the geology of the country around cork and cork harbour

8/10/2019 The Geology of the country around cork and cork harbour

1/161

MEMOIRS

OP TIIE

GI &~JCh-b

SU -Y;

IRELAND.

\I

THE GEOLOGY OF

THE COUNTRY AROUND

CORK

AND CORK

HARBOUR.

(EXPLANATIONF THE CORK COLOUR-PRINTEJ)RIFT ikl~~.)

BY

G. W. LAMPLUGH, F.G.S., J. R. KILROE,

A. MHENRY, M.R.I.A., H. J. SEYMOUR, B.A., F.G S.,

W. B. WRIGHT, B.A., F.G.S.,

and H. B. MUFF, B.A., F.G.S.

PUBLISHED BY ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTYS TREASURY.

DUBLIN:

PRINTED FOR HIS MAJESTYS STATIONERY OFFICE,

BY A\I,EX. THOM CGCO., LIMITED,87,88, & 89, ABBEY-STREET,

To

be purchased from

E. STANFORD, 12, 13, & 14, Long Acre, London,W.C.

;

HODGES, FIGGIS, it CO., LIMITED, 104, Grafton-street, Dublin

;

JOHN MENZIES & CO., Rose-street, Edinburgh.

From any Agent for the sale of Ordnance Survey Mapr:or through auy Bookseller

from the Ordnance Survey Of?ice, Southampton.

--.-

1905.

Price Three fWilli?zqs.


2/161


3/161


4/161

PREFACE:

THIS Memoir has been prepared to aoco_mpany the new colour-

printed map of the Cork district.

The boundaries of the map

have been arranged to embrace the country around the city of

Cork, and including the whole of Cork Harbour. This area

formed part of four sheets of the previous solid geological

maps. It is expected that the present arrangement will be

found more convenient for local purposes and for visitors to

this beautiful district.

The recent survey had for itIs object the mapping of the

glacial Idrifts and other superficial deposits which were not

included witshin the scope of the original survey made half a

century ago. No re-examination of the solid rocks was

attempted, and the boundaries of these formations shown on

the new map have been transferred from the solid maps,

with the exception that certain limited tracts of dark shale in

the south-western part of the sheet, which were shown as

Coal-IVle.asures

on the last edition of the solid m,ap, are

not now shown separately from the Lower Carboniferous rocks,

for reasons given in the sequel.

The short description of the solid rocks contained in the

present volume is mainly compiled from the published- Sheet

Explanations, of the origin.al solid maps, with the addition

of some new matter indicating the results of later researches.

This description, together with a general account of the super-

ficial deposits,

forming Part I. of the Memoir, has been

prepared by Mr. G. W. Lamplugh.

The detailed d,escription of the superficial deposits, forming

Part II.,, has been written by Messrs. Lamplugh, J. R. Kilroe,

A. MHenry, H. J. Seymour, W. B. Wright, and H. B. Muff,

by whom the recent survey w,as made ; the respective work of

these officers is indicated by the initials after the paragraphs.

Until this survey was carried out our knowledge of the Glacial

deposits in the district was extremely scanty, and it is believed

that the present Memoir will adcd materially to our knowledge

of the later geological history of the South of Ireland.

The discovery by Messrs.

Wright and Muff of an ancient

shore-line beneath the Glacial deposits at very nearly the same

level as .the existing shore-line, h,as wide bearings upon much-

debated questions relating to the geographical conditions of the

British Island at the beginning of the Glacial period, and to

the origin of the present flor#a and fauna of Irerand.

In Part III., the economic geology of the district is dealt

with, including #an account of the water supply and of the

soils. TJader the last-mentioned head Mr. J. R. Kilroe gives

the results of his ex.amination and mechanical analysis of some

characteristic samples of the soils and subsoils of the district.


5/161

It is my pleasant duty to acknowledge with thanks t)he

assistance received from Mr. J. Wrig.ht, of Belfast, Dr.

Wheelton Hind, and Dr. A. H. Foord, in preparing the account

of the Carboniferous rocks and their fossils ; and also from

several local engineers and firms for detiails of well-borings and

other information used in the Economic chapter and other

parts of this Memoir,

whose names ar,e mention&d in the

subsequent pages.

The plates ,are from excellent photographs taken for the

purpose by Mr. B. Welch, of Belfast.

J. J. H. TEALL,

Director.

Geologicat Survey Office,

28

Jermyn-street, London.

January 26t71,1905.

--

____

__.__ ._ ___. -____- --


6/161

TABLE OF CONTENTS

Page

Preface by the.

Directoq . . . . .

11

PART I.--GENERAL DESCRIPTION.

CHAPTER I.-INTN.ODUCTION,

. . . . . .

Area of the Map, 1.

Scope of the Map, 2. Table of

Formations, 3.

Form of the Ground and its

relation to the Geological Strnoture, 4.

1-8

CHAPTER II.-THE OLD RED SANDSTOND, . . . .

0-14

Position and Structure, 9. Lower Old Red Sandstone, 9.

Upper Old Red &and&one, 11.

.

CHAPTBR III.-THE CARBONWEROUSROCKS, . . .

15-35

Position and Classifxation, 15. Lower Limestone Shale

and Carboniferous Slate, 16. Discurfiion

as to Age

of Carboniferoue Slate, 18. Fossils of the Shale and

Slate, 26. Carboniferous Limestone, 28. Fossils of

.

the Limestone, 29.

The Upper Shale, or

Posidcmomya Becheri

Be&, 32.

CHAPTER W.-THE YOST-TERTIARY OR SUPERFICIAL

DEPOSITS, . . . . , . . .

Preliminary Note,

Shore-line, 36.

36, Pre-Glacial or Early Glacial

The Glacial Deposits :-Boulder-clay, 40

;

Boulders, 41;

Glacial Strise, 42

;

Glacial Sand and Gravel, 42

;

Origin of the Glacial Deposits, 44.

Post-Glaoial Deposits

:-Old River Gravels, 47

;

Allu-

vium, 47

;

Peat (absence of), 48

;

Intake, 48

;

Raised

Beach 1 48.

3a9

PART II.--DE\ThlLED DESCRIPTION,

CHA~TFJRV.-D~TA~LED DESCRIVTION OF

THE

SUPERFNIAL

DEPOSITS, . . . . . . . .

50-108

Introduction, 50.

1. The Upland north of the Cork Valley, 50-65.

Upland north-east of Blarneey, 50. Blarney Valley,

5% Eastern end of Bla#rney Valley and CYountry

northward, 54.

Country beltween the Cork and

Blarney Valleys, 53.

Upland east of Kilcully and

north of the C.%rk Valley, between Dunkettle and

Queenstown Juncltion, %. Kilcully, 57, ~Glashaboy

River, 58. Butlerstown a,nd Knockraha, 58. Bally-

nagaul, 59. Upland between Queenstown Junction

and Pigeonhill, 59. Upland to the earth of C&r&to-

hill land Midleton, 61.


7/161

2. The Cork and Midlcton Valley, 65-86.

I%, low ground around Cork, with the bordering

slopes, 65. Carrigrohane and neighbourhood, 66.

Einvirons of ciolrk city and ea#stward to Blackrock,

66. Blackpool, /U. Gouldings Glen, 71.

Bride

Valley, 72. Leo Valley, 73. Douglas, 76. Allu- ,

vium of the Lee Valley, 77. Cork Lough, 77. Arti-

ficial changes around (York, 78.

Llow ground be-

tween Duukettlo and Queenstown Junction, 81.

Little Island, 81.

Harpers Island, 82. Brown

Is~land, 82.

Foaty Isl,and, 82.

Cork Valley be-

tween Foaty Island and Midleton, 82.

3: The Central Ridge, 86-91.

High ground south land south-west of Cork, 86.

R~ochestown, Passage West, and Monkstown, 88.

Great Island, 89. East of Great Island, 91.

4. The Oloyne and Carriga.line Valley, 91-97.

Ballinhassig to Carrigalinel, 931. R+affan and Shanbally,

92. Railway Cuttings from Raffeen to Carrigaline,

93.

Coast Sections near Ringaskiddy, 93.

Coast

Sections at Curraghbinny and Loughbeg, 94. Estuary

of the Owenboy, 94. rhe crlo~yns Valley, east of

Cork Harbour, 95. Corkbeg Island, 96.

5. Tho Southern Ridge and Co.ast-line, 97-1108.

1Jpland south of Bldlinhassig, 917. Upland south and

. south-east of Oarrigalino, 97. Coast sections

from Ringabella Bay to Crosshaven, 98. Poulna-

callee or ahwrch Bav and Ooast northward, 98.

The Upland

south-east of Colrk Harbour, 100.

Aghada, 100. White Bay, 101. I&hes Point, 102.

Trabolgan, 102. Gyleen, 103. Powerhtead Bay, 104.

Power Head, 104. Ballycroneen Bay, 104. Inbrjor

north of Powelr Head, 106. Upland between Cork

.

Harbtour and the open Coa#st, 1107. The Topography

aml Drainage of t.he Upiand, 108.

.

PART III.-ECONOMIC GEOLOGY.

.

CHAPTERVI.-ECONOMIC GEOLOGY, . . . , , 109-X%

Absence of Metalliferous Ores, 109. Building Stone

and Ornamental Marble, 199. Ra#re Minerals, 110.

