have the strata of the earlier eras also been formed, and their
miles of thickness prove, not the violence of extreme and sudden
catastrophes, but only the length of time that was necessary to remove
such mighty masses here and pile them up there. It was not sudden
general revolutions of great violence, but the slowly working forces,
small only to appearance, well known from our present-day surroundings,
which destroy in one place and build up again in another with the
material obtained from the destruction--it was these which were the
causes of the gradual transformation of the earth in all periods of its
history comparable to the present. According to this new conception of
geological processes, a general destruction of plants and animals at
the end of eras, and a new creation at the beginning of the following
ones, was no longer a postulate of science as it had been. The living
creatures of the earliest eras could now be claimed as ancestors of
those living to-day; the chain seems nowhere completely broken. The
ancestors of the human race were also to be sought in the strata of the
earlier geological periods.
[Illustration: This indicates a vast stretch of the lost land of
England, looking towards the Scilly Isles from Land’s End. All between
the broken lines was once land as far as Scilly, thirty miles away and
fifty miles thence to Lizard Point.]
[Illustration: In old maps Bavent was formerly the most easterly point
of England; now that is Lowestoft.]
[Illustration: The coast of England is being slowly worn away by the
sea. In many places houses have been swallowed up. Here we see the
disintegrating process going on at Holderness, where the sea front
presented this appearance after a gale.]
[Illustration: SLOW INFLUENCES THAT DESTROY IN ONE PLACE AND BUILD UP
IN ANOTHER
The coming of the sea over the land is so slow as to be almost
imperceptible, but these pictures illustrate its progress. The
pictures in the upper half of the page show how the sea is
encroaching on the coast; the opposite result is shown in the
bottom view from Reigate Hill, where we see an ancient arm of the
sea now a rich and populous valley.
]
Among the forces which we find attended by a transformation of the
fauna and flora of the earth’s eras, the influences of climatic changes
in particular are clearly and surely shown. In that primeval period in
which the coal group was formed the climate in widely different parts
of the earth was comparatively equable, little divided into zones, and
of a moist warmth; this is proved by the really gigantic masses of
plant growth implied by the formation of many coal strata, in which the
remains of a luxuriant cryptogamic flora are everywhere embedded. In
Greenland, in the strata belonging to the chalk period, and even in the
deposits of the Tertiary Period, which immediately precedes the Drift
Era, the remains of higher dicotyledonous plants of tropical character
are found. The occurrence of palæozoic coral reefs in high latitudes
also goes to prove that the temperature of the sea water there was
higher at that time: in fact, that a tropical climate existed in the
farthest north--an extreme contrast to the present ice-sheet on its
land and the icebergs of its seas.
[Illustration: EUROPE BEFORE THE BRITISH ISLES WERE FORMED
This map and section illustrate the coast line of Prehistoric
Europe when the British Isles were part of the Continent and the
North Sea did not exist. The black parts of the section were all
above the level of the Atlantic.
]
[Illustration: THE SUBMERGED LANDS OF EUROPE
This map and section show how the Continental shelf of Europe runs
out to the Atlantic, and how enormous is the area now submerged in
the comparatively shallow water of the North Sea, the Irish Sea,
and the Channel.
]
In Central Europe the climatic conditions can have been only slightly
different. During the middle Tertiary Period palms grew in Switzerland;
and even at the end of the Tertiary Period, as it was slowly passing
into the Drift Era, the climate in Central Europe was still warmer than
now, being much like that of Northern Italy, and its protected west
coast the Riviera. There was also a rich flora, partly evergreen,
and a fauna adapted to such mild surroundings. Even in the oldest
(Preglacial) strata, and again in the middle (Interglacial) strata of
the Central European drift, there was still an abundant plant-growth
requiring a temperate climate, at any rate not more severe than Central
Europe possesses at the present day. Our chief forest trees grew even
then--the pine, fir, larch, and yew, and also the oak, maple, birch,
hazel, etc. On the other hand, Northern and Alpine forms are absent
among the plants. The same holds good of the animal world, which was
certainly much farther removed than the plant world from the conditions
prevailing now. The gigantic forms--the elephant, rhinoceros, and
hippopotamus--appear particularly strange to us, as also the large
beasts of prey--the hyena, lion, etc. But besides these, and the giant
deer with its powerful antlers, and two large bovine species--the bison
and the urus--there were also the majority of the present wild animals
of Central and Northern Europe that were originally natives--as the
horse, stag, roe, wild boar, and beaver, with the smaller rodents and
insectivora, and the wolf, fox, lynx, and bears, of which last the
cave-bear was far larger than the present brown bear, and even than the
Polar and grizzly bears.
