CLOSE OF THE POST-PLIOCENE, AND ADVENT OF MAN.
_In_ closing these sketches it may seem unsatisfactory not to link the
geological ages with the modern period in which we live; yet, perhaps,
nothing is more complicated or encompassed with greater difficulties
or uncertainties. The geologist, emerging from the study of the older
monuments of the earth's history, and working with the methods of
physical science, here meets face to face the archæologist and
historian, who have been tracing back in the opposite direction, and
with very different appliances, the stream of human history and
tradition. In such circumstances conflicts may occur, or at least the
two paths of inquiry may refuse to connect themselves without
concessions unpleasant to the pursuers of one or both. Further, it is
just at this meeting-place that the dim candle of traditional lore is
almost burnt out in the hand of the antiquary, and that the geologist
finds his monumental evidence becoming more scanty and less distinct.
We cannot hope as yet to dispel all the shadows that haunt this
obscure domain, but can at least point out some of the paths which
traverse it. In attempting this, we may first classify the time
involved as follows: (1) The earlier Post-pliocene period of geology
may be called the _Glacial_ era. It is that of a cold climate,
accompanied by glaciation and boulder deposits. (2) The later
_Post-pliocene_ may be called the Post-glacial era. It is that of
re-elevation of the continents and restoration of a mild temperature.
It connects itself with the pre-historic period of the archæologist,
inasmuch as remains of man and his works are apparently included in
the same deposits which hold the bones of Post-glacial animals. (3)
The _Modern_ era is that of secular human history.
It may be stated with certainty that the Pliocene period of geology
affords no trace of human remains or implements; and the same may I
think be affirmed of the period of glaciation and subsidence which
constitutes the earlier Post-pliocene. With the rise of the land out
of the Glacial sea indications of man are believed to appear, along
with remains of several mammalian species now his contemporaries.
Archæology and geology thus meet somewhere in the pre-historic period
of the former, and in the Post-glacial of the latter. Wherever,
therefore, human history extends farthest back, and geological
formations of the most modern periods exist and have been explored, we
may expect best to define their junctions. Unfortunately it happens
that our information on these points is still very incomplete and
locally limited. In many extensive regions, like America and
Australia, while the geological record is somewhat complete, the
historic record extends back at most a few centuries, and the
pre-historic monuments are of uncertain date. In other countries, as
in Western Asia and Egypt, where the historic record extends very far
back, the geology is less perfectly known. At the present moment,
therefore, the main battle-field of these controversies is in Western
Europe, where, though history scarce extends farther back then the
time of the Roman Republic, the geologic record is very complete, and
has been explored with some thoroughness. It is obvious, however, that
we thus have to face the question at a point where the pre-historic
gap is necessarily very wide.
Taking England as an example, all before the Roman invasion is
pre-historic, and with regard to this pre-historic period the evidence
that we can obtain is chiefly of a geological character. The
pre-historic men are essentially fossils. We know of them merely what
can be learned from their bones and implements embedded in the soil or
in the earth of the caverns in which some of them sheltered
themselves. For the origin and date of these deposits the antiquary
must go to the geologist, and he imitates the geologist in arranging
his human fossils under such names as the "Paleolithic," or period of
rude stone implements; the "Neolithic" or period of polished stone
implements; the Bronze Period, and the Iron Period; though inasmuch as
higher and lower states of the arts seem always to have coexisted, and
the time involved is comparatively short, these periods are of far
less value then those of geology. In Britain the age of iron is in the
main historic. That of bronze goes back to the times of early
Phoenician trade with the south of England. That of stone, while
locally extending far into the succeeding ages, reaches back into an
unknown antiquity, and is, as we shall see in the sequel, probably
divided into two by a great physical change, though not in the abrupt
and arbitrary way sometimes assumed by those who base their
classification solely on the rude or polished character of stone
implements. We must not forget, however, that in Western Asia the ages
of bronze and iron may have begun two thousand years at least earlier
then in Britain, and that in some parts of America the Palaeolithic
age of chipped stone implements still continues. We must also bear in
mind that when the archæologist appeals to the geologist for aid, he
thereby leaves that kind of investigation in which dates are settled
by years, for that in which they are marked merely by successive
physical and organic changes.
