The Arrival of Man in Europe

TOWARD the close of the Pleistocene age, the general outlines of the European continent had assumed very much their present appearance everywhere except in the northwest. The British Islands still remained joined to one another and to the Gaulish mainland, and occupied the greater part of the area of the German Ocean. According to Mr. James Geikie, the connection with Norway again became complete, and the Atlantic ridge was again so far elevated as to bring Scotland into connection with Greenland through the Faroe Islands and Iceland. The whole of Britain stood at an average elevation of from 600 to 1000 feet above its present level. The Thames, Humber, Tyne, and Forth must all have flowed into the Rhine, which emptied itself into the North Sea beyond the latitude of the Shetlands. The glaciers of Europe had retreated within the Arctic Circle, or up to the higher valleys of the great mountain ranges ; and the climate was beginning to assume its present temperate and equable character.

At this remote epoch Europe had already been inhabited by human beings during several thousand years. How long before the beginning of the Pleistocene period man had arrived in Europe is still open to question ; but there is no doubt whatever that he lived in Gaul and Britain as a contemporary of the big-nosed rhinoceros, and before the arrival of the arctic mammalia which were driven from the north as the glacial cold set in. This race of man — described by Mr. Boyd Dawkins as the “ River-Drift-Man ” — is probably now as extinct as the cave-bear or the mammoth. Late in the Pleistocene period it disappeared from Europe, and was replaced by a new race, coming from the northeast, along with the musk-sheep and reindeer, and called by the same eminent writer the “ Cave-Man.” Both the Cave-men and River-drift men were in the stage of culture known as the Palæolithic, or Old Stone Age ; that is, they used only stone implements, and these implements were never polished or ground to a fine edge, but were only roughly chipped into shape, and were very rude and irregular in contour. The Palæolithic Age, referring as the phrase does to a stage of culture, and not to any chronological period, is something which has come and gone at very different dates in different parts of the world. It may be convenient to remember that in northwestern Europe it seems to have very nearly coincided with the Pleistocene period, provided we also bear in mind that the coincidence is purely fortuitous. The implements of the Riverdrift men, found in Pleistocene riverbeds, are very rude, and imply a social condition at least as low as that of the Australian savages of the present day. “ They consist,” says Mr. Dawkins, “ of the flake; the chopper or pebble roughly chipped to an edge on one side ; the hâche or oval-pointed implement, intended for use without a handle ; an oval or rounded form with a cutting edge all round, which may have been used in a handle ; a scraper for preparing skins ; and pointed flints used for boring.” Man did not then seek for the materials out of which to make these weapons or tools, but “ merely fashioned the stones which happened to be within his reach — flint, quartzite, or chert — in the shallows of the rivers, as they were wanted, throwing them away after they had been used.” No pottery of any sort has been found in association with these implements, nor were there at that period any domesticated animals. The River-drift men were evidently no tillers of the ground, neither were they herdsmen or shepherds ; but they gained a precarious subsistence by hunting the great elk and other deer, and contended with packs of hyænas for the caves which might serve for a shelter against the storm. As to what may have been the social organization of these primeval savages, nothing whatever is known. They were a wide-spread race. Their implements have been found, in more or less abundance, in Britain, Germany, France, Spain, Italy, Greece, northern Africa, Palestine, and Hindustan. Their bones have been found in the valleys of the Rhine, the Seine, the Somme, and the Vezère, in sufficient numbers to show that they were a dolicocephalic or long-headed race, with prominent jaws, but no complete skeleton has as yet been discovered.

