The evidence of the Mammalia as to Climate.—The Southern Group.—The Northern Group.—Probable cause of Association of Northern and Southern Groups.—The Temperate Group.—Species common to Cold and Tropical Climates.—Extinct Species.—Two Periods of Glaciation in Britain.—Three Climatal Changes represented on the Continent.—Europe invaded by Pleistocene Mammals before the Glacial Period.—Mammals lived in Britain during the Second Ice or Glacial Stage.—The Glacial Period does not separate one Life-era from another.—Relation of PalÆolithic Man to Glacial Period.—Age of Contents of Caves in Glaciated Districts.

The Evidence of the Mammalia as to Climate.

In the last three chapters we have seen that the cave-mammalia throw great light on the pleistocene geography of Europe, and that there is reason for the belief that the land surface then extended northwards and westwards, so as to include Ireland; and southwards to join Africa, in the direction of Sicily, Malta, and Gibraltar. We must now pass on to the consideration of the climate on this great continental area, which would allow of so large and varied a fauna existing in our quarter of the world.

The Southern Group of Animals.

The pleistocene fauna is remarkable for the mixture of species. It consists of forms now banished to South Africa, Northern Asia, and America, or to the severe climate of high mountains, mingled with those which lived in Europe in the historic age, and those which have wholly disappeared from the face of the earth. We will take the living species first.

The southern group consists of the following animals:—

Lion.
Caffir Cat.
Spotted HyÆna.
Striped HyÆna.
Serval.
Hippopotamus.
African Elephant.
Porcupine.

At the present day the lion ranges over the whole of Africa, with the exception of Egypt and the Cape Colony, whence it has been driven out by the hand of man. In Asia, the maneless variety inhabits the valley of the Tigris and Euphrates, and the districts bordering on the Persian Gulf; and in India, according to Mr. Blyth, the province of Kattywar in Guzerat. Although now only found in these hot regions, it is proved, by the concurrent testimony of Herodotus, Aristotle, Xenophon, Ælian, and Pausanias, to have inhabited the mountains of Thrace, and of Asia Minor, and it probably became extinct in Europe before the end of the first century after Christ.259 We may therefore infer that it possessed a sufficient elasticity of constitution to endure a considerable degree of cold, although its present distribution implies that it is better fitted to thrive in a tropical than in a cold climate. The Caffir cat (Felis caffer of Desmarest) is an African species, which has been discovered by Mr. Ayshford Sanford and myself, in Somersetshire; it also occurs in the caves of Germany, France, and Gibraltar. The spotted hyÆna now lives only in South Africa, while the striped species ranges through Africa and the warmer regions of Asia. It was extremely rare in Europe in the pleistocene age, and has not been identified in any deposit further north than Lunelviel, in southern France. The hippopotamus, now found only in middle and southern Africa, is proved by its fossil remains to have formerly dwelt in the region of the Lower Nile, as well as in Algeria. The serval and African elephant have been found in the Iberian peninsula, and the latter in Sicily.

The evidence afforded by the animals, as to the pleistocene climate of those portions of Europe which they inhabited, differs considerably in point of value, but on the whole indicates that it was temperate, or comparatively hot; for although the elasticity of constitution which we know to have been possessed by the lion, was probably shared by the spotted hyÆna, it is very unlikely that so aquatic an animal as the hippopotamus could have ranged from southern Europe, as far north as Yorkshire, under any other than temperate conditions. It could not have endured a winter sufficiently severe to cover the rivers with a thick coating of ice, without having its present habits profoundly modified; and such an alteration of habits would certainly leave its mark, in other modifications in the fossil skeleton than those minute differences which have been observed, when it is compared with that of the living Hippopotamus amphibius. The porcupine of southern Europe has been found as far north as the caves of Belgium (Schmerling).

The Northern Group.

The northern group consists of those animals which are now only to be met with in the colder regions of the northern hemisphere, either in low latitudes or at great altitudes.

Marmot.
Pouched Marmot.
Lemming.
Alpine Hare.
Tailless Hare.
Glutton.
Arctic Fox.
Musk-sheep.
Reindeer.
Ibex.
Chamois.

