ANCIENT GLACIERS IN THE EASTERN HEMISPHERE.
About two million square miles of northern Europe were covered with
perennial ice during the Glacial period. From the scratches upon the
rocks, and from the direction in which material has been transported,
it is evident that the main centre of radiation is to be found in the
mountains of Scandinavia, and that the glaciers still existing in Norway
are the lineal descendants of those of the great Ice age.
So shallow are the Baltic Sea and the German Ocean, that their basins
were easily filled with ice, upon which Scandinavian boulders could be
transported westward to the east shore of England, southward into the
plains of Germany, and eastward far out upon the steppes of Russia. The
islands north of Scotland bear marks also of an ice-movement from the
direction of Norway. If Scotland itself was not overrun with Scandinavian
glaciers, the reason was that it had ice enough of its own, and from
its highlands set up a counter-movement, which successfully resisted
the invasion from the Scandinavian Peninsula. But, elsewhere in Europe,
Scandinavian ice moved freely outward to the extent of its capacity.
Then, as now also, the Alps furnished centres for ice-movement, but the
glaciers were limited to the upper portions of the valleys of the Rhône,
the Rhine, and the Danube upon the west and north, and to a still smaller
area upon the southern side.
[Illustration: Fig. 40.
MAP showing
GLACIATED AREAS
in North America and Europe.]
_Central and Southern Europe._
The main centres of ice-movement in the Alps during the Glacial period
are the same as those which furnish the lingering glaciers of the present
time. From the water-shed between the Rhine, the Rhône, and the Aar,
glaciers of immense size descended all the valleys now occupied by those
streams. The valley of the Rhône between the Bernese and the Pennine
Alps was filled with a glacier of immense depth, which was maintained
by fresh supplies from tributaries upon either side as far down as
Martigny. Glacial markings at the head of the Rhône Valley are found upon
the Schneestock,[BK] at an elevation above the sea of about 11,500 feet
(3,550 metres), or about 1,500 feet above the present surface of the
Rhône Glacier. At Fiesch, about twenty miles below, where tributaries
from the Bernese Oberland snow-fields were received, the thickness of
the glacier was upwards of 5,000 feet (1,680 metres). Near Martigny,
about fifty miles farther down the valley, where the glacier was abruptly
deflected to the north, the depth of the ice was still upwards of 1,600
metres. From Martigny northward the thickness of the ice decreased
rapidly for a few miles, where, at the enlargement of the valley above
the head of Lake Geneva, it was less than 1,200 metres in thickness, and
spread out over the intervening plain as far as Chasseron, with a nearly
level surface, transporting, as we have before said, Alpine boulders
to the flanks of the Juras, and landing them about 3,000 feet (1,275
metres) above the level of Lake Geneva. The width of the main valley is
here about fifty miles, making the slope of the surface of the ice about
twenty feet to the mile.
[Footnote BK: A. Falsan's La Période Grlaciaire étudiée principalement en
France et en Suisse, chapitre xv.]
From its "vomitory," at the head of Lake Geneva, the ice of the ancient
Rhône Glacier spread to the right and to the left, while its northern
boundary was abruptly terminated by the line of the Jura Mountains. The
law of glacial motion was, however, admirably illustrated in the height
to which the ice rose upon the flanks of the Jura. At Chasseron, in the
direct line of its onward motion, it rose to its highest point, while
both to the southwest and to the northeast, along the line of the Juras,
the ice-action was limited to constantly decreasing levels.
Down the valley of the Rhône the direction of motion was determined by
the depression of Lake Geneva, at the lower end of which it received its
main tributary from Mont Blanc, which had come down from Chamouni through
the valley of the river Arve. From this point it was deflected by a spur
of the Jura Mountains more and more southward to the vicinity of Culoz,
near the mouth of Lake Bourget. Here the glacier coming down from the
western flanks of the Alps, through the upper valley of the Isère, past
Chambéry, became predominant, and deflected the motion to the west and
north, whither the ice extended to a line passing through Bourg, Lyons,
and Vienne, leaving upon one of the eminences on which Lyons is built a
boulder several feet in diameter, which is duly preserved and labelled
in the public park in that portion of the city. Farther south, glaciers
of less extent marked the Alps most of the way to the Mediterranean, but
they were not at all comparable in size to those from the central region.
To the right of Lake Geneva the movement started by the Rhône Glacier
spread eastward, being joined in the vicinity of Berne by the confluent
ice-stream which descended from the north flank of the Bernese Oberland,
through the valley of the Aar. These united streams filled the whole
valley with ice as far down as Soleure.[BL]
[Footnote BL: See map of Rhône Glacier, on p. 58.]
[Illustration: MAP OF
GLACIAL MOVEMENTS
IN FRANCE AND
SWITZERLAND.]
Farther eastward, other ice-streams from the Alps became predominant,
one of which, moving down the Reuss, deployed out upon the country lying
north of Lucerne and Zug. Still farther down, the ancient glacier which
descended the Limmatt spread itself out over the hills and lowlands about
Zürich, one of its moraines of retrocession nearly dividing the lake into
two portions.
Guyot and others have shown that the superficial deposits of this
portion of Switzerland are just such as would be distributed by glaciers
coming down from the above-mentioned Alpine valleys. Uniting together
north of Zürich, these glaciers pushed onward as far as the Rhine below
Schaffhausen. In Frickthal the glacial ice was still 1,200 feet thick,
and at Kaisterberg between 400 and 500 feet.
At Lucerne there is a remarkable exposure of pot-holes, and a glaciated
surface such as could be produced only by the combined action of moving
ice and running water; thus furnishing to tourists an instructive
object-lesson. Among the remarkable instances of boulders transported
a long distance in Switzerland, is that of a block of granite carried
from the Valais to the vicinity of Soleure, a distance of one hundred
and fifteen miles, which weighs about 4,100 tons. "The celebrated
Pierre-à-Bot, above Neufchâtel, measures 50' × 20' × 40', and contains
about 40,000 cubic feet of stone; while the Pierre-des-Marmettes, near
Monthey, contains no less than 60,840 cubic feet."
The ancient glacier of the Rhine, receiving its initial impulse in
the same centre as that of the Rhône, fully equalled it in all its
dimensions. Descending eastward from its source near the Schneestock
to Chur, a distance of fifty miles, it turned northward and continued
forty-five miles farther to the head of Lake Constance, where it spread
out in fan-shape, extending northwest to Thiengen, below Schaffhausen,
and covering a considerable area north and northeastward of the lake,
reaching in the latter direction Ulm, upon the Danube--the whole distance
of the movement being more than one hundred and fifty miles. Through
other valleys tributary to the Danube, glaciers descended upon the upper
plains of Bavaria, from the Tyrolese Alps to the vicinity of Munich.
From Gross Glockner as a centre in the Noric Alps, vast rivers of ice,
of which the Pasterzen Glacier is the remnant, poured far down into the
valleys of the Inn and the Enns on the north and into that of the Drave
on the southeast. Farther eastward in this part of Europe the mountains
seem to have been too low to have furnished centres for any general
dispersion of glacial ice.
[Illustration: Fig. 41.--Map showing the Lines of _Débris_ extending
from the Alps into the Plains of the Po (after Lyell). _A._ Crest of
the Alpine water-shed; _B._ Névé-fields of the ancient glaciers; _C._
Moraines of ancient glaciers.]
Upon the south side of the Alps the ancient glaciers spread far out
upon the plains of Lombardy, where moraines of vast extent and of every
description enable the student to determine the exact limits of the
ancient ice-action. From the southern flanks of Mont Blanc and Monte
Rosa, and from the snow-fields of the western Alps, glaciers of great
volume descended into the valley of Dora Baltea (vale of Aosta), and
on emerging from the mountain valley Spread Out over the plains around
Ivrea, leaving moraine hills in some instances 1,500 feet in height.
The total length of this glacier was as much as one hundred and twenty
miles. From the snow-fields in the vicinity of Mont Cenis, also, glaciers
extended down the Dora Ripera to the vicinity of Turin, and down other
valleys to a less extent. The lateral moraines of the Diore, on the south
side of Mont Blanc, at the head of the Dora Baltea, are 2,000 feet above
the present river, and extend upon the left bank for a distance of twenty
miles.
From the eastern Alps, glaciers descended through all the valleys of the
Italian lakes and deposited vast terminal moraines, which still obstruct
the drainage, and produce the charming lakes of that region. A special
historic interest pertains to the series of concentric moraines south of
Lake Garda, since it was in the reticulations of this glacial deposit
that the last great battle for Italian liberty was fought on June 24,
1859. Defeated in the engagements farther up the valley of the Po, the
Austrian general Benedek took his final stand to resist the united forces
of France and Italy behind an outer semicircle of the moraine hills south
of this lake (some of which are 500 or 600 feet above the surrounding
country), with his centre at Solferino, about ten miles from Peschera.
Here, behind this natural fortification, he awaited the enemy, who was
compelled to perform his manoeuvres on the open plain which spread out
on every side. But the natural fortifications furnished by the moraine
hills were too extensive to be defended by an army of moderate size.
The troops of Napoleon and Victor Immanuel concentrated at Solferino
and broke through the line. Thus the day was lost to the Austrians, and
they retired from Lombardy, leaving to Italy both the artificial and the
natural fortifications that guard the southern end of this important
entrance to the Tyrolese Alps. When once his attention is called to the
subject, the traveller upon the railroad cannot fail to notice this
series of moraines, as he enters it through a tunnel at Lonato on the
west, and emerges from it at Soma Campagna, eighteen or twenty miles
distant to the east. A monument celebrating the victory stands upon a
moraine hill about half-way between, at Martino della Battaglie.
In other portions of central and southern Europe the mountains were too
low to furnish important centres for glacial movements. Still, to a
limited extent, the signs of ancient glaciers are seen in the mountains
of the Black Forest, in the Harz and Erzgebirge, and in the Carpathians
on the east and among the Apennines on the south. In Spain, also, there
were limited ice-fields on the higher portions of the Sierra Nevada
and in the mountains of Estremadura, and perhaps in some other places.
In France, small glaciers were to be found in the higher portions
of the Auvergne, of the Morvan, of the Vosges, and of the Cevennes;
while, from the Pyrenees, glaciers extended northward throughout nearly
their whole extent. The ice-stream descending from the central mass of
Maladetta through the upper valley of the Garonne, was joined by several
tributaries, and attained a length of about forty-five miles.
_The British Isles._
During the climax of the Glacial period the Hebrides to the north of
Scotland were covered with ice to a depth of 1,600 feet. How far westward
of this it moved out to the sea, it is of course impossible to tell. But
in the channels between the Hebrides and Scotland it is evident that
the water was completely expelled by the ice, and that, from a height
of 1,600 feet above the Hebrides to the northern shores of Scotland,
there was a continuous ice-field sloping southward at the rate of about
twenty-five feet a mile.
Scotland itself was completely enveloped in glacial ice. Prevented by
the Scandinavian Glacier from moving eastward, the Scotch movement was
compelled to be westward and southward. On the southwest the ice-stream
reached the shores of Ireland, and became confluent with the glaciers
that enveloped that island, completely filling the Irish Sea.
There are so many controverted points respecting the glacial geology of
England, and they have such an important bearing upon the main question
of this volume, that a pretty full discussion of them will be necessary.
I have recently been over enough of the ground myself to become satisfied
of the general correctness of the views entertained by my late colleague,
the lamented Professor Henry Carvill Lewis, whose death in 1888 took
place before the publication of his most mature conclusions. But the
lines of investigation to which he gave so powerful an impulse have since
been followed out by an active body of scientific observers. To give the
statement of facts greater precision and authority, I have committed
the preparation of it to the Secretary of the Northwest of England
Boulder Committee, Percy F. Kendall, F. G. S., Lecturer on Geology at
the Yorkshire College, Leeds, and at the Stockport Technical School,
England.[BM]
[Footnote BM: Mr. Kendall's contribution extends to page 181.]
