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44



PROBLEMS OF THE FUTURE, 45

facts with the account of creation in Genesis, that he becomes totally un-
reliable when the human era is approaching.

Quite recently, a very different authority, Professor Prestwich, reason-
ing on strictly scientific grounds, concludes, " that the Glacial period, or
epoch of extreme cold, may not have lasted longer than from 15,000 to
25,000 years, and the Post-Glacial period of the melting away of the ice-
sheet to from 8000 to 10,000 years or less ; giving to palaeolithic man no
greater antiquity than perhaps about 20,000 to 30,000 years, while should
he be restricted to the so-called Post-Glacial period, his antiquity need
not go farther back than from 10,000 to 15,000 years before the time of
neolithic man."

Prestwich cannot be accused of theological bias, and in fact this esti-
mate is as inconsistent with theological theories of Adam and Noah, as if
the figures were multiplied tenfold. But he was influenced by the wish
to make geological time accord with the short-date estimates of Sir W.
Thomson, as to the possible duration of solar heat. Be this as it may,
the fact that an authority like Prestwich reduces to 20,000 years a period
to which Lyell and modern geologists generally have assigned a duration
of more like 200,000 shows in what a state of uncertainty we are as to
this vitally important problem. For even the longest period for man's
antiquity assigned by Prestwich would be clearly insufficient to allow for
the development of Egyptian civilization as it existed 7000 years ago,
from savage and semi-animal ancestors, and still less for the evolution of
the human race from earlier types, as is proved to have been the case
with the horse, stag, elephant, ape, and other mammals, with whom man
is so intimately connected, both in physical structure and in geological
association.

It is highly important, therefore, to consider the grounds on which
the various theories are based, of the probable cause and duration of the
Glacial period. The first natural guess was to attribute it to the preces-
sion of the equinoxes. Owing to this cause the North Pole is alternately
turned towards the sun every summer, and away from it every winter,
the reverse being the case in the southern hemisphere. But owing to the
eccentricity of the earth's orbit, the duration of the seasons is not exactly
equal, and summer and winter may occur either when the earth is nearest
to or farthest away from the sun. At present winter occurs in the North-
ern hemisphere when the earth is nearest the sun and moving with the
greatest velocity, so that it is shorter by some days, and summer longer,
than in the Southern hemisphere. Now it is a fact that what may be
called a Glacial period prevails at present in the Southern hemisphere,
while corresponding latitudes in the Northern hemisphere enjoy a tem-
perate climate. It might be thought that this fact afforded an explana-
tion of the Glacial period ; but this conjecture is negatived when it is
considered that this revolution of the earth's axis is periodical, and com-
pleted in about 22,000 years, so that if it were the sole or principal cause



45 BEACON LIGHTS OF SCIENCE.

of Glacial epochs, they must have recurred from the beginning of geolog-
ical time at this short interval, which is altogether inconsistent with the
evidence of facts.

Croll expanded this crude theory into one which had vastly more
plausibility, viz., that although the effects of precession might be imper-
ceptible while the earth's orbit was nearly circular as at present, they
might become very powerful when they coincided with one of the long
periods at which the earth's orbit became flattened out into an ellipse of
maximum eccentricity. He showed by calculation that one such period
began 24,000 years ago, attained its maximum in 80,000 years, and passed
away about 80,000 years before the present era. These figures fitted in
so well with those deduced by Lyell and other eminent geologists from
geological data, that Croll's theory received very general acceptance.
But it is open to the same objection, though in a less degree, that it re-
quires us to assume a periodical succession of Glacial epochs. The os-
cillations of the eccentricity of the earth's orbit, about its maximum and
minimum limits, though slow as measured by centuries, are not so slow
according to the standards of geological time. Croll's calculations have
shown that another position, such as is assumed to have caused the latest
Glacial period, must have occurred 500,000 years earlier. The calcula-
tions have not been carried further back, but it is tolerably certain that,
if Croll's theory be correct, at least two or three Glacial periods must
have occurred during each of the great geological epochs. This is op-
posed to geological evidence. The Permian is the only formation in
which what looks like traces of glacial action have been unmistakably
found, and even these are considered doubtful by many geologists. Still
more doubtful are the proofs of older Glacial epochs deduced from iso-
lated cases of boulders, as in the Miocene conglomerate of Monte Superga,
near Turin, the Flysch of Switzerland, and in some of tne conglomerates
of the old Devonian. "Not proven " is the verdict which most geolo-
gists would return on the few alleged instances of earlier Glacial periods;
while if Croll's theory were true, we might expect to find them frequently.
Above all, it is difficult to conceive how two or three great changes of
temperature could have occurred during each geological formation with-
out showing unmistakable traces in the fauna, and still more distinctly in
the flora, of the epoch. Ferns must have died out and been succeeded
by mosses ; and these in their turn given place to ferns two or three times
over or more, during the growth of the Coal-measures, if any changes of
climate had occurred at all resembling those of the recent Glacial period.
The confidence, therefore, with which Croll's theory was at first re-
ceived has been a good deal shaken, and although many geologists
still believe that it may have been one among other causes of the last
great refrigeration, it can no longer be considered as affording a reliable
standard by which to measure the time in historical years, either of the
Quaternary, or still less of any previous geological epoch.