To this list the palÆolithic man of the caves must be added, since he is probably related by blood to the Eskimos, and appeared in Europe simultaneously with the arctic group of animals.

The testimony of these animals as to climate is directly opposed to that of the preceding group, since they now only flourish in the arctic regions, or in mountainous districts in which the climate is severe. The marmot, in the pleistocene age, lived in Belgium, and descended from the Alpine heights as far as the shores of the Mediterranean, where it has been met with in the caverns near Nice. The pouched marmot, Spermophilus citillus of the Don and Volga, penetrated as far to the west as Somersetshire. The Alpine hare, now found only in the colder climates of northern Europe, Asia, and America (with the solitary exception of Ireland), ranged as far down the valley of the Rhine as Schussenreid, in Suabia. The two carnivores now dwelling in the colder regions of the north, the glutton or wolverine, and the arctic fox, have been discovered, the one as far south as France, the other as far as Schussenreid, and both probably occupied the whole of Germany, and of northern Russia, in the pleistocene age.

The musk-sheep,260 the most arctic in its habit of all the herbivores, is, at the present time, restricted to the high latitudes of North America, where it thrives in the desolate, treeless, barren grounds, not even being driven from its haunts by the extreme severity of the winter. It has been traced, by its fossil remains, from its present abode, across Behring’s Straits, and through the vast Siberian steppes, into Russia in Europe, Germany, Britain, and as far south and west as the barrier offered by the Pyrenees. Throughout this large area its remains occur in association with the reindeer, and both these animals, as I have remarked above, were hunted by the palÆolithic dwellers in the caves of Aquitaine, just as they are now hunted by the Eskimos on the shores of the Arctic Ocean.

If the present habits of these animals be any index to their mode of life in the pleistocene age, their presence in the area north of the Alps and Pyrenees implies that the climate in France, Germany, and Britain was severe, or analogous to that which they now enjoy on the tops of lofty mountains, or in the northern Asiatic steppes, or the high northern latitudes of America. But this conclusion is diametrically opposed to that which is based on the evidence of the southern group of animals.261 And the remains of the two groups of animals are so associated together in the caves, and river-deposits of Europe, north of the Pyrenees, that it is impossible to deny the fact that it was the common feeding-ground of both during the same era.262

Probable Cause of Association of Northern and Southern Groups.

Must we then infer that in the pleistocene age the present habits of the musk-sheep, the reindeer, chamois, or ibex, were so changed as to allow them to flourish side by side with the hippopotamus, or vice versÂ? Was the climate colder than it is now in Europe, or was it hotter? How was this singular association of northern and southern species brought about? The problem may be solved if we refer to the present distribution of animals in northern Asia and North America. As the winter comes on the arctic species gradually retreat southwards, and occupy the summer feeding-grounds of the elk, red-deer, and other creatures which are unable to endure the extreme severity of an arctic winter. In the spring the latter pass northwards, to enjoy the summer herbage of that area, which had been the winter-quarters of the arctic group of animals. Thus there is a continued swinging to and fro, over the same region, of the arctic and the temperate animals, and their remains must necessarily become more or less associated in the river-deposits, as well as in caves, where these last happen to occur. In northern Asia, and in America, the only boundary between the northern and temperate zoological provinces is that constituted by the fluctuating annual temperature, and there are no great hilly barriers running east and west, to prevent free migration to the north or south. If reference be made to the map, Fig.126, it will be seen that these conditions were amply satisfied in the pleistocene age. There were no physical barriers to migration, from the shores of the Mediterranean, as far north as Ireland. If the winter cold were severe, the reindeer and musk-sheep might advance as far south as the Pyrenees, and if the summer heat were intense there would be nothing to forbid the hippopotamus and the African carnivores advancing northwards. It seems to me that this is the only hypothesis which will satisfy all the facts of the case. The traces of glaciers and snow-fields where they are no longer found prove that the winter was severe; while the warmth of the summer seems to be sufficiently demonstrated by the presence of African species. Such extremes of temperature are presented, more or less, by all continents extending from high to low latitudes. They are modified in Europe at the present time by the warm current of the Gulf Stream, by the large area now occupied by the Mediterranean Sea, and by the submergence of the pleistocene lowlands on the Atlantic border.

