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Prometheus:

This period fixed, we have a datum ..for estimating the
duration of the interglacial periods.C_The moraines of
the Wurm glaciation present everywhere a very fresh
appearance, and the chemical change which the boulders
they contain have undergone is slight, while weathering
extends to a depth of scarcely a foot. The moraines of
the Riss glaciation are weathered somewhat more deeply,
and "those of the Mindel glaciation very much more.
Assuming that chemical weathering has proceeded
uniformly during the interglacial periods and ceased
during the glaciations, Penck and Brückner* who.. have
studied exhaustively the glaciation of the Alps, find that
  50 THE EV0LUTI0N OF CLIMATE

the Riss-Wurm interglacial lasted about three times as
long as the interval between the Wurm gladation and
the présent day, or 60,000 years, and the Mindel-Riss
interglacial about twelve times as long, or 240,000
years. No data are available for the Gunz-Mindel
interglacial, but it is provisionally made equal to the
Riss-Wurm, another 60,000 years.

No possibility of such direct measurement of the
duration of the glacial periods themselves has yet been
found. Penck and Brückner assume that the duration
equalled that of the Riss-Wurm interglacial, or 60,000
years in each case. This seems unnecessarily long.
The Yoldia Sea, the deepest part of which coincided
with the centre of the Scandinavian glaciation, appears
to have reached its greatest depth not more than 6000
years after the maximum of glaciation, indicating a lag
of this period. The subsidence of the land due to the
weight of the ice-sheet may have commenced some time
before the maximum of glaciation, but the duration of
the subsidence can hardly have been more than 10,000
years, and this is the limit for the second half of the Wurm
glacial period. Further, we know that during the growth
of the ice-sheets there was comparatively little melting,
for the rivers then had little power of carrying debris.
Recent measurements in Greenland give the rate of ice-
growth on the surface of the ice-sheet as 40 cm., or j.5
inches ,a_year; let us say a foot, and assume a marginal
loss equivalent to half this amount over the whole ice-
sheet. This gives us an average increase of six inches
a year, or 10,000 years for growth to a maximum thick-
ness of 5000 feet. On these grounds the estimated
duration of the Rissian glacial period has been reduced
to 30,000 years, and that of the Wurm period to 22,000
years. Only in the case of the long and complicated
Mindelian period, which, as will be seen later, was virtu-
ally a series of overlapping glaciations from various centres,
has the figure of 60,000 years been accepted. In the
present state of our knowledge no estimate of the
  THE GREAT ICE AGE   51

duration of the Gunz-Mindel interglacial can have any
value, and the dates are accordingly carried back only
to the Mindelian. In this way we obtain the time-scale
given on page 48.

The fourfold gladation has been recognized with
certainty only in Europe and North America, and even
in these countries there is considerable doubt whether
the northem ice-sheets shrank back as far as their present
narrow limits during the interglacial periods. The
long Mindel-Riss interglacial, which was probably the
Chellean stage of flint industry,1 was characterized by a
very warmth-loving fauna, and it is possible, even
probable, that during this period the glaciers melted
completely away, except on the very highest summits.
Of the climate of the Gunz-Mindel interglacial (termed
by J. Geikie the “ Norfolkian,” from the Cromer
Forest Bed), we have comparatively little evidence.
If the suggestion put forward in the following chapter
is correct, the Gunz-Mindel interglacial was merely a
local incident in the glaciation of the Alps, and not a
true interglacial at all. Even the Cromer Forest Bed
itself is not conclusive, since it is a river deposit largely
composed of material drifted from lower latitudes.
The Riss-Wurm interglacial (J. Geikie’s “ Neudeckian ”)
nowhere gives us evidence of a climate as warm as the
present, and as regards the Scandinavian and Canadian
ice-sheets may have been merely an extensive and pro-
longed oscillation of the ice-edge.

As regards the glaciation of Norway, the question has
been investigated recently by H. W. son Ahlmann, who
has published a long and detailed paper in English in
volumes 1 and 2 of the Swedish Geographiska Annalen.
He concludes that the morphology of Norway, without
reference to stratigraphical or biological data, gives
conclusive evidence of two glaciations. The first of
these was the greater, and between that time and the

1 This hai been the subject of much discussion recently. For a summary
see Science Progress, 17, 192a, October, p. 233.
  52 THE EVOLUTION OF CLIMATE

second smaller glaciations there occurred an interglacial
period of such considerable length that the greater
part of the present gorges was then formed by fluvial
erosion.

We may, accordingly, consider the Ice Age as fourfold
or doublé, according to the point of view from which we
regard it. In the Alps and other mountain ranges on
the borders of the great northern ice-sheets, which
respond very readily to small changes, it was fourfold.
In the peripheral regions of the northern ice-sheets
themselves it has an appearance of being threefold or
fourfold. In the more central regions of these great
ice-sheets, where response to climatic change is very
slow, there is no evidence of more than two glacia-
tions; but in these regions, where the destructive
effect of the ice reached its maximum, it is only by
the merest chance that evidence of interglacial periods
is preserved at all. And finally, in all other parts of
the world we have evidence of only two glaciations
at most.

. There is one deposit which is of considerable im-
pört'ance in the study of interglaciaTclimates, and that
is the loess. Loess is an exceedingly fine-grained hömo-
geneous deposit resulting from the gradual accumulation
of wind-blown dust on a surface sparsely covered with
vegetation. It is to be seen accumulating at the present
day in parts of south-east Russia and central Asia.
lts formation, except in closed basins, needs a climate
of the steppe character, with not much rainfall, and
especially with a long dry season. Now loess was very
extensively developed in Europe during the Qüaternary.
lts occurrence is peculiar, since it is found most widely
developed resting on the deposits of the Rissian glaciation,
and is never found resting on the moraines of the Wurm
glaciation. A little loess is found below the Riss
moraines, and it has also been found between the Riss and
Wurm moraines. In the pre-Rissian loess an implement
of Acheulian age was discovered in 1910 at Achenheim
  THE GREAT ICE AGE   53

(Alsace), by R. R. Schmidt and P. Wernert, indicating
that the deposit was formed towards the close of the
Chellean industry, when the climate was already cold and
dry. In the same section the younger loess seems to
fill completely the Riss-Wurm interglacial, since Mous-
terian implements were found at the base and Aurignacian
implements in the middle. The younger loess contains
remains of the jerboa and other rodents at present
inhabiting the Siberian steppes. It is therefore reason-
able to conclude that steppe conditions prevailed in
central Europe through practically the whole of the
Riss-Wurm interglacial, and the same probably applies
to the corresponding pre-Wisconsin interglacial in
America. But if a steppe climate prevailed in central
Germany there must have been very severe conditions
in Scandinavia, and probably the ice-sheet maintained
a quite considerable area there throughout the whole
period, though without encroaching on the Baltic basin.
In North America the loess was deposited by westerly
winds, indicating that the ice-development was not
sufficiënt to impose anticyclonic conditions in place of
the present prevailing westerly winds, and the same
appears to be true of Europe. Similar climatic con-
ditions were developed for a short time at the close of
the Wurm glaciation, but without any appreciable
development of loess. (See Chapter XIII.)

BIBLIO GRAPHY

Wright, W. B. “ The Quaternary Ice-age.” London, Macmillan,
I9H-

Brooks, C. E. P. “ The correlation of the Quaternary deposits of the British
Isles with those of the continent of Europe.” Ann. Rep. Smitbsonia*
Inst., 1917, pp. 277-375.

de Geer, G. “ A thermographical record of the late Quaternary climate.”
Ber. Internat. Gcologcnkongr., Stockholm, 1910. “ Die Veranderingen
des Klimas,” p. 303.

---------------. “ A geochronology of the last 12,000 years.” Ber

Internat. Geologenkongr., Stockholm, 1910, Vol. 1, p. 241.
  54 THE EVOLUTION OF CLIMATE

Penck, A., and Brückner, E. “ Die Alpen in Eiszeitalter.” Leipzig, 3 Vols.,-
1901-9.

Ahlmann, H. W., son. “ Geomorphological studies in Norway.” Stockholm,-
Geografiska Annaler, i, 1919, pp. 1-157, 193-252.

Richthofen, F. “On the mode of origin of the loess.” Geol. Mag.,
1882, p. 293.
  CHAPTER V

THE GLACIAL HISTORY OF NORTHERN AND CENTRAL EUROPE

The literature of the glacial period in Europe is stu-
pendous and is, further, of a highly contradictory nature.
Space does not permit of any summary of the great
conflict between the monoglacialists and the poly-
glacialists; it is sufficiënt to say that the latter often
went to extremes and so laid themselves open to defeat,
but the twofold nature of the glaciation is now widely
accepted. It must be understood, however, that the
following summary represents the views of a certain
section of geologists only, views which are not universaUy
held. In the British Isles especially, where the remains
of the maximum glaciation completely dominate those
of all the others, the theory of a single glaciation still
largely prevails.

When ice began to accumulate on the rising Scandi-
navian plateau it naturally formed at first on the
Norwegian mountains near the Atlantic, which was the
chief source of snowfall. These mountain glaciers
spread rapidly down the steep seaward slopes to the
west and more slowly down the gentler landward slopes
to the east. At this stage the centre of the ice-sheet,
and consequently the centre of the glacial anticyclone,
as soon as the latter developed a definite existence, lay
quite near the Norwegian coast. Under anticyclonic
conditions the circulation of the winds round the centre
is in the same direction as the motion of the hands of a
watch, combined with an outward inclination at an angle
of about thirty to forty-five degrees. Consequently,
while the centre lay in Norway, due north of the Alps,
35
  56   THE EVOLUTION OF CLIMATE

the prevailing winds in the latter must have been from
north-east, and therefore very cold. Accordingly, this
stage is probably contemporaneous with the Gunz
glaciation of the Alps. In the same way, over the
North Sea area the winds must have been easterly,
causing the currents which piled up the great sheÜ-
banks of the East Anglian coast, already referred to as
marking the end of the Tertiary and beginning of the
Quaternary period.