Turning, then, to our familiar geological methods, and confining
ourselves mainly to the Northern Hemisphere and to Western Europe, two
pictures present themselves to us: (!) The physical changes preceding
the advent of man; (2) The decadence of the land animals of the
Post-pliocene age, and the appearance of those of the modern.
In the last chapter I had to introduce the reader to a great and
terrible revolution, whereby the old Pliocene continents, with all
their wealth of animals and plants, became sealed up in a mantle of
Greenland ice, or, slowly sinking beneath the level of the sea, were
transformed into an ocean-bottom over which icebergs bore their
freight of clay and boulders. We also saw that as the Post-pliocene
age advanced, the latter condition prevailed, until the waters stood
more then a thousand feet deep over the plains of Europe. In this
great glacial submergence, which closed the earlier Post-pliocene
period, and over vast areas of the Northern Hemisphere, terminated the
existence of many of the noblest forms of life, it is believed that
man had no share. We have, at least as yet, no record of his presence.
Out of these waters the land again rose slowly and intermittently, so
that the receding waves worked even out of hard rocks ranges of coast
cliff which the further elevation converted into inland terraces, and
that the clay and stones deposited by the Glacial waters were in many
places worked over and rearranged by the tides and waves of the
shallowing sea before they were permanently raised up to undergo the
action of the rains and streams, while long banks of sand and gravel
were stretched across plains and the mouths of valleys, constituting
"kames," or "eskers," only to be distinguished from moraines of
glaciers by the stratified arrangement of their materials.
Further, as the land rose, its surface was greatly and rapidly
modified by rains and streams. There is the amplest evidence, both in
Europe and America, that at this time the erosion by these means was
enormous in comparison with anything we now experience. The rainfall
must have been excessive, the volume of water in the streams very
great; and the facilities for cutting channels in the old Pliocene
valleys, filled to the brim with mud and boulder-clay, were
unprecedented. While the area of the land was still limited, much of
it would be high and broken, and it would have all the dampness of an
insular climate. As it rose in height, plains which had, while under
the sea, been loaded with the _débris_ swept from the land, would be
raised up to experience river erosion. It was the spring-time of the
Glacial era, a spring eminent for its melting snows, its rains, and
its river floods.[AL] To an observer living at this time it would have
seemed as if the slow process of moulding the continents was being
pushed forward with unexampled rapidity. The valleys were ploughed out
and cleansed, the plains levelled and overspread with beds of
alluvium, giving new features of beauty and utility to the land, and
preparing the way for the life of the Modern period, as if to make up
for the time which had been lost in the dreary Glacial age. It will
readily be understood how puzzling these deposits have been to
geologists, especially to those who fail to present to their minds the
true conditions of the period; and how difficult it is to separate the
river alluvia of this age from the deposits in the seas and estuaries,
and these again from the older Glacial beds. Further, in not a few
instances the animals of a cold climate must have lived in close
proximity to those which belonged to ameliorated conditions, and the
fossils of the older Post-pliocene must often, in the process of
sorting by water, have been mixed with those of the newer.
[AL] Mr. Tylor has well designated this period as the Pluvial age.
_Journal of the Geological Society_, 1870.
Many years ago the brilliant and penetrating intellect of Edward
Forbes was directed to the question of the maximum extent of the later
Post-pliocene or Post-glacial land; and his investigations into the
distribution of the European flora, in connection with the phenomena
of submerged terrestrial surfaces, led to the belief that the land had
risen until it was both higher and more extensive then at present. At
the time of greatest elevation, England was joined to the continent of
Europe by a level plain, and a similar plain connected Ireland with
its sister islands. Over these plains the plants constituting the
"Germanic" flora spread themselves into the area of the British
Islands, and herds of mammoth, rhinoceros, and Irish elk wandered and
extended their range from east to west. The deductions of Forbes have
been confirmed and extended by others; and it can scarcely be doubted
that in the Post-glacial era, the land regained fully the extent which
it had possessed in the time of the Pliocene. In these circumstances
the loftier hills might still reach the limits of perpetual snow, but
their glaciers would no longer descend to the sea. What are now the
beds of shallow seas would be vast wooded plains, drained by
magnificent rivers, whose main courses are now submerged, and only
their branches remain as separate and distinct streams, The cold but
equable climate of the Post-pliocene would now be exchanged for warm
summers, alternating with sharp winters, whose severity would be
mitigated by the dense forest covering, which would also contribute to
the due supply of moisture, preventing the surface from being burnt
into arid plains.