PROBLEMS OF THE FUTURE. 47

We have to fall back, therefore, on the geological evidence of deposi-
tion and denudation, of the rise and fall of continents, of the erosion of
rivers, valleys, and so forth, in any attempt to decide between the 200, ooo
years of Lyell, and the 20,000 years of Prestwich. The former period,
based on the minute and careful investigations of Lyell, Geikie, Croll, and
other eminent geologists, held the field until the recent attempts of Prest-
wich and others to reconcile geology with Sir W. Thomson's theory of
solar heat, by reducing geological time to about one-tenth of the ac-
cepted amounts.

Prestwich, in his recently-published works on geology, states that he
has been influenced mainly by two considerations.

1. The wish to bridge over the wide chasm between geologists and
physicists as to the possible duration of the supply of solar heat

2. The difficulty of conceiving that man could have existed for
a period of 80,000 or 100,000 years without change and without pro-
gress.

And the principal, or rather the sole fact on which he relies is, that
the advance of the glaciers of Greenland is found to be much more rapid
than that of the Swiss glaciers upon which previous theories had been
based of the time required for the advance of the Scandinavian and Lau-
rentian ice-fields over Northern Europe and America,

The two considerations may be briefly discussed. The first, as I have
already shown, is based on a theory as to solar heat which is in the high-
est degree uncertain, and which requires rather to be tested by the posi-
tive facts of geology than accepted as an admitted conclusion, to which
those facts must be squared. To allow it to distort those facts, or even
to influence us in interpreting them, is a prepossession only one degree
less mischievous than the theological prepossession which so long retarded
the progress of true science.

The second consideration, as to the rate of human progress, is a mere
question of what each individual inquirer may think probable estimates,
which will depend very much on his habit of mind and previous bias.
There are positively no facts on which to base a conclusion as to the rate
of progress of isolated savage tribes living in the hunter stage, without
contact with more civilized races. The Australian savages, the South
African bushmen, the Negritos of the Andaman Islands, may have lived
as they were first found by Europeans, any time you like from loco to
100,000 years, for aught we know to the contrary. There is, in fact, no
record of any such savage race emerging into comparative civilization by
any effort or natural progress of its own. Even much more advanced
races trace back their knowledge of the higher arts and civilization to
some divine stranger, like the Peruvian Manco-Capac, or Chaldaean Cannes,
who lands on their shores : or else, like the Egyptians, assign these in-
ventions to gods, which means that they are lost in the mists of antiquity.
The neolithic men of Europe were clearly invaders, who brought a higher



48 BEACON LIGHTS OF SCIENCE.

civilization with them from Asia, and the knowledge of polished stone and
metals was diffused by commerce.