These River-drift men, as already observed, belonged to the southern fauna which inhabited Europe before the approach of the glacial cold. As the climate of Europe became arctic and temperate by turns, the River-drift men appear to have by turns retreated southward to Italy and Africa, and advanced northward into Britain, along with the leopards, hyænas, and elephants, with which they were contemporary. But after several such migrations they returned no more, but instead of them we find plentiful traces of the Cave-men, — a race apparently more limited in its range, and clearly belonging to a subarctic fauna. The bones and implements of the Cave-men are found in association with remains of the reindeer and bison, the arctic fox, the mammoth, and the woolly rhinoceros. They are found in great abundance in southern and central England, in Belgium, Germany, and Switzerland, and in every part of France; but nowhere as yet have their remains been discovered south of the Alps and Pyrenees. A diligent exploration of the Pleistocene caves of England and France, during the past twenty years, has thrown some light upon their mode of life. Not a trace of pottery has been found anywhere associated with their remains, so that it is quite clear that the Cave-men did not make earthenware vessels. Burnt clay is a peculiarly indestructible material, and where it has once been in existence it is sure to leave plentiful traces of itself. Meat was baked in the caves by contact with hot stones, or roasted before the blazing fire. Fire may have been obtained by friction between two pieces of wood, or between bits of flint and iron pyrites. Clothes were made of the furs of bisons, reindeer, bears, and other animals, rudely sewn together with threads of reindeer sinew. Even long fur gloves were used, and necklaces of shells and of bear’s and lion’s teeth. The stone tools and weapons were far finer in appearance than those of the Riverdrift men, though they were still chipped, and not ground. They made borers and saws as well as spears and arrowheads ; and besides these stone implements they used spears and arrows headed with bone, and daggers of reindeer antler. The reindeer, which thus supplied them with clothes and weapons, was also slain for food; and, besides, they slew whales and seals on the coast of the Bay of Biscay, and in the rivers they speared salmon, trout, and pike. They also appear to have eaten, as well as to have been eaten by, the cave-lion and cave-bear. Many details of their life are preserved to us through their extraordinary taste for engraving and carving. Sketches of reindeer, mammoths, horses, cave-bears, pike and seals, and hunting scenes have been found by the hundred, incised upon antlers or bones, or sometimes upon stone; and the artistic skill which they show is really astonishing. Most savages can make rude drawings of objects in which they feel a familiar interest, but such drawings are usually excessively grotesque, like a child’s attempt to depict a man as a sort of figure eight, with four straight lines standing forth from the lower half to represent the arms and legs. But the Cave-men, with a piece of sharp-pointed flint, would engrave, on a reindeer antler, an outline of a urus so accurately that it can be clearly distinguished from an ox or a bison. And their drawings are remarkable not only for their accuracy, but often equally so for the taste and vigor with which the subject is treated.

Among uncivilized races of men now living, there are none which possess this remarkable artistic talent save the Eskimos ; and in this respect there is complete similarity between the Eskimos and the Cave-men. But this is by no means the only point of agreement between the Eskimos and the Cave-men. Between the sets of tools and weapons used by the one and by the other the agreement is also complete. The stone spears and arrow-heads, the sewing-needles and skin-scrapers, used by the Eskimos are exactly like the similar implements found in the Pleistocene caves of France and England. The necklaces and amulets of cut teeth and the daggers made from antler, show an equally close correspondence. The resemblances are not merely general, but extend so far into details that if modern Eskimo remains were to be put into European caves they would be indistinguishable in appearance from the remains of the Cavemen which are now found there. Now, when these facts are taken in connection with the facts that the Cave-men were an arctic race, and especially that the musk-sheep, which accompanied the advance of the Cave-men into Europe, is now found only in the country of the Eskimos, though its fossil remains are scattered in abundance all along a line stretching from the Pyrenees through Germany, Russia, and Siberia, — when these facts are taken in connection, the opinion of Mr. Dawkins, that the Cavemen were actually identical with the Eskimos, seems highly plausible. Nothing can be more probable than that, in early or middle Pleistocene times, the Eskimos lived all about the Arctic Circle, in Siberia and northern Europe as well as in North America; that during the coldest portions of the Glacial period they found their way as far south as the Pyrenees, along with the rest of the sub-arctic mammalian fauna to which they belonged ; and that, as the climate grew warmer again, and vigorous enemies from the south began to press into Europe and compete with them, they gradually fell back to the northward, leaving behind them the innumerable relics of their former presence, which we find in the late Pleistocene caves of France and England. The Eskimos, then, are probably the' sole survivors of the Cave-men of the Pleistocene period : among the present people of Europe the Cave-men have left no representatives whatever.