But the ice which reached the northern North Sea
broke up into icebergs not far from the coast, and floated
away, while that which moved east into the north of
Sweden could only be dissipated by melting and ablation,
processes which we have reason to believe went on very
slowly. Hence ice began to accumulate and spread over
a wide area east of the main Scandinavian mountain
chain. Fresh snow was deposited directly on this ice-
surface, until it gradually overtopped the mountains
which originally gave rise to it, and reversed the flow,
so that the ice actually moved uphill across the mountain
chain. As the centre of the ice-sheet moved eastward
the glacial anticyclone moved with it, and this new
position to the eastward caused an alteration in the
direction of the prevailing winds over the rest of Europe.
The Alps were now south-west of the anticyclonic
centre, and the winds in that district accordingly became
easterly instead of north-easterly. Of course, the
glacial anticyclone was now more intense, but in summer
in central Europe easterly winds are naturally so much
warmer than north-easterly winds that at first this in-
crease in intensity was not enough to counterbalance
the change in direction, and there was a slight improve-
ment in the Alpine climate. In the same way, over the
North Sea district the prevailing winds had now become
south-easterly instead of easterly, which would make
for a slight rise of temperature, as also would the
occasional depressions which would be able to make their
way in from the westward, bringing warm moist air from
  GLACIAL HISTORY OF EUROPE 57

the Atlantic and occasional rainfall. By this time the
process of elevation had converted the North Sea floor
into an extensive plain.

From Sweden and the Gulf of Bothnia the ice spread
out in all directions, extending in the east to the foot of
the Ural Mountains, which formed an independent
centre of glaciation; in the south-east over a large part
of European Russia, where it reached as far south as
latitude 40° in the Dnieper valley; in the south over
almost the whole of Germany as far as the Riesengebirge
and Harz Mountains; and in the south-east over the
whole of Holland and the North Sea basin. It should
be noted that Holland and Denmark were glaciated, not
by Norwegian ice, but by ice from the Baltic sheet which
had crossed Southern Sweden. The North Sea glacier
extended across East Anglia as far as Cambridge, while
a northem branch of it swept across Caithness and the
Orkney and Shetland Islands, but most of the British
Isles were glaciated from independent centres—the
Scottish Highlands, the Pennines, Cumberland, Wales
and northern Ireland.

With the growth of the glaciated area, and particularly
with its extension south-westward across the North Sea,
the Alpine climate again became very severe, and the
local glaciers and Piedmont ice-sheets of the Alps reached
their maximum development in the Mindelian. At
the same time the central plateau of France developed
a local plateau glacier of its own, and the Pyrenees
underwent their first and greatest glaciation, no tracés
of the Gunzian having been found in this range.

The British Isles show an interesting outward migration
of the local centres of maximum ice-development. The
Scandinavian glacier which invaded East Anglia extended
arctic anticyclonic conditions across the North Sea, and
induced a heavy snowfall over the high lands of Great
Britain. These, in consequence, developed independent
glaciers, which on their eastern sides fused with the
Scandinavian glacier and, partly by deflecting its flow,
  58 THE EVOLUTION OF CLIMATE

partly by intercepting some of its snowfall, pushed it
back into the North Sea plain. The Scottish glaciers
became strong enough to encroach on Ireland, partly in
the north-east, and partly by way of the Irish Sea and
St. George’s Channel (then a valley) on to the south-
east. This further extension of the cold area enabled
the Irish glaciers to develop, and these in turn pushed
back the Scottish glaciers until Ireland was solely
glaciated by Irish ice.

The Southern margin of the ice-sheet did not extend
beyond the Thames valley, but at some stage the English
Channel carried floating ice, which formed the deposits
of ice-borne boulders, of which that at Selsey is a well-
known example.

This great ice-sheet nowhere formed marked terminal
moraines, but its deposits fade away in thin beds of stiff
boulder-clay. This absence of moraines is probably
connected with the great thickness of .the ice-sheets,
which did not leave any appreciable nunataks or rocky
“ islands ” exposed in its path, so that there was nothing
to give rise to detritus on the surface of the ice. All the
transportation had to be carried on beneath the ice-
sheets, and these, penetrating into comparatively low
latitudes where the sun is powerful in summer, would
suffer gradual melting and ablation for some distance
from their margins. Near the actual ice-limit the
motion must have been slow and the thickness of the ice
small, so that conditions were against the accumulation
of thick beds of detritus.

On the borders of the ice-sheet the climate cannot
have been over-rigorous, for pre-Chellean man was able
to live almost up to the ice-edge. The air must have
been extremely cold, and there was a belt of high arctic
climate round the ice, but in the south and south-west
this appears to have been very narrow, and sub-arctic
conditions, no worse than those in which many races live
to-day, prevailed not very far from the ice. The con-
figuration of the ice-surface largely explains this. A
  GLACIAL HISTORY OF EUROPE 59

high steeply sloping wall of ice causes intensely violent
winds, carrying dense clouds of drift-snow—blizzards, in
fact, similar to those now experienced in parts of Antarc-
tica under similar circumstances, which sweep the land
bare of all life for a considerable distance. But a low
and gradually sloping surface, such as seems to have
existed near the borders of the maximum glaciation,
favours instead comparatively gentle winds without much
drift snow. It is only on the north-west ice-ridge,
where ice-cliffs fronted the sea and where severe storms
from the Atlantic were frequent in winter, that blizzards
occurred.

When the land in Scandinavia began to sink under the
ice-load more rapidly than the supply of snow could
build up the surface of the ice-sheet the force which
pushed out the ice in all directions from the centre
gradually died away, and the ice-masses over the North
Sea area—now probably again below sea-level—and
the low grounds of Europe were left derelict, with no
resources but the snowfall on their own surfaces. Under
these conditions they melted away more or less rapidly.
While these derelict ice-masses were still large, the
auxiliary peripheral centres in the Alps, Pyrenees and
British Isles maintained an independent existence for a
while, probably with fluctuations similar to those which
markecf the close of the last glaciation in the Alps, though
the evidence of these has now been wiped away. It is
even likely that the beginnings of the weakening of the
central source of supply helped the British ice to divert
the Scandinavian ice into the North Sea. Had there
been any powerful rivers bearing great masses of detritus
from.the south, as there are in Siberia, some of these
derelict ice-sheets might have been preserved for a time,
at least, as “ fossil ice,” but in western Europe conditions
were not favourable for this.

With the disappearance of the ice-sheets the general
climate of Europe must have passed through a series of
stages of amelioration, of which tracés can be found here
5

Prometheus:

  6o THE EVOLUTION OF CLIMATE

and there, though the details are lost to us. Ültimately
temperate conditions again prevailed; and for a veiy long
time, approaching a quarter of a million years, Europe
cannot have differed greatly from present climatic
conditions. In Scandinavia the mammoth roamed in
forests of birch, pine and spruce ; further south the
mammoth is absent, and we find instead more Southern
forms—Elephas antiquus, resembling the Indian elephant,
Rhinoceros merckii, a Southern form, the sabre-toothed
tiger, cave-lion, cave-bear and cave-hyaena, wolf, beaver,
horse and various forms of deer, while the flora included
even such warmth-loving trees as the fig. Obviously,
during part of this interglacial period, the climate
must have been even warmer than the present.

Let us glance for a moment at the probable con-
ditions. One of the dominant features in the present
weather of Europe is the accumulation of floating ice
in the Arctic basin. This keeps the temperature low
and the pressure high—forms in fact during the spring
and summer months a temporary glacial anticyclone
similar in kind to, though of less intensity than, that
which has been described as covering the Scandinavian
ice-sheet. This anticyclone maintains on its Southern
edges a belt of easterly winds, and these winds enter into
the general circulation of the earth. Their effect is to
push southward the permanent storm-centres normally
situated near Iceland and the Aleutian Islands, and it
is these storm-centres which play a large part in causing
the rainy weather of northern and central Europe.
But occasionally—as in the remarkable spring and summer
of 1921—these conditions break down. The Arctic
Ocean becomes unusually ice-free and warm, the pressure
falls, and in consequence the storm-centres move
northward. Europe comes under the influence of the
permanent anticyclones of sub-tropical latitudes, rain-
bearing storms pass far to the northward, and we have a
dry warm summer of the Mediterranean type.

This is presumably what happened during the long
  GLACIAL HISTORY OF EUROPE 61

warm Mindel-Riss interglacial. For some reason, possibly
connected with a temporary widening and deepening
of the Bering Strait, the waters of the Arctic Ocean
became warmer and the amount of floating ice less.
Pressure became lower in the polar basin and therefore
higher over' the Atlantic and Europe, and fine warm
conditions prevailed in Europe as the normal climate
instead of only as an occasional event.

This warm interval was finally brought to a close by
the renewed elevation of Scandinavia, .and the ice-sheets
began to develop again, heralded by a period of dry
steppe climate. This time, however, the conditions
were different; the elevation was not so great, and was
more local. Hence the resulting glaciation was less
intense ; it filled the Baltic basin and extended some
distance on to the North German plain and into Holland.
It failed to reach the coast of Britain, but that it extended
some way across the North Sea plain is indicated by the
peculiar distribution of the Newer Drift of Britain, to
be referred to later. In the north of Norway the slope
of the ice towards the sea was very steep, so that many of
the Coastal hills extended above it as nunataks. The ice
extended into the channel between the mainland and the
Lofoten Islands (then a peninsula), but according to
Ahlmann these islands were an independent centre of
local glaciation, as the British Isles had been during the
preceding period, and the local ice met the main ice-
sheet in the fiords. On the coast of Nordland sufficiënt
land lay bare to harbour a small Arctic flora, and Vkero,
the southernmost island of Lofoten, had only small
hanging snow-banks.   1

The interpretation of the British glacial deposits is
still very much under discussion, but it seems probable
that the Scottish highlands formed a subsidiary centre
which glaciated the whole of Scotland and north-east
England, sending a stream south-eastward, which was
prevented from spreading across the North Sea plain by
the presence of Scandinavian ice to the east and impinged
  62 THE EVOLUTION OF CLIMATE

on the coast of Yorkshire and Lincolnshire, just reaching
the northern extremity of Norfolk. Many British
geologists regard this development as the concluding
phase of a single glaciation of Britain, but the differences
in the amount of weathering undergone are against such
an interpretation. At the same time there were local
glaciers in Cumberland, Wales and Ireland.