We have sure proofs that through a decrease in the yearly temperature
a glacial period set in over Europe, North Asia, and North America,
burying vast areas under a sheet of ice, of the effect and extent of
which Northern Greenland, with its ground-relief veiled in inland ice,
can give us an idea.
The immediate consequence of this total climatic change was an
essential change in the fauna. Forms that were not suited to the
deteriorated climate, that could neither stand it nor adapt themselves
to it, were first compelled to retire, and then were exterminated.
This fate befell the hippopotamuses, and also one of the two elephant
species, _Elephas antiquus_, with its dwarf breeds in Sicily and Malta,
probably thus developed by this retreat; then the rhinoceros-like
_Elasmotherium_, a species of beaver; the _Trogontherium_, and the
powerful cat _Machairodus_ or _Trucifelis_, which still lived in
England, France, and Liguria during the Drift Period. Other animals,
like the lion and hyena, withdrew to more southerly regions, not
affected by the increasing cold and more remote from its effects.
[Sidenote: The Older Drift Animals]
On the other hand, according to Von Zittel’s description, an
immigration of cold-loving land animals took place, which at the
present day live either in the Far North or on the wild Asiatic
steppes, or in the high mountain ranges. These new immigrants mixed
with the surviving forms of the older drift fauna. The latter lived,
as we have seen, by no means in a warm climate, but only in a temperate
“northerly” one, even in the warmer periods of the epoch. So we can
understand that many of this older animal community were well able
to adapt themselves to colder climatic conditions, and among them
two of the large Drift pachydermata, the elephant and rhinoceros,
whose kin we now find only in the warmest climes. But a thick
woolly coat made these two Drift animals well fitted to defy a raw
climate--namely, the woolly-haired mammoth, _Elephas primigenius_, one
of the two Drift species of elephants of Europe, and the woolly-haired
rhinoceros, _Rhinoceros antiquitatis_. A second species of rhinoceros,
_Rhinoceros merckii_, was also preserved, and maintained its region of
distribution. The horse was now more largely distributed, and inhabited
the plains in herds; but, above all, the reindeer immigrated along
with other animals that now belong only to Far Northern and Arctic
regions, and pastured in large herds at the edges of the glaciers.
With the reindeer, although less frequent, was the musk-ox of the Far
North, besides many other cold-loving species, such as the lemming,
snow-mouse, glutton, ermine, and Arctic fox. Many of the animal
forms that were very frequent then, in the Drift Period, appear now
in Central Europe only as Alpine dwellers, living on the borders of
eternal snow, such as the ibex, chamois, marmot, and Alpine hare.
[Sidenote: The Animal Invasion of Europe]
[Sidenote: The Change of the Ice Age Climate]
Of special importance for our main question is the great invasion of
Europe by Central Asiatic animals; immigrants direct from the Asiatic
steppes pushed westward “as in a migration of nations,” among them the
wild ass, saiga antelope, bobac, Asiatic porcupine, zizel, jumping
mouse, whistling hare, and musk shrew-mouse. According as the glaciers
and inland ice grew or shrank, the animals of the glacial period
advanced more or less far to the North or retired more to the South,
extending or reducing their range of distribution. The Glacial Period
was no invariable climatic phenomenon. It is perfectly certain that a
first Glacial Period with a low yearly temperature, under the influence
of which the ice-masses, with their moraines, advanced a long way
from the North and from the high mountains, so that in Germany, for
instance, only a comparatively narrow strip remained free and habitable
for higher forms of life between the two opposing rivers of ice--was
succeeded by at least one period of warmer climate, and that certainly
not a short one. The mean yearly temperature had increased so much
that the ice-masses melted to a considerable extent, and had to retire
far to the North and into the high valleys of the Alps. In this warmer
Interglacial Period, as it is called, the Drift animals advanced far
to the North, especially the mammoth, which, with the exception of
the greater part of Scandinavia and Finland (districts which remained
covered with ice during the Interglacial Period), is distributed
throughout the drift strata of the whole of Europe and North Africa,
and as far as Lake Baikal and the Caspian Sea in Northern Asia. Even
the older Drift fauna, so far as it had not yet died out or retired,
returned to its old habitats, so that the Interglacial fauna of Central
Europe appear very similar to the Preglacial fauna. A long-sustained
decrease of temperature led once more to the growth of the ice, which
in this second Glacial Period almost reconquered the territory it had
won at first.
