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Full text of "Geology of the British Isles"

E 



GEOLOGY 



OF 



THE BRITISH ISLES 



BY 



P. G. H. BOSWELL, GRENVILLE A. J. COLE, ARTHUR MORLEY DAVIES, 
CHARLES DAVISON, JOHN W.EVANS, J.WALTER GREGORY, ALFRED 
HARKER, OWEN THOMAS JONES, PERCY FRY KENDALL, LINSDALL 
RICHARDSON, WILLIAM WHITEHEAD WATTS, H. J. OSBORNE WHITE 



EDITOR: J.W.EVANS 



WITH AN APPENDIX: 

THE CHANNEL ISLANDS 



BY 



JOHN PARKINSON 




MICROFORMED BY 

PRESERVATION 

SERVICES 

SEP 21 1Q87 



DATE 




THE HAGUE 

MARTINUS NIJHOFF 

1918 



The British Isles 



Grenville A. J. Cole, Arthur Morley Davies, Charles Davison, 

John W. Evans, J. Walter Gregory, Alfred Harker, Owen Thomas Jones, 

Percy Fry Kendall, John Parkinson, Linsdall Richardson, 

William Whitehead Watts, H. J. Osborne White. 



Preliminary Note by the local Editor. 



The completeness of the geological record in the British Isles, the variations in the 
facies of the different formations from place to place, and the immense volume of the 
literature that has accumulated, render it impossible for one man to do justice to the 
Regional Geology of the area. It was therefore decided to divide the work among a number 
of specialists, each of whom could write with authority on the subject allotted to him and 
be individually responsible for his contributions. Every effort has, however, been made to 
secure as much uniformity as was possible in bibliographical and typographical details. 

The majority of the illustrations have been taken by permission from the official Reports 
of the Geological Surveys and the publications of the Geological Society and of the Geo- 
logists' Association, the exact source being given in each case. The general maps have 
been prepared by A. Morley Davies, who has made a careful study of the structural 
geology of the whole country. He also had the advantage of detailed information supplied to 
him by other contributors. I am however responsible for the symbols employed on the 
structural maps, and the system of shading adopted in those showing the distribution 
of the different formations at the surface. Other maps and diagrams have been 
specially prepared for the present work by the contributors, who are identified by their 
initials. John W. Evans. 



I. Morphology. 



a. England and Wales. 

By Arthur Morley Davies. 

The folds and faults of England and Wales are usually grouped in four systems, 
according to their general axial directions: 

1. The Charnian system, with N.W. — S.E. direction; 

2. The Caledonian system, with N.E. — S.W. direction; 

3. The Malvernian system, with N. — S. direction; 

4. The Armorican system, with direction varying from E.N.E. — W.S.W. through 
E.— W. to W.N.W.— E.S.E. 

To each of these systems an age of predominance may be assigned, but the 
use of any name must not be taken as implying age: it denotes merely direction. 

Handbuch der regionalpn Geologic III. 1. 1 



! (III. 1.) 



The British Isles. — Morphology. 



The Charnian system is principally developed in the pre-Cambrian rocks of 
Charnwood Forest (Fig. 8). As both Carboniferous and Triassic strata lap up uncon- 
formably against these ancient rocks, and Cambrian strata, present only 24km. (15 
miles) away, are there wanting, it is probable that the folding of the Charnian rocks is 
itself pre-Cambrian in age. Movement on the same lines, however, was repeated 
at later periods, notably in post-Carboniferous time, when the boundary-faults 
of the Leicestershire and Warwickshire coalfields were formed. These are in the 
near neighbourhood of Charnwood Forest. Other folds and faults with the same 
axial direction are found at greater distances and separated by areas with other 
dominant directions, so that their relationship to the Charnian system must be 
regarded as more doubtful. Such are a) the Eden Valley fault of Cumberland 
(Fig. 4); b) one set of faults in the Lancashire and Yorkshire coalfields (Fig. 5); 
c) the post-Carboniferous Woolhope anticline of Herefordshire (Fig. 8); d) part of 
the system of pre-Bajocian and Bajocian folds, of very slight amplitude, detected 
in the Cotteswolds by the minute zonal work of Buckman (Fig. 8); e) a series 
of post- Jurassic pre-Cretaceous folds, with one fault, in the Oxford district 
(Fig. 8); and f) possibly the post-Eocene folds in the neighbourhood of Lambourn, 
Berkshire (Fig. 8). 

The Caledonian system is mainly of post- Silurian age, though movement 
on these lines seems to have begun in the Ordovician period. It is the dominant 
system throughout North and Central Wales (Fig. 7). As the folds and faults 
approach South Wales they become deviated under the influence of the Armorican 
movement, while as they approach the English border of North Wales they are 
similarly modified by the Malvernian movement. 



A. Arcrtotan Gneiss. 

B. Metamorphosed Sedimentary Rocks. 

E. Prat-Cambrian Sedimentary Rocks. 

F. Cambrian and Ordovician. 
P. Jurassic. 

Y. Tertiary Volcanic Rocks. 
2. TerCiary Intrusive Rocks. 



FaulC (downthrow 
on dotted side) 

Fau/C(Chrow doubtful.) 

Thrust-plane with 
overthrust To N.W 



o. 



Cap e Wrath . 




F,g. 1. Tectonic Map of the British Isles— Section I.— Hebrides and North- West 

Highlands. Region of thrust planes of Caledonian system. A. M. D. 

The scale of these structural maps of the British Isles is about 1: 2 650 000 or 42 miles to an inch 



Davies: England and Wales. 



(III. 1.) 3 




Islands 



JO 




\ 



AnCieline. 

Syncli ne. 

FaulC (downChroiv 
on doCCed side.} 

Dip. 



B. MeCamorphosed Sedimentary Rocks. 
D. Prae-Cambrian Intrusive Rocks. 
J. Devonian (Old Red Sandstone.) 
©Derived Cam brian pebbles. 
N. Triass ic. 
P Jurassic. 

W Palaeozoic Volcanic Rocks. 
X. Palaeozoic InCrusive Rocks. 
S]Cretaceous in boulder c lay. 



Fig. 



Tectonic Map of the British Isles — Section II. — Nor th-E ast- Scot 1 and, 
Orkneys and Shetland s. Caledonian system dominant. A. M. D. 



To this system belong two of the most powerful faults in the country — a) the 
Dee Valley fault, traceable from Cheshire to Cardigan Bay, and b) the Church 
Stretton fault, part of a series of faults that form an almost continuous line of 
fracture from Morecambe Bay to Carmarthen Bay. Beginning with a Charnian 
direction in Morecambe Bay it extends to the neighbourhood of Manchester, when 
it curves round into the Caledonian direction, forming first the western boundary 
fault of the 'North Staffordshire coalfield, and later the eastern boundary of the 



4 (III. 1.) 



The British Isles. 



Morphology. 



Longmyndian horst. Other important disturbances are e) the faults to which the 
Menai Straits owe their existence; d) the Snowdon syncline; e) the Harlech anti- 
clinorium; f) the Builth anticlinorium, with its igneous rocks; g) the Berwyn anti- 
clinorium; h) the St. David's anticlinorium. 

Besides the many folds and faults in Wales, there also belongs to the Cale- 
donian system a series of post-Carboniferous faults in Northumberland, in close 
association with the structure of the Southern Uplands of Scotland (Fig. 4), includ- 
ing the well-known 90-fathom "dyke" of the Newcastle district (the term "dyke", 
as used by Northumbrian miners, meaning simply a fault — not an igneous dyke). 

The post-Carboniferous folds of the Lancashire coalfield and the district to the 
north of it (Fig. 4) may also possibly indicate a revival of Caledonian movements; 
and in the Yorkshire coalfield there are two intersecting series of faults having 
respectively the Charnian and Caledonian as their dominant directions. 

The Malvernian system of north-and-south direction includes more faults 
than folds. It is of post-Carboniferous and partly of post-Triassic age. 

Starting at the northern end in the neighbourhood of Manchester with 
a series of north-and-south faults, these pass into a series of anticlines and synclines 
which radiate out southwards and determine the form of the North Staffordshire 
and adjacent coalfields. They are continued southwards by the boundary faults of the 
South Staffordshire coalfield (Fig. 8) and parallel faults in the Trias of Worcester- 



B. Metamorphosed Sedimentary Flocks 

D. Prae- Cambrian InCrusiVe Rocks. 

F. Cambrian. 

G Ordovfcian. 

H Silurian (GJothlandlan) 

K. Lower Carboniferous. 

L. Upper Carboniferous. 

Q. C reCa. ceous. 

X. Palaeozoic Intrusive Rocks. 



Anticline 

Syncline. 

Fault, with downthrow 
on dotted side 

Fault wiTh doubtful 
throw. 




Fig. 3. Tectonic Map of the British Isle s. — Section III. — N orth- West-Ireland. 
Caledonian system dominant. A. M. D. 



Davies: England und Wales. 



(III. 1.) 5 




Fig. 4. Tectonic Map of the British I sles. — Section IV. — Nort h-E ast-Ireland, Scot- 
land (tirampian Highlands, Central Valley, Southern Uplands), England (Lake 
District) and the Isle of Man. Caledonian system dominant. A. M. D. 



shire. But the main feature of this system is the great Malvern fault which for 
many miles separates the Archaean and Palaeozoic rocks on the west from the 
Trias to the east. Crossing the Severn it is continued by the syncline of the Bristol 
coalfield, and ends abruptly against the Armorican folds of the Mendips — unless, 
indeed, we regard it as continued by the cross-faults of that system, in which case 
it can be traced on by post- Jurassic faults into the neighbourhood of Yeovil. 



6 (III 1.) The British Isles. — Morphology. 

The diagrammatic representations of the Pennine chain (Fig. 5) as a simple 
anticline, usually given in text-books, would, if they were correct, justify the extension 
of the Malvernian system northwards to Northumberland. There is, however, no such 
simple anticlinal structure. The only indication in the tectonic map of this north- 
ward extension is the fact that the Caledonian trend of the west is replaced to the 
east by an east-and-west trend of folds and faults — much as is the case on crossing 
the Malvernian system farther south. These east-and-west disturbances are notice- 
able at intervals throughout the east of England. Such are the folds and faults 
at the southern margin of the Durham coalfields (Fig. 5), the great Craven fault, 
the post- Jurassic disturbances of the Vales of York and Pickering, the southern 
boundary faults of the Carboniferous-limestone area of Derbyshire (Fig. 8) and their 
post- Jurassic extension eastwards, with probable unmapped disturbances determining 
the position of the Wash and the north coast of East Anglia, and many minor post- 
Jurassic disturbances, as in the Cotteswolds and the area north-west of Oxford. 

The Armorican system is primarily post-Carboniferous in age, but includes 
slight intra- Jurassic and important post- Jurassic, post-Cretaceous and post-Oligo- 
cene revivals. Its greatest development is seen in the South Wales coalfield (Fig. 7) 
and the Mendip Hills (Fig. 8). The northern margin of the former is partly influenced 
by Caledonian movement, and a Malvernian interference cuts it off to the east and 
separates the small coalfield of the Forest of Dean. The Mendip Hills consist of a 
series of long and narrow domes of Carboniferous limestone with cores of Upper Old 
Red Sandstone and in one case of Silurian (Gothlandian). They repeat the structure 
of the South of Ireland, except that (possibly owing to Malvernian influence) the 
axes are not continuous for such long distances. 

The rocks of Cornwall and Devonshire (Fig. 7) also show Armorican folding, 
and it is in connexion with it that the granitic intrusions, el van-dykes, and tin- and 
copper-veins were produced. 

As the Palaeozoic rocks of the south-west of England pitch under the Mesozoic 
strata to the east, evidence of the continuity of folding is seen in the latter. The 
intra-Liassic denudation of the Radstock district appears to be due to movement 
parallel to the Mendip axes. It is very probable that when detailed zoning of the 
Corallian rocks has been carried out, their irregularities of distribution will be found 
due to similar causes. The faults in the Jurassic rocks of Somerset and Dorset (Fig. 8) 
have a dominant Armorican trend, and still more strikingly is this the case with 
the post-Cretaceous and post-Eocene disturbances. These include 

(a) The Isle of Purbeck and Isle of Wight, anticlines possibly continuous 
with that of the Pays de Rray; 

(b) the Isle of Purbeck thrust-fault; 

(c) the syncline of the Hampshire basin; 

(d) the Portsdown anticline; 

(e) the Salisbury-Chichester-Worthing syncline; 

(f) the anticline of the Vale of Wardour (partly pre-Cretaceous) ; 

(g) the series of anticlines constituting the Wealden axis, one of which is 
continued into the Ras Roulonnais; 

(h) the Pewsey-Kingsclere-Peasemarsh anticline accompanying the steep 
southern margin of the London Rasin, with associated minor folds and 
faults, including a slight northwardly thrust-fault at the Hog's Rack near 
Guildford. 

(i) the series of synclines that form the London basin. 

The London basin is not a simple syncline: a minor crumpling brings up the 
Chalk along the lower Thames, and there is some disturbance of the axial direction 



Davies: England unci Wales. 



(III. 1.) 7 




AnCicfine. 

Syncline. 

*"**" FaulC with downthrow 
on dotted side. 

"•"""••'• g Trouyd- FaulC. 

B. MeCamorphosed SedimenCary Rocks. 

H. Silurian (Gothlandian.) 

J. Devonian. 

K. Lower Carboniferous. 

L. Upper Carboniferous. 

M. Permian. 

N. Triassic 

P. Jurassic. 

Q. Cretaceous. 

V Quaternary. 




Fig. 5. Tectonic Map of the British Isle s. — Section V. — N orth-East-England. A. M. D 

in the centre of the basin, as shown by the Windsor inlier, but the very gentle angle 
of dip makes determination of the nature of this disturbance very difficult. It is 
not impossible that it may be connected with the series of folds with Charnian 
direction near Oxford, as the distribution of Jurassic rocks underneath London 
suggests an extension of those folds as far as London. 

Physiography. The most fundamental fact in the geography — physical, 
economic and racial — of England and Wales is the contrast between the Palae- 
ozoic areas of the west and north and the Neozoic areas of the south and east. The 
former consist of a series of separate districts, of high relief, .each a deeply dissected 



8 (III. 1.) 



The British Isles. — Morphology. 



ancient peneplain with an epigenetic river-system more or less re-adapted to the 
rock-structure now exposed; while the latter is an area of low relief and gently- 
dipping strata, with a river-system in an advanced stage of adaptation to the rock- 
structure, but in places greatly modified by glacial diversion. The former areas include 
all the main coalfields, and most of the other sources of mineral wealth, and the 




BD 

F-J? 

KQRY 



BDF-JP 

QRY 

K 



Anticline. 

Syncii ne. 

i aulC with downthrow 
on doCCed side. 

Troug-h - Fault. 

Fault with horizontal 
movement (Northwards, 
reUXively, on Che .side 
marked by obliaue strokes.) 

Fault with doubDful throw 



B. Metamorphosed Sedimentary Rocks 

D.Prae-Cambrlan Intrusive Rocks. 

F\ Cambrian. 

H. Silurian(Qothlandian.) 

J. Devonian 

K. Lower Carboniferous. 

L. Upper Carboniferous. 

Q. Cretaceous. 

R. Eocene. 

Y. TerCiary Volcanic Rocks. 



Fig. 6. Tectonic Map of the British Isles. — Section VI. — South-W est-Ireland. 
Armorican system dominant. A. M. D. 



majority of the manufacturing towns, and their inhabitants are largely of the 
races that inhabited the British Isles prior to the Teutonic invasion. The latter 
are less industrial than agricultural, and their population is mainly Teutonic 

The four great Palaeozoic areas are 1) the south-western peninsula 
of Devon and Cornwall, 2) Wales, with the border counties of Shrop- 



Davies: England und Wales. (III. 1.) 9 

shire, Herefordshire, Monmouthshire and part of Gloucestershire, 
3) the Pennine area, of Northumbria, Lancashire and Yorkshire, 
and 4) the Lake District of Cumberland and Westmorland. To these 
may be added 5) the Isle of Man. 

Most, if not all, of these areas were submerged in the Upper Cretaceous trans- 
gression, if not previously, and have been re-exposed by Kainozoic erosion. There 
are also a number of minor areas, less completely stripped of their Mesozoic cover — 
1) the Mendip Hills, with the Somerset and Bristol coalfields, 2) the 
South Staffordshire, Warwickshire and Leicestershire coalfields, 
and 3) Charnwood Forest. 

1) The South-western peninsula (Devon and Cornwall) (Fig. 7) may be described 
broadly as an Armorican synclinal area, with Carboniferous and Permian rocks 
in the centre, Devonian on the north and, the same, with Silurian, Ordovician 
and Metamorphic rocks, on the south. The southern limb is complicated by large 
granite intrusions, igneous dykes and metalliferous veins. The river system is 
obviously epigenetic, but so complex and intricate in its character, that it has hither- 
to defied explanation. Tin- and copper-mining have been carried on here from 
prehistoric times, and china-clay is now extensively produced from the kaolinized 
granites. 

2) Wales (with the border counties) (Fig. 7) is an area in which Caledonian 
structure predominates, the trend lines passing into a Malvernian direction in 
the north, while in the south they end off against well-marked Armorican folds. 
The rocks include members of all the pre-Palaeozoic and Palaeozoic systems except 
undoubted Permian, but Ordovician and Old Red Sandstone cover the widest areas. 

Wales is classical as the case in which a mountainous country was first recog- 
nized as a deeply dissected plateau^ Jukes and Ramsay having pointed out the 
uniform gentle slope of the plane surface tangential to the highest mountain-tops. 
In the west, the river-system has become well-adapted to the rock-structure, but 
in the South-Wales coalfield the epigenetic character is well shown. Most of the 
rivers, like the Taff, traverse the coalfield completely from north to south, though 
in the west the Towy, working on the soft Ordovician shales, has beheaded the 
transverse river Loughor or Llwehwr. Still more striking is the lower Wye, of which 
the entrenched meanders cross and recross the boundary between Old Red Sand- 
stone and Carboniferous Limestone, forming deep narrow gorges in the latter and 
wide vales in the former. 

The broad subsequent valleys of Wales are devoted to agriculture, but the 
rest of the country consists of barren moors, thinly populated, except where coal- 
mining and iron-smelting has drawn together a huge industrial population. 

3) The Pennine area (Fig. 5) is mainly a series of moorlands of grit, with 
limestone areas characterized by caverns and underground drainage. The north- 
to-south trend of the area is believed to have been blocked out in the Kainozoic 
era, and by no means corresponds to the tectonic structure of the rocks, almost 
entirely Carboniferous, of which it is composed. The drainage is mainly eastwards 
and westwards, but in the south the Derwent, working along an outcrop of shale, 
at the foot of a grit escarpment, has disturbed the simplicity of the river-system. 

4) The Lake district (Fig. 4) consists of an area of slaty and volcanic rocks, 
of Lower Palaeozoic age, and has a strikingly radial drainage practically in- 
dependant of the structure. 

The Neozoic part of Britain consists mainly of alternations of escarp- 
ments and vales, with a maturely - adjusted river-system showing numerous 



10 (III. 1.) 



The British Isles. 



Morphology. 



examples of capture. The principal resistant beds, forming the main escarpments 
are 1) the Permian Magnesian Limestone (included with the Mesozoic for 
topographical convenience), 2) certain of the Triassic sandstones, 3) the 
Marlstone of the Lias, 4) the limestones of the Lower Oolites and 
5) the Upper Chalk. Of the two main escarpment-lines of England, one is formed 
in part (as near Bath) of the Great Oolite, in part (as near Cheltenham and again 
near Lincoln) of the Inferior Oolite, and elsewhere where neither of these is well- 
developed, by the Marlstone; the other is the striking Chalk escarpment. 




\ 



— AnCicline. 

— Syncline 

Fa-uJC (downthrow on 
dotted side) 

'-+** FaulC( throw doubtful.) 

FoxjIC with horizontal ►movement 
(north-wesCWard-s releiOvely on 
Side marked by oblique strokes) 



J I I 1 



ThrusC-plane wiCh 



Over thrust to northwards. 



, Tri 



B. Metamorphosed Sedimentary F^ocKs. 

C. FVae-Cambrian Volcanic F^ochs. 

D. FVat-Cambrian InCrusive F\ocfos. 
£. Prae-Cambrian Sedimentary Rocks, 
r. Cambrian. 
G. Ordovician.@ Pebbles 
H.Silurian. 
J. Devonian. 
K. Lower Carboniferous. 
L. Upper Carboniferous. 
M. Permian- 
N Triassic. 
P. Jurassic. 
Q. Cretaceous. 
V. Quaternary. 

W palaeozoic „« Volcanic FjocKs 
X Palaeozoic ' Intrusive Flocks 




Fig 7. Tectonic Map of the British Isles. 
Wales and South- West-En gland. Meeting of 



—Section VII. — S outh-East-Ireland, 
Caledonian and Armorican systems. A. M. D. 



Davies: England and Wales. 



(111. 1.) 11 



Epigenetic drainage is well-shown by the Bristol Avon, which cuts 
through the Carboniferous Limestone at Clifton in the gorge which gives the standard 
section of that formation — a gorge 90 metres (300 ft.) deep, though an easier course 
over the Triassic red marl seems open to it. 