In England limits of this glaciation are characterized
by a well-marked series of end-moraines, which indicate
that the ice carried much surface detritus, and probably
ended in a steep clifiE. In Scandinavia, on the other hand,
the centre of glaciation again lay over the low ground
well to the east of the mountains, and the ice which
reached Germany and Denmark was still largely free of
surface detritus, and so did not form marked end-
moraines. There was a difference, however. On this
occasion, owing to the local nature of the elevation in
Scandinavia, the ice-sheet did not extend its borders so
far to the eastward, and the glaciation of Asia, as
described in Chapter VII, was slight. Europe came
more under the influence of cold north-easterly and
northerly winds, and life on the ice-borders was not so
easy as during the preceding glaciation. Man could still
live near the ice, but he took to makinghis home in caves,
and to clothing himself in skins for warmth.

After the ice had reached its Rissian maximum of
glaciation the climate improved somewhat. The ice-
edge retreated, leaving Denmark and the German coast,
and vacating the Baltic basin, but not disappearing
altogether from Scandinavia. At Rixdorf, near Berlin,
there is a bed of gravel deposited in this “ interglacial,”
containing numerous and well-preserved bones of the
mammoth, woolly rhinoceros, aurochs, bison, horse,
reindeer, red deer and other species of Cervus, musk ox
and wolf—a cold temperate to sub-arctic fauna. In
south Germany fresh water mollusca indicate that the
summers in that district were almost as |ivarm as at
present, but the winters were probably1 severe. As
  GLACIAL HISTORY OF EUROPE 63

described in the preceding chapter this “ interglacial ”
was the time of loess formation por excellence, with a
Continental climate and steppe conditions over much of
central Europe.

Investigations at Skserumhede in Denmark show that
this recession of the ice was accompanied by, and pre-
sumably due to, a fall in the level of the land relatively
to that of the sea, for at the beginning of the oscillation
the land lay about 350 feet above its present level, sink-
ing gradually to only 30 feet above present. Even at
its best during this interglacial the climate was almost
sub-arctic in Denmark. In northern Finland, on the
eastern edge of the ice-sheet, there was also an “ inter-
glacial,” with a slight improvement in the climate
accompanying a temporary submergence. But in
Scandinavia there are no tracés of any interglacial
deposits of this period, and considering the cold climates
which prevailed in Denmark and North Germany, it
seems probable that Scandinavia continued to be glaciated
during the whole period.

The mode of life among Mousterian men, who lived
during this “ interglacial,” also points to a severe
climate. For at this time man did not live in the open,
but in caves and rock-shelters, and the practice of wearing
the fur skins of animals as a protection against the cold,
begun in the preceding Rissian glacial period, was not
discontinued.

After the temporary subsidence had ceased, elevation
again set in, causing a readvance of the ice-sheet/s and
glaciers. The limits feil short of those of the precjeding
maximum, and the climate was not so severe, but;in its
general character it resembled that of the preceding
maximum, but was much stormier, and there were
probably frequent blizzards of the Antarctic type,
carrying drift-snow. The new ice-sheet carried more
surface detritus than its predecessors, presumably because
all the high ground was not covered, and it formed high
terminal moraines. The close association of cold ice
  64 THE EVOLUTION OF CLIMATE

and irregular masses of bare sand and stones, strongly
heated by the summer sun, set up a belt of powerful
conviction very favourable for the development of
blizzards; possibly there was something in the nature of
an ice-clifï down which the cold winds could blow wifh
great strength. At any rate, man found the near
neighbourhood of the ice unpleasant, and went, so that
there are no contemporaneous human implements near
the moraines. The lïmits of the Scandinavian ice-sheet
ran from the Norwegian coast across Denmark from north
to south, through North Germany and northern Russia,
and included Finland. The ice probably did not extend
far across the North Sea plain, and in the British Isles
there was no ice-sheet, but the high mountains of Scot-
land, Ireland, Wales and Cumberland bore small local
glaciers, which were long enough to reach the sea in the
Scottish highlands. The Alps bore considerable glaciers,
indicating a depression of the snow-line of about 3500
feet, corresponding to a temperature n° F. lower than
the present.

After this ice-development had reached its maximum
limits and remained there for perhaps a thousand years,
retreat set in, and the Scandinavian ice once more with-
drew from Germany and Denmark to the Baltic basin.
But its edge was never far from the German coast, and
occasionally readvanced across it, for numerous fos-
siliferous deposits are intercalated in boulder clay. The
fauna and flora, which are well known, point to an
arctic climate. At its best the mean temperature of
July rosé to about 50° F., and there was a vegetation
period of three or four months with an average
temperature of about 40° F., but these relatively mild
conditions lasted at most for a few decades or perhaps a
century at a time, and the winters were severe through-
out. The duration of the whole of this “ Baltic Inter-
stadial ” was from one to two thousand years.

Next followed the final readvance of the ice forming
the great “ Baltic ” moraines which fringe the Baltic
  GLACIAL HISTORY OF EUROPE 65

coast of Germany, turning northward in the west into
Denmark and in the east into Finland. There was a
correspondinj» redevelopment of glaciers in the Alps
(Bühl stage) and in the mountains of Ireland and Scot-
land, though these probably failed to reach the sea even
in Scotland. This period gave us a repetition of the
climate of the preceding maxima. In this case we have
definite evidence of the presence of a belt of easterly
winds on the Southern side of the ice-sheet, in a
series of “ barkans ” or fossil dunes in Holland,
Germany and Galicia. These dunes were formed
of fine ice-deposited material, and they are crescent-
shaped, with their convexities to the east, indicating
that they were built by strong easterly winds. A
moment’s consideration will show the truth of the
latter statement. Suppose there is an isolated round
hillock of sand exposed to strong easterly winds. The
sand grains will travel up the easterly windward slope
of the hillock and roll down the westerly leeward side.
In this way the whole hillock will advance very slowly
westwards. But in the centre, where the hillock reaches
its greatest height, the grains will take longer to reach
the highest point than near the edges, where they have
not to rise so high. At the edges a strong gust will
carry some of the heavier grains right over the dune,
while nearer the centre they will be left half-way, and
when the gust ceases will perhaps roll back to their
original position. In this way the margins of the /dune
will advance westward more rapidly than the c/entre,
producing the crescent shape with the convex side to
the east. At the time of their formation these dunes
must have had their steepest side to the westward, but
the westerly winds which have prevailed during the last
few thousand years have succeeded in modifying that
detail, without destroying the general shape of the
dunes, and the steepest slopes are now on the eastern
side. The preservation of the original shape, in spite of
the subsequent development of westerly winds, is due in
  66 THE EVOLUTION OF CLIMATE

part to the coating of vegetation, which protected the
dunes as soon as more favourable conditions occurred,
and probably in part to the lesser velocity of the wester-
lies. If the period of east winds and dune formation
had been long enough, we might have had another
deposit of loess, but it was short, and vegetation, which
is necessary to the genesis of true loess, had no time to
establish itself before the climate changed again with
the final retreat of the ice. The climate of this period
in Rumania has been ably described by G. Murgoci:
“ In general the prevailing climate of the time of the
formation of loessoid soils and blown sands must have
been that which is named by E. de Martonne the aralian
climate, a dry climate with some rain in spring to call
forth a poor and transient vegetation and to maintain
the flowing water in rivers and lakes. The temperature
with great extremes, in summer up to 1200 F. and in
winter below 20° F., was the characteristic of this
climate ; the atmosphere was very dry in the hot season,
but in the rest of the year there was some humidity in
the air and moisture in the soil, the water of the subsoil
being not very deep. The atmospheric precipitation
in this region was caused by the south-west wind just as
at present; but the dominant wind giving the character
of a dry Continental climate was the north-east wind
(Crivat) which has left its tracés in the fossil dunes of
the Baragan.”

A history of the changes of climate in Europe which
followed the maximum of the last readvance of the
ice-sheet must be left to later chapters.

BIBLIOGRAPHY

Brooks, C. E. P. “ The correlation of the Quaternary deposits of the Britiih
I»le» with those of the continent of Europe.” Ann. Rep. Smitbsonian
Jnst., 1917, pp. 277-375* [FuU list of references.]

Penck, A., and Briickner, E. “ Die Alpen in Eiszeitalter.” 3 Vols. Leipzig,
1901-9.
  GLACIAL HISTORY OF EUROPE 67

Gagel, C. “ Die Beweise für eine mehrfache Vereisung Norddeutschlands
in dikmaler Zeit.” Geol. Rundschau, 4, 1913, p. 39.

Wahmchaffe, F. “ Die Oberflachengestaltung des norddeutschen Flach-
landes.” Stuttgart, 1910.

Syastos, R. “ Le postglaciare dans 1’Europe centrale du nord et oriëntale.”
Ann. Sci. Univ. Jassy, 4, 1908, p. 48.

1

1
  CHAPTER VI

THE MEDITERRANEAN REGIONS DURING THE GLACIAL
PERIOD

Our knowledge of the histoiy of the Mediterranean
basin during the Glacial period is not nearly so com-
plete as is that of the more northem regions, chiefly for
the reason that during most of the period the land lay
above its present level, and except forlocal glaciers in
the mountain regions there was no ice to leave us a record
of the changing climates. Most of what we do know
relates to the relatively brief periods of submer-
gence.

At the beginning of the Glacial period the sea lay
some 500 feet above its present level, and we can tracé
the first appearance of a northem marine fauna. This
stage is known as the Calabrian; it is divided into two
horizons—a lower, in which northem forms are still rare,
and an upper, in which they are becoming abundant.
The most typical species are two mollusca whose present
habitat is the coast of Iceland—Chlamys (Pecteri) islandicus
and Cyprina islandica.

The Calabrian beach is not found on the coast of Spain
or at Gibraltar, and in Algeria it probably occurs at a
lower level. This suggests that the subsidence at this
period was local, and the western lands stood up as a
barrier against the Atlantic. There must have Deen a
channel of some sort, however, on the site of the present
Straits of Gibraltar, to provide an inlet for the im-
migrating northem mollusca. In the Maritime Alps,
68
  THE MEDITERRANEAN REGIONS 69

and again in the eastern Mediterranean, the Calabrian
beaches are at a much greater height owing to local
elevation.

