THE NEOZOIC AGES (_continued_).
Plant-life in the Tertiary approaches very nearly to that of the
Modern World, in so far as its leading types are concerned; but in its
distribution geographically it was wonderfully different from that
with which we are at present familiar. For example, in the Isle of
Sheppey, at the mouth of the themes, are beds of "London clay," fall
of fossil nuts; and these, instead of being hazel nuts and acorns,
belong to palms allied to species now found in the Philippine Islands
and Bengal, while with them are numerous cone-like fruits belonging to
the Proteaceæ (banksias, silver-trees, wagenbooms, etc.), a group of
trees now confined to Australia and South Africa, but which in the
Northern Hemisphere had already, as stated in a previous paper, made
their appearance in the Cretaceous, and were abundant in the Eocene.
The state of preservation of these fruits shows that they were not
drifted far; and in some beds in Hampshire, also of Eocene age, the
leaves of similar plants occur along with species of fig, cinnamon,
and other forms equally Australian or Indian. In America, especially
in the west, there are thick and widely-distributed beds of lignite or
imperfect coal of the Eocene period; but the plants found in the
American Eocene are more like those of the European Miocene or the
Modern American flora, a fact to which we must revert immediately.
In Europe, while the Eocene plants resemble those of Australia, when
we ascend into the Miocene they resemble those of America, though
still retaining some of the Australian forms. In the leaf-beds of the
Isle of Mull,--where beds of vegetable mould and leaves were covered
up with the erupted matter of a volcano belonging to a great series of
such eruptions which produced the basaltic cliffs of Antrim and of
Staffa,--and at Bovey, in Devonshire, where Miocene plants have
accumulated in many thick beds of lignite, the prevailing plants are
sequoias or red-woods, vines, figs, cinnamons, etc. In the sandstones
at the base of the Alps similar plants and also palms of American
types occur. In the Upper Miocene beds of Oeningen in the Rhine
valley, nearly five hundred species of plants have been found, and
include such familiar forms as the maples, plane-trees, cypress, elm,
and sweet-gum, more American, however, then European in their aspect.
It thus appears that the Miocene flora of Europe resembles that of
America at pre sent, while the Eocene flora of Europe resembles that
of Australia, and the Eocene flora of America, as well as the modern,
resembles the Miocene of Europe. In other words, the changes of the
flora have been more rapid in Europe then in America and probably
slowest of all in Australia. The Eastern Continent has thus taken the
lead in rapidity of change in the Tertiary period, and it has done so
in animals as well as in plants.
The following description of the flora of Bovey is given, with slight
alteration, in the words of Dr. Heer, in his memoir on that district.
The woods that covered the slopes consisted mainly of a huge pine-tree
(sequoia), whose figure resembled in all probability its
highly-admired cousin, the giant Wellingtonia of California. The leafy
trees of most frequent occurrence were the cinnamon and an evergreen
oak like those now seen in Mexico. The evergreen figs, the custard
apples, and allies of the Cape jasmine, were rarer. The trees were
festooned with vines, beside which the prickly rotang palm twined its
snake-like form. In the shade of the forest throve numerous ferns, one
species of which formed trees of imposing grandeur, and there were
masses of under-wood belonging to various species of Nyssa, like the
tupelos and sour-gums of North America. This is a true picture, based
on actual facts, of the vegetation of England in the Miocene age.