Of glacial disturbances of drainage two striking cases may be given. 
The upper Severn emerges from the Palaeozoic upland of Wales on to the Triassic 




Fig. 8. Tectonic Map of the British Isle s. — Section VIII. — E nglanrt (Central, 
Southern and Eastern). Malvernian, Charniiin and Armorican systems. The London Basin is 
seen to be composed of two separate synclines, not in line: the connexion between them is obscure 

owing to slightness of dip. A. M. D. 



12 (III. 1.) The British Isles. — Morphology. 

plain of North Shropshire, where its natural course would appear to be northwards 
to join the Dee. This was probably its course until the Glacial Epoch, when the 
Irish Sea ice blocked its course and formed a lake that overflowed southwards 
and cut the gorge at Ironbridge, through which the Severn was permanently 
diverted into a valley that had been tributary to the Warwickshire Avon. 

The second case is that of the Yorkshire Derwent. The upper waters of this 
stream were originally gathered into a river occupying the vale of Kimmeridge 
Clay at the foot of the Chalk Escarpment of the Yorkshire Wolds, and entering 
the sea near Filey. The North Sea ice dammed up this stream, and made a lake, 
the alluvial floor of which now forms the Vale of Pickering. This lake overflowed 
south-westwards into the Vale of York, and in doing so cut the gorge at Malton 
which now forms its permanent course. 

In the south-east of England, the anticlinal dome of the Weald exhibits the 
effects of mature adjustment of drainage, of which it is a classical example. Its 
original continuation in the Bas Boulonnais has been severed from it by marine 
erosion. 

The coasts of England afford many fine examples of the effects of marine 
erosion, of submergence and of accumulation. Drowned river-valleys are character- 
istic of the southern coasts from Milford Haven round to the mouth of the Thames. 
Plymouth Sound and Portsmouth Harbour are the two most important ports 
due to submergence. The original central river-valley of the Hampshire basin 
(the continuation of the Dorset Frome) has been converted by the combined effects 
of submergence and erosion into the Solent and Spithead. The Isle of Wight has 
been separated from the Purbeck peninsula by marine erosion, and its river-system, 
heading in the south coast, shows that it once extended as land much farther south. 
Along the Dorset coast, where Upper Jurassic and Cretaceous beds dip steeply 
landward, the progress of marine erosion has led to a number of beautiful features, 
of which Lulworth Cove is the finest. This is a nearly circular bay, hollowed out 
in the soft Lower Cretaceous strata, with a narrow opening to the sea through 
the hard Portland limestone. Other coves in various stages of growth or destruction 
are found along the same coast. 

Extensive alluvial areas, deposited partly by rivers, partly by the sea, are 
seen in the Fens of Cambridgeshire and Lincolnshire, in Sedgemoor (Somerset) 
and elsewhere. 

Of accumulations of shingle, the most interesting is the Chesil Bank, which 
unites the Isle of Portland to the mainland, and extends north-westwards along 
the coast for 19km (12 miles). The pebbles decrease in size westwards, although 
they are all of rocks of westerly origin, but they make their way to Portland 
apparently along the sea-bottom on a line some distance south of the coast. 
Another important accumulation of shingle is at Dungeness: this appears to have 
accumulated entirely since the formation of the Straits of Dover. 



b. Scotland. 

By J. W. Gregory. 

Scotland, the northern part of Great Britain, is separated from England 
in part by the Tweed and one of its tributaries, in part by the watershed along 
the Cheviot Hills, whence the boundary is continued westward along a less natural 
line to the Solway Firth. Scotland is bounded to the east by the shallow basin 
of the North Sea and to the west by the Atlantic. The continental platform extends 
westward and bears the numerous Western Isles, of which the most remote is the 



Gregory: Scotland. (III. 1.) 13 

small island of St. Kilda. At a distance of usually over 160 km. (100 miles) from 
the mainland the sea floor sinks rapidly to the North Atlantic basin*. The morpho- 
logy of Scotland both as regards outline and structure has been largely determined 
by earth-movements, directly by those of recent date, and indirectly by ancient 
movements which have guided modern denudation. The northernmost part of 
Scotland is a denuded horst standing between the sunken areas of the North Minch 
to the west and a series of faults trending approximately from north-east to 
south-west along the coast of Caithness and Sutherland. The archipelagoes of the 
Hebrides, Orkneys and Shetlands are all remnants of this once more extended land. 

Scotland consists morphologically of three divisions. 

1) The largest is the Highlands, which, from the structural standpoint, include 
the whole country north of a line across Scotland from Stonehaven on the east 
to the estuary of the Clyde at Helensburgh; the line continues westward across Bute 
and Arran, the northern parts of which belong geologically to the Highlands 
(Fig. 4, p. 5). The sharpness of the southern boundary is due to a great fault known 
as the Highland Boundary Fault, by which the younger rocks to the south have been 
brought against the older rocks of the Highlands. 

2) The second division, the Midland Valley of Scotland (Fig. 4, p. 5), lies 
to the south of the Highlands and has been formed by a great trough fault. It 
includes the chief industrial centres, the largest coalfields and the most populous 
districts of Scotland. The Midland Valley extends across Scotland from the Firths 
of Forth and Tay on the east to the Firth of Clyde on the west and includes the 
rich agricultural districts of Ayrshire. Its coastal limits are on the east from Stone- 
haven to Dunbar, and on the west from the estuary of the Clyde to near Girvan in 
southern Ayrshire. The Midland Valley is bounded to the south by the "Southern 
Boundary Fault", which consists of a series of parallel step faults; hence the 
southern border of the Midland Valley is less sharply defined than the northern. 

3) The third element in Scotland is formed by the Southern Uplands, 
which consist mainly of moorlands, separating the Midland Valley from the Solway 
Firth and the English Border (Fig. 4). 

Geologically the three divisions of Scotland are essentially distinct, both 
in composition and structure. 

The Highlands (Figs. 1, 2, 4) consist in the main of a block of crystalline 
schists and gneisses, which are generally regarded as of Archean age. The Archean 
rocks have been invaded by plutonic masses, mainly granites of Palaeozoic and 
Archean ages. A belt of Pre-Cambrian sandstones (theTorridonian) and of Cambrian 
and Ordovician rocks lies along the north-western margin of the Highlands, and there 
is a thin band, probably Cambrian, along the southern border; wide sheets of sedi- 
mentary and volcanic rocks, belonging to the Old Bed Sandstone, lie upon the 
Archean block; some comparatively small areas of Carboniferous and Mesozoic 
rocks have been preserved by trough faults or by a cover of Kainozoic lavas; some 
sheets of Jurassic rocks rest upon its north-eastern slopes; some small patches 
of Cretaceous have been preserved beneath the lavas of the Western Isles, and 
there is a significant Cretaceous outlier on the Highland plateau in Morven. In 
some of the Western Isles, as Mull, Skye and Eigg, and on the peninsula of Ardna- 
murchan, vast eruptions of Kainozoic volcanic rocks have been piled upon the older 
rocks. 



* On it rises the westernmost of the British Isles, the stack of Rockall. 



14 (HI. 1.) The British Isles. — Morphology. 

There is accordingly abundant evidence that the Pre-Cambrian rocks of the 
Highlands have been covered by a long series of later deposits, most of which 
have been swept away, leaving the country as a dissected block of Archean rocks. 
The two southern divisions of Scotland, on the other hand, contain no out- 
crops of Archean rocks in situ, though pebbles found in the Palaeozoic conglome- 
rates indicate the former extension of the Archean into southern Scotland. 

The Midland Valley (Fig. 4) is occupied mainly by Upper Palaeozoic rocks, 
chiefly Old Red Sandstone, Carboniferous and Permian. The Old Red Sandstone is 
exposed to the north and south of the valley, beside the boundary faults; while the 
central area consists of Carboniferous rocks and includes the chief coalfields. The 
largest area of the Permian rocks is preserved by a basin-shaped depression around 
Mauchline in Ayrshire. Silurian rocks occur in the inlier at Lesmahagow and in the 
Pentland Hills. The essential structure of the Midland Valley may be regarded as an 
irregular geosynclinal of Upper Palaeozoic rocks, dropped by trough faults between 
the Archean rocks of the Highlands and the Lower Palaeozoic rocks of the 
Southern Uplands. 

The Southern Uplands (Fig. 4) have quite a distinct structure from 
either of the two other divisions, as they consist mainly of Lower Palaeozoic 
rocks belonging to the Ordovician and Silurian (Gtrthlandian). The rocks, though 
intensely folded, have a predominant dip to the south-east. The oldest rocks, the 
Arenig (Lower Ordovician), occur along the northern edge of the Southern Uplands. 
They are followed to the south by the Llandeile (Middle Ordovician) and Caradoc- 
(Upper Ordovician). The slope downward to the Solway Firth and the lower 
Tweed is formed mainly by Silurian rocks. This Lower Palaeozoic foundation is 
capped by sheets of Old Red Sandstone, some Carboniferous rocks, as in the coal- 
field of Sanquhar, and some Permian and Trias. The Southern Uplands have also 
been invaded by masses of Devonian granites. Their essential structure however is a 
broad band of Lower Palaeozoic rocks cut off to the north by faults and having a 
long and very disturbed dipslope south-eastward. 

The three structural divisions of Scotland are more sharply defined than the 
political and ethnographic divisions. The differences between the Upper Palaeo- 
zoic rocks of the Midland Valley and the Lower Palaeozoic of the Southern 
Uplands are less marked than those of the Highlands and the Midland Valley. 
Hence there are less striking geographical differences between the two southern 
areas which are grouped together as the Lowlands, and are both occupied 
by the same race. Owing to the more favorable agricultural conditions of the 
eastern as compared with the western Highlands, the Lowland race has crossed 
the eastern end of the Highland Boundary Fault and has extended northward 
occupying parts of Aberdeenshire and the adjacent counties; this area, though 
geologically Highland, is therefore ethnographically Lowland. 

The Highlands were once a plateau having its main slope from north-west 
to south-east, but the old plateau surface has been destroyed by denudation, which 
has been guided by bands of weakness due to earth movements of at least three 
dates. 

The oldest of these three is post-Cambrian and probably Silurian. It thrust 
the schists and gneisses of the Highlands westward over the Ordovician, Cambrian 
and Torridonian rocks. This great overthrust can be traced from the northern 
coast of Scotland at Loch Eriboll for one hundred miles south-south-westward 
to Skye (Fig. 1). This line of movement separates a western area of varied geological 
character, including Lewisian and Moine gneisses, Torridonian Sandstone, Cambrian 
quartzites and Durness limestones from an eastern area of more monotonous 



Gregory: Scotland. (III. 1.) 15 

geological character, as it consists mainly of gneisses covered in places by Old 
Red Sandstone (Figs. 1, 2). 

The second movements happened in Devonian times and are known as the 
Caledonian. A series of faults along the eastern coast of Sutherlandshire and in 
eastern Ross-shire dropped the Lower Old Red Sandstone against the Archean 
gneisses (Fig. 2). Faulting at the same date occurred along the line of the Great 
Glen, which now traverses Scotland from Loch Linnhe to the Moray Firth at 
Inverness (Figs. 2, 4); and strips of the Old Red Sandstone are preserved in the 
valley along the course of this fault. The typical Caledonian direction, as seen 
in northern Scotland, is approximately from north-north-east to south-south-west; 
but further southward the line trends from east-north-east to west-south-west, 
as along the boundary faults which border the Midland Valley (Fig^ 4). That 
these faults were formed in Middle Devonian times is indicated by the evidence 
near Loch Lomond, where the Upper Old Red Sandstone is nearly horizontal, 
while the Lower Old Red Sandstone is uptilted against the fault. The main strike 
of the rocks in the Southern Uplands was doubtless determined by the Caledonian 
movements. 

The third series of movements happened in Kainozoic times and was connected 
with those that formed the Alps and the North Atlantic. These movements broke up 
the great volcanic plateau of which the islands of Mull, Skye and some of the smaller 
of the western islands were part. The subsidence, as suggested by Mackinder, 
of a submarine rift-valley formed the deeper part of the Little Minch, which sepa- 
rates the Hebrides from Skye; and various faults produced rift valleys, such 
as the Sound of Mull, and caused rifts and lines of weakness, which have been enlarged 
by rivers and ice into the glens and lochs of western Scotland. 



One of the most striking features in the structure of the Highlands is the 
contrast between the western and eastern sides of the country. The western coast 
is skirted by an archipelago of innumerable islands, and the coast is indented by 
a series of lochs which include fiords. There are, on the other hand, very few islets 
off the eastern coast, and they are volcanic necks belonging to the Midland Valley. 
The eastern coast of the Highlands extends in unbroken stretches, of which the 
longest are in Aberdeenshire and on the north-western side of the Moray Firth, and 
trend from north-north-east to south-west, parallel to the main Caledonian lines. 
The intervening coast line of Nairn, Elgin and Ranff trends from east to west 
parallel to an important series of Highland valleys, such as Glens Oykell, Strath- 
connan, Strathbrae, Strathfarrar, Glengarry, Loch Arkaig, Loch Morar, Loch 
Eil, etc. 

The only important indentations on the eastern coast of the Highlands are 
at the head of the Moray Firth (Fig. 2), which continues inland as the Firths of 
Cromarty, Beauly and Dornoch. The connexion of Cromarty Firth with Moray 
Firth past the town of Cromarty is of post-Glacial date, the former outlet having 
been into the Dornoch Firth, to the west of Tarbat Ness. 

The great difference between the western and eastern coasts of the Highlands 
is due partly to geological structure and partly to earth-movements. The Archean 
rocks sink eastward below sea level and are covered by wide sheets of Old Red 
Sandstones and their associated shales, and by the largest Jurassic areas in Scot- 
land. Fluvioglacial gravels and sands have been laid down along the river valleys 
and over the low country along the eastern coasts. Hence the Eastern Highlands 
are bordered by wide plains, which have a better soil, a drier climate and more 
sunshine than the western districts and thus enjoy great agricultural advantages 



16 (III. 1.) The British Isles. — Morphology. 

over the isolated patches of cultivable land on the floors of the western glens. 
As the prevalent winds are from the south-west, they strike first the high western 
area which, therefore, receives a heavy rainfall and snowfall. In Glacial times the 
first glaciers were doubtless formed on the western side of Scotland, and they pro- 
bably lasted there latest. The material left by pre-Glacial rock decay in western 
Scotland has been very largely carried eastward and south-eastward and has helped 
to fill up many of the old valleys in eastern Scotland. The glaciers flowed out to 
sea in eastern Scotland in great strength, but the tectonic conditions there were not 
suitable for fiord formation. The many branched lochs of the western Highlands 
are probably due to the area having been a high plateau shattered by Middle Kaino- 
zoic earth movements, and the valleys then begun have been moulded by river 
and ice into the present lochs and glens. 

Kainozoic denudation and fresh movements along the line of Caledonian 
faults have formed the Great Glen (Figs. 2,-4) and thus broken the Highlands 
into two main divisions. The main Highland valleys in early Kainozoic 
times ran from north-west to south-east; the formation of the Great 
Glen broke these valleys into two series, both still preserving in the 
main their original direction from north-west to south-east. In the northern 
Highlands the longest rivers rise on the hills behind the western coast and flow 
south-eastward to the Moray Firth or the Great Glen ; and the level lower courses, or 
estuaries of these rivers form the lochs such as the Beauly Firth, Loch Garry, 
Loch Arkaig, Loch Eil on the northern side of the Great Glen. 

The southern Highlands, between the Great Glen and the Highland Boundary 
Fault, consist of a second block with a main slope from north-west to south-east. 
Its peneplane surface can still be recognised in views across the country from the 
summits of the chief peaks. The remains of the old consequent drainage is still 
apparent as in Glen Garry, the former main stream of the Tay, or in the continuous 
valleys from the hills of mid-Argyll across Loch Fyne and through Hell's Glen 
to Loch Goil and the Gareloch, and along Loch Eck to the estuary of the Clyde. 

The valley system of the Highlands was not originated by the glaciers, but 
they modified it, especially by the frequent diversion of the drainage ; many of the 
notches on the sides of the valley have been used as overflow channels and cut down 
to the general base level of the local river system. Thus the Highland plateau 
has been intersected by many low valleys and passes which afford easy means 
of intercommunication. The old drainage system has been greatly altered by 
the formation of large valleys along the strike of the rocks, such as the valleys of 
the Spey, upper Tay, upper Forth, Dee and Don. These rivers deposited along 
their valleys and over the eastern plains wide sheets of alluvium, which, combined 
with the sunny and drier climate, have given the eastern Highlands their special 
agricultural advantages over the western. 

The western Highlands and islands owe some of their most striking geographical 
features to Kainozoic volcanic activity; the gabbro masses, which form the pictur- 
esque mountains of the Coolins in Skye, and the wide sheets of basalts that constitute 
most of northern Skye both belong to this period. The islands of Rum, Eigg, 
Mull and the peninsula of Ardnamurchan all contain volcanic masses resting on 
foundations of Mesozoic or older rocks. 

The MidlandValley of Scotland (Fig. 4) is politically the most important of 
the three divisions of Scotland, although much smaller than the Highlands. It owes 
its industrial importance primarily to its coalfields, with their beds of coal, iron ore, 
fire clay and oil shale. Its land moreover, is of higher value agriculturally than 
that of the Highlands, as the rocks are softer and more readily decompose to soil, 



Cole: Ireland. (III. 1.) 17 

while large parts of the country are covered by thick clays and loams deposited 
during the glacial period; and these superficial deposits often form fertile soils, 
as they have been enriched by the waste of the extensive basic igneous rocks. 
As the level of the country is lower than that of the other two parts of Scot- 
land, the soils can be used to better advantage as the climate is warmer. 

The floor of the Midland Valley is, however, hilly, for it includes moorlands 
of Old Red Sandstone, ranges of Silurian sediments and Devonian igneous rocks; 
and from Renfrewshire to Stirling is a series of plateaus formed of Lower 
Carboniferous volcanic rocks, the Renfrewshire Hills, the Kilpatrick Hills, the 
Campsie Fells and the Fintry Hills. 

The general structure of the Midland Valley is essentially a disturbed irregular 
geosynclinal. The Old Red Sandstones form the moorlands on both northern and 
southern sides; the Carboniferous rocks form most of the middle of the valley. The 
coal seams occur at two horizons — the Lower Carboniferous Limestone Series, and 
a higher horizon which corresponds with the Coal Measures of England. The Lower 
Carboniferous coals are found in numerous scattered basins; the upper or true Coal 
Measures occur in the Lanarkshire coalfield, a great basin. 

The coast of the Midland Valley includes the two great Firths of Forth and 
Tay on the east, and the Firth of Clyde on the west, though the branches of the 
last are lochs belonging to the Highlands. 

The Southern Highlands (Fig. 4) are geographically the simplest division 
of Scotland. They are composed mainly of Ordovician and Silurian rocks, which are 
covered in places by sheets of Old Red Sandstone and of New Red Sandstone, and 
have been invaded by masses of Devonian granite. The country consists mainly of 
moorlands used for sheep farms, while the valleys and plains in the south-eastern and 
south-western districts include much valuable agricultural land and dairy farms. 
The mineral wealth is of secondary value; there are lodes with ores of lead and 
silver at Leadhills etc., and a patch of Carboniferous rocks preserved in a depression 
in the older rocks forms the coalfield of Sanquhar. The country as a whole has 
its high ground near the northern border and the level falls to the south-east and 
south-west. The highest summits are remnants of an old peneplane destroyed 
by river valleys begun in early or perhaps mid-Kainozoic times; the main con- 
sequent valleys trend from the N. W. to S. E., and the wind gaps left at their 
heads are used as the chief routes for roads and railways from the Midland Valley 
to the English border. 



c. Ireland. 
By G. A. J. Cole. 

The general outline of Ireland is roughly rectangular, its four sides respect- 
ively facing the cardinal points of the compass. Considerable variety, however, 
is discoverable when the details of its coast-line are examined, and features are 
revealed which connect this or that part of its structure with the west coast of 
Scotland, the Southern Uplands, or South Wales. Situated as the country is on 
the great European plateau, which drops on the west of Ireland into oceanic waters, 
it soon becomes clear that a comparatively recent subsidence has separated Ireland 
from Great Rritain, and that prominent tectonic lines may be expected to pass 
from one region to the other. It is as difficult to consider Ireland, from a geographic 
point of view, apart from Rritain, as it is to consider the islets off the Irish coast 
apart from the features of the mainland. 

Handbuch der regioiialen Geologie. III. 1. 2 



18 (III. 1.) The British Isles. — I. Morphology. 

As a matter of convenience, the line indicating a depth of 100 fathoms 
(183 metres) has been usually accepted as the edge of the continental shelf; and 
this serves well for western Europe generally. On account, however, of the broad 
area of shallow water that extends westward from Co. Galway, the line of 300 fathoms 
(548.5 m.), expresses more accurately, in the case of Ireland, the limit of the Atlantic 
basin. This line sweeps out westward from off northern Mayo to beyond 27° 
W. Long., and returns towards the coast of Kerry, after a hook-like bend south- 
ward in 26° W. Long. It includes the Porcupine Bank, where rock is known to 
rise within 159 m. (87 fathoms) of the surface. An elevation of some 600 metres 
(2000 ft.) would thus add a territory nearly 300 km. (186 miles) in width and some 
200 km. (124 miles) from north to south to the existing area of Ireland, while the 
gain off the coasts of Scotland, England, and France would be very little more than 
would be occasioned by an uplift of 200 m. (656 ft.). 