After the formation of the Calabrian beach the whole
Mediterranean region was elevated above its present
level. This elevation must be contemporaneous with
the period of maximum elevation in north-west Europe
associated with the great Mindelian glaciation. It is
suggested that the “ sill ” of the outlet channel at
Gibraltar was raised above the level of the Atlantic,
and the Mediterranean became, first a closed salt lake,
and then a pair of lakes, the eastern fresh draining into
the western, which was salt, the two being separated by
a ridge of land between Italy and Tunis. This period
of elevation was long enough for a great deal of denuda-
tion to take place. Even in the Mediterranean this
was a time of severe climate. On the eastern side of
Gibraltar there are breccias, known as the “ Older
Limestone Agglomerate,” which reach a thickness of
100 feet in places, and are now much weathered. Similar
agglomerates are found in Malta. These resemble the
“ head ” of the south of England, and appear to be due
to frost action in a severe climate. In Corsica there are
tracés of four periods of mountain glaciation, and the
two oldest of these are provisionally correlated with the
Gunzian and Mindelian of the Alps. In the Balkan
highlands there are tracés of two distinct glaciations:
the older, which was the more general and reached the
greater intensity, probably corresponding to / the
Mindelian. In the Atlas Mountains there are great
boulder moraines which seem to belong to three disitinct
glaciations, the oldest extending to about 2000 feet
above sea-level, and the second terminating at about
4000 feet, while the third glaciation consisted of small
valley glaciers only.

Towards the close of the Mindelian glacial period the
land sank or the ocean rosé again, and the waters of the
Atlantic poured in, bringing with them a great number
  70 THE EV0LUTI0N OF CLIMATE

of high northern and Arctic mollusca. The theory has
been put forward that this influx was in the nature of a
debacle and carved out a deep gorge through the present
Straits of Gibraltar. The beaches deposited by this
sea lie at a height of 250 to 330 feet above the present
sea-level. The fauna resembles that inhabiting the
northemmost parts of Europe at the present day, and
the waters must have been several degrees colder than at
present. This stage is termed the Sicilian.

As the climate improved the land gradually rosé again,
and the next general raised beach lies at a height of
only about 100 feet in Southern Italy (except where
it has been elevated by local earth movements). Further
west it lies still nearer the present sea-level—twenty
. feet in the Balearic Islands and only seven feet on the
coast of Spain. On the coast of Algeria and Tunis this
beach is found at a height of about forty-five feet.

Prometheus:

The beach contains no tracé of the northern fauna
found in the Sicilian stage; instead it is marked by an
assemblage of mollusca of a sub-tropical aspect, including
Strombus bubonius, Mytilus senegalensis and Cardita
senegalensis. The bones of large mammals are also
found, including the hippopotamus and Southern forms
of elephant (E. antiquus) and rhinoceros (Rh. merckiï).
This warm stage corresponds to the Chellean inter-
glacial fauna of northern Europe, though so far as I am
aware no Chellean implements have been found associated
with it.

About this time the Older Limestone Agglomerate of
Gibraltar had been worn into caves, in which are found
the bones of ibex, wild boar, leopard, spotted hyena,
Rhinocerus leptorhinus, Elephas meriaionalis, lion, Southern
lynx, bear, wolf, stag, horse, etc., so that the rock must
have been covered by a rich vegetation, and must haye
had a greater extent than now, and a connexion with
the continent of Africa. This is said to have been
followed by a submergence of about 700 feet with
numerous oscillations. This submergence, if it is really
  THE MEDITERRANEAN REGIONS 71

attributable to the interglacial, must have been extremely
local, and possibly it is much older.

After the warm CheUean period the Mediterranean
region rosé again, probably contemporaneously with the
rise which caused the Rissian glaciation of northern
Europe. But the climate was nothing like so severe as in
the Sicilian. We have no old beaches containing a mollus-
can fauna of this period, but at the Grotte au Prince near
Mentone, investigated by M. Boule, the Strombus beach
is overlain by a bed of cemented pebbles and “ hearths ”
containing Mousterian implements and bones of a
temperate fauna. The Newer Limestone Agglomerate
on the east of Gibraltar may have been formed during
this period. The Mediterranean lands remained above
their present level until the close of the Glacial
period.

Each glaciation of northern Europe must have been
a time of greater rainfall as well as of lower temperature
in the Mediterranean. The glacial anticyclone in the
north displaced the storms from the Atlantic, which
now mostly either skirt the north-west coast of Norway
or pass across Denmark into the Baltic. These storms
had to take a more southerly course, and entered the
Mediterranean basin either across the south of France
or in the neighbourhood of Gibraltar: tracks which are
still occasionally followed in winter. These storms
brought a rainfall much heavier than the present, and of
a different character. The Mediterranean is now a
“ winter rain region,” and the north of Africa is entirely
rainless for several months in the summer. But during
the “ Pluvial periods ” it is probable that rainj feil
throughout the year, though the winter still had more
than the summer. The winter rains were in the form
of steady falls of long duration, such as we experience
now in England, whüe the summer rains feil in short,
heavy showers, perhaps accompanied by thunder. The
Older Pluvial period, which corresponds to the Mindelian
glaciation, had these conditions in their greatest develop-
  72 THE EVOLUTION OF CLIMATE

ment. Depressions cannot live long without a supply
of moisture, either from the sea or from transpiring
vegetation, and at present such winter storms as enter
the Mediterranean are almost confined to its surface,
and on the African side rarely penetrate more than
one hundred miles inland. But at the period of greatest
elevation the shrunken Mediterranean offered no such
great attraction, and with a comparatively well-watered
Sahara the storms were able to pass much further south.
Consequently, northern Africa possessed a number of
large and permanent rivers which reached the sea. It
was along these rivers and their banks that the fauna
still inhabiting the Saharan oases made its way, to be
isolated there by the decrease of the rainfall, so that
crocodiles and many species of fish now live in isolated
pools and in rivers which lose themselves in the
sand.

In Egypt and Syria the first Pluvial period is doublé,
corresponding to the Gunz and Mindel glaciations,
with an intervening phase of feeble desert conditions,
during which, however, the rainfall remained greater
than the present. The second stage, corresponding to
the Mindelian, indicates very great activity; at this
time the Jordan Sea (Dead Sea) reached its greatest
area, extending to the northern end of the Sea of
Tiberias.

Conditions in Egypt at this time are very interesting.
South of Cairo the aïïuvial Nile muds are at most thirty
to thirty-five feet thick, and ten feet of this thickness
has been deposited since the time of Ramesis II. If
the rate of deposition has been uniform, this gives a
period of only 14,000 years for the deposition of the
whole thickness of the muds. The theory put forward
by Hume and Craig (British Association Report, 191^,
p. 382) is briefly as follows: The mud deposits of the
Nile valley are carried down with the flood waters of
the Blue Nile, Atbara, etc. These rivers rise in the
highlands of Abyssinia, where they are fed by the rains
  THE MEDITERRANEAN REGIONS 73

of the south-west monsoon. The incidence of the
monsoon is determined by anumber of factors, prominent
among which is the temperature of Southern Asia.
During the winter, at present, the low temperature of
the Himalayan and Tibetan region results in a great
outflow of cold air, which strikes the coast of Africa as
the cool dry north-east monsoon. During this time
there is very little rain in Abyssinia. It is only when
the Asiatic land-mass warms up in summer that the
south-west monsoon is established.

But during the Glacial period, as we shall see, there
was a great development of snow and ice on the Hima-
layas. The result was that winter conditions, i.e. the
north-east monsoon, prevailed more or less throughout
the year, and the rivers which feed the Nile contained
only a small volume of water. Hence they lost them-
selves in the desert before reaching Cairo, and the Nile
in its present form did not exist. On the other hand,
the westerly winds which at present bring a moderate
winter rainfall to the coast of Syria were greatly increased
in intensity and extended further south, replacing the
dry north and south winds now occupying the Nile
valley. The northerly winds prevailing in the Nile
valley in summer are associated with the low pressure
area over the neighbourhood of the Persian Gulf, which
in turn is due to the extremely high temperature expe-
rienced there. Even at the present day the highest hills
of Sinai penetrate above the north winds into a westerly
current, and a moderate fall of temperature over the
Persian Gulf would inhibit the north winds in the Nile
valley altogether and allow the westerly winds to reach
the surface. These strong westerly winds brought a
heavy rainfall to the hills, now almost rainless, between
the Nile and the Red Sea. Powerful streams descended
the western slopes of these hills, bringing great quantities
of debris, which formed delta-terraces forty or fifty feet
thick where the streams debouched on to the Egyptian
plain. These are especially well developed at Oina,
  74 THE EVOLUTION OF CLIMATE

the meeting place of several dry valleys from the hills,
and it is remarkable that they jtctually cross the present
site of the Nile valley and reach the desert on its western
side, additional evidence that the Nile was not then in
existence.

These gravel terraces contain numerous stone imple-
ments of early (pre-Chellean) types, showing that at
this time Egypt had sufficiënt rainfall of its own to
support human life.

The moist westerly winds carried the climate of the
Mediterranean coast far into the desert. For instance, in
the oasis of Khargeh, in latitude 250, grew the evergreen
oak and other 1   ' not now founa south of Corsica

The Mindelian Pluvial period was followed by a long
dry period corresponding to the Chellean, when desert
conditions supervened. The Nile as we know it first
appeared during this period. Terraces were formed on
the sides of the valley, probably during the submergence
which produced the Strombus beaches of the western
Mediterranean; these contain Chellean implements.
During the succeeding elevation the Nile cut its bed
below the present level.

The Rissian glaciation of northem Europe is repre-
sented in Egypt by a second rainy period, the Lesser
Pluvial period. Rain again feil on the Red Sea hills,
forming a newer set of gravel terraces, but these are
much smaller than the great Mindelian terraces. No
terraces are known representing the Wurmian period,
and the country does not seem to have been inhabited
at this time. Probably the climate was semi-desert,
with not enough rainfall of its own to support human
life, and yet without the fertilizing Nile floods to enable
human life to exist without rainfall. As has been said,
the present regime did not begin until the last glaciation
was nearly over, about 12,000 b.c.

and Southern
  THE MEDITERRANEAN REGIONS 75

BIBLIOGRAPHY

Gignoux, M. “ Le» formations marines pliocènes et quatemaires de 1’Italie
du Sud et de la Sicilië.” Ann. VUttiv. Lyon, n.s., Vol. i, fase. 36,
Paris, 1911, pp. 693.