"All the characteristic evidences of the action of land-ice can be found
in the greatest perfection in many parts of England and Wales. Drumlins,
kames, _roches moutonnées_, far-travelled erratics, terminal moraines,
and perched blocks, all occur. There are, besides, in the wide-spread
deposits of boulder-clay which cover so many thousands of square miles on
the low grounds lying on either side of the Pennine chain, evidences of
the operation of ice-masses of a size far exceeding that of the grandest
of existing European glaciers. But, while the proofs of protracted
and severe glaciation are thus patent, there are, nevertheless, many
apparently anomalous circumstances which arrest the attention when the
whole country is surveyed. The glacial phenomena appear to be strictly
limited to the country lying to the northward of a line extending from
the Bristol Channel to the mouth of the Thames; and within the glaciated
area there are many extensive tracts of land devoid of 'drift' or other
indications of ice-action.
"By comparison with the phenomena displayed in the North American
continent, English glacial geology must seem puny and insignificant; but,
just as with the features of the 'Solid Geology,' we have compressed
within the narrow limits of our isles an epitome of the features which
across the Atlantic require a continent for their exposition. It has
resulted from this concentration that English geology requires a much
closer and more minute investigation. And the difficulty which has been
experienced by glacial geologists of dealing with an involved series of
facts has, in the absence of any clue leading to the co-ordination of a
vast series of more or less disconnected observations, resulted in the
adoption, to meet certain local anomalies, of explanations which were
very difficult if not impossible of reconciliation with facts observed
in adjacent areas. Thus, to account for shell-bearing drift extending up
to the water-shed on one side of a lofty range of hills, a submergence
of the land to a depth of 1,400 feet has been postulated; leaving for
independent explanation the fact, that the opposite slopes of the hills
and the low ground beyond were absolutely destitute of drift or of any
evidence of marine action.
"In the following pages I must adopt a somewhat dogmatic tone, in order
to confine myself within the limits of space which are imposed; and trust
rather to the cohesion and consistency of the explanations offered and
to a few pregnant facts than to the weighing and contrasting of rival
theories.
"The facts point conclusively to the action in the British Isles of
a series of glaciers radiating outward from the great hill chains or
clusters, and, as the refrigeration progressed, becoming confluent and
moving though in the same general direction, yet with less regard to the
minor inequalities of the ground. During these two stages many glaciers
must have debouched upon the sea-coast, with the consequent production of
icebergs, which floated off with loads of boulders and dispersed them in
the random fashion which is a necessary characteristic of transport by
floating ice.
"With a further accentuation of the cold conditions the discharge of
bergs from terminal fronts which advanced into the extremely shallow
seas surrounding the British shores would be quite inadequate to relieve
the great press of ice, and a further coalescence of separate elements
must have resulted. In the case of enclosed seas--as, for example, the
Irish Sea--the continued inthrust of glacier-ice would expel the water
completely; and the conjoined ice-masses would take a direction of flow
the resultant of the momentum and direction of the constituent elements.
In other cases--as, for example, in the North Sea--extraneous ice
approaching the shores might cause a deflection of the flow of the native
glaciers, even though the foreign ice might never actually reach the
shore.
"To such a system of confluent glaciers, and to the separate elements
out of which they grew, and into which, after the culmination, they were
resolved, I attribute the whole of the phenomena of the English and Welsh
drift. And only at one or two points upon the coast, and raised but
little above the sea-level, can I recognise any signs of marine action.
"_The Preglacial Level of the Land._--There is very little direct
evidence bearing upon this point. In Norfolk the famous forest bed, with
its associated deposits, stands at almost precisely the level which it
occupied in preglacial times. At Sewerby, near Flamborough Head, there
is an ancient beach and 'buried cliff' which the sea is now denuding of
its swathing of drift-deposits, and its level can be seen to be almost
absolutely coincident with the present beach. Mr. Lamplugh, whose
description of the 'Drifts of Flamborough Head,'[BN] constitutes one of
the gems of glacial literature, considers that there is clear evidence
that the land stood at this level for a long period. The beach is covered
by a rain-wash of small extent, and that in turn by an ancient deposit
of blown sand, while the lowest member of the drift series of Yorkshire
covers the whole. Mr. Lamplugh thinks that the blown sand may indicate
a slight elevation of the land; but the beach appears to me to be the
storm beach, and the reduction in the force of the waves such as would
result from the approach of an ice-front a few miles to the seaward would
probably produce the necessary conditions.
[Footnote BN: Quarterly Journal of the Geological Society, vol. xlvii.]
"Six miles to the northward of Flamborough, at Speeton, a bed of
estuarine silt containing the remains of mollusca in the position of life
occurs at an altitude of ninety feet above high-water mark. Mr. Lamplugh
inclines to the opinion that this bed is of earlier date than the 'buried
cliff'; he also admits the possibility that its superior altitude may be
due to a purely local upward bulging of the soft Lower Cretaceous clays
upon which the estuarine bed rests by the weight of the adjacent lofty
chalk escarpment.
"The evidence obtained from inland sections and borings in different
parts of England has been taken to indicate a greater altitude in
preglacial times. Thus, in Essex, deep-borings have revealed the
existence of deep drift-filled valleys, having their floors below
sea-level. The valley of the Mersey is a still better example. Numerous
borings have been made in the neighbourhood of Widnes and at other places
in the lower reaches of the river, making it clear that there is a
channel filled with drift and extending to 146 feet below mean sea-level.
This, with several other instances, has been taken to indicate a greater
altitude for the land in preglacial times, since a river could not
erode its channel to such a depth below sea-level. The argument appears
inconclusive for one principal reason: no mention is made of any river
gravels or other alluvium in the borings. Indeed, there is an explicit
statement that the deposits are all glacial, showing that the channel
must have been cleared out by ice. This, therefore, leaves open the
vital question, whether the deposits removed were marine or fluviatile.
It may be remarked that the great estuary of the Mersey has undoubtedly
been produced by a post-glacial (and probably post-Roman) movement of
depression.
"_The Preglacial Climate._--In all speculations regarding the cause
of the Glacial epoch, due account must be taken of the undoubted fact
that it came on with extreme slowness and departed with comparative
suddenness. In the east of England an almost perfect and uninterrupted
sequence of deposits is preserved, extending from the early part of the
Pliocene period down to the present day.
"These in descending order are:
"1. Post-glacial sands, gravels, etc.
"2. Glacial series.
"3. The 'Forest Bed' and associated marine deposits.
"4. Chillesford clay and sand.
"5. The many successive stages of the Red Crag. (The Norwich Crag is a
local variation of the upper part of the Red Crag.)
"6. The Coralline Crag.
"The fossils preserved in these deposits, apart from the physical
indications, exhibit the climatal changes which accompanied their
deposition. The Coralline Crag contains a fauna consisting mainly
of species which now range to the Mediterranean, many of them being
restricted to the warm southern waters. Associated with these are a few
boreal forms, but they are represented in general by few individuals.
Here and there in the deposits of this age far-travelled stones are to
be found, but they are always accounted great rarities.
"The Red Crag consists of an irregular assemblage of beaches and
sand-banks of widely different ages, but their sequence can be made out
with ease by a study of the fauna. In the oldest deposits, Mediterranean
species are very numerous, while the boreal forms are comparatively rare;
but in successive later deposits the proportions are very gradually
reversed, and from the overlying Chillesford series the Mediterranean
species are practically absent. The physical indications run _pari
passu_ with the paleontological, and in the newer beds of the Red Crag
far-travelled stones are common.
"In the Forest Bed series there is a marine band--the _Leda myalis_
bed--which contains an almost arctic assemblage of shells; while at about
the same horizon plant remains have been found, including such high
northern species as _Salix polaris_ and _Betula nana_.
"The glacial deposits do not, in my opinion, contain anywhere in England
or Wales a genuine intrinsic fauna, such shells as occur in the East
Anglian glacial deposits having been derived in part from a contemporary
sea-bed, and, for the rest, from the older formations, down perhaps to
the Coralline Crag. In the post-glacial deposits we have hardly any trace
of a survival of the boreal forms, and I consider that the whole marine
fauna of the North Sea was entirely obliterated at the culmination of the
Glacial epoch, and that the repeopling in post-glacial times proceeded
mainly from the English Channel, into which the northern forms never
penetrated.
"_The Great Glacial Centres._
"Where such complex interactions have to be described as were produced
by the conflicting glaciers of the British Isles it is difficult to
deal consecutively with the phenomena of any one area, but with short
digressions in explanation of special points it may be possible to
accomplish a clear presentation of the facts.
"_Wales._--The phenomena of South Wales are comparatively simple. Great
glaciers travelled due southward from the lofty Brecknock Beacons,
and left the characteristic _moutonnée_ appearance upon the rocky bed
over which they moved. The boulder-transport is in entire agreement
with the other indications, and there are no shells in the drift. The
facts awaiting explanation are the occurrence in the boulder-clays of
Glamorganshire, at altitudes up to four hundred feet, of flints, and of
igneous rocks somewhat resembling those of the Archæan series of the
Wrekin. At Clun, in Shropshire, a train of erratics (see map) has been
traced back to its source to the westward. On the west coast, in Cardigan
Bay, the boulders are all such as might have been derived from the
interior of Wales. At St. David's Peninsula, Pembrokeshire, striæ occur
coming in from the northwest, and, taken with the discovery of boulders
of northern rocks, may point to a southward extension of a great glacier
produced by confluent sheets that choked the Irish Sea. Information
is very scanty regarding large areas in mid-Wales, but such as can be
gathered seems to point to ice-shedding having taken place from a north
and south parting line. In North Wales, much admirable work has been done
which clearly indicates the neighbourhood of Great Arenig (Arenig Mawr)
as the radiant point for a great dispersal of blocks of volcanic rock of
a characteristic Welsh type.
"_Ireland._--A brief reference must be made to Ireland, as the ice which
took origin there played an important part in bringing about some strange
effects in English glaciation, which would be inexplicable without a
recognition of the causes in operation across the Irish Sea. Ireland
is a great basin, surrounded by an almost continuous girdle of hills.
The rainfall is excessive, and the snow-fall was probably more than
proportionately great; therefore we might expect that an ice-sheet of
very large dimensions would result from this combination of favouring
conditions. The Irish ice-sheet appears to have moved outward from about
the centre of the island, but the main flow was probably concentrated
through the gaps in the encircling mountains.
"_Galloway._--The great range of granite mountains in the southwestern
corner of Scotland seems to have given origin to an immense mass of ice
which moved in the main to the southward, and there are good grounds
for the belief that the whole ice-drainage of the area, even that which
gathered on the northern side of the water-shed, ultimately found its
way into the Irish Sea basin and came down coastwise and across the low
grounds of the Rinns of Galloway, being pushed down by the press of
Highland ice which entered the Firth of Clyde. It is a noteworthy fact
that marine shells occur in the drift in the course taken by the ice
coming on to the extremity of Galloway from the Clyde.
"_The Lake District._--A radial flow of ice took place down the valleys
from about the centre of the Cumbrian hill-plexus, but movement to the
eastward was at first forbidden by the great rampart of the Cross Fell
escarpment, which stretches like a wall along the eastern side of the
Vale of Eden.
"During the time when the Cumbrian glaciers had unobstructed access
to the Solway Frith, to the Irish Sea, and to Morecambe Bay, the
dispersal of boulders of characteristic local rocks would follow the
ordinary drainage-lines; but, as will be shown later, a state of affairs
supervened in the Irish Sea which resulted, in many cases, in a complete
reversal of the ice-flow.
"_The Pennine Chain_ was the source of glaciers of majestic dimensions
upon both its flanks in the region north of Skipton, but to the southward
of that breach in the chain (see map) no evidence is obtainable of any
local glaciers.
"_The Confluent Glaciers._
"With the growth of ice-caps upon the great centres a condition of
affairs was brought about in the Irish Sea productive of results which
will readily be foreseen. The enormous volumes of ice poured into
the shallow sea from north, south, east, and west, resulted in such
a congestion as to necessitate the initiation of some new systems of
drainage.