With the passing away of Pleistocene times, further considerable changes occurred in the geography of Europe and in its population. Early in the Recent period the British Islands had become detached from each other and from the continent, and the North Sea and the English and Irish channels had assumed very nearly their present sizes and shapes. The contour of the Mediterranean, also, had become nearly what it is now ; and in general such changes as have occurred in the physical structure of Europe during the Recent period have been comparatively slight. Of the mammalia living at the beginning of this period, only one species, the Irish elk, has become extinct. The gigantic cave-bear, the cave-lion, the mammoth, and the woolly rhinoceros had all become extinct at the close of the Pleistocene period, and the elephants and hyænas had finally retreated into Africa. In Europe were now to be found the brown and grizzly bears, the elk and reindeer, the wild boar, the urus or wild ox, the wolf and fox, the rabbit and hare, and the badger ; and along with these there came those harbingers of the dawn of civilization, — the dog and horse, the domestic ox and pig, with the sheep and goat. A new race of men, also, the tamers and owners of these domestic animals, had appeared on the scene. These new men could build rude huts of oak logs and rough planks, made by splitting the treetrunks with wedges. Such work was not done with chipped flint-flakes. The men of the early Recent period had the grindstone, and used it to put a fine edge on their stone hatchets and adzes ; so that their appearance marks the beginning of a new era in culture. The sharp and accurate edge of the axe, unattainable save by grinding, is the symbol of this new era, which is known to archæologists as the Neolithic, or New Stone Age. The huts of the Neolithic farmers and shepherds were built in clusters, and defended by stockades. Wheat and flax were raised, and linen garments were added to those of fur. The distaff and loom, in rude shape, were in use, and grain was pounded in the mortar with a pestle. Rude earthenware vessels were made, sometimes ornamented with patterns. Canoes were also in use. The dead were buried in long barrows, and from the almost constant presence of arrow - heads, pottery, or trinkets in these tombs it has been inferred that the Neolithic men had some idea of a future life, and buried these objects for the use of the departed spirits, as is the custom among most savage races at the present time.

The celebrated lake-villages of Switzerland belong to the Neolithic or early Recent period; and the remains of their cattle and of their cultivated seeds and fruits have thrown light upon the origin of the Neolithic civilization. It is certain that the domestic animals did not originate in Europe, but were domesticated in central Asia, which was the home of their wild ancestors ; and, moreover, they were not introduced into Europe gradually and one by one, but suddenly and en masse. It is clear, therefore, that they must have been brought in from Asia by the Neolithic men ; and the same is true of the four kinds of wheat, two of barley, the millet, peas, poppies, apples, pears, plums, and flax, which grew in the gardens and orchards of Neolithic Switzerland.

This rudimentary Neolithic civilization was spread all over Europe, with the exception of the northern parts of Russia and Scandinavia; and there can be no doubt that it lasted for a great many centuries. It certainly lingered in Gaul and Britain long after the valley of the Nile had become the seat of a mighty empire ; perhaps even after the Akkadian power had established itself at the mouth of the Euphrates, and “ Ur of the Chaldees ” had become a name famous in the world. Still more, it is clear that the Neolithic population has never been swept out of Europe, like the Cave-men and the River-drift men who had preceded it, but has remained there, in a certain sense, to this day, and constitutes a very important portion of our own ancestry.

So many skeletons have been obtained of the men and women of the Neolithic period that we can say, with some confidence, that the whole of Europe was inhabited by one homogeneous population, uniform in physical appearance. The stature was small, averaging 5 feet 4 inches for the men, and 4 feet 11 inches for the women ; and the figure was slight. The skulls were “ dolicocephalic,” or long and narrow ; but the jaws were small, the eyebrows and cheek-bones were not very prominent, the nose was aquiline, and the general outline of the face oval and probably handsome. In all these points the men of the Neolithic age agree exactly with the Basks of northern Spain, the remnant of a population which at the dawn of history still maintained an independent existence in many parts of Europe. By their conquerors, the Kelts, who led the van of the great Aryan invasion of Europe, these small-statured Basks were known as “ Iberians ” or “ westerners” (Gael iver, Sanskr. avara, " western ”), and Iberian” is now generally adopted as the name of the race which possessed the whole of Europe in the Neolithic age and until the Aryan invasions, and which still preserves its integrity in the little territory between the Pyrenees and the Bay of Biscay. The Iberian complexion is a dark olive, with black eyes and black hair; so that we may figure to ourselves with some completeness how the prehistoric inhabitants of Europe looked.

It is probable that in Neolithic times this Iberian population was spread not only all over Europe, but also over Africa north of the Desert of Sahara ; so that the Moorish and Berber peoples are simply Iberians, with more or less infusion of blood from the Arabs, who conquered them at the end of the seventh century after Christ. And it is also probable that the Silures of ancient Britain, the Ligurians of southern Gaul and northern Italy, and the rich and powerful Etruskans all belonged to the Iberian race.