Depéret, C. “ Les anciennes lignes de rivage de la cöte frangaise de la
Mediterranée.” Buil. Soc. Geol. de France, ser. 4, Vol. 6, pp. 207-30.

Douvillé, R. “ Espagne,” Hanibucb regional Geol., H. 7, 1911. (Includes
Gibraltar and Balearic Is.)

Hume, W. F., and Craig, J. I. “ The Glacial period and climatic change in
North-east Africa.” Rep. Brit. Assoc., 1911, p. 382.

6
  CHAPTER VII

ASIA DURING THE GLACIAL PERIOD

The great area of Asia is at present but little explored
for glacial tracés, but a certain amount of evidence has
been collected, and the data from the various mountain
districts are consistent enough to map out the general
trend of the history of the continent during the Ice Age.

The earth-movements which brought about the
present configuration of Asia were completed as regards
their major details by the close of the Tertiary period.
These movements left a number of great basins closed
in on all sides by enormous mountain walls; at first all
these basins contained lakes, and the subsequent geo-
graphical history has consisted largely in the gradual
silting up of the lakes and the development of more and
more arid conditions. The fluctuations of the Ice Age
were superposed on this secular desiccation, but except
in northern Siberia the part played by glaciation in the
history of the country has been relatively small.

Consider for a moment the relief of Asia. The
orographic centre may be taken as the great Pamir
plateau, the “ Roof of the World,” with an average
elevation exceeding the height of Mont Blanc, diversified
by ranges of mountains exceeding 25,000 feet in places.
East of this is the great plateau of Tibet, 10,000 to
17,000 feet, bounded on the south by the mighty Hima-
layas, and on the north by the mountains of Kuen Lun.
On the north the Pamir plateau 'is bounded by the
Alai range, passing north-east into the Tian-Shan
mountains, rising to 24,000 feet in Khan-tengri. Still
76
  ASIA DURING GLACIAL PERIOD 77

further north-east comes the Altai range, with an
elevation of 9000 feet. East of Lake Baikal lie a series of
ranges averaging 8000 feet in height, and passing into
the Stanovoi range of eastern Siberia and the mountains
of Kamchatka.

The Himalayas, owing to their heavy snowfall derived
from the south-west monsoon, bear numerous great
glaciers, but with the series of ranges extending from
the Pamirs to north-east Siberia the case is different.
These ranges all rise above the snow-line in places, but
owing to the scanty snowfall they bear at most a few
small glaciers on their northern sides, and none at all
on the slopes which face towards the deserts of western
China, and in all cases the glaciation is very slight in
comparison with their elevation.

This distribution was characteristic also of the Ice Age.
In the Pamirs there is evidence of two periods when the
glaciers had a greater extent; ..in the first they extended
to a level of 5000 feet, in the second to 7000 feet. The
present limit of the glaciers lies at about 10,000 feet.
The first glaciation was remote, for the moraines are
worn and weathered, but the second was much more
recent, for the moraines are fresh, and in some cases
there are still masses of “ dead ” ice buried beneath
great accumulations of debris and occasionally exposed
by slips.

In the Tian-Shan mountains there are remains of
two glaciations. The earlier was the greater, and the
glaciers descended well below 10,000 feet. This glacia-
tion was followed by a long interval, when the erosion
of the rivers converted the U-shaped glacial valleys into
V-shaped gorges. A second glaciation descended to
a level of 10,000 feet, and again developed U-valleys to
this level; the end moraines of these glaciers are young
and fresh-looking. In the Altai range there were also
two glacial periods. In the older and greater the snow-
line was depressed by 3000 feet. The glaciers attained
a length of twelve miles and descended to a level of
  78 THE EVOLUTION OF CLIMATE

only 3000 feet above the sea. The second glaciation
was less extensive.

So far we have been dealing with small mountain
glaciers only. But in north-eastern Siberia we find a
different state of affairs. The Stanovoi and Verkhoiansk
mountains were heavily glaciated, and during the first
glaciation were probably the centre of an actual ice-sheet
similar to that of Scandinavia. The ice descended the
valleys of the rivers Yana, Indijirka and Kolyma and
covered the New Siberian Islands, which were at that
time connected with the mainland. The upper valley
of the Lena was also heavily glaciated by an ice-sheet
moving southward, probably from the Patom highlands.
When this glaciation drew to a close the source of
supply among the mountains ceased, and the ice on the
lowlands and in the lower parts of the river valleys was
left stranded as “ dead ” ice. When the mountains
became free of ice, the re-born rivers carried great
quantities of moraine clay and other debris with them,
and flooding the ice-surface over wide areas deposited
their load above the ice. In course of time the remains
of the ice-sheet were deeply covered by a layer of earth
and stones, which prevented the ice from melting and
preserved it to the present day. This is the probable
origin of the well-known “ fossil ice ” of Siberia. Other
theories have been put forward, such as the freezing
of ground water during the winter, but none are satis-
factory, and that given here was generally adopted by
Russian geologists.

During the long warm interglacial which followed,
the surface of the thick earth-layer covering the ice bore
low-growing herbage in the same way as any other
earth-surface. (A parallel to this is found in Alaska,
where the glaciers terminate among the forests, which
actually grow over the moraines covering their snouts.)
The rivers cut their way down through the earth and ice,
exposing ice-cliffs, which were quickly buried by talus
from above. The mammoth and woolly rhinoceros
  ASIA DURING GLACIAL PERIOD 79

roamed the land, and their tusks remain in great numbers
as the “ fossil ivory ” of Siberia and the Arctic Ocean.
Still more remarkable is the fact that mammoths have
been found buried entire, and preserved by the frozen
ground to the present day. It is difficult to say how
the animals reached such a position, but most probably
they sank into swamps formed during the summer and
were quickly frozen.

In western Europe the mammoth and woolly rhino-
ceros are regarded as indications of severe climate, but
their presence in north-eastern Siberia in large numbers
is evidence of a climate probably somewhat warmer
than that of the present day, especially as regards the
length of the vegetation period. Probably the winter
snowfall also was less than now. It is difficult to see
how the fauna could have moved from, say, the New
Siberian islands into a warmer climate each winter,
for the winter climate becomes markedly more severe
as one penetrates south from the Arctic coast into the
interior. It is possible that the mammoth and woolly
rhinoceros hibernated during the winter.

After this interglacial there came a recrudescence of
glacial conditions. In this case, however, the Stanovoi
and Verkhoiansk mountains and the Patom highlands
were not buried in an ice-sheet, but became the centre
of great valley glaciers, which reproduced the well-
known glacial phenomena—corries, glacial terraces,
U-valleys, etc. The ice extended down the great river
valleys, leaving a typical moraine landscape on either
side, and again reached the New Siberian islands. In
course of time the climate ameliorated, again commencing
in the south, and again the ice of the glaciers was buried.
In the New Siberian islands the happenings are sum-
marized very expressively by a rock-section described by
Vollossovitsch. The bottom of the section is formed
by the older layer of “ fossil ice.” Above this is a sandy
clay with remains of meadow vegetation and shrubs,
followed by a fine clay with remains of alder and white
  80 THE EVOLUTION OF CLIMATE

birch, and the bones of mammoth and rhinoceros.
Above this comes another layer of “ fossil ice,” followed
by clay with the dwarf birch, Arctic willow, and bones
of musk ox, horse and later mammoth. After this the
Coastal regions sank beneath the sea for a time and
marine clays were formed in a climate somewhat warmer
than the present. When the land rosé again the con-
ditions resembled those now prevailing.

Though not part of Asia, reference may be made here
to the glaciation of Spitzbergen, which runs strictly
parallel with that of northern Siberia. The first glacia-
tion was of the “ ice-sheet ” type, originating in the
region north of Storfjiord, filling the whole of that
fiord and extending south of South Cape. Barentz
Land and Stans Foreland were at least partially ice-
covered. The ice-floor of Spitzbergen, which resembles
that of Siberia, may have originated during this glaciation.
This was followed by subsidence to 230 feet below
present level, and the ice retreated, giving place to an
“ interglacial,” during which frost was very active and
largely obliterated the tracés of the ice-sheet. This
“ interglacial ” was followed by a second extension of
the ice, which affected the valleys and fiords only, leaving
the plateaux free. This again was followed by subsidence
and a warm period.

In Southern Kamchatka there was a great develop-
ment of ice, but in the form of a network of glaciers
rather than of an inland ice-sheet. In the east the i,ce
reached the sea, but on the west it left a zone forty to
sixty miles broad, and up to a thousand feet high un-
glaciated, so that there was the same difference then as
now between the rainy east side and the drier west side
of the peninsula. The present snow-line in the centre
of Southern Kamchatka is about 5500 feet, and at the
maximum of the glaciation it must have been fully
3000 feet lower.

Prometheus:

This glaciation was followed after an interval by a
second, which was confined to the mountains. The
  ASIA DURING GLACIAL PERIOD 81

moraines of this glaciation are much fresher than are
those of the earlier one.

In Japan the mountains were only just high enough
for glaciers to develop in the north. The moraines are
old and weathered, and their meaning has been disputed;
but recent work by Simotomai and Oseki seems to have
established their glacial origin. The depression of the
snow-line necessary to produce them—about 3000 feet—
fits in very well with that observed in adjoining parts
of the continent. The phenomena were confined to
small hanging glaciers in the Hida mountains which cut
out corries and descended to a level of about 8000 feet,
leaving small morainic ridges. This glaciation was
probably contemporaneous with the earlier and greater
glaciation of Siberia. To the succeeding interglacial
may be attributed the marine deposits found near
Tokio containing corals, at present living some distance
further south. No tracé of any subsequent glaciation
of Japan has yet been found.

J. S. Lee has recently called attention to the existence
of a glaciated area in northern China, the evidence for
which consists of moraines and striated slabs found in
Southern Chi-li, and a glaciated valley with travelled
boulders in the north of Shan-si. The glacial deposits
in Chi-li are closely associated with a layer of quartzite
pebbles which continues southward beneath the loess on
the eastern side of the Tai-hang range, and is attributed
to either torrential rain or the melting of glaciers.
J. Geikie had long ago stated that there once existed
ice-masses all over northern China, and considered that
the ice came from the Himalayas. This origin is impos-
sible, the probable source of the ice being the Yablonoi
mountains in Southern Mongolia.