The Temperate Group.

The third group of pleistocene mammalia consists of those still living in the temperate zones of Europe, Asia, and America:

Beaver.
Hare.
Rabbit.
Wild Cat.
Martin.
Stoat.
Weasel.
Otter.
Brown Bear.
Grizzly Bear.
Wolf.
Fox.
Horse.
Urus.
Bison.
Antelope saiga.
Wild Boar.
Stag.
Roe.

The range of many of these animals has been profoundly modified since the pleistocene age. The Antelope saiga of the Don and Volga lived as far to the west as Aquitaine. The grizzly bear, instead of being restricted to its American habitat in the Rocky Mountains, ranged over the whole of Siberia into Europe, as far to the south as the Mediterranean, and westwards as far as Gibraltar.

The urus263 still lives in the larger domestic cattle, and the bison is represented in Europe by those which are protected by the forest laws of Lithuania, and in North America by the vast herds which are rapidly being exterminated, like the red Indian, by the rifles of the settlers. The horse was as abundant, and as widely spread over Europe, as the urus and the bison; according to Prof. Brandt it now no longer lives in Siberia in a wild state.

Species common to Cold and Tropical Climates.

The panther or leopard, which has been found alike in Britain, France, and Germany, has at the present day a most extended range through Africa, from Barbary to the Cape of Good Hope, and throughout Persia into Siberia. In this latter country Dr. Gothelf Fischer describes it as living in the same districts in the Altai Mountains, and in Soongaria, as the tiger. The fox and wolf are like instances of carnivores being able to endure great variations in temperature without being specifically modified. These three animals, therefore, tell us nothing as to the pleistocene climate.

Extinct Species.

The extinct pleistocene species may also be divided into the same classes as the living, by an appeal to their geographical distribution. Two out of the three species of rhinoceros found in the caves (R. megarhinus and R. hemitoechus), and an elephant with slightly curved tusks (E. antiquus), had their head-quarters south of the Alps and Pyrenees, whence they wandered northward as far as the latitude of Yorkshire. The pigmy elephant and the dwarf hippopotamus are peculiar to the south, and the Machairodus latidens, or large sabre-toothed felis, is a survival, from the pleiocene age, of a peculiarly southern type.

The woolly rhinoceros, on the other hand, may be viewed as a northern form, since it is met with in vast abundance in the arctic regions of Siberia, as well as in Europe, and has not been found south of the Alps and Pyrenees. The cave-bear has not been discovered either in the extreme north or in the south of Europe, and may therefore be considered of temperate range; and the Irish elk, identified by Prof. Brandt, from the caves of the Altai Mountains, had a similar range in middle Europe. The mammoth, endowed with an elastic constitution, was able to endure the severity of an arctic climate in Siberia and North America, and the temperature of the latitude of Rome and the Gulf of Mexico,264 and consequently tells us as little of the pleistocene climate as the panther, fox, or wolf.

The evidence, therefore, as to climate, offered by the extinct animals in the caves is of the same nature as that of the living. There is the same mixture of northern and southern forms, which can only be accounted for satisfactorily by seasonal migrations, according to the summer heat and winter cold, such as those which are now observed to take place in Siberia and North America.

Before we consider the relation of the pleistocene animals buried in the caves and river deposits to the glacial period, it is necessary to define what is meant by the term glacial.

Two Periods of Glaciation in Britain.