In consequence of these oscillations in the climatic conditions of the
Drift Era as a whole, we have to distinguish the Preglacial Era and
the Interglacial Era, as warmer sub-periods of the Drift, from the
real Glacial Periods. The latter appear as a first, or earlier, and a
second, or later Glacial Period, as remains of which the zone of the
older moraines and the zone of the later ones clearly mark the limits
of the former glaciation.
[Illustration: Alpine Hares
The Chamois
The Ibex
The Marmot Dando
TYPES OF ANIMALS SURVIVING IN CENTRAL EUROPE FROM THE DRIFT PERIOD
Many of the animal forms that were very frequent in the Drift
Period appear now in Central Europe only as Alpine dwellers, living
on the borders of eternal snow. Such are the ibex, chamois, marmot,
and Alpine hare.
]
[Sidenote: Breaking up of the Earth]
It was this second deterioration of the climate, with the fresh
advances made by the glaciers and masses of inland ice, which
definitely did away with the older Drift fauna that was not equal to
the sudden climatic change. Nor did the woolly-haired rhinoceros, the
_Rhinoceros merckii_, and the cave-bear survive the climax of the new
Glacial Period. Even the woolly-haired mammoth succumbed. It and the
woolly-haired rhinoceros, accompanied by the musk-ox and bison, had
made their way into the Far North of Asia. But while the two last
species bore the inclemencies of the climate, the rhinoceroses and
elephants met their end here. And yet they had long preserved their
lives on the borders of eternal ice. Whole carcases, both of the
woolly-haired and Merckian rhinoceroses, and also of the woolly-haired
mammoth, the bison, and the musk-ox, with skin and hair and
well-preserved soft parts, have been discovered in the ice and frozen
ground between the Yenisei and Lena, and on the New Siberian Islands
at the mouth of the Lena. The carcases of the mammoth and rhinoceros
found imbedded in the ice were covered with a coat of thick woolly hair
and reddish-brown bristles ten inches long; about thirty pounds of hair
from such a mammoth were placed in the St. Petersburg Natural History
Museum. A mane hung from the animal’s neck almost to its knees, and on
its head was soft hair a yard long. The animals were therefore in this
respect well equipped for enduring a cold climate. As regards their
food they were also adapted to a cold climate, traces of coniferæ and
willows--that is, “Northern plants”--having been found in the hollows
of the molar teeth of mammoths and rhinoceroses. The mammoth proves to
have had greater resisting power, and to have been more fit for further
migrations, than the rhinoceros. The latter’s range of distribution
extended over the whole of Northern and Temperate Europe, China and
Central Asia, and Northern Asia and Siberia. But, as we have seen, the
mammoth penetrated not only into North Africa, but, what is of the
highest importance for the proper understanding of the settling of the
New World, even into North America.
[Sidenote: Companions of the Mammoth]
[Sidenote: Mammoth’s Arrival in Europe]
The connection which in earlier geological periods had united
Europe, Asia, Africa, and North America in the greatest homogeneous
zoogeographical kingdom, the Arctogæa, was broken during the Tertiary
and Drift Periods, so that several zoogeographical provinces were
formed. The connection with North America was the first to be broken,
so that even in the last two divisions of the Tertiary Period, the
Miocene and Pliocene Epochs, the Old and the New Worlds stood in the
relation of independent zoogeographical provinces to one another.
Now, it is of the greatest importance to note that during the Drift
Period North America again received some Northern immigrants from
the Old World, according to Von Zittel “probably viâ Eastern Asia.”