In the Himalayas the glaciers formerly had a much
greater extension. The glaciers at present extend
downwards to 11-13,000 feet, but old moraines are
found at 7000 feet, and near Dalhousie on the Southern
slopes of the Dholadar range to 4740 feet.
  82 THE EVOLUTION OF CLIMATE

On the northern side of the Himalayas there was a
great development of ice over Tibet, but there was not
a real ice-sheet such as occurred further north. OJdham
records three separate periods of glaciation in Kashmir,
but it is not yet possible to discuss the glacial history
of the Himalayas in detail. The latter is likely to prove
complicated, since the range is still rising, and has prob-
ably been doing so either continually or intermittently
throughout the Quaternary.

The great development of ice in Tibet, which is now
semi-arid, owing to interception of the rain-bearing
winds by the Himalayan range, suggests a considerable
alteration in the present meteorological conditions.
The Tibetan snowfall was probably due to the Mediter-
ranean storms, which now give a small winter rainfall
in north-west India, and which during the Glacial period
greatly increased in strength and frequency and occurred
throughout the year (Chapters IV and VI), giving the
Pluvial period of North Africa. These storms would
pass across Persia and continue to the north of the
Himalayas, probably breaking up over the Tibetan
plateau.

It is evident that, taking northern Asia as a whole,
there have been two general glaciations, of which the
first was the more severe, separated by a long inter-
glacial, during which, in Japan at least, the climate
became appreciably warmer than the present. The first
glaciation is related to elevation in the Arctic basin,
which closed Bering Strait and united the New
Siberian islands to the mainland. It was almost cer-
tainly contemporaneous with the first glaciation (Gunz-
Mindel) of Europe. The ice began as glaciers on
the mountains as in Scandinavia, but, owing to the
scanty supply of snow, developed more slowly and only
reached the dignity of ice-sheets in north-east Siberia.
Then followed subsidence below the present level,
wider opening of the Bering Strait, warm ocean
currents and a long interglacial. After this there was
  ASIA DURING GLACIAL PERIOD 83

again elevation and a re-development of ice-sheets, but
apparently once only, and not twice as in Europe. This
glaciation probably corresponded in point of time
more or less with the Rissian, for the post-glacial dry
of central Asia appears to have been of enormous period
length.

There is one other phenomenon which must be con-
sidered in connexion with the glacial history of Asia,
and that is the loess. Loess has already been referred
to in connexion with the glaciation of Europe, but in
China its development is much greater. Richthofen,
who first studied this deposit attentively, and to whom
we owe the seolian theory of its origin, found that ït
was formerly deposited in China over a much greater
area than that over which it is accumulating at present,
and attributes this cessation of growth to the heavier
rainfall brought by the Glacial period, which enabled
the rivers to cut back their valleys and drain some of
the mountain basins, formerly enclosed. He considered
that loess can accumulate more rapidly in a closed
basin, where occasional floods leave behind them layers
of bare sand and mud, easily dried to dust, than in a
well-drained river valley where floods are rare.

In western Asia outside the limits of glaciation we
have further evidence of at least one Pluvial period in
the former far greater extent of all the enclosed lakes,
due partly to greater precipitation and partly to de-
creased evaporation. The Caspian Sea and Aral Sea
were extended to several times their present size and
united into a single sheet of inland water. Lake Lop-nor
was greatly increased in size, and many of the desert
basins, at present dry, were the sites of salt lakes. This
is especially the case in central Persia, where there were
large salt or brackish lakes.

These Pluvial conditions have not yet been correlated
with the glaciations of Asia, but, by analogy with the
conditions in America discussed in the next chapter,
there is little doubt that they were contemporaneous
  84 THE EVOLUTION OF CLIMATE

with one at least of the glaciations, and probably there
were two main Pluvial periods coinciding with the two
Glacial periods. At Baku, on the shores of the Caspian
river, Pumpelly has found old shore lines at heights
of 600, 500, and 300 feet above the present level of the
water. Still more interesting are the conditions found
by Sven Hedin in the Kavir basin of Persia. Here there
are lacustrine clays and silts referable to a Pluvial period
covered by beds of almost pure salt, suggesting a rapid
and complete drying up of the lake. Above this again
are further silts indicating a return of Pluvial conditions.
In addition to this the succession of silts and clays show
that there were several minor fluctuations superposed
on the main wet periods, giving ten moist phases
altogether.

BIBLIOGRAPHY

Many of the more important references are in Russian, and for theie

reference is made to summaries in other languages.

Sevastianov, D. P. “ On the glaciation of the extreme north-east of Siberia.”
J. 12 Congr. Russ. Nat., Moscow, 1910, No. 10, p. 491. (Russian, see
Geol. Centralblatt, 15, p. 205.)

Riesnitschanko, W. “ Ancient and modem glaciers of the south-western
Altai.” Mem. Russ. Geogr. Soc., 48, 1912, p. 357. (Russian, see
Geol. Centralblatt, 19, p. 131.)

Komarov, W. “ On the Quaternary glaciation of Kamchatka—Travels in
Kamchatka in 1908-9,” Vol. 1 (Russian, see N. J. Min., 1915, Pt. 2,
p. 117).

Merzbacher, G. “ Zur Eiszeitfrage in der nordwestlichen Mongolei.”
Peterm. Mitt., Gotha, 57, 1911, p. 18.

Prinz, Gyula. “ Die Vergletscherung des nördlichen Teiles des zentralen
Tien-8chan-Gebirges.” Wien, Mitt. K. K. geogr. Gesellscb, 52, 1909,
p. 10.

Obrutscher, W. A. “ Geological map of Lena gold-bearing region.” St.
Petersburg, 1907. [Text in Russian; see Geol. Centralblatt, 12,
PP-. 5°7-9-l

Simotomai, H. “ Die diluviale Eiszeit in Japan." Berlin, Zs. Ges, Erdkunde,
1914, p. 56.

Oseki, K. “ Some notes on the glacial phenomena in the North Japanese
Alps.” Edinburgh, Scot. Geogr. Mag., 31, 1915, p. 113.

Lee, J. S. “ Note on tracés of recent ice-action in North China," Geol,
Mag., 59, 1922, p. 14.

Burrard, S. G., and Hayden, H. H. “ A sketch of thé geography and geology
of the Himalaya Mountains and Tibet.” Calcutta, 1907-8.
  ASIA DURING GLACIAL PERIOD 85

Hogböm, G. “ Bidrag till Isfjordsomradets kvartargeologi.” Geol. Foren.

Stockholm Forh., ign. (Spitzbergen; résumé in German.)
Richthofen, F. Freih. von. “China.” 5 Vols., 1907-12. (Loess, see Vol. 1,
. P- 74 ff.)

Hedin, Sven. ** Some physico-geographical mdications of post-Pluvial
climatic changes in Persia.” Internat. Geol. Congr., Stockholm, 1911.
“Die Veranierung des Klim as."
  CHAPTER VIII

THE GLACIAL HISTORY OF NORTH AMERICA

The glaciation of North America was even greater and
more complicated than was that of Europe. It spread
from three main centres, the CordiUeran or Rocky
Mountain centre, the Keewatin centre west of Hudson
Bay, and the Labradorean centre. Vancouver Island
in the west and New Brunswick and Newfoundland in
the east, were also independent centres of glaciation,
and ice from the latter may have reached the coast of
the United States in places. The ice covered an area
of about 4,000,000 square miles, and the main ice-sheet
extended to 38° N., or twelve degrees further south than
the Scandinavian ice-sheet. Nine stages are recognized
by American geologists, though opinion is divided as
to whether all the stages of “ deglaciation ” represent
real interglacial periods. The sequence is as follows:

1.   Nebraskan, Jerseyan or pre-Kansan glaciation.

2.   Aftonian deglaciation.

3.   Kansan glaciation.

4.   Yarmouth deglaciation.

5.   Illinoian glaciation.

6.   Sangamon deglaciation.

7.   Iowan glaciation.

8.   Peorian deglaciation.

9.   Wisconsin glaciation.

On the other hand, in the northern part of the Rocky
Mountains there is evidence of only two Glacial periods,
separated by a single long interglacial, though perhaps
86
  THE GLACIAL HISTORY OF N. AMERICA 87

the second glaciation was doublé. Further south, out
of reach of the main ice-sheets, there are tracés of two
and in places three separate developments of valley
glaciers resembling those of the Alps.

As in the case of Europe, the literature of the subject
is extensive and conflicting, but the following summary
of the course of events represents the views of most
moderate American geologists.

The Quaternary period opened with extensive eleva-
tion of the whole North American continent, which
raised the Rocky Mountains several thousand feet above
their present level and extended the Continental area
over much of the northern archipelago. In the east
Newfoundland is considered to have been raised at
least 1000 feet, a movement which converted the
banks into dry land and interposed a large cold area in
the path of the moisture-bearing southerly winds. As
in northern Europe the high mountains of the west
were the first to develop large glaciers, which coalesced
into an ice-sheet, filling the valleys and rising up the
slopes of the mountains until it reached a thickness of
5000 feet. In Puget Sound the ice was 4000 feet
thick, but seawards the slope is very rapid and the ice
was unable to extend far from the shore. This ice-sheet
extended south-eastwards some distance into the United
States, forming the first ground moraine of that district.
Probably while this Cordilleran glaciation was still in
progress ice began to spread outwards also from the
Labradorean centre, forming the oldest drift of that
region. These oldest deposits are, however, not yet
well understood.

This oldest boulder-clay is separated from the moraines
of the main glaciation near its Southern limit by river
gravels containing the remains of mollusca and large
herbivorous mammals—extinct species of horse, the
hairy mammoth of the old world (Elephas primigenius),
and two other extinct species of elephant, and also the
true American mammoth. This is the Aftonian fauna
  88 THE EVOLUTION OF CLIMATE

which has been claimed as evidence of an Interglacial
period. That it evidences a retreat of the ice-edge in
that particular region is certain, but that the climate
became really temperate is very doubtful. More prob-
ably it corresponds to the Gunz-Mindel “ interglacial ”
of the Alps, and was formed when the Cordilleran
ice-sheet was retreating, but before the Keewatin sheet
had reached its maximum.

