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.

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. Günther and Dr. Boulenger. The valuable works on Mammalia by Sir W. Flower, Mr. Lydekker, Mr. Grevé, 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]).

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 rôle 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 larvæ 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 Europæus) 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 Phœnix 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 rôle 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 versâ, 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.

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.

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 rôle in the peopling of our continent, but this is quite a mistake. The eminent Swiss palæontologist Rütimeyer 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 palæontological point of view. In a letter which I received from Professor Charles Depéret, 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 Lebéron (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 Clausiliæ 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 Clausiliæ, 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 Clausiliæ increase once more. It is interesting to note, however, that almost all these eastern forms belong to the sub-genus Phædusa (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 Clausiliæ 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 Arionidæ 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, Hyænas, 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 viâ 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 Hyæna 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 palæarctic 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 (palæarctic) 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 Rütimeyer, 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. Köppen 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.

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 ægagrus) 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 Köppen, 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 période glacière, 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, Depéret, 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 hyæna 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 Bicêtre, near Paris. It is stated by the same authority (p. 115) that much the same conditions exist in Germany. "The lion and the spotted hyæna, 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 Hyæna 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° 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 moutonnées 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 moutonnées, 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 Palæarctic 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 Salmonidæ—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 viâ 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—

  1. The Channel Isles.
  2. South-east of England (including Cambridgeshire).
  3. South-west of England.
  4. North-east of England.
  5. North-west of England (including Isle of Man).
  6. North of Ireland.
  7. South of Ireland.
  8. South of Scotland.
  9. North of Scotland.
  10. 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:—

  1. England and Wales (except the South-west).
  2. 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 Palæarctic 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 palæontologist 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.

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 palæontological 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 Æpophilus Bonnairei, the Crustaceans Achæus 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.

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.

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 from Greenland by the name of Lepus glacialis, from the European Alps as Lepus alpinus, and under other names from Arctic North America; but though slight differences in the fur and even in the skull can be pointed out, there is no doubt that all these are only varieties or races of what, in the British Islands, is known as the Irish or the Scotch Mountain Hare, Lepus variabilis. In the Arctic Regions this Hare remains white throughout the year, but in Scandinavia and some other parts its fur becomes brown in the summer, and in Ireland it frequently remains entirely brown during the whole year, and never, or only in very rare cases, becomes entirely white in winter. Besides Scandinavia, Scotland, and Ireland, it is found in Northern Russia, and also in the Pyrenees, the Alps, and the Caucasus. In Asia it occurs not only on the mainland of Siberia, but it has been obtained on the Akita Mountains in Japan and on the Mioko San Mountain, and also on the island of Saghalien. It had in former times a more extensive range, and its remains have been discovered in England and in a number of places on the continent of Europe. The peculiarity of its range, which will be explained more fully directly, lies in the fact of the occurrence of isolated colonies in the mountains of Europe, in Ireland and Scotland, and in the mountains of Japan ([Fig. 8]). From a distributional point of view, it is one of the most interesting species of mammals, and its history throws a flood of light on the geographical changes which have occurred in former times.

Fig. 8.—Map of the northern hemisphere, to show the geographical distribution of the Arctic Hare (Lepus variabilis) indicated in black.

One more species must be mentioned, and that is the Banded Lemming (Cuniculus torquatus), which occurs chiefly in Arctic America, Northern Siberia, and Greenland. Though frequently mistaken for the Scandinavian Lemming, there is a striking difference in the character of the teeth, which has induced zoologists to put them into distinct genera. The Arctic Lemming, moreover, is distinguished from the Scandinavian by the absence of external ears, the densely furred feet, and by the great length of the two middle claws in the fore-feet. There are two species of the true Lemming, namely, the one just referred to, Myodus lemmus, and Myodus obensis. These may be looked upon as more or less Arctic species, since they occur within the Polar Circle, but they are not so exclusively confined to that region as the Banded Lemming (Cuniculus torquatus). The remains of both Cuniculus torquatus and of Myodus lemmus have been found in British pleistocene deposits.

Until recently no Lemming remains had been found to the south of France, but Mr. Barrett-Hamilton announced to us a short time since that Dr. Gadow had discovered some skeletons with their skins still preserved in a cave in Northern Portugal. These were found to belong to the Scandinavian Lemming (M. lemmus), and the author incidentally expressed the opinion that there was some possibility of this species still inhabiting the mountains of Spain.