Consequently, during the Drift Period communication existed, at least
temporarily, between Asia and North America in the region of Bering
Strait, sufficient to allow the mammoth and some companions to migrate
from the one continent to the other. In Kotzebue Sound mammoth remains
are found in the “ground-ice formation,” together with those of the
horse, elk, reindeer, musk-ox and bison. Mammoth remains are also known
to have been found in the Bering Islands, St. George in the Pribylov
group, and Unalaska, one of the Aleutian Islands. In that period the
mammoth arrived in the New World as a colonist driven from the Old.
It spread widely over British North America, Alaska, and Canada; it
has also been found in Kentucky. A relatively recent union of the
circumpolar regions of the Northern Hemisphere--of Europe, Asia, and
North America--is also proved by the occurrence of animals that we
recognise as companions of the mammoth, but which, surviving the
Glacial Period, are still distributed over the whole region, such as
the reindeer, elk, and bison. The absence in Asia of several animals
specially characteristic of the European Drift (the hippopotamus, ibex,
chamois, fallow-dear, wildcat, and cave-bear) explains also their
absence in the North American Drift fauna. It is particularly strange
that the cave-bear did not reach Northern Asia. It is otherwise the
most frequent beast of prey of the Drift Period, and hundreds of its
carcases often lie buried in the caves and clefts it once inhabited.
In Southern Russia numerous remains of it are found, whereas in the
English caves it is rarer, the cave-hyena predominating here. Apart
from the exceptions just mentioned, J. F. Brandt considers North
Asia and the high Northern latitudes to be the region in which the
European, North Asiatic, and North American land fauna had concentrated
during the Tertiary and Drift Periods, and whence their migrations and
advances took place according as it grew older. As the northern fauna
spread over more southern latitudes during the Drift Period, they
took possession of the habitats of the species there belonging to the
Tertiary Period, drove them back into tropical and subtropical regions,
and formed the real stock of the Drift fauna, as described by Von
Zittel in his “Palæozoology.”
[Illustration: AN ACTUAL PHOTOGRAPH OF THE PREHISTORIC MAMMOTH
This stuffed carcase of a mammoth is the rarest treasure of St.
Petersburg Academy. Skeletons of these creatures exist in plenty,
but actual carcases are very rare. This was found embedded in
the ice on the New Siberian Islands. One carcase so embedded was
discovered five years before it could be freed from the ice.
]
One thing is certain--namely, that the northern borders of Siberia
were not the real home of the mammoth and its companions; the
original habitat of these animals points to the far interior of Asia,
particularly to the wild table-lands, where they so far steeled
themselves in enduring the climate that in the course of the Glacial
Period half the world became accessible to them. As far as is known
to-day, the mammoth arrived in Europe earlier than on the northern
borders of Asia, where, protected by climatic conditions, its remains
are most numerous and best preserved. The number of these gigantic
animals must have been very considerable in this Far Northern region
for a time, judging from the abundance of bones found there. In Central
Europe only a few places are known--such as Kannstatt, Predmost in
Moravia, etc.--where the mammoth is found with similar frequency. The
mammoth attained its widest distribution in the Interglacial Period.
In that period it crossed the Alps, and arrived on the other side, in
North Asia, at the border of the “stone-ice” masses of inland ice that
were still preserved from the first Glacial Period. The vegetation
there was richer then than it is to-day; now only the vegetation of
the tundra can exist. Animals found coniferæ, willows, and alders in
sufficient quantity to enable them to keep in herds. All the same, we
have not to imagine the climate on the borders of the ice to have been
“genial,” for from that period originate the mammoth carcases that are
found frozen entire in crevasses of the ice-fields. When the new period
of cold--the second Glacial Period--began, these Far Northern regions
must have become unsuitable for the mammoth owing to the want of food.
Von Toll, who has examined the fossil ice-beds and, their relation to
the mammoth carcases particularly on New Siberian Islands, says:
The mammoths and their contemporaries lived where their remains
are found; they died out gradually in consequence of physical
geographical changes in the region they inhabited, and through no
catastrophe; their carcases were deposited during low temperatures,
partly on the river-terraces, and partly on the banks of lakes or
on glaciers (inland ice), and covered with mud; like the ice-masses
that formed the foundation of their graves, their mummies were
preserved to the present day, thanks to the persistent or
increasing cold.
[Illustration: SKELETON OF A MAMMOTH
in the Natural History Museum, South Kensington.