The Aftonian stage was followed by the Kansan
glaciation, when the ice-sheets reached their maximum
area over the greater part of North America. The
chief centre of glaciation at this stage was the Keewatin,
west of Hudson Bay. While it is certain that the
Keewatin centre reached its maximum later than the
Cordilleran, geological opinion in America is divided
as to whether or no the two ice-sheets ever coalesced,
but it is difficult to understand how an independent
ice-sheet could have grown up on the comparatively
low ground of the Keewatin centre. Most probably
the course of events here was an exact parallel of that
in the better-known Scandinavian region—the Cordil-
leran ice-sheet extended eastwards over the lower
ground until a glacial anticyclone developed east of the
Rockies. When this happened the supply of moisture
to the western part of the ice-sheet feil ofï somewhat,
and the eastern part took on an independent life, ulti-
mately becoming the main centre of glaciation. It was
while these changes were in progress that the Southern
limit of the ice retreated northwards and the “ Aftonian ”
deposits were formed.

The next stage (Kansan) occurred when the ice
from the Keewatin centre spread outwards in all direc-
tions, and in the south reached the maximum limits of
glaciation in America. In the west this sheet overlapped
on to the ground-moraine of the former Cordilleran ice,
but the Rocky Mountains were too far away and too
high for Keewatin ice to dominate them and overflow
them from east to west. Instead these mountains must
  THE GLACIAL HISTORY OF N. AMERICA 89

have maintained an extensive glaciation of their
own.

With the growth of the Keewatin centre the Labra-
doTean also decreased, but more slowly, and this change
was not associated with a retreat of the Southern ice-
edge, so that there was no corresponding “ interglacial ”
in the east of the United States. The moraines of these
older glaciations resemble those of the early ice-sheets
of Europe in presenting only featureless level surfaces
of boulder-clay without morainic ridges, lakes and the
other characteristics of ice-bearing surface detritus, and
there is no doubt that conditions at the Southern edge
were similar—the climate was severe in winter, but not
insupportable in summer. At the same time it was
decidedly more severe than the present, even as far
south as Florida} where there are colonies of northern
plants, which migrated southwards during the Ice Age,
still living on local cold slopes with a northerly aspect.
After the maximum of glaciation the disappearance of
the ice took place gradually and chiefly by ablation, for
there are none of the extensive river gravels and flood
terraces which we should find had the melting been
rapid. It is only in the valleys of the Rocky Mountains
that such deposits occur, testifying to conditions such
as obtained in the Alps.

The succeeding Yarmouth stage of deglaciation was
very long, corresponding in this respect to the Mindel-
Riss interglacial of Europe. The Kansan moraine was
weathered to a depth of ten or twenty feet, and four-
fifths of its surface was removed by the erosion of
streams and rivers. In the mountain districts the side
streams which had been left occupying “hanging
valleys” by the over-deepening of the heavily glaciated
main valleys, had time to cut out uniformly graded
broad V-shaped valleys descending to the level of the
main stream. In the Great Basin also, where the
periods of high water-level are considered to correspond
to the main glaciations, the interval of low water
  90 THE EV0LUTI0N OF CLIMATE

corresponding to the Yarmouth stage was very long.
A rough estimate of its length is about 200,000 years
—somewhat shorter than the Mindel-Riss. Actually,
though the Kansan and Mindelian glaciations were
approximately contemporaneous, the subsequent re-
currence of glaciation in America appears to have
preceded slightly that in Europe.

Of the climate of this stage we have unfortunately
httle evidence. Old land surfaces of this age are known,
containing deposits of peat and bones of the wood
rabbit and common skunk, but both of these animals
have a wide range. Perhaps the climate resembled the
present during most of the period ; there is no evidence
that it was ever warmer, and it appears quite likely that
ice-sheets maintained their existence in the far north
through the whole of this stage.

After this interglacial there set in a period of renewed
elevation in the Rocky Mountains and in the Labrador-
Newfoundland centres, which brought about a recur-
rence of the glaciation. In the Rocky Mountains the
ice was not so thick as in the preceding stage, but all
the valleys were occupied to a considerable depth and
the ice spread out to the eastward. The Labrador
ice-sheets also developed again, forming the Illinoian
glaciation, the moraines of which are found as far west
as Illinois, but no moraines are known of this age due
to the Keewatin ice-sheet. The latter developed later,
and is classed by some American geologists as a separate
glaciation, the Iowan, which is only certainly found in
northem Iowa, but may be represented further east
by a thin sheet of boulder-clay overlapping the Illinoian
moraine. The supposed interglacial between the Illi-
noian and Iowan, the “ Sangamon Stage,” is represented
only by land surfaces formed of the Illinoian ’ moraine
and covered by the loess or locally by the equivalent of
the Iowan moraine, and there is no evidence that the
ice-edge retreated far. Other American geologists,
including F. Leverett, do not recognize the existence of
  THE GLACIAL HISTORY OF N. AMERICA 91

Prometheus:

a separate Iowan glaciation, and as the amount of
weathering and denudation undergone by the two
moraines differs very little, this seems the more natural
view. The natural explanation seems to be that this
was another case of “ glacial piracy,” the Keewatin ice-
sheet, owing to its lesser snowfall, developing more
gradually, and finally diverting the supply of moisture
from the Labradorean ice-sheet, until it reached a
maximum after the latter was already on the wane.
Both these sheets of drift present similar flat features
to the Kansan sheet, without morainic ridges.

Leverett’s interpretation of the succession is as
follows: The third (Illinoian-Iowan) glaciation was
followed by a period of moist climate, when peat-bogs
were formed on level poorly-drained surfaces, while
elsewhere coniferous forests developed. This was fol-
lowed by a period of dry steppe-like conditions with a
cold temperate climate, when the great American loess
sheet was deposited. This loess sheet extends northwards,
overlapping the Iowan moraine, and in places passing
under the Wisconsin drift. The material has come
from the west, and probably most largely from the dry
plains east of the Rocky Mountains, from which it
diminishes in thickness eastwards. But unlike Europe
this phase of steppe conditions was followed in America
by a definite interglacial, when the climate seems to
have become rather warmer than the present. In the
northem States an old land-surface formed on the loess,
and, termed the Peorian stage, is overlain by the Wisconsin
drift; but near Toronto, on the shores of Lake Ontario
and in the Don valley, the gap represented by this land-
surface is partly filled by a remarkable series of lacustrine
deposits known as the Toronto stage. The Lake
Ontario beds indicate a climate slightly colder than the
present, but the Don valley beds contain plants and
animals living in the central States, and refer to conditions
more favourable than those now found in the district.

The duration of this interglacial has been worked out

7
  92 THE EVOLUTION OF CLIMATE

in a remarkable way by A. P. Coleman, who on the
basis of wave-action estimated it as 62,000 years, which
agrees very closely with the 60,000 years found by
Penck and Brückner in the Alps. This period was not
long enough for streams in the “ hanging valleys ” to
cut out uniformly graded valleys down to the main
rivers, and was consequently much shorter than the
preceding interglacial.

The last glaciation of North America was the Wisconsin,
which closely resembles the Wurmian of Europe both
in its relations to the older glaciations and in the rough
topography and unworn character of its moraines. It
extended within the limits of the Kansan drift across
fully two-thirds of the continent, from Nantucket and
Cape Cod through Long Island, northern New Jersey,
Pennsylvania, Southern New York, Ohio, Indiana,
Illinois, Michigan, Wisconsin, Minnesota, Iowa and the
Dakotas, Manitoba, Saskatchewan and Alberta. At the
same time the Cordilleran centre probably bore increased
local valley glaciers.

Like the Wurm glaciation, the Wisconsin was doublé.
The older moraines are well-marked, and in places are
covered by a foot or two of loess, though thls deposit
reaches nothing like the thickness of that overlying the
moraines of the earlier glaciations. The moraine under
this loess is very little weathered, so that the time interval
was very short; possibly this loess is redistributed older
loess associated with glacial east winds. The ice of the
first glaciation melted very slowly and there is very little
gravel outwash to the moraines. But “ after the
Wisconsin ice-sheet had reached a position a little
outside the limits of the Great Lakes the retreat became
much more rapid, and large outwash aprons were formed
from which valley trains of gravel led far down the
drainage lines. From this position . . . the moraines
are practically free from loess-like silts.”1

From this point onwards the glacial history of America

1 Leverett, F. (see Bibliography).
  THE GLACIAL HISTORY OF N. AMERICA 93

is one of irregular retreat, with occasional halts or even
readvances resembling those of the Scandinavian ice.
Banded clays are found similar to those used so success-
fully by Baron de Geer in dating the retreat stages of
Scandinavia, and this geologist has recently been investi-
gating them, but until his results are worked out no
correlation with Europe can be attempted.

A natural clock of another type is provided by Niagara
Falls, which are cutting their Way back up the gorge
at a rate which has been definitely ascertained. Taking
into account the varying amounts of water which have
passed over the falls at different stages of post-glacial
geography, the duration since the region became free of
ice has been calculated at about 20,000 years, which
agrees closely with the time elapsed since the Scandi-
navian ice-sheet left the North German coast.

Before leaving North America it is necessary to give
a brief account of the phenomena outside the main
centres of glaciation, and especially of the history of
the Great Basin between the Siërra Nevada and Wasatch
Mountains. The lowest levels of this basin are at
present occupied by several salt lakes without outflow,
of which the largest is the Great Salt Lake, the level of
the water being determined by the balance between
inflow of the rivers and evaporation from the surface.
Twice in the past this balance has been decidedly more
favourable, and then the lakes grew to many times their
present size. The two greatest of these old lakes have
been fully described under the names of Lake Bonneville
(of which the Great Salt Lake is a vestige) and Lake
Lahontan, further to the west. The investigations have
shown that before the Glacial period, and extending
back into an unknown past, there was a period of great
aridity. To this succeeded a long period of high water,
during which, however, neither of the lakes overflowed.
This stage was followed by a very long period of great
aridity, during which the lakes dried up completely,
and all their soluble matter was deposited and buried
  94 THE EVOLUTION OF CLIMATE

by alluvial material. This period was followed by a
return of moist conditions, during which the water
reached a higher level than before, and in the case of
Lake BonneviUe actually overflowed into the Snake
river, cutting a deep gorge. This period, however,
was shorter than the preceding moist period. It was
followed by an irregular fall interspersed with occasional
slight rises, but ultimately both lakes descended below
their present level and probably again dried up com-
pletely. Both lakes suggest that this low level was
followed by a third rise to a height very slightly above
the present level, followed by a slow fall in recent years.