"_The Irish Sea Glacier._--The ice from Galloway, Cumbria, and Ireland
became confluent, forming what the late Professor Carvill Lewis termed
'the Irish Sea Glacier,' and took a direction to the southward. Here it
came in diametrical conflict with the northward-flowing element of the
Welsh sheet, which it arrested and mastered; and the Irish Sea Glacier
bifurcated, probably close upon the precipitous Welsh coast to the
eastward of the Little Orme's Head, and the two branches flowed coastwise
to eastward and westward, keeping near the shore-line.
"The westerly branch swept round close to the coast in a southwesterly
direction, and completely overrode Anglesea; striating the rock-surfaces
from northeast to southwest (see map), and strewing the country with
its bottom-moraine, containing characteristic northern rocks, such
as the Galloway granites, the lavas and granites of the central and
western portions of the Lake District, and fragments of shells derived
from shell-banks in the Irish Sea. One episode of this phase of the
ice-movement was the invasion of the first line of hills between the
Menai Straits and Snowdon. The gravels and sands of Fridd-bryn-mawr,
Moel Tryfaen, and Moel-y-Cilgwyn, are the coarser washings of the
bottom-moraine, and consequently contain such rock-fragments and shells
as characterise it. From Moel-y-Cilgwyn southward, evidence is lacking
regarding the course taken by the glacier, but it probably passed over or
between the Rivals Mountains (Yr Eifl), and down Cardigan Bay at some
distance from the coast in confluence with the ice from mid-Wales; and,
as I have suggested, may have passed over St. David's Head.
"Returning now towards the head of the glacier we may follow with
advantage its left bank downward. The ice-flow on the Cumberland coast
appears to have resembled very much that in North Wales. A great press of
ice from the northward (Galloway) seems to have had a powerful 'easting'
imparted to it by the conjoint influences of the thrust of the Irish ice
and the inflow of ice from the Clyde. Whatever may have been the cause,
the effect is clear: about Ravenglass cleavage took place, and a flow to
northward and to southward, each bending easterly. By far the larger mass
took a southerly course and bent round Black Combe, over Walney, and a
strip of the mainland about Barrow in Furness, and out into and across
Morecambe Bay. Its limits are marked in the field by the occurrence of
the same rocks which characterise it in Anglesea, viz., the granites of
Galloway and of west and central Cumbria.
"The continued thrust shouldered in the glacier upon the mainland of
Lancashire, but the precise point of emergence has not yet been traced,
though it cannot be more than a few miles from the position indicated on
the map. I should here remark, that all along the boundaries the Irish
Sea Glacier was confluent with local ice, except, probably, in that part
of the Pennine chain to the southward of Skipton. Down to Skipton there
was a great mass of Pennine ice which was compelled to take an almost
due southerly course, and thus to run directly athwart the direction of
the main hills and valleys. A sharp easterly inflection of the Irish Sea
Glacier carried it up the valley of the Ribble, and thence, under the
shoulder of Pendle, to Burnley, where Scottish granites are found in the
boulder-clay.
"On the summit of the Pennine water-shed, at Heald Moor, near Todmorden
(1,419 feet), boulder-clay has been found containing erratics belonging
to this dispersion; while in the gorge of the Yorkshire Calder, which
flows along the eastern side of the same hill, not a vestige of such a
deposit is to be found, saving a few erratic pebbles at a distance of
eight or ten miles, which were probably carried down by flood-wash from
the edge of the ice.
"From this point the limits of the ice may be traced along the flanks of
the Pennine chain at an average altitude of about 1,100 feet.
"At one place the erratics can be traced to a position which would
indicate the formation of an extra-morainic lake having its head at a
col about 1,000 feet above sea-level, separating it from the valley of
an eastward-flowing stream, the Wye, about twelve miles down which a few
granite blocks have been found. Other extra-morainic lakes must have
been formed, but very little information has been collected regarding
them. The Irish Sea Glacier can be shown to have spread across the whole
country to the westward of the line I have traced, and beyond the estuary
of the Dee.
"I may now follow its boundaries on the Welsh coast, and pursue the line
to the final melting-place of the glacier. From the Little Orme's Head
the line of confluence with the native ice is pretty clearly defined. It
runs in, perhaps, half a mile from the shore, until the broad low tract
of the Vale of Clwyd is reached. Here the northern ice obtained a more
complete mastery, and pushed in even as far as Denbigh. This extreme
limit was probably attained as a mere temporary episode. Horizontal striæ
on a vertical face of limestone on the crags dominating the mouth of the
vale on the eastern side attest beyond dispute the action of a mass of
land-ice moving in from the north.
"I may here remark, that in this district the deposits furnish a very
complete record of the events of the Glacial period. In the cliffs on
the eastern side of the Little Orme's Head, and at several other points
along the coast towards the east, a sequence may be observed as follows:
"4. Boulder-clay with northern erratics and shells.
"3. Sands and gravels with northern erratics and shells.
"2. Boulder-clay with northern erratics and shells.
"1. Boulder-clay with Welsh erratics and no shells.
"A similar succession is to be seen in the Vale of Clwyd. The
interpretation is clear: In the early stages of glaciation the Welsh
ice spread without hindrance to, and laid down, bed No. 1; then the
northern ice came down, bringing its typical erratics and the scourings
of the sea-bottom, and laid down the variable series of clays, sands, and
gravels which constitute Nos. 2, 3, and 4 of the section.
[Illustration: Fig. 42.--The Cefn Cave, in Vale of Clwyd. (Trimmer.) _a_,
Entrance; _b_, mud with pebbles and wood covered with stalagmite; _c_,
mud, bones, and angular fragments of limestone; _d_, sand and silt, with
fragments of marine shells; _e_, fissure; _f_, northern drift; _g_, cave
cleared of mud; _h_, river Elwy, 100 feet below; _i_, limestone rock.]
"In the Vale of Clwyd an additional interest is imparted to the study of
the drift from the circumstance that the remains of man have been found
in deposits in caves sealed with drift-beds. The best example is the Cae
Gwyn caves, in which flint implements and the bones and teeth of various
extinct animals were found embedded in 'cave-earth' which was overlaid
by bedded deposits of shell-bearing drift, with erratics of the northern
type.
"It has been supposed that the drift-deposits were marine accumulations;
but it is inconceivable that the cave could ever have been subjected to
wave-action without the complete scouring out of its contents.
"To resume the delineation of the limits of the great Irish Sea Glacier:
From the Vale of Clwyd the boundary runs along the range of hills
parallel to the estuary of the Dee at an altitude of about nine hundred
feet. As it is traced to the southeast it gradually rises, until at
Frondeg, a few miles to the northward of the embouchure of the Yale of
Llangollen, it is at a height of 1,450 feet above sea-level. Thence it
falls to 1,150 feet at Gloppa, three miles to the westward of Oswestry,
and this is the most southerly point to which it has been definitely
traced on the Welsh border, though scattered boulders of northern rocks
are known to occur at Church Stretton.
"Along the line from the Vale of Clwyd to Oswestry the boundary is
marked by a very striking series of moraine-mounds. They occur on the
extreme summits of lofty hills in a country generally almost driftless,
and their appearance is so unusual that one--Moel-y-crio--at least
has been mistaken for an artificial tumulus. The limitation of the
dispersal of northern erratics by these mounds is very clear and
sharp; and Mackintosh, in describing those at Frondeg, remarked that,
while no northern rocks extended to the westward of them, so no Welsh
erratics could be found to cross the line to the eastward. There are
Welsh erratics in the low grounds of Cheshire and Shropshire, but their
distribution is sporadic, and will be explained in a subsequent section.
"Having thus followed around the edges of this glacier, it remains to
describe its termination. It is clear that the ice must have forced its
way over the low water-shed between the respective basins of the Dee and
the Severn. So soon as this ridge (less than 500 feet above the sea)
is crossed, we find the deposits laid down by the glacier change their
character, and sands and gravels attain a great predominance.[BO] Near
Bridgenorth, and, at other places, hills composed of such materials
attain an altitude of 200 feet. From Shrewsbury _via_ Burton, and thence,
in a semicircular sweep, through Bridgenorth and Enville, there is an
immense concentration of boulders and pebbles, such as to justify the
designation of a terminal moraine. To the southward, down the valley
of the Severn, existing information points to the occurrence merely of
such scattered pebbles as might have been carried down by floods. In the
district lying outside this moraine there is a most interesting series of
glacial deposits and of boulders of an entirely different character. (See
map.)
[Footnote BO: Mackintosh, Q. J. G. S.]
"From the neighbourhood of Lichfield, through some of the suburbs of
Birmingham, and over Frankley Hill and the Lickey Hills to Bromsgrove,
there is a great accumulation of Welsh erratics, from the neighbourhood,
probably, of Arenig Mawr.
"The late Professor Carvill Lewis suggested that these Arenig rocks
might have been derived from some adjacent outcrop of Palæozoic rocks--a
suggestion having its justification in the discoveries that had been made
of Cumbrian rocks in the Midlands. To test the matter, an excavation was
made at a point selected on Frankley Hill, and a genuine boulder-clay
was found, containing erratics of the same type as those found upon the
surface.
"The explanation has since been offered that this boulder-clay was a
marine deposit laid down during a period of submerge nee.[BP] Apart
from the difficulty that the boulder-clay displays none of the ordinary
characteristics of a marine deposition, but possesses a structure,
or rather absence of structure, in many respects quite inconsistent
with such an origin, and contains no shells or other remains of marine
creatures, it must be pointed out that no theory of marine notation
will explain the distribution of the erratics, and especially their
concentration in such numbers at a station sixty or seventy miles from
their source.
[Footnote BP: Proceedings of the Birmingham Philosophical Society, vol.
vi, Part I, p. 181.]
"Upon the land-ice hypothesis this difficulty disappears. During the
early stages of the Glacial period the Welsh ice had the whole of
the Severn Valley at its mercy, and a great glacier was thrust down
from Arenig, or some other point in central Wales, having an _initial
direction_, broadly speaking, from west to east. This glacier extended
across the valley of the Severn, sweeping past the Wrekin, whence it
carried blocks of the very characteristic rocks to be lodged as boulders
near Lichfield; and it probably formed its terminal moraine along the
line indicated. (See lozenge-shaped marks on the map.) As the ice in
the north gathered volume it produced the great Irish Sea Glacier,
which pressed inland and down the Vale of Severn in the manner I have
described, and brushed the relatively small Welsh stream out of its path,
and laid down its own terminal moraine in the space between the Welsh
border and the Lickey Hills. It seems probable that the Welsh stream
came mainly down the Vale of Llangollen, and thence to the Lickey Hills.
Boulders of Welsh rocks occur in the intervening tract by ones and twos,
with occasional large clusters, the preservation of any more connected
trail being rendered impossible by the great discharge of water from
the front of the Irish Sea Glacier, and the distributing action of the
glacier itself.
"Within the area in England and Wales covered by the Irish Sea Glacier
all the phenomena point to the action of land-ice, with the inevitable
concomitants of subglacial streams, extra-morainic lakes, etc. There is
nothing to suggest marine conditions in any form except the occurrence
of shells or shell fragments; and these present so many features of
association, condition, and position inconsistent with, what we should
be led to expect from a study of recent marine life, that conchologists
are unanimous in declaring that not one single group of them is on the
site whereon the shells lived. It is a most significant fact--one out of
a hundred which could be cited did space permit--that in the ten thousand
square miles of, as it is supposed, recently elevated sea-bottom, not a
single example of a bivalve shell with its valves in apposition has ever
been found! Nor has a boulder or other stone been found encrusted with
those ubiquitous marine parasites, the barnacles.