It is incorrect, however, to say that palaeolithic man shows no signs of
change or progress. On the contrary, the evidence of palaeolithic deposits
shows everywhere a progress which, although it may have been extremely
slow, is uniformly in the same direction, viz., upwards. There is no ex-
ception in the hundreds, or rather thousands of instances in which pa-
laeolithic implements have been found, to the law that the rudest imple-
ments are found in the lowest deposits, and that improvements are traced
in an ascending scale with ascending strata. This is most markedly the
case in caves, where, as in Keat's Cavern, deposits of different ages have
been kept distinct and securely sealed under separate sheets of stalagmite.
In the rock-shelters also, and river gravels, in which the relative antiquity
is proved by their higher or lower levels, the same law prevails. In the
oldest, where the cave bear and mammoth are the characteristic fossils, the
stone axes, knives and scrapers are of the rudest description. The celts
or hatchets are mere lumps of stone, roughly chipped, and with a blunt
butt-end, evidently intended to be held in the hand. In the next stage
we find finer chipping, and celts adapted for hafting ; while arrow and
javelin heads appear, at first rude, but gradually becoming barbed and
finely wrought. Still late, with the advent of the reindeer in large herds,
affording in their horns a softer material than stone, a remarkable im-
provement takes place, and eyed needles, barbed harpoons, and in some
cases engraved and sculptured portraits of animals of the chase, testify to
a decided advance in the arts of civilization. Above all these, come the
weapons and implements of the Neolithic age which, as already stated, are
separated by a sharp line from the earlier records of palaeolithic man.
No polished stone has ever been found in deposits belonging clearly to
the Palaeolithic period, and a decided change has taken place in the fauna,
which in the Neolithic age corresponds closely with that of recent times,
in the same locality.

It is impossible, therefore, to deny that both change and progress have
existed from the first appearance of man, and there are absolutely no data
to enable us to say what may have been the intervals of time required for
the successive stages of this progress. All we can say is, that the more
nearly primitive man approximated to a state of semi-animal existence, the
slower must have been the steps by which he emerged from it into com-
parative civilization.

We must fall back, therefore, on geology for anything like reliable
data on which to base any estimate of the time required for the Quatern-
ary or any preceding geological epoch. Here, at any rate, we are on com-
paratively certain ground. So many feet of deposition, so many of
erosion, so many of elevation or depression; these are measurable facts
which have been ascertained by competent observers. How much time
required to account for them ? This can only be an approximation,



PROBLEMS OF THE FUTURE. 49

based on our knowledge of the time in which similar results, on a smaller
scale, have been produced by existing natural laws within the Historical
period. Still, if we argue from natural causes, and ignore imaginary
cataclysms and supernatural interferences, we may arrive at some sort of
maximum and minimum limits of time within which the observed results
must lie.

This was the process by which Lyell and his school of geologists arrived
at their estimates of geological time, and it is only by a careful study of
their works that it is possible to see how closely the chain is woven, and
what a mass of minute investigations support their conclusions. The
one solid fact which Prestwich opposes to them is the rapid advance of
the glaciers of Greenland. Recent observations by Rink and other ex-
plorers have shown that the fronts of these glaciers advance much more
rapidly than the rate which has been assumed from the advance of the
Swiss glaciers.

The average rate of advance of the great glaciers which discharge them-
selves into Baffin's Bay is about 35 feet daily, or 2| miles yearly. Cal-
culating from these data, Prestwich arrives at the conclusion that the old
ice-sheets which radiated from the Scandinavian and Canadian mountains
to a distance of about 500 miles, might have been formed in from 4000 to
6000 years. The great changes which have taken place since the retreat
of the ice-sheets, he accounts for by supposing that with a greater rainfall
these changes went on much more rapidly than they have done during the
Historical period. These views, however, did not command the assent
of other eminent geologists, who were present when Professor Prestwich's
paper was read, and they are open to very obvious objections.