Slates, 111. Bricks, 111.


8/161

[ vii ]

LIST OF ILLUSTRATIONS.

PLATES.

PLATE I.-East P,assage, Cork Harbour

:

A Transverse

VaJley,

Bon t& piece.

PP

II.-Antioline in Old Red Sandstone near Weaver

Point,

To

face p. 9

?S

III.-Carboniferous Limestone, Carrigmore Quarry,

Ballintemple,

?I >,

P* 28

I)

IV.dff of Boulder&y near Ring&skiddy,

,, >?

p. 41.

9) V.-High-level Glacial Gravells nelar Blackpool, ,, ,, p. 72

?)

VI.-Raised Beaoh and Rock Platform near mouth

of Uork Harbour,

?) 2)

p. 99

FIGURES IN TEXT.

Page

Fig. 1. Outline-map showing area of Cork Sheet, . . , 1

99

2.

9,

3.

?, 4.

*t 5:

0 6.

9) 7.

19 9.

$9 9.

9, 19.

1) 11.

tl 12.

)? 13.

), 14,

## 15.

Se&on across the western part of the Map, . .

,

Archceopteris (A&&&s) hibemiq from Kiltorcan,

.

Ar chamodolz (Anodonta) Jukesi,

from Kiltolroan, . .

Structure of Carboniferous Slate at Ring,abella Bay,

.

Czc~mot2ls

from Carbonifereus Slate and Coomhola Grit,

Diagram to explain relations between Carboniferous

Lime-

stone and Uarboniferous Slate

(J. I ?. J& es),

.

.

Diagrammatic section of the Raised Beach and overlying

deposits on the coast near ithe mouth of C?ork Harbour,

Plan of Leamlara Valley system, . . . . .

Cavity in Carboniferous Limestone filled in with drift,

Ballinaspig More Quarry, . . . . .

Diagrammatic section of the Blackpool Gravels and Gould:

ings Glen, . . . . . . . . .

Section across Cork, showing Superficial Deposits of Lee

Valley, . . . . . . . . . .

Plan of Cork in tihreSixteenth Century, . . . .

Plan of Cork in the Eighteenth Century,

. . . .

View of a Delta-Gravel f,an near Carrigtohill,

. .

,,

4

12

13

16

17

21

37

64

70

72

75

78

79

85


9/161

. . _ _ . .

- . _-


10/161

THE GEOLOGY

OF THE COUNTRY AROUND

CORK AND CORK HARBOUR

PART I.-GENERAL DESCRIPTION.

CHAPTER l.-INTRODUCTION.

Area of the Map,

In carrying out the plan of surveying the superficial deposits

in Ireland first in the neighbourhood of the chief centres of

population, the field-work during the year 1903 was concen-

trated upon the country around Cork, and an area equal to

that of an ordinary one-inch sheet of the Ordnance Map was

surveyed.

This ground included portions of four sheets of the

regularly numbered ,series of Ordnance one-inch maps, as the

marginal boundaries of these sheets fall inconveniently in

regard to the city and it,s suburbs.

The field-work has there-

fore been reproduced on a special or unnumbered sheet,

prepared at the Ordnance Survey Ofice, and so arranged that

it includes the surroundings of Cork and all the waterways

Fig 1.

~TOCORKLWDCORKfaRROUR &IEET.

--G?idazs1czQ. 2sgauw;~*4&&6m.

and inlets between the city and the open sea.

This map, to

be known as the

Cork District Sheet, is of the same size

as the ordinary numbered sheets, namely, 18 inches by 12

inches, representing an area of 216 square miles.

The greater

part lay within Sheet,s 187 and 195 of the previous survey,

with a smaller portion within-the eastern borders of Sheets 186

and 194. The accompanying Index-map, Fig. 1, will serve

to show the limits of the new sheet, and also the principal

places, rivers, heights,

&a.,

included within it.

I)


11/161

a

THE GEOLOGY OF CORK AND CORK HARBOUR.

Scope of the Drift Survey.

The previous work of the Geological Survey in the district,

published on the numbered one-inch sheets above referred to,

wa.s devoted to t,he m,apping of the

solid

rocks only, and,

except in the case of the alluvium of the principal valleys, the

maps contain no indication of the boulder-clay, gravels and

other

superficial

deposits under which these rocks are often

deeply buried.

On the present map the superficial deposits arc

shown by distinctive colours, according to (their composition,

wherever they are of #sufficient thickness to conceal the under-

lying rocks, while the colours representing the solid formations

are confined to the places where these rocks occur at the

surface or are covered only by a thin layer of soil and detritus

derived from the local disintegration {of the rocks.

The field-work on which this map is based was done on the

six-inches-to-the-mile maps of the Ordnance Survey, and has

been reduced from these maps to the one-inch scale for publica-

tion. Manuscript coloured-copies of the six-inch maps have

been prepared and are available for public reference at the

Dublin office of the Geological Survey.

As the recent investigation was confined to the superficial

deposits and did not include a re-examination of the solid rocks,

the boundary lines of the latter shown on the present map

have been transferred from the published maps of the previous

survey. For the same reason the description of the solid

rocks embodied in subsequent pages of this memoir is based

on the information contained in three previous memoirs of the

Geological Survey, viz. ,

the Explanation of Sheets 187, 195

and 196 (published in 1864)

;

Explanation of Sheets 185 and

186 (published, 1861) ; and

and 202 (published, 1862).

Explanation of Sheets 194, 201

The local details given in these

Explanations have not been reproduced ; and where fuller

information with regard to the solid rocks is required the

original memoirs, which are still obtainable through the usual

channels, should be ,consulted.

Since the publication of these

memoirs, however, some revision-work has been carried out

on the solid rocks of the district, resulting in the issue of revised

editions of #all the sheets in the years 1878 and 1879, showing

alterations in the classification and boundaries of the Old Red

Sa.ndstone series ; with further alterations of Sheets 194 snd

195 in the year 1891, consisting in the sep,aration and dis-

tinctive colouring of small tracts of shales supposed to be of

Upper Carboniferous ( Coal Measures ) age. These altera-

tions, which have not hitherto been described, will be briefly

discussed in the present memoir, with references also to other

literature relating to the geology of the district which has been

published since the original memoirs.


12/161

INTRODUCTION.

8

.

A short description of the Glacial and Post-Glacial deposits

is given as a sequel to the account of the solid rocks in Part I.

of this memoir. The detailed description of these superficial

deposits, containing the fuller results of the recent field-work,

is given separately, forming Part II.

;

while in Part III. the

economic geology of the district is dealt with.

Table of Formations occurring within the Map.

RECENT.

GLACIAL.

Reclaimed Land (Intak8) = Estuarine

I,

lluvium.

River Alluvium.

River Gravel and Gravelly D&as.

Sand and Gravel.

Boulder-Clay.

Local Rubble ( Head ).

Infra-Glacial Beach.

OLD RED SANDSTONE.

.

I

Upp8.r Shale or Po&doynonvya

Becheri

Beds (formerly termed Coal-Metl-

sUr8s

?),

not S8~&d~ EJhQWll, 8% p. 3@e

Carboniferous Limestone.

.

Lower Lim8&me Shale, and Carboni-

ferous Slate and Grits.

Upper Old Red Sandstone ( Kiltrbrcan

Beds of the

solid

maps).

Lower Old Red Sandstone ( Dingb

Beds of the solid maps).


13/161

4 THE GEOLOGY OF CORK AND CORK HARBOUR.

Form of the Ground and itpJ relation to the

Geological Structure.

In its leading outlines the geological structure of the district

is remarkably simple, and is very clearly expressed in the form

of the -groGd.

The Carboni-

ferous and Old Red Sandstone

rocks have been compressed

into a series of broad folds or

elongated

1

troughs and ridges

with axes ranging approxi-

mately east and west.

From

these axes the strata dip away

steeply on both sides, forming

a succession of anticlines and

synclines, with the newer rocks

descending into the troughs and

the older rocks rising into the

ridges.

The period of the earth-

movements causing this struc-

ture appears to have been

toward or at the close of Car-

bonif erous times.

Although very great thick-

nesses of rock have been stripped

away and the whole country

has been remodelled by denuda-

tion since the period of folding,

these anticlines and synclines

still govern the surface-features.

The less durable limestones

and shales of the Carboniferous

series are worn away relatively

more quickly than the more

resistant sandy and slaty rocks

which constitute the Old Red

Sandstone ; so that the synclines

are marked by broad deep

hollows of the present surface,

and the anticlines by hilly

ridges.

These features are

illustrated by the coloured sec-

tion at the foot of the map, and

by the following figure (fig, 2)

reproduced

from a former

memoir.

The broad undula-

tions of the rocks are compli-

cated by many minor folds

contained within them, which

are revealed in the contorted

structure frequently visible in

the open sections (see Plate II)


14/161

but these minor folds are without much effect upon the outline

of the land.

The position and direction of the principal folds are indicated

on the foregoing Index-ma& Fig. 1, the nomenclature adopted

being mainly that used by Prof. J. B. Jukes in the earlier

memoirs.