"The evidences of the action of land-ice within the area are everywhere
apparent in the constancy of direction of-- (1.) Striæ upon rock
surfaces. (2.) The terminal curvature of rocks. (3.) The 'pull-over' of
soft rocks. (4.) The transportal of local boulders. (5.) The orientation
of the long axes of large boulders. (6.) The false bedding of sands
and gravels. (7.) The elongation of drift-hills. (8.) The relations
of 'crag and tail.' There is a similar general constancy, too, in the
directions of the striæ upon large boulders. Upon the under side they run
longitudinally from southeast (or thereabouts) to northwest, while upon
the upper surface they originate at the opposite end, showing that the
scratches on the under side were produced by the stone being dragged from
northwest to southeast, while those on the top were the product of the
passage of stone-laden ice over it in the same direction.
"Such an agreement cannot be fortuitous, but must be attributed to the
operation of some agent acting in close parallelism over the whole
area. To attribute such regularity to the action of marine currents is
to ignore the most elementary principles of marine hydrology. Icebergs
must, in the nature of things, be the most erratic of all agents, for
the direction of drift is determined--among other varying factors--by
the draught of the berg. A mass of small draught will be carried by
surface currents, while one of greater depth will be brought within the
influence of under-currents; and hence it not infrequently happens that
while floe-ice is drifting, say, to the southeast, giant bergs will go
crashing through it to the northwest. There are tidal influences also to
be reckoned with, and it is matter of common knowledge that flotsam and
jetsam travel back and forth, as they are alternately affected by ebb and
flood tide.
"Bearing these facts in mind, it is surely too much to expect that
marine ice should transport boulders (how it picked up many of them also
requires explanation) with such unfailing regularity that it can be said
without challenge,[BQ] 'boulders in this district [South Lancashire and
Cheshire] never occur to the north or west of the parent rock.' The
same rule applies without a single authentic exception to the whole
area covered by the eastern branch of the Irish Sea Glacier; and hence
it comes about that not a single boulder of Welsh rock has ever been
recorded from Lancashire.
[Footnote BQ: Brit. Assoc. Report, 1890, p. 343.]
"_The Solway Glacier._--The pressure which forced much of the Irish Sea
ice against the Cumbrian coast-line caused, as has been described, a
cleavage of the flow near Ravenglass, and, having followed the southerly
branch to its termination in the midlands, the remaining moiety demands
attention.
"The 'easting' motion carried it up the Solway Frith, its right flank
spreading over the low plain of northern Cumberland, which it strewed
with boulders of the well-known 'syenite' (granophyre) of Buttermere.
When this ice reached the foot of the Cross Fell escarpment, it suffered
a second bifurcation, one branch pushing to the eastward up the valley
of the Irthing and over into Tyneside, and the other turning nearly due
southward and forcing its way up the broad Vale of Eden.
"Under the pressure of an enormous head of ice, this stream rose from
sea-level, turned back or incorporated the native Cumbrian Glacier
which stood in its path, and, having arrived almost at the water-shed
between the northern and the southern drainage, it swept round to the
eastward and crossed over the Pennine water-shed; not, however, by the
lowest pass, which is only some 1,400 feet above sea-level, but by the
higher pass of Stainmoor, at altitudes ranging from 1,800 to 2,000
feet. The lower part of the course of this ice-flow is sufficiently
well characterised by boulders of the granite of the neighbourhood of
Dalbeattie in Galloway; but on its way up the Vale of Eden it gathered
several very remarkable rocks and posted them as way-stones to mark its
course. One of these rocks, the Permian Brockram, occurs nowhere _in
situ_ at altitudes exceeding 700 feet, yet in the course of its short
transit it was lifted about a thousand feet above its source. The Shap
granite (see radiant point on map) is on the northern side of the east
and west water-sheds of the Lake District, and reaches its extreme
elevation, (1,656 feet) on Wasdale Pike; yet boulders of it were carried
over Stainmoor, at an altitude of 1,800 feet literally by tens of
thousands.
"This Stainmoor Glacier passed directly over the Pennine chain, past the
mouths of several valleys, and into Teesdale, which it descended and
spread out in the low grounds beyond. Pursuing its easterly course, it
abutted upon the lofty Cleveland Hills and separated into two streams,
one of which went straight out to sea at Hartlepool, while the other
turned to the southward and flowed down the Vale of York, being augmented
on its way by tributary glaciers coming down Wensleydale. The final
melting seems to have taken place somewhere a little to the southward
of York; but boulders of Shap granite by which its extension is
characterised have been found as far to the southward as Royston, near
Barnsley.
"The other branch of the Solway Glacier--that which travelled due
eastward--passed up the valley of the Irthing, and over into that of the
Tyne, and out to sea at Tynemouth. It carried the Scottish granites with
it, and tributary masses joined on either hand, bringing characteristic
boulders with them.
"The fate of those elements of the Solway Frith Glacier which reached
the sea is not left entirely to conjecture. The striated surfaces near
the coast of Northumberland indicate a coastwise flow of ice from the
northward--probably from the Frith of Forth--and the glaciers coming out
from the Tyne and Tees were deflected to the southward.
"There is conclusive evidence that this ice rasped the cliffs of the
Yorkshire coast and pressed up into some of the valleys. Where it passed
the mouth of the Tees near Whitby it must have had a height of at least
800 feet, but farther down the coast it diminished in thickness. It
nowhere extended inland more than a mile or two, and for the most part
kept strictly to the coast-line. Along the whole coast are scattered
erratics derived from Galloway and the places lying in the paths of the
glaciers. In many places the cliffs exhibit signs of rough usage, the
rocks being crumpled and distorted by the violent impact of the ice. At
Filey Brigg a well-scratched surface has been discovered, the striation
being from a few degrees east of north.
"At Speeton the evidence of ice-sheet or glacier-work is of the most
striking character. On the top of the cliffs of Cretaceous strata a line
of moraine-hills has been laid down, extending in wonderful perfection
for a distance of six miles. They consist of a mixture of sand,
gravel, and a species of clay-rubble, with occasional masses of true
boulder-clay, the whole showing the arched bedding so characteristic
of such accumulations. At the northerly end the moraine keeps close to
the edge of the chalk cliffs, which are there 400 feet high, and the
hills are frequently displayed in section; but as the elevation of the
cliffs declines they fall back from the edge of the cliffs and run quite
across the headland of Flamborough, and are again exposed in section in
Bridlington Bay. One remarkable and significant fact is pointed out,
namely, that behind this moraine, within half a mile and at a lower
level, the country is almost absolutely devoid of any drift whatever.
[Illustration: Fig. 43.--Moraine between Speeton and Flamborough
(Lamplugh).]
"The interpretation of these phenomena is as follows: When the
valley-glaciers reached the sea they suffered the deflection which has
been mentioned, partly as the result of the interference of ice from
the east of Scotland, but also influenced directly by the cause which
operated upon the Scottish ice and gave direction to it--that is, the
impact of a great glacier from Scandinavia, which almost filled the North
Sea, and turned in the eastward-flowing ice upon the British coast.
"It is easy to see how this pressure must have forced the glacier-ice
against the Yorkshire coast, but vertical chalk cliffs 400 feet in
height are not readily surmounted by ice of any thickness, however
great, and so it coasted along and discharged its lateral moraine upon
the cliff-tops. As the cliffs diminished in height we find the moraine
farther inland, and, as I have pointed out, the ice completely overrode
Flamborough Head. Amongst the boulders at Flamborough are many of Shap
granite, a few Galloway granites, a profusion of Carboniferous rocks,
brought by the Tyne branch of the Sol way Glacier as well as by that of
Stainmoor, and, besides many torn from the cliffs of Yorkshire, a few
examples of unquestionable Scandinavian rocks, such as the well-known
_Rhomben-porphyr_. It is important to note that about ten to twenty
miles from the Yorkshire coast there is a tract of sea-bottom called
by trawlers 'the rough ground,' in allusion to the fact that it is
strewn with large boulders, amongst which are many of Shap granite. This
probably represents a moraine of the Teesdale Glacier, laid down at a
time when the Scandinavian Glacier was not at its greatest development.
"On the south side of Flamborough Head the 'buried cliff' previously
alluded to occurs. The configuration of the country shows--and the
conclusion is established by numerous deep-borings--that the preglacial
coast-line takes a great sweep inland from here, and that the plain of
Holderness is the result of the banking-up of an immense thickness of
glacial _débris_. In the whole country reviewed, from Tynemouth to
Bridlington, wherever the ice came on to the land from the seaward, it
brought in shells and fragmentary patches of the sea-bottom involved in
its ground moraine. Space does not permit of a detailed description of
the several members of the Yorkshire Drift, and I pass on to deal in a
general way with the glacial phenomena of the eastern side of England.
"_The East Anglian Glacier._--The influence of the Scandinavian ice is
clearly seen in the fact that the entire ice-movement down the east
coast south of Bridlington was all from the _seaward_. Clays, sands, and
gravels, the products of a continuous mass of land-ice coming from the
northeast are spread over the whole country, from the Trent to the high
grounds on the north of London overlooking the Thames.
"The line of extreme extension of these drift-deposits runs from Finchley
(near London), in the south across Hertfordshire, through Cambridgeshire,
with outlying patches at Gogmagog and near Buckingham, and northwestward
over a large portion of Leicestershire into the upper waters of the
Trent, embracing the elevated region of Palæozoic rocks at Charnwood
Forest, near Leicester.
"Reserving the consideration of the very involved questions connected
with the drifts of the upper part of the Trent Valley, I may pass
on to join the phenomena of the southeastern counties with those at
Flamborough Head. From Nottinghamshire the limits of the drift of the
East Anglian Glacier seem to run in a direction nearly due west to east,
for the great oolitic escarpment upon which Lincoln Cathedral is built
is absolutely driftless to the northward of the breach about Sleaford.
However, along the western flank of the oolitic range true boulder-clay
occurs, bordering and doubtless underlying the great fen-tract of
mid-Lincolnshire; and the great Lincolnshire Wolds appear to have been
completely whelmed beneath the ice.
"The most remarkable of the deposits in this area is the Great Chalky
Boulder-Clay, which consists of clay containing much ground-up chalk,
and literally packed with well-striated boulders of chalk of all sizes,
from minute pebbles up to blocks a foot or more in diameter. Associated
with them are boulders of various foreign rocks, and many flints in a
remarkably fresh condition, and still retaining the characteristic white
coat, except where partially removed by glacial attrition.
"One of the perplexing features of the glacial phenomena in the eastern
counties of England is the extension of true chalky boulder-clay to the
north London heights at Finchley and elsewhere; for only the faintest
traces are to be found in the gravel deposits of the Thames Valley of any
wash from such a deposit, or from a glacier carrying such materials.
"It has been suggested that the deposit may have been laid down in an
extra-morainic lake, or in an extension of the North. Sea, but these
suggestions leave the difficulty just where it was. If a lake or sea
could exist without shores, a glacier-stream might equally dispense with
banks. Within the area of glaciation, defined above, abundant evidence
of the action of land-ice is obtainable, though striated surfaces are
extremely rare--a fact attributable to the softness of the chalk and
clays which occupy almost the whole area. Well-striated surfaces are
found on the harder rocks, as, for example, on the oolitic limestone at
Dunston, near Lincoln.
"Mr. Skertchly has remarked that the proofs of the action of land-ice
are irrefragable. The Great Chalky Boulder-Clay covers an area of
3,000 square miles, and attains an altitude of 500 feet above the
sea-level, thus bespeaking, if the product of icebergs, 'an extensive
gathering-ground of chalk, having an elevation of more than 500 feet.
But where is it? Certainly not in Western Europe, for the chalk does not
attain so great an elevation except in a few isolated spots.'[BR]
[Footnote BR: Geikie's Great Ice Age, p. 360.]
[Illustration: Fig. 44.--Diagram-section near Cromer (Woodward). 6.
Gravel and sand (Middle Glacial) resting on contorted drift (loam, sand,
and marl, with large included boulders of chalk); 5. Cromer till: 4.
Laminated clay and sands (Leda myalis bed); 3. Fresh-water loams and
sands: 3_a_. Black fresh-water bed of Runton (upper fresh-water bed); 2.