It seems not improbable that it was when the continents had attained
to their greatest extension and when animal and vegetable life had
again over-spread the new land to its utmost limits, that man was
introduced on the eastern continent, and with him several mammalian
species, not known in the Pliocene period, and some of which, as the
sheep, the goat, the ox, and the dog, have ever since been his
companions and humble allies. These, at least in the west of Europe,
were the "Palaeolithic" men, the makers of the oldest flint
implements; and armed with these, they had to assert the mastery of
man over broader lands then we now possess, and over many species of
great animals now extinct. In thus writing, I assume the accuracy of
the inferences from the occurrence of worked stones with the bones of
post-glacial animals, which must have lived during the condition of
our continents above referred to. If these inferences are well
founded, not only did man exist at this time, but man not even
varietally distinct from modern European races. But if man really
appeared in Europe in the Post-glacial era, he was destined to be
exposed to one great natural vicissitude before his permanent
establishment in the world. The land had reached its maximum
elevation, but its foundations, "standing in the water and out of the
water," were not yet securely settled, and it had to take one more
plunge-bath before attaining its modern fixity. This seems to have
been a comparatively rapid subsidence and re-elevation, leaving but
slender traces of its occurrence, but changing to some extent the
levels of the continents, and failing to restore them fully to their
former elevation, so that large areas of the lower grounds still
remained under the sea. If, as the greater number of geologists now
believe, man was then on the earth, it is not impossible that this
constituted the deluge recorded in that remarkable "log book" of
Noah preserved to us in Genesis, and of which the memory remains
in the traditions of most ancient nations. This is at least the
geological deluge which separates the Post-glacial period from the
Modern, and the earlier from the later pre-historic period of the
archæologists.[AM]
[AM] I have long thought that the narrative in Gen. vii. and viii. can
be understood only on the supposition that it is a contemporary
journal or log of an eye-witness incorporated by the author of Genesis
in his work. The dates of the rising and fall of the water, the note
of soundings over the hill-tops when the maximum was attained, and
many other details, as well as the whole tone of the narrative, seem
to require this supposition, which also removes all the difficulties
of interpretation which have been so much felt.
Very important questions of time are involved in this idea of
Post-glacial man, and much will depend, in the solution of these, on
the views which we adopt as to the rate of subsidence and elevation of
the land. If, with the majority of British geologists, we hold that it
is to be measured by those slow movements now in progress, the time
required will be long. If, with most Continental and some American
geologists, we believe in paroxysmal movements of elevation and
depression, it may be much reduced. We have seen in the progress of
our inquiries that the movements of the continents seem to have
occurred with accelerated rapidity in the more modern periods. We have
also seen that these movements might depend on the slow contraction of
the earth's crust due to cooling, but that the effects of this
contraction might manifest themselves only at intervals. We have
further seen that the gradual retardation of the rotation of the earth
furnishes a cause capable of producing elevation and subsidence of the
land, and that this also might be manifested at longer or shorter
intervals, according to the strength and resisting power of the crust.
Under the influence of this retardation, so long as the crust of the
earth did not give way, the waters would be driven toward the poles,
and the northern land would be submerged; but so soon as the tension
became so great as to rupture the solid shell, the equatorial regions
would collapse, and the northern land would again be raised. The
subsidence would be gradual, the elevation paroxysmal, and perhaps
intermittent. Let us suppose that this was what occurred in the
Glacial period, and that the land had attained to its maximum
elevation. This might not prove to be permanent; the new balance of
the crust might be liable to local or general disturbance in a minor
degree, leading to subsidence and partial re-elevation, following the
great Post-glacial elevation. There is, therefore, nothing
unreasonable in that view which makes the subsidence and re-elevation
at the close of the Post-glacial period somewhat abrupt, at least when
compared with some more ancient movements.
