of the Irish species reached Ireland by way of Scotland,
another from the south. He assumes, of course, that Great Britain and
Ireland were connected at that time.
Within the last few years the spell which has bound naturalists to
accept the theory of a total destruction of life during the Glacial
period is happily vanishing, and more enlightened views are gaining
ground. The Lusitanian species of plants in the west of Ireland, which
had already furnished Forbes with an argument in favour of survival, are
also regarded by Mr. Bulman as the remnants of a pre-glacial flora which
was exterminated everywhere else by the cold (p. 265). This view of the
survival of a pre-glacial fauna and flora has since been accepted by Mr.
Carpenter, whilst I also have endeavoured to bring fresh evidence into
the field in its favour. We both agree with Edward Forbes in considering
the Lusitanian element as the oldest section of our fauna and flora, and
that it came long before the Glacial period. But we differ somewhat from
him, in so far as we do not limit that element to Ireland. It seems also
to be represented in South-western England and Wales, though it is there
less conspicuous.
This decision as to the relative age of the British South-western fauna
has not been arrived at from any geological considerations. The
conviction that it must be older than the other sections has been gained
solely from a study of the geographical distribution of the species
belonging to that fauna. Many of them exhibit what is known as
"discontinuous distribution," which zoologists are agreed to regard as
a sign of antiquity. Thus _Geomalacus maculosus_, the Kerry Slug, is in
the British Islands confined to South-western Ireland (see Fig. 19, p.
300), and on the Continent it is unknown north of North-western Spain.
The Millipede, _Polydesmus gallicus_, has a wider range in Ireland, and
is also known from France and the Azores. Two Earthworms of the Spanish
and Mediterranean region, viz., _Allolobophora veneta_ and _Georgii_,
have been discovered in Ireland, but are apparently unknown in England
or France; whilst the Weevil, _Otiorrhynchus auropunctatus_, does not
occur north of the Auvergne Mountains in France except in Ireland. A
very large number of instances might be mentioned of species found in
South-western Europe, France, the South-west of England and Ireland.
Enough, however, has been said to show the nature of the fauna, and
there is, as Forbes has pointed out, a corresponding flora.
A great number of the species belonging to the South-western British
element seem to have originated in South-western Europe, or at any rate
to have spread over our continent from that part. Their home lay
therefore probably in a warm, damp climate, and it seems a reasonable
inference to suppose that they spread north at a time when the
temperature over the British Islands was much higher than what it is
now. Any one familiar with our Bristle fern, or Killarney fern, as it is
called in Ireland (_Trichomanes radicans_), will readily admit that it
must have come to us at such an epoch. It at once suggests some shady
waterfall in a tropical forest, and indeed the home of the genus is
South America. It is one of those plants which have evidently migrated
to us from South-western Europe, a mere remnant of a once luxuriant
flora.
Sir Archibald Geikie tells us (p. 837), and in the main every one agrees
with him, that at the beginning of the Tertiary era in which we now
live, the climate was of a tropical and subtropical character in Europe.
Gradually it became more temperate, and eventually it passed into a
phase of extreme cold, but since that time the cold has again gradually
diminished. It is quite evident, therefore, that from a purely
geological point of view our south-western flora must have migrated
northward before the cold came on, and survived in sheltered localities
under the influence of the mild coast climate. Some, however, suppose
that there occurred a phase of extreme mildness immediately after the
Glacial period, and that it was during that time that the Lusitanian
fauna and flora became established in the British Islands. To this
Professor James Geikie replies (_b_, p. 169), "there are few points we
can be more sure of than this, that since the close of the Glacial
epoch--since the deposition of the clays with Arctic shells and the
Saxicava sands--there have been no great oscillations, but only a
gradual amelioration of climate. It is quite impossible to believe that
any warm period could have intervened between the last Arctic and the
present temperate conditions without leaving some notable evidence in
the superficial deposits of Scotland, Scandinavia, and North America."
Thus it appears that on the whole the assumption that the Lusitanian
fauna and flora are very ancient and pre-glacial is also supported on
geological evidence.
[Illustration: Fig. 5.--Map of Europe, with arrows indicating
approximately the course taken by the different streams of migration
towards the British Islands.]