Forest bed--laminated clays and sands, with roots and _débris_ of wood,
bones of mammalia, estuarine mollusca, etc., the upper part in places
penetrated by rootlets (rootlet bed); 2_a_. Weybourn crag; 1. Chalk with
flints; * Large included boulder of chalk.]
"It has been further pointed out by Mr. Skertchly, that the condition of
the flints in this deposit furnishes strong evidence that they could not
have been carried by floating ice nor upon a glacier, for, in either of
the latter events, there must have been some exposure to the weather,
which, as he remarks, would have rendered them worthless to the makers of
gun-flints, whereas they are now regularly collected for their use.
"The way in which the boulder-clay is related to the rocks upon which
it rests is a conclusive condemnation of any theory of floating ice;
for example, where it rests upon Oxford Clay, it contains the fossils
characteristic of that formation, as it is largely made up of the clay
itself. The exceptions to this rule are as suggestive as those cases
which conform to it. Each outcrop yields material to the boulder-clay to
the south westward, showing a pull-over from the northeast.
"One of the most remarkable features of the drift of this part of
England is the inclusion of gigantic masses of rock transported for
a short distance from their native outcrop, very often with so small
a disturbance that they have been mapped as _in situ_. Examples of
chalk-masses 800 feet in length, and of considerable breadth and
thickness, have been observed in the cliffs near Cromer, in Norfolk, but
they are by no means restricted to situations near the coast. One example
is mentioned in which quarrying operations had been carried on for some
years before any suspicion was aroused that it was merely an erratic.
The huge boulders were probably dislodged from the parent rock by the
thrust of a great glacier, which first crumbled the beds, then sheared
off a prominent fold and carried it along. This explanation we owe to Mr.
Clement Reid.[BS] The drift-deposits of this region frequently contain
shells, but they rarely constitute what may be termed a consistent fauna,
usually showing such an association as could only be found where some
agent had been at work gathering together shells of different habitats
and geological age.
[Footnote BS: See Geology of the Country around Cromer, and Geology of
Holderness, Memoirs of Geological Survey of England and Wales.]
[Illustration: Fig. 45.--Section at right angles to the cliff through
the westerly chalk bluff at Trimingham, Norfolk, showing the manner in
which chalk masses are incorporated into the till (Clement Reid). Scale,
250 fret to an inch. A. Level of low-water spring-tides; B. Chalk, with
sandy bed at *; C. Forest-bed series, etc., seen in the cliffs a few
yards north and south of this point; D. Cromer till, stiff lead-colored
boulder-clay; E. Fine, chalky sands, much false-bedded; F. Contorted
drift, brown bouldery-clay with marked bedding- or fluxion-structure; G.
The bed, above the white line were seen and measured by more snow and
measured by Mr. Reid; * Chalk seen _in situ_ on beach.
"If the ice-sheet, instead of flowing over the beds, happens to plough
into them or abut against them, it would bend up a boss of chalk, as at
Beeston. A more extensive disturbance, like that at Trimingham drives
before it a long ridge of the bads, and nips up the chalk, till, like
a cloth creased by the sliding of a heavy book, it is folded into an
inverted anticlinal. A slight increase of pressure, and the third stage
is reached--the top of the anticlinal being entirely sheared off, the
chalk boulder driven up an incline, and forced into the overlying
boulder-clays." (Clement Reid.)]
"Attempts have been made to correlate the deposits over the whole area,
but with very indifferent success. A consideration of the consequences
of the invasion of the country by an ice-stream from the northeast will
prepare us for any conceivable complication of the deposits.
"The main movement was against the drainage of the country, so that
the ice-front must have been frequently in water. There would be
aqueous deposition and erosion; the kneading up of morainic matter into
ground-moraine; irregularities of distribution and deposition due to ice
floating in an extra-morainic lake; flood-washes at different points of
overflow; and other confusing causes, which make it rather matter for
surprise that any order whatever is traceable.
"I now turn to the valley of the Trent. We find that it occupies such a
position that it would be exposed, successively or simultaneously, to
the action of ice-streams of most diverse origin. I have shown that the
area to the westward of Lichfield was invaded at one period by a Welsh
glacier, and at a subsequent one by the Irish Sea Glacier, and both of
these streams entered the valley of the Trent or some of its affluents.
From the eastward, again, the great North Sea Glacier encroached in like
manner, carrying the Great Chalky Boulder-Clay even into the drainage
area of the westward-flowing rivers near Coventry.
"The glacial geology of the Trent Valley from Burton to Nottingham has
been ably dealt with by Mr. R. M. Deeley,[BT] who recognises a succession
which may be generalised as follows: (1.) A lower series containing rocks
derived from the Pennine chain; (2.) A middle series containing rocks
from the eastward (chalky boulder-clay, etc.); and (3.) An upper series
with Pennine rocks. Mr. Deeley thinks the Pennine _débris_ may have
been brought by glaciers flowing down the valleys of the Dove, the Wye,
and the Derwent; but, while recognising the importance of the testimony
adduced, especially that of the boulders, I am compelled to reserve
judgment upon this point until something like moraines or other evidences
of local glaciers can be shown in those valleys. In their upper parts
there is not a sign of glaciation. Some of the deposits described must
have been laid down by land-ice; while the conformation of the country
shows that during some stages of glaciation a lake must have existed
into which the different elements of the converging glaciers must have
projected. This condition will account for the remarkable commingling of
boulders observed in some of the deposits. Welsh, Cumbrian, and Scottish
rocks occur in the western portion of the Trent Valley. The overflow of
the extra-morainic lake would find its way into the valleys of the Avon
and Severn, and may be taken to account for the abundance of flints in
some of the gravels.
[Footnote BT: Quarterly Journal Geological Society, vol. xlii, p. 437.]
"_The Isle of Man._--This little island in mid-seas constituted in the
early stages of the Glacial epoch an independent centre of glaciation,
and from some of its valleys ice-streams undoubtedly descended to the
sea; but with the growth of the great Irish Sea Glacier the native ice
was merged in the invading mass, and at the climax of the period the
whole island was completely buried, even to its highest peak (Snae Fell,
2,054 feet), beneath the ice. The effects of this general glaciation
are clearly seen in the mantle of unstratified drift material which
overspread the hills; in the _moutonnée_ appearance of the entire
island; and in the transport of boulders of local rocks. The striations
upon rock surfaces show a constancy of direction in agreement with the
boulder-transport which can be ascribed to no other agency than a great
continuous sheet of such dimensions as to ignore minor hills and valleys.
"The disposition of the striæ is equally conclusive, for we find that on
a stepped escarpment of limestone both the horizontal and the vertical
faces are striated continuously and obliquely from the one on to the
other, showing that the ice had a power of accommodating itself to the
surface over which it passed that could not be displayed by floating ice.
There is a remarkable fact concerning the distribution of boulders on
this island which would strike the most superficial observers, namely,
that foreign rocks are confined to the low grounds. It might be argued
that the local ice always retained its individuality, and so kept the
foreign ice with its characteristic boulders at bay. But, apart from
the _a priori_ improbability of so small a hill-cluster achieving what
the Lake District could not accomplish, the fact that Snae Fell, an
isolated _conical_ hill, is swathed in drift from top to bottom, is
quite conclusive that the foreign ice must have got in. Why, then, did
it carry no stones with it? The following suggestion I make not without
misgivings, though there are many facts to which I might appeal that seem
strongly corroborative:
"The hilly axis of the island runs in a general northeast and southwest
direction, and it rises from a great expanse of drift in the north with
singular abruptness, some of the hills being almost inaccessible to a
direct approach without actual climbing. I imagine that the ice which
bore down upon the northern end of the island was, so far as its lower
strata were concerned, unable to ascend so steep an acclivity, and was
cleft, and flowed to right and left. The upper ice, being of ice-sheet
origin, would be relatively clean, and this flowing straight over the
top of the obstruction would glaciate the country with such material as
was lying loose upon the ground or could be dislodged by mere pressure.
It would appear from published descriptions that the Isle of Arran
offers the same problem, and I would suggest the application of the same
solution to it.
"Marine shells occur in the Manx drift, but only in such situations
as were reached by the ice-laden with foreign stones. They present
similar features of association of shells of different habitat, and
perhaps of geological age, to those already referred to as being common
characteristics of the shell-faunas of the drift of the mainland. Four
extinct species of mollusca have been recognised by me in the Manx drift.
"The Manx drift is of great interest as showing, perhaps better than any
locality yet studied, those features of the distribution of boulders of
native rocks which attest so clearly the exclusive action of land-ice.
There are in the island many highly characteristic igneous rocks, and I
have found that boulders of these rocks never occur to the northward of
the parent mass, and very rarely in any direction except to the southwest.
"Cumming observed in regard to one rock, the Foxdale granite, that
whereas the highest point at which it occurs _in situ_ was 657 feet
above sea-level, boulders of it occurred in profusion within 200 feet of
the summit of South Barrule (1,585 feet), a hill two miles only, in a
southwesterly direction, from the granite outcrop.
"They also occur on the summit of Cronk-na-Irrey-Lhaa, 1,449 feet above
sea-level. The vertical uplift has been 728 and 792 feet respectively.
"In the low grounds of the north of the island a finely developed
terminal moraine extends in a great sweep so as to obstruct the drainage
and convert thousands of acres of land into lake and morass, which is
only now yielding to artificial drainage. Many fine examples of drumlin
and esker mounds occur at low levels in different parts of the island;
and it was remarked nearly fifty years ago by Cumming, that their long
axes were parallel to the direction of ice-movement indicated by the
striated surfaces and the transport of boulders.
"The foreign boulders are mainly from the granite mountains of Galloway,
but there are many flints, presumably from Antrim, a very small number
of Lake District rocks, and a remarkable rock containing the excessively
rare variety of hornblende, Riebeckite. This has now been identified with
a rock on Ailsa Crag, a tiny islet in the Frith of Clyde; and a Manx
geologist, the Rev. S. N. Harrison, has discovered a single boulder of
the highly characteristic pitchstone of Corriegills, in the Isle of Arran.
"_The So-called Great Submergence._
"It may be convenient to adduce some additional facts which render the
theory of a great submergence of the country south of the Cheviots
untenable.
"The sole evidence upon which it rests is the occurrence of shells,
mostly in an extremely fragmentary condition, in deposits occurring at
various levels up to about 1,400 feet above sea-level: A little space may
profitably be devoted to a criticism of this evidence.
"_Moel Tryfaen_ ('The Hill of the Three Rocks').--This celebrated
locality is on the first rise of the ground between the Menai Straits and
the congeries of hills constituting 'Snowdonia'; and when we look to the
northward from the top of the hill (1,350 feet) we see the ground rising
from the straits in a series of gentle undulations whose smooth contours
would be found from a walk across the country to be due to the thick
mask of glacial deposits which obliterates the harsher features of the
solid rocks.
"The deposits on Moel Tryfaen are exposed in a slate-quarry on the
northern aspect of the hill near the summit, and consist of two wedges
of structureless boulder-clay, each thinning towards the top of the
hill. The lower mass of clay, wherever it rests upon the rock, contains
streaks and irregular patches of eccentric form, of sharp, perfectly
angular fragments of slate; and the underlying rock may be seen to be
crushed and broken, its cleavage-laminæ being thrust over from northwest
to southeast--that is, _up-hill_. The famous 'shell-bed' is a thick
series of sands and gravels interosculated with the clays on the slope of
the hill, but occupying the entire section above the slate towards the
top. The bedding shows unmistakable signs of the action of water, both
regular stratification and false bedding being well displayed. The stones
occurring in the clays are mainly if not entirely Welsh, including some
from the interior of the country, and they are not infrequently of large
size--two or three tons' weight--and well scratched.
"The stones found in the sands and gravels include a great majority of
local rocks, but besides these there have been recorded the following:
Rock. Source. Highest Minimum
point uplift
_in situ_. in feet.
Granite Eskdale, Cumberland 1,286 64
Granite Criffel, Galloway ..... ...