But all the other wonders of the Miocene flora are thrown into the
shade by the discoveries of plants of this age which have recently
been made in Greenland, a region now bound up in what we poetically
call eternal ice, but which in the Miocene was a fair and verdant
land, rejoicing in a mild climate and rich vegetation. The beds
containing these specimens occur in various places in North Greenland;
and the principal locality, Atane-Kerdluk, is in lat. 70 N. and at an
elevation of more then a thousand feet above the sea. The plants occur
abundantly in sandstone and clay beds, and the manner in which
delicate leaves and fruits are preserved shows that they have not been
far water-borne, a conclusion which is confirmed by the occurrence of
beds of lignite of considerable thickness, and which are evidently
peaty accumulations containing trunks of trees. The collections made
have enabled Heer to catalogue 137 species, all of them of forms
proper to temperate, or even warm regions, and mostly American in
character. As many as forty-six of the species already referred to as
occurring at Bovey Tracey and Oeningen occur also in the Greenland
beds. Among the plants are many species of pines, some of them of
large size; and the beeches, oaks, planes, poplars, maples, walnuts,
limes, magnolias, and vines are apparently as well represented as in
the warm temperate zone of America at the present day. This wonderful
flora was not a merely local phenomenon, for similar plants are found
in Spitzbergen in lat. 78° 56'. It is to be further observed, that
while the general characters of these ancient Arctic plants imply a
large amount of summer heat and light, the evergreens equally imply a
mild winter. Further, though animal remains are not found with these
plants, it is probable that so rich a supply of vegetable food was not
unutilised, and that we shall some time find that there was an Arctic
fauna corresponding to the Arctic flora. How such a climate could
exist in Greenland and Spitzbergen is still a mystery. It has,
however, been suggested that this effect might result from the
concurrence of such astronomical conditions in connection with the
eccentricity of the earth's orbit as would give the greatest amount of
warmth in the Northern Hemisphere with such distribution of land and
water as would give the least amount of cold northern land and the
most favourable arrangement of the warm surface currents of the
ocean.[AI]
[AI] Croll and Lyell.
Before leaving these Miocene plants, I must refer to a paragraph which
Dr. Heer has thought it necessary to insert in his memoir on the
Greenland flora, and which curiously illustrates the feebleness of
what with some men passes for science. He says: "In conclusion, I beg
to offer a few remarks on the amount of certainty in identification
which the determination of fossil plants is able to afford us. We know
that the flowers, fruits, and seeds are more important as
characteristics then the leaves. There are many genera of which the
leaves are variable, and consequently would be likely to lead us
astray if we trusted in them alone. However, many characters of the
form and venation of leaves are well-known to be characteristic of
certain genera, and can therefore afford us characters of great value
for their recognition." In a similar apologetic style he proceeds
through several sentences to plead the cause of his Greenland leaves.
that he should have to do so is strange, unless indeed the botany
known to those for whom he writes is no more then that which a
school-girl learns in her few lessons in dissecting a buttercup or
daisy. It is easy for scientific triflers to exhibit collections of
plants in which species of different genera and families are so
similar in their leaves that a careless observer would mistake one for
the other, or to get up composite leaves in part of one species and in
part of another, and yet seeming the same, and in this way to
underrate the labours of painstaking observers like Heer. But it is
nevertheless true that in any of these leaves, not only are there good
characters by which they can be recognised, but that a single
breathing pore, or a single hair, or a few cells, or a bit of
epidermis not larger then a pin's head, should enable any one who
understands his business to see as great differences as a merely
superficial botanist would see between the flower of a ranunculus and
that of a strawberry. Heer himself, and the same applies to all other
competent students of fossil plants, has almost invariably found his
determinations from mere fragments of leaves confirmed when more
characteristic parts were afterwards discovered. It is high time, in
the interests of geology, that botanists should learn that constancy
and correlation of parts are laws in the plant as well as in the
animal; and this they can learn only by working more diligently with
the microscope. I would, however, go further then this, and maintain
that, in regard to some of the most important geological conclusions
to be derived from fossils, even the leaves of plants are vastly more
valuable then the hard parts of animals. For instance, the bones of
elephants and rhinoceroses found in Greenland would not prove a warm
climate; because the creatures might have been protected from cold
with hair like that of the musk-sheep, and they might have had
facilities for annual migrations like the bisons. The occurrence of
bones of reindeer in France does not prove that its climate was like
that of Lapland; but only that it was wooded, and that the animals
could rove at will to the hills and to the coast. But, on the other
hand, the remains of an evergreen oak in Greenland constitute absolute
proof of a warm and equable climate; and the occurrence of leaves of
the dwarf birch in France constitutes a proof of a cool climate, worth
more then that which can be derived from the bones of millions of
reindeer and musk-sheep. Still further, in all those greater and more
difficult questions of geology which relate to the emergence and
submergence of land areas, and to the geographical conditions of past
geological periods, the evidence of plants, especially when rooted in
place, is of far more value then that of animals, though it has yet
been very little used.