The course of events in the origin of the British fauna might have been
therefore somewhat as follows:--In early Tertiary times, when the
climate all over Western Europe was moist and semi-tropical, a migration
proceeded northward from the south-western corner of Europe. This was
strengthened by Oriental migrants which had moved westward along the
Mediterranean basin (Fig. 5, No. 1). Owing to geographical changes
supervening, the Alpine fauna (No. 2) was then enabled to colonise the
British Islands, and subsequently another migration had begun to come in
from the south-east (No. 3). The climate had meanwhile gradually become
more temperate and drier. About the same time, or even earlier, an
Arctic migration commenced to pass southward (No. 4), and finally the
Siberian animals (No. 5) poured into our continent. The arrows in the
map indicate the directions followed by the different migrants as they
travelled to the British Islands. The arrows are not meant to represent
the whole nor the full extent of the migrations from any particular
centre, but only in so far as they affect our islands. Moreover, it
would be impossible to indicate on one map the geographical conditions
which obtained during the several migrations. It must be remembered that
during the time which elapsed while they passed into the British
Islands, these were joined in the north to Scandinavia and in the south
to Belgium and France. The various phases of geographical evolution of
Europe will be studied in the subsequent chapters, and maps will then be
given to show as far as possible in a general way the leading
characteristics of these great changes.
I have now given some reasons for the belief that several different
migrations of animals entered the British Islands in later Tertiary
times. I have also shown why some of them must be looked upon as being
older than others, and in so far we have come to a decision as to their
relative ages. It still remains for us, however, to examine how their
geological ages can be approximately determined. We require for this
purpose palaeontological aid.
In the fifth chapter will be found the history of the Siberian
migration. And since we possess most valuable records of it in the
numerous fossil remains discovered in Central and Western Europe, we are
able to trace their progress from the east to the west in a very
complete and satisfactory manner. In England their first appearance
dates from the Forest-Bed, for here we find remains of the Glutton
(_Gulo luscus_), Musk-Ox (_Ovibos moschatus_), and others (see p. 204).
It seems reasonable to suppose, therefore, that the first entry of these
Siberian mammals into Europe took place at or just before the Forest-Bed
period. But Professor Nehring tells us in his remarkable work on the
Tundra and Steppes (p. 222), that in Germany the remains of the same
mammals occur in deposits which are certainly more recent than the lower
continental boulder clay; and he is inclined to the belief that they
migrated into Europe during the inter-glacial phase which is supposed to
have separated the earlier from the later stage of the Glacial period.
It is evident that in this case the inter-glacial period in Germany
would have corresponded to, and be contemporaneous with, our Forest-Bed
period. The deposits immediately preceding the Forest-Bed would also be
contemporaneous with the lower continental boulder clay. Although this
may seem rather a startling statement to make, from the evidence which
will be brought forward in the fourth and fifth chapters I am inclined
to the belief that such is probably the case.
Having once arrived at a determination of the exact geological period
during which the Siberian mammals invaded our continent, and having also
previously determined the relative ages of the various other migrations,
we have advanced another step in the direction we are aiming at. Let us
suppose that the Siberian migration actually reached the British Islands
during the Forest-Bed period. Since the Siberian migration is the most
recent of those which entered the British Islands, the others must have
commenced their march before the Forest-Bed period. Now it was Professor
Boyd Dawkins who first indicated to us, as I have remarked before, the
method of research to be adopted in an attempt to determine the
geological age of the different migrations in so far as they affected
the British Islands. I may be excused, therefore, for again quoting the
following important passage in one of his works. "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." The Beaver, Dormouse, and
Common Hare are either Siberians or later migrants from elsewhere, and
there can be no doubt that at the Forest-Bed period Ireland was already,
or was just being, separated from England. All the southern species,
that is to say all the Lusitanian, Alpine, and Oriental forms occurring
in Ireland, must therefore be older than that period. I have advocated
similar views in a former essay on this subject. Mr. Carpenter recently
advanced some interesting and valuable criticisms on these views, which
we may examine a little more closely (p. 385). "While, then," he
remarks, "I find myself in almost complete agreement with Dr. Scharff
with regard to the older sections of our fauna, I think that those
widespread species which survived the Glacial period must have been
confined to the more southern parts of our area, and have only
subsequently spread northwards and westwards to Scotland and Ireland."