Flint Antrim (?) 1,000 350
To these I can add:
Granophyre Buttermere, Cumberland ..... ...
Eurite [BU] Ailsa Craig, Frith of Clyde 1,097 253
[Footnote BU: The altitude at which this rock occurs on Ailsa Craig
has not been announced, so 1 have put it as the extreme height of the
island.]
"The shells in the Moel Tryfaen deposit have been fully described, so far
as the enumeration of species and relative frequency are concerned, but
little has been said as to their absolute abundance and their condition.
The shells are extremely rare, and daring a recent visit a party of five
persons, in an assiduous search of about two hours, succeeded in finding
_five whole shells_ and about two ounces of fragments. The opportunities
for collecting are as good as could be desired. The sections exposed have
an aggregate length of about a quarter of a mile, with a height varying
from ten to twenty feet of the shelly portion; and besides this there are
immense spoil-banks, upon whose rain-washed slopes fossil-collecting can
be carried on under the most favorable conditions.
"I would here remark, that the occurrence of small seams of shelly
material of exceptional richness has impressed collectors with the idea
that they were dealing with a veritable shell-bed, when the facts would
bear a very different interpretation. A fictitious abundance is brought
about by a process of what may be termed 'concentration,' by the action
of a gently flowing current of water upon materials of different sizes
and different specific gravities. Shells when but recently vacated
consist of materials of rather high specific gravity, penetrated by pores
containing animal matter, so that the density of the whole mass is far
below that of rocks in general, and hence a current too feeble to move
pebbles would yet carry shells. Illustrations of this process may be
observed upon any shore in the concentration of fragments of coal, corks,
or other light material.
"Regarding the interpretation of these facts: The commonly received
idea is, that the beds were laid down in the sea during a period of
submergence, and that the shells lived, not perhaps on the spot, but
somewhere near, and that the terminal curvature of the slate was produced
by the grounding of icebergs which also brought the boulders. But if
this hypothesis were accepted, it would be necessary to invest the
flotation of ice with a constancy of direction entirely at variance with
observed facts, for the phenomena of terminal curvature is shown" with
perfect persistence of direction wherever the boulder-clay rests upon the
rock; and, further, there is the highly significant fact, that neither
the sands and gravels nor the rock upon which they rest show any signs of
disturbance or contortion, such as must have been produced if floating
ice had been an operative agent.
"The uplift of foreign rocks is equally significant; and when we take
into account the great distances from which they have been borne and
the frequency with which such an operation must have been repeated, the
inadequacy becomes apparent of Darwin's ingenious suggestion, that it
might have been effected by a succession of uplifts by shore-ice during
a period of slow subsidence; while the character and abundance of the
molluscan remains invest with a species of irony the application of the
term 'shell-bed' to the deposit.
"I now turn to the alternative explanation (see _ante_, p. 145), viz.,
that the whole of the phenomena were produced by a mass of land-ice which
was forced in upon Moel Tryfaen from the north or northwest, overpowering
any Welsh ice which obstructed its course. This view is in harmony with
the observations regarding the 'terminal curvature' of the slates, the
occurrence of sharp angular chips of slate in the boulder-clay, and the
coincidence of direction of these indications of movement with the carry
of foreign stones. The few shells and shell-crumbs in the sands and
gravels would, upon this hypothesis, be the infinitesimal relics of huge
shell-banks in the Irish Sea which were destroyed by the glacier and in
part incorporated in its ground-moraine or involved in the ice itself.
The sands and gravels would represent the wash which would take place
wherever, by the occurrence of a 'nunatak' or by approach to the edge of
the ice, water could have a free escape.
"Two principal objections have been urged to the land-ice explanation
of the Moel Tryfaen deposits. An able critic asks, 'Can, then, ice walk
up-hill?' To this we answer, Given a sufficient 'head' behind it, and
ice can certainly achieve that feat, as every _roche moutonnée_ proves.
If it be granted that ice on the small scale can move up-hill, there is
no logical halting-place between the uplift of ten or twenty feet to
surmount a _roche moutonnée_, and an equally gradual elevation to the
height of Moel Tryfaen. Furthermore, the inland ice of Greenland is known
to extrude its ground-moraine on the 'weather-side' of the nunataks, and
the same action would account for the material uplifted on Moel Tryfaen.
"The second objection brought forward was couched in somewhat these
terms: 'If the Lake District had its ice-sheet, surely Wales had one
also. Could not Snowdonia protect the heart of its own domain?' Of
course, Wales had its ice-sheet, and the question so pointedly raised
by the objector needs an answer; and though it is merely a question
of how much force is requisite to overcome a certain resistance (both
factors being unknown), still there are features in the case which render
it specially interesting and at the same time comparatively easy of
explanation. It seems rather like stating a paradox, yet the fact is,
that it was the proximity of Snowdon which, in my opinion, enabled the
foreign ice to invade Wales at that point.
"A glance at the map will show that the 'radiant point' of the Welsh ice
was situated on or near Arenig Mawr, and that the great mass of Snowdon
stands quite on the periphery of the mountainous regions of North Wales,
so that it would oppose its bulk to fend off the native ice-sheet and
prevent it from extending seaward in that direction.
[Illustration: Fig. 46.--Section across Wales to show the relationship of
native to foreign ice.]
"As a consequence, the only Welsh ice in position to obstruct the onward
march of the invader would be such trifling valley-glaciers as could form
on the western slopes of Snowdon itself.
"The peak of Snowdon is 3,570 feet above sea-level, and Arenig Mawr,
2,817 feet high, is eighteen miles to the eastward, and a broad, deep
valley with unobstructed access to Cardigan Bay intervenes; so, if any
ice from the central mass made its way over the Snowdonian range, it
performed a much more surprising feat than that involved in the ascent of
Moel Tryfaen from the westward.
"The profile shows in diagrammatic form the probable relations of the
foreign to the native ice at the time when the Moel Tryfaen deposits were
laid down.
"From what has been said regarding the great glaciers, it would seem
that ice advanced upon the land from the seaward in several parts of the
coast of England, Wales, and the Isle of Man. Now, it is in precisely
those parts of the country, and those alone, that the remains of marine
animals occur in the glacial deposits. If the dispersal of the shells
found in the drift had been effected by the means I have suggested, it
would follow, as an inevitable consequence, that wherever shells occur
there should also be boulders which have been brought from beyond the
sea. This I find to be the case, and in two instances the discovery of
shells was preliminary to the extension of the boundaries of the known
distribution of boulders of trans-marine origin.
"The officers of the Geological Survey some years ago observed the
occurrence of 'obscure fragments of marine shells' in a deposit at
Whalley, Lancashire, in which they could find only local rocks. One case
such as this would be fatal to the theory of the _remanié_ origin of the
shells, but on visiting the section with Mr. W. A. Downham, I found,
amongst the very few stones which occurred in the shell-bearing sand at
the spot indicated, two well-marked examples of Cumbrian volcanic rocks,
and, at a little distance, large boulders of Scottish granites.
"The second case is more striking. The announcement was made that shells
had been found on a hill called Gloppa near Oswestry, in Shropshire, and,
as it lay about five miles to the westward of Mackintosh's boundary of
the Irish Sea Glacier, and therefore well within the area of exclusively
Welsh boulders, it furnished an excellent opportunity of putting the
theory to the test. An examination of the boulders associated with the
shells showed that the whole suite of Galloway and Cumbrian erratics
such as belong to the Irish Sea Glacier were present in great abundance.
Not only this, but in the midst of the series of shell-bearing gravels I
observed a thin lenticular bed of greenish clay, which upon examination
was found to be crowded with well-scratched specimens of Welsh rocks; but
neither a morsel of shell nor a single pebble of a foreign rock could be
found, either by a careful examination in the field or by washing the
clay at home, and examining with a lens the sand and stones separated out.
"The fact that predictions such as these have been verified affords a
very striking corroboration of the theory put forward; and, though shells
cannot be found in every deposit in which they might, _ex hypothesi_,
be found, yet the strict limitation of them to situations which conform
to those assigned upon theoretical grounds cannot be ascribed to mere
coincidence. If the land had ever been submerged during any part of
the Glacial epoch to a depth of 1,400 feet, it is inconceivable that
clear and indisputable evidence should not be found in abundance in the
sheltered valleys of the Lake District and Wales, which would have been
deep, quiet fiords, in which vast colonies of marine creatures would have
found harbour, as they do in the deep lochs of Scotland to-day.
"It has been urged, in explanation of this absence of marine remains
in the great hill-centres, that the 'second glaciation' might have
destroyed them; but to do this would require that the ice should make a
clean and complete sweep of all the loose deposits both in the hollows
of the valleys and on the hill-sides, and further that it should destroy
all the shells and all the foreign stones which floated in during the
submergence. At the same time we should have to suppose that the drift
which lay in the paths of the great glaciers was not subjected to any
interference whatever. But, assuming that these difficulties were
explained, there would still remain the fact that the valleys which have
never been glaciated--as, for example, those of Derbyshire--show no
signs whatever of any marine deposits, nor of marine action in any form
whatever.
"The sea leaves other traces also, besides shells, of its presence
in districts that have really been submerged, yet there are no signs
whatever to be found of them in all England, except the _post_-glacial
raised beaches. Furthermore, in all the area occupied by glacial
deposits there are no true sea-beaches, no cliffs nor sea-worn caves,
no barnacle-encrusted rocks, nor rocks bored by Pholas or Saxicava. Are
we to believe that these never existed; or that, having existed, they
have been obliterated by subsequent denudations? To make good the former
proposition, it would be necessary as a preliminary to show that the
movement of subsidence and re-elevation was so rapid, and the interval
between so brief, that no time was allowed for any marine erosion to
take place. If this were so, it would be the most stupendous catastrophe
of which we have any geological record; but we are not left in doubt
regarding the duration of the submerged condition, for the occurrence
of forty feet of gravel upon the summits of the hills indicates plainly
that, if they were accumulated by the sea, the land must have stood at
that level for a very long period, amply sufficient for the formation of
a well-marked coast-line.
"The alternative proposition, that post-glacial denudation had removed
the traces of subsidence, is equally at variance with the evidence.
Post-glacial denudation has left kames and drumlins, and all the other
forms of glacial deposits, in almost perfect integrity; the small
kettle-holes are not yet filled up; and it is therefore quite out of the
question that the far more enduring features, such as sea-cliffs, shore
platforms, and beaches, should have been destroyed.
"The only reasonable conclusion is, that these evidences of marine action
never existed, because the land in glacial times was never depressed
below its present level. If the level were different at all (as I think
may have been the case on the western side of England), it was higher,
and not lower.
"The details of the submergence hypothesis have, so far as I am aware,
never been dealt with by its advocates, otherwise I cannot but think that
it would have been abandoned long since. It has been stated in general
terms that the subsidence was greatest in the north and diminished to
zero in the south, but no attempt was made to trace the evidence of
extreme subsidence across country and along the principal hill-ranges--in
fact, to see how it varied in every direction.
"If we take a traverse of England, say from Flamborough Head upon the
east to Moel Tryfaen on the west, and accept as evidence of submergence
any true glacial deposits (except, as in the case of the interior of
Wales, the deposits are obviously the effects of purely local glaciers
and contain, therefore, no shells), we shall find that the subsidence, if
any, must have been not simply differential but sporadic.
[Illustration: Fig. 47.--Section of the cliff on the east side of South
Sea Landing, Flamborough Head. Scale, 120 feet to 1 inch; length of
section 290 yards; average height, 125 feet. (See above map of moraine
between Speeton and Flamborough.)
Explanation.--_4._ Brownish boulder-clay, a band of pebbles; _4a_,
in places about seven feet from top. _3._ Washed gravel, with thin
sand-seams, well-bedded, pebbles chiefly erratics. _2._ "Basement"
boulder-clay, with many included patches of sand, gravel, and silt; _2a_,
at _B_, one of these _2b_ contain shells. _1b_. Sand and silt, overlying
and in places interbedded with _1_. _1._ Rubble of angular and subangular
chalk-blocks and gravel, with occasional erratic, passes partly into
chalky boulder-clay, _1a_. _x_. White chalk, without flints, surface much
shaken.]