But what is the evidence of the deposits formed at this period? Here
we meet with results most diverse and contradictory, but I think there
can be little doubt that on this kind of evidence the time required
for the Post-glacial period has been greatly exaggerated, especially
by those geologists who refuse to receive such views as to subsidence
and elevation as those above stated. The calculations of long time
based on the gravels of the Somme, on the cone of the Tinière, on the
peat bogs of France and Denmark, on certain cavern deposits, have all
been shown to be more or less at fault; and possibly none of these
reach further back then the six or seven thousand years which,
according to Dr. Andrews, have elapsed since the close of the
boulder-clay deposits in America.[AN] I am aware that such a statement
will be regarded with surprise by many in England, where even the
popular literature has been penetrated with the idea of a duration of
the human period immensely long in comparison with what used to be the
popular belief; but I feel convinced that the scientific pendulum must
swing backward in this direction nearer to its old position. Let us
look at a few of the facts. Much use has been made of the "cone" or
delta of the Tinière on the eastern side of the Lake of Geneva, as an
illustration of the duration of the Modern period. This little stream
has deposited at its mouth a mass of _débris_ carried down from the
hills. This being cut through by a railway, is found to contain Roman
remains to a depth of four feet, bronze implements to a depth of ten
feet, stone implements at a depth of nineteen feet. The deposit ceased
about three hundred years ago, and calculating 1300 to 1500 years for
the Roman period, we should have 7000 to 10,000 years as the age of
the cone. But before the formation of the present cone, another had
been formed twelve times as large. Thus for the two cones together, a
duration of more then 90,000 years is claimed. It appears, however,
that this calculation has been made irrespective of two essential
elements in the question. No allowance has been made for the fact that
the inner layers of a cone are necessarily smaller then the outer;
nor for the further fact that the older cone belongs to a distinct
time (the pluvial age already referred to), when the rainfall was much
larger, and the transporting power of the torrent great in proportion.
Making allowance for these conditions, the age of the newer cone, that
holding human remains, falls between 4000 and 5000 years. The peat bed
of Abbeville, in the north of France, has grown at the rate of one and
a half to two inches in a century. Being twenty-six feet in thickness,
the time occupied in its growth must have amounted to 20,000 years;
and yet it is probably newer then some of the gravels on the same
river containing flint implements. But the composition of the
Abbeville peat shows that it's a forest peat, and the erect stems
preserved in it prove that in the first instance it must have grown at
the rate of about three feet in a century, and after the destruction
of the forest its rate of increase down to the present time diminished
rapidly almost to nothing. Its age is thus reduced to perhaps less
then 4000 years. In 1865 I had an opportunity to examine the now
celebrated gravels of St. Acheul, on the Somme, by some supposed to go
back to a very ancient period. With the papers of Prestwich and other
able observers in my hand, I could conclude merely that the
undisturbed gravels were older then the Roman period, but how much
older only detailed topographical surveys could prove; and that taking
into account the probabilities of a different level of the land, a
wooded condition of the country, a greater rainfall, and a glacial
filling of the Somme valley with clay and stones subsequently cut out
by running water the gravels could scarcely be older then the
Abbeville peat. To have published such views in England would have
been simply to have delivered myself into the hands of the
Philistines. I therefore contented myself with recording my opinion in
Canada. Tylor[AO] and Andrews[AP] have, however, I think, subsequently
shown that my impressions were correct. In like manner, I fail to
perceive, and I think all American geologists acquainted with the
pre-historic monuments of the western continent must agree with me,
any evidence of great antiquity in the caves of Belgium and England,
the kitchen-middens of Denmark, the rock-shelters of France, the lake
habitations of Switzerland. At the same time, I would disclaim all
attempt to resolve their dates into precise terms of years. I may
merely add, that the elaborate and careful observations of Dr. Andrews
on the raised beaches of Lake Michigan, observations of a much more
precise character then any which, in so far as I know, have been made
of such deposits in Europe, enable him to calculate the time which has
elapsed since North America rose out of the waters of the Glacial
period as between 5500 and 7500 years. This fixes at least the
possible duration of the human period in North America, though I
believe there are other lines of evidence which, would reduce the
residence of man in America to a much shorter time. Longer periods
have, it is true, been deduced from the delta of the Mississippi and
the gorge of Niagara; but the deposits of the former have been found
by Hilgard to be in great part marine, and the excavation of the
latter began at a period probably long Anterior to the advent of man.