He suggests, in fact, that the widespread British species belong to a
younger or newer section of our fauna than the local ones. In many cases
this may be quite true, but we possess also a large number of common and
widely-spread forms which bear the impress of antiquity upon them. We
have the most positive proof of the antiquity of the very common small
circular Snail (_Helix rotundata_), since it was found in miocene
freshwater deposits near Bordeaux. Many other examples might be
mentioned to show that, though discontinuous range is generally a proof
of antiquity, continuous range is not always a sign of the opposite.
Some species, in fact, appear to be short-lived and disinclined to
spread, whilst others multiply rapidly even under a change of
temperature and climate, and are to be found almost everywhere. But even
if we supposed, with Mr. Carpenter, that these widely-ranging species
must have been confined during the Glacial period to the more southern
parts of England, the idea that they afterwards made their way
northwards along the eastern shore of the Irish Sea and then passed into
Ireland, does not appeal to me. Southern England was occupied at that
very same time by an assemblage of Siberian mammals. Mr. Carpenter
thinks these might have been kept out of Ireland by an arm of the sea
until the land-connection with North-western England had broken down.
But if an arm of the sea could keep out the Siberian mammals it would
also keep out the widely-spread British species of the general fauna. On
the other hand, I quite admit that my view of the survival in Ireland
of the pre-glacial fauna is somewhat difficult to accept, considering
that we have such undoubted evidence of a very extensive submergence.
The case of Isle of Man, quoted by Mr. Carpenter, can be met, I think,
by the supposition that it was connected with Cumberland until quite
recently, and quite independently of any connection between England and
Ireland; that the Isle of Man, in fact, was always a cape or peninsula
of the mainland, and only recently became separated by local subsidences
or by the action of the sea.
Part of the history of the British fauna will be referred to again in
the next chapter, which deals with the Arctic migration. We need not
therefore dwell any longer on this subject here. There is one matter,
however, which is of importance in connection with the geographical
conditions of the British Islands at the time when the greater portion
of our fauna arrived from abroad.
On page 60 will be found a map indicating the physical geography of that
part of the ancient continent on which what are now the British Islands
were situated. Only one large river has been marked on that map, namely,
that flowing out of a lake which occupied part of the Irish Sea. Another
probably discharged its waters into the Atlantic midway between France
and England, whilst the Thames may have been a tributary of the Rhine,
as it emptied itself into the sea near our south-east coast. I have
shown in a previous essay that the former presence of a freshwater lake
between England and Ireland is indicated by the distribution of the
Charrs and also by the various species of British Coregonus. There are
three British species of Coregonus, viz., _C. clupeoides_, _C.
vandesius_, and _C. pollan_. These are confined to the lakes of North
Wales, North-western England, South-western Scotland, and Ireland. All
but the latter communicate at present directly with the Irish Sea. The
lakes of the latter country, however, must have done so at a time when
the west of Ireland stood at a higher level than it does now. The
ancestors of the three Coregonus species, and also those of the Charrs,
then lived in the large freshwater lake indicated on the map (p. 60),
and when the sea gradually crept up the river valley and finally
converted the lake into a gulf, the freshwater fish took refuge in the
rivers which supplied it with water.
Now as for the continuous sea-shore between the coast of Brittany and
the south-west of Ireland, zoological distribution again aids us in
proving that such must have actually existed at no very distant
geological date. Most of our common shore forms of life migrate along
the coast exactly as land animals do--step by step. Their eggs are
carefully attached to fixed objects, so as not to be carried away by the
waves, whilst the young often remain and grow old in some particular
little pool, rarely venturing farther than a few yards from the spot
where they first saw the light of day. A number of such shore forms are
found on the west coast of France, the same species recurring again on
the south-west coasts of England and Ireland, thus clearly indicating a
former continuity of coast-line between these points, now separated by
deep sea. A very familiar example to British zoologists is the purple
rock-boring Sea-urchin (_Strongylocentrotus lividus_), but there are a
great many others, such as the semi-marine Beetles _Octhebius Lejolisii_
and _AEpophilus Bonnairei_, the Crustaceans _Achaeus Cranchii_, _Inachus
leptochirus_, _Gonoplax angulata_, _Thia assidua_, _Callianassa
subterranea_, the Fishes _Blennius galerita_ and _Lepadogaster
Decandollii_, and the Molluscs _Otina otis_, _Donax politus_, and
_Amphidesma castaneum_.