In very recent times — probably not more than twenty centuries before Christ — Europe was invaded by a new race of men, coming from central Asia. These were the Aryans, a race tall and massive in stature (the men averaging at least 5 feet 8 inches, and the women 5 feet 3 inches), with “ brachycephalic” or round and broad skulls, with powerful jaws and prominent eyebrows, with faces rather square or angular than oval, with fair, ruddy complexions and blue eyes, and red or flaxen hair. Of these, the earliest that came may perhaps have been the Latin tribes, with the Dorians and Ionians ; but the first that made their way through western Europe to the shores of the Atlantic were the Gael, or true Kelts. After these came the Kymry ; then the Teutons ; and finally — in very recent times, near the beginning of the Christian era— the Slavs. These Aryan invaders were further advanced in civilization than the Iberians, who had so long inhabited Europe. They understood the arts which the latter understood, and, besides all this, they had learned how to work metals ; and their invasion of Europe marks the beginning of what archæologists call the Bronze Age, when tools and weapons were no longer made of polished stones, but were wrought from an alloy of copper and tin. The great blonde Aryans everywhere overcame the small brunette Iberians, but, instead of one race exterminating or expelling the other, the two races everywhere became commingled in various proportions. In Greece, southern Italy, Spain,and southern France, where the Iberians were most numerous as compared with the Aryan invaders, the people are still mainly small in stature and dark in complexion. In Russia and Scandinavia, where there were very few Iberians, the people show the purity of their Aryan descent in their fair complexion and large stature. While in northern Italy and northern France, in Germany and the British Islands, the Iberian and Aryan statures and complexions are intermingled in endless variety.

We have now carried this brief account of the arrival of man in Europe as far as is requisite for our present purpose. Starting from ages of which only a palæontological record is preserved, we have gradually come down to a period almost within the ken of history. We have seen Europe inhabited in succession by four distinct races of men : firstly, the men of the River-drift, who belonged to a warm climate, and who during the Glacial period became extinct, along with many of the sub-tropical mammals with which they were contemporary ; secondly, the Cave-men, who belonged to a cold climate, and of whom the Eskimos are now probably a surviving remnant; thirdly, the swarthy Iberians ; and, fourthly, the fair-skinned Aryans, — these two latest races having by intermarriage given rise to the present mixed population of Europe.

Our next problem is to see how far it may be possible to introduce anything like chronology into this series of events. How long is it since the River-drift men inhabited Europe? Or when did the first Iberians, with their polished stone axes and their herds of cattle, begin to build their rude villages in Switzerland and Gaul? To such questions no very positive answers can be returned. But still we are not left wholly in the dark. A method of inquiry can be pointed out, by following which we may at least come to understand the “ orders of magnitudes ” in time with which we have to deal. We can substitute partially definite conceptions for wholly vague ones. And we can see how, by following the same line of inquiry with more ample data, it may be possible by and by to introduce something like chronology into the geologic history of the earth’s surface.

The so-called “ Glacial epoch ” here all at once acquires a wonderful interest for us. We have seen that it is certain that men inhabited Britain contemporaneously with the big-nosed rhinoceros, which became extinct about the beginning of the Glacial period. How long men lived upon the earth before that time we do not know ; but it is clearly established that there were men in Britain then. It would accordingly be very interesting to know when the Glacial period began to come on in Europe. But on this point it has already become possible to form something like a definite opinion.

To understand how we can arrive at a date for the Glacial period, it is necessary first to understand, the cause of that wonderful change of climate which allowed all Europe as far south as Dresden, and alt America as far south as Philadelphia, to become swathed in an ice-sheet like that which now covers Greenland. The causes of this event were many and complicated, but the arch-cause — the cause which unlocked all the others and set them going— was an astronomical cause. It has been proved by Mr. Croll that the primary cause of the glaciation of the northern hemisphere was a change in the shape of the earth’s orbit, such as had occurred before and will occur again ; and the dates of these changes in the orbit, whether past or future, can be determined by astronomical methods with great accuracy.

The reason why the weather is warmer in summer than in winter is that in summer the days are longer than the nights, so that the surface of the earth receives more heat in the day-time than it can lose by radiation during the night; while in winter the case is exactly the reverse. Another circumstance tends to make the earth warmer at one time than another, — namely, the fact that the earth’s orbit is not quite circular, but slightly elliptical or eccentric, so that at one season of the year the earth is nearer to or farther from the sun than at another season. At present the northern hemisphere is nearest the sun in winter and farthest from it in summer, but the difference is only about 3,000,000 miles. It must also be remembered that when the earth is near perihelion it moves faster than when it is near aphelion, so that the season when it is nearer the sun is always a little shorter than the season when it is farther from the sun. Thus in our northern hemisphere at present the winter half of the year, or the interval from the autumnal to the vernal equinox, is nearly 8 days shorter than the summer half of the year. Thus the difference in length between our summer and winter seasons, and the difference between our distances from the sun at the two extremes of the year, are not great differences, but the advantage, such as it is, is on the side of summer.