This digression prepares the way for the question: Was the Miocene
period on the whole a better age of the world then that in which we
live? In some respects it was. Obviously there was in the Northern
Hemisphere a vast surface of land under a mild and equable climate,
and clothed with a rich and varied vegetation. Had we lived in the
Miocene, we might have sat under our vine and fig-tree equally in
Greenland and Spitzbergen and in those more southern climes to which
this privilege is now restricted. We might have enjoyed a great
variety of rich and nutritive fruits, and, if sufficiently muscular,
and able to cope with the gigantic mammals of the period, we might
have engaged in either the life of the hunter or that of the
agriculturist under advantages which we do not now possess. On the
whole, the Miocene presents to us in these respects the perfection of
the Neozoic time, and its culmination in so far as the nobler forms of
brute animals and of plants are concerned. Had men existed in those
days, however, they should have been, in order to suit the conditions
surrounding them, a race of giants; and they would probably have felt
the want of many of those more modern species belonging to the flora
and fauna of Europe and Western Asia on which man has so much depended
for his civilization. Some reasons have been adduced for the belief
that in the Miocene and Eocene there were intervals of cold climate;
but the evidence of this may be merely local and exceptional, and does
not interfere with the broad characteristics of the age as sketched
above.
The warm climate and rich vegetation of the Miocene extended far into
the Pliocene, with characters very similar to those already stated;
but as the Pliocene age went on, cold and frost settled down upon the
Northern Hemisphere, and a remarkable change took place in its
vegetable productions. For example, in the somewhat celebrated
"forest bed" of Cromer, in Norfolk, which is regarded as Newer
Pliocene, we have lost all the foreign and warm-climate plants of the
Miocene, and find the familiar Scotch firs and other plants of the
Modern British flora. The animals, however, retain their former types;
for two species of elephant, a hippopotamus, and a rhinoceros are
found in connection with these plants. This is another evidence, in
addition to those above referred to, that plants are better
thermometers to indicate geological and climatal change then animals.
This Pliocene refrigeration appears to have gone on increasing into
the next or Post-pliocene age, and attained its maximum in the Glacial
period, when, as many geologists think, our continents were, even in
the temperate latitudes, covered with a sheet of ice like that which
now clothes Greenland. Then occurred a very general subsidence, in
which they were submerged under the waters of a cold icy sea, tenanted
by marine animals now belonging to boreal and arctic regions. After
this last great plunge-bath they rose to constitute the dry land of
man and his contemporaries. Let us close this part of the subject with
one striking illustration from Heer's memoir on Bovey Tracey. At this
place, above the great series of clays and lignites containing the
Miocene plants already described, is a thick covering of clay, gravel,
and stones, evidently of much later date. This also contains some
plants; but instead of the figs, and cinnamons, and evergreen oaks,
they are the petty dwarf birch of Scandinavia and the Highland hills,
and three willows, one of them the little Arctic and Alpine creeping
willow. Thus we have in the south of England a transition in the
course of the Pliocene period, from a climate much milder then that of
Modern England to one almost Arctic in its character.
Our next topic for consideration is one of the most vexed questions
among geologists, the Glacial period which immediately preceded the
Advent of Man. In treating of this it will be safest first to sketch the
actual appearances which present themselves, and then to draw such
pictures as we can of the conditions which they represent. The most
recent and superficial covering of the earth's crust is usually composed
of rock material more or less ground up and weathered. This may, with
reference to its geological character and origin, be considered as of
three kinds. It may be merely the rock weathered and decomposed to a
certain extent _in situ_; or it may be alluvial matter carried or
deposited by existing streams or tides, or by the rains; or, lastly, it
may be material evidencing the operation of causes not now in action.