On the south the outcrop of the Old Red Sandstone

which forms the chief constituent of the

Southern Anticline

is marked by

undulating high ground, interrupted only by the

water-channel giving entrance to Cork Harbour.

This tract

culminates westward in Doolieve, 600 feet high, but east of

Cork Harbour the ground does not rise, in the present map,

above 318 feet.

The depression on the northern aide of the upland, #marked

en the Index-map as the Cloyne Syncline, is partly filled, in

its lowest and broadest portion, by Cork Harbour, and is here

mainly underlain by Carboniferous Limestone.

This belt of

limestone, however, becomes contracted westward of Carriga-

line and disappears before reaching Fivemilebridge ; and the

valley then assumes a narrower and steeper aspect.

The

Central Anticline

to

the northward of this depression

traverses the mlap from east to west as a steep-sided ridge of

Old Red Sandstone, broken only by the transverse water-filled

gorges of East Passage (Plate I.) and West Passage by

which the Great Isl*and portion of the ridge is insulated. At

the eastern margin of the map the ridge from side to side is

less than a mile in width and its greatest altitude is about

330 feet ; but it expands gradually westward to about three

miles in width, its flattened crest then forming a gently undu-

lating upland with summits ranging up to 579 feet in elevation.

This ridge is deeply trenched on both flanks by the ravines of

small ,streame draining from shallow basins on the summit

;

and on Great Island it is also indented by a large valley running

nearlypartillel with its strike for about tlwo miles.

The

Cork Syncline,

which forms the principal valley of

the map, is underlain by Carboniferous Limestone and Lower

Limestone Shales brought down in a deep infold between

the OId Red Sandstone rocks of the Central Anticline and the

similar rocks of the Cork or Northern Anticline. It is about

two miles wide in the west, and increases to over three miles

near Midleton at the e.astern margin of the sheet. The lowest

ground of this valley usually occurs immediately at the foot of

the steep slopes by which it is bounded on both sides, and is

due to the rapid weathering of the Lower Limestone shale.

In the middle of the syncline, between the outcrops of this

shale, the massive limestone frequently rises in irregular knolls

which, in a few places,

carry the ground above the loo-foot

contour.

The River Lee runs along the northern edge of the valley

from the western #margin of the map to three miles east of tbe

city of Cork, and then turns southward through Lough Mahon

and the gorge ,at West Passage to Cork Harbour.

After being

deserted by the Lee, the low flat on the northern side of tht


15/161

Q

Cork Syncline is in part occupied by tidal waters, and is con-

firmed eastward to the eastern extremity of Little Island and

Harpers Island.

Tidal chann,els then branch southward from

it around Foaty Island and join the broader inlet which sepa-

rates the northern shores of Great Island from the mainland.

The seemingly aberrant deflection of the Lee. from the broad

longitudinal or

strike

valley to the narrow transverse gorge

by which it breaks through the Central ridge is a good example

of the phenomenon which recurs again and again in the courses

i>f some of the rivers of the South of Ireland, particularly in

respect to the Lee, the Blackwater, and the Suir. It was from

the study of the peculiarities of these river-courses that Jukes

was led to enunciate, in the year 1862,l his famous principle

that the erosion of such valleys must have been commenced on

a plane which lay above the level of the hills and ridges through

which the gorges have been cut, and that the present hills are

the out,come of the differential resistance of the rocks under

the influence of long-continued subserial erosion. This prin-

ciple, which has since found universal application, was stated

as follows by Jukes in describing the Cork district in a

previous memoir (Explanation of Sheets 187, 195 and 196,

p. 32).

This

marine action

[by which the original high-level surface is sup-

posed to have been produced] cannot now be traced anywhere except in a

P

eneral way. The surface produced by it must have been a gently undu-

ating plain, which was wholly above the present surface, unless the

summits of some of the present hills and ridges may possibly have-formed

%

art of it. That formerly existing plain has been eaten into vertically

y the action of the rain and rivers running over it, and these have

removed all the rock that intervened between it and the present surface

of the ground. The result has been that the hard and insoluble sand-

&ones and grit&ones, whether of the Old Red or C?a#rboniferous late, now

form hills and ridges, while the soluble limestones, and the more easily

eroded shales and clay mslartesave ,been worn down into valleys and ffats.

It was long before I arrived at the conviction that this action wad truly

and solely an atmospheric one, but the conclusion was at la& forced

upon me . . . .

Under the explanation given by Jukes, we should regard the

West Pamage as part of the valley initiated by the south-flow-

ing Glashaboy River on an original high-lying land-surface

which rose gently toward the north.

Afterwards, through the

rapid development of the east and west valley along the strike

of the perishable Carboniferouq rocks, more and more of the

drainage of the country to the west,ward w4as drawn through

the gorge, until this water, combined in the River Lee, far

exceeded in voIume that of the original main-stream.

Similarly, the East Passage (Plate I.) represents the con-

tinuation of the valley of the Owennacurra River; and the

entrance of Cork Harbour marks the course taken by the

confluent streams from both gaps in their further passage

Routhward. The present condition of the channels has been

1 On the Mode of Formation of some of

the

River-valleys of the South of

fretand, by J. Reete Jukea.

Quart. Journ. Oed. B loc.,vol. xviii., p. 378.


16/161

PHYB1OQRAPHICAL FfiAlfURfi8.

r

brought about by later depression

of

the land, whereby the

lower

parts of

the valleys were converted into marine inlets,

or ~iaa, as submerged land-features of this kind are sometimes

now termed by geographers.1

Prof. E., Hull, in his

Physical Geology and Geography of

Ireland (2nd ed.

,

1891, p. 208) proposed certain modifications

in Jukess viewIs, by introducing th,e supposition that the west-

flowing streams may have been diverted southward by obstruc-

tions due to faults or folds, but there seems no need to call in

this factor.

More recently Mr. J. Porter, in a suggestive

paper on Geographical Evolution in Cork,2 has arrived at

the conclusion that river-diversion on a large scale may have

taken place through the blocking up of the original channels

by drift d,eposits during the Glacial Period. But it will be

shown in the context that although some minor instances of

river-diversion of this kind have taken place in the district and

are readily recognisable, the principal transverse gorges are of

Pre-Glacial age


17/161

t3

3~14 GI~OLOGY oP CORK

ANY

COOK BARBOUY~.

_

along boat-shaped troughs.

Thus, to the north-east of the

city of Cork the anticline is split into a northern and a southern

branch by thie intervention of the lens-shaped strip of Lower

Limestone Shale occupying the minor Riverstown Syncline,

which gives rise to a small longitudinal valley

;

and again, in

the north-western corner of thie map there is a deep wedge of

Carboniferous Limestone and associated beds, forming the

Blarney Syncline, which is marked by thle broad low strath in

which stand the celebrated ruins of Blarney Castle.

But dis-

regarding these minor infolds, the country north of the Cork

valley may be ,described as an undulating upland of Old R,ed

Sandstone rising gradually toward the north and merging into

the great belt of similarly constituted country which stretches

across Ireland from the west coast south of Dingle Bay to the

east coast south of Dungarvan, generally referred to as the

Mangerton

Axis or Anticline. The highest ground of the

present mlap lies within this tract, the greatest elevation

reached being \640 feet, on the summit of a rounded hill 2%

miles north of Carrigtohill.

by

The margin of this upland is high and st,eep, and is trenched

deep narrow ravines in which the principal streams have

graded their channels to a low level in agreement with the

drainage-level of the Cork valley. But in all parts beyond the

immediate influence of these deep channels, the plateau shows

a mature topography, with gently rounded features and

broad shallow valleys, evidently the relics of a past period

when the base-level of erosion had been nearly attained and

the country was being slowly reduced to the condition of a

penceplain. This period was certainly anterior to Glacial

times, as the Glacial drift not only rests on the gently rounded

features of the plateau, but also in places has been lodged

within the deep ravines. It may be surmised, therefore, that

at some time about the close of fhe Tertiary epoch, the

drainage-system which had become mature and sluggish was

rejuvenated by a relatively rapid deepening of the longitudinal

valleys, probably as the result of some change of climate

accompanied by elevation of the land. The gradient of the

trunk-valleys draining the Old Red Sandstone tracts was thus

sharply raised at their debouchure into the limestone-valleys,

and they commenced to cut rapidly backward into the upland.

We shall revert to the probable reason for this renewal of

erosive activity in a later part of the memoir.


18/161


19/161

,


20/161

THE PAL2EOZOIC ROCKS.

.

9

CHAPTER IT.-THE OLD RED SANDSTONE.

The Old Red Sandstones, which constitute the oldest rocke

of thi*s district, consist of alternating bands of sandy and clayey

composition, of which the prevalent tints are various shades

of dull red, brown and green.

The clayey beds are indurated

and converted by a Fell-marked slmatyclelavage into a soft clay-

slate, and the sam,e cleavage-structure also often pervades the

sandstones; thus giving an e,ssentially slaty character to the

whole series (Plate II). The strike of this cleavage is approxi-

mately E. 25 N., its dip being either northerly or southerly,

at angles varying from 60 up to vertical. There are no con-

glomerates in the *series in this district, though in the prolonga-

tion of these rocks to the westward, conglomerates are fre-

quently con,spicuous.

