The History of the European Fauna Part 3

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 lat.i.tudes of a northern fauna and flora.

Mr. Charles Martins, who based his calculations on the temperature during the Glacial period on the glaciers of Chamounix, concluded that it only needed a lowering of the temperature to the extent of four degrees Centigrade to bring the glaciers down to the plain of Geneva, and in fact give us back the Glacial period. It need not surprise us, therefore, that the French geologist, Mr. Falsan, the author of _La periode glaciere_, is of opinion (p. 230) that the mean annual temperature of France during the Glacial period was approximately from 6-9 degrees Centigrade, perhaps more. Close to the immense glaciers of the Rhone, it might have been about six degrees. This is the actual mean annual temperature of the South-west of Sweden and Norway, or the North of Scotland.

Although all these investigations tend to show that the climate of Europe during the Glacial period was by no means so severe as we are often led to believe, yet there exists also a school of geologists who maintain there was actually a higher temperature than at present. The inconsistency of mentioning heat in connection with ice and snow is more apparent, however, than real, for we must remember Tyndall's original remark on this subject. It is the snow, he says, which feeds the glaciers. But the snow comes from the clouds, and these again originate from the vapours which the sun causes to be absorbed from the ocean.

Without the sun's heat, we should have no water vapour in the atmosphere; without vapour, no clouds; without clouds, no snow; without snow, no glaciers. The ice of glaciers, therefore, owes its origin indirectly to the sun's heat. It has been supposed that if the sun's heat diminished, larger glaciers would form than those existing to-day, but the diminution of the solar heat would infallibly reduce the amount of water vapour in the air, and would thus stop the very source of glaciers.

Mr. Falsan even admits that without a change of the mean annual temperature (p. 201) of Europe, the central portions of our continent might at this period have enjoyed an insular climate. This more equable and humid climate could, within certain limits, favour the development of the ancient glaciers by increasing the snowfall and slackening the summer rate of melting.

It seems evident then, according to these views, that with a comparatively slight change of the atmospheric conditions in the British Islands, we might have glaciers back again on all our highest mountain ranges in England, Scotland, and Ireland. But a widespread belief seems to prevail that the presence of glaciers implies a very low temperature.

Snow and ice, however, are formed as soon as the temperature falls below freezing point; it does not matter whether there be 1 or 20 degrees of cold. Winters with a few degrees of frost will be just as favourable for the growth of glaciers as winters with the most severe cold.

Let us now see what the fauna and flora, as far as we know it, tell us of the climate of the Glacial period. At the very outset of our inquiry we are confronted with one very serious difficulty in the problem, and that is the supposed occurrence of inter-glacial mild phases alternating with colder ones during the Ice Age. At first, when traces of a temperate flora and fauna were discovered intercalated between two layers of boulder clay, their presence was explained by the supposition of a mild inter-glacial period. The famous Forest-bed on the east coast of England was also p.r.o.nounced to be an inter-glacial deposit, though not coming precisely under this definition. In a few places one such bed was found, in some two or more, and in others none at all. Professor James Geikie discovered the evidences of no less than five of such inter-glacial epochs (p. 612) in Europe. Lest a reader of that author's remarkable work on the Ice Age might carry with him the idea that his hypotheses had met with general acceptance, a few quotations from almost equally high authorities on glacial matters will be useful. "That the glaciers," remarks Professor Bonney (p. 245), "were liable to important oscillations seems to be proved, but whether the evidence suffices to establish inter-glacial epochs, in the usual sense of the words, is more doubtful. When the snow-fields, as in the Alps, were much more extensive than they are at present, the glaciers which radiated from them would be more sensitive to minor climatal change. Even now they oscillate considerably. But during a Glacial epoch, an inch, either more or less, of precipitation might mean a considerable advance or retreat of the ice in the lowlands." French geologists look with even less favour on Professor Geikie's theories. Mr. Falsan (p. 212) says that he agrees with Messrs. Favre, de Saporta, Lory, de Mortillet, Desor, de Lapparent, Lortet, Chantre, Benoit, Fontannes, Deperet, and many other geologists, that there was only a single Glacial period, which, according to each particular region, might be divided into several phases, or into their equivalents--viz., one or more extensions of the ancient glaciers. But, on the whole, the view that there was at least one inter-glacial phase in the Glacial period meets with more general acceptance among geologists, I think, though the other opinion agrees much better with the nature of the fauna and flora as it has been revealed to us from the pleistocene deposits.