At the close of the pleistocene period the climate gradually became colder, until ultimately it was arctic in severity in northern Europe. The researches of many eminent observers prove that an enormous sheet of ice, like that under which Greenland now lies buried, extended over North Britain, Wales, and Ireland, leaving its mark in the far-travelled blocks of stone, the moraines, and the grooves which pass over the surface irrespective of the minor contours. The land then, most probably, as Prof. Ramsay and Sir Charles Lyell believe, stood higher than it does now. To this succeeded a period of depression, during which the mountains of Wales were submerged to a height of at least 1,300 feet; and the waves of the sea washed out of the pre-existing glacial detritus the shingle and sand, termed the “middle drift,” which occurs also in Scotland and Ireland.265 Then the land was re-elevated above the waves, and a second period of glaciers set in, traces of which occur abundantly in Wales, Scotland, and Ireland, in the white areas in Fig.126. They were, however, of far less extent than those which preceded them, occupying isolated areas instead of forming one continuous icy covering to the country. The glacial phenomena may be briefly summed up as follows: 1. As the pleiocene temperature was lowered, the glaciers crept down from the tops of the mountains, until at last they united to form one continuous ice sheet, moving resistlessly over the smaller hills and valleys to the lower grounds, and the first ice or glacial period set in. 2. Then followed the era of depression beneath the sea. 3. And, lastly, on the land re-emerging from the sea the second ice or glacial period began. The climate during the marine depression must obviously have been milder than that of either of the glacial periods, because of the moderating effect of the wide extent of sea. The exact relation of the boulder clays with marine shells, in the centre and south of Britain, to the detritus left behind by the ice-sheet in the north, has not as yet been satisfactorily ascertained. It is very probable that the elevation of land in the north was simultaneous with a southern depression, which allowed of icebergs depositing their burdens in the eastern counties, in the valley of the Thames, and as far south as Selsea, on the coast of Sussex.

Three Climatal Changes represented on the Continent.

These changes of climate have also been observed on the continent of Europe. The Swiss geologists have shown that the Alpine glaciers extended farther than they do at the present time, and that they present two stages of extension, the first of which is of greater magnitude than the second. The Alpine blocks and moraines have been traced far down into the plains of Lombardy, northwards into the valley of the Rhine, and in France as far south in the valley of the Rhone as Valence. The admirable essay and map brought by MM. Falsan and Chantre, before the meeting of the French Association for the Advancement of Science at Lyons, in 1873, show that there were two periods of glaciation in the valley of the Rhone, the one being due to the movement of an ice-sheet irrespective of the lower hills, the other being merely the work of the glaciers localized in the valleys. These in all probability correspond in point of time with the like stages of the complicated glacial phenomena in Britain. At this time the glaciers of the Pyrenees, now so small, extended at least from thirty to forty miles from their present position down into the plains, leaving behind most astounding evidences of their presence in the valley of the Garonne and elsewhere. On the Spanish frontier, for example, one of the precipitous sides of the valley, near the Pont du Roy, is so smoothed and polished that it is bare of vegetation except in the deep grooves, which offer a precarious support to the roots of ferns and of dwarf beeches. The hills of Dauphiny also and Auvergne were crowned with glaciers, and those of the latter have been shown by MM. Falsan and Chantre to have been conterminous with those of the Alps.

The interglacial period of marine depression in Britain is represented in Switzerland by the lignite beds of DÜrnten, Utznach, and Pfaffikon, the last of which rests upon and is covered by the boulder drift. The fossil remains from DÜrnten, identified by Dr. Falconer and Prof. RÜtimeyer, prove that two southern animals, Elephas antiquus and Rhinoceros megarhinus, inhabited the district in the interval between the retreat of one set of glaciers and the advance of another. They probably migrated from the plains of Lombardy, where they abounded in the pleistocene age.

Europe invaded by Pleistocene Mammals before the Glacial Period.

