THE EUROPEAN CLIMATE IN THE PLEISTOCENE AGE.
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 urus[263] 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. hemitœchus_), 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.