The relations of the periods of high water to the
glaciations are not clear in these large lakes, but in the
Mono Basin, a small basin further west, there is no
doubt that the two were almost contemporaneous, high
water accompanying the maxima of glaciation and
extending some way into the retreat phase. The very
long interval between the first and second period of high
water, several times that since the second period, agrees
with this correlation. We find then that south-west
of the main glaciated area there was a district of greater
precipitation or less evaporation, or more probably both.
This is confirmed by the vafley moraines of all this region
—Siërra Nevada, Uinta and Wasatch mountains,
Medicine Bow Range of northem Colorado, etc., all
of which indicate two glaciations, of which the first was
the greater, separated by a very long interval. In
several ranges the moraines of the second glaciation are
doublé, and some geologists consider that there were
three Glacial periods in these regions.

In the extremely arid region of Arizona, on the other
hand, which is considerably further south, the evidence
of the Gila conglomerates indicates that while frost was
very active, the increase of precipitation, though un-
doubtedly present, was comparatively slight. This
.shows that the climatic balance was not greatly disturbed,
the chief effect being an important lowering of tempera-
  THE GLACIAL HISTORY OF N. AMERICA 95

ture, probably due to cold northerly winds. The Gila
conglomerates are doublé, separated by a period repre-
senting present-day conditions.

Summing up the evidences of glacial climate in North
America, we find a striHng siimlarity to Europe. In
the north elevation and increased land area caused the
development of large ice-sheets, which appeared first
in the mountainous regions with a heavy snowfall, and
later spread over the drier plains and plateaux of the
interior. This first glaciation was long and complex.
Owing to the anticyclonic conditions which formed over
the ice, the rain- and snow-bearing depressions were
forced to pass further southward, causing greater snow-
fall on the mountains and high water-level in the lake
basins. This greater snowfall, together with the cold
conditions due to the existence of the ice-sheets to the
north, caused the development of mountain glaciers
south of the main glaciated region. In the east there
were cold northerly winds which carried a severe climate
as far south as Florida. This Glacial period was followed
by subsidence, and a long spell of dry, moderately warm
climate lasting perhaps 200,000 years, after which eleva-
tion and glacial conditions again set in. These conditions
were not so severe as the first, and their duration was
much less, while they were broken up by several intervals
of temporary recession of the ice, one of which, corres-
ponding to the Riss-Wurm period, lasted for 60,000
years, and perhaps should be considered as an “ inter-
glacial.” This period was marked in its early stages
by the deposition of the curious seolian deposit known
as “ loess,” indicating steppe conditions. After the last
glaciation there set in a stage of irregular retreat.

BIBLIO GRAPHY

Leverett, F. “ Comparison of North American and European glacial
deposit».” Zs.f. Gletsclerkünde 4, 1910, pp. 280, 323.

Wright, W. B. “ The Quaternary Ice Age.” London, 1914, Chs. 8-9.
  96   THE EVOLUTION OF CLIMATE

Attwood, W. W. “ The gladation of the TJinta Mountains.” J. Geol., 15,
,9°7> P- 79°*

Henderson, J. “Extinct glaciers of Colorado.” Col». U*iv. Studies, 3,
>905. P- 39-

Gilbert, G. K. “ Lake Bonne-nlle.” Washington, U.S. Geol. Survey Mono-
grapb I, 1890.

Russell, I. C. “ The geological history of Lake Lahontan.” Washington,
U.S. Geol. Survey Monograpb XI, 1885.

Coleman, A. P. “ An estimate of post-Glacial and interglacial time in
North America.” Rep. 12 Internat. Congr. Geol., 1913, p. 435.
  CHAPTER IX

CENTRAL AND SOUTH AMERICA

The scarcity of data which was bewailed in dealing
with Asia is still more marked in the case of South
America, and it will be necessary to present the glacial
history of that continent in the bar est outline only.
This is the more unfortunate as the chain of the Andes,
extending from north of the equator to high Southern
latitudes, is of enormous importance in glacial theory,
and especially in the question of simultaneity of glaciation
in the two hemispheres.

The beginnings of glaciation in South America are
obscure. The distribution of animals shows that towards
the close of the Tertiary the Falkland Islands were
greatly elevated and were United to Tierra del Fuego
and Patagonia, and this enlarged land area was connected
in some way with Australia and Tasmania, but the mode
of this latter connexion is not definitely known. This
question will be discussed more fully in Chapter XI;
it is sufficiënt to say here that the amount of elevation
may have reached 12,000 feet in Tierra del Fuego.
Equatorwards the elevation diminished, and near the
equator the land probably lay somewhat lower than
now.

In South Georgia the present glaciers greatly expanded,
until practically the whole island was buried in ice, and
the same is true of the Falkland Islands and Tierra del
Fuego, only the highest peaks remaining above the ice.
In the latter district there is so'me evidence of two
glaciations separated by an interglacial,jFthe earlier
97
  98 THE EVOLUTION OF CLIMATE

glaciation being due to a regional ice-sheet and the
later to smaller valley glaciers. The intricate coast-line
of the Falkland Islands and Tierra del Fuego points to
fiord er osion by ice which extended well beyond the
present limits of the land, and can only have occurred
during considerable elevation. As to the character of
the interglacial, little is known. In the Falklands there
is a bed of black vegetable soil full of tree-trunks, indi-
cating the existence of luxuriant forests and a temperate
climate. This deposit is overlain by boulder-clay, and
may be either interglacial or pre-glacial, but since it
was formed when the land stood at a comparatively low
level, while we have reason to believe (see Chapter XII)
that during the close of the Tertiary period these
islands were greatly elevated, it is probably an inter-
glacial formation, and indicates a great amelioration of
climate. In Gable Island, Tierra del Fuego, Halle
found beneath boulder-clay a Quaternary fauna of
barnacles and marine mollusca indicating a climate
slightly warmer than the present, and this probably
belongs to the same period. To the concluding stages
of the Glacial period in the Falklands belong the curious
“ stone rivers,” great streams of moss-grown boulders
which fiU the valleys, and under the influence of
temperature changes are probably still slowly ad-
vancing.

Passing further north to the Andes, between 390 and
440 south latitude, the glaciation was not so severe,
and its records are therefore clearer. The first result
of elevation was the cutting of deep canyons by the
rivers. This was followed, possibly without much
further elevation, by a fall of temperature, which in
this connexion may be attributed to the extension of
the Antarctic and Tierra del Fuego ice-sheets. Glaciers
now developed and spread down the canyons, leaving
moraines of great volume and height, associated with aü
the other criteria of glaciation. The snow-fields from
which these glaciers originated lay between 5000 and
  CENTRAL AND SOUTH AMERICA 99

6000 feet above the sea, and the snow-line lay at about
3000 feet instead of above 6000 as at present.

This glaciation was followed by a long interglacial,
during which the glaciers retreated to the highest
summits of the Andes. The length of this period is
indicated by the fact that the earlier moraines have
been eroded to such an extent that they no longer
present distinctly the typical features of glacial topo-
graphy, while the materials of which they are composed
are decayed to somewhat the same extent as the older
moraines of North America, the granite boulders espe-
cially being rotten and friable. This interglacial was
followed by a re-development of the glaciers, but to
nothing like the same extent as formerly ; their moraines
are smaller and fresh-looking, indicating that this
glaciation was comparatively recent.

Still further north, in latitude 2o°-25° S., we come
to a region of very slight snowfall, where the snow-line
lies higher than anywhere else on the face of the earth.
The glaciation here was comparatively unimportant,
the snow-line descending only 1600 to 2500 feet.
Here Keidel found moraines of three glacial advances,
and from his description it appears probable that the
earliest and greatest was separated by a considerable
interval from the two younger, the interglacial between
which was short and not characterized by a return to
present-day climatic conditions, since during this interval
there was very little weathering. Probably we have
here to do with two glaciations, of which the second
was doublé. In fact, some writers have described no
less than five glacial advances in the Argentine Andes,
but most of these are probably merely retreat stadia.

In Peru, W. Sievers reports the existence of two
glaciations separated by a considerable interval. The
present limit of the glaciers is about 15,200 feet; during
the first glaciation they descended to about 11,000 feet,
and during the second to 12,800 feet. The evidence is
very complete. In Ecuador, H. Meyer records a similar
  IOO THE EVOLUTION OF CLIMATE

bipartition. The oldest glaciation is represented by
trough-Kke valleys, enormous gravel terraces, and old
moraines much weathered ; the limits are far below the
present limits of glaciers, but have been much obscured
by subsequent erosion. This glaciation was followed
by a long period of steppe climate resembling the
present, during which the loess-like Cangagua formation
was deposited. This in turn was followed by a re-
advance of the glaciers to a level about 2700 feet below
the present limit. This glaciation is associated with
crescent-shaped moraines, corrie lakes, hanging valleys
and gravel terraces, covered with vegetation, but other-
wise fresh-looking. The snow-line lay about 1600 feet
below the present. Probably during the first glaciation
the Andes were invaded by numerous mountain plants
and animals related to North American forms—a valuable
piece of evidence which indicates that the glaciation
was contemporaneous with that in North America. In
Columbia and Venezuela there are tracés of Glacial
periods, but these have not yet been studied in detail.
The most northerly evidence of a Glacial period comes
from the Siërra Nevada de Santa Maria, near the north
coast of Venezuela in II0 N.

Except in Tierra del Fuego and Patagonia the ice
did not extend far from the mountains. But in the
eastern Argentine there is a great series of Quaternary
deposits known as the Pampean. This formation covers
200,000 square miles, and consists of at least ninety feet
of fine loam without a single pebble (except for a few
thin calcareous layers), but containing large numbers
of complete skeletons of mammals. It raises several
interesting problems. Apparently it represents the
whole course of the Glacial period. By some- geologists
it is considered to be a delta deposit of the combined
Parana and Paraguay rivers, but the absence of mollusca,
except in a marine intercalation near its summit, is
against this view, and Steinmann attributes it to seolian
agencies and compares it to the loess of Europe and
  CENTRAL AND SOUTH AMERICA ioi

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