The rate of advance of a glacier thrust outwards by such an immense
mass of ice as caps Greenland, through a narrow fiord, on a steep de-
scending gradient, into a deep sea which floats off its front in icebergs,
affords little test of the advance of an ice-sheet spread out with a front of
1000 miles over a whole continent, unaided by gravity, and obstructed by
ranges of mountains 2000 or 3000 feet high, which it has to surmount
Nor does the rate of advance of such a sheet afford any clue to the time
during which it may have remained stationary, or been receding. The
two latter conditions evidently depend on the climate at the extremity of
the ice-sheet, when the ice pushed forward by it is melted by the summer
heat As long as the climate of Switzerland remains the same, the Swiss
glaciers will remain at their present level, with slight local and temporary
variations ; and this must have been equally true of the great Scandinavian
and Canadian glaciers. They may have advanced in 5000 years, remained
stationary for 50,000 years, and taken 100,000 years to retreat, for any-
thing we know to the contrary, from the Greenland glaciers. Nor is it a
question of one advance and retreat only, for there is distinct evidence of
several advances and retreats, and of prolonged Inter-Glacial periods.
In the cliffs of the east of England four boulder-clays are found, sepa-



50 BEACON LIGHTS OF SCIENCE.

rated by sands and gravels deposited as each ice-sheet successively receded

and melted ; and in France there is evidence of at least one Inter-Glacial
period, sufficiently warm and prolonged to allow the Canary laurel and
fig-tree to supplant the lichen and Arctic willow. The only real test of
time is from the amount of geological work that has been done in the way
of denudation, deposition, elevation, and depression, since Northern
Europe and Northern America were covered by such an ice-cap as now
covers Greenland.

Tried by these tests the conclusions point uniformly to a longer rather
than a shorter duration of the Quaternary, including the Glacial period.
If we take denudation, we may refer to the fact that since palaeolithic man
left his implements on the banks of the old Solent river above Bourne-
mouth, the level of its valley and of the adjacent land has been denuded
by that small stream to a depth of 1 50 feet, and the erosion of the sea now
going on at the Needles has eaten away a wide range of chalk downs,
which were then continuous from the Isle of Wight to Dorsetshire. The
same action of waves and tides as is now eroding Shakespeare's Cliff has
removed the chalk ridge between that cliff and Cape Grisnez, and made
England an island. The valleys of the Thames, the Somme, and other
rivers of the south of England and north of France, have been excavated
to a depth of more than 100 feet and a width of miles, by streams which
have produced no perceptible change since the Roman period. And a
still more striking proof of the immense time which has elapsed since the
Glacial period is afforded by the fact stated in Prestwich's Geology, that
the great basaltic plateau of the Cascade Range in British Columbia,
which is cut through by the Columbia river to the depth of 2000 to 3000
feet, is underlain by the Northern Boulder-drift. Consider what a lapse
of time this requires. Since the Boulder-drift, and therefore since the
Glacial period, vast sheets of basalt must have been poured out by vol-
canoes now extinct, and those sheets of hard rock cut down by river ac-
tion to the levels at which the relics of the old ice-cap now appear.

As regards the erosion of valleys, it is said that there may have been a
much greater rainfall formerly than in historical times, and therefore ero-
sion may have gone on much more rapidly. Doubtless there may have
been more extensive inundations while great masses of ice and snow were
melting under the summer heat of an improving climate, but there seems
no adequate reason to account for a much greater rainfall. The maxim
"ex nihilo nihil fit" applies to rain as to the other operations of nature,
and more rainfall implies more evaporation, brought by warm winds blow-
ing over warm oceans, and deposited when it comes in contact with land
at a lower temperature. We already have these conditions in Western
Europe, and the Gulf Stream and prevalent westerly winds make the cli-
mate more moist and genial than is due to the latitude. To have had it
still more moist these conditions must have been intensified, and there is
no reason to suppose that in recent times, and with the present configura-



PROBLEMS OF THE FUTURE. 51

tion of sea and land, the Gulf Stream could have been much warmer than
it now is. If the land had extended farther to the westward, the effect
must have been to diminish rather than increase the rainfall in the dis-
tricts where the Somme and the Thames were excavating their valleys ;
and with more extensive forests and morasses rain-water would be ab-
sorbed as in a sponge, and descend more gradually and less in tumultuous
floods.