The. lowest beds are exposed along the

crest of the Central anticline and in the Cork (anticlme toward

the northern m,argin of the m.ap, but it is probable that these

beds are still far above the base of the series. In estimating

the thickness of the formation at not less than 5,000 feet,

Jukes remarked that the continuous section at Monkstown

shows a thickness of 4,300 feet, without any change appearing

in the lower beds there shown, or any sign of the base of the

formlation being approached.

l

Fossils are extremely rare in th,e Old Red Sandstone of this

district, being entirely unknown in the lower part of the Beries,

and in the upper part represent,ed only by scanty remains of

plants, #and a shell, ArcIzuznodon (AnodoGa) Jukei It is

believed that the whole series is of fresh-water origin and has

been accumulated in a large lake fed by a powerful river or

rivers.

The series is divided into two parts by slight lithological

differences_the Low,er Old Red Sandstone or so-called

Dingle Beds , and the Upper Old Red Sandstone or Kil-

torcan Beds

-which will now be separately discussed.

Lower Old Red Sandstone,

The lower division, which includes the greater part of the

series, is characterized by the prevalen,ce of brown and purplish

tints in its sandstones and sl.ates, and by the comparative rarity

of the yellowish and greenish beds which prevail in the upper

division. The )boundary between them in this district is, how-

ever, &more or less arbitrary and can only be approximately

defined.

The ,alternative term Dingle Beds was applied to the

Lower Old Reid Sandstone in the revised editions of the solid

sheets published in 1879 and in subsequent editions

;

but it

has not been thought advisable to reproduce this term on the

1 Hem.

t&sol.

ihrvey.

Explantttion of Sheets 187, 196, and 196, p. 7. It is

probable; however, that in this estimate insufficient allowance has been made

for the effect of folding in increasing the apparent thickness of the beds, as this

effect was imperfectly understood et the time when the estimate wss made.

The

preeenoe of

cleava

e in itself implies thst the beds have undergone severe lateral

compression, whia% almost always implies considerable vertiosl expansion.


21/161

OEOLO(fY OP CORK AND CORK HARBOUR.

some confusion appears to have arisen in regard

. . __

. . _

ti it. The name was orlgmally appllled to a, series of sand-

stones, sh#ales and conglomerates in the

Dingle Promontory

which

are supposed to be closely asslociated with Upper Silurian

rocks and are overlain unconformably by part of the Old Red

Sandstone. Professor E. Hull1 believed that this Dingle series

W&S he equivalent of the Glengariff Grits and of the lower part

of the Old Red Sandstone throughout the South of Ireland.

Consequently he held that a great break existed between the

Lower Old Red or so-called Dingle Beds and the Upper Old

Red or Kiltorcan Beds

;

and he reglarded thle former division as

being ,clogely allied with the Upper Silurian, and proposed that

it

nshould be relegated to a new system to be called the

Devono-Silurian formation,2 while the l.atter division was

recognised as being only slightly older than the Carboniferous.

Even wh,ere the two divisions were apparently condormable

and in direct sequence,

Prof. Hull believed that the great

unconflormity existed, but was concealed by the prevalent later

8 olding.

Mr. A. McHenry, who took part in the re-examination of the

ground which led to the issue of the r,evised maps in X379-1880,

is of opinion however that the correlation of the beds showing

Silurian affinities in the Dingle Promontory with the lower

part of the Old Red Sandstone of the country farther eastward

and south-eastw,ard ,cannot be


22/161

OLD RED SANDBTONE. 11

But the question is one which could only be settled by the

critical re-exlamination of a l,arge number of sections in the

south-west of Ireland, and this work is at present beyond the

scope of the survey.

Meanwhile,

designation of

by reverting to the original

Lower Old Red proposed by Jukes, it is

granted that the inference implied in the adoption of the term

Dingle Beds

corroboration.

on the revised

solid

map requires further

Upper Old Bed Sandstone.

The description of this *division given by Juk,es is a,s folc

lows1 :- The Upper or Yellow San&tone differs from that

below chiefly in the greater abundance of yellowish and

greenish cl*ays and sandstones, though often interstratified with

red beds.

The boundary between the upper and lower parts

of the Old Red is quite arbitrary, though their characters are

sometimes sufficiently di.stinct to enable one to recognize them

if a sufficient mass of either be exposed. Beds of rusty brown

colour, readily decomposing into a loamy sand, occur in both,

but chiefly in the upper group. These are decomposed Corn-

stones, ,and, when unweathered, are found to be full of strings

of crystalline carbonate of lime. Many of the clays or slates

of the upper part are also full of holes or lcells, looking at first

like places from which fossils have been removed by decdm-

position. These beds precisely resem,ble Isome beds in the

Old Red Sandstone of South Wales, from which indeed that

of Cork differs only in the presence of slaty cleavage.

Rocks of this character form the greater part of the crest of

the low Southern Anticline (Fig. l), and occur in a narrow

belt along both sides of the Central Anticline. They also

occupy the edge of the upland north of the Cork valley and

surround the depressions which mark the Riverstown and

Blarn,ey synclines. Their thickness is estimated at from 400

to 500 feet.

Fossils are extremely rare in these rocks, but those which

have been found are of great interest, inasmuch as they show

that the beds are of fresh-water origin, and that they are equi-

valent to, the celebrated fossiliferous rocks of Kiltoroan in

Kilkenny .

The term Kiltorcan Beds, which has been applied as an

alternative title to the Upper Old Red Sandstone, expresses

this relationship.

, >

The principal locality for the fossi1.s obtained from these beds

in the Cork district was from an excavation at Tivoli Villa on

the lower Glanmire Road, one mile and a h,alf east of Cork.

The specimens included fragments of the well-known Kiltorcan

plant, Archaopteris (Ad&&ites) Izibernica, Forbes, and the

bivalve mollusc Arckxn~d~n (Andonh)

Jukesi,

Forbes. It

is also stated in a former memoir ( Explanation of Sheet

187 ,

&c., .p. 23, footnote) th,at Sir R. Griffith procured a

large frond of the plant from the cutting at the mouth of the

railway tunnel in the strike of the same beds.

1

Mem. Oed.

Survey.

&planstion of Sheet 187, &cc.,

p. 7.


23/161

The following figures represent the better-preserved apeci-

mens of theBe f&s& obtained from iltorcan.1 The plant-

Fro. 3.

Archceopterie (Adiuntitee)

habernicu

(Forbes), (from Mem. CfeoZ. Burvey.

Explanation of Sheem 147 and 167)

;

Kiltorcan Hill, co. Kilkenny.

c

WkE3

a is a representation in outline, somewhat restored, of a large portion of

one of the fronds reduced to one-sixth of the natural size ; b is a sketch of one of

the leaflets, natural size, showing the venation by longitudinal striae, which are

occasionally forked; c is a single branch in fructification, taken from another

specimen; it shows the spore csses which were originally aggregated into clusters

end grctnulated. (&I&J).

1 R. Griffith and A.

Bron

in the Yellow Sandstone

%

niart

On the Remains of Fossil Plants discovered

t&a,

&c.,

Journ. R. Dubli n fl oe.,

vol. i., p. 313.

W. H. Baii

Hill, co. Ki kenny.

On Fossils from the Upper Old Red Sandstone of Kiltorcen

SC.

Proc. R. Irieh Acad.,

ser. 2, vol. ii., p. 46. See also 6.

Htlughton On the Evidence afforded by Fossil Plants as to the Boundary Line

between the Devonian and Carboniferous Rocks.

Joum. Bed. Sot., Dublin,

vol. vi., p. 227*; 0. Heer On .

Jown. Ued. ~oc.,

vol. xxviii., p.

les;

L [plants] from Kiltorcan. QUMt.

&d later works on Palaeobotany.


24/161

OLD REID SANDSTONE.

13

remains are of peculiar interest,

ELS

hey represent the oldest

land-plants known in the British Islands. The magnificent q

series of these fossils from Kiltorcan preserved in the Survey

Collection in the Dublin Museum of Science and Art include

specimens showing the fructification.

Fro. 4.

Archanodon (Anodonta) Jukesi

(Forbes), (From

Mem. Ueol. Survey:

Explanation

of Sheets 147 and 167 ): Kiltorcan Hill, co. Kilkenny.

Reduced to half natural size. . . . . a exhibits the exterior of this

elongated shell, with its well-marked lines of growth, characters common to

existing fresh-water unios and river mussels

; b

is from a cast of the interior of

the left valve of a very large specimen

;

it shows the impression or cicatrice of

the adductor muscle, and the straight toothless hinge line. (Buily).

There is no sharp line of demarcation between the Upper

Old Red Sandstone And the overlying elaty shales and grits

which are assigned to the Lower Carboniferous system. The

junction is apparently everywhere conformable, with indica-

tions of a gradual passage from the one series to the other,

although a change of conditions is indicated, since the over-

lying beds oontain a *marine fauna.

So close is the association

that it was at one time thought desirable to include the Kil-

torcan Beds with the Carboniferous, and as will presently be

shown, Prof. Jukes in his later papers advocated a return to

this mode of classification.

But on the other hand it would


25/161

I$.


appear to be more in keeping with the method adopted in

England and on the Continent if part of the #division known in

Ireland as the

Lower Carboniferous Slate and Coomhola

Grits were regarded as marine Upper Devonian, and there-

for,e separated from the Carboniferous rocks and chased along

with the Old Red Sandstone system.