When we examine the present coast-line of Ireland, certain distinct morpho- 
logical types are met with. These depend partly on the geological structure of 
each district, partly on recent movements of subsidence or elevation, and partly on 
the extent to which the rocks are exposed to the battering action of the sea. Thus 
from Dublin Bay to Carnsore Point in Go. Wexford (Fig. 7) the shore is practically 
parallel with the strike of the strata, and with the axis of high ground that runs 
north-east and south-west at some little distance within the coast. Broad bays 
have been carved out between headlands of more resisting rock; but the coast-line 
is one of fairly regular erosion, and shows few features due to the subsidence 
of ancient valleys. The mouths, indeed, of many of the valleys have been cut 
away by marine erosion. When we pass westward round the granite promontory of 
Carnsore, we find far more rugged features, where the sea is attacking the country up 
the strike of the beds, and where rocks of various hardness have thus a prominent 
influence in producing promontories or recesses (Fig. 6). Near Dungarvan we find 
a third type of coast, which extends round to the mouth of the Shannon. East- 
and-west folds dominate the country, hard sandstone weathering out along the 
anticlines, and limestone or slate forming lower ground along the synclinal hollows. 
The subsidence of the coast has produced numerous sea-inlets along the lower 
courses of the rivers. Cork Harbour, with its "passages", represents a system of 
streams that here cuts across the strike of the folds. The "rias" of western Kerry 
represent streams that flowed seaward down the hollows worn out along the syn- 
clinals. The islets off the coast are the unsubmerged peaks of the former valleywalls. 

The violence of the Atlantic storms prevents the accumulation of delta- 
material on the west Irish coast, except in sheltered inlets. Here the winds pile up 
blown sand on any alluvial bank or barrier that may rise to the surface of the sea. 
Fine cliffs have been cut out in the west of Clare (Fig. 6). North of Galway Bay, 
a fault-line seems responsible for a straight stretch of coast; and thence to the 
north of Mayo a characteristic region of rugged headlands, irregular sea-inlets, 
and outlying rocky isles, indicates severe marine erosion combined with features due 
to subsidence (Fig. 3). The same type recurs throughout the Donegal coast, the milder 
interval between Killala Bay and Donegal town being due to the presence of limestone 
along the shore, and the consequent lack of resistance offered to erosion. The long 
inlets of Mulroy Bay, Lough Swilly, and Lough Foyle, indicate the subsidence which 
has increased the basin of the North Atlantic in Pliocene or later times, and which 
limits Ireland in a northerly direction. A far less indented coast, dominated by a 
scarped edge of basaltic plateaus, continues from Lough Foyle to Belfast Lough 
(Fig. 4). Here we see how the old valley of the Lagan was entered by the sea when 
Ireland became cut off from Britain; Strangford and Carlingford Loughs furnish 
additional evidence of subsidence as we go southward. From Dundalk down to Dublin, 



Cole: Ireland. (IN. 1.) 19 

still milder features prevail, and signs of uplift, or recovery from the last downward 
movement, become prominent in the form of raised beaches. Similar beaches 
occur, indeed, from Lough Foyle eastward and southward, and provide flat land 
at the heads or on the flanks of many inlets, such as the level shore on which the 
Lagan alluvium has gathered at Belfast. Close to Dublin, the village of Baldoyle 
stands on a raised beach that now joins the rocky mass of Howth with the mainland. 

When we pass from the coast to the interior of Ireland, we are at once struck 
with the fact that the highlands are grouped upon its margins. The coast-line is 
almost everywhere picturesque, with mountains rising abruptly from the sea, as 
in Kerry or Donegal, or forming a wall-like background to a comparatively narrow 
lowland, as along the Leinster shore. Broad stretches of the interior, however, are 
devoid of any prominent features, and a great plain, rising in places as plateaus 
120 m. (400 ft.) above the sea, stretches between Dublin and Galway, and from 
Boyle in the north of Roscommon to Nenagh in the north of Tipperary. The 
lower parts of this level land are often covered by bog, and lakes, which are 
broad expansions of the rivers that run through them, occupy extensive areas. 
No clearly defined watershed exists to mark off the river system of the Shannon 
from that of the Boyne, the Liffey, or the Barrow. The only prominent hills 
are formed of glacial gravels, deposited as long winding eskers upon the worn- 
down surface of the plain. The same type of country extends between the 
ranges of hills as far south as the borders of Cork and Waterford, and as far 
north as Dungannon and Donegal Bay. Local offshoots of the great central plain 
thus occur far beyond the limits above assigned to it; and these are found to repeat 
in their geological structure the far narrower valleys which lie between the ranges 
of the south of Ireland. 

A broad triangular area of broken hummocky country stretches from an 
apex on the central plain near Longford to the eastern coast, where the base of 
the triangle extends from Belfast to Drogheda. The axis of this upland thus runs 
north-east and south-west, and is a continuation of that which forms the Southern 
Uplands of Scotland (Fig. 4). At its west end it forms a. watershed between the river- 
systems of the Erne and the Shannon. North-west of it, there are two or three areas of 
high ground. The most important of these lies round about Lough Allen, a region 
of scarps of stratified rock, rising in terraces, and culminating in Cuilcagh, 667 m. 
(2188 ft.), where the first waters of the Shannon gather. 

Farther west, the Irish plain is broken by the range of the Curlew Hills, and 
then by the Ox Mountains, which appear as a north-easterly offshoot of the Mayo 
highlandsy'South of the line between Dublin and Galway, numerous interruptions 
of the plain occur, in the form of somewhat round-backed masses, often with 
basin-shaped depressions in their centres. Such are the Slieve Bloom Mountains, 
Slieve Aughty, Slieve Bernagh, and the broad upland from Devilsbit Mt. to Slieve 
Felim. The range of the Galtees and the Ballyhoura Hills has the same structure; 
Galtymore is 919m (3115ft.) in height. Slievenaman (720m., 2364ft.) on the borders 
of Tipperary and Kilkenny forms a bold promontory in the south-east angle of the 
plain. From its western end a ridge runs towards Kilkenny city, a typical piece of 
plain-land being thus enclosed. North of Kilkenny, the plateau of the Leinster Coal- 
field rises in bold terraces to heights of over 300 m. (1000 ft). 

The general lowland of the interior is thus greatly broken towards the south; 
but the intervals between the hills, which often have rivers in their floors, are 
important for agriculture, and the commercial routes, whether roads, canals, or 
railways, have been carried along them. In the Galtee range we reach truly moun- 
tainous country. This is repeated on the Knockmealdown and Comeragh Moun- 
tains immediately to the south, and generally throughout the west of the county 



20 (III. 1.) The British Isles. — I. Morphology. 

of Cork and the whole of that of Kerry. The trend of the ranges is here east and 
west. Carrauntoohil in Macgillicuddy's Reeks rises 1040 m (3414 ft.) above the sea, 
and is the highest Irish mountain. 

The west of Clare is a country of high plateaus. The county of Galway, with 
its irregular peaks of stratified quartzite rising among granites and mica-schists, 
introduces us to a complex highland type, which occurs generally throughout 
Mayo, and again from Donegal town across to Londonderry. In the latter region, 
as in the Ox Mountains, a north-east and south-west trend is conspicuous. In 
a stretch intervening between Ballina and Donegal town, limestone plateaus pre- 
vail, resembling those of southern Derbyshire. The high margin of Ireland is main- 
tained across the east of Co. Londonderry and the whole of Co. Antrim by the 
basalt plateaus, which are tilted down in the latter country to the south-west and 
attain their highest points (some 450 m., 1500 ft.) along their north-east border. Then 
we meet the region of hummocky country already referred to as reaching to the coast 
from Co. Longford. The granite crests of the Mourne Mountains (750 m.), and 
the older granite ridge from Newry to Slieve Croob on the north-west, diversify 
this part of the landscape. The coast is actually low from the south of Carlingford 
Mt. to Dublin; but here the great range of the Leinster granite rises from the sea 
at Killiney, and forms a high barrier on the edge of the central plain, until it unites 
with the east-and-west ridge of Slievenaman. The north-east and south-west trend 
of the Leinster Chain (Fig. 7) clearly links it with the axis of Newry and Slieve 
Croob, with the Ox Mountains, and with the ridged moorlands of the county of Donegal. 

We thus have one series of marginal ridges that suggests the Caledonian 
or early Devonian chains of Europe. The country from Longford to the coast of 
Co. Down expresses the same general structure. In the south, the close-set east- 
and-west ranges, with valleys running between them, recall the Armorican or 
early Permian chains. The protruding masses that break the central plain will 
be found to be connected with these southern ranges, though they have been in- 
fluenced in their trend by the pre-existing Caledonian obstacles, and thus have 
often a north-easterly direction. 

The great plain itself merely repeats on a broad scale the features of the long 
valleys among the southern Armorican ranges. Limestone, which has been removed 
by denudation from the intervening ridges, remains in these valleys, and also 
forms the floor of the central plain. Long ages of denudation have worn it down 
to a general and nearly level surface, a true "peneplain", and this has been uplifted 
again sufficiently in recent geological times to allow the streams to notch its 
margins. 

The longest river in Ireland, the Shannon, lies almost entirely in the plain, 
rising in the Lough Allen upland in the west of Co. Cavan, and running southward 
to western Tipperary, with intervening expansions in the form of lakes. It cuts 
across the Slieve Bernagh mass, has a more rapid fall towards Limerick, and then 
enters the submerged part of its valley, the long sea-inlet stretching down to Kerry 
Head. The courses of the southern rivers among the Armorican ranges will be 
considered in connexion with the geological structure of the orographic features of 
Ireland (p. 23). 

The two directions of folding that control the main orographic features of 
the Irish area have already been referred to. The whole floor of this 
area must have been remodelled, like so much of north-west Europe, by 
the Caledonian earth-movements at the close of Silurian, and therefore 
in early Devonian, times. Possibly the Dingle Promontory represents a 
region where the floor of the Silurian sea was at first uplifted more gently, as in 



Cole: Ireland. (III. 1.) 21 

parts of South Wales and the west of England, so that the striking unconformity be- 
tween its deposits and those of the Old Red Sandstone lakes was here for a time avoided. 
But everywhere else in Ireland there are signs of the formation, by extensive crump- 
ling, of continental land, prior to the deposition of the Old Red Sandstone. The 
most continuous feature produced by these Caledonian movements is the Leinster 
Chain. 

The Ordovician and Gothlandian sediments became raised in the south-eastern 
Irish area into a huge anticlinal arch, the visible part of which is 150 km. (94 miles) 
in length (Fig. 7). The little isle of Rockabill off Balbriggan is the last relic of the 
north-east end of the anticlinal, where it becomes lost in the Irish Channel. The south- 
west end has been cut into by the Atlantic waves along the coast of Waterford. 
As the arch rose, numerous subsidiary crumplings went on in the strata forming 
its cover and its flanks, while a granitic magma, perhaps in successive inflows 
(Sollas 1891, 1893), followed it from below, and cooled as a strengthening mass 
along its core. The strata in contact with it were greatly altered, and flake after 
flake of the schists that were produced was eaten off and became assimilated by the 
granite, which is thus highly charged with biotite in many places along its margins. 
The foliation of the schists has taken place along their uptilted bedding-planes, 
and the gneissic structure that is often traceable in the granite runs parallel with 
this foliation. Long tongues of schist are included in the granite, as near Wicklow 
Gap and near Mount Leinster, showing the mode in which the igneous core has 
attacked its bounding walls. Denudation in Devonian and Carboniferous times 
reduced the height of the chain, stripped off any Gothlandian strata, carved deep 
valleys in the Ordovician and Cambrian slates, and exposed the granite in the form 
of a central moorland. It is doubtful if this moorland was ever covered by marine 
Carboniferous strata, though the coal-forests probably grew across it. Denudation 
may have acted continuously on the chain since the Armorican uplift, and at the 
present day, while the Carboniferous beds near Dublin are being removed, features 
of the early Devonian topography must be slowly coming to light. The contrast be- 
tween the central granite and the stratified foothills is very picturesque. The 
granite, with its large curving joints, and its fairly uniform and crumbling system 
of decay, forms a rounded moorland ridge, on either side of which the head-waters 
of numerous rivers, assisted by upland glaciers, have cut out broad basins. When 
the streams, however, reach the Ordovician slates and sandstones, or the some- 
what similar Cambrian beds, they carve their way down along more definite lines, 
keeping ahead of the results of the lateral and pluvial denudation. Gorges are 
thus frequent, and waterfalls occur at their heads, as the streams cut backward; 
until, as may be seen at Glenmacnass in Co. Wicklow, the streams fall steeply 
from the granite moorland over the actual junction of igneous and stratified material. 
(On the association of mature and immature features on the Leinster Chain, see 
G. A. J. Cole, 1912.) The great domes, such as those of Kippure, Tonlagee, Lugna- 
quilla, and Mount Leinster, are mere protuberances on a granite core that lies 
mainly 600 m. (2000 ft.) above the sea. The few roads that cross this highland have 
to ascend passes some 550 m. (1800 ft.) in height. In the foothills, valleys are numerous, 
and communications are far more easy. A great variety of surface-features is here 
produced by the juxtaposition of rocks of different hardness and different resistance to 
the atmosphere, such as quartzite, slate, eurite, and diorite. Woods grow freely in 
the hollows, and numerous private dwellings, set in their own parks ("demesnes"), 
characterise eastern Leinster. On the west side of the chain, the overlapping of 
the Carboniferous Limestone is far more obvious, and this brings the features of 
the great arable plain abruptly against the granite highland, from Athy down 
to Goresbridge, as we follow the valley of the Barrow. The same contrast is repeated 



22 (III. 1.) The British Isles. — I. Morphology. 

on the south of Dublin city, where the limestone boundary crosses the strike of 
the Leinster Chain. 

The Newry axis (Fig. 4). The granite axis near Newry recalls the features of the 
Leinster Chain on a less imposing scale. The reappearance of granite at Crossdoney 
close to Cavan town shows that a long bar of igneous rock in reality occupies 
the core of the Caledonian fold from Longford to the sea. The Ordovician and 
Gothlandian strata have here been much contorted, and their general trend is best 
realised when we observe that of the granite along the axis of uplift. Carboniferous, 
and probably Triassic beds, once covered the whole triangular area now exposed 
by denudation. The region does not become mountainous until we reach the granite 
of Slieve Croob in Co. Down (535 m., 1755 ft.); but it affords an interesting 
illustration of what the Leinster Chain must have been like before it had become 
seriously attacked by denudation. 

Western Caledonian masses (Fig. 3, 4). The whole structure of Donegal has been 
controlled by the Caledonian folding. The Dalradian rocks, already invaded and 
metamorphosed by older igneous masses, became rearranged along folds with 
a north-easterly and south-westerly trend. The intrusion of the great central mass 
of granite from Ardara nearly to Mulroy Bay probably dates from this epoch of 
compression. Its contact-effects on the old sediments are complicated by earth- 
pressures accompanying and following its intrusion; and faulting has taken place 
along the trend of the folds. The line of weakness along which we find the Gweebarra 
River running south-west, and the great eroded hollow of Glen Veigh running 
north-east, seems due to one of these earth-fracturings. In the north of Tyrone, 
the Sperrin Mountains are a Caledonian chain running east and west, possibly 
influenced by the proximity of the Pre-Cambrian mass immediately to the south. 

The Ox Mountain axis (Fig. 3), 100 km. (62 miles) long, running from the north 
of Manorhamilton to Castlebar, is revealed as a narrow moorland, some 450 m. (1500 ft.) 
in height, with a core of granite intimately intruded into Dalradian quartzites, schists, 
and epidiorites. The arrangement of the highly siliceous masses in the portion of the 
ridge near Sligo suggests that the original strike of the sediments was north and south. 
The rounded summits rise in marked contrast with the Carboniferous landscapes on 
either side. Through western Mayo and Galway, the Dalradian masses form an 
irregular highland country, and the stratification of their quartzites may be seen 
on the hillsides from a distance of n\any kilometres. In Donegal and in the Dalradian 
country generally, these quartzites have weathered out into massive conical moun- 
tains, or ridges displaying striking features of bare rock. Muckish, Errigal and 
Aghla in Donegal, Nephin in central Mayo, Croaghaun in Achill Island, and the 
Twelve "Bens (misnamed Twelve Pins) in Connemara, are alike evidences of the 
resisting power of the quartzites. Round Killary Harbour, the Silurian masses, 
standing out upon a Dalradian foundation, form great fort-like bluffs marked by 
almost horizontal terraces of stratification. 

Central Armorican masses. The Armorican folding is seen in the small range 
of the Curlew Hills (Fig. 3), and in the denuded dome-like uplands that break the 
central plain. These are described in the Silurian and Devonian pages of the section 
dealing with Irish stratigraphy. The influence of the pre-existing Leinster Chain 
on the trend of these Armorican masses is conspicuous. The Upper Carboniferous 
outlier that includes Slieve Ardagh and the Castlecomer coalfield similarly shows 
a north-easterly trend. 

Armorican ranges of the south (Fig. 6). But throughout the south the 
characteristic east - and - west Armorican direction controls the orographic 



Cole: Ireland. (III. 1.) 23 

features. Owing to the difference in resisting power the Carboniferous 
strata and the underlying Old Red Sandstone, the latter series forms (fee 
ridges, while Carboniferous Limestone remains along the synclinal hollows. These 
hollows, occupied by streams, are usually well wooded, and are set with 
numerous farms and market-towns. The Old Red Sandstone slopes above are bare 
and mountainous, or covered locally by plantations of coniferous trees. The wildest 
rock-scenery of Ireland occurs amid the Old Red Sandstone of MacGillicuddy's 
Reeks, where Carrauntoohil reaches 1040 m. (3414 ft.) above the sea. The famous Upper 
Lake of Killarney lies in this region, and the broad Lough Leane below rests on a lime- 
stone synclinal, recalling, with its low shores, all the features of the central plain. 

The influence of the rocks brought up by the Armorican folding on the local 
river-system was pointed out by J. B. Jukes in a memorable paper in 1862. He 
explained how the main Irish rivers had begun to flow on a great denuded surface 
of Carboniferous rocks, which sloped generally towards the south. Such a 
surface, which would now be described as a peneplain, was attributed in Jukes's 
time to marine denudation. The rivers, as usually happens, were able to cut their 
way downwards more quickly than atmospheric denudation could reduce the general 
level of the uplifted peneplain. The peneplain gradually came to show great ir- 
regularities of surface, as the Carboniferous rocks were stripped off from the crests 
of the Armorican folds. Though the "consequent" rivers could cut right across 
these folds, whether working against limestone, shale, or the underlying sandstone, 
their "subsequent" tributaries gradually extended up the synclinals in which soft 
Carboniferous rocks still lay. The Shannon system, aided by general atmospheric 
denudation, wore out a broad basin in a Carboniferous area, which is now part 
of the central Irish plain, while the main stream, well fed by its tributaries con- 
tinued to carve its way across the Devonian and Silurian mass at Killaloe. The 
general denudation could not remove this mass so rapidly as could the concen- 
trated stream along its own southerly course ; and we now find the river apparently 
sawing its way across a mountain-ridge. In the southern ranges, the tributaries, 
i'\ lending westward up the long synclinals, gradually became the more important 
portions of the streams; but the main courses are still seen in the abrupt bends 
of the rivers southward, across the sandstone ranges, shortly before they reach the 
sea. As Jukes (1862) contended, there was a tendency for the waters of the district 
to be "always turned down the transverse ravines, because, at whatever rate the 
ground in the longitudinal valleys sank [through denudation], the erosion of these 
rivers was able to keep the bottom of the ravines sufficiently below it; while other 
brooks, being unable to effect this, were ultimately drawn down into the longi- 
tudinal valleys, and their water [was] carried out to the ravines." Here we find 
truly stated the process now known as river-capture. The longitudinal valley 
of one stream, by extension westward or eastward, may have cut off the head-waters 
of the transverse part of another stream, and an original consequent transverse 
valley may now be found divided into several portions which drain into successive 
and parallel subsequent valleys. The Brinny was thus held by Jukes to be an 
original transverse stream, of which the Bandon was an exaggerated tributary. 

The Finisk River, he urged, once ran south across the folding to the sea 
parallel with the southern course of the Blackwater; but the lowering of the limestone 
surface just east of the Blackwater drew off the waters of the Finisk westward 
into the Blackwater itself. It is obvious that, the greater number of captures a 
river can effect, the greater will be its flow and its power to maintain its own trans- 
verse course across the Armorican folds. 

The Lava-plateaus (Fig. 4). The highlands of eastern Londonderry and Antrim 
are due to successive outpourings of basalt in early Kainozoic times. There are no - 



24 (III. 1.) The British Isles. — II. Earthquakes. 

mountain-ranges in this region, and the volcanic neck of Slemish, a prominent 
mass of olivine-dolerite, is the only striking feature of the interior. The falling 
in of the plateaus towards the present basin of Lough Neagh gives the country 
the structure of a basin, with high marginal escarpments, worn out by atmospheric 
denudation (Hardman 1876). 