The Lemming multiplies with great rapidity under favourable conditions. In speaking of his experiences in Siberia Dr. Brehm says (p. 79): "All the young of the first litter of the various Lemming females thrive, and six weeks later at the most these also multiply. Meanwhile the parents have brought forth a second and a third litter, and these in their turn bring forth young. Within three months the heights and low grounds of the tundra teem with lemmings, just as our fields do with mice under similar circumstances. Whichever way we turn we see the busy little creatures, dozens at a single glance, thousands in the course of an hour. But the countless and still increasing numbers prove their own destruction. Soon the lean tundra ceases to afford employment enough for their greedy teeth. Famine threatens, perhaps actually sets in. The anxious animals crowd together and begin their march, hundreds join with hundreds, thousands with other thousands, the troops become swarms, the swarms armies. They travel in a definite direction, at first following old tracks, but soon striking out new ones; in unending files—defying all computation—they hasten onwards; over the cliffs they plunge into the water. Thousands fall victims to want and hunger; the army behind streams on over their corpses; hundreds of thousands are drowned in the water or are shattered at the foot of the cliffs; the remainder speed on; other hundreds and thousands fall victims to the voracity of Arctic and red foxes, wolves and gluttons, rough-legged buzzards and ravens, owls and skuas which have followed them; the survivors pay no heed. Where these go, how they end, none can say; but certain it is, that the tundra behind them is as if dead, that a number of years pass ere the few who have remained behind and have managed to survive slowly multiply and visibly re-people their native fields." This eloquent passage reminds us of the manner in which migrations of all kinds of animals have taken place in former times, and are still taking place. It is principally want of food which compels them to search for new homes.

On page [91] I have referred to some birds which have come to us from the north. One of these, the Snow Bunting (Plectrophenax nivalis), is a typically Arctic species. In summer it is widely distributed, and is found in Spitsbergen, Novaya Zemlya, Siberia, and the Arctic Regions generally. In winter it migrates down into North America, into Japan, Northern China, Turkestan, Southern Russia, and occasionally even across Europe into North Africa. Very characteristic Arctic birds are the Eider Ducks belonging to the genus Somateria. Three species have visited the British Islands. The common Eider Duck (S. mollissima), which is of such high commercial value, is abundant in Norway and northward, throughout the Polar Regions. The appearance of the King Eider (S. spectabilis) on our coasts is an extremely rare occurrence, and even in Norway it is only known as a visitor, but on Novaya Zemlya and along the Arctic shores of Siberia, in Greenland and Arctic North America, it is known to breed. The third species, Steller's Eider (S. Stelleri), seems to be still rarer, and only in the Aleutian islands and in the north of Alaska can it be said to be at all abundant. It is probable that the famous Great Auk (Alca impennis, [Fig. 9]) also was a typical Arctic species. Its range extended to both sides of the Atlantic. In Newfoundland and on the coast of Iceland it is known to have been met with in considerable numbers within historic times; and no doubt, like all Arctic species, it extended farther southwards at a more remote period.

Fig. 9.—The Great Auk (Alca impennis).

The members of the genus Lagopus, including the various species of Grouse, are likewise of northern origin. The British Red Grouse (L. scoticus), which may be looked upon as a form of the Scandinavian Willow Grouse (L. albus) (compare p. [91]), constitutes in some respects a curious case of parallelism with the Arctic Hare, since the latter, in its more southern station, generally retains the summer fur throughout the year. The allied Ptarmigan (L. mutus) inhabits Scandinavia, the Ural Mountains, and some of the Asiatic mountain ranges. It is also found in the European Alps and in the Pyrenees. The North European range of the Ptarmigan suggests that we are dealing with an ancient species which came south from the Arctic Regions at about the same time as the Arctic Hare; but it is more probable, as I have shown in a subsequent chapter (p. [334]), that this species has entered Europe more recently with the Siberian migrants from Central Asia, where indeed the genus had its original home. The Black Cock (Tetrao tetrix) and the Capercaillie (Tetrao urogallus) have also come to us from the east, and have even penetrated into Ireland. They are therefore some of the few instances of members of the Siberian invasion having become temporarily established there.

Reptiles and amphibia are altogether unknown in the Polar Regions, but a large number of fish, chiefly marine, have taken their origin there. The Salmon family are of Arctic origin, as also are the Sticklebacks and the Perches, many of the Cod family, the Herrings, and several of the Flat fish.