An extensive literature

ha,s arisen upon these questions of technical classification, and

there is little doubt that if the Cork rocks were to be re-sur-

veyed at the present day, modifications would be introduced

into the scheme on which the rooks were originally mapped.

But so-long as the true order -of succession of the strata is

expressed upon the map, as in the present case, the scheme of

classification under which the rocks are arranged, though

technically important, will not greatly affect the direct purpose

of the map.


26/161

LOWER CARBONIFEROUS ROCKS.

15

CHARTER I&--THE CARBONIFEROUS ROCKS.

The method of classification adopted in the original survey

of the Carboniferous rocks of the Cork


27/161

16

THE GPOLOGY

OF CORK AND CORK HARBOUB.

Lower Limestone Shale and Carboniferous Slate,

The following is the description of these beds given by

Jukes in 1864 in the Explanation of Sheebs 187, 195 and

196 :-

In the neighbourhood of the Cork valley this group mn&te of dark

gray or

black shale, usually cleaved into clay slate, interstratified with

thin bands of fine-grained gritstone or sandstone of a gray or yellowish

colour.

In some places the lower gray grits alternate with red beds for a

short distance, so that it seems to pass down by insensible gradation

into the upper part of the Old Red Sandstone, although no marine fossils

are known to occur beneath a red bed. Its upper part is nowhere well

seen, except at Riverstown, where it seems as if about to graduate upwards

into the limestone, as thin flaggy limestones alternating with black shales

are visible there.

A curious little bed of conglomerate, consisting of a

base of gray grit in which pebbles of white quartz are enclosed, occurs in

the middle of the slates.

*

FIG. 6.

RingabellalBay, looking E.

~WVOSS

the mouth of CorkHarbour (from Hem. Geol.

Burvey,

Explanation of Sheets 187, 195, and 196 ).

CarboniferousSlate, showing beds, dipping to the S. at 36 ; join@ cutting

the beda at right an lea in two directions ; and cleavage,dipping N. at 70. The

p+ &view_ lies

a out a~,~~~~,,_tq,th~,?~~th~~~~_ zf

i~~~~i~~l~~-~

-@3s&?&-

( From wanti of &ygontinuous section from

up to the limestone,

it is impossible to determine the thickness of the

intermediate beds with any accuracy ;

but it can hardly ever exceed 1,000

or 1,500 feet, when the limestone is present above it.

( It is in many places very fossiliferous, the fossils, except the plant

remains, being all of marine origin ; and it is remarkable that no un-

doubted marine fossils are ever found in the red beds, but frequently

make

their appearance in the gray.

The characters here assigned to the Lower Limestone Shale do not,

except in the element of thickness and slaty cleavage, differ from those

which are found in similar beds between the top of the Old Red Sandstone

and the base of the Carboniferous Limestone generally in the south of

Ireland and also in S. Wales.

The descriptionapplies to the whole valley


28/161


17

of Cork, and to the neighbourhood of Ballycottin, Cloyne, Queenstown,

and Monkstown.

Near Monkstown, they are certainly 1,000 feet thick,

where they dip beneath the Carboniferous Limestone ; but where they

rise again from beneath it, about Carrigaline and Coolmore, they seem to

be much thicker, so that it appears impossible to assign them a less

thickness than 2,000 or 3,000 feet.

This thickness must be again doubled

in the Kinsale country, as excellent sections are seen on both sides of the

promontory of the Old Head, exposing a thickness of not less than 6,000

feet of dark gray shales and sandstones.

(See

Explanation of Sheet 194,

&c.)

The grits which come in in the lower part of this series were called

by myself Coomhola grits, from the name of a place in Bantry Bay,

where they assume a far greater importance than near Cork.

They have

rather a peculiar assemblage of fossils, which occur either in the grits, or

in the slates which are interstratified with the grits, such as shells of the

genera Cuc&Zcea, and

Curtomtus,

the

Avicula

Damn.onie&s, and others,

FIG. 6.

Curtonotus from Carboniferous Slate and Coomhola Grit; County Cork (from

1Mem. Geol. Survey : Explanation of Sheets 187, 195, and 196 ).

a, Curtonotus elegans

(Salter), cast of interior of shell.

b. Exterl%r of shell.

c, G?.

Ourtonotus

var.

elongatue,

cast of interior of shell. d. From gutta-percha

impression of hinge.

e.

&rtonotus

var.

rotundatus,

cast of interior of shell.

f.

Curtonotus

species, cast of interior of shell.

g.

Curtonotus central&,

cast of in-

terior of shell. (Baily.)

but these are mingled with many other species which are found in the

shales and limestones of the Carboniferous formation throughout the

British Islands.

If we give to these gray beds the name of the Lower

Limestone Shale (which they have in S. Wales and near Bristol) in all

those places where it has the Carboniferous Limestone above it, it will be

better to adopt Sir R. Griffiths term of Carboniferous Slate for those

districts where it acquires so great a thickness, and is no longer covered

by the Carboniferous Limestone.

This is the more necessary, because I now believe that the part thus

called

hhn~ferozls slate

never had the

Carboniferous Limestone

above

it, but is contemporaneous with that limestone-mud, sand, and silt being

deposited over one part of the district, while calcareous matter was being

accumulated in another,

c


29/161

18

THE GEOLOGY OF CORE AND CORK HARBOUR.

A list of the fossils which have been recorded from the Lower

Limestone Shale and associated deposits within the area of the

present sheet or from localities only just beyond its boundaries

is given subsequently (pp. 26 and 27). The list h,as been com-

piled from that of the late W. H. Baily, published in the

Explanation of Sheets 187, 195 and 196, with additions from

a

later paper published by Jukes, for which the fossil-lists were

also prepared by Baily.

The names of the fossils in this list,

and also in the subsequent lists, are reprinted as given in the

original records cited, as it was found that much confusion and

risk of error would have arisen if the names had been altered

to their supposed equivalents in present nomenclature without

re-examination of the original specimens, which is beyond the

scope of the present drift-survey.

It will be noticed that there are very few species in the list

obtained from that part of the Iseries classified as Lower

Limestone Shale by Jukm which have not al,so been obtained

from the Carboniferous Slate district or from the Coom-

hol,a Grits of 4he same district. Therefore if these lists may

be taken m fairly representative of the fauna of the different

rock-groups, there is no palEeontologica1 evidence on which to

establish a distinction between them. Neither do we find any-

thing in the fossils to support the view of Jukes, on the one

hand, that part of the Carboniferous Slate of the south-

western district may be equivalent to the C,arboniferous Lime-

stone of the north and north-east, and therefore in part newer

than the Lower Limestone Shale

;

nor, on the other hand, to

support the widely held opinion that the CoomhoLa Grit

series may be older than th,e Lower Limestone Shale. If the

Carboniferous Slate and Coomhola Grits be relegated to the

Upper Devonian, it would appear to be necessary to regard the

greater part of the Lower Limestone Shale of the Cork district

as Upper Devonian also.

(See Note at end of list, p. 27.)

The views of Jukes on the question of classification, to which

reference has been made, are expressed in the following state-

ment, extracted from the Explanation of Sheets 187, 195 and

196, pp. 32-37 :-

I havz, however, arrived at a conclusion difEerent from my original

one respecting the relations between the rock groups of the district,

which it will be well to give a brief account of here. Wherever th6 Car-

boniferous Limestone occurs in this district, it lies above beds of dark

gray or black shale or slate.

These beds are thicker near Cork than they

are farther to the north, about

Mallow for instance, or anywhere in

that latitude, either at Kenmare to the west, or at Dungarvan to the east.

Proceeding from, &Fk to the aou+h and west towards Kinsale, these

gray slates become still thicker, but are still capped by the limestone as

far as Carrigaline.

The most obvious supposition is that the lowest lime-

stone beds about ,Cork are the same beds which are the lowest at Mallow,

and that the lowest beds about Carrigaline are the same as the lowest

at Cork ; in fact, that while the limestone remained the same over the

whole area of the south of Ireland, a great thickening took place in the

oeds below the limestone in the south-western part of the county of Cork.

This increase of thickness in those beds, as we proceed towards the south-

wesi, is an undoubted fact. ; but I now believe that it was accompanied

by a corresponding thinning out and dying away of the limestone, and


30/161


19

that the bottom beds of the limestone at Carrigaline correspond to beds

which are above the bottom beds near Cork, and the bottom beds of Cork

are in like manner contemporaneous with beds that lie above the bottom

beds at Dungarvan and Mallow.

The first suspicion that such an interpretation was the true one, was

derived from the examination of the fossils. Some specimens of fossil

fish were found by the late Mr. Flanagan, in some black shale near

Ballyheedy R.C. Chapel, SW. of Ballinhassig (in Sheet 194). Professor

Edward Forbes recommended me, in the year 1852, to send these to Sir

P, de M. Grey Egerton, for his inspection and determination. Sir R.

Egerton was kind enough to inform me that they belonged to the genus

Ccrzlacunthus

which he said he had never seen any trace of in any beds

below the Coal Measures.1

These fish remains were accompanied by shells of the genus Po&

donomya. The same shells occurred also near the inner corner of the

.