Finally, the Mourne Blountains (Fig. 4) are formed by a knot of granite that broke 
through the Silurian slates and sandstones of Co. Down in Kainozoic times. Denu- 
dation has carved deep valleys in the mass, and has left dome-like crests upstanding, 
on which crags and pinnacles still remain, in spite of the formation of long grey 
taluses on their flanks. The surface-forms of this picturesque highland, as viewed 
from Slieve Donard (852 m., 2796 ft.) or Slieve Bingian (746 m., 2449 ft.), are clearly 
far less mature than those of the adjacent Newry axis or of the Leinster Chain. 
Glacial moraines form barriers across several of the valleys, and the lowland along 
the coast is cumbered with detritus from the hills. South of Carlingford Lough, a 
mass of granite has invaded gabbro. The granite has become worn down into a 
basin, while the gabbro forms an upstanding and rugged ring about it, the chief 
peak of which rises among the black crags of Carlingford Mountain. 



Bibliography of the Morphology of Ireland. 

1898. Cole, G. A. J. Knowledge. Vol. 21, p. 74 (Structure of Ireland). 

1912. — Proc. Roy. Irish. Acad. Vol. 30 Sect. B, p. 8 (Liffey Valley). 

1876. Hardman, E. T. Jour. Roy. Geol. Soc. Irel. Vol. 4, p. 170 (Lough Neagh). 

1862. Jukes, J. B. Quart. Jour. Geol. Soc, Vol. 18, pp. 378 and 395 (River Valleys 

of S. Ireland). 
1893. Sollas, W. J., Proc. Geol. Assoc. Vol. 13, p. 108 (Dublin etc.). 
1891. — Trans. Roy. Irish. Acad. Vol. 29, p. 427 (Leinster Granites). 
1888. Suess, E. Das Antlitz der Erde. Vol. 2, pp. 185—6 (Armorican Movement). 



II. British Earthquakes. 

By Charles Davison. 



The most complete catalogue of British earthquakes is that published in 1889 
by the Mr. W. Roper. This includes notices of all the more important known 
earthquakes until the beginning of 1889, though few details are given with regard 
to any shock. As British earthquakes seldom cause damage to buildings and rarely 
result in loss of life, they have attracted little notice, and, with a few exceptions, 
it is now impossible to determine the position of the epicentre of any earthquake 
before the year 1889. From the beginning of that year, however, they have been 
continuously studied, and the present section therefore deals mainly with the 
earthquakes of this period. 

During the twenty one years 1889 — 1909, 250 earthquakes occurred in Great 
Britain, 50 in England, 27 in Wales and 173 in Scotland. In Ireland and the Isle 
of Man, none is known to have originated in the same period, though five strong 
earthquakes originating in England and Wales were felt in the eastern and south- 
eastern counties of Ireland, and two in the Isle of Man. British earthquakes may 
be divided into three classes, according to the area included within the isoseismal 



Davison: British Earthquakes. (III. 1.) 25 

4 of the Rossi-Forel scale. An earthquake may be regarded as strong when 
this area exceeds 13000 km 2 . (5000 square miles), as moderate when it lies 
between 2600 and 13000 km 2 . (1000 and 5000 square miles), and as slight when 
it is less than 2600 km 2 . (1000 square miles). Of the earthquakes here considered, 
9 were strong, 7 moderate, and 223 slight, while 11 were earth-sounds without 
any accompanying tremor. Of the strong earthquakes, only three reached an 
intensity as high as 8, namely, the Hereford earthquake of 1896, the Inverness 
earthquake of 1901 and the Swansea earthquake of 1906. 

Of the 250 earthquakes, it is possible to associate 199 with known lines of 
fault or folding. The distribution of the earthquakes among the principal directions 
of faulting is shown in the following table: 

Caledonian Charnian Malvernian Armorican 

England 15 22 6 5 

Wales 9 — 5 8 

Scotland . . . . . 128 1 — — 

Total 152 23 11 13 

Certain characteristics of all British earthquakes may be first referrred to. 
1. So far as our limited survey goes, the growth of any fault is now extremely local- 
ized. The epicentres of successive shocks rarely coincide, but their migrations 
are confined within small limits. 2. Measuring the length of the seismic focus by 
the difference between the lengths of the longer and shorter axes of the innermost 
isoseismal, the average length of focus for strong earthquakes is 19.6 km. (12 1 / 4 miles) 
and for moderate earthquakes 20.8 km. (13 miles). Slight earthquakes are divisible 
into two subclasses, one in which the focus is 14.4 km. (9 miles) or more in length, 
the other in which it is 9.6 km. (6 miles) or less in length. The average length of 
focus in the former is 19.2 km. (12 miles), in the latter 6.4 km. (4 miles) or less. 
The grouping of the average length of focus about 19.2 or 20.8 km. (12 or 13 miles) 
is probably connected with the average distance between the crests of successive 
crust-folds. 

In Scotland nearly all the earthquakes that can be referred to known 
faults are connected with the two great faults, which bound the Highland district 
to the north-west and south-east, and the fault, which skirts the southern margin 
of the Ochil Hills. The first of these, which runs in a southwesterly direction from 
Inverness, is now growing in two portions, one lying between Inverness and the 
northeast end of Loch Ness, the other in the neighbourhood of Fort William. In 
the former district, important earthquakes occurred in 1816, 1888, 1890 and 1901. 
In most or all of these, the seismic focus probably extended-Jrom Inverness to 
Loch Ness. With the exception of the earthquake of 1888, they were followed by 
a succession of after-shocks, the foci of which show a marked tendency to migrate 
to the south-westward, some of them lying beneath the north-east end of Loch Ness. 
In the neighbourhood of Fort William, five earthquakes, all of them very slight, 
occurred between 1889 and 1909. 

The southern boundary fault of the Highland district is remarkable for 
the numerous earthquakes in the region immediately surrounding the village 
of Comrie. The epicentres, though not fixed, are confined to a very short length 
of the fault. The more important earthquakes in this district occurred in 1801 and 
1839, and on each occasion were followed by a great number of after-shocks, that 
of Oct. 23, 1839, being followed by not less than 334 within the next five years. 
Since 1845 they have gradually decreased in number and intensity and between 
1889 and 1909 only three very slight shocks occurred. 



26 (III. 1.) The British Isles. 

The third fault is that which forms the southern margin of the Ochil Hills, 
and which, in the neighbourhood of Airthrey, Menstrie, Alva and Tillicoultry has 
produced 82 earthquakes between Sep. 1900 and the end of 1909. The majority 
of them were slight, though two attained to the degree 7 of the Rossi-Forel scale. 

The Scottish earthquakes differ from those of England and Wales in several 
respects: 1. with one exception, so .far as known, they originated in faults belonging 
to the Caledonian system; 2. they are invariably "simple" earthquakes, that is, 
they originate in a single continuous portion of the fault; 3. they are followed by 
a large number of after-shocks; and 4. they originate in foci that are situated at 
a comparatively small depth below the surface. This is shown by their great inten- 
sity considering the small area disturbed by them, and by the closeness of the 
centres of the innermost isoseismals to the fault-lines with which the earthquakes 
are associated. The latter circumstance is no doubt the reason why it is possible 
so frequently to identify the parent fault. 

The earthquakes of Wales are for the most part confined to two districts, 
the northwest of Carnarvonshire and the three southern counties. The Aber-Dinlle 
fault, which must extend for some distance under the sea, is responsible for a strong 
earthquake in 1903 and not less than seven successors. A movement near Bala 
along the great Bala fault caused a slight shock in 1903. These two faults belong 
to the Caledonian system. In the south of Wales, there have been three strong 
earthquakes, two in Pembrokeshire in 1892 and 1893, and one in the neighbourhood 
of Swansea in 1906. All three were "twin" earthquakes, that is, they originated 
nearly or quite simultaneously in two detached regions of the parent-fault. In 
the case of the Pembroke earthquakes, it is difficult to assign the earthquakes to 
any particular faults, owing to the large number which traverse the crust in that 
district. The Swansea earthquake was caused by a twin movement along a great 
fault running nearly east and west from the neighbourhood of Llanelly to that 
of Llwynypia. The fault lies too deep for recognition by geological methods, but 
there can be no doubt as to its existence, as two nearly simultaneous movements 
took place in foci separated by about 22 miles. 

In England, the faults which are responsible for recent earthquakes belong 
chiefly to the Charnian and Caledonian systems. Among the former must be in- 
cluded the fault which bounds the Woolhope anticlinal to the south-west or one 
very near it, which gave rise by a twin movement, to the Hereford earthquake 
of 1896; one of the anticlinal faults of Charnwood Forest, which must be continued 
for several miles under the newer rocks to the south-east, along which a twin dis- 
placement occurred in 1893 and simple slips in 1904; and the Pendleton or Irwell 
Valley fault in Lancashire, which was the seat of the Bolton earthquake of 1889, 
and of several earth-shakes in the neighbourhood of Pendleton, the fault-slips in 
the latter case being precipitated by mining operations. To unknown and probably 
deep-seated Caledonian faults must be attributed the strong twin earthquakes of 
Colchester in 1884 and Derby in 1903 and 1904. Among Malvernian faults lately 
in action may be mentioned that which skirts the eastern side of the Malvern Hills, 
along which a small slip occurred in the neighbourhood of Great Malvern in 1907, 
and a great fault, which traverses the crust at a considerable depth below the Lake 
District, and which by a twin movement extending over at least 23 miles caused 
the Carlisle earthquake of 1901. 

The earthquakes of England and Wales possess the following characteristics: 
1. they are due to slips along faults of all systems, 2. all the strong earthquakes, 
with the exception of the Carnarvon earthquake of 1903, were twins; 3. they 



III. Stratigraphy. — 1. Pre-Cambrian. — Watts: England and Wales. (III. 1.) 27 

are seldom followed by after-shocks; and 4. they originate in foci that are situated 
at a comparatively great depth below the surface, so that it is only occasionally 
that the parent-fault can be identified. 

The Irish area is not at present one of seismic activity, and the few earth- 
quakes that now reach it seem to originate in Great Britain and to be connected 
with British earth-movements. 



III. Stratigraphy. 



1. Pre-Cambrian. 

a. England and Wales. 
By W. W. Watts. 

The Pre-Cambrian rocks of England and Wales make their appearance in a 
number of isolated inliers, rising from beneath Cambrian or newer rocks. These 
localities range from Anglesey in the north to the Lizard and the Eddystone Light- 
house in the south, and from Pembrokeshire on the west to Charnwood Forest in 
Leicestershire on the east. 

In any one area a single type of rocks alone may be present, or there may 
be two or more types of different ages. In the latter case it is generally possible, 
though by no means easy on account of the disturbance of the rocks, to ascertain 
the relative ages of the different types. The correlation of separate areas will always 
be a difficult task and one that must depend on close comparison of lithological 
characters. Such comparison is rendered exceptionally difficult by the variability 
of the types within the areas themselves and also when they are traced from one 
area to another. 

It will therefore be best to indicate in the first place the general characters 
of the rock-types, treating them in the order dictated by convenience. This order 
of the groups is not necessarily that of age, nor is it certain that some of the indi- 
vidual groups may not contain rocks of more than one age. This will be followed by 
a brief description of the separate areas. Finally, the question of correlation will 
be discussed in the light of our present knowledge of the rock groups. 

The following are the chief rock-types: 

1. Foliated rocks, such as gneisses, schists, granulites, quartzites, and crystalline limestones, 
mainly derived from the metamorphism of igneous rocks, though some members are 
undoubtedly altered sediments. This type is conspicuously represented in Anglesey, 
Malvern, and Cornwall. 

2. Igneous rocks, mostly of volcanic and hypabyssal types, and of acid or intermediate 
composition. Certain abyssal rocks in places are associated and appear to be genetically 
connected with them. Usually pyroclastic rocks occur with the lavas. Shropshire may 
be regarded as a type locality for these igneous rocks, which are well developed in 
other parts of the Midland province as at Malvern and Charnwood, while they are also 
met with in North and South Wales. 

3. Sedimentary rocks, conglomerates, greywackes, quartzites, grits, and slates, red, green 
and purple in colour, of great thickness, highly disturbed, and covering large areas of 
ground where they often give rise to a characteristic landscape. This type of rocks 
has not yet been recognised with certainty outside the Shropshire area, but reasons 
will be given for believing that rock-series of different aspect, but corresponding age, 
may exist in other regions. 



28 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

Shropshire. 

As most of the types of Pre-Cambrian rocks are present in Shropshire, it will 
be well to begin with a description of that area. 

What is probably the oldest rock, is found at the village of Rushton, where 
a small area, very ill exposed, of quartz-mica-schist was discovered by Charles 
Callaway. Its relation to other rocks is unknown. It does not seem to be part of 
the plutonic rocks to be shortly mentioned, but to be a representative of the 
oldest foliated rocks of Anglesey. 

Probably later in age there comes a volcanic group called Uriconian, after 
its typical occurrence at the Wrekin, a mountain from which the Romans named 
their City of Uriconium. Uriconian rocks occur at a number of places aligned along 
a fault which runs south-westward from Lilleshall through the Wrekin, Caer Caradoc 
and other Church Stretton hills, to Warthill Knoll, and possibly on to a group of 
hills near New Radnor. Where the igneous rocks crop out along the fault, they 
give rise to hog-tacked hills. These are flanked, on the west side at Wrockwardine 
and on the east side at Cardington, by rounded hills, where the rock is not directly 
on the line of the fault. 

The chief rocks are rhyolitic and andesitic lavas and tuffs, associated with 
acid intrusions, probably of Pre-Cambrian date, and with basic sills and dykes 
certainly of much later date. The tuffs vary from coarse breccias, through medium- 
grained crystal tuffs, to close-grained ashes made of the finest volcanic dust. 
The fine-grained type is especially well developed at Lilleshall, where the rocks 
are in the condition of halleflintas. Near Church Stretton and elsewhere, there are 
quartz-felspar grits deposited in water, but there is no evidence as to whether the 
majority of the tuffs were laid down in water or on land. The lavas present the 
characters of devitrified glassy rhyolites with the usual textures of such rocks, 
phenocrysts of quartz and orthoclase, spherulites, fluxion structure, and often well- 
developed perlitic shrinkage cracks. In certain localities the lavas show large 
pyromerides with concentric cracks and hollow interiors, filled up with quartz. 
These rocks furnished Allport (1877) with material for his classic memoir on the 
devitrification of volcanic glasses. 

The strike of the Pre-Cambrian rocks is, in general, across the ridges, a structure 
spoken of by Callaway as "plagioclinal". Both at the north and the south 
end of the Wrekin there are found plutonic rocks of acid composition. They are 
aplites, granites with little or no ferro-magnesian constituents. To the north 
they are intrusive into a series of crystal tuffs; to the south their relations are ob- 
scure, and here they sometimes possess a rude foliation. 

The Uriconian Rocks are covered unconformably by Cambrian, Ordovician, 
or Gothlandian, rocks, but their relations to the Longmyndian Group, to be 
next described, are invariably obscured by faulting. Fragments of rhyolites are, 
however, frequently found in the Longmyndian conglomerates, so that there is 
no doubt as to their Pre-Cambrian age. 

The outcrop of the Longmyndian Rocks forms the wild, moorland tract 
called the Longmynd, a high plateau dissected by water-cut valleys known locally 
as "gutters" or "batches". The rocks dip steeply from east to west and, even if, 
as is likely, there is repetition by faulting and overfolding, there must be a great 
thickness of rock. It is generally agreed that the succession is best divided into 
two Series, an Eastern or older, and a Western or newer Series. The eastern rocks 
are for the most part grey, green, or purple, in tint, and are largely composed of 
minerals derived, directly or indirectly, from volcanic rocks and laid down in water; 
the western ones are usually deep red or purplish-red in colour due to staining by 



Watts: England and Wales. (III. I.) 29 

oxide of manganese, with which the pebbles of the conglomerates are often coated. 
The detailed succession given by Charles Lapworth (1910) who has been 
engaged for many years in mapping the rocks, is as follows: 

Wentnor Series. (Western Longmyndian.) 

7. Ratlinghope Group: red and purple grits and shales, with conglomerates. 
6. Bayston Group: red and grey grits, with the three zonal conglomerates of Stan- 
batch, Darnford, and Haughmond (in descending order); the last rich in pebbles 
of Uriconian volcanic rocks. 
Stretton Series. (Eastern Longmyndian.) 

5. Portway Group: purple, grey, and green slates and flags with the Narnells grit 

and conglomerate band near the base. 
4. Lightspout Group: massive grey and green grits and flags, with few shales. 
3. Synalds Group: purple shales and occasional flaggy grits and green shales, with 

the Carding Mill Grit at the base. 
2. Burway Group: grey-green flags and shales, having as a basement band the 

siliceous Buckstone Grit. 
1. Stretton Shale Group: consisting of, 

b) Brockhurst Shales: hard grey-blue and dark green laminated shales, with 

rare calcareous nodules, 
a) Watling Shales: green shales with occasional purple mudstones, flaggy beds, 
and rare calcareous bands. 

J. F. Blake claimed to have made out that an unconformity exists between 
his upper and lower groups (which do not exactly correspond with those given 
above), but, though there are marked lithological distinctions between the two 
groups, Lapworth has been unable to confirm this observation. The Western 
Group compares very closely with the Torridonian Rocks of Scotland, and it now 
appears to be generally admitted that this correlation is justifiable. 

The highest beds of the Western Longmyndian pass up with apparent con- 
formity into a volcanic group typically exposed at Pontesford Hill, but 
occurring also in several isolated localities along a line running south-westward from 
that hill. These rocks comprise green shales, purple and green grits, andesitic and 
rhyolitic lavas and tuffs, the latter of intermediate composition and bearing pala- 
gonite fragments. Acid and basic intrusions also occur, but no plutonic rocks are 
at present known. The series is strikingly like the Uriconian even in its peculiar 
petrological details (Boulton 1904). These rocks are cut off on the western side 
by faults, beyond which Upper Cambrian Rocks immediately succeed. 

The succession of Pre-Cambrian Rocks in Shropshire would therefore appear 
to be: 

5. Western Uriconian or Pontesfordian Series. 

4. Western Longmyndian or Wentnor Series. 

3. Eastern Longmyndian or Stretton Series. 

2. Eastern Uriconian or Cardingtonian Series. 

1. Rushtonian Schists. 

Rocks, which have been referred to the Longmyndian underlie Upper Cambrian 
shales at Pedwardine in Herefordshire, and crop out from beneath the Gothlandian 
at May Hill in Gloucestershire and at Kington in Herefordshire; in the last locality 
they are associated with igneous rocks correlated with the Uriconian by Charles 
Callaway (1879). 

The Midlands. 

Rocks, which are probably Pontesfordian, but possibly Cardingtonian, in age, 
are found at the Lickey Hills, S. W. of Birmingham, (the Barnt Green Rocks), 
and at Caldecote near Nuneaton (Lapworth 1886). The latter are mostly quartz- 
felspar tuffs, intruded upon and mingled with basaltic intrusions, all unconformably 



30 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

.covered by the basal Cambrian rocks. East of Herefordshire Beacon on the Malvern 
Hills, there are volcanic rocks (the Warren Hill Series) which must be referred to 
one or other of these volcanic series. The principal rocks of the Malverns are however 
the gneisses and schists of the main range. These in places are massive diorites 
associated with pegmatites, but there also occur foliated gneisses, hornblendic and 
micaceous schists, and phyllites. The majority of these are considered by Callaway 
(1880, 1887) to be plutonic and volcanic rocks which have acquired a foliated tex- 
ture by reason of dynamo-metamorphism. The relationship of these rocks to the 
volcanic series is not known, but both groups are unconformable beneath 
Cambrian and younger rocks. 

At Charnwood Forest, in Leicestershire, there occurs a great thickness of 
Pre-Cambrian rocks which seem at first to stand apart from all other British Pre- 
Cambrian volcanic rocks. They show the following divisions: 

3. Brand Series. 

b) The Swithland Slates. 

a) Conglomerates, sandstone, and quartzite. 
2. Maplewell Series. 

e) Bradgate Beds. 
d) Woodhouse Ashes. 

c) Slate Agglomerate. 

b) Beacon Hill Hornstones. 
a) Felsitic Agglomerate. 

1. Blaekbrook Scries. 

Fine-grained tuffs and hornstones. 



NNE 




Fig. 9. Generalised section across Charnwood Forest to show the Structure and 

Faulting. W. W. Watts. 
NF = Normal Faults. OF = Overthrust Faults. 10. Swithland Slates. 9. Brand Conglomerate. 
4. Slate Agglomerate. 3. Beacon Hill Beds. 2. Felsitic Agglomerate. 1. Hornstones and Grits. 
Reproduced from the Geologists' Association, Jubilee Volume, Geology in the Field, p. 780, 1910; 

with the permission of the Council. 