It would lead me too far to refer to the invertebrate fauna of the Polar Regions, but a few remarks on the Arctic plants may not be out of place.

The principal Arctic genera are Salix, Ranunculus, Draba, Pedicularis, Potentilla, Saxifraga, Carex, Juncus, Luzula, Eriophorum, and others.

Among the most characteristic Arctic plants may be mentioned Dryas octopetala, to which I have already referred as occurring in the west of Ireland; Saxifraga oppositifolia, another British species, occurs in the higher mountains of Scotland, Ireland, and Wales; Braya alpina, Papaver nudicaule, Lychnis apetala, Diapensia lapponica, and Lobelia Dortmanna, which is found in the lakes of Scotland and Ireland. The dwarf birch (Betula nana) also, which still occurs in Scotland and the North of England, and which had formerly a wider range in the British Islands, should be included among these; but there are other plants probably of Arctic origin, though not now occurring in the Arctic Regions, and to these may be classed the so-called American species of plants which are found on the northern and western coasts of Ireland, in the Hebrides, in Scotland, and in North America. These are no doubt the relics of an Arctic flora which flourished in high latitudes in past times when the climate there was more temperate. A list of these species will be found on page [166].

As none of them occur in Siberia, they must either have found their way to North America and to Europe from the Arctic Regions, or have travelled from North America across the latter to Europe. In any case a former land-connection between the two continents must have existed. This becomes the more evident when we examine the remarkable results obtained by the late Professor Heer, who first described the Tertiary plant-beds in North Greenland. No less than 282 species of plants have been described by this eminent botanist from these deposits. A large number of the plants found were trees belonging to the genus Sequoia, Thujopsis, and Salisburia, besides beeches, oaks, planes, poplars, limes, and magnolias. That they grew on the spot is proved by the fruits, which have been obtained from these beds in various stages of growth.

From a similar deposit in Spitsbergen a large number of fossil plants have also been brought to light, many of which are identical with those found in Greenland; and some of the Greenland forms (such as Taxodium distichum and Sequoia Langsdorfii) have been found too in Alaska, showing that there was probably a continuity of land between Spitsbergen and North America by way of Greenland. Two species of Sequoias, namely, S. sempervirens and S. gigantea, the well-known Californian giant trees, are very closely allied to the Greenland forms discovered by Professor Heer.

Heer assigned the Arctic plant-bearing beds to the Miocene epoch, but doubts have been recently thrown upon this opinion by Mr. Starkie Gardner, who brought forward arguments in support of his theory of their being of the Eocene age. Professor Heer, however, was able to meet these criticisms, and he is ably supported in his views by Professor Engler and other eminent continental botanists.

It is evident that under the present conditions of temperature none of those plants could have flourished in Greenland. The climate must have been much milder than it is at present. Professor Heer estimated from the general aspect of the fossil flora that the mean annual temperature of North Greenland was at least nine degrees centigrade, and that the mean winter temperature was not below zero.

It will hardly be necessary for me to review here the various theories which have been advanced by geologists and botanists to account for this remarkably high temperature in such northern latitudes. Any one who has read the writings of the late Dr. Croll cannot help being struck by the facts he adduces to show the importance of ocean currents in relation to the distribution of heat over the globe, and it seems to me that the view which attributes the mild climate prevailing in former times in Greenland to warm ocean currents reaching the Polar Circle is the one least open to serious objections. If we suppose that the North Atlantic Ocean was bridged by a land-connection between Scandinavia and Greenland by way of Spitsbergen, and between Greenland and North America, the Polar Ocean would be practically a closed sea. If, then, a wide passage existed somewhere about Behring Straits to allow a warm current to enter and circulate within the Arctic Seas, we should have the southern shores of Greenland washed by the warm Atlantic current and the northern shores by a warm Pacific current, which combination would undoubtedly produce the effect of raising the temperature throughout the Polar Regions very considerably; and especially would that be the case with regard to Greenland and the neighbouring islands.

It might be urged that the constant darkness during winter must have had an injurious action upon the flora, but it is found that in countries such as Northern Russia, where southern plants are housed during winter in greenhouses, the light being almost entirely excluded by a covering of straw, no serious damage is done thereby to the plants.

It seems probable that a similar gradual refrigeration of climate in northern latitudes has taken place after Miocene times as has been proved to have occurred in Europe.