But these relations between the earth and the sun are perpetually altering. Firstly, owing to the great revolution known as the li precession of the equinoxes,” the earth’s perihelion 10,500 years ago came in midsummer in the northern hemisphere, and it will come so again 10,500 years hence. In this state of things the winter half of the year was and will be 8 days longer than the summer half. Secondly, the shape of the earth’s orbit changes from time to time, under the influence of the variously-compounded attractions exerted upon it by its companion planets. These changes occur at irregular intervals, but they admit of accurate calculation, and have been computed for 3,000,000 years in the past and 1,000,000 years in the future by Mr. Croll, from formulas furnished by Leverrier. It has thus been ascertained that at three several times within the past 3,000,000 years the earth’s orbit has become very much elongated, so that the difference between its greatest and least distances from the sun has been between four and five times as great as at present, — that is, it has been from 12,000,000 to 14,000,000 miles. The first of these periods of high eccentricity began 2,650,000 years ago, and lasted 200,000 years ; the second began 880,000 years ago, and lasted 180,~ 000 years ; the third began 240,000 years ago, and lasted 160,000 years. For the last 50,000 years, the departure of the earth’s orbit from the circular form has been exceptionally small.

Now let us suppose one of these long periods of high eccentricity to coincide with one of the short periods of 10,500 years, when the northern hemisphere has its aphelion in winter ; and this, of course, has happened not once only, but a great many times. Under such circumstances, the northern hemisphere is 98,000,000 miles distant from the sun at midwinter instead of 91,000,000, as at present, and the winter is 26 days longer than the summer instead of 8 days shorter, as at present. On the other hand, at midsummer the sun’s distance is only 86,000,000 miles instead of 94,000,000, as at present. Now how must this state of things affect the climate of the northern hemisphere ?

In the first place, the diminution in the quantity of heat received daily from the sun in winter would be such as to lower the average temperature of the whole northern hemisphere by about 35° F., so that for example the average January temperature of England, which is now 39°, would fall to 4°. And, conversely, heat enough would be received to raise the mean summer temperature by about 60° above what it now is.

So far very good, as concerns the amount of heat actually received from the sun. But would the summer temperature be raised like this ? It would not; and this is because our earth has a means of storing up cold, so to speak, which gives winter the advantage over summer in such a contest. With the mean January temperature of England at 4° F. instead of 39°, all the moisture which now falls as rain would fall as snow, and would accumulate on the ground. At the coming of summer, all the snow and ice would have to be melted, and it takes a great deal of heat to melt snow and ice. As Mr. Wallace graphically puts it, “ to melt a layer of ice only one and a half inch thick would require as much heat as would raise a stratum of air 800 feet thick from the freezing-point to the tropical heat of 88° F. ! ” Until the snow is all melted, no amount of solar heat can raise the temperature much above the freezing-point; and this is the reason why, in regions where much moisture is condensed as snow, as in Greenland, and at the summits of the Andes, Alps, and Himalayas, snow is perpetual. So that., in the case we have supposed, the extra heat received from the sun in the short summer would largely be exhausted in melting the snow, and, instead of raising the mean temperature 60°, it is doubtful if it would raise it at all above the point which it attains at the present time. Besides all this, it must be remembered that the rapid melting of great masses of snow produces fog, and thus not only obscures the sun’s heat, but leads to further heavy condensation in the shape of cold rains. Now bear in mind that this state of things goes on for at least half of the period of 10,500 years, when the aphelion of the northern hemisphere occurs between September and March, and it is easy to see how the snow and ice must so far gain the upper hand that the intense summer heat cannot produce any considerable impression on them, but the region of “ eternal snow,” no longer confined to the tops of lofty mountains, descends to the sea-level throughout a large part of the northern hemisphere. Thus we get far toward an explanation of the causes of the Glacial epoch. But still other causes have conspired with those here pointed out to enhance the general effect.

While the northern hemisphere was situated as just described, the state of things in the southern hemisphere must have been entirely different. There the perihelion occurring in winter and the aphelion in summer, with the same high eccentricity, the summer would be 26 days longer than the winter, and the climatic result would be perpetual spring. And this would affect the flow of oceancurrents in such a way as to deprive the northern hemisphere of its only possible chance of escaping the glaciation we have just depicted. Let us notice this point carefully, for it is one of great importance.