But even if a greater rainfall were granted, it would not affect the ero-
sion of solid chalk cliffs by the sea, and the argument from the disappear-
ance of the downs between the Isle of Wight and Dorsetshire, and between
France and England, would remain the same. Sir John Lubbock esti-
mates the rate of erosion of a perpendicular cliff of solid chalk at only a
few inches per century, at which rate it must have taken an enormous
time to wear away the chalk ridge between the Needles and Ballard downs ;
but even if we read yards, instead of inches, it must have taken a far
longer time than Prestwich assigns for the whole Glacial period. There
is nothing upon which reliable data are more wanted than as to the rate
of erosion of solid cliffs by the action of the sea, for here the hypothesis
of a larger rainfall and greater floods could not be invoked to accelerate
the rate, as in the case of the erosion of valleys.

If from denudation we turn to deposition, we find equally conclusive
evidence of the immense duration of the Glacial period. The deposit
known as " loess" is universally admitted to be one of fine glacial mud,
deposited tranquilly from sheets of inundation water, which have over-
flowed wide tracts during the melting of the ice and snow, as the climate
improved and glaciers retreated. It is, in fact, just such a loam as the
Arve deposits every summer on the meadows of Chamouni, when the tur-
bid river issues in a swollen stream from the bottom of the mer-de-glace,
and overflows its banks. Now this loess covers, as with a mantle, the
valley systems of all the great rivers of the Northern hemisphere, whose
upper courses lie within the area which was covered by ice and snow dur-
ing the Glacial period. The Rhone, the Rhine, the Danube, the Missis-
sippi, the Yang-tse-kiang, all run through cliffs of loess, which also fills
their tributary valleys and spreads to a considerable height up the slopes
of the hills and over the adjoining plateaux. It lies thickest in the val-
leys, dying off as it ascends the slopes, though it can often be traced to a
height of 2000 or 3000 feet. The thin beds of loess at these heights, and
on the plateaux, are probably the result of the melting of frozen snow ;
but the great masses in the valleys are evidently the accumulations of
mud from the overflows of the existing rivers, as they gradually cut their
valley-systems down from higher to lower levels.

These accumulations invariably correspond to the configuration of the
existing valleys, and overlie coarser sands and gravels, showing that they
have been made since the rivers lost the transporting power which they
possessed, when they ran with a more rapid current during the earlier



S2 HEACON LIGHTS OF SCIENCE.

stages of the retreat of the glaciers. The thickness of this accumulation
of fine mud is stated by Lyell to be 800 feet or more above the existing
alluvial plain of the Rhine, and in other rivers it is even greater. It is
impossible that such a thickness could have been accumulated in anything
like the shorter time assumed by some geologists for the duration of the
whole Glacial period. And yet it represents only one phase of its con-
cluding period, and it not only contains human remains but is itself
clearly posterior to many o* the sands and gravels in which remains of
man and his associated Quaternary fauna have been undoubtedly found.
It is difficult to suppose that the loess can have accumulated much
more rapidly than the alluvium of the Nile, which has been proved to
raise the soil :> Egypt at the rate of about three inches in a century.
At this rate it would require 320,000 years to accumulate the 800 feet
assigned by Lyeli to the loess of the Rhine valley. Making every allow-
ance for a quicke rate of deposition, it seems impossible that this de-
posit, which is on-> an interlude in one of the later stages of the Glacial
period, can have been accumulated in anything like the time assigned by
Prestwich for the wh. >le of that period.

If we consider the elevations and depressions of land which have taken
place since the commencement of the Glacial period, the evidence all
points to the same conclusion of immense antiquity. There is a distinct
evidence that since the first epoch of intense cold a great part of Britain
has been surmerged, until only a few of the highest mountains stood
out from the Arctic Sea as an archipelago of frozen islands and has been
since elevated, with several minor fluctuations, to its present height.
Marine shells of an Arctic character have been found on Moel-Tryfane, a
hill in North Wales, in glacial drift 1392 feet above the level of the sea,
and similar drift is traced continuously, both in Wales and Scotland, to
a height of over 2000 feet It rests on rocks which had been already
rounded and polished by glaciers.

It is evident, therefore, that sufficient time must have elapsed during
an intermediate phase of the Glacial period, for a depression of more
than 2000 feet, followed by a re-elevation of an equal amount. Consider
what this means. All we know of these secular movements of large
masses of land shows them to be excessively slow. Even the small local
elevations and depressions, like those of the temple of Serapis at Pozzuoli,



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