[AN] "Transactions, Chicago Academy," 1871.
[AO] "Journal of Geological Society," vol. xxv.
[AP] "Silliman's Journal," 1868.
But another question remains. From the similarities existing in the
animals and plants of regions in the southern hemisphere now widely
separated by the ocean, it has been inferred that Post-pliocene land
of great extent existed there; and that on this land men may have
lived before the continents of the northern hemisphere were ready for
them. It has even been supposed that, inasmuch as the flora and fauna
of Australia have an aspect like that of the Eocene Tertiary, and very
low forms of man exist in that part of the world, these low races are
the oldest of all, and may date from Tertiary times. Positive evidence
of this, however, there is none. These races have no monuments; nor,
so far as known, have they left their remains in Post-pliocene
deposits. It depends on the assumptions that the ruder races of men
are the oldest; and that man has no greater migratory powers then
other animals. The first is probably false, as being contrary to
history; and also to the testimony of palaeontology with reference to
the laws of creation. The second is certainly false; for we know that
man has managed to associate himself with every existing fauna and
flora, even in modern times; and that the most modern races have
pitched their tents amid tree-ferns and Proteaceæ, and have hunted
kangaroos and emus. Further, when we consider that the productions of
the southern hemisphere are not only more antique then those of the
northern, but, on the whole, less suited for the comfortable
subsistence of man and the animals most useful to him; and that the
Post-pliocene animals of the southern hemisphere were of similar types
with their modern successors, we are the less inclined to believe that
these regions would be selected as the cradle of the human race.
CONDENSED TABULAR VIEW OF THE AGES AND PERIODS OF THE NEOZOIC.
Key to Symbols
### Recent species of Aquatic Invertebrates. Teleostian Fishes and
Squaloid sharks prevail.
--- Ages of Angiosperms and Plants.
=== "And God said--let the land bring forth herbivorous beasts and
carnivorous beasts, after their kinds; and it was so."
+++ "And God created man in His own image."
Time.
Ages. Periods. Animals and Plants.
NEOZOIC OR CAINOZOIC.
{Newer. Still future (?) Age of +
Modern {Middle. Historic. Man +
{Older. Pre-historic. +
+
{N. Post-Glacial gravels and cave # +
{ deposits. Saxicava sand and # +
Post- { terraces (America). # +
Pliocene {M. Marine Clays. Leda clays. Erie # - +
{ clay (America). # - +
{O. Glacial Drift. Boulder clay # - +
{ (America). # - +
# - +
{N. Norwich crag; Sicilian and # -
{ Val d'Arno beds. # -
Pliocene {M. ____________ Sumter group (America). # -
{O. Red and Coralline crag; Sub-appenine # - =
{ beds. # - =
# - =
{N. Faluns of Loraine; Upper Molasse; # - =
{ Siwalik beds; Oeningen plant beds. # - =
{ York-town beds (America). # - =
Miocene {M. ____________ # - =
{O. Upper Paris beds; Hempstead and Bovey # - =
{ beds; Lower Molasse. Nebraska beds # - =
{ (West America). # Mammals. - =
# - =
{N. Gypseous series, Paris. Vicksburg # - =
{ group (America). # =
Eocene {M. Calcaire Grossier, Bagshot and Alum # =
{ Bay beds. Jackson group (America). =
{O. Argile Plastique; London clay. =
{ Claiborne group (America). =