We have supposed the lowering of the average winter temperature of England, for example, due to the great aphelion distance of the sun, to be 35° F. There is one way in which this effect might be partially modified, and that is by the equalizing influence of the Gulf Stream. But in the case we have supposed, this influence would almost certainly be cut off. The direction of the main ocean-currents is determined by the trade-winds, and the trade-winds are caused by the difference of temperature between the poles and the equator. As the heated air at the equator rises, the cooler air from north and south flows in to take its place, and these atmospheric currents flowing from the north and south poles toward the equator are what are called the trade-winds. The strength of the trade-winds depends entirely upon the difference in temperature between the equator and the pole; the greater the difference, the stronger the wind. Now, at the present time, the south pole is much colder than the north pole, and the southern trades are consequently much stronger than the northern, so that the neutral zone in which they meet lies some five degrees north of the equator. The trade-winds, pushing stupendous masses of surface ocean-water, produce the main ocean-currents ; and accordingly these currents now tend chiefly from south to north, so that most of the heated water of the central Atlantic, both north and south of the equator, gets carried into the northern temperate zone. In this way the Gulf Stream, coming northward up the west coast of Africa, sweeps across the Atlantic to the easternmost point of Brazil, where part of it gets deflected southward toward the Antarctic Ocean, but most of it flows northwesterly into the Gulf of Mexico, whence it is deflected northeasterly toward the European coast, giving to England its climate of perpetual spring in the latitude of Labrador, and tempering the cold of the North Sea even beyond the Arctic Circle. According to Mr. Croll, the quantity of extra heat which the northern hemisphere receives from this source, over and above that which it would get simply from direct solar radiation, amounts to fully one fourth of the latter quantity. But when the aphelion of the northern hemisphere occurred in midwinter, along with a very high eccentricity, all this must have been changed. The tendency of these circumstances, as we have seen, was to make the northern hemisphere very cold, while producing a perpetual spring in the southern hemisphere. Now, when once the north pole had become colder than the south pole, the northern trades would begin to blow with greater force than the southern, until after a while the neutral line between the two would be shifted south of the equator, and, instead of the warm waters of the southern tropical ocean being carried into the northern seas, the case would be just the reverse. The great ocean-currents, instead of all tending northward, as they do to-day, would all tend southward. A very little deflection of this sort would, at the easternmost point of Brazil, turn the whole of the Gulf Stream southward down the coast of South America, and prevent any part of it from flowing up into the North Atlantic; and in this way the progressing refrigeration of Europe and North America would be most powerfully enhanced.

Thus, when the eccentricity of the earth’s orbit was three or four times as great as at present, and during the period when aphelion in the northern hemisphere occurred in the winter season between September and March, the tendency must have been toward perpetual snow and ice over a large part of the northern hemisphere, and toward perpetual spring throughout the southern hemisphere. But when winter aphelion occurred in the southern hemisphere, then everything was reversed ; then the tendency south of the equator was toward glaciation, and north of the equator it was toward perpetual spring. In Europe you would have, for 10,500 years, a period during which the climate would gradually become more and more arctic for 5250 years, thenceforward gradually becoming less severe; and upon this would ensue another period of 10,500 years, during which the climate would grow more and more equable for 5250 years, thenceforward gradually increasing again the differences between summer and winter; and in a period of 160,000 years such 21,000year cycles would naturally occur nearly eight times. So that, upon a geological survey of what is called the Glacial epoch, we might expect to find an alternation of severe and mild climates in Europe, — an alternation of epochs in which Britain was inhabited by the hippopotamus with epochs in which the reindeer roamed in the south of France. And this is, in fact, what we do find. It is not long since the Glacial period in Europe was supposed to have been one long monotonous period of extreme cold ; but now the foremost geologists — such as Mr. James Geikie, who has more than any one else illustrated this subject — have discovered at least four or five alternations of warm and cold periods in Europe during the Glacial epoch ; and with further and more minute research we may expect the agreement between observation and deduction to become still more convincing.

Enough has now been said to give the reader some idea of the magnificent line of reasoning by which Mr. Croll has unfolded the causes of the Glacial period. And it also becomes apparent at once why we must probably select the latest period of high eccentricity in the earth’s orbit as the period for which we have been seeking. For that period — which began 240,000 years ago, and terminated 80,000 years ago — presented such a set of astronomical circumstances as must have resulted in the repeated glaciation of the northern hemisphere, after the manner above described. And the antiquity of that period seems to be sufficiently great to allow for the geological changes which have occurred since the Pleistocene age. If we were to assign an earlier epoch of high eccentricity for the Glacial period, it would then become necessary to show why, with the present relations of land and sea on the globe, the latest epoch of high eccentricity should not have produced a subsequent glacial period. But the Glacial period which Agassiz first taught us to understand, and which in recent years has been made the subject of such minute study, is clearly the latest glacial period that has occurred in the northern hemisphere ; for it is the one of which the traces are now everywhere around us ; it is the one which has carved the mountains of Scotland and New England in their present beautiful outlines, and covered their sides with bowlders, and filled the valleys with romantic tarns or magnificent lakes. If we adopt Mr. Croll’s theory of the causes of glaciation, we are clearly bound to look to the latest rather than to any earlier manifestation of those causes, in order to account for that glacial period the effects of which are still visible all around us. Accordingly, among the foremost geologists who have adopted Mr. Croll’s conclusions, there has been a general agreement that the period of high eccentricity which began 240,000 years ago and ended 80,000 years ago must have been coincident with the great period of glaciation which occurred during the Pleistocene age in Europe and America.