Old Head of Kinsale, near Lispatrick Lower, where they had been pro-

cured by Sir R. Griffith, and have since been found by ourselves. Posi-

donomya, although very characteristic of the lower Coal Measure Shales

in the south of Ireland, does occur in the Carboniferous Limestone also.

I therefore concluded that it might occur in the Carboniferous Slates which

I then supposed to lie wholly below the limestone, and that the genus

Codacmthw might also be found in earlier rocks in the south of Ireland

than elsewhere.

Still the possibility of these black shales being Coal Measures, resting

on the Carboniferous Slate by overlap or unconformability, remained

present to my mind, accompanied, however, by a repugnance to the sup-

position that the Carboniferous Slate could possibly be contemporaneous

with the Carboniferous Limestone.

A short visi$ however, in Se tember,

Fl

1852, to the neighbourhood of

Barnstaple, in N. Devon, and t e

acquisition of a set of fossils from

Mr. Symons, of Braunton, collected in that parish, removed this repug

nance. I saw that both lithologically and palseontologically, bed for

bed, and fossil for fossil, the Braunton and Pi&own rocks of Devon were

identical with the Carboniferous Slate of Cork. The Marwood Sand-

stones, and the gray grits below them that form Baggy Point, were ob-

viously the same as our Coomhola Grits, and the red and green rocks

that rise up from beneath those rocks in Morte Bay, are exactly similar

to:? Upper Old Red Sandstone of large parts of the we& of County

Rut the Coal-Measures of Devon rest on the Carboniferous Slate,

without the intervention of any Carboniferous Limestone in its ordinary

form, often without any appearance of limestone at all.

The whole

series of N. Devon seemed to me to be a conformable one, and in many

instances it a.ppeared difficult to draw any very decided boundary between

the Coal Measures and the rocks below. If, however, we have Coal

Measures abov& and Old Red Sandstone below, the rocks between them

must be of the age,of the Carboniferous Limestone.

It is possible, there-

fore, that the sa,me may take place in Cork, and that the small patches

of black shale, which in Cork contain fish of the genus Caelacanthus, and

shells of the following species-Posidomomyn Becheri and P. mern&raru;ccea,

Avi oul opect en papyraceus, Lw nw l i cardi um sp.,

Orthoceras

inctum,

0. sea-

Zcvre, nd 0. zcn&2;atum, and

Goni at i t es sphceri cus,

an assemblage so pecu-

liarly characteristic of the lower Coal Measure shales throughout, Ireland,

from Kerry to Dublin-are really themselves Coal Measure shales also.

The plants identified by Mr. Baily as Nceggemthiu dichotoma, also occur

in the same locality as the C& acanthus.

If we add to this the fact that these patches of black shale differ in

lithological character from the general mass of the Carboniferous slate,

and are precisely like the lower Coal Measure shales* of Kerry, Limerick,

1 See pages 32-35 for discussion of these supposed Coal Measures.

* This is espeoially emarkable n one

a small quarry by the roadside, at Rag z

lace, where saw them freshlyo

P

ened, at

ridge, three miles S.W. of

between CooloulithaHouse and TemplemichaelChurch.

Bnl inhassig,

C2


31/161

2


Tipperary, Kilkenny, Carlow, and Dublin, the evidence in favour of

Ei;tteally those beds becomes sufficient to warrant us in accepting

.

On a reexamination of the Carboniferous limestone between

their

it as

Car-

rigaline and Cork Harbour, with this idea as a basis, I saw that two

points, that had previously struck me as remarkable, favoured this

hypothesis.

One of these points is near Carrigaline Church and Castle.

A mass

of dark gray, fine-grained grit is visible at the corner of the cross-roads,

while immediately north of it there comes in thick, massive, gray, crystal-

line, crinoidal limestone.

Neither of these rocks are at all like the beds

that usually occur at the base of the limestone, where it passes down into

the Lower Limestone shale, so that it is probable that the bottom beds

at this locality are not the regular basal beds of the limestone, but some

higher ones.

I was at one time half inclined to suspect that the lime-

stone might be unconformable to the lower rocks at this place, but the

exposure of the latter is too small and obscure to found such a sup-

position on.

I The other instance i.s much more telling, though it has to be sought

in an obscure locality. It is on the south side of the promontory of

Ringaskiddy, on the eastern shore of the shoal inlet there

where some beds of dark gray shale and thin gray grit bands, verk liketh;?

Carboniferous slate beds (and not like any beds that are called Calp),

come in above some 800 or 900 feet of thick, gray, crystalline limestone.

These look very much like beds of Carboniferous slate beginning to be

intercalated between beds of the limestone, or like beds of Carboniferous

slate con&g in over the Eimestme, and as if the limestone was begin-

ning to die away as an

inlier

in the slate.

Lastly, we may appeal to the general palseontological evidence procur-

able from the Carboniferous slate itself.

With t-he exception of the shells

called Czcc~ZZcca nd Cwrtomtus, and a few other fossils which are found

almost solely in the gritstones (and which we m.ay suppose, therefore, to

have been sand-loving animals)., and a few species, such as Modiola

Macada,mi and Avicula Danmomensis, which are found chiefly in shales

or slates (and appear, therefore, to have been inhabitants of muddy

bottoms), most of the species found in the Carboniferous Slate are also

found in the Carboniferous Limestone. It is true that the limestone has

many species which are not found in the grits or in the shales or slates,

but it is obvious that we may attribute this also to the nature of the

different sea bottoms which were favourable to them, and not to the dif-

ferent periods of their existence.

Certain animals loved clear seas and calcareous bottoms, certain

others preferred sand, and others again mud, all inhabiting simulta-

neously different parts of the same sea ; while others, and those the most

abundant in individuals, ranged indiscriminately throughout. Among

the latter we may include those common Carboniferous species, Fenestella

antiqua,

A thy ri s ambigua,

Producta scabricula,

Rhynchonella plezlrodon,

Spirzfem

czcspidata and

S. striata

(varieties of which latter species are

probably the

disjmcta

of Sowerby,

Vmmezci l l i i

of Murchison),

Strepto-

rhynchus crennistria,

and

Terebratbla hastata,

which range throughout

the Carboniferous Slate, as thev do throughout the Carboniferous Lime-

stone, occurring in the grits and slates side by side with the fossils that

are peculiar to those beds.

[ I feel, then, now assured that the Carboniferous Slate must be taken

to be contemporaneous with the Carboniferous Limestone, and that here

and there in the Carboniferous Slate country of Cork, small patches of

Coal Measure shales come in conformably on the topmost bed of the

Carboniferous Slate, just as they do on the top of the Carboniferous

Limestone in the northern part of County Cork, and the rest of the S.

of Ireland.

The deposits of sand and mud which first succeeded the formation of

the Old Red Sandstone in South Ireland and South Wales, were con-

tinued uninterruptedly through the whole Carboniferous period to the

southward and westward of a line which runs through Kenmare Bay,


32/161

ark

Harbuur, and the Bristol Channel, while to the

north of that line

those muddy and sandy deposits were interrupted during a large part

of the period, and the Carboniferous Limestone was formed from the

waste of the bodies of marine animal organisms, which flourished in the

abeence of the mtchanic$ detritus.

Coomhols Grits.

,

-

.

,

-

.

.

-

.

.

.

--

*

.

.

.

.

1

Carboniferous lA;meatone,

The Carboniferous Limestone was mainly derived from the debris of

submarine forests of Crinoidal animals

; just as many great bulks of

limestone are being now formed in tropical seas from the debris of


33/161


34/161

L;OWE R CA~kO~IFtiROU$ R6CK&.

This conclusion will apply to the Eifel limestones and the other rocks now called

Devonian in Europe and America, as well as to those of the British Islands.

It

will also follow that no part of the Old Red sandstone can properly be called

Devonian, as the topmost bed of the Old Red sandstone will then be shown to

have been in existence before any of the beds containing the marine Devonian

shells were deposited.

The upper art of the series called Old Red sandstone, that containing plant

remains and fis

%

of the genera Pterichthys, Coccosteus, &c., will then form the

conformable base of the Carboniferous series, while the lower

art, containing fish

of the genera Cephalaspis, &c., %ill more properly belong to t

Silurian Series.

e top of the Upper

These hypothetical conclusions, however, are here put forth as problems for

solution, having a sufficient amount of probability to make them worth enter-

taming, and not as demonstrated theorems.

E.B.J.]

It will be noticed that much stress is laid by Jukea in the

above-quoted passages on the supposed Coal Measures directly

overlying the Carboniferous Slate in the neighbourhood of

Ballinhassig . But, as already mentioned, it must now be

acknowledged, for reasons to be subsequently discussed, that

the correlation of these beds with the Coal Measurers can no

longer be sustlained. Their fa,una, though newer than that

of the Carboniferous Slates themselves is still a

Lower

Car-

bonifer0u.s fauna, being one which iss found in other parts of

Ireland in the ,sh&les associ.at,ed with the upper part of the

Carboniferous Limestone (p. 33).