The occurrence of the remains of such arctic species of mammals as the Musk-Ox, Arctic Fox, Glutton, Lemming, and many others in these deposits, is frequently held up to us by geologists as a proof of the prevalence of an arctic climate while these beds were laid down. And indeed this appears at first a most satisfactory explanation of the phenomenon. But we must not judge the climate of Europe by their presence alone. As I shall explain more fully in Chapter V., these species invaded Europe owing to two circ.u.mstances. 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 const.i.tuting 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 succ.u.mbed. 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 pa.s.s northwards, and in the winter time the northern would sway southwards, and thus occupy at different times of the year the same tract of ground, as is now the case with the elks and reindeer." "In some of the caverns," he continues (p. 114), "such as that of Kirkdale, the hyaena preyed upon the reindeer at one time of the year, and the hippopotamus at another."

A similar mingling of northern and southern faunas has also been observed in France. Mr. Falsan tells us (p. 236), that the remains of the mammals gathered and determined by Lartet and Gaudry belong partly to species which have been wrongly regarded as indications of a severe climate, and partly to such as are accustomed to a relatively mild temperature. In several localities in France, viz., at Levallois, St.

Acheul, and Arcy, the remains of the Hippopotamus have occurred together with those of the Reindeer; whilst, according to Sir H. Howorth, the Lion has been found together with northern Voles at Bicetre, near Paris.

It is stated by the same authority (p. 115) that much the same conditions exist in Germany. "The lion and the spotted hyaena, the mammoth and rhinoceros, were found with the marmot, the suslik, the lemming, the pica, and the reindeer." At another locality near Thiede, remains of the Mammoth, woolly Rhinoceros, Horse, Ox, Reindeer, Arctic Fox, Lemming, and Pica are met with in the same deposit. In quoting the presence of these northern animals in Europe as evidence of an arctic climate, we commit a fatal mistake. Indeed, breeders of animals and those acquainted with zoological gardens know perfectly well that it is much easier to keep a northern species in a southern climate, than a southern species in a northern one. If in a Central European deposit occur a mixture of northern and southern forms of animals, the presence of the latter is more remarkable than that of the former. Logically, we should look upon the occurrence of southern species in the north, therefore, as supporting the view that a mild climate had induced them to travel northward. The only indication, indeed, of the presence of a Monkey in the British Isles in former times comes to us from the very same strata which have also yielded the remains of the Siberian mammals.

