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.
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—
- The Channel Isles.
- South-east of England (including Cambridgeshire).
- South-west of England.
- North-east of England.
- North-west of England (including Isle of Man).
- North of Ireland.
- South of Ireland.
- South of Scotland.
- North of Scotland.
- 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:—
- England and Wales (except the South-west).
- 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.