The lower and middle divisions are pyroclastic rocks of intermediate com- 
position and varying degrees of coarseness, deposited on the flanks of volcanoes 
and probably sorted and stratified under water. They pass, however, on the western 
side of the area, into coarse agglomerates and breccias, probably formed above 
water, and associated with lavas and massive intrusive rocks. The latter are quartz- 
bearing "porphyroids", related to the dacites in composition and allied to those 
of the Ardennes. Like them, they are often highly sheared, and in places pass into 
schists. The Brand Series consists of conglomerates, grits, quartzites, and slates, 
made up chiefly of terrigenous material transported by water but deposited while 
vulcanicity was still in progress in the immediate neighbourhood. Worm casts, 
similar to those found in the upper part of the Eastern Longmyndian Rocks, have 
been found in the grits. It is possible to institute a close comparison between these 
Longmyndian rocks and those of the Maplewell and Brand Series, allowance being 
made for the fact that the volcanoes of the period were situated in the Charnwood 
district. No representative of the Torridonian has yet been discovered in Charn- 
wood Forest. The "Charnian Rocks" are overlain by the Carboniferous and Triassic 



Watts: England and Wales. (III. 1.) 31 

rocks, but there can be no doubt as to their Pre-Cambrian age, or as to the correctness 
of the correlation with the Eastern Longmyndian (see also page 51). 

Pembrokeshire (South Wales.) 

The Pre-Cambrian rocks of Pembrokeshire are somewhat like those of the 
Midlands. At St. David's, the rocks are mainly acid tuffs and lavas with intrusions 
of felsite and rhyolite; there is also an aplite which was at one time supposed, as 
at the Wrekin, to be part of an older series, named Dimetian by Hicks (1897). 
This rock is now known to be likewise intrusive into the volcanic series. To the 
latter the name Pebidian was given by Hicks. J. F. N. Green (1908) has recently 
divided the series into the following: 

4. The Ramsay Sound Series. 

Schistose and slaty rocks with tuffs. 
3. Caerbwdy Series. 

Fine grained felspathic rocks and halleflintas with a bed of conglomerate. 
2. Treginnis Series. 

Mainly trachyte and andesite with some rhyolite. 
1. Penrhiw Scries. 

Red and green volcanic tuffs and halleflintas. 

The whole Pebidian sequence cannot be much less than 1500 m. (5,000 ft.) 
thick. The rock types compare closely with those of the Uriconian of Shropshire, 
except that they appear to have been more highly disturbed. The whole series is 
covered unconformably by the Cambrian beds which were laid down after the folding 
and denudation of the Pebidian rocks, and after the intrusion of a set of basic dykes, 
which have at many localities become epidiorites and hornblende schists. 

A somewhat similar succession occurs farther east, near Brawdy and Hays- 
castle (Thomas and Jones 1912). The earlier Pebidian tuffs, of acid and inter- 
mediate composition, pass up into more distinctly acid rocks which are related to 
soda-rhyolites and keratophyres. Into these are intruded granites, quartz-por- 
phyries, and diorites, with some later basic dykes. The whole are unconformably 
covered by Cambrian rocks. 

North Wales. 

The Pre-Cambrian rocks of North Carnarvonshire present a great volcanic 
series for the most part of acid composition. It was divided by Hicks into three 
parts, the plutonic rocks were named Dimetian, the lavas Arvonian, and the 
tuffs Pebidian; but the whole is now considered to be a single volcanic series. The 
strip of rocks, which extends from Bangor to Carnarvon, displays a series of grits, 
breccias, and tuffs, associated with rhyolites, which are probably lava-flows. A mass 
of aplitic granite at Carnarvon ("Dimetian"), is now correlated with the plutonic 
rocks of St. David's and the Wrekin. A larger mass of rhyolitic lavas ("Arvonian") 
crops out near Llanberis. It is associated with a small proportion of ashy sediment, 
and is unconformably covered by the basement bed of the Cambrian slate rocks 
of Llanberis. Tuffs and associated rocks similar in character have been described by 
T. G. Bonne y (1883) at Beaumaris on the Anglesey side of the Menai Straits. 

A large area in Anglesey is occupied by gneisses and schists which present 
a closer resemblance to the Lewisian Archean rocks than any others in England or 
Wales. The whole of the rocks of the Island are now being mapped and described 
in detail by E. Greenly, and parts of them have been dealt with by Calla- 
way, Blake, and C. A. Matley. Towards the centre of the Island, there 
occurs an area of crystalline, acid and intermediate, plutonic rocks, in part 
massive but frequently foliated. There are granite-gneisses and diorite-gneisses, 
sometimes porphyritic or with augen structure, associated with hornblende-schists 



32 (III. 1. 



The British Isles. — III. Stratigraphy. — 1. Pre-Gambrian. 



and mica-schists. The bulk of the rocks seem to be of igneous origin and to 
have received a foliated structure partly during injection (Callaway 1897), and 
partly as the result of subsequent disturbance; but there are undoubtedly some 
altered sediments associated with them. Into what rocks this plutonic complex 
was intruded is not certain, but it is flanked by great masses of highly contorted 
micaceous, chloritic, chloritoid, and glaucophane schists. At least two other groups 
of Pre-Gambrian rocks occur in Anglesey as well as those just mentioned and the 
rocks of Beaumaris, an older one named by Matley (1899, 1900) the "Green 
Series", and a newer the "Llanbadrig Series". The former consists of flaggy and 
phyllitic grits, chloritic and micaceous phyllites, and slates. The latter Series is in 
the main gritty, it contains irregular bands of quartzite, limestone, and intercalated 
spilites or "pillow lavas". The rocks have undergone extensive earth-movement, 
and the limestones, quartzites, and volcanic rocks, have been sheared into lenticular 
masses ("quartz knobs" etc.). Much overthrusting has obscured the mutual relations 
of these rocks, but there is evidence which seems to indicate that the two Series 
are unconformable to one another. It is also clear that they are pre-Llandeilo in 
age, and therefore almost certainly pre-Cambrian. 

Greenly (1902) has described in south-eastern Anglesey, jaspers, jaspery 
phyllites, and slates, associated with limestones and pillow lavas. These rocks 
seem to be also pre-Ordovician, and, though Greenly declines to refer them 
to any particular part of the Pre-Cambrian sequence, they may presumably be refer- 
red to one or other ofMATLEY's groups. Similar rocks also occur on the western 
side of the Lleyn Peninsula, and at Bardsey Island. 

The North of England. 

Near Ingleton in Yorkshire, there exists a group of grits, slates, and conglo- 
merates, underlying, probably with unconformity, Ordovician rocks. Though these 
are probably of Pre-Cambrian age, it has not been found possible to parallel them 
exactly with any British rocks. Perhaps they may find their representatives in 
the Longmynd. 

The South of England. 
In the Lizard district of Cornwall, there exists a series of mica-schists (Geo- 
logical Survey 1906, 1907, 1908, 1912), granulites, and quartzites, of sedimentary 
origin, and hornblende-schists of igneous origin. These are associated with serpen- 

The country rock is serpentine (A) 
which has a weak fluxion foliation 
almost due north; this is cut by a dyke 
of gabbro schist (B) running into a 
north-west direction, perfectly foliated 
and in places highly schistose. It con- 
tains many blocks of serpentine but 
both these inclusions and the walls of 
the dyke are almost quite massive. 
The gabbro-schist is cut in turn by 
a straight dyke of coarse gabbro 
pegmatite (C) with crystals of felspar 
and diallage up to two inches in 
diameter; it runs north-north-east and 
shows very little foliation. This dyke 
Fig. 10. Plan of dykes in shoreatwest- a,so contains inclusions of serpentine, 

end of Coverack, Lizard Peninsula. The whole series is crossed in a west- 

Reproduced from the Memoirs of the Geological north-west direction by a dyke of 

Survey of England and Wales. Sheet 359— Lizard olivine dolerite (D) which is in a per- 

and Meneage, p. 94, 1912; with the permission of . " . v '. L . r 

the Director and of H. M. Stationery Office. fectly massive condition. 




Watts: England and Wales. 



(III. 1.) 33 



tines, gabbros, granulites, and other rocks. This complex appears to be of Pre-Cambrian 
age, as the rocks seem to be quite distinct from the older Palaeozoic rocks to the 
north and west. The rocks on which the Eddystone Lighthouse is built are pre- 
Cambrian gneisses. Again, about the Start Point in Devonshire, Bonney 
describes sections of highly folded micaceous and chloritic schists, which he con- 
siders to be older than the Devonian rocks, and therefore possibly of pre-Cambrian 
age. With this group the phyllites of the Dodman in Cornwall may also be compared. 




Fig. H. Kennack Gneiss; Streaky type. Kennack (Lizard Peninsula). X'/». 

Reproduced from the Memoirs of the Geological Survey of England and Wales; sheet 359. — Lizard and 

Meneage, p. 132, 1912; with the permission of the Director and of H. M. Stationery Office. 

The Kennack Gneisses (the Granulite Series of Bonney) were preceded by doleritic 
intrusions shown in Fig. 10 and succeeded by red gneissic granite. They are believed 
to represent an imperfect combination of these two elements. 



\y 



Summary and Correlation. 

From the foregoing description, it would appear to de doubtful whether the 
Lewisian gneisses are represented at all in England or Wales, except possibly in 
Anglesey, or at Malvern, or in Cornwall. Probably the chief of the foliated rocks, 
like those of Rushton and Anglesey, more nearly correspond with the Moinian or 
Dalradian Systems. The Pebidian System would appear to be of wide occurrence, 
from Pembrokeshire and Carnarvonshire into Anglesey on the one side, and into 
Shropshire and perhaps farther east in the Midlands on the other. The Longmyndian 
and Charnian Rocks appear to have a more limited range, though they may be 
represented in some of the newer Pre-Cambrian groups of Anglesey, and possibly at 
Ingleton. The Upper Longmyndian Rocks may be safely correlated with the Tor- 
ridonian of Scotland. The Pontesfordian Group has not been recognised else- 
where with certainty, though it seems very probable that the acid volcanic rocks of 
other Midland localities are of this age. 

It is clear that the Pre-Cambrian history of England and Wales was one 
of active vulcanicity and the intrusion of igneous rocks, that marine areas were 
limited in extent and of restricted duration, and that conditions were highly un- 
favourable for the preservation of fossils. 

Handbuch der regionalen Geologie. III. 1. 3 



34 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

Bibliography — Pre-Cambrian of England and Wales. 

1877. Allport, S. Quart. Journ. Geol. Soc. vol. 33, pp. 449-460 (Shropshire). 
1883. Bonney, T. G. Quart. Journ. Geol. Soc. vol. 39, pp. 470-486 (Anglesey). 

1896. — Quart. Journ. Geol. Soc. vol 52, pp. 17-51 (Lizard). 

1914. — "The Crystalline Rocks of the Lizard", Cambridge (Lizard). 

1904. Boulton, W. S. Quart. Journ. Geol. Soc. vol. 60, pp. 450-466 (Pontesford). 

1879. Callaway, C. Quart. Journ. Geol. Soc. vol. 35, pp. 643-669 (Shropshire). 

1880. — Quart. Journ. Geol. Soc. vol. 36, pp. 536-539 (Malvern). 
1887. — Quart. Journ. Geol. Soc. vol. 43, pp. 525-536 (Malvern). 

1897. — Quart. Journ. Geol. Soc. vol. 53, pp. 349-349 (Anglesey). 
1912. Flett, J. S., Mem. Geol. Surv., Sheet 359, pp. 34—146 (Lizard). 

1908. Green, J. F. N. Quart. Journ. Geol. Soc. vol. 64, pp. 363-383 (St. Davids). 
1902. Greenly, E. Quart. Journ. Geol. Soc. vol. 58, pp. 425-440 (Anglesey). 

1897. Hicks, H. Quart. Journ. Geol. Soc. vol. 53, Proc. pp. lxv-xcii (Pre-Cambrian Rocks). 
1886. Lapworth, C. Geol. Mag. dec 3. vol 3, pp. 319-322 (Nuneaton). 

1910. — and Watts W. W. Geol. Assoc, Jub. Vol., Geology in the Field, pp. 739-769 
(Shropshire). 

1898. — (Watts, W. W. and Harrison W. J.) Proc. Geol. Assoc, vol. 15, pp. 313-416 

(Midland England). 

1899. Matley, C. A. Quart Journ. Geol. Soc. 55, pp. 635-680 (Anglesey). 

1900. — Quart. Journ. Geol. Soc. vol. 56, pp. 233-256 (Anglesey). 

1912. Thomas, H. H. and Jones, O. T. Quart. Journ. Geol. Soc. vol. 68, pp. 374-401 

(Pembrokeshire). 
1896. Watts, W. W. Geol. Mag., pp. 485-486 (Charnwood). 

1910. — Geol. Assoc, Jub. Vol., Geology in the Field, pp. 770-785 (Charnwood). 

Geological Survey. 
Summary of Progress for 1906, p. 30., for 1907, p. 25 (Cornwall). 
See also Flett, J. S. 

b. Scotland (see plate I opposite p. 40). 
By J. W. Gregory. 

The whole of Scotland north of the Highland Boundary Fault may be regarded 
as a block of Pre-Cambrian crystalline schists and gneisses, with various intrusive 
rocks many of which are of Pre-Cambrian age. The Pre-Cambrian rocks outcrop 
over most of the area, though the old foundation is covered in places by piles of 
Kainozoic volcanic material, by small remnants of once wide sheets of Mesozoic and 
upper Palaeozoic sediments, by large areas of Old Red Sandstone, and along the north- 
western edge by a tract of Cambrian and Ordovician quartzites, shales, and limestones. 
There is also a narrow band of rocks, apparently of Cambrian age, beside the High- 
land Boundary Fault, which forms the Southern boundary of the Pre-Cambrian area. 

The schists and gneisses were first studied in the Southern Highlands; the 
less crystalline of the schists were then regarded as the metamorphosed continuation 
of the rocks of the Southern Uplands, which are now known to be Silurian and 
Ordovician. The coarsely crystalline rocks were at first regarded as older than 
any of the fossiliferous rocks of southern Scotland. 

Prominent attention was attracted to the Scottish Pre-Cambrian rocks in 
1819, when Macculloch described the apparent interstratification of fossiliferous 
limestones and quartzites between two series of gneisses on the shores of Loch 
Eriboll in north-western Sutherland. He concluded that the gneisses above the 
fossiliferous rocks were younger in age than the limestones; and as these gneisses 
rested on red sandstone regarded as Old Red Sandstone and as the fossils in the 
limestones were identified as Carboniferous, Macculloch regarded the overlying 
gneisses as altered rocks of Carboniferous or post-Carboniferous age. The fossils 
however, were subsequently shown by Salter to be Ordovician and the overlying 
gneisses were therefore regarded as altered Silurian rocks. 

This problem was investigated by Murchison who adopted Macculloch's 
conclusion that the upper gneisses were younger than the fossiliferous limestones; 



Gregory: Scotland. (HI. 1.) 35 

and this view was supported by Sir Archibald Geikie's discovery of the section 
at Craig a Knochan, north of Ullapool, where the gneisses apparently rested con- 
formably on the fossiliferous sedimentary series. It appeared therefore that the 
western gneisses of north-western Scotland were Archean; while the eastern gneisses, 
which constitute nearly the whole of the Scottish Highlands, were Silurian. This 
view was opposed by Nicol who regarded the apparently ascending sequence from 
sedimentary to crystalline rocks as delusive, and explained the undeniable super- 
position of the eastern gneisses by overthrust faulting. Nevertheless, the authority 
of Murchison and Geikie, the simplicity of their explanation of the facts, and 
Nicol's rejection of the obvious differences between the western and eastern gneisses 
led to the almost unanimous acceptance of Murchison's theory. The first fatal 
blow to it was struck in 1880 by Bonne y, who showed, that some of the eastern 
gneisses at Loch Maree, were petrographically identical with the western gneisses. 
Subsequently Lapworth (1883) proved that at Loch Eriboll, the locality for which 
the Palaeozoic age of the eastern gneisses was first advanced, the eastern gneisses 
were, as Nicol had held, old rocks which hed been thrust over the fossiliferous 
sediments; and this conclusion was established beyond doubt by the work of the 
Geological Survey. The eastern gneisses are therefore to be included in the Pre- 
Cambrian rocks of Scotland, which comprise four main groups: 

4. Torridonian. Sedimentary rocks mainly sandstone, grits, conglomerates 

and shales. 
3. Dalradian. A varied series of gneisses, schists, crystalline limestones, 

amphibolites, etc.; they are no doubt a metamorphosed stratified series. 
2. Moinian. A thick series of granulitic gneisses and mica-schists. 
1. Lewisian. The basal or "Fundamental Complex"; composed mainly of 

gneisses, with the characters of altered igneous rocks; they are traversed 

by a varied series of dykes and are associated with some schists, cherts 

and limestones of sedimentary origin. 

1. Lewisian System. The oldest Scottish rocks unquestionably belong to the 
series of coarse gneisses, which form the foundation of north-western Scotland and 
the whole of some of the Hebrides. From their resemblance to some of the 
Laurentian gneisses of Canada they have been called Laurentian. As they are 
well exposed on the Hebrides they have been named Hebridean; but as they are 
especially well developed in the island of Lewis, they are now generally known as 
the Lewisian Gneisses. 

These Lewisian rocks underlie all the other Archean groups, and they are 
therefore regarded as the "fundamental complex". The rocks are very varied in 
character; they are mostly coarse gneisses, which have the mineralogical characters 
of gneiss formed from altered plutonic rocks; but as Teall has pointed out the 
metamorphism of an arkose would give rise to precisely similar gneisses, and it is 
therefore not certain that the whole of these rocks were directly of igneous origin; 
they may include altered gabbro-arkose, diorite-arkose, as well as granitic arkose. 

The rocks of the Lewisian complex are divided by Teall into five groups. 
1. rocks of ultra-basic composition, such as banded amphibolites, pyroxenites and 
peridotites. 2. Rocks in which pyroxene is the predominant ferromagnesian con- 
stituent combined with felspar and usually quartz; the series includes pyroxene- 
granulites, augite-gneiss, and hypersthene-gneiss. 3. Amphibolites, hornblende- 
schist, and hornblende-gneiss, with or without quartz. 4. Rock rich in biotite, 
including biotite-schist and biotite-gneiss. 5. Rocks containing both biotite and 
muscovite, such as muscovite-biotite-gneiss. 

3* 



36 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

In the northern part of the Lewisian district as around Cape Wrath the cha- 
racteristic rocks are coarse-grained, pink and green gneisses charged with numerous 
intrusive pegmatites, and bands of schist due to the alteration of basic dykes. Further 
to the south in the area between Scourie and Loch Broom the characteristic rock 
is a gray, quartzose pyroxene-gneiss. 

The Lewisian rocks are greatly folded and disturbed, but the characteristic 
strike, of their foliation is on an average from west-north-west to east-south-east 
or from west to east. The rocks have been penetrated by a vast series of dykes and 
sills of Archean age. These intrusive rocks range from picrites to granites; some 
of the basic dykes still retain their igneous structure and are diabase or dolerite; 
but others are now hornblende schists. The Scourie dyke, described by Teall 
in 1885, shows the gradual passage of sub-ophitic diabase into typical hornblende 
schist. Dykes of intermediate composition are represented by microcline-mica- 
schist at Kylesku, and biotite-diorite dykes near Little Assynt. The acid dykes 
include granite, gneissose granite, and pegmatite. 

The altered sedimentary rocks belonging to the Lewisian System are best 
developed near Loch Maree and the Gairloch. They include platy mica-schist, 
silvery garnetiferous mica-schist, and some graphitic schist which contains graphite 
in a fine-grained foliated rock composed of felspar, apparently andesine, mica and 
quartz. A sedimentary origin is still more evident in the case of some quartz schists, 
jaspers, cherts, quartz-magnetite rocks, and some of the crystalline limestones. The 
Lewisian limestones are well developed near Glenelg, as at the locality of Balvaig. 

The Lewisian rocks frequently form a broad undulating plateau, which has 
been worn into an irregular moorland containing a large series of lakes and pools. 
On this plateau rest isolated hills of Torridon Sandstone and Cambrian rocks, 
but the continuity of the Lewisian rocks from the Pentland Firth southward to 
Skye admits of no doubt. In the Scottish central highlands there are many isolated 
areas of a coarse gneiss resembling the Lewisian. They were described in the Survey 
Memoir of 1907 as probably inliers, and the same view has been more definitely 
advanced in recent years. Some of these coarse-grained gneisses appear to be intru- 
sive in some of the later pre-Cambrian rocks, and it has been suggested that others 
are only coarse-grained varieties of the eastern gneisses. The balance of opinion 
is however, in favour of the larger of these outcrops being exposures of the 
Lewisian foundation. 

2. The Moine Gneisses. From the Pentland Firth on the north to nearly 
the southern edge of the highlands, and from the great overthrust fault on 
the west to the Tay Valley on the east, most of the Scottish highlands 
are composed of a series of siliceous gneisses which weather into flag-like 
slabs. Many different names have been given to this series of rocks. They 
are the Younger or Silurian gneisses of Murchison. From their flag like 
character they have been called the "gneissose flagstones" and the "flaggy 
schists". Callaway, in 1883, named them the Caledonian gneisses in contra- 
distinction to the Lewisian gneisses. The Geological Survey at first called them 
the Eastern Schists, but they are shown in the later maps as the "Moine". As the 
term Caledonian is coming into use in Goodchild's sense, it is perhaps best to adopt 
for this group of rocks the name of the Moine System. The typical rock is the flaggy 
granulitic gneiss of the Moine Peninsula of north-western Sutherland; and this 
rock extends with striking uniformity of character, as far south-eastward as the 
Tay valley, where, as Barrow has shown, it is represented by the Strowan Flags. 
In western Scotland the Moine Gneiss occurs as far south as Tyndrum. 



