THE QUATERNARY PERIOD IN IRELAND
—AN ASSESSMENT, 1960.
BY F. M. SYNGE, Geological Survey, Dublin,
and N. STEPHENS, Dept. of Geography, The Queen's
University of Belfast.
During the last two glaciations of the Quaternary Period
(the Saale and Weichsel of Northern Europe) most of Ireland
was covered by an ice sheet,
and although very cold conditions
occurred even earlier,1 corresponding with the Elster Glaciation of Northern Europe, there is no clear evidence that
glacial deposits of that period are present. Possibly the oldest
drifts known in Ireland belong to this early glaciation, as for
example, the 2 shelly boulder clay recorded to the south of
Lough Foyle.
This and a similar boulder clay at Belderg,
Co. Mayo4 are like the drift at Tangy, West Kintyre.3 These
drifts suggest glaciation from the north, although there is
a possibility that this north-to-south movement is an early
phase of the succeeding glaciation from the north-east and
east. The peculiar
southward carriage of erratics of Cushendun
micro-granite5 may also indicate one or other of these early
glaciations.
On the south and east coasts of Ireland the glacial drifts
rest upon the ' pre-glacial' beach platform, which
stands
at a more or less uniform height of 25-30ft. O.D.6 The ' preglacial ' beach, which can be seen to rest upon the rock platform, is composed of rounded pebbles
of local rock, occasional
flint and local erratic pebbles.7 These stray pebbles
have
been attributed to either9 a very early boulder clay,8 floating
ice or floating seaweed. No shells have been found in the
beach material. The presence of an early boulder clay beneath the beach cannot be proved, although a greenish clay
with fragments of local rock, at Nemestown, 10Co. Wexford,
has been regarded as a possible glacial deposit. The oldest
glacial drift resting on the beach and rock platform corresponds to the Saale glaciation, because sealed below it are
temperate sediments (Hoxne
Interglacial) at Kilbeg and
Newtown in Co. Waterford,1112 and a deposit of the same
age is known from Boleyneendorrish, near Gort, Co. Galway.13
At Gort and Kilbeg lake sediments containing pollen and
fragments of silver pine (abies), spruce (picea), and a species
of rhododendron (r. ponticum) rest upon sediments containing
121
an arctic flora resting on rock. In both cases boulder clay
overlies the lake sediments. At Newtown a thin layer of peat
rests upon the rock platform beneath boulder clay. This rock
platform may therefore have been cut during the Elster-Saale
(Hoxne) interglacial, but may be older and therefore ' preglacial.'
In Co. Wicklow, where the glacial succession has been more
fully investigated, the first phase of glaciation was represented
by an expansion of local ice from the mountains (the Enniskerry advance).14 This early movement was succeeded by the
later advance of Scottish ice in the basin of the Irish Sea.
Between the mouth of the Boyne and Nemestown, and between Dungarvan and Power Head, this ice stream pushed
across the present coastline towards the south-west, carrying
with it a brown or purple plastic shelly boulder clay, containing
few stones.15 This drift, so different from the gravelly and
stony boulder clay of the Enniskerry advance, has been recorded as far inland as the vicinity of Blessington, Co. Wicklow, 25 miles south-west of Dublin!16 Marine shells noted in
the drift of the Midlands from time to time, may have been
carried there by this ice movement.17 In the south, between
Dungarvan and Nemestown, ice from the north-west (termed
the Munster General Glaciation by G. F. Mitchell) was powerful enough to keep the Scottish ice off the coast.18 This latter
ice movement may have originated in Connemara as it appears
to be associated with a southward carriage of Galway granite
to the Mullaghareirk Mts.,19 to Cork Harbour20 and to South
Kilkenny.21
In Ulster the western limit of the invading Scottish ice
from the east, as shown by erratics from that quarter, runs
south-east from L. Swilly, round the east slopes of the Sperrins,
to Slieve Beagh.22 In the Carlingford peninsula this glaciation
deposited a stony boulder clay with boulders of basalt from
the Antrim plateau. On the Mourne erratics were carried up
to 1837ft. O.D.23, and may post-date the formation of large
corries formed during a local glacierisation. In Co. Donegal
a local ice-cap may have held off invading ice, while further
south a powerful ice-stream crossed N.W. Mayo going in a
north-westerly direction.24
During the decay of this ice-sheet, meltwaters deposited
sands and gravels, and cut immense channels in solid rock.