]
The woolly-haired mammoth did not survive the second Glacial Period
anywhere; in the post-Glacial Period its traces have disappeared.
The Drift series of strata are nowhere so clearly exemplified as in
the New Siberian Islands, where the Drift stone-ice still forms very
extensive high “ice-cliffs,” always covered with a layer of loam, sand,
and peat, and having precipices often of great height--in one place
seventy-two feet.
Embedded in these cliffs of stone-ice have been found the mammoth
carcases, which formerly sank into crevices in the ice. These crevices
are partly filled up with snow, which has turned into “firn” and
finally into ice, but partly also with loam or sand, which are merged
above immediately into the strata overlying the stone-ice. In the year
1860 Bojavski, the mammoth-hunter, found a mammoth, with all its soft
parts preserved, sticking upright in a crevice in the ice filled with
loam; in 1863 it was thrown down, together with the coast-wall that
sheltered it, and washed away by the sea.
[Illustration: A SURVIVOR OF THE DRIFT PERIOD
Only one representative of the great Drift fauna, the musk-ox, has
been able to preserve its life to the present day on the larger
remnants of its former vast home, such as Greenland and Grinnell
Land.
]
The Tunguse Schumachow had been more fortunate as early as 1799.
During his boating expeditions along the coast, on the look-out for
mammoth-tusks, he observed one day, between blocks of ice, a shapeless
block which was not at all like the masses of driftwood that are
generally found there. In the following year the block had melted a
little, but it was only at the end of the third summer that the whole
side and one of the tusks of a mammoth appeared plainly out of the ice;
the animal, however, still remained sunk in the ice-masses. At last,
towards the end of the fifth year, the ice between the ground and the
mammoth melted more quickly than the rest, the base began to slope, and
the enormous mass, impelled by its own weight, glided down on to the
sand of the coast. Here Adams found the carcase in 1806, or as much as
the dogs and wild animals had left of it. The whole skeleton, with a
portion of the flesh, skin, and hair, has since formed one of the chief
ornaments of the collection in the Academy at St. Petersburg. According
to Von Toll, who personally visited the site of Bojavski’s discovery,
the following profile presented itself there: first the tundra stratum;
then an alternation of thin strata of loam and ice; under these a
peat-like layer of grass, leaves, and other vegetation, that had been
washed together; then a fine layer of sand, with remains of _Salix_,
etc., and finally stone-ice. At another place, in Gulf Anabar, in 73°
north latitude, Von Toll also found the ground-moraine under a fossil
ice-bed, which appears to prove his theory of a Drift region of inland
ice, of which the stone-ice beds of New Siberia and Eschscholtz Bay are
remains.
Of these strata the frozen loam deposits over the stone-ice, containing
the willow and the alder, are doubtless Interglacial. Some of the
remains of the alder are in such wonderful preservation that there are
still leaves and whole clusters of catkins on the branches.
The land-mass to which the present New Siberian Islands belong was
only dismembered at the end of the Interglacial Period, when colder
sea-currents procured an entrance, and the accumulation of snow-masses
diminished simultaneously with the sinking of the land, whereas the
cold increased. The flora died off, says Von Toll, and the animal world
was deprived of the possibility of roaming freely over vast areas. Only
one representative of the great Drift fauna, the musk-ox, has been able
to preserve its life to the present day on the larger remnants of its
former vast home, such as Greenland and Grinnell Land.
[Sidenote: Remains of the Ice Age]
As we have said, the geological and climatic conditions in all regions
of the earth affected by the Glacial Period were closely similar to
those just described. In other places the Drift stone-ice has long
disappeared, but the ground-moraines of the former inland ice-masses,
and the surface-moraines (terminal and lateral) of the former gigantic
glaciers, constitute its unobliterated traces. On the moraines of the
earlier Glacial Period we find the strata of the Interglacial Period
deposited, and on the later moraines of the second (last) Glacial
Period lie the remains of the post-Glacial Period, in the course of
which a continual increase in the yearly temperature--probably only
a few degrees of the thermometer--caused the glaciers to melt and
retreat, and opened the way for the return of plants and animals to
what had been deserts of snow and ice. The place formerly occupied by
the Interglacial and Glacial fauna is then taken by the post-Glacial
fauna, which proves considerably different.