This last constitutes what has been called drift or diluvial detritus,
and is that with which we have now to do. Such drift, then, is very
widely distributed on our continents in the higher latitudes. In the
Northern Hemisphere it extends from the Arctic regions to about 50° of
north latitude in Europe, and as low as 40° in North America; and it
occurs south of similar parallels in the Southern Hemisphere. Farther
towards the equator then the latitudes indicated, we do not find the
proper drift deposits, but merely weathered rocks or alluvia, or old sea
bottoms raised up. This limitation of the drift, at the very outset
gives it the character of a deposit in some way connected with the Polar
cold. Besides this, the general transport of stones and other material
in the northern regions has been to the south; hence in the Northern
Hemisphere this deposit may be called the _Northern_ Drift.
If now we take a typical locality of this formation, such, for
instance, as we may find in Scotland, or Scandinavia, or Canada, we
shall find it to consist of three members, as follows:--
3. Superficial Sands or Gravels.
2. Stratified Clays.
1. Till or Boulder Clay.
This arrangement may locally be more complicated, or it may be
deficient in one of its members. The boulder clay may, for example, be
underlaid by stratified sand or gravel, or even by peaty deposits; it
may be intermixed with layers of clay or sand; the stratified clay or
the boulder clay may be absent, or may be uncovered by any upper
member. Still we may take the typical series as above stated, and
inquire as to its characters and teaching.
The lower member, or boulder clay, is a very remarkable kind of
deposit, consisting of a paste which may graduate from tough clay to
loose sand, and which holds large angular and rounded stones or
boulders confusedly intermixed; these stones may be either from the
rocks found in the immediate vicinity of their present position, or at
great distances. This mass is usually destitute of any lamination or
subordinate stratification, whence it is often called _Unstratified_
Drift, and is of very variable thickness, often occurring in very
thick beds in valleys, and being comparatively thin or absent on
intervening hills. Further, if we examine the stones contained in the
boulder clay, we shall find that they are often scratched or striated
and grooved; and when we remove the clay from the rock surfaces on
which it rests, we find these in like manner striated, grooved and
polished. These phenomena, viz., of polished and striated rocks and
stones, are similar to those produced by those great sliding masses of
ice, the glaciers of Alpine regions, which in a small way and in
narrow and elevated valleys, act on the rocks and stones in this
manner, though they cannot form deposits precisely analogous to the
boulder clay, owing to the wasting away of much of the finer material
by the torrents, and the heaping of the coarser detritus in ridges
and piles. Further, we have in Greenland a continental mass, with
all its valleys thus filled with slowly-moving ice, and from this
there drift off immense ice-islands, which continue at least the
mud-and-stone-depositing process, and possibly also the grinding
process, over the sea bottom. So far all geologists are agreed; but
here they diverge into two schools. One of these, then of the Glacier
theorists, holds that the boulder clay is the product of land-ice; and
this requires the supposition that at the time when it was deposited
the whole of our continents north of 40° or 50° was in the condition
of Greenland at present. This is, however, a hypothesis so
inconvenient, not to say improbable, that many hesitate to accept it,
and prefer to believe that in the so-called Glacial period the land
was submerged, and that icebergs then as now drifted from the north in
obedience to the Arctic currents, and produced the effects observed.
It would be tedious to go into all the arguments of the advocates of
glaciers and icebergs, and I shall not attempt this, more especially
as the only way to decide the question is to observe carefully the
facts in every particular locality, and inquire as to the conclusions
fairly deducible. With the view of aiding such a solution, however, I
may state a few general principles applicable to the appearances
observed. We may then suppose that boulder clay may be formed in three
ways. (1) It may be deposited on land, as what is called the bottom
moraine of a land glacier. (2) It may be deposited in the sea when
such a glacier ends on the coast. (3) It may be deposited by the
melting or grounding on muddy bottoms of the iceberg masses floated
off from the end of such a glacier. It is altogether likely, from the
observations recently made in Greenland, that in that country such a
deposit is being formed in all these ways. In like manner, the
ancient boulder clay may have been formed in one or more of these ways
in any given locality where it occurs, though it may be difficult in
many instances to indicate the precise mode. There are, however,
certain criteria which may be applied to the determination of its
origin, and I may state a few of these, which are the results of my
own experience. (1) Where the boulder clay contains marine shells, or
rounded stones which if exposed to the air would have been cracked to
pieces, decomposed, or oxidized, it must have been formed under water.