Such channels are well displayed in East Wicklow where they
mark marginal drainage southwards along the edge of the Irish
Sea Glacier, and in North Kerry at the foot of the hills south
of Listowel, where a similar drainage system flowed south-west.
In certain areas ice from local centres covered ground thus
122
IRELAND
duaternary
Geology
mm^wwsm
^ ^ ^ ^ ^ f e p l l i ^ K"b"
I
S3 milts
UNCLACIATEO AREAS
Midland
Eastern Ben era I Blaciation
Eeneral Elacittion
FIUCS
\—S\
LIMITS
-^^
tlAtlH SWAl
X—
( itrectimi ol ici movemint hdicitti by arm* )
]fJ/ff»J
FIG. 1.
123
vacated by the main ice-sheet. In the Wicklow Mts. this ice 25
extended west to Brittas, Co. Dublin (the Brittas advance) ;
in Co. Cork a similar advance eastwards
of the West CorkKerry ice cap reached Youghal.26
Records of the following Interglacial phase are very scanty.
Only at Ardcavan in Co. Wexford has peat of this age been
reported. It was a thin deposit
between boulder clay below,
and solifluction deposit above.27 In Co. Limerick, at Baggotstown, interglacial deposits of Elster-Saale age underlie some
20ft. of boulder clay. This clay contains in its upper part
a thin interglacial horizon. No beach deposits that can be
dated to this interglacial have been found on the Irish coasts,
and it can only be assumed that mean sea-level was not
significantly higher than at the present day.
The return of cold conditions heralded the beginning of the
Last Glaciation (Weichsel Glaciation of Northern Europe).
The type of weathering which these conditions brought,
acting as it did upon drift and rock already leached during
the previous interglacial period, tended to smooth and level
the minor features of the old landscape. Such weathering
may be recognised by certain structures occurring outside
the limits of the Last Glaciation. On sloping ground mass
wastage took place and the drift moved or ' flowed ' down to
lower levels. The rock itself was shattered into angular
fragments, and moved down the slope as head or scree. On
level ground, in drift, ' festoon structures ' were produced—
a rude segregation of the drift into pockets of fine material,
with the individual stones in the coarser intervening material
tending to stand vertically. Also on level ground, the coarse
material was arranged in stone polygons, with the finer
material in the middle; these occur in
Curraun, Co. Mayo28
29
and at Kingwilliamstown, Co. Cork.
As in the preceding glaciation, the local mountain glaciers
seem to have attained their maximum development before
that of the main ice sheet. In the Wicklow mountains this
development of local valley glaciers—the Athdown advance
—radiated from a snowfield on the east side of the watershed.30
It is evident that throughout most, if not the whole, of
its life the ice streams of this Last Glaciation flowed from
sources within Ireland and were not derived from Scottish
sources. The main icesheet consisted of an iceshed extending
north-east from L. Rea to Tyrone, and the Lough Neagh
basin. This coalesced with powerful local centres developed
in Donegal, and in Connemara, while a separate ice cap lay
over West Cork—S.E. Kerry. Analysis of the glacial drifts
124
and striae on the Antrim plateau and in north Down shows
that the extension of Scottish ice across the plateau
during
the last glaciation, as Dwerryhouse envisaged,31 cannot be
accepted without reservation ; the area is being re-examined.
The southern limit of this Last or Midland General Glaciation is denned in many places by a clearly marked
moraine
along the southern edge of the Central Lowlands.32 From a
maximum upper limit of 1250ft. O.D. at the north end of the
Wicklow Mts. its course runs south-west, reaching the west
coast at Kilkee. On the east coast the Limit passes out to sea
at Wicklow Head, but swings back on to the coast north of
Wexford Harbour. It is very doubtful that the ice succeeded
in surmounting the Castlecomer Plateau or the Slievefelims;
.the patchy distribution of the drift there and the absence of
sharp topographical features suggest that it is an older deposit. Likewise North-West Mayo lay outside the limits of
this glaciation.