Gregory: Scotland. (III. i.) 37 

The typical Moine rock is a granulitic quartz-felspar schist or gneiss; and 
it consists mainly of grains of equal size of quartz and alkali-felspar. The foliation 
is often remarkably regular and the rock breaks along the micaceous divisional 
planes into thin flat slabs. Some of the cliffs of Moine rocks weather into the aspect 
of a series of ordinary flags. They have therefore been described as gneissose flag- 
stones. In places, as east of Ullapool, the rock includes pebbles of quartz and felspar, 
a quarter of an inch in diameter, and such bands were no doubt originally fine 
grained conglomerates. The rock is holocrystalline, and the mica flakes often run 
through the grains of quartz and felspar, so that the minerals have crystallized in 
situ. Nevertheless the foliation closely resembles bedding planes and sometimes 
even shews false-bedding; hence the foliation may have developed along the old 
bedding planes, and the layers of biotite may represent argillaceous bands inter- 
stratified with the quartz-felspar sands. 

The granulitic Moine Gneiss is the most widely distributed rock in Scotland. 
It is sometimes associated with garnetiferous mica-schists, with mica-schists in 
which the foliation is less regular, and with "flaser gneiss". It rests unconform- 
ably on the Lewisian. 

In the neighbourhood of the thrust planes the Moine gneisses have been 
broken down into mylonites; and in some localities, as near Craig a Knochan, sills 
of foliated igneous rocks, which are probably post-Cambrian in age, have been 
crushed into schists with the foliation planes parallel to those in the Moine. In such 
cases the existing foliation planes in the Moines may have been due to the over- 
thrusting; but in other cases it is clear that the Moines had their present characters 
before the date of these movements. The folds in the Moines, for example, trend 
from west-north-west to east-south-east at right angles to the direction of the 
earth-thrusts. 

At Tarskavaig, at the northern end of the Sleat of Skye is an area of Moine 
composed of siliceous schists, phyllites, and granulitic schists, which are faulted 
against the Torridon Sandstone. 

3. Dalradian. The name Dalradian was introduced by Sir Archibald Geikie in 
1891. The Southern Highlandsof Scotland are composed of a complex series of schists, 
gneisses and crystalline limestones which have a general strike from east-north-east 
to west-south-west. They extend across Scotland in a broad belt from Banff, Aber- 
deenshire and Kincardine on the eastern coast, to Argyll and the Firth of Clyde 
on the west. The schists are invaded by masses of granites, diorites, quartz-por- 
phyries etc., and they contain bands of hornblende schist due to foliated igneous 
rocks; but the Dalradian System as a whole consists of altered sediments. 

The stratigraphical relations of these rocks have given rise to special diffi- 
culties. Sir Archibald Geikie in 1891 grouped these rocks together under the name 
Dalradian, which he proposed as the name of a petrographic group rather than 
a distinct geological system; for he considered that these rocks included Palaeozoic 
and earlier rocks folded together and so altered that their separate elements are 
inextricably welded. Later work renders it probable that the Dalradian rocks 
may be regarded as the Scottish representatives of a pre-Torridonian system. 

The sequence of the Dalradian rocks is shewn in sections north and south 
across the Southern Highlands. The Dalradian system has been divided into five 
series in the following order from north to south: 



38 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 
N. ^ ^-*^ s 




Fig. 12. Diagrammatic Section across the Southern Highlands, secondary folds and faults omitted. J. W. G. 



Lower Old Red Sandstone 



rrrnj.Lb 



H. B. F. 



Aberfoyle Slates 
Aberfoyle Grits 
Conglomerate 



Aberfoyle Series 



BlairAtholl Limestone and\ Dloi „ .»,,„,, c „.;„„ 
Graphitic Schists ^BlairAtholl Series 



Cammock Hill Quartzite 

Basal Quartzite 

Ben Lawers "Phyllite" 



Garnetiferous Mica Schist 
Loch Tay Limestone 
Garnetiferous Mica Schist 



Green Beds 
Schistose Grits 
Granulitic Gneisses &c. 



Ben Lawers Series 



Loch Tay Series 



Ben Lomond Series 



Dalradian 



5. Schichallion Series 

— Quartzites and 
Boulder Bed. 

4. Blair Atholl Series 

— Graphitic Schists, 
Blair Atholl Limes- 
tone, and Cammock 
Hill Quartzite. 

3. Ben Lawers Series" 

— Ben Lawers 
"Phyllite", Loch 
Gair Quartzite. 

2. Loch Tay Series — 
Garnetiferous Mica 
Schists and Loch 
Tay Limestone. 

1. Loch Lomond Series 

— Epidotic Schis- 
tose Grits (Green 
Beds), Granulitic and 
Albite Gneisses, Ben 
Ledi Schistose Grits. 



Moine Gneiss 



Highland Boundary Fault 



The names of these 
series are from typical 
localities on the main 
Dalradian band. The 
sequence of these five divisions can be traced across Scotland, but it is still 
undecided which is the youngest series and which the oldest member of the system. 
The southern Dalradian rocks near Loch Lomond dip southward, and they are 
covered by slates and grits, which rest upon the schists and also dip southward. 
Further east, as in the Pass of Leny near Callender, the same succession can be 
recognized, but the slates and grits there dip northward under the schist series. 

Nicol concluded that the sequence in the Loch Lomond area was in the 
original order and that the beds in the Pass of Leny have been inverted; and this 
conclusion is supported by the comparatively unaltered condition of the southern 
rocks and by their being more disturbed near the Pass of Leny than near Loch 
Lomond. The view has however been held, as by Bailey, that the rocks on the 
southern border are older than the schists to the north of them, and that the beds 
near Loch Lomond are inverted. 

According to Nicol's complete view, the whole of the Dalradian sequence 
is in ascending order from north to south. It appears to the writ<T however that 



Gregory: Scotland. 



(III. 1.) 39 



there is a descending sequence southward from the unfoliated felspathic quartzites 
(the Schichallion Quartzites) and the graphitic schists of the Blair Atholl Series — 
the two northern members of the Dalradian System — to the albite schists and 
granulitic gneisses of the Loch Lomond Series. Further south, however, the order 
is reversed and the beds probably follow in an ascending order to the south. 

South of the Loch Lomond Gneisses is a band of slates and grits, which is 
well developed at Aberfoyle and is therefore called the Aberfoyle Series. These 
rocks are also found in the Peninsula of Cowal, and at Luss on Loch Lomond. 
This Aberfoyle series is probably post-Dalradian and was deposited unconformably 
upon the southern edge of the Dalradians. 

The typical rocks of the Dalradian Series are as follows: The Schichallion 
quartzite is a massive felspathic quartzitic grit; it forms the ridge of Schichallion 
and constitutes the Ben-y-Ghloe Mountains. At its base a boulder bed occurs 
in several localities along the northern edge of the Dalradian band. The 
characteristic rocks of the Blair Atholl Series are graphitic schists and 
crystalline limestone. The characteristic rock of the Ben Lawers Series is known 
as "phyllite"; it is a calc-sericite-schist. The Loch Tay Series consists of garneti- 
ferous mica schists 
and gneisses, some 
quartzitic schists, 
the Loch Tay Limes- 
tone and some 
bands of amphibo- 
lite which represent 
basic lava flows, 
sills and earthy lim- 
estones. The Loch 
Lomond Series con- 
sists of a series of 
crushed schistose 
grits, which in pla- 
ces are albite 
gneiss and granulitic 
gneiss. The Loch 
Lomond granulitic 
gneisses are associa- 
ted with bands of 
epidote chlorite 
schists, which from 
their colour are 
known as the Green 
Beds and have prov- 
ed of great value in the field mapping. Some of the granulitic gneisses have been 
formed from the alteration of grits, and the clastic grains are sometimes still re- 
cognisable. 




Fig. 13. Main or Blair Atholl Limestone restingonthe 
eroded surface of Moine. Glen Tilt, below Marble Lodge ( George 
Barrow). Reproduced from the Quarterly Journal of the Geological 
Society vol. 60, p. 430, 1914; with the permission of the Council and 
of the author. 



4. The Torridonian. The Torridonian System consists of a thick series of 
red sandstones, conglomerates and shales, which range in northwestern Scotland 
for a length of 184 km (115 miles) from north to south and for a width of about 
32 km (20 miles). The beds are often almost horizontal and they are so little 
altered, that they were originally identified, not unnaturally, as part of the 
Old Red Sandstone. They are especially well developed at the head of Loch 



40 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

Torridon and there rise in bold precipices. The Torridon Sandstone often rests 
on the Lewisian platform and masses isolated by denudation, such as Suilven 
and Stack Poli, form some of the most striking in aspect of Scottish mountains. 

The material of the lowest beds has been in many localities derived from the 
decomposition of the Lewisian rocks and contains much oligoclase; but most of 
the Torridon Sandstone is rich in microcline, which is not a characteristic Lewisian 
felspar. The pebbles in the Torridon conglomerates are also not of common Lewisian 
types. They include various felsites and other igneous rocks, and pebbles of quart- 
zite, chert, jasper and grit, which do not resemble the Lewisian rocks. The Torridon 
Sandstone therefore appears to have been formed of sediments derived from some 
post-Lewisian deposits. 

The maximum thickness of the Torridon Sandstone appears to be about 
6000 m. (20000 ft). It is divided into three series, which in descending order 
are as follows: 

3. The Aultbea Series, sandstone and flags with some calcareous bands and 
shales. 

2. The Applecross Series, mainly red arkose with bands of conglomerate 
composed of pebbles of quartzite and jasper. 

1. The Diabaig group which reaches its maximum thickness in Skye; it is 
mainly composed of fine red sandstone and shales with calcareous lenticles. The 
lowest part of this series consists of a conglomerate made from the underlying 
Lewisian. 



SAIL MHOR 

-Co- 




Fig. 14. Section across Beinn Eigne to A Gairbhe, south of Kinlochewe. 
A. Lewisian Gneiss. Ba. Diabaig Group (Torridonian). Bb. Applecross group. Ca. Basal Quartzite 
(Cambrian). Cb. Pipe-rock. Cc. Fucoid-beds. Cd. Serpulite-grit. M'. Mylonized Rocks, Phyllites, 
and Siliceous Schists. M. Moine-schist. T. Thrusts. ?T". Moine thrust. T. Minor thrusts. F. Fault. 
Reproduced from the Memoirs of the Geological Survey of Great Britain — The Geological Structure 
of the North-Western Highlands of Scotland, 1907, p. 550, with the permission of the Director and of 

H. M. Stationery Office. 



As a general rule the coarsest varieties of the Torridonian rocks are in the north, 
and they become finer in grain to the south. Some of the rocks in the Torridon 
Sandstone were clearly formed under water, but the pebbles in many places are 
faceted ; and both the form of the sand grains and the polishing of the pebbles show 
that they were deposited on land under arid terrestrial conditions. Owing to the 
remarkable freshness of some of the grains, L. Hinxman has suggested that the 



Handbuch der regionalen Geologie. (III. 1.) The British Isles. Plate 




J. w. u. 



Carl Winters Universitatsbuchhandlung, Heidelberg. 



Gregory: Scotland. (III. 1.) 41 

rocks were rapidly accumulated in a cold climate, while J. G. Goodchild regarded 
the rocks as accumulated under desert conditions. The rocks have smothered an old 
Archean land surface, which is now being slowly reexposed by the denudation of 
the sandstones. 

The rocks are so little altered that the shales might well have retained any 
fossils originally present in them; but the only certain traces of fossils that have 
been discovered hitherto are some spherical bodies and brown fibres, discovered 
by J. J. H. Teall; they occur in phosphatic grains found in the upper Torridon 
shales from Loch Broom. 

The relationship of these Archean systems involves many problems on which 
opinion is still divided. The Lewisian System is unquestionably the oldest though 
there are some younger gneisses of Lewisian aspect. 

The Moinian System, according to the evidence near Glenelg and in Ross-shire, 
rests unconformably upon the Lewisian, and the base of the Moinian is there a thick 
conglomerate. The fact that many of the dykes in the Lewisian do not penetrate the 
adjacent Moinian also gives some evidence in support of the view that the deposition 
of the two series of rocks was separated by a considerable interval of time. According 
to Barrow however the Moinian and the Lewisian are parts of one system. 

The Moine gneiss has also been regarded as metamorphosed Torridon Sand- 
stones, a view suggested by B. N. Peach, and several facts concerning the petro- 
graphy and distribution of the rocks appeared to favour that hypothesis; but the 
view appears now to be generally accepted that the Moinian is an older system 
than the Torridonian (Gregory 1915). 

The Dalradian System is a very varied collection of rocks which according 
to the writer are later than the Moinian and were deposited unconformably upon 
the southern flanks of a land composed of Lewisian and Moinian rocks. On the 
other hand, according to P. Macnair and some members of the Geological Survey, 
the Dalradian rocks are earlier than the Moinian and the superposition of the Dal- 
radians upon the Moinian is explained by great overfolds. 

According to Barrow the less altered condition of the Dalradian Series 
is due to the fact that the Scottish Highlands are a great metamorphic aureole, in 
which the metamorphism is most intense in the centre • and the beds become less 
crystalline to the north-west and the south-east. 

The author regards it as most probable that the Lewisian and Moinian Systems 
formed an ancient land which had been greatly denuded before the deposition of 
the Dalradian sediments upon its south-eastern border. 

Another area of the Lower Archean rocks must have existed in southern 
Scotland, and the Dalradian sediments were deposited on the north-western slopes 
of these highlands; the Lewisian and the Moinian rocks formed a foreland, against 
which the Dalradian beds were intensely puckered by pressure from the south-east. 
These southern highlands must have been destroyed before the Upper Cambrian, 
as some beds of that age have been laid down along the south-eastern edge of the 
Dalradian; but the existence of Archean areas south of the Midland Valley of Scot- 
land in Devonian times is indicated by the large boulders of Schichallion grit found 
in the Old Red Sandstone conglomerates near Lesmahagow. 



42 (111. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

Bibliography of the Pre-Cambrian of Scotland 1 . 

1910. Bailey, E. B., Quart. Journ. Geol. Soc, vol. 66, pp. 586 — 618 (Overfolding of 

Southern Highlands). 

1911. — Proc. Geol. Assoc, vol. 22, pp. 179 — 203 (Fort William). 

1913. — Quart. Journ. Geol. Soc, vol. 69, pp. 280 — 307 (Loch Awe Syncline). 

1912. — & MacGrecor, Quart. Journ. Geol. Soc, vol. 68, pp. 164 — 178 (Glen Orchy 
— Anticline). 

1893. Barrow, G., Quart. Journ. Geol. Soc, vol. 49, pp. 330 — 358 (Gneiss Intrusion in 

South East Highlands). 
1901. — Quart. Journ. Geol. Soc, vol. 57, pp. 328—345 (Highland Border). 
1904. — Quart. Journ. Geol. Soc, vol. 60, pp. 400 — 449 (East Central Highlands). 
1912. — Proc Geol. Assoc, vol. 23, pp. 274—290 (South-East Highlands). 
1880. Bonney, T. G., Quart. Journ. Geol. Soc. vol. 36, pp. 93—103 (Lech Maree). 
1910. Clough, C. T., Crampton, C. B. & Flett, J. S., Geol. Mag., dec. 5, vol. 7, pp. 337 

to 345 (Ross-shire). 
1897. Geikie, Sir Archibald, Ancient Volcanoes of Great Britain, vol. 1 (1897), pp. 109 

to 126 (Volcanic rocks). 
1910. Gregory, J. W, Trans. Geol. Soc. Glasgow, vol. 14, pp. 1 — 29 (Classification of 

Dalradian). 
1915. — Geol. Mag. pp. 447 — 450 (Torridonian and Moinian). 

1883. Lapworth, C, Geol. Mag., pp. 120—128, 193—197 (North-Western Highlands). 
1908. MacNair, P., Geology & Scenery of the Grampians and the Valley of Strathmore 

(2 vols.). 
1912. Peach, B. N. & Horne, J., Geol. Mag., Dec. 5, vol., pp. 513—514 (Lewis). 

Geological Survey. 
District Memoir: 

The Geological Structure of the North-Western Highlands of Scotland (B. N. Peach, 

J. Horne & others). 1907 (Contains bibliography). 
Sheet Memoirs: 

28. Knapdale &c (B. N. Peach & others). 1911. 

35. Colonsay and Oronsay (E. H. Cunningham Craig & others). 1911. 

36. Mid-Argyll (B. N. Peach & others). 1909. 

37. Mid-Argyll (J. B. Hill & others). 1905. 

45. Oban & Dalmally (H. Kynaston & others). 1908. 

55. Blair Atholl, Pitlochry & Aberfeldy (G. Barrow & others). 1905. 

64. Upper Strathspey &c (G. Barrow & others). 1913. 

65. Braemar &c (G. Barrow). 1912. 

71. Glenelg &c. (B.N.Peach & others). 1910. 

75. West Aberdeenshire &c. (L. W. Hinxman & others). 1896. 

82. Central Ross-shire (B. N. Peach & others). 1913. 

83. Beauly and Inverness (J. Horne, L. W. Hinxman & others) 1914. 

92. Fannich Mountains (B. N. Peach & others). 1913. 

93. Ben Wyvis &c. (B. N. Peach & others). 1912. 



c. Ireland. 

By G. A. J.Cole. 

In Ireland there' is no certain exposure of a rock-floor of a fundamental and 
"primitive" character. Ancient gneisses occur, but they seem to have resulted in 
all cases from the invasion of sedimentary rocks by granite. These sedimentary rocks 
are older than the Arenig series, as may be clearly proved in southern Mayo and 
northern Galway; and comparison with Scotland and Wales makes it practically 
certain that they are Pre-Cambrian, like the successive sedimentary series that are 
now well established in Fennoscandia. The name Dalradian, given to them by Sir 
A. Geikie, is a safe one, pending an accurate delimitation of these early systems. 
In eastern Tyrone, from north of Carrickmore to the Londonderry border, biotite- 
gneiss and schist form a moorland country; we probably meet here the oldest rock- 
masses in Ireland (Nolan 1879, Geikie 1897, Geol. Surv. Mem. Sheet 26). Granite in- 

1 Some of these works were published after the manuscript had been sent to the editor. 



Cole: Ireland. 



(III. 1.) 43 



vades this series at Fir Mt., and produces a composite rock, the features of which are 
so similar to those of the gneiss to the south-west that we may conclude that this 
also had a composite origin. Were the granitic material removed from this ancient 
gneiss, it might resemble an ordinary Dalradian schist. The later granite in this 
district is pre-Devonian (Cole 1899) and the proximity of masses of it to the little 
altered Ordovician slates of Pomeroy goes far to show that it is not one of the 
"Caledonian" intrusive masses, but is of late Pre-Cambrian age. Above the gneisses 
and schists are greenish diabases, sometimes massive and crystalline, sometimes 
volcanic, and with a scoriaceous structure, which form the flanks of the moorland. 
They are associated with red and green cherts, containing very dubious traces of 
organisms, and are invaded by the younger granite. Though at one time these 
rocks were compared with the Arenig series of southern Scotland, it seems probable 
that they also are Pre-Cambrian. Devitrified rhyolites and rhyolite-tuffs occur in 
this series at Crcggan and other places. Gneisses, probably of intrusive or composite 
origin, come out to the north-east in connexion with a series of mica-schists and 
dark crystalline limestones at Torr Head on the Antrim coast. The area of old rocks 
here, in which the Glendun and Glenshcsk valleys have been cut, is mostly occupied 
by the normal Dalradian series. This series consists throughout western Londonderry 
of much folded mica-schists and quartzose pebble beds, with occasional slates. 
Traces of the original bedding are clear in places; but in general the most prominent 



Road 



Schist Diorite 



Dolerite 



Dolerite 



Road 




Massive Quartzite 

Fig 15. Section through the King and Queen of the Mintiaghs, showing 

influence of sills of dolerite on the surface features of Co. Donegal, Pre-Cambrian area, Irishowen. 

Reproduced from the Memoirs of the Geological Survey of Ireland, Nos. 1, 2, 5, 6 and 11. 

Inishowen, Co. Donegal, p. 31, 1890; with the permission of the Director and of 

H. M. Stationery Office. 

divisional planes are those of cleavage. Disturbances during the Caledonian folding 
have crumpled these cleavage-surfaces and have sometimes developed a second 
cleavage (Geol. Surv. 1908). A greater variety of rocks occurs to the west in Donegal. 
Crystalline limestones, quartzites and mica-schists have been invaded by basic 
igneous rocks, which, during a general epoch of metamorphism, have passed into 
an epidiorite state. Great masses of granite, mainly lying in the strike of the Cale- 
donian folds, have risen through this series, and have enriched themselves with 
biotite on their margins of contact against the schists and epidiorites. The strike 
impressed upon the region at the close of Silurian times remains recorded in numerous 
strips of schist included in the granite itself, whereby the igneous rock has locally 
become a composite gneiss, with a foliation running north-east and south-west. 
Contact phenomena may be well studied in the southern area of metamorphic rocks 
near Lough Erne. Great eyes of amphibolite, consisting of quartz, basic felspars, 
pyroxene, amphibole, and garnet, lie in the granite round Lough Derg near Pettigo, 
and gneissic features have been produced along the contact-zone. The invading 
granite has, not unnaturally, been taken in places for a "fundamental gneiss". 
Yet here, as elsewhere, in Ireland, the Dalradian sediments are the oldest traceable 
series. (Haughton 1862; Scott 1862-4; Geol. Surv. 1891; Cole 1900-2.) 