The most serious objection that has been urged against Mr. Croll’s theory is that it seems to require us to suppose that there have been recurrent glacial epochs, at irregular intervals, during the whole past duration of the earth’s history. And in particular it would seem to be implied that there must have been a great glacial period from 880,000 to 700,000 years ago, and another one from 2,650,000 to 2,450,000 years ago, both of these dates being long subsequent to the beginning of the Tertiary period. Mr. Croll has sought to meet these objections by showing that such must really have been the case. He alleges evidence of glaciation in every one of the geological periods back to the Cambrian, with the single exception of the Triassic. And he argues, in particular, that the epoch of high eccentricity which began 880,000 years ago corresponded with a glacial epoch in the Miocene period, and that in like manner the date of 2,650,000 years ago witnessed the beginning of a great glacial epoch in the Eocene period. But these conclusions are not generally adopted by geologists. There are some evidences of local glaciation in the Miocene period in the neighborhood of the Alps, which were probably higher then than they are at present, but the weight of evidence is entirely in favor of the conclusion that the general climate of Europe throughout the Eocene and Miocene periods was much warmer than it has been at any later date. From the Eocene period down to the Pleistocene, there can be little doubt that there was a slow but steady lowering of the mean temperature of Europe, until in the latter period there occurred that comparatively rapid refrigeration which brought about a glacial epoch. In earlier than Tertiary times, on the other hand, Mr. Croll seems to have been more successful. There are distinct and numerous evidences of extensive glaciation in Europe during the remote Permian period; and it is not improbable that similar phenomena may have taken place in Silurian times. On the whole, however, it does not seem likely that there have been many periods of extreme glaciation, like that which we suppose to have ended about 80,000 years ago ; and it is quite unlikely that there has been any other such period since the beginning of Tertiary times. How, then, shall we explain the occurrence of two periods of high eccentricity, one lasting 200,000 and the other 180,000 years, without an accompanying glaciation of the northern hemisphere ?

This difficulty has been sometimes cited as fatal to Mr. Croll’s theory; but when we fully consider all the conditions of the case, we shall see that it is not so. For we must remember that it is not simply the cold, but it is the snow of the glacial winter, that chills the summers and renders possible the accumulation of ice. To produce a glacial epoch, according to Mr. Croll’s theory, it is not enough that the mean winter temperature of the northern hemisphere should be lowered 35° F., unless there is enough condensation of moisture going on to produce an abundant snowfall. Under such geographical conditions as exist to-day, and as existed during the Pleistocene period, there would be such a condensation and such a snowfall ; but in the Eocene and Miocene periods it was probably otherwise. The explanation is not difficult.

The most efficient promoters of condensation are mountains, which, thrusting their cold summits high into the air, precipitate the surrounding moisture. It is a familiar fact that mountainous districts are apt to be rainy, and that very high mountains are usually covered with snow in midsummer, even while oranges and palms are flourishing a few thousand feet below. It is not quite so familiar a fact that no intensity of arctic cold will suffice to prevent a warm or mild summer unless there is an extensive deposit of snow in the winter. Now, nowhere on the earth do we find any lowlands of great extent covered with perpetual snow. The coldest winters on the globe occur in eastern Siberia, where the temperature often averages —40° F. for several weeks in succession, and, according to Professor Pumpelly, sometimes sinks to —120° F. ! Yet so dry is the atmosphere that but little snow falls, and after this has been melted in the Spring the weather rapidly grows warm. “ At Yakutsk, in 62 degrees N. latitude, the thermometer stands often at 77° in the shade, and wheat and rye produce from fifteen to forty fold,” while the prairies are covered with grass and flowers. As Mr. Wallace observes, " it is only where there are lofty mountains or plateaus — as in Greenland, Spitzbergen, and Grinnell Land — that glaciers, accompanied by perpetual snow, cover the country, and descend in places to the level of the sea.” The coast of the Antarctic Continent is girdled with lofty mountains, which effect such condensation in the damp sea-air about them that the continent is buried under a mass of ice more than a mile in thickness. The antarctic islands South Georgia and South Shetland “ are very mountainous, and send down glaciers into the sea; and as they are exposed to moist sea-air on every side, the precipitation, almost all of which takes the form of snow even in summer, is of course unusually large.”