Before I conclude the consideration of the pleistocene fauna, it may be of interest to hear what Mr. Lydekker, one of our highest authorities on fossil mammals, has to say on this subject. "The most remarkable feature connected with this fauna is the apparently contradictory evidence which it affords as to the nature of the climate then prevalent. The Glutton, Reindeer, Arctic Fox, and Musk-Ox are strongly indicative of a more or less arctic climate; many of the Voles (_Microtus_), Picas (_Lagomys_), and Susliks (_Spermophilus_), together with the Saiga Antelope, appear to point equally strongly to the prevalence of a Steppe-like condition; while the Hippopotamus and Spotted Hyaena seem as much in favour of a sub-tropical state of things. Many attempts have been made to reconcile these apparently contradictory circ.u.mstances; 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 acc.u.mulated 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 sh.e.l.ls 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 a.s.sumed 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 lat.i.tudes 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 ent.i.tled to have a voice in the matter. Professor Warming is of opinion that the main ma.s.s 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 lat.i.tudes, 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 gla.s.s 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 const.i.tution 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 lat.i.tudes of Arctic animals and plants, it still remains for me to give a succinct statement of the light thrown by this fauna and flora on the widespread phenomena of glaciation. It is necessary to do so, because, though the greater development of glaciers on the mountains of Europe in former times does not presuppose the prevalence of an Arctic climate, the survival through the Ice Age of a fauna and flora could not possibly have taken place in northern Europe if the theories of glaciation now so much in vogue are really true. Professor Geikie reminds us, in speaking of his native country (p. 67), that "we must believe that all the hills and valleys were once swathed in snow and ice; that the whole of Scotland was at some distant date buried underneath one immense _mer de glace_, through which peered only the higher mountain tops." That under such conditions no fauna or flora to speak of could have survived in Scotland is evident. Then again he argues (p. 426) that because in the great plain of Europe we meet occasionally with striated rock-surfaces and _roches moutonnees_ very similar to those produced by the glaciers of Switzerland, it must have been traversed by "inland ice" flowing from Scandinavia and the Baltic southward. The boulder clay of Germany is supposed to have acc.u.mulated 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 acc.u.mulations of gravel, sand, and clay. The latter is generally spoken of as "boulder clay," and, with the a.s.sociated 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 acc.u.mulations, and hence they came to be known as the 'great northern drift formation.'" "But," he adds (p. 433), "when the phenomena came to be studied in greater detail and over a wider area, this explanation did not prove satisfactory. The facts described in the preceding paragraphs--the occurrence of striated surfaces and _roches moutonnees_, the disturbed appearances a.s.sociated 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 lat.i.tudes, 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 a.s.sume 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 ma.s.s. 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 a.s.signed 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 ma.s.s 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 acc.u.mulated round the sh.o.r.e 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 ma.s.s 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 b.u.t.terflies and snails have not been neglected, and at least one very remarkable work on the latter has been published dealing with their origin in Europe and in the remainder of the Palaearctic region.

The former distribution of land and water is intimately connected with the origin of the European fauna, and the changes which have taken place in this respect may be best traced by the present distribution of mammals, snails, and earthworms. In this manner the British Islands may be shown to have been connected with one another and with the Continent; Spain with Morocco across the Straits of Gibraltar; Greece with Asia Minor, and so forth.

The British fauna has played such an important part in the evolution of the European fauna, that it forms the key to the solution of the wider problem. In it five elements are recognisable, of which the Lusitanian element is the oldest, and the Siberian the most recent. It has been deemed advisable to conclude this chapter with a short review of the history of the Glacial period in its climatic effects on the animals and plants of Europe. A number of writers are quoted who have conducted special researches in determining the temperature of our continent at the time. The fauna of Europe is frequently described as having been of an Arctic nature, but as a matter of fact there existed during the Ice Age a striking and most remarkable mingling of a northern and a southern fauna. The presence of Siberian mammals in Europe is said to have been due to the prevalence of a dry steppe climate, but this view is not supported by other evidence. The Alpine flora in a wide sense is probably pre-glacial in origin, and appears to have survived the Ice Age where it is now known to exist. A few words on the phenomena of glaciation are added before bringing the chapter to a close.

CHAPTER III.

THE FAUNA OF BRITAIN.

The British Islands are, as I have remarked, very suitable as a starting-point for our investigations. Their fauna and flora are fairly well known, and the distribution of the large animals at any rate, which are of course of much importance in these researches, has been as much studied as that of any other area in Europe. We possess in England an abundance of the remains of past animal life, and a combination of the data furnished by both of these important factors will enable us to draw up a history of the origin of the present British fauna.

In the first chapter I indicated that in the fauna of the British Islands three divisions or elements are recognisable--a northern, a southern, and an eastern. These elements correspond to migrations which can be proved to have arrived in this country at different periods in past times. When we investigate these migrations more closely, the eastern is found to be composed partly of European and partly of Siberian species. The southern is made up of European and of Central and Southern Asiatic species. To make matters still more complex, the southern and eastern migrations insensibly merge into one another, so that it is often very difficult to determine to which of them an animal may belong. The European species spread princ.i.p.ally 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 sh.o.r.es 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.