Before concluding this chapter, a few words as to my views on the
conditions prevailing during the Glacial period will not be out of
place. They do not differ very much from those held formerly by most
geologists; and even at present there are, as I have mentioned before, a
few upholders of those older views.
The sea, I think, must have gradually crept across England from the east
during, or shortly after, the Forest-Bed period, so as to separate the
south from the north, whilst Ireland and Scotland were then still
connected with one another. At a later stage, the sea also partially
invaded Ireland, and this condition is very roughly represented on the
accompanying map. Mr. Kendall kindly drew my attention to the fact that
several notable areas on which shelly drift has been observed are here
placed upon the land; but it must be remembered that one stage only can
be shown on the map, and that the sea covered more ground a little
later. Many of the smaller islands in the glacial sea, too, are not
shown. The map, in fact, is merely meant to give a general idea of the
manner in which the great northern sea moved westward and slowly covered
a large portion of the British Islands. These peculiar geographical
conditions explain, I think, better than anything, the absence from
parts of the Midlands and the north of England of such a number of
terrestrial invertebrates which are otherwise widely distributed over
the British Islands. In spite of the fact that a large portion of the
British Islands became submerged, we possessed at that time an extensive
area which has since been claimed by the sea, so that there was ample
room for the present fauna to survive the Glacial period. The climate
during this period was probably much the same as it is at present,
though moister, with cooler summers and milder winters.
[Illustration: Fig. 6.--Map of the British Islands, showing
approximately in what manner the sea may have invaded the country from
the east during, or shortly after, the Forest-Bed period. The darkly
shaded parts indicate the areas covered by water, and the lightly shaded
and white portions what was land at that time.]
It may be asked what proof we have of such an extensive submergence of
England and Ireland. My own views are principally based on the general
distribution of the fauna in the British Islands, and the belief that
nothing but a mild climate during the Glacial period could have brought
it about. On purely geological grounds, however, some geologists,
notably Mr. Mellard Reade, have come to a similar conclusion. "The whole
of Lancashire and Cheshire," he remarks (_a_, p. 542), "from sea-level
up to about 400 feet, and in places 600 feet, is covered by a continuous
mantle of boulder-clay and sands." "These clays, as a rule, contain
distributed through them, in a greater or less degree, fragments of
shells and some perfect ones. I myself have recorded forty-four
species." Again he continues (pp. 545 and 546): "A large part of
Ayrshire is covered with similar shelly boulder-clays from sea-level to
1061 feet at Dippal. These Ayrshire high-level shells have, in the
majority of cases, been taken, not from sand and gravel beds, but from
boulder-clay, and in that respect they are most important and unique. In
Moel Tryfan the shells are found in sands and gravels at 982 feet; on
the range of hills from Miaera to Llangollen from 1000-1200 feet; also
in sands and gravels at Gloppa, near Oswestry, at 1100-1200 feet; and
near Macclesfield at a level of about 1200 feet. In Ireland marine
shells can be traced almost from sea-level to a height of over 1000
feet."
"Again," continues the same author, "if we look broadly at the
distribution of these shelly deposits, we find that they occur all round
our maritime coasts in Lancashire, Cheshire, and Wales, in Cumberland
and Westmoreland, Wigtonshire and Ayrshire, and along the eastern coast
of Ireland. The same is to be said of the eastern coasts of England and
Scotland."
That a very considerable change of sea-level has taken place in some
parts of the British Islands would appear to a zoologist the most
logical conclusion after an examination of these "high-level shelly
sands and gravels," but the shells contained in them are now generally
supposed to have been carried there frozen in the sole of a glacier or
pushed up in front of it. The older view, however, which agrees so much
better with the facts of distribution, fortunately has not disappeared
among geologists. "When we call up," says Mr. Mellard Reade (_b_, p.
435), "before our mental vision the simple and well-known facts of
nature which suffice to explain the marine drifts on the theory of
submergence, it seems unnecessary to resort to the ingenious and
artificial system of physics elaborated to explain the phenomena of
land-ice."
"When we have more knowledge of the glaciers of the Arctic Regions, and
facts, in place of ingenious suppositions, to base our reasoning upon,
we may possibly have to revise all our glacial conceptions. In the
meantime, the submergence theory of the origin of high-level shelly
gravels and sands seems to me by far the simpler of the two theories,
and the most consistent with the facts and phenomena which the labours
of a succession of enthusiastic geologists have made us acquainted
with."