In the south an independent icecap in West Cork extended
east to Killumney, but
failed to cross the south coast as far
west as Skibbereen.33 The north limit of glaciation is represented by a terminal moraine of valley
glaciers between
Killamey and Killorglin in Co. Kerry.34
Outside the limits of the main ice sheet fresh corries and
the impressive block moraines associated with them would
appear to correspond to the maximum of this glaciation.
They all occur in areas not overrun by the general ice sheet,
both in mountain groups outside its limits ; the mountains of
N. W. Mayo, A'chill, Dingle Peninsula, Iveragh Peninsula,
Galtees, Knockmealdowns, Slievenamon, Comeraghs, Mt.
Leinster and the Wicklow Mts.; and on large nunataks which
include Slieve League, Partry Mountains and the Mournes.
They are notably absent from the mountain areas that underlay the ice sheet, for example, in Connemara and Co. Donegal.
The deposits left by the decay of this ice sheet have survived virtually unaffected by erosion and leaching. The fresh
topography of the drumlins, kames, eskers, and kettle-holes
stand out in marked contrast to the featureless areas of older
drift.
The decay of this ice-sheet commenced by a regular recession of the ice-margin. Eskers were formed by infilling
of the main sub-glacial rivers that led to the ice margin. They
are aligned parallel to the direction of ice
movement and were
exposed after the ice had melted back.35
After the main ice had withdrawn from the edge of the
Wicklow Mountains certain valley glaciers seem to have advanced. Outwash from the terminal moraines cut down
125
North
Antrim
Readvance
INDEX
MAP
MIDLAND
GENERAL
EASTERN
GENERAL
FIG.
2
126
through the
drift left by the Midland ice, escaping freely
seawards.36
Further retreat of the ice sheet margin towards the northwest was interrupetd by a still-stand of the ice along a line
Edenderry — Tara — Duleek — Gormanstown, marked by
a narrow morainic ridge (The Galtrim moraine). Further
retreat north-west is emphasised by a system of feeding eskers
between Tara and Edenderry. To the south-west the main
esker chains of the Central Plain seem to be associated with
the steady shrinkage of a sluggish ice-cap, from east to west.
Retreat moraine features were observed transverse to the
eskers around Tullamore. Another esker system in the Plains
of Mayo is- associated with ice retreating south.
No clear evidence of a readvance of the ice has been found
so far in the Midlands, although the great kame-and-kettle
morainic
belt running from Kilkeel to Dundalk, Ardee and
Kells37 seems to mark a significant halt of the ice retreat.
This feature marks the southern edge of the great drumlin
belt and probably marks a change over from orderly retreat
to wholesale stagnation of the ice-cap. The pattern of the
drumlins reflect the course of the main glacial currents during
the maximum of glaciation.38 In places the decaying ice
sheet has deposited gravel in the form of kames and eskers
among them. The final dissolution of the ice left large areas
of kame and kettle moraine west of L. Neagh in Tyrone and
Deny County, and similar areas occur in S.E. Galway.
Post-dating the dissolution of the ice, at any rate in the
coastal area, a marine transgression occurred in North East
Ireland. Its deposits and shorelines have been observed in
Inishowen, L. Foyle (up to 70ft. O.D.), in N. Antrim, and in
the Ards Peninsula as a shelly marine39 clay enveloping drumlins and extending up to 50 ft. O.D.
During the maximum of the transgression Inishowen was
an island, Island Magee was also disconnected from the mainland and much of the Ards peninsula was submerged and L.
Neagh may have been linked to the north coast by a long
inlet in the Lower Bann valley. Meltwater from the remnants
of the ice sheet carried sand and gravel into this high sea
level down the valley of the Foyle and Faughan.