In order, therefore, to get a centre from which to start an accumulation of snow and ice sufficient to bring on a glacial epoch in the northern hemisphere, it would seem absolutely necessary that there should be a considerable amount of high land within the Arctic Circle. But in the Eocene and Miocene periods this condition does not seem to have been satisfied. Throughout the greater part of these two periods the area within the Arctic Circle was less elevated than it has been ever since the beginning of the Pliocene age. Greenland stood lower than at present, and the greater part of Siberia was submerged. Moreover, as already stated in the preceding paper,¹ the continents of Europe and Asia did not become " united into one unbroken mass ” until the Pliocene period. In the earlier Tertiary times the warm waters of the Indian Ocean flowed northwestward between Asia and Europe even into the Arctic Ocean, the mountains of Armenia and the Caucasus protruding as islands from this vast sea surface. Again, Mr. Wallace has pointed out a number of peculiarities in the distribution of plants and animals in the southern hemisphere which “ render it almost certain ” that in the early Tertiary times the antarctic land was much more extensive than at present. Now an elevation in the antarctic region, increasing the deposit of snow and ice about the south pole, and thus increasing the difference of temperature between the south pole and the equator, would be just what was needed to convert the fickle monsoons of the Indian Ocean into a steady and powerful tradewind, that would drive the warm water northward through the channel between Europe and Asia even as far as the north pole. This current from the Indian Ocean must have been more than equal to the Gulf Stream in heating power, and its effect would be to prevent any accumulation of ice within the Arctic Circle, and to produce in Greenland such a climate as it is known to have enjoyed in the Miocene period, when it was covered with a vegetation as luxuriant as that of Virginia at the present day.

This question is discussed at considerable length and with great ability by Mr. Wallace, in his treatise on Island Life. His argument is in some respects the most valuable contribution that has ever been made to our understanding of past climatic changes. He makes it perfectly clear that while Mr. Croll’s astronomical interpretation of the Glacial period is perfectly correct in principle, nevertheless extensive glaciation cannot take place unless the geographical conditions are such as to enable a great accumulation of ice to begin. We are not, therefore, obliged, on Mr. Croll’s view, to suppose that every epoch of high eccentricity has inaugurated a glacial period ; and we see, in particular, why such a result was not likely to follow 2,650,000 years ago or 800,000 years ago, supposing the latter date to have occurred before the beginning of the Pliocene age; and thus the only serious objection to Mr. Croll’s theory is effectually disposed of.

We have every reason to believe, then, that the great Glacial period of the Pleistocene age began 240,000 years ago, and came to an end 80,000 years ago. But at the beginning of this period men were living in the valley of the Thames ; at the end of it the men of the River-drift had probably become extinct, and their place in Europe had been taken and held for ages by the boreal Cave-men, who now in turn were about starting on their long retreat to the arctic regions. How long a time may have elapsed before the swarthy Iberian settled in Europe, with his dogs and cattle, we have no means of deciding ; nor can we say when the blue-eyed Aryan began his invasions, though we know that this last event must have been very recent, — not very long before the dawn of history. Nor can we tell how long there had been human beings on the earth before the Glacial epoch began. But, as I have said already, it must have been a great while, because, even before the close of the Pliocene age, they had had time to spread over the earth as far as Portugal in one direction, and as far as California in the other. And if we are to take the date of 240,000 years ago for the beginning of the Glacial epoch, we can hardly allow for the close of the Pliocene age an antiquity of less than 400,000 years.

It only remains to add that the enormous length of time during which the human race has existed is of itself a powerful argument in favor of the opinion — now generally accepted — that the human race was originated, by a slow process of development, from a race of non-human primates, similar to the anthropoid apes. We see man living on the earth for perhaps half a million years, to all intents and purposes dumb, leaving none but a geological record of his existence, progressing with infinite slowness and difficulty, making no history. Yet his geologic record is not quite like that of the dog or the ape, who could not chip a flint, and in the incised antlers of the Cave-men we see the first faint gleams of the divine intelligence that was by and by to shine forth with the glories of a Michael Angelo. We cannot but suppose that during those long dumb ages, through infinite hardship and through the stem regimen of deadly competition and natural selection, man was slowly but surely acquiring that intellectual life which was at last to bloom forth in history, and which has made him “ the crown and glory of the universe.”

John Fiske.