What is the precise relation of the pleistocene mammals to these two periods of cold? Did they invade northern and central Europe during the first or the second, before or after, the marine submergence indicated by the “middle drift?” We might expect, À priori, that as the temperature became lowered, the northern mammalia would gradually invade the region occupied before by the pleiocene forms, and that the reindeer, the mammoth, and woolly rhinoceros would gradually supplant the southern Rhinoceros Etruscus and Elephas meridionalis. Traces of such an occupation would necessarily be very rare, since they would be exposed to the grinding action both of the advancing glacial sheet, and subsequently to that of the waves on the littoral zone during the depression and re-elevation of the land. At the time also that the greater part of Great Britain was buried under an ice-sheet, it could not have been occupied by animals, although they may have been, and most probably were, living in the districts farther to the south, which were not covered by ice. The labours, however, of Dr. Bryce, Prof. Archibald Geikie, and others prove that one at least of the characteristic pleistocene mammalia—the mammoth—lived in Scotland along with the reindeer before the deposit of the lower boulder-clay; while Mr. Jamieson has pointed out that it could not have occupied that area at the same time as the ice, and therefore must be referred to a still earlier date.266 The teeth and bones discovered in the ancient land surface at Selsea, under the boulder drift, also very probably indicate that the mammoth lived in Sussex before the glacial submergence, although they were never admitted by Dr. Falconer to be of the same age as the remains of Elephas antiquus from the same preglacial horizon. The animal also occurs in the preglacial forest-bed of Norfolk and Suffolk. On a careful examination of the whole evidence, I am compelled to believe, with Mr. Godwin-Austen and Prof. Phillips, that the À priori belief that the pleistocene mammalia occupied Great Britain before the period of the ice-sheet and submergence is fully borne out by the few incontestable proofs that have been brought forward of the remains being found in preglacial deposits. And the scanty evidence on the point is just what might be expected from the rare accidents under which the bones in superficial deposits could have withstood the grinding of the ice-sheet, and the subsequent erosive action of the waves on the coast-line. It may therefore be concluded, that the pleistocene mammalia arrived in Europe before the temperature had reached its minimum in the glacial period. On the other hand, the occurrence of mammaliferous river strata, either in hollows of the boulder-clay as at Hoxne, or in valleys excavated after its deposition as at Bedford, prove that the characteristic animals occupied Britain after the retreat of the ice-sheet, and after the re-emergence of the land from beneath the glacial sea.

Mammalia lived in Britain during the Second Ice or Glacial Period.

The distribution of the animals in the river deposits gives us a clue to the physical geography during the second ice period. In an essay read before the Geological Society in 1869, and in a second printed in the “Popular Science Review” in 1872, I showed that there was a singular irregularity in the contents of the river strata, and that while the fossil mammalia were abundant throughout the area (marked with dots in the map, Fig.126), there were certain districts in which they had not been met with. One of these barren areas comprises (plain in the map, Fig.126), nearly the whole of Wales. A second includes a large portion of Lancashire, Yorkshire, Cumberland, Westmoreland, and the whole of Scotland (if the preglacial mammals in the low district between the Frith of Forth and Frith of Clyde in the map be omitted), and a third is represented by nearly the whole of Ireland. These areas are remarkable for the absence of the mammalia from the river deposits. They are also characterised by the freshness of the ice marks which they present. Nearly every valley has its own system of grooves and its own set of moraines; and the mounds of clay and marl left behind by the local glacier, as it slowly retreated to higher levels till it finally disappeared, are to be observed in great abundance. If we bring these facts into relation, the barrenness of the areas may be reasonably explained by the presence of glaciers, while the pleistocene mammals were living in the south and east (see map, Fig.126). A barrier of some kind may reasonably be inferred to have prevented their range over those districts, and its nature is indicated by the ice marks. It is very probable that these glaciers had not passed away before the close of the pleistocene age: for in that case the characteristic animals would be discovered in the river gravels, which are later than the deposits of local glaciers in those districts.

The Glacial Period does not separate one Life-era from another.

The lowering of the temperature which culminated in the glacial period has left palpable traces behind in the changes which it caused in the European fauna. As the pleiocene climate became colder, the animals unfitted to endure the cold, such as the deer of the Indian types of Axis and Rusa, either migrated to the south or became extinct, while their feeding-grounds were invaded by the dwellers in the temperate zone, the stag, roe, bison, and other animals. These in their turn were pushed forward by the arctic group of animals, the musk-sheep, lemming, reindeer, and others, the progress being in the main steadily to the south while the cold was increasing, and the retreat being steadily to the north while it was decreasing. It will follow from this, that the same district in central or north-western Europe would be traversed by these migratory bodies of animals, both in their southern advance in preglacial and glacial times and their northern retreat in postglacial times, and that, therefore, their fossil remains cannot afford a means of fixing the preglacial, glacial, or postglacial, age of the deposit in which they are found, where it is not marked by traces of glaciation. Sir Charles Lyell’s view, that the glacial period cannot be taken as a landmark in the classification of the European pleistocene deposits, is fully borne out by the facts, and still less can it be taken as a hard and fast line between one fauna and another. It cannot be considered a life-era like the eocene, meiocene, pleiocene, or prehistoric divisions of the tertiary period.