A readvance of the ice from Scotland south-westwards
across the north coast of Ireland has been established.40 It
destroyed the drumlins of the previous movement from the
south, and deposited a well-marked terminal moraine extending east from Moville to Coleraine, Ballymoney, Armoy,
and Ballycastle where it runs off the coast just west of Fair
Head. 41 The extension of this readvance to Belfast Lough
127
is considered doubtful. At Portballintrea, boulder clay of the
readvance rests on clay similar to the marine clays described
above. As there is no evidence of a high sea level in late-glacial
times after the ice had again retreated, the marine transgression probably occurred before the ice advanced. Frostwedges and head deposits resting on the marine deposits
around Lough Foyle and in Co. Down may correspond with
ihis cold phase; also ice patches which may have lingered
in the Mourne corries at some late period could date to this
readvance.
Very mild conditions followed (AllerSd period) with the
•development of birch and pine scrub. Open lakes were more
plentiful, and the fauna was dominated by the Giant Irish
T)eer. Deposits from this period are widespread in lake sediments ; they occur as a blue mud overlying a grey mud with
an arctic flora; thus the sediments show a change from cool
•conditions (Zone I) to temperate conditions (Zone II).
Cold conditions returned for the last time in Zone III,
•when a second grey mud with an arctic flora was laid on top
•of the blue mud. Although an advance of valley glaciers
•occurred in Scotland there are no signs of a similar development
in Ireland, where there may have been an accumulation
of
perennial snow and ice only in the larger corries.42 Apart
from enhanced hillwash on steep slopes the weathering effects
•of the Zone III deterioration in climate cannot have been
very great.
A general amelioration of climate followed Zone III, and
isostatic adjustments continued during the post-glacial
periodas shown by the raised beaches and estuarine deposits
as many coastal sites.43
REFERENCES
1
Watts, W. A.
—' Interglacial Deposits at Kilbeg and Newtown, Co. Waterford.' Proc. Roy. Irish Acad'
Vol. 60, Sect. B., No. 2. 1959. p. 113-4.
2
Kilroe, J. R.
—' The Geology of the Country around
Londonderry ' Mem. Geol. Surv. of Ireland,
1908. p. 53-4.
3
Horne, J. et al.
—' The Character of the High-level Shellbearing Deposits in Kintyre.'
British
Assoc. 1896. p. 378-389.
4
Hinch, J. de Witt —' The Shelly Drift of Glenulra and Belderrig, Co. Mayo.' Irish Naturalist. Vol. 22.
1913. pp. 1-6.
5
Charlesworth, J. K. —' Some Observations on the Glaciation of
North-East Ireland.' Proc. Roy. Irish Acad.
Vol. 45. 1939. p.259.
128
6
Stephens, N.
—' Some Observations on the " Interglacial "
Platform and Early Post-Glacial Raised
Beach on the East Coast of Ireland."
Proc. Roy. Irish Acad. Vol. 58 Sect. B.
No. 6. 1957. p. 140.
7
Wright, W. B. and —' The Pre-Glacial Raised Beach of the
Muff, H. B.
South Coast of Ireland.'
Proc. Roy.
Dublin Soc. Vol. 10. 1904. p. 261-2.
8
Mitchell, G. F.
—" The Pleistocene Epoch ' in ' A View of
Ireland,' publ. for British Association,
Dublin, 1957. p. 33.
9
Wright.W. B. and —1904 ibid. p. 262.
Muff, H. B.
10
Mitchell, G. F.
—' The Pleistocene Period in Ireland.' Medd.
fra Dansk Geol. Foren. Bd. 12. Köbenhavn.
1951. p. 111.
11
Watts, W. A.
—1959, ibid. pp. 122-126.
12
Mitchell, G. F.
—' Two Interglacial Deposits in SouthEast Ireland' Proc. Roy. Irish Acad.
Vol. 52. B, No. 1. 1948. p. 11.
13
Jessen, K.
—' Rhododendron ponticum in the Irish
Inter-glacial flora.' Irish Naturalist's
Journ. Vol. 9. 1948. p. 174-5.
14
Farrington, A.
—' The Glacial Drifts of the District around
Enniskerry, Co. Wicklow.' Proc. Roy.
Irish Acad. Vol. 50., B. 1944 p. 154.