In the above argument Jukes fully recognized the close

relationship of the Carboniferous Slate series with the Pilton

and Marwood Beds of Devonshire both in their respective

faunas and in their lithological characters. This correla-

tion has indeed been accepted by all geologists who have

attempted to compare the Cork rocks with those of Devon-

shire.1 Thus, Davidson, in dealing with Devonian brachiopods

in his great Monograph on the Brachiopoda, vol. iii., part vi.,

pp. 106-107 (Palaont. Sot. for 1863), pointed out the close

resemblance of these fossils from the two countries, and en-

forced the comparison by a tabular list. He contributed a

further discussion of the correlation to the Geological Surveg

Memoir on Sheets 192 and 199 (pp. 28-30)) published in 1864,

from which the following passages may be quoted :-

it would appear that about twenty-one species of Brachio-

pod;

hkebeen found to occur in the North Devon grits and slates, while

about sixteen have been recognised in the Irish corresponding beds.

Of the twenty-one North Devon species, nine or ten only have been

recognised in the Irish brown grits, not quite half of the species being

common to the two.

They contain in common

Athyr is

(perhaps concentrica),

Spkifera

disjuncta

and

Cyrt ina het erocl i t a 1

hitherto considered to belong to the

Devonian age, but there is no reason why they should not have existed

also in that of the Carboniferous period.

The absence, however, in these Irish beds of any example of

Eh.

l at i costa, St rophdosia caperat a, Product us pra& ngus,

and Gngulla

mola,

species so common and characteristic of the ,North Devon beds, is very

remarkable ; but our not having met them among the specimens sent from

Ireland fovr e,xamination, is no proof that they do really not occur in

these Irish grits.

1

Since the above was written, this correlation has been restated by Dr.

Wheelton Hind in a paper to which further reference is given on p. 26.


35/161

ti4


In a paper1 published in 1866, Jukes expressed his convic-

tion, after personal examination of the Devonshire sections,

that

the rocks of North Devon belong partly to the group

called Carboniferous Slate in Ireland, and partly to the Old

Red Sandstone. And Ias he still adhered to the view that the

Csrboniferous Slate was in part deposited synchronously with

the Carboniferous Limestone, he suggested that the upper

portion of the Devonian series in Devon might also be equiva-

lent to the Carboniferous Lime,stone.

The following concise re-statement of his views with regard

to the Gork rocks as a whole, is given by Jukes in his last-

quoted paper (p. 345) :-

One general conclusion may be briefly stated as the result of the

examination of t.he western part of @ounty (York, namely, t,hat there are

two great formations in it, the Old Eed Sandstone below, and the Car-

boniferous Slate above ;

the Old Red Sandstone containing no marine

fossils and scarcely any fossils at all, except Elands in its upper portion ;

the Carboniferous Slate containing some of these plants, but also marine

fossils, sometimes in grea,t profusion. The Old Ited Sandstone has a

prevailing red tinge t,hroughout

with no beds of black or bluish-grey

slate ; the Carboniferous Slate has a prevailing black or bluish-grey

colour, with no beds of a red tinge. Both are greatly affected by slaty

cleavage.

It may also be stated that where the Carbonifcrous Slate and Car-

boniferous Limestone are both present together, the Carboniferous Lime-

stone is uppermost

; but that where the Carboniferous Limestone has a

thickness of 2,000 feet, or upwards, the dark slates between it and the

Old Red Sandstone are very thin, rarely more than 200 feet in thickness

;

while where these dark slates thicken out to more than 2,000 feet, there

is no great thickness of Carboniferous Limestone over them. Where the

Carboniferous Slate attains a still greater thickness, and swells out to

three, four, or five thousand feet, it has never any Carboniferous Lime-

stone over it at all, but there appear here and there patches of black

slate upon it, which both lithologically and paheontologica.lly resemble

the Coal-Measures. If so, the Carboniferous Slate occupies, there, the

whole interval between the top of the Old Red Sandstone and the base

of the Coal-Measures, with a perfectly conformable and continuous series

of beds to the exclusion of the Carboniferous Limestone ; and therefore

replaces that limestone.

Prof. E. Hull2 at la later date expressed the same opinion as

to the relationship between the Carboniferous Slate and the

Pilton and Marwood Beds of Devonshire, and the correlation

has been frequently referred to by other writers. On the

1 On the Carboniferous Slate (or Devonian Rocks) and the Old Red Sandstone

of South Ireland and North Devon.

Quart. Joum. Geol. Sot., vol. xxii., pp.

320-371. See also the following other papers by Jukes :- Additional Notes

on the Grouping of the Rocks of North Devon and West Somerset, privately

printed, Dublin, 1867.

Notes for a Comparison between the Rocks of the

South-west of Ireland and those of North Devon and of Rhenish Prussia [con-

taining a :ood list of fossils and fossil-localities], Journ. R. Geol. Sot. of Ireland.

vol. i. (1867), pp. 103-138

;

Further Notes on the Cla.ssification of the Rocks

of North Devon, ibid., vol. i. (1867), pp. 138-143 ; and Notes on parts of South

Devon and Cornwall, ibid., vol. ii. (1871), pp. 66-107.

2 A possible explanation of the North Devon Section, Geol.

Mag.,

dec. ii.,

vol. v. (1878), p. 532 ; and

,.Cn a proposed Devono-Silurian Formation, Quart.

Journ. GwZ. Qoc.,

vol. xxxvm. (1882), p. 208.


36/161

LOW&%

CAttkbNIFEBOUS

ROCKS.

25

strength of

this correlation some authors,

including Jukes and

Hull, have

Lower

urged that the Devonshire beds

CarboGif erous .1

should be classed as

It has, however, been supposed by most later workers that

the Carboniferous Limestone period is represented in Devon

and Cornwiall by part of the Culm series2-a shaly and sandy

group differing widely from its equivalents in other parts of

Britain-and fhat the Pilton and Mtarwood beds which under-

lie this series are older than the Carboniferous Limestone and

must be retained in the Upper Devonian. If this method of

classification be finally adopted for the English rocks it will

re-act to some extent upon the system adopted by Jukes in

Ireland, and, as previously rioted, it would probably become

requisite to relegate a large part of the Carboniferous Slate

series to the Upper Devonian.

Within recent years the fossils of the Pilton and Marwood

beds have been carefully re-described by the Rev. G. F. Whid-

borne in vol. iii. of his Monograph of the Devonian Fauna of

the South of England (& onogr. P zon.t.ot.,01s. l., 1896,

li., 1897, and iii., 1898) ; but no similar work has yet been done

on the Cork fossils, and the list given below is based entirely

on the determinations made by Baily over forty years ago.

It is highly desirable that the fauna of the Carboniferous Slate

and Coomhola Grits should be re-examined in the light of

present palpontological knowledge, ,and until this has beer1

done further discussion of the correlation is hardly possible.

But the absence of some characteristic Devonshire species,

commented on by Davids,on,

and the comparative poverty of

the Irish fauna, suggest that the conditions in the two regions

were not identical, and that only part of the Pilt,on and Mar-

wood series is represented by m.arine deposits in Ireland.

.

As a summary of our present knowledge, .it may be con-

cluded that in the dilstrict under discussion, after the long

period of lacustrine conditions represented by the Old Re,l

Sandstone, a wide-reaching depression occurred by which the

area was submerged beneath the sea. This submergence took

place before the close of the Devonian period-if we accept the

limits usually assigned to that period in the south of England-

and was continued throughout Lower Carboniferous times.

The earliest sediments accumulated during this submergence

are therefore of Ialte TJpper Devonian age, but .pass insensibly

1 See Correlation Tables in

Renort of Sub-Committee on Carboniferous,

Devonian, and Old Red Sandstone,

published in

Report of International Leo-

logical Congre.%s,London 1888.

2For some recent conclusions regarding the Culm Series, see Mr. W. A. E,

Usshers papers The British Culm-measures, Proc. Somerset drchocol. & Nat.

Hist. Sot., vol. xxxviii. (1892), pp. 111-219, and The Culm-measure types of

Great Britain, Trans. Inst. Mining

Engineers,

vol. xx. (1901), pp. 360-387.

See

also Messrs. G. J. Hinde and H. Fox, on Radiolarian Rocks in the Lower Culm,

Quart. Journ. Oeol. Soe., vol. li. (1 395), p. 662. Since the above was written,

however, Dr. Wheelton Hind has urged, on palnontological grounds, that the

Lower Culm is equivalent to the Pendleside Series of the North of

England, and t,herefore newer than the main mass of the Carboniferous Lime-

stone ; see his paper


37/161

26

THE GEOLOGY OIf CORK AND CORK HARBOUR.

upward into similar sediments of Lower Carboniferous age.

These sediments include the Carboniferous Slate and Coomhola

Grits, and the Lower Limestone Shale. In this conformable

sequence any division to be drawn between Upper Devouian

and Lower Carbomferous rocks must be more or less arbitrary

i

and for purposes of local stratigraphy it is more convenient to

adhere to the existing method, by which the marine beds are

united as a group.

For the sake-of analogy we may cite the case of the

Rhatic Beds, which lie conformably between the salt-lake

deposits of the Triassic or New Red period and the marine

sediments of the Lias, and are classed sometimes with the

underlying and sometimes with the overlying series. It is

noteworthy, moreover, that the Rh&ic fauna in its broader

features bears a distinct resemblance to that of the Carboni-

ferous Slate. The classification of such passage-beds in our

conventional scheme of geological systems has ever been a

source of difficulty and divergent opinion.