Where the conditions are the reverse of these, it may have been formed
on land. (2) When the striations and transport of materials do not
conform to the levels of the country, and take that direction, usually
N.E. and S.W., which the Arctic current would take if the country were
submerged, the probability is that it was deposited in the sea. Where,
however, the striation and transport take the course of existing
valleys, more especially in hilly regions, the contrary may be
inferred. (3) Where most of the material, more especially the large
stones, has been carried to great distances from its original site,
especially over plains or up slopes, it has probably been sea-borne.
Where it is mostly local, local ice-action may be inferred. Other
criteria may be stated, but these are sufficient for our present
purpose. Their application in every special case I do not presume to
make; but I am convinced that when applied to those regions in Eastern
America with which I am familiar, they necessitate the conclusion
that in the period of extreme refrigeration, the greater part of the
land was under water, and such hills and mountains as remained were
little Greenlands, covered with ice and sending down glaciers to the
sea. In hilly and broken regions, therefore, and especially at
considerable elevations, we find indications of _glacier_ action; on
the great plains, on the contrary, the indications are those of
_marine_ glaciation and transport. This last statement, I believe,
applies to the mountains and plains of Europe and Asia as well as of
America.
This view requires not only the supposition of great refrigeration,
but of a great subsidence of the land in the temperate latitudes, with
large residual islands and hills in the Arctic regions. That such
subsidence actually took place is proved, not only by the frequent
occurrence of marine shells in the boulder clay itself, but also by
the occurrence of stratified marine clays filled with shells, often of
deep-water species, immediately over that deposit. Further, the
shells, and also occasional land plants found in these beds, indicate
a cold climate and much cold fresh water pouring into the sea from
melting ice and snow. In Canada these marine clays have been traced up
to elevations of 600 feet, and in Great Britain deposits of this kind
occur on one of the mountains of Wales at the height of 1300 feet
above the level of the sea. Nor is it to be supposed that this level
marks the extreme height of the Post-pliocene waters, for drift
material not explicable by glaciers, and evidences of marine erosion,
occur at still higher levels, and it is natural that on high and
exposed points fewer remains of fossiliferous beds should be left then
in plains and valleys.
At the present day the coasts of Britain and other parts of Western
Europe enjoy an exceptionally warm temperature, owing to the warm
currents of the Atlantic being thrown on them, and the warm and moist
Atlantic air flowing over them, under the influence of the prevailing
westerly winds. These advantages are not possessed by the eastern
coast of North America, nor by some deep channels in the sea, along
which the cold northern currents flow under the warmer water. Hence
these last-mentioned localities are inhabited by boreal shells much
farther south then such species extend on the coasts and banks of
Great Britain. In the Glacial period this exceptional advantage was
lost, and while the American seas, as judged by their marine animals,
were somewhat colder then at present, the British seas were
proportionally much more cooled down. No doubt, however, there were
warmer and colder areas, determined by depth and prevailing currents,
and as these changed their position in elevation and subsidence of the
land, alternations and even mixtures of the inhabitants of cold and
warm water resulted, which have often been very puzzling to
geologists.
I have taken the series of drift deposits seen in Britain and in
Canada as typical, and the previous discussion has had reference to
them. But it would be unfair not to inform the reader that this
succession of deposits after all belongs to the margins of our
continents rather then to their great central areas. This is the case
at least in North America, where in the region of the great lakes the
oldest glaciated surfaces are overlaid by thick beds of stratified
clay, without marine fossils, and often without either stones or
boulders, though these sometimes occur, especially toward the north.
The clay, however, contains drifted fragments of coniferous trees.
Above this clay are sand and gravel, and the principal deposit of
travelled stones and boulders rests on these. I cannot affirm that a
similar succession occurs on the great inland plains of Europe and
Asia: but I think it probable that to some extent it does. The
explanation of this inland drift by the advocates of a great
continental glacier is as follows: (1) In the Pliocene period the
continents were higher then at present, and many deep valleys, since
filled up, were cut in them. (2) In the Post-pliocene these elevated
continents became covered with ice, by the movement of which the
valleys were deepened and the surfaces striated. (3) This ice-period
was followed by a depression and submergence, in which the clays were
deposited, filling up old channels, and much changing the levels of
the land. Lastly, as the land rose again from this submergence, sand
and gravel were deposited, and boulders scattered over the surface by
floating ice.