"At Flamborough Head shelly drift attains an altitude of 400 feet,
but half a mile from the coast the country is practically driftless
even at lower levels. The Yorkshire Wolds were not submerged. On the
western flanks of the wolds drift comes in at about 100 to 150 feet, and
persists, probably, under the post-glacial warp, from which it again
protrudes on the western side of the valley of the Ouse, and however the
drift between there and the Pennine water-shed may be interpreted, it
shows not a sign of marine origin; but, even granting that it did, we
find that it does not reach within a thousand feet of the water-shed.
When the water-shed is crossed, however, abundant glacial deposits are
met with which are not to be differentiated from others at slightly lower
levels which contain shells.
[Illustration: Fig. 48.--Enlarged section of the shelly sand and
surrounding clay at _B_ in preceding figure. Scale, 4 feet to 1 inch.
Explanation.--_2._ "Basement" boulder-clay. _2a_. Pure compact blue and
brown clay of aqueous origin, bedding contorted and nearly obliterated,
but the mass is cut up by shearing planes. _2b_. Irregular seam, and
scattered streaks, of greenish-yellow sand with many marine shells. _2c_.
Patch of pale-yellow sand, different from _2b_, without trace of fossils.]
"If we suppose that the line of our traverse crosses the Pennine Chain
at Heald Moor, we shall find that on the eastern side no traces of drift
occur above about 300 feet; while the very summit of the water-shed is
occupied by boulder-clay, and thence downward the trace is practically
continuous, and at about 1,000 feet and downward the drift contains
marine shells. Across the great plain of Lancashire and Cheshire
the 'marine' drift is fully developed--though it may be remarked in
parentheses that it contains a shallow-water fauna, albeit _ex hypothesi_
deposited, in part at least, in a depth of 200 fathoms of water--and to
the Welsh border at Frondeg, where it again reaches a water-shed at an
altitude of 1,450 feet; but at 100 yards to the westward of the summit
all traces of subsidence disappear, and through the centre of Wales no
sign is visible; then we emerge on the western slopes at Moel Tryfaen,
and they assume their fullest dimensions, though only to finish abruptly
on the hill-top, and put in no appearance in the lower grounds which
extend from there to the sea.
"The conclusions pointed to by the evidence (and, as I have endeavoured
to show, all the evidence which existed at the close of the Glacial
period is there still) are, that a subsidence of the Yorkshire Wolds
took place on the east, but not in the centre or west; that the Pennine
Chain was submerged on the western side to a depth of 1,400 feet, and
on the east to not more than 300 feet, even on opposite sides of the
same individual hill; that all the lowlands between, say, Bacup and the
Welsh border, were submerged, and that the hills near Frondeg partook of
this movement, but only on their eastern sides; that the centre of Wales
was exempt, but that the summit of Moel Tryfaen forms an isolated spot
submerged, while the surrounding country escaped. These absurdities might
be indefinitely multiplied, and they must follow unless it be admitted
that the phenomena are the results of glacial ice, and that ice can move
'up-hill.'
"The south of England certainly has partaken of no movement of
subsidence. A line drawn from Bristol to London will leave all the true
glacial deposits to the northward, except a bed of very questionable
boulder-clay at Watchet, and a peculiar deposit of clayey rubble which
has been produced on the flanks of the Cornish hills probably, as the
late S. V. Wood, Jr, suggested, by the slipping of material over a
permanently frozen subsoil.
"For the remainder of the southern area the evidence is plain that there
has been no considerable subsidence during glacial times. The presence
over large areas of chalk country of the 'clay with flints'--a deposit
produced by the gradual solution of the chalk and the accumulation in
situ of its insoluble residue--is absolute demonstration that for immense
periods of time the country has been exempt from any considerable aqueous
action. The enormous accumulations of china clay upon the granite bosses
of Cornwall and Devon tell the same tale. A few erratics have been found
at low levels at various points on the southern coasts, usually not
above the reach of the waves. These consist of rocks which may have been
floated by shore-ice from the Channel Islands or the French coast.
"This imperfect survey of the evidence against the supposed submergence
has been rendered the more difficult by the fact that it is not
considered necessary to produce the evidence of marine shells in all
cases. Indeed, it has been argued that post-Tertiary beds covering
thousands of square miles might be absolutely destitute of shells without
prejudice to the theory of their formation in the sea.
"But such a suggestion, one would think, could hardly come from anyone
familiar with marine Tertiary deposits, or even with the appearance of
modern sea-beaches. Admitting, however, for the purposes of argument,
that the beaches along a great extent of coast might be devoid of shells,
it cannot be argued that the deep waters were destitute of life; and
hence the boulder-clays, if of marine origin, should contain a great
abundance of shells and other remains, and, once entombed, it is beyond
belief that they could all be removed from such a deposit in the short
lapse of post-glacial time.
"Now, some of the boulder-clays--as, for example, those of Lancashire
and Cheshire--are held to be of marine origin, and this is indeed
a vital necessity to the submergence theory; for, if these are not
marine deposits, neither are the other shelly deposits; but these
boulder-clays are absolutely indistinguishable from those lying within
the hill-centres, and, as it passes belief that such deposits could be of
diverse origin and yet possess an identical structure and arrangement,
then we should have a right to demand that these clays should have
enclosed shells and should still contain them, but they do not.
"I may here mention that I am informed by Mr. W. Shone, F. G. S.--and
he was good enough to permit me to quote the statement--that the
boulder-clay of Cheshire and the shelly boulder-clay of Caithness are 'as
like as two peas.' The importance of this comparison lies in the fact
that, since Croll's classical description, all observers have agreed
that it was the product of land-ice which moved in upon the land out of
the Dornoch Firth. It was pointed out then, as since has been done for
England, that it was only where the direction of ice-movement was from
the seaward that any shells occur in the boulder-clay.
"_The Dispersion of Erratics of Shap Granite._--So great a significance
attaches to the peculiar distribution of this remarkable rock, that I
may add a few details here which could not be conveniently introduced
elsewhere.
"This granite occupies an area which lies just to the northward of the
water-shed between the basins of the Lime and the Eden, and its extreme
elevation is 1,656 feet. Boulders occur in large numbers as far to the
northward as Cross Fells, while, as already described, they pass over
Stainmoor and are dispersed in great numbers along the route taken by the
great Stainmoor branch of the Solway Glacier. But a considerable number
of the boulders also found their way to the southward, and a well-marked
trail can be followed down into Morecambe Bay; and at Hest Bank, to the
north of Lancaster, the boulder-clay contains many examples, together
with the 'mica-trap' of the Kendal and Sedbergh dykes and other local
rocks, but no shells or erratics from other sources than the country
draining into Morecambe Bay. To the southward the ice which bore these
rocks was deflected by the great Irish Sea Glacier, and, so far as
present information enables me to state, the Shap granite blocks mark the
course of the medial moraine between these two ice-streams. It has been
found near Garstang, at Longridge, and at Whalley, this being the exact
line of junction of the Irish Sea Glacier with the ice from Morecambe Bay
and the Pennine Chain.
"It is a very remarkable and significant fact, that not a single
authentic occurrence of the rock across the boundary indicated has yet
been recorded."
_Northern Europe._
On passing over the shallow German Sea from England to the Continent,
the southern border of the Scandinavian ice-field is found south of
the Zuyder Zee, between Utrecht and Arnhem--the moraine hills in the
vicinity of Arnhem being quite marked, and a barren, sandy plain dotted
with boulders and irregular moraine hills extending most of the way to
the Zuyder Zee. From Arnhem the southern boundary of the great ice-field
runs "eastward across the Rhine Valley, along the base of the Westphalian
Hills, around the projecting promontory of the Hartz, and then southward
through Saxony to the roots of the Erzgebirge. Passing next southeastward
along the flanks of the Riesen and Sudeten chain, it sweeps across Poland
into Russia, circling round by Kiev, and northward by Nijni-Novgorod
towards the Urals."[BV] Thence the boundary passes northward to the
Arctic Ocean, a little east of the White Sea.
[Footnote BV: A. Geikie's Text-Book of Geology, p. 885.]
The depth of this northern ice-sheet is proved to have been upwards
of 1,400 feet where it met the Hartz Mountains, for it has deposited
northern _débris_ upon them to that height; while, as already shown, it
must have been over 2,000 feet in the main valley of Switzerland. In
Norway it is estimated that the ice was between 6,000 and 7,000 feet
thick.
The amount of work done by the continental glaciers of Europe in the
erosion, transportation, and deposition of rock and earthy material is
immense. According to Helland, the average depth of the glacial deposits
over North Germany and northwestern Russia is 150 German feet, i. e.,
about 135 English feet. As the deposition towards the margin of a glacier
must be commensurate with its erosion near the centre of movement, this
vast amount implies a still greater proportionate waste in the mountains
of Scandinavia, where the area diminishes with every contraction of
the circle. Two hundred and fifty feet is therefore not an extravagant
calculation for the amount of glacial erosion in the Scandinavian
Peninsula.
It is not difficult to see how the Scandinavian mountains were able
to contribute so much soil to the plains of northern Germany and
northwestern Russia. Previous to the Glacial period, a warm climate
extended so far north as to permit the growth of semi-tropical vegetation
in Spitsbergen, Greenland, and the northern shores of British America.
Such a climate, with its abundant moisture and vegetation, afforded most
favourable conditions for the superficial disintegration of the rocks.
When, therefore, the cold of the Glacial period came on, the moving
currents of ice would have a comparatively easy task in stripping the
mantle of soil from the hills of Norway and Sweden, and transporting it
towards the periphery of its movement. Of course, erosion in Scandinavia
meant subglacial deposition beyond the Baltic. Doubtless, therefore, the
plains of northern Germany, with their great depth of soil, are true
glacial deposits, whose inequalities of surface have since been much
obliterated, through the general influences of the lapse of time, and by
the ceaseless activity of man.
An interesting series of moraines in the north of Germany, bordering the
Baltic Sea, was discovered in 1888 by Professor Salisbury, of the United
States Geological Survey. Its course lies through Schleswig-Holstein,
Mecklenburg, Potsdam (about forty miles north of Berlin), thence swinging
more to the north, and following nearly the line between Pomerania and
West Prussia, crossing the Vistula about twenty miles south of Dantzic,
thence easterly to the Spirding See, near the boundary of Poland.
Among the places where this moraine can be best seen are--"1. In Province
Holstein, the region about (especially north of) Eutin; 2. Province
Mecklenburg, north of Crivitz, and between Bütow and Kröpelin; 3.
Province Brandenburg, south of Reckatel, between Strassen and Bärenbusch,
south of Fürstenberg and north of Everswalde, and between Pyritz and
Solden; 4. Province Posen, east of Locknitz, and at numerous points to
the south, and especially about Falkenburg, and between Lompelburg and
Bärwalde. This is one of the best localities. 5. Province West Preussen,
east of Bütow; 6. Province Ost Preussen, between Horn and Widikin."
Comparing these with the moraines of America, Professor Salisbury remarks:
"In its composition from several members, in its variety of development,
in its topographic relations, in its topography, in its constitution, in
its associated deposits, and in its wide separation from the outermost
drift limit, this morainic belt corresponds to the extensive morainic
belt of America, which extends from Dakota to the Atlantic Ocean. That
the one formation corresponds to the other does not admit of doubt. In
all essential characteristics they are identical in character. What may
be their relations in time remains to be determined."
[Illustration: Fig. 49.--Map showing the glaciated area of Europe
according to J. Geikie, and the moraines in Britain and Germany according
to Lewis and Salisbury.]
The physical geography of Europe is so different from that of America,
that there was a marked difference in the secondary or incidental effects
of the Glacial period upon the two regions. In America the continental
area over which the glaciers spread is comparatively simple in its
outlines. East of the Rocky Mountains, as we have seen, the drainage
of the Glacial period was, for a time, nearly all concentrated in the
Mississippi basin, and the streams had a free course southward.