15
Wright, W. B.
—1904 ibid. p. 252.
and Muff, H. B.
16
Farrington, A.
—Drift Survey, Wicklow Sh.10, 1924, Geol.
Survey.
17
Oldham, T.
—' On the more Recent Geological deposits,
in Ireland, Journ. Geol. Soc. Dublin, Vol.3.
1849 p.64-66.
18
Mitchell, G. F.
—1957. ibid. p. 33.
19,21 M. F. O'Meara
—Manuscript maps of the G e o l o g i c a l
Survey.
20
Jukes, J. B.
—Mem. Geol. Survey. Sh. 187, 195 & 196.
1861. p. 59.
22
Charlesworth, J. K. —' Glacial Geology of North-West Ireland *
Proc. Roy. Irish Acad. Vol. 36, B, 1924.
p. 187.
23
Dwerryhouse, A. R. —The Glaciation of North-Eastern Ireland.
Quart. Jour. Geol. Soc. Vol.79. 1923. p.403.
24
Haughton, J. P.
—' The Mullet of Mayo.' Irish Geog. Vol.4.
1959. p. 2.
25
Farrington, A.
—' The Glacial Drifts of the Leinster Mountains.' Journ. of Glaciology. Vol. 1. No.5.
1949. p. 221.
26
Farrington, A.
—' A Note on the Correlation of the KerryCork Glaciations with those of the Rest of
Ireland' Irish Geog. Vol. 3. No. 1. 1954.
p. 52.
27
Mitchell, G. F.
—' Two Interglacial Deposits in South-East
Ireland. Proc. Roy. Irish. Acad. 52B.
1948. pp.1-14.
129
28
Flatrès, P .
—' La Péninsule de Corran, Comté de Mayo,
Irlande ' Bull, de la Soc. Geol. et Mineralog.
de Bretagne, Rennes. N.S. Fasc. 1. 1957.
p. 41.
29
Mitchell, G. F .
—1957. ibid. p . 34.
30
Farrington, A.
—' The Glaciation of the Wicklow Mountains.'
Proc. Roy. Irish Acad. Vol. 42., B, 1934.
p.205.
31
Dwerryhouse, A. R. —1923. ibid. p . 420.
32
Charlesworth, J. K. —' The Glacial Retreat from Central and
Southern Ireland.'
Quart. Journ. Geol.
Soc, London Vol. 84 (2). No. 334. 1928
p. 295-300.
33
Farrington, A.
—' The Lee Basin.
Part I : Glaciation.'
Proc. Roy. Irish Acad. Vol. 60. B. No. 3.
1959. p . 153.
34
Wright, W. B.
—'
The Geology of Killarney and Kenmare.'
Mem. Geol. Surv. 1927.
35
Synge, F . M.
—' T h e Glacial Deposits a r o u n d Trim, Co,
M e a t h ' Proc. R o y . Irish Acad. Vol. 53
B . N o . 10. 1950 p . 99-110.
34
Farrington, A.
—' T h e I c e Age i n t h e Dublin District.' Vol.5.
The Inst. of Chemistry of Ireland Journal.
1957. p . 23-27.
37
Charlesworth, J . K. —' The Carlingford Re-advance
between
Dundalk, Co. Louth, a n d Kingscourt a n d
Lough Ramor, Co. Cavan.' The Irish N a t
Journ. Vol. 11, N o . 1 1 . 1955. p . 299.
38
Charlesworth, J . K. —1939. ibid. p . 266.
39
Stephens, N .
—' The Evolution of t h e Coastline of NorthEast Ireland.' Adv. of Science. 56. 1958.
pp.389-391.
40
Dwerryhouse, A. R . —1923. ibid. p . 358.
41
Charlesworth, J . K. —1924. ibid, p.298.
42
Farrington, A.
—' Local Pleistocene Glaciation and t h e
Level of t h e Snow Line of Croaghaun
Mountain in Achill Island, Co. Mayo,
Ireland.' Journ. of Glaciology. Vol. 2.
No. 14, 1953 p . 267.
43
Mitchell, G. F.
—1957. ibid p. 37.
130