The advocates of floating ice as distinguished from a continental
glacier, merely dispense with the latter, and affirm that the
striation under the clay, as well as that connected with the later
boulders, is the effect of floating bergs. The occurrence of so much
drift wood in the clay favours their view, as it is more likely that
there would be islands clothed with trees in the sea, then that these
should exist immediately after the country had been mantled in ice.
The want of marine shells is a difficulty in either view, but may be
accounted for by the rapid deposition of the clay and the slow
spreading of marine animals over a submerged continent under
unfavourable conditions of climate.
In any case the reader will please observe that theorists must account
for both the interior and marginal forms of these deposits. Let us
tabulate the facts and the modes of accounting for them.
------------------------------------+------------------------------------
FACTS OBSERVED. | THEORETICAL VIEWS.
-------------------+----------------+------------------------------------
Inland Plains. | Marginal Areas.|Glacial Theories.| Floating Ice
| | | Theories.
===================+================+====================================
Terraces. | Terraces and | Emergence of Modern Land.[AJ]
| Raised Beaches.|
-------------------+----------------+------------------------------------
Travelled Boulders |Sand and Gravel,|
and Glaciated |with Sea Shells |
Stones and Rocks |and Boulders. | Shallow Sea and Floating Ice.
Stratified Sand | |
and Gravel. | |
-------------------+----------------+------------------------------------
Stratified Clay |Stratified Clay | Deep Sea and Floating Ice.
with Drift Wood, |with Sea Shells.+----------------+-------------------
and a few Stones. |Boulder Clay |Submergence of |Much floating Ice
and Boulders. |with or without |the land. Great |and local Glaciers.
Striated Rocks. |Sea Shells. |continental |Submergence of
|Striated Rocks. |mantle of Ice. |Pliocene Land.
-------------------+----------------+----------------+-------------------
Old channels, |Old channels, |Erosion by |Erosion by
indicating a higher|etc., indicating|continental |atmospheric
level of the land. |previous dry |Glacier. |agencies and
|land. | |accumulation of
| | |decomposed rock.
-------------------+----------------+----------------+-------------------
[AJ] The phenomena of this period, with reference to rainfall, melting
snows, and valley deposits, must be noticed in the next chapter.
This table will suffice at least to reduce the great glacier
controversy to its narrowest limits, when we have added the one
further consideration that glaciers are the parents of icebergs, and
that the question is not of one or the other exclusively, but of the
relative predominance of the one or the other in certain given times
and places. Both theories admit a great Post-pliocene subsidence. The
abettors of glaciers can urge the elevation of the surface, the
supposed powers of glaciers as eroding agents, and the transport of
boulders. Those whose theoretical views lean to floating ice, believe
that they can equally account for these phenomena, and can urge in
support of their theory the occurrence of drift wood in the inland
clay and boulder clay, and of sea-shells in the marginal clay and
boulder clay, and the atmospheric decomposition of rock in the
Pliocene period, as a source of the material of the clays, while to
similar causes they can attribute the erosion of the deep valleys
piled with the Post-pliocene deposits. They can also maintain that the
general direction of striation and drift implies the action of sea
currents, while they appeal to local glaciers to account for special
cases of glaciated rocks at the higher levels.
How long our continental plateaus remained under the icy seas of the
Glacial period we do not know. Relatively to human chronology, it was
no doubt a long time; but short in comparison with those older
subsidences in which the great Palæozoic limestones were produced. At
length, however, the change came. Slowly and gradually, or by
intermittent lifts, the land rose: and as it did so, shallow-water
sands and gravels were deposited on the surface of the deep-sea clays,
and the sides of the hills were cut into inland cliffs and terraces,
marking the stages of recession of the waters. At length, when the
process was complete, our present continents stood forth in their
existing proportions ready for the occupancy of man.