But in Europe there was no free drainage to the south, except over
a small portion of the glaciated area in central Russia, about the
head-waters of the Dnieper, the Don, and the Volga; though the Danube
and the Rhône afforded free course for the waters of a portion of the
great Alpine glaciers. But all the great rivers of northern Europe
flow to the northward, and, with the exception of the Seine, they all
for a time encountered the front of the continental ice-sheet. This
circumstance makes it difficult to distinguish closely between the direct
glacial deposits in Europe and those which are more or less modified
by water-action. At first sight it would seem also somewhat hazardous
to attempt to correlate with any portion of the Glacial period the
deposition of the gravelly and loamy deposits in valleys, which, like
those of the Seine and Somme, lie entirely outside of the glaciated area.
Upon close examination, however, the elements of doubt more and more
disappear. The Glacial period was one of great precipitation, and it
is natural to suppose that the area of excessive snow-fall extended
considerably beyond the limit of the ice-front. During that period
therefore, the rivers of central France must have been annually flooded
to an extent far beyond anything which is known at the present time.
Since these rivers flowed to the northward, at a period when, during
the long and severe winters, the annual accumulation of ice near their
mouths was excessive, ice-gorges of immense extent, such as now form
about the mouths of the Siberian rivers, would regularly occur. We are
not surprised, therefore, to find, even in these streams, abundant
indications of the indirect influence of the great northern ice-sheet.
The indications referred to consist of high-level gravel terraces
occasionally containing boulders, of from four to five tons weight, which
have been transported for a considerable distance. The elevation of the
terraces above the present flood-plains of the Seine and Somme reaches
from 100 to 150 feet. We are not to suppose, however, that even in
glacial times the floods of the river Seine could have filled its present
valley to that height. The highest flood in this river known in historic
times rose only to a height of twenty-nine feet. Mr. Prestwich estimates
that, without taking into consideration the more rapid discharge, a flood
of sixty times this magnitude would be required to fill the present
valley to the level of the ancient gravels, while at Amiens the shape of
the valley of the Somme is such that five hundred times the mean average
of the stream would be required to reach the high-level gravels. The
conclusion, therefore, is that the troughs of these streams have been
largely formed by erosion since the deposition of the high-level gravels.
Connected with these terrace gravels in northern France is a loamy
deposit, corresponding to the loess in other parts of Europe, and to a
similar deposit to which we have referred in describing the southwestern
part of the glaciated area in North America. In northern France this fine
silt overlies the high-level gravel deposits, and, as Mr. Prestwich has
pretty clearly shown, was deposited contemporaneously with them during
the early inundations and before the stream had eroded its channel to its
present level.
The distribution of loess in Europe was doubtless connected with the
peculiar glacial conditions of the continent. Its typical development
is in the valley of the Rhine, where it is described by Professor
James Geikie "as a yellow or pale greyish-brown, fine-grained, and
more or less homogeneous, consistent, non-plastic loam, consisting of
an intimate admixture of clay and carbonate of lime. It is frequently
minutely perforated by long, vertical, root-like tubes which are lined
with carbonate of lime--a structure which imparts to the loess a strong
tendency to cleave or divide in vertical planes. Thus it usually presents
upright bluffs or cliffs upon the margins of streams and rivers which
intersect it. Very often it contains concretions or nodules of irregular
form.... Land-shells and the remains of land animals are the most common
fossils of the loess, but occasionally fresh-water shells and the bones
of fresh-water fish occur."
"From the margins of the modern alluvial flats which form the bottoms
of the valleys it rises to a height of 200 or 300 feet above the
streams--sweeping up the slopes of the valleys, and imparting a rich
productiveness to many districts which would otherwise be comparatively
unfruitful. From the Rhienthal itself it extends into all the tributary
valleys--those of the Neckar, the Main, the Lahn, the Moselle, and the
Meuse, being more or less abundantly charged with it. It spreads, in
short, like a great winding-sheet over the country--lying thickly in the
valleys and dying off upon the higher slopes and plateaux. Wide and deep
accumulations appear likewise in the Rhône Valley, as also in several
other river-valleys of France, as in those of the Seine, the Saône, and
the Garonne, and the same is the case with many of the valleys of middle
Germany, such as those of the Fulda, the Werra, the Weser, and the upper
reaches of the great basin of the Elbe. It must not be supposed that the
loess is restricted to valleys and depressions in the surface of the
ground.
"It is true that it attains in these its greatest thickness, but
extensive accumulations may often be followed far into the intermediate
hilly districts and over the neighbouring plateaux. Thus the Odenwald,
the Taunus, the Vogelgebirge, and other upland tracts, are cloaked with
loess up to a considerable height. Crossing into the drainage system of
the Danube, we find that this large river and many of its tributaries
flow through vast tracts of loess. Lower Bavaria is thickly coated with
it, and it attains a great development in Bohemia, Upper and Lower
Austria, and Moravia--in the latter country rising to an elevation of
1,300 feet. It is equally abundant in Hungary, Galicia, Bukowina, and
Transylvania. From the Danubian flat lands and the low grounds of Galicia
it stretches into the valleys of the Carpathians, up to heights of 800
and 2,000 feet. In some cases it goes even higher--namely, to 3,000
feet, according to Zeuschner, and to 4,000 or 5,000 feet, according to
Korzistka. These last great elevations, it will be understood, are in
the upper valleys of the northern Carpathians. In Roumania loess is
likewise plentiful, but it has not been observed south of the Balkans.
East of the Carpathians--that is to say, in the regions watered by the
Dniester, the Dnieper, and the Don--loess appears also to be wanting,
and to be represented by those great steppe-deposits which are known as
_Tchernozen_, or black earth."[BW]
[Footnote BW: Prehistoric Europe, pp. 144-146.]
The shells found in the loess indicate both a colder and a wetter climate
during its deposition than that which now exists. The relics of land
animals are infrequently found in the deposit, yet they do occur, but
mostly in fragmentary condition--the principal animals represented being
the mammoth, the rhinoceros, the reindeer, and the horse; which is about
the same variety as is found in the gravel deposits of the Glacial
period, both in western Europe and in America.
A species of loess--differing, however, somewhat in color from that on
the Rhine--covers the plains of northeastern France up to an elevation of
700 feet above the the sea, where, as we have already said, it overlies
the high-level gravels of the Seine and the Somme. Above this height
the superficial soil in France is evidently merely the decomposed upper
surface of the native rock.
The probable explanation of all these deposits, included under the term
"loess," is the same as that already given by Prestwich of the loamy
deposits of northern France. But in case of rivers, which, like the
Rhine, encountered the ice-front in their northward flow, a flooded
condition favouring the accumulation of loess was doubtless promoted by
the continental ice-barrier. In the case of the Danube and the Rhône,
however, where there was a free outlet away from the glaciated region,
the loess in the upper part of the valleys must have accumulated in
connection with glacial floods quite similar to those which we have
described as spreading over the imperfectly formed water-courses of the
Mississippi basin during the close of the Ice age. That the typical loess
is of glacial origin is pretty certainly shown, both by its distribution
in front of glaciers and by its evident mechanical origin when studied
under the microscope. It is, in short, the fine sediment which gives the
milky whiteness to glacial rivers.
In central Russia there is a considerable area in which the glacial
conditions were, in one respect, similar to those in the northern part
of the Mississippi Valley in the United States. In both regions the
continental ice-sheet surmounted the river partings, and spread over the
upper portion of an extensive plain whose drainage was to the south. The
Dnieper, the Don, and the western branch of the Volga, like the Ohio
and the Mississippi, have their head-waters in the glaciated region. In
some other respects, also, there is a resemblance between the plains
bordering the glaciated region in central Russia and those which in
America border it in the Mississippi Valley. Mr. James Geikie is of the
opinion that the extensive belt of black earth adjoining the glaciated
area in Russia, and constituting the most productive agricultural portion
of the country, derives its fertility, as does much of the Mississippi
Valley, from the blanket of glacial silt spread pretty evenly over it.
Thus it would appear that in Europe, as in America, the ice of the
Glacial period was a most beneficent agent, preparing the face of the
earth for the permanent occupation of man. On both continents the seat
of empire is in the area once occupied by the advance of the great
ice-movements of that desolate epoch.
_Asia._
East of the Urals, in northern Asia, there is no evidence of moving ice
upon the land during the Glacial period; but at Yakutsk, in latitude 62°
north, the soil is frozen at the present time to an unknown depth, and
many of the Siberian rivers, as they approach and empty into the Arctic
Sea, flow between cliffs of perpetual ice or frozen ground. The changes
that came over this region during the Glacial period are impressively
indicated by the animal remains which have been preserved in these
motionless icy cliffs. In the early part of the period herds of mammoth
and woolly rhinoceros roamed over the plains of Siberia, and waged an
unequal warfare with the slowly converging and destructive forces. The
heads and tusks of these animals were so abundant in Siberia that they
long supplied all Russia with ivory, besides contributing no small
amount for export to other countries. "In 1872 and 1873 as many as 2,770
mammoth-tusks, weighing from 140 to 160 pounds each, were entered at the
London clocks."[BX] So perfectly have the carcasses of these extinct
animals been preserved in the frozen soil of northern Siberia that when,
after the lapse of thousands of years, floods have washed them out from
the frozen cliffs, dogs and wolves and bears have fed upon their flesh
with avidity. In some instances even "portions of the food of these
animals were found in the cavities of the teeth. Microscopic examination
showed that they fed upon the leaves and shoots of the coniferous trees
which then clothed the plains of Siberia." A skeleton and parts of
the skin, and some of the softer portions of the body of a mammoth,
discovered in 1799 in the frozen cliff near the mouth of the Lena, was
carried to St. Petersburg in 1806, from which it was ascertained that
this huge animal was "covered with alight-coloured, curly, very thick-set
hair one to two inches in length, interspersed with darker-colored hair
and bristles from four to eighteen inches long."[BY]
[Footnote BX: Prestwich's Geology, vol. ii, p. 460.]
[Footnote BY: Prestwich's Geology, vol. ii, p. 460.]
In the valleys of Sikkim and eastern Nepaul, in northern India, glaciers
formerly extended 6,000 feet lower than now, or to about the 5,000-foot
level, and in the western Himalayas to a still lower level. The higher
ranges of mountains in other portions of Asia also show many signs of
former glaciation. This is specially true of the Caucasus, where the
ancient glaciers were of vast extent. According, also, to Sir Joseph
Hooker, the cedars of Lebanon flourish upon an ancient moraine. Of the
glacial phenomena in other portions of Asia little is known.
_Africa._
Northern and even central Africa must likewise come in for their share
of attention. The Atlas Mountains, rising to a height of 13,000 feet,
though supporting none at the present time, formerly sustained glaciers
of considerable size. Moraines are found in several places as low as the
4,000-foot level, and one at an altitude of 4,000 feet is from 800 to 900
feet high, and completely crosses and dams up the ravine down which the
glacier formerly came.
Some have supposed that there are indubitable evidences of former
glaciation in the mountain-ranges of southwestern Africa between latitude
30° and 33°, but the evidence is not as unequivocal as we could wish, and
we will not pause upon it.
The mountains of _Australia_, also, some of which rise to a height of
more than 7,000 feet, are supposed to have been once covered with glacial
ice down to the level of 5,800 feet, but the evidence is at present too
scanty to build upon. But in _New Zealand_ the glaciers now clustering
about the peaks in the middle of the South Island, culminating in Mount
Cook, are but diminutive representatives of their predecessors. This is
indicated by extensive moraines in the lower part of the valleys and by
the existence of numerous lakes, attributable, like so many in Europe and
North America, to the irregular deposition of morainic material by the
ancient ice-sheet.[BZ]
[Footnote BZ: See With Axe and Rope in the New Zealand Alps, by G. E.
Mannering, 1891.]