44 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Pre-Cambrian. 

In Donegal, the Geological Survey has revealed a sequence in these sediments, 
which may be thus summarised, in descending order: 

4. Quartzites (often forming mountain-crests). 

"Boulder-bed" at base, possibly of glacial origin. 
3. Crystalline limestones and schists. 
2. Mica-schists, with some black slates. 
1. Quartzose and felspathic grits and flags. 

The Dalradian rocks reappear in western Mayo and Galway, and their uncon- 
formable relation to the Ordovician and Gothlandian strata is clearly seen in Conne- 
mara. At Recess in central Galway, a band of limestone has become metamorphosed 
by contact with diorite into a handsome serpentinous marble, known as Connemara 
marble. The structure of this rock, which is similar to that of the "Eozoonal" marble 
of Canada, was relied on by W. King and T. H. Rowney (1866, 1870) in attacking 
the alleged organic origin of Eozoon (See also Sanford and Jones 1865). A large 
area of intrusive granite occupies the north coast of Galway Ray. The formation 
of gneiss by the action of the granites on the Dalradian epidiorites was first demon- 
strated by Callaway (1887) in this region. There is no doubt that the Pre-Cambrian 
rocks extend south-westward under the sea from the coast of Galway. The De- 
vonian conglomerate of Inch in the Dingle Promontory shows that a schistose 
mass lay somewhere near at hand in Co. Kerry, from which the pebbles in this 
conglomerate were derived. 

The range of the Ox Mountains in the counties of Mayo and Sligo consists 
of an elongated mass of Dalradian rocks, including handsome banded gneisses, 
resulting from granitic intrusions into an older metamorphic series. 

It is difficult to determine the character of the Irish area in early Pre-Cambrian 
times. When the stratified Dalradian beds were being deposited, still older masses 
of land must have lain near at hand, probably in the west and north, from which 
the abundant detrital material was derived. There is nothing to show that the 
conditions of sedimentation were different from those of the present day, and sandy 
muds, now converted into mica-schists, sandstones, now converted into quartzites, 
and occasional grits and conglomerates, show that a shore was not far distant. The dis- 
tinctly bedded limestones may be of chemical origin, if at this remote period there were 
no organisms capable of accumulating calcium carbonate in their shells. The strati- 
fication of the whole series indicates deposition in water, which was probably that 
of a marine basin. Towards the close of the Dalradian periods — for the rocks pro- 
bably include more than one system of strata — the "boulder-bed", a coarse con- 
glomerate of remarkable persistence, was formed, and seems to point to glacial 
action. Drift-ice in this case may have dropped the boulders on the sea-floor during 
a time of general glacial extension, for striated rock-surfaces have not been found 
beneath the boulder-bed. It is proper to state, moreover, that no striations have 
yet been found on the boulders themselves. 

The period of Dalradian deposition was followed by earth-movements which 
allowed of the invasion of the series by an immense number of bosses, sills, and 
dykes of basic rock. These very probably produced lava-flows, and even lava- 
plateaus, on the surface, which were worn away before Ordovician times. The whole 
Dalradian area subsequently suffered from metamorphism, the shales being con- 
verted into slates or puckered mica-schists, yet sometimes retaining their strati- 
fication; the sandstones passed into quartzites, with less profound modification; 
the limestones, which were in part dolomitized, lost any trace of original structure; 
and the basic intrusive rocks, probably in large part originally pyroxenic, became 
diorites and even hornblende-schists. Masses of granite welled up in certain places, 
adding greatly to the metamorphism that had already taken place, and here and 



2. Cambrian. — Watts: Great Britain, including the Isle of Man. (III. 1.) 45 

there forming a floor to the series invaded by them, so as to resemble an earlier and 
"fundamental" series. One of the most difficult problems is to distinguish these 
late Dalradian granites from those that long afterwards accompanied the Caledonian 
folding in the same areas. Pebbles of granite, however, occur in the Gothlandian 
beds of Connemara, and prove conclusively the intrusion of a granite magma 
at an early epoch. 

The handsome red granites of Galway and of Burton Port in Co. Donegal 
are connected with the Dalradian series, and are quarried to some extent. 

The only Pre-Cambrian crystalline limestone successfully quarried is the serpen- 
tinous marble of Co. Galway ("Connemara Green"), which is an exceptionally 
striking ornamental stone. It results, as above stated, from the alteration of a sedi- 
mentary limestone by basic igneous intrusions; bands of olivine were developed 
in it, which have now passed into serpentine, and the streaky character of the 
marble forms one of its chief attractions. 



Bibliography of the Pre-Cambrian of Ireland. 

1885. Callaway, C, Quart. Journ. Geol. Soc London, vol. 41, pp. 221 — 241 (Donegal). 
1887. — Quart. Journ. Geol. Soc. London, vol. 43, pp. 517 — 524 (Epidiorites). 

1899. Cole, G. A. J., Quart. Journ. Geol. Soc. London, vol. 55, pp. 273 — 275 (Granites 

of Tyrone & Londonderry). 

1900. — Trans. Roy. Irish Acad., vol. 31, pp. 431 — 472 (Tyrone and Donegal). 
1902. — Proc. Roy. Irish Acad., vol. 24, Section B, pp. 203 — 230 (Composite gneiss, 

West Donegal). 

1897. Geikie, Sir Archibald, Ancient Volcanoes of Great Britain, vol. 1, pp. 123, 240. 

1862. Haughton, S., Quart. Journ. Geol. Soc. London, vol. 18, pp. 403 — 420 (Granites 
of Donega^. 

1866. King, W. and Rowney, T. H., Quart. Journ. Geol. Soc. London, vol. 22, pp. 185 
to 218 (Eozoon). 

1870 — 1874. — — Proc. Roy. Irish Acad., ser. 2, vol. 1, Science, pp. 140 — 153 
(Eozoon). 

1879. Nolan, J., Geol. Mag., pp. 154—160 (Tyrone). 

1843. Portlock, J. E., Mem. Geol. Surv. Report on the Geology of the County of London- 
derry and parts of Tyrone and Fermanagh. 

1865. Sanford, W. A. and Jones, T. R., Geol. Mag., pp. 87—89 (Eozoon). 

1862 & 1864. Scott, R. H., Journ. Geol. Soc. Dublin, vol. 9, pp. 285—294 & vol. 10, 
pp. 13 — -24 (Granitic Rocks of Donegal). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets: 

3, 4. North West & Central Donegal (E. Hull & others). 1891. 

26. Tyrone & Londonderry (J. Nolan & W. H. Baily). 1884. 

31 & 32. Parts of Counties Donegal, Tyrone & Fermanagh (R. G. Symes & others). 

1891. 
See also Portlock J. E. 



2. Cambrian. 

a. Great Britain, including the Isle of Man. 
By W. W. Watts. 
The Cambrian rocks make their appearance in numerous scattered areas, 
for the most part of small size, but the North Wales area and that of the Highlands 
of Scotland, each covers some hundreds of square miles. The rocks are exposed 
in many parts of Wales and the border counties, and they are known from borings 
as far east as Leicestershire and Buckinghamshire. They appear to thin out to the 



46 (III. 1.) The British Isles. — III. Stratigraphy. — 2. Cambrian. 

north-west and are not found in Anglesey. They are not known with certainty in 
southern England, nor are they typically developed in the north of England. They 
may be present, though they have not been recognised, in southern Scotland, and 
they appear in force in the northern part of that country. 

The rocks present three facies. One, the Welsh or "Merioneth Facies", is 
characterised by its great thickness, by the presence of coarse-grained rocks, and 
in that the succession is nearly complete. The other two facies are less distinct 
from one another, but both differ remarkably from the Welsh facies. That of the 
Midlands, the "Shropshire Facies", is characterised by the presence of quartzites 
in the lower part of the succession, followed by deep-water shales. The middle and 
lower part of the Upper Cambrian are sometimes not well represented. In the 
Scottish or "Highland Facies", quartzites are present, but the Middle and Upper 
Cambrian, if present at all, are represented by limestones, which find no parallel 
elsewhere in British geology. 

The rocks will be considered in each group of localities under the following 
heads, although, in those cases where the rocks have not yielded characteristic 
fossils, an exact allocation to any particular division may not be possible. 

tt««„„ n„ m K„io^ ( Transition Series Tremadoc Slates. 

Upper Cambrian | , enus geries Lingu , a p , ags 

Middle Cambrian, Paradoxes Series { ^^K" Beds . . 

Lower Cambrian, Olenellus Series Lower Harlech Beds. 

A. North Wales. 

The great dome of Harlech exposes the grandest succession of the Lower 
Cambrian Rocks known in the country; and round the dome, from Criccieth and 
Portmadoc to Cader Idris, the Middle and Upper Cambrian Rocks crop out in suc- 
cessive rings, usually broken and distorted, but on the whole fairly complete and 
regular. An important area of Cambrian rocks is also exposed near Llanberis, and 
one or two other smaller patches occur in isolated localities in Carnarvonshire. 

Where the lowest rocks of the centre of the dome strike out to sea, rocks of 
Pre-Cambrian type have been found. The general succession of the older Cambrian 
rocks, as established by Charles Lapworth and Stacey Wilson (Andrew 
1910), is the following: 

2. The Menevian Scries. 

Black shales and slates. 
1. The Harlech Series. 

e) Gamlan Shale Group: grey and purple shales, slates, and flags, with occa- 
sional grit bands, 229— 366m. (750 to 1200 feet). 

d) Barmouth Grits: Massive felspathic grits or greywackes, with pebble 
bands, about 180 m. (600 feet). 

c) Hafotty or Manganese Shale Group: Grey and green shales and flags, 
some subordinate grits about 300 m. (1000 feet). 

b) Rhinog Grits: very massive, forming the Rhinog and other mountains, 
760 m. (2500 feet). 

a) Cefn or Llanbedr Slate Group: blue and purple shales, slates and flags. 

The outcrop of the Lower Cambrian Rocks forms a barren and desolate tract 
almost without habitations, with block-like mountains where the two great grit 
bands make the surface of the ground. The rocks are thrown into innumerable 
minor folds and are traversed by joint and fault planes, which determine the conspi- 
cuous features of the landscape. A band, important by reason of the presence of 
carbonate and oxide of manganese, occurs in the Hafotty group between the two 
main grit bands, and has been much mined in the past. 



Watts: Great Britain, including the Isle of Man. (III. 1.) 47 

Hitherto the Harlech beds have not yielded fossils, other than worm tracks 
or "fucoids" found commonly in the highest division, but from the fact, that 
the fossiliferous Menevian Beds succeed without unconformity, there can be little 
doubt that they represent the Lower Cambrian and possibly part of the Middle 
Cambrian. 

When the Cambrian rocks rise up again from under the Snowdon syncline, 
they are much finer in texture, and constitute the Llanberis Slates, which rest 
unconformably on the Pebidian rhyolites. Grits, thinner than those of Harlech, 
are present on several horizons, but the chief rocks are purple and green slates 
in which a vast series of quarries has been opened all along the line extending from 
Penrhyn, through Llanberis, to Nantlle. The perfect cleavage of the rocks, due to 
considerable mineral change, has been connected by Harker with the presence 
of the resistant Pre-Cambrian mass of Llanberis, against which the slates have been 
pressed by earth movement and converted into fine-grained phyllites. The only 
fossils hitherto found in the Llanberis Slates are two specimens of Conocoryphe viola, 
a species not known elsewhere. A small patch of Cambrian rock also occurs in the 
south of the Lleyn Peninsula. In Anglesey the Cambrian Rocks appear to be 
overlapped by Ordovician Rocks, and they nowhere come to the surface. 

The Upper part of the Paradoxidian Series, called by Belt and Salter the Mene- 
vian, is a group of dark, almost black, shales and slates indicating the deepening 
of the sea. They are generally characterised by a small-scale cuboidal jointing. 
Fossils have been found at several places, and among them, the following are the 
chief: Protospongia fenestrata, Agnostus punctuosus, A. altus, Anopolenus salteri, 
Microdiscus punctatus, Paradoxides davidis, and P. hicksi. The slates are not so 
black as the famous "black band" of the Dolgelly Stage, and the colour seems to 
be due to the presence of pyrites, which tends to collect in bands that weather white. 
The beds are traversed by numerous intrusions of "porphyry" and "pale diabase". 
It is in association with these igneous rocks that mineral veins occur, especially 
the gold-bearing lodes for which the district has been long famous. 

The Upper Cambrian Rocks have been divided on lithological grounds into 
the Lingula Flags and the Tremadoc Slates. The former is characterised by species 
of Olenus and other Trilobites, the latter by Niobe, Shumardia, and Asaphellus, 
and by Dictyonema and Clonograptus. The latter division is now often placed in 
the Ordovician System, but for convenience of description, it is found better to 
include it in Britain with the Cambrian and to treat it as a Transition Series. 

The lower members of the Lingula Flags are coarse-grained flaggy rocks depo- 
sited in shallow water, but the highest division is characterized by the presence 
of a well marked, intensely black band, deposited in deep water. These upper beds 
were evidently deposited slowly and they may comprise a period much more lengthy 
than the rest of the Series (Fearnsides 1905, 1910). The chief divisions are the 
following: 

3. Dolgelly Stage; 80—200 m. (250-650 ft.). 

d) Zone of Peltura scarabaeoides; sooty-black mudstones. 
c) Zone of Agnostus trisectus; blue-black mudstones. 

b) Orusia lenticularis bands in black slates. 

a) Zone of Parabolina spinulosa; dark flaggy slates. 
2. Ffestiniog Stage. 

c) Band rich in Lingulella davisi, 9 to 12 m. (30 — 40 ft.). 

b) Tough blue-grey flags. 

a) Blue and brownish-grey fine-grained flags 575 m. (1900 ft.). 
1. Maentwrog Stage. 

b) Upper, or Pen Rhos Beds: dark blue slates, weathering bright red. 

a) Vigra Beds: dark grey and blue slates, with hard siliceous beds, known 
as "ringers". 



48 (III. 1.) The British Isles. — III. Stratigraphy. — 2. Cambrian. 

Among the characteristic fossils of the Lower Lingula Flags are Agnostus 
reliculalus, A. piriformis, Olenus truncatus, and 0. cataractes; of the Dolgelly Beds, 
Agnostus obtusus, A. rudis, and Sphaerophthalmus alatus. 

The Tremadoc Slates occur near the village of that name in Carnarvonshire, 
from which they are traceable discontinuously to Criccieth on the west and Cader 
Idris in the south. The highest beds are hidden sometimes by the unconformable 
overlap of the overlying beds, sometimes by the occurrence of a great overthrust 
fault (Fearnsides 1909, 1910). The sequence is as follows: 

6. Garth Hill Beds : grey-blue slates with Angelina sedgwicki; over 36 m. (120ft.) thick. 
5. Penmorfa Beds: flaggy mudstones with Shumardia pusilla, and a rich fauna of 

other trilobites like that found in the Shineton Shales. 
4. Portmadoc Beds: thick felspathic slates with Asaphellus homfrayi. 
3. Moel-y-Gest Beds: banded grey slates and mudstones; Acrotreta and Bellerophon; 

few fossils 75 m. (250 ft.). 

2. Dictyonema Band: blue-grey mudstones, bright-rusting, with abundant Dictyo- 

nema sociale; about 6 m. (20 ft.) 

1. Tynllan Beds: thin bedded rusty shales, with some hard bands containing Niobe 

homfrayi, Psilocephalus innotatus, and Hymenocaris vermicauda ; about 60 m. 
(200 ft.). 

The Tremadoc Series as a whole shows the recurrence of shallower water 
after the deeper phase indicated by the "Black Band" of the Dolgelly Stage. Vol- 
canic rocks of Upper Cambrian age are known to occur on the north-western slopes 
of Cader Idris. There are andesitic lavas in the Dolgelly Beds and rhyolitic lavas 
and tuffs above the Dictyonema Band. No Tremadoc rocks have been identified 
north-west of the Snowdon Syncline. 

B. South Wales. 

The Cambrian Rocks of South Wales are closely comparable with those of 
the north of that country, in that there are two fine grained and two coarser-grained 
series. The Tremadoc Series is not typically developed. The divisions given by 
Hicks (1892, 1894) at St. Davids in Pembrokeshire are summarized below: 

3. Upper Cambrian: Lingula Flags with Lingulella davisii. 

b) Upper Lingula Flags. 

a) Lower Lingula Flags. 

2. Middle Cambrian. 

b) Menevian Series. 

3. Highest Beds with Conocoryphe. 

2. Zone of Paradoxides davidis. 

1. Zone of Paradoxides hicksi. 
a) Solva Series. 

3. Zone of Paradoxides aurora. 

2. Zone of Paradoxides solvensis. 

1. Zone of Paradoxides harknessi, Plutonia etc. 
1. Lower Cambrian. 

Caerfai Series, with Olenellus, Lingulella ferruginea. 

The Lower Cambrian rocks consist of conglomerates, red and purple flaggy 
sandstones, and red shales and flags, with a thickness somewhat over 450m. (1500 ft.). 
Certain crustacean fragments found in this series have been referred by Hicks 
to Olenellus. The Solva Series shows grey, purple, and red sandstones, flags, and 
slates, with a thickness.of 610 m. (2000 ft.). The Menevian Series is as usual made up of 
dark flags and black slates about 230 m. (750 ft.) thick, in which several species of Para- 
doxides have been recognised. This deeper-water series is followed by the Upper 
Cambrian, shallow-water, rocks, of which the various members have been corre- 
lated with the three divisions of the Lingula Flags, but few fossils, except the charac- 



Watts: Great Britain, including the Isle of Man. — South Wales, The Midlands. (III. 1.) 49 

teristic Lingulella davisii, have been found in the lower beds. The well-marked 
fauna of the Dolgelly Beds is represented at Trefgarn Bridge and elsewhere. The 
rocks referred by Hicks to the Tremadoc Series, occurring on Ramsey Island and 
at Whitesand Bay are almost certainly of Arenig age. 

East of St. Davids, at Brawdy and Hayscastle, Lower and Middle Cambrian 
Rocks occur, which have been compared by H. H. Thomas and 0. T. Jones 
(1912) with parts of the Gaerfai and Solva Series of St. Davids. Very few 
fossils have been found in these rocks. J. E. Marr and T. Roberts (1885) 
recognised in this neighbourhood Lingula Flags with Agnostus pisiformis and 
Parabolina spinulosa. In the neighbourhood of Carmarthen and Llanarthney, 
dark shales and mudstones, making their appearance in the cores of sharp anticlinal 
folds, have been relegated to the Tremadoc. The principal fossils found in them 
are Peltura punctata and Ogygia marginata with Dikellocephalus serratus, and Para- 
bolinella rugosa. 

C. The Midlands. 

Cambrian Rocks have been detected in the following areas: Shropshire, 
The Lickey Hills, Nuneaton, Malvern, and at Pedwardine in Herefordshire. 
The succession, which is not usually complete in any one area, is as follows: 

3. Upper Cambrian 

c) Shumardia Beds, 
b) Dictyonema Beds. 

a) 01 en us Shales. 
2. Middle Cambrian. 

b) Menevian Shales. 

a) Paradoxides Limestone. 
1. Lower Cambrian. 

b) Sandstone or quartzite with Olenellus and Hyolithus. 
a) Quartzite. 

The Quartzite of the Wrekin and Caradoc rests unconformably on Carding- 
tonian volcanic rocks, with a conglomerate, made from the denudation of them, at 
its base. In the main it is uniform in texture and it has yielded worm-tracks to 
Callaway (1877). It passes up gradually into a green glauconitic sandstone 
(the Comley Sandstone) in which several beds of limestone have been discovered 
(Lapworth and Watts 1894, 1910). These limestones present many points of 
comparison with the lowest Cambrian limestones of Oeland. In them have been 
found the faunas of the Olenellus and Paradoxides stages. In the neighbourhood 
of Comley, near Church Stretton, E. S. Cobbold (1910, 1910, 1911) estimates the 
Wrekin Quartzite to be about 30m. (100 ft.), and the Lower Comley Sandstone 
between 90 and 120 m. (300 and 400 ft.) thick. In the Sandstone two species 
of Callavia, one of Wanneria and several other fossils have recently been found. 
At the top of this occur two limestones in juxtaposition, the lower containing 
Callavia callavei, the upper Protolenus, Microdiscus bellimarginatus, and M . lobatus. 
Separated by an unconformity occur grits, shales, and flags, considerably over 120 m- 
(400 ft.) thick carrying Paradoxides groomi, followed by Dorypyge in the lower part, 
Ptychoparia in the middle, and zones of Paradoxides rugulosus, and P. davidis in 
the upper part. Above the last horizon come shales with Orthis (Orusia) lenti- 
cularis and other shales with Dictyonema, but the relations of these shales to one 
another and to the beds below are unknown as the complete succession is not 
exposed. 