Bone-caves inhabited before and after Ice Period.

If we allow that the lowering of the temperature was the principal cause of the presence of temperate and arctic animals, in a region before inhabited by species fitted to live in a comparatively warm climate, it will follow that bone-caves cannot be said to be either pre- or postglacial, by an appeal to their fossil mammalia. If they were open before the minimum of temperature was reached, they would afford shelter to the animals then in the neighbourhood, and they would continue to be occupied in the south during the vast period of time represented by the enormous physical changes in the region north of the line of the Thames, during the development of the ice-sheet, the submergence and the re-elevation of nearly the whole of Britain and Ireland. As, however, the cold increased, the percentage of arctic animals would also increase, and the more temperate species be weeded out. For these reasons it has seemed to me, that the machairodus of Kent’s Hole, and the Rhinoceros megarhinus of Oreston, represent an early stage of the pleistocene period, before the arctic mammalia were present in full force in the caves. It is very probable that vast herds of reindeer lived in the south of France, while northern Britain lay buried under the ice-sheet, as well as during the two succeeding physical changes.

Relation of PalÆolithic Man to Glacial Period.

What then is the relation of the palÆolithic hunter of reindeer in France and Britain to the glacial period? Is he pre- or postglacial? The only evidence on the point is that offered by the associated mammalia which occupied France, Germany, and Britain before and after the point of minimum temperature was reached in these latitudes. Man may have inhabited the caves not merely of France, but of Devonshire and Somerset, at any time during that long period. The position of the palÆolithic refuse-heap discovered by Prof. Fraas at Schussenreid, resting on a moraine of the extinct glacier of the Rhine, proves that the palÆolithic Eskimos lived in Suabia after the retreat of the glacier when the temperature became warmer, towards the close of the pleistocene age or in the later glacial stage. The same conclusion has been arrived at by Mr. Prestwich as to the sojourn of palÆolithic man (of the river-bed type) in Bedfordshire and Suffolk, the gravels in which the implements are found being of a later age than the boulder-clay of those districts. We have therefore proof that man lived in Germany and Britain after the maximum glacial cold had passed away, and we may also infer with a high degree of probability that he migrated into Europe along with the pleistocene mammalia in the preglacial age.

Test of age of contents of caves in Glaciated Districts.

The probable date of the introduction of the contents into ossiferous caves in glaciated areas may be ascertained by an examination of the river deposits. If the animals found in the caves inhabited the surrounding country after the melting of the ice, their remains will occur in the postglacial gravels. If they are not found, it may be inferred that they had retreated from the district, before the latter were deposited. It is obvious that they could not have lived in any district while it was covered with ice or by the sea. It may therefore be concluded that their remains in the caves were most probably introduced before the glacial conditions had set in. Preglacial deposits in a cavern would be protected from the grinding of the ice-sheet, the action of the waves in the depression, and re-elevation of the land, and the subsequent glacial erosion which would inevitably destroy nearly all the fluviatile ossiferous strata. By this test the pleistocene strata in the Victoria Cave, near Settle, may be considered preglacial, as well as the hyÆna-den at Kirkdale, which has always been referred by Prof. Phillips to that age. If this be allowed, the small fragment of human bone found by the Settle Cave Exploration Committee in the former cave in 1872 establishes the fact that man lived in Yorkshire before the glacial period. The man to whom it belonged was probably devoured by the hyÆnas which dragged into their den the woolly rhinoceros, reindeer, and other creatures whose gnawed bones were strewn on the floors.