Some years ago Dr. Haacke propounded the hypothesis that the centre of creation of all the larger groups of animals was situated in the region of the North Pole, and that the newly originated groups must always push the older ones farther and farther south into the most remote corners of the earth. As instances of the correctness of his view he quotes the fact that the more ancient mammals, such as Monotremes, Marsupials, Lemurs, Edentates, and Insectivores, all inhabit the more southerly parts of the world. The Apteryx, Moa, Rhea, and the Ostrich, as well as Æpyornis, which is only recently extinct, are found in the same regions. But we have no palæontological evidence in favour of these extravagant views. Fossil Edentates and Marsupials are almost entirely confined to the Southern Hemisphere, and the supposition that because these primitive mammals inhabit the extreme south of our great continental land-masses, they therefore came from the north, cannot be said to be an argument. Nevertheless, I am quite with Dr. Haacke in considering that the North Pole, or, we might say, the lands within the Arctic Circle, have been the place of origin of some of our European mammals, and there can be no doubt that certain species in other groups, among invertebrates and also plants, have originated in the Polar Regions. The facts of geographical distribution teach us that in these regions there has been a centre of origin within comparatively recent geological times. I have on a previous occasion drawn attention to the range of the Reindeer: that it lives almost throughout the Polar lands, and that it spreads into North America, Northern Europe, and Northern Asia. We have, again, fossil proof that its range extended down to the Pyrenees in Europe in pleistocene times. But there is not a scrap of evidence that it ever during any time occurred farther south, either in Europe, Asia, or North America. Its original home must therefore have been in the Polar Regions, for if it had originated either in Central Europe, Asia, or America, there is no reason why it should not, in the natural course of events, have extended its range to the south as well as to the north.

The Arctic Hare presents us with a very similar case of distribution. Like the Reindeer, it inhabits, as we have learned, the Polar Regions and the northerly parts of the Old World and the New; but while we have only fossil evidence of the former, more southerly, extension of the range of the Reindeer, the Arctic Hare furnishes us with a still stronger proof of its past southward range in the survival of small isolated colonies in some of the southern mountain ranges of Europe and Asia. It is generally believed that the occurrence of the Arctic Hare in these southern mountains is a standing testimony to the severity of the climate at the time when it commenced its southerly increase of range, but I have already shown that the climate of Europe at that time was not necessarily colder than it is at present, but that it may have been somewhat milder (p. [80]). I think that a vast increase of ice in the Polar Regions has taken place only at a comparatively recent date, and that both the Reindeer and the Arctic Hare originated there during a much more temperate climate than obtains at present. A great sensation was produced among European zoologists and anthropologists when the discovery was first announced that the remains of the Reindeer had been found in the Pyrenees, and it naturally gave rise to many speculations as to the nature of the climate at the time when its range extended so far south.[1] The greater number of our best authorities are still of opinion that the existence of the Reindeer in Southern Europe points to the prevalence of an arctic climate in that region. It is generally overlooked, however, that the Reindeer-remains occur in company with many typically southern animals, which, if they had been found alone, would have been held to be a certain indication of a warm climate. The French geologist Professor Lartet, indeed, was of opinion that the temperature during the time when the Reindeer lived in the Pyrenees must have been rather milder than it is at present (compare pp. [71]-[75]). Similarly, Mr. Harlé argues, that the extremely cold climate probably did not extend to South-western France, since that area only received occasional visits from some of the representatives of the Arctic fauna.

Long ago North American zoologists recognised the existence in their country of two well-marked races of the Reindeer (Caribou)—a smaller one with rounded antlers ([Fig. 10]), and a larger one in which the antlers are more or less flattened out ([Fig. 11]). Two somewhat similar races can also be traced in the fossil remains of the Reindeer in Europe. It was, I think, Gervais who first pointed out that the Reindeer remains from the north of France differed from those found in the south; and Lartet referred to the fact that the southern remains were more like what, in America, is called the Barren-ground Caribou, while those from Central European deposits all belonged to the Siberian variety, which is more like the Woodland Caribou of North America. In Ireland, Professor Leith Adams also drew attention to the curious fact that all the Irish Reindeer remains resemble the Norwegian variety rather than the Siberian; and Mr. Murray was so much struck by the close resemblance between the Spitsbergen and Greenland forms with the Barren-ground Caribou, that he based some speculations on a former land-connection between these countries on this circumstance.