Among those geologists, and they form the majority, who hold that
Ireland was covered by land-ice, there is a great diversity of opinion
as to its extent. Messrs. Close, Kinahan, J. Geikie, and others believe
that the ice covered practically everything, whilst others who claim to
have examined the ground with equal care, such as Professor Carvill
Lewis, were led to believe that the south of Ireland, with the exception
of a few local glaciers, was free from ice. The glacial phenomena of
the country can therefore be interpreted in different ways, even by
those who are convinced that they are due to land-ice and not to
icebergs or mud-glaciers.
SUMMARY OF CHAPTER III.
The history of the British fauna is not only of interest to us from a
sentimental point of view, it is a convenient starting-point in the
study of the larger European problem. The fauna, broadly speaking, is
composed of three foreign elements, viz., the northern, eastern, and
southern, to which may be added a small endemic one. Examples are given
of the more noteworthy forms belonging to each of these. This leads us
to the subject of the natural divisions of the British Islands according
to their animal inhabitants. Zoologists attempted at first to subdivide
these countries, on the lines laid down by botanists, into a large
number of provinces. Forbes proposed ten such divisions for mollusca,
and subsequently five, which were ultimately reduced by others to two or
three.
The opinions of biologists are almost unanimous in attributing the bulk
of the British fauna and flora to migrations by land from the Continent,
but two other theories, viz., those of Professor Cole and Messrs.
Kinahan and Lamplugh, are also referred to. The first believes in a
possible migration eastward from Western Europe, and the latter support
the view of the former existence of ice-bridges to assist the fauna in
their migrations.
An endeavour is next made to determine at what geological periods the
various migrations entered the British Islands. There is considerable
difference of opinion on this subject. Some believe that the British
fauna is altogether post-glacial; a few think that it is partly so and
the remainder glacial; others again hold that a portion is pre-glacial
and the rest glacial and post-glacial. Those who have studied the
subject most closely feel convinced that the south-western or Lusitanian
fauna, and also the flora, must have arrived before the Glacial period
and survived the latter in these Islands. It seems reasonable to
suppose, therefore, that the climate cannot have been very severe during
the so-called Ice-Age. This Lusitanian fauna must be looked upon as the
oldest portion of the British fauna. The Alpine and Oriental migrations
arrived next. After these came the Arctic, and finally the Eastern or
Siberian. As the fossil evidence is most complete with regard to the
last, we are able to determine with precision not only the direction
whence this migration came, but approximately its geological age. It
arrived in Germany from the east after the deposition of the lower
boulder-clay. Since the boulder-clay is looked upon as a glacial
deposit, the Siberian migration reached Central Europe after the first
portion of the Glacial period had passed. In England it makes its first
appearance in the Forest-Bed, which would therefore correspond to the
"Loess" formation of Central Europe. All the other migrations are older
than the Siberian. They must therefore have come to Great Britain during
the earlier part of the Glacial period or before it.
The chapter concludes with a short statement on the physical geography
of the British Islands during the time when these migrations entered
them. That there existed a continuous coast-line between France and
Ireland is proved by the occurrence of a considerable number of
identical shore species, whilst the former existence of a freshwater
lake on the site of the present Irish Sea is indicated by the
distribution of some freshwater fishes.
CHAPTER IV.
THE ARCTIC FAUNA.
The lands lying within the Polar Circle are inhabited by an assemblage
of animals and plants, many of which are peculiar to those regions. They
are mostly adapted to the abnormal conditions of life prevailing in the
high latitudes of our globe--the long, dark winters, and the short
summers of one long day. Though the numbers of species and of
individuals are few, there is a keen struggle for existence in those
regions. The prevailing colour of the ground is white, and since a
resemblance in the colour of an animal to the ground it lives on acts as
a protection to weak ones, and also enables Carnivores to approach their
prey with greater facility, it is not surprising that we should find the
majority of polar animals coloured white. As I remarked, the polar area
contains a very distinct set of species; most of them, however, range
beyond the confines of the Arctic Circle. It is therefore scarcely
justifiable to raise this Arctic area into a distinct zoological region
equivalent to the great zoogeographic regions, which have been
established by Sclater and Wallace, though we might, with Dr. Brauer,
look upon it as a sub-region.