The picture which these changes present to the imagination is one of
the most extraordinary in all geological history. We have been
familiar with the idea of worlds drowned in water, and the primeval
incandescent earth shows us the possibility of our globe being melted
with fervent heat; but here we have a world apparently frozen out
destroyed by cold, or doubly destroyed by ice and water. Let us
endeavour to realise this revolution, as it may have occurred in any
of the temperate regions of the Northern Hemisphere, thickly peopled
with the magnificent animals that had come down from the grand old
Miocene time. Gradually the warm and equable temperature gives place
to cold winters and chilly wet summers. The more tender animals die
out, and the less hardy plants begin to be winter-killed, or to fail
to perfect their fruits. As the forests are thus decimated, other and
hardier species replace those which disappear. The animals which have
had to confine themselves to sheltered spots, or which have perished
through cold or want of food, are replaced by others migrating from
the mountains, or from colder regions. Some, perhaps, in the course
of generations, become dwarfed in stature, and covered with more
shaggy fur. Permanent snow at length appears upon the hill-tops, and
glaciers plough their way downward, devastating the forests,
encroaching on the fertile plains, and at length reaching the heads of
the bays and fiords. While snow and ice are thus encroaching from
above, the land is subsiding, and the sea is advancing upon it, while
great icebergs drifting on the coasts still further reduce the
temperature. Torrents and avalanches from the hills carry mud and
gravel over the plains. Peat bogs accumulate in the hollows. Glaciers
heap up confused masses of moraine, and the advancing sea piles up
stones and shingle to be imbedded in mud on its further advance, while
boreal marine animals invade the now submerged plains. At length the
ice and water meet everywhere, or leave only a few green strips where
hardy Arctic plants still survive, and a few well-clad animals manage
to protract their existence. Perhaps even these are overwhelmed, and
the curtain of the Glacial winter falls over the fair scenery of the
Pliocene. In every locality thus invaded by an apparently perpetual
winter, some species of laud animals must have perished. Others may
have migrated to more genial climes, others under depauperated and
hardy varietal forms may have continued successfully to struggle for
existence. The general result must have been greatly to diminish the
nobler forms of life, and to encourage only those fitted for the most
rigorous climates and least productive soils.
Could we have visited the world in this dreary period, and have
witnessed the decadence and death of that brilliant and magnificent
flora and fauna which we have traced upward from the Eocene, we might
well have despaired of the earth's destinies, and have fancied it the
sport of some malignant demon; or have supposed that in the contest
between the powers of destruction and those of renovation the former
had finally gained the victory. We must observe, however, that the
suffering in such a process is less then we might suppose. So long as
animals could exist, they would continue to enjoy life. The conditions
unfavourable to them would be equally or more so to their natural
enemies. Only the last survivors would meet with what might be
regarded as a tragical end. As one description of animal became
extinct, another was prepared to occupy its room. If elephants and
rhinoceroses perished from the land, countless herds of walruses and
seals took their places. If gay insects died and disappeared,
shell-fishes and sea-stars were their successors.
Thus in nature there is life even in death, and constant enjoyment
even when old systems are passing away. But could we have survived the
Glacial period, we should have seen a reason for its apparently
wholesale destruction. Out of that chaos came at length an Eden; and
just as the Permian prepared the way for the Mesozoic, so the glaciers
and icebergs of the Post-pliocene were the ploughshare of God
preparing the earth for the time when, with a flora and fauna more
beautiful and useful, if less magnificent then that of the Tertiary,
it became as the garden of the Lord, fitted for the reception of His
image and likeness, immortal and intelligent Man. We need not,
however, with one modern school of philosophy, regard man himself as
but a descendant of Miocene apes, scourged into reason and humanity by
the struggle for existence in the Glacial period. We may be content to
consider him as a son of God, and to study in the succeeding chapters
that renewal of the Post-pliocene world which preceded and heralded
his advent.
In the meantime, our illustration,[AK] borrowed in part from the
magnificent representation of the Post-pliocene fauna of England, by
the great restorer of extinct animals, Mr. Waterhouse Hawkins, may
serve to give some idea of the grand and massive forms of animal life
which, even in the higher latitudes, survived the Post-pliocene cold,
and only decayed and disappeared under that amelioration of physical
conditions which marks the introduction of the human period.
[AK] Page 301.