FOSSILS OF THE LOWEIR LIMESTONE SHALE, CARBONI-

FEROIJS SLATE AND COOMHOLA GRIT from localitim within the

limits of the Cork map or olosely adjacent to its outer boundaries, com-

piled from W. H. Bailys list (marked B.) in Xem. Geol. Szcruey,

Explanation of Sheets 187, 195 and 196 (1864), pp. 8-18 : with additions

from I the neighbourhood of Ballea (marked J.) from the paper of

J. Beete Jukes,

On the Carboniferous Slate (or Devonian Rocks) and

the Old Red Sandstone of South Ireland and North Devon, in Qwurt.

Jowm. GC&. Hoc., vol. xxii. (1866), p. 336-7. For the exact localities

at which the fossils were found reference should be made to the above-

mentioned publications.

.

Lower

1

ar-

t

itll3dIN3

bog feous

T--

oomhole

Grit.

PLANT q.

Filicites line&us, Baily . . . .

B

B

AOTINOZOA.

Cyathophyllum(P&r&) celticum, Lonsd.

.

. .

Pleurodictyum problematicum, QoZdf.

.

. :

5

EOHINODERMATA.

Actinocrinus polydactylus, Miller .

.

Cyethocrinus pinnatus, Qoldf. .

---- (1Actinocrinus) varisbilis, Phi& .

:

Cyathocrinus (1 Actinocrinus), and other crin-

oidal remains.

. .

. . JJ

ii

J

B

Plstyorinua . . . . . .

CRUSTAOEA.

. .

J

Cypridina (Leperditia) subrecta, PO&. .

.

B J

1The classification of the Coomhola series as passage-beds is

ado ted also

by Dr. Wheelton Hind in the correlation table in his paper on The Sub

ivisions

of the CarboniferousSeries n Great Britain and some of their European Equiva-

lents. Trans. Ed&b. Geol. Sot.. vol. vii. (ZSSS), p. 360.


38/161

POSSILS OF THE LOWER LIMESTONE SHALE, ETC.

27

BRYO~OA.

Ceriopora rhombifera, Phi& . . .

Fenestella antiqua,

Goldf.

. . .

BRACHIOPODA.

Athyris ambigua, &our.

. . . .

Discina nitida, Phi&

Orthis Michelini, Lkv. (including some speci:

mens which may possibly be 0. inter-

lineata, Sow.)

Productus scabriculus, Martin . . .

---

semireticulatus, var. Martini, Sow.

.

Renssellseria stringice s ? F. Roemer

.

Rhynchonella pleuro on,

.

Phil?. (or R. lati-

Costa).

Spirifera cuspidata, Martin

. . .

----

striata, Martin (along with forms

usually named S. disjuncta or S. Verneuili)

Spirifefep cristata, var. octoplicata, J. de 0.

Streptorhynchus crenistria, Phill. . .

Terebratula hastata,

J. de C. Sow.,

. .

LAMELLIBRANcHI_~TA.

Avicula damnoniensis, Sow. . . .

Aviculopecten nexilis, Sow.

. . .

Cucullaea Hardingi, Sow. (including vars.

trapezium and amygdalina).

Curtonotus elegans Salter (and vars. elongatus

and rotundatus).

Cy ricardia Phillipsi, &Orb.

. . .

Po abra ? sp.

Modiola Macadami, P&X

: : : :

Nucula, sp.

Sanguinolites, sp: 1 1 1 1 1

Sedgwickia bullata ? MCoy . . .

GASTEROPODAwith HETEROPODA).

Acroculia striata, Philt.

. .

Bellerophon subglobatus, MCo~ . .

----

sp.

Euomphalus, sp.

: : : : :

Natica, sp.

Pleurotomaria, sp.

1 1 1 1 1

Turbo, sp.

. . . . . .

CEPHALOPODA.

Goniatites, sp.

Orthoceras unduiatum; SOW:

: : :

---- sp. . . . . . .

Lower

LiK&;ne

.

. .

. .

BB

B

B

. .

::

B

. .

B

. .

B

B

B

BB

B

B

. .

B

B

ti

. .

. .

. .

ii

B

~~-

bOll;OUS

.

i

J

ii

J

. .

J

3

B

J

J

J

. .

J

J

. .

. .

;

J

. .

J

J

. .

. .

. .

3

. .

J

oomhob

Qrit.

. .

. .

z

.

..

.

ii

B

B

:

B

ii

B

. .

BB

B

. .

. .

. .

i3.

ii

. .

. .

. .

. .

. .

Note.-As it was held by Jukes that the Lower Limestone Shale, Carboniferous

Slate, and Coomhola Grit were equivalent deposits and all of Carboniferous

age, their classification for purposes of fossil-collecting was probably considered

to be of secondary conse uence,

original list, from which tx

and therefore the separation indicated in the

more or less arbitrary.

e above table has been compiled, has evidently been

xxii., p. 337) that

Jukes stated in his paper (Quart. Journ. Geol. Sot., vol.

CucuZZ@a, and Curtonotus were found at several localities,

but always in grits, the situation of which showed them to be low down in the

Carboniferous Slate.

As these fossils are recorded in the list from all three

divisions, it may be inferred that the grit-bands with the peculiar fauna ocour in

the Lower Limestone Shale as well as in the Carboniferous Slate.


39/161

ab

TEtE GEOi;Oc;P F CORK AND C6BR RARBOUR.

Carboniferous Limestone.

The following is the short description of the Carboniferous

Limestone given by Jukes in the Explanation of Sheets 187,

195 and 196 (p. 9) :-

The Carboniferous Limestone

preserves nearly the same characters

over the whole

area, being a pale gray compact

or crystalline limestone,

almost

always thick bedded.

It is, however, so much cut up by numerous

joints, and

often so much affected

by an imperfect slaty cleavage, that

it is generally impossible to say which are the original planes of stratify-

cation, and

determine its dip by any observatioss

made in the limestone

itself.

Where this can be determined, it always agrees with that of the

rocks below,

no appearance of the slightest unconformity having ever

.been observed in any of the beds of the district.

It may be further noted that in many places the limestone

is seamed or veined with dolomite, usually of a, brown colour.

It also includes irregular bands and nodules of chert. Though

usually f

a grey or blu.ish grey colour, in a few places it has

been stained pink or red, and then affords a handsome orna-

mental marble when polished. The principal localities for

this red limestone lie a little to the south and south-west of

Midleton, where the rock is quarried as an ornamental stone

(p. 110). The ordinary grey limestone


40/161


41/161


42/161

CARBONIFEROUS LIMESTONE.

29

The groups of fossils thus dealt with are as follows :-The

Entomostraca, by Prof. T. Rupert Jones, J. W. Kirkby, and

G. S. Brady (Monogr.

Palaont. Sot.

between 1874 and 1899) ;

the Trilobites and other Crustacea, by Dr. H. Woodward

(Mon. Pal. Sot. for 1878,1883 and 1884) ; the Lamellibranchs,

by Dr. W7. Hind (Mon. Pal. Sot. between 1896 and 1904-not

yet complet,ed)

;

and the Cephalopod,s, by Dr. A. H. Foord

(Mon. Pal. Sot. between 1897 and 1903). In most cases these

rnonographs contain numerous figures of Cork fossils.

From the above works and other publications hereafter men-

tioned the following list has been compiled :-

LIST OF FOSSILS FROM THE CARBONIFEROUS LIMESTONE

OF THE CORK DISTRICT

;

compiled from the following

publications

: -

BAILY, W. H.-List in previous Memoir Geol. Survey : Explanation of Sheets

187, 195 and 196 (1864), pp. 8-18.

DAVIDSON,

T.-List of Brachiopoda in Mem. Geol. Survey : Explanation

of Sheets 192 and 199 (1864), pp. 27-28.

DONALD, MISS J.- Notes on some new and little known species of Carbon-

iferous Murchisonia, Quart.

J

ourn. Geol. Sot., vol. xlviii. (1892)

;

and Notes

on Murchisonia and its allies,

ibid.

vol. li. (1895), p. 221.

FOORD, A. H.- Monograph of the Carboniferous Cephalopoda of Ireland,

Fa,Gzont. Sot. for 1897-1903.

HAU~HTON, S.- On some Fossil Pyramidellidae from the Carboniferous

Limestone of Cork and Clonmel,

Proc. Dubli n Univer. * Zool. & Botan. Assoc.,

vol. i. (1859), p.

282.

HIND, W.--- MFmograph of the British Carboniferous Lamellibranchiata,

Pakeont Sot. for 1897-1904.

JONE;. T. R., J. W. KIRKBY, and G. S.

BR.\DY.-

Monograph of the British

Fossil Bivalved Entomostraca from the Carboniferous Formations, Palceont.

SOS. for 1874 and 1884.

JONES, T. R., and H. WOODWARD.

Monograph of the British Palaeozoic

Phyllopoda, Palaeont Sot. for 1899.

WOOD WARD, H.-- Monograph

of the British Carboniferous Trilobites,

Pakont Sot. for 1883 and 1884

;

and Monogr. of the British Fossil Crustacea

belonging to the Order MerJstomata, Part V., ibid

the geology of the country around cork and cork harbour

Documents