There are six typical Polar Land-mammals, one of which, the Polar Bear,
is semi-aquatic. The Reindeer (_Rangifer tarandus_) occurs upon almost
all the polar lands, and it has often been a source of speculation in
what manner it has reached such remote islands as Spitsbergen and Novaya
Zemlya--the former of the two being so remote from a continent. There is
no doubt that Reindeer are great wanderers, owing to the difficulty of
finding sufficient food-supply for the large herds in which they are
accustomed to travel; and for this reason they can cross, and have been
known to cross, distances of from ten to twenty miles on ice. The
Behring Straits, when frozen over in winter, is frequently traversed by
them. But I quite agree with Dr. Brauer (p. 260) that it is impossible
to account for their presence in Spitsbergen by an immigration from
either Novaya Zemlya, Greenland, or Scandinavia, under the present
geographical conditions. The seas between the former island and the
other land-masses referred to are rarely entirely frozen over. Even if
this should occur, the distances between Spitsbergen and Greenland,
Novaya Zemlya, or Scandinavia are so great, that a migration across ice
is quite excluded from the range of possibilities, since Reindeer could
not subsist without food during the time it would take to travel from
one to the other. The manner in which it did reach Spitsbergen and
Greenland will be discussed more fully below, and I will therefore
proceed to mention the other Arctic mammals.
One of the most important and most typical species is the Polar Bear
(_Ursus maritimus_), the greater part of whose life is spent on the ice
and in the sea. The fact that its favourite nourishment consists of
seals proves its excellent and keen faculties of sight and hearing, and
its facility in swimming. But it is not a dainty feeder, and lives upon
almost all animals which come within its reach; birds, land-mammals, or
fish are not despised in times of scarcity. Its fur throughout the year
is coloured white, though in old bears it assumes a more yellowish hue.
[Illustration: Fig. 7.--The Musk-Ox (_Ovibos moschatus_). (From Flower &
Lydekker's _Mammals_, p. 358. London: Adam & Chas. Black.)]
Another large mammal, perhaps less well known, is the Musk-Ox (_Ovibos
moschatus_, Fig. 7), which resembles in size the smaller varieties of
Oxen, but in structure and habits is closely allied to the Sheep. As is
implied by the specific name, it exhales a musky odour; this does not,
however, appear to be due to the secretion of a special gland, as is the
case in other animals with a similar smell. The skin is covered with
long brown thickly-matted hair, interspersed with white. It is confined
to the most northerly parts of North America and the American Arctic
islands, and to North Greenland. Though not now living in the Old World,
it seems formerly to have been abundant in Siberia, and, as we shall
learn later on, it was one of the species which took part in the great
Siberian invasion of Europe. Its remains have been found not only in
Germany and France, but also in the south of England.
The Polar Fox (_Canis lagopus_) occurs throughout the Polar Regions, and
on islands where even the Reindeer and the Musk-Ox are unknown. Beyond
the Polar Circle, its range extends into Northern Asia, to the extreme
north of North America, and the mountains of Scandinavia. Like its
congeners, it had in pleistocene times a more southerly extension, and
fossil remains have been met with in various parts of continental Europe
and in England.
The Stoat (_Mustela erminea_), which is known and much valued in
commerce under the name of Ermine, was formerly believed to occur only
in Arctic America and the northern parts of the Old World, but in more
recent years it has been discovered in a number of the northern
islands, such as Saghalien, in the islands of the Behring Straits, the
Aleutian islands, and also in Greenland and Spitsbergen. In Europe, it
is found as far south as the Arctic Hare, or perhaps even farther, and
it flourishes in the Alps up to a height of 9000 feet. It offers a
parallel to the Arctic Hare in the fact that in some countries, such as
Ireland, it only rarely turns white in winter. The Irish form of the
Stoat differs so much from the English, that Messrs. Thomas and
Barrett-Hamilton are of opinion that it is specifically distinct, as I
mentioned in speaking of the divisions of the British fauna (p. 90).
The Arctic Hare (_Lepus variabilis_) is almost the only one of the
typical Arctic mammals which still inhabits the British Islands, and for
that reason it is to most of us more familiar than any of the preceding
species. Hares have been described fro
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