Near the Wrekin the highest shales are well developed. Low down in the 
sequence the Dictyonema Band occurs, carrying D. sociale and Clonograptus; then 

Handbuch der regionalen Geologie. III. 1. 4 



50 (IH. 1.) The British Isles. — III. Stratigraphy. — 2. Cambrian. 

follows a considerable thickness of barren shales, in the upper part of which 
Callaway (1877) detected the rich fauna of the Shumardia zone, including Macro- 
cystella mariae, Lingulella nicholsoni, Asaphellus homfrayi, Olenus salteri, 0. triarthus, 
Agnostus dux, Niobe, and Shumardia pusilla. The beds are uncleaved and the 
fossils beautifully preserved. They enable correlation to be effected with certain 
parts of the Tremadoc Series of North Wales, although the Niobe beds below and 
the Angelina beds above have not yet been identified. The highest rocks exposed 
are unconformably overlapped in some places by the basal beds of the Ordovician 
and in others by the Gothlandian. 

At Pedwardine Farm, near the village of Brampton Bryan, in Herefordshire, 
richly fossiliferous Dictyonema beds of Tremadoc age have been found. 

At the Lickey Hills, south-west of Birmingham, the Barnt Green Rocks 
(Lapworth, Watts and Harrison 1898) are followed by a quartzite, the basal 
beds of which contain fragments derived from the Pre-Cambrian Rocks; but the 
bulk of the rock is a typical quartzite much quarried for road-metal. No fossils 
have been discovered, but the fact that it is overlain unconformably by basal Va- 
lentian beds, and comparison with the Wrckin and Nuneaton Quartzites, make 
it practically certain that it is of Lower and possibly Middle Cambrian age. 

North and north-west of Nuneaton, the Carboniferous Rocks are underlain 
by a considerable series of Cambrian Rocks recognised and worked out by 
Lapworth (1886, Strahan 1886, Lapworth, Watts and Harrison 1898) and the 
Geological Survey. Overlying the Caldecote Volcanic Series come grits and massive 
conglomerates made up of fragments of the underlying ashes and the rocks intrusive 
into them. These soft rubbly beds are followed by compact and flaggy quartzites 
exposed in a large series of quarries where the rock is worked for road-metal. In 
this division there are two or three seams of shale, and worm-tracks have been found 
in the quartzites. 

The highest division of the Quartzite consists of softer sandy strata, of little 
use for road-metal, and hence less favourably exposed. In this division however, 
a band of limestone have been discovered (Lapworth 1886, Strahan 1886, 
Lapworth, Watts and Harrison 1898). It is rich in the remains of Hyolithus, 
Orthotheca, Coleolides, Stenotheca rugosa, and Kutorgina cingulata. The genera and 
species found in these beds at Camp Hill Quarry compare closely with those found 
elsewhere in the 01 en ell us Series, and with those of the Etcheminian Series of 
New Brunswick. In spite of the absence of trilobites this limestone may be safely 
correlated with part of the 1 e n e 1 1 u s Series. The quartzites immediately associated 
with it yield worm-tracks and other markings like those found in the "Fucoid 
Beds" of North Scotland in which the 01 en ell us fauna has been found. On this 
horizon, oxide of manganese occurs and was at one time mined. 

The top beds of the Quartzite are interbedded with purple shales and are 
followed by a thick shale series named, after its occurrence at the village of that 
name, "The Stockingford Shales". These have been subdivided by Lapworth as 
follows : 

3. Grey or Merevale Shales. 
2. Black or Oldbury Shales. 
1. Purple or Purley Shales. 

The recent discovery of Olenellus in the Lower Purley Shales by the Geo- 
logical Survey places the line of division between Lower and Middle Cambrian 
above the base of these shales, in which Lingulella ferruginea and Acrothele granu- 
lata have also been found. V. C. Illing has found the species of Paradoxides, 
Anopolenus, Conocoryphe, Liostracus, Microdiscus, and Agnostus characteristic 
of the zones of Agnostus atavus, P. hicksi, and P. davidis in the lower part of 



Watts: Great Britain. — The Midlands, North of England. (III. 1.) 51 

t 

the Oldbury Shales; while, in the higher part of the same shales he has been able 
to recognise the characteristic fossils of the Maentwrog, Ffestiniog, and Dolgelly 
divisions of the Lingula Flags. The highest shales yield Dictyonema sociale, 
and therefore clearly belong to the Tremadoc. 

East of Nuneaton, Cambrian Rocks have not been found at the surface of 
the ground, but borings near Leicester have brought up cores of shales of Stocking- 
ford type yielding Upper Cambrian trilobites and associated with characteristic 
sills of intrusive rock like those of Nuneaton. It is interesting to find these rocks 
so near to the axis of Charnwood Forest in an unaltered and uncleaved condition. 
They not only prove the extension of Cambrian Rocks in this direction, but they 
also clinch the other arguments which have been put forward for the pre-Cambrian 
age of the Charnian Rocks. Another boring recently carried out at Calvert in Bucking- 
hamshire, has struck Cambrian Rocks beneath the Lower Lias and a small thickness 
of Trias. The rocks are shales of Stockingford type which have yielded to Arthur 
Morley Davie s perfectly preserved specimens of Clonograptus. 

At the Malvern Hills, the Cambrian succession combines the characters shown 
in Shropshire with those of the Nuneaton area (Groom, 1901). At several localities 
in these hills, and to the north, caught in faults and overfolds, there occurs a quartzite, 
"The Malvern Quartzite", which forms the lowest member of the Cambrian System. 
It contains fragments derived from both the plutonic and volcanic members of 
the Pre-Cambrian Rocks. It is succeeded by a mass of green glauconitic sandstone 
known as the Hollybush Sandstone, probably not less than 270—300 m. (900—1000 ft.) 
in thickness. The lower part is flaggy and shaly, with calcareous layers and a thin 
band of limestone ; the upper part is massive and contains Kutorgina phillipsi, and two 
or three species of Hyolithus. These rocks correspond with the Comley Sandstone 
of Shropshire and the Upper Quartzites of Nuneaton, and therefore they seem to 
represent the upper part of the Lower Cambrian System. 

This division is followed by a considerable thickness of shales, black in the 
lower part, the " White-leaved-Oak Shales", and grey in the upper part, the "Bron- 
sil Shales"). The black shales have yielded S pkaerophthalmus alatus, Peltura scara- 
baeoides, and Agnostus trisectus, while Polyphyma lapwortki, and Protospongia 
paradoxica, have been found in the lowermost beds. These shales therefore repre- 
sent at least the Dolgelly Stage of the Lingula Flags, but they probably range 
much lower, and the sequence may even include part of the Paradoxides beds. 
Groom parallels them with the Oldbury Shales of Nuneaton. The shales are not 
less than 150—180 m. (500 to 600 ft.) thick, and include a dark-grey shelly lime- 
stone probably discontinuous. 

The grey shales, bluish, grey, or yellow in tint, are characterised by Dic- 
tyonema sociale in the lower part. In the higher beds Dictyonema is again found, 
but it is associated with Niobe homfrayi, Platypeltis crofti, and an Agnostus allied 
to A. dux. These shales may be correlated with the Merevale Shales of Nuneaton, 
with the lower part of the Shineton Shales, and the Tremadoc of North Wales. 

Instrusive camptonites and diabases are frequently found in association 
with the Midland Cambrian strata, occurring as dykes or sills (Lapworth, Watts 
and Harrison 1898). They are found at Nuneaton both in the shales and the quartz- 
ites, forming a valuable source of road-metal. They also occur in Shropshire in the 
Shineton Shales and in the Longmyndian Rocks, at the Lickey Hills, and at 
Malvern, and they have even been found in Leicestershire and Buckinghamshire. 
Similar rocks are met with on in the Cambrian of the Highlands of Scotland. 

D. The North of England and Isle of Man. 

In the Lake District of Cumberland and Westmorland, fossil evidence proves 
that the upper parts of the "Skiddaw Slates" are of Arenig age. It is therefore highly 

4* 



52 (III. 1.) The British Isles. — III. Stratigraphy. — 2. Cambrian. 

probable that the bulk of these slates must belong to the Cambrian System. Slabs 
containing a Bryograptus allied to, or identical with, B. callavei have been found at 
Barf. In the Isle of Man the older Palaeozoic Rocks are made up of the Manx 
Slates and the Lonan Flags (Geol. Surv., Distr. Memoir). The order of 
succession of these two divisions is as yet unknown. No undoubted fossils have 
been found in them, but the slates present considerable resemblances to the Skiddaw 
Slates. In all probability part of the Manx Slates must also belong to the Cam- 
brian System. 

E. Scotland. 

Between the area occupied by the Lewisian Gneisses in the North West High- 
lands of Scotland and the huge tract of the "Eastern Gneisses", there runs a broad 
belt of sediments from Loch Eriboll to Loch Carron and the Island of Skye. The 
western part of this belt consists of Torridonian Rocks, the eastern of rocks, in part 
at least and possibly altogether, belonging to the Cambrian System. The succession 
given by the Geological Survey of Scotland (1907) is as follows: 

3. Durness Limestone. Dolomites and Limestones with certain fossiliferous zones. 

2. "Serpulite Grit" and "Fucoid Beds" yielding the Olenellus fauna. 

1. Quartzites with worm-casts in the upper portion and false-bedded grits below. 



LOCH GLCHOHU 



BEINH A/HO DA LOCH 



Fig. 16. Section across Loch Glendhu and the North-East Side of Beinn 

AirddaLoch. Scale about l : 40,000. 

A = Lewisian Gneiss; Ca = Basal Quartzite (Cambrian); Cb = Pipe-rock; Cc = Fucoid-beds; Cd = 

Serpulite-grit; Cel = Ghrudaidh group; M = Eastern Schists; F = Porphyrite Sill. T = Thrusts. 

T' = Moine-Thrust; t = Minor thrusts. 
Reproduced from the Memoirs of the Geological Survey of Great Britain. The Geological Structure 
of the North-Western, Highlands of Scotland. 1907, p. 500, with the permission of the Director and of 

H. M. Stationery Office. 

The total thickness of these Cambrian strata is about 630 m. (2,100 ft.) 
The lower Quartzite is based upon a thin brecciated conglomerate; this is 
followed by false-bedded flaggy grits and quartzites. The upper Quartzites are 
fine-grained and perforated by vertical worm-casts and burrows which become 
more numerous towards the top ("Pipe Rock"). It has been found possible to sub- 
divide this division into five sub-zones each distinguished by its own peculiar 
type of "pipes". 

The next division consists of two zones. The lower is made up of dolomitic 
shales and mudstones, traversed by numerous worm-casts, usually flattened, and 
resembling fucoidal impressions. The fossils found in this zone include (Peach 
1894) Hyolithus, Coleolides, Salterella, Paterina (Kutorgina) labradorica, Olenellus 
lapworthi, O. reticulatus, O. gigas, and Olenelloides armatus. These fossils, which 
exhibit a close parallelism with Eastern American forms, are sufficient to establish 
correlation with the beds of the Olenellus Stage found elsewhere. The upper zone 
consists of a massive band of quartzite and grit, passing upwards into carious 
dolomitic grit, crowded in patches with Salterella ("Serpulite Grit"), and yielding 
Olenellus Lapworthi, Orthoceras, and lingulids. 



Watts: Great Britain. 



Scotland. 



(III. 1.) 53 



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The British Isles. — III. Stratigraphy. — 2. Cambrian. 



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The Limestones have been 
divided into seven stages. 
They are mostly dark and 
light grey dolomites, some- 
times granular, sometimes 
massive, with some bands of 
true limestones, and occasional 
bands of chert nodules. Se- 
veral of the beds are marked 
by worm-casts, but in certain 
others, mainly in the higher 
divisions, well-preserved fossils 
have been found. These fossils 
include Archaeoscyphia, Cama- 
rella, Orthisina festinata, Eu- 
chasma, Maclurea, Ophileta, 
Murchisonia (Hormotoma and 
Ectomaria) Pleurotomaria, Pi- 
loceras, Endoceras, Orthoceras, 
and Trocholites. Trilobites are 
extremely scarce, only one 
species, Bathyurus nero, has 
been with certainty deter- 
mined, but it is possible that 
Soleno pleura, Conocoryphe, and 
Paradoxides may be present. 
From the palfflontological evi- 
dence it would appear that all 
the calcareous beds, "overlying 
the Salterella dolomites repre- 
sent the Middle and Upper 
Cambrian Formations. But 
owing to the American facies 
of the fauna, it is impossible 
to correlate these sub-divisions 
either with the Welsh or Scan- 
dinavian succession". 

Along the fault which 
forms the southern border of 
the Central Highlands of Scot- 
land from Stonehaven to Loch 
Lomond, patches of Palaeozoic 
rocks occasionally make their 
appearance, generally emerg- 
ing from beneath thrust planes. 
These include (1) Jaspers and 
Green Rocks and (2) the 
Margie Series of shales and 
limestones. In these rocks 
fossils, mainly hingeless bra- 
chiopods, have been found, 



Watts: Great Britain. — Summary, Bibliography. (III. 1.) 55 

which seem to indicate that the rocks are of Cambrian age. Dr. Flett has found 
pebbles of Cambrian limestone in one of the Old Red Sandstone conglomerates of 
Orkney. 

Summary and Correlations. 

The principal correlations are given in the annexed table (p. 53). There is evi- 
dently very considerable variation in faunal as well as lithological facies, the fossils of 
the Scottish area standing apart from those of Wales and England. The lithological 
characters of the strata and the overlap which occurs in Anglesey, indicate the 
presence of a shore-line in that direction, possibly a large island with smaller islands 
about Llanberis, the Longmynd, and elsewhere in the Midlands. ' The main land- 
mass, however, would appear to have lain towards the north-west, with the North- 
west Highlands of Scotland and Ireland on its margin. Eastward and to the south- 
east the sea deepened sharply and so far no evidence has been obtained in England 
of any eastern shore to the trough. The chief period of depression was in Upper 
Cambrian time and though this was but temporary in North and South Wales, 
it appears to have lasted till the end of the Period farther east. Volcanic action 
broke out on the flank of the Harlech anticline in later Cambrian time, the beginning 
of the long and important volcanic history of the succeeding Period. 



Bibliography of the Cambrian of Great Britain. 

1910. Andrew, A. R., Geol. Mag. dec. 5. vol 7, pp. 159-171 (Harlech). 

1888. Blake, J. F., Quart. Journ. Geol. Soc, vol. 44, pp. 534-547. 

1877. Callaway, C., Quart. Journ. Geol. Soc, vol. 33, pp. 652-672 (Shropshire). 

1910. Cobbold, E. S., Quart. Journ. Geol. Soc, vol. 66, pp. 19-51 (Shropshire). 

1911. — Quart. Journ. Geol. Soc, vol. 67, pp. 282-311 (Shropshire). 

1911. — Rep. Brit. Assoc, for 1910, pp. 113-122 (Shropshire). 

1898. Elles, Miss G. L., Quart. Journ. Geol. Soc, vol. 54, pp. 463-539 (Skiddaw 

Slates). 

1905. Fearnsides, W. G., Quart. Journ. Geol. Soc, vol. 61, pp. 608-640 (Arenig). 

1910. — Geol. Assoc, Jub. Vol., Geology in the Field, pp. 786-825 (N.Wales). 

1910. — Quart. Journ. Geol. Soc, vol. 66, pp. 142-188 (Tremadoc). 

1902. Groom, T. T., Quart. Journ. Geol. Soc vol. 58, pp. 89-149 (Malvern). 

1892. Hicks, H., Geol. Mag. dec. 3, vol. 9, pp. 21-24 (Olenellus Beds). 

1894. — Geol. Mag. dec. 4, vol. 1, pp. 368-371, 399-405, 441-448 (Cambrian Life Zones). 

1914. Illing, V. C, Rep. Brit. Assoc, for 1913, p. 498 (Nuneaton). 

1886. Lapworth, C, Geol. Mag. dec. 3, vol. 3, pp. 319-322 (Nuneaton). 

1897. — Trans. Edin. Geol. Soc, vol 7, pp. 231-232 (Hyolithus Limestone). 
1894. — and Watts, W. W., Proc Geol. Assoc, vol. 13, pp. 297-355 (Shropshire). 

1898. — and Watts, W. W., and Harrison, W. J., Proc. Geol. Assoc, vol.15, pp. 

313-416 (Midland England). 
1910. — and Watts, W. W., Geol. Assoc, Jub. Vol., Geology in the Field, 
pp. 739—769. (Shropshire). 

1885. Marr, J. E. and Roberts, T., Quart. Journ. Geol. Soc, vol. 41 pp. 476-491 

(Haverfordwest). 
1894. — Geol. Mag., dec. 4, vol.1, pp. 122-130 (Skiddaw Slates). 
1894. Peach, B. N., Quart. Journ. Geol. Soc, vol. 50, pp. 661-676 (Olenellus Beds, 

Scotland). 

1886. Strahan, A., Geol. Mag. dec. 3, vol. 3, pp. 540-566 (Nuneaton). 

1912. Thomas, H. H. and Jones, O. T., Quart. Journ. Geol. Soc, vol. 68, pp. 374-401 

(Pembrokeshire). 



56 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

Geological Survey of England and Wales. 
Sheet Memoirs, new ser. : 

229. (Carmarthen, A. Strahan and others, 1909), and 

230. (Ammanford, A. Strahan and others, 1907.) 
District Memoir: 

Isle of Man (G. W. Lampluch, 1903). 

Geological Survey of Scotland. 
The Geological Structure of the North West Highlands of Scotland (B. N. Peach, J. Horne 
and others, 1907). 

b. Ireland. 
By G.A. J.Cole. 

No good fossiliferous representatives of the Cambrian system have been found in 
Ireland; but a series of crushed and folded slates and quartzites in the east of 
Leinster has generally been referred to the Cambrian. These rocks are exposed 
from Bray in Co. Wicklow to near Wicklow town, and they also form the pro- 
montory of Howth on the north side of Dublin Bay. They reappear at Boney 
Point in Co. Wexford, and extend south-westward to the south coast of Ireland 
at Bannow Bay. The radiated or fan-like markings known respectively as Old- 
hamia radiata and antiqua characterise the pink and green slates, and are 
properly regarded as organic in origin, though referred variously to hydrozoa and 
to worms (J. B. Kinahan 1858). Undoubted casts of worm-burrows occur at Bray, 
including Histioderma, and Sollas (1895 and 1900) and Byan and Hallissy (1912) 
have described other organisms. G. W. Lamplugh (Geol. Surv. 1903, 1875, 1869) has 
suggested, from analogy with the Isle of Man, that the rocks of Bray and Howth 
are closely linked with those styled Ordovician nearer to the Leinster granite 
axis, and that the whole may be a descending series. J. F. Blake (1888) proposed 
to place them, however, in analogy with Anglesey, in his Pre-Cambrian Monian system. 

The quartzites produce striking features in the northern area near Bray, in 
contrast with the more easily weathered slates. Knob-like bosses of them form 
the crests of Howth and Bray Head, and a relic of an uptilted bed, dipping steeply 
seaward, stands out as the sharp summit of the Great Sugarloaf, 506 m. (1660 ft.) 
above the sea. The ravines of the Dargle near Enniskerry and of the Dartry in the 
Devil's Glen near Ashford have been excavated in the slates by streams falling 
rapidly from the granite chain. The quartzites form striking castellated features 
along the ridge of the Mountains of Forth, south-west of Wexford town. 

These problematic rocks seem to have been laid down in a basin which subsided 
slowly, allowing of a great accumulation of shore and estuarine deposits. 



Bibliography of the Cambrian of Ireland. 

1888. Blake, J. F., Quart. Journ. Geol. Soc. London, vol 44, pp. 534-536. (Howth 

Hill & Bray Head.) 
1857. Kinahan, J. R., Journ. Geol. Soc. Dublin, vol. 7, pp. 1884—187 (Bray Head). 
1860. — Journ. Geol. Soc. Dublin, vol. 8, pp. 68—73, 116—120 (Bray & Howth). 
1859. — Trans. Roy Irish Acad., vol. 23, pp. 547-562 (Oldhamia). 
1912. Ryan, W. J. and T. Hallissy, Proc. Roy. Irish Acad., vol. 29 B, pp. 246-251 

(Bray Head). 
1895. Sollas W. J., Sci.Proc. Roy. Dublin Soc, vol. 8, pp. 297-303 (Pucksia). 
1900. — Quart., Journ. Geol. Soc. London, vol. 56, pp. 273-286 (Worm track, 
Bray Head). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets: 

102-112. Parts of Counties Dublin and Meath( J. B. Jukes and others). 2 nd. Ed. 1875. 

112. Dublin (G. W. Lamplugh and others). 1903. 

121, 130. Parts of Counties Wicklow & Dublin (J.B. Jukes and others). 1869. 



Watts: Great Britain, incl. the Isle of Man. — Sedimentary and Volcanic Rocks. (III. 1.) 57 

3. Ordovician. 

a. Great Britain, including the Isle of Man. 

I. Sedimentary and Volcanic Rocks. 

By W.W. Watts. 

The Ordovician Rocks occupy a large area of ground in three separate districts 
in Great Britain: 1. The Southern Uplands of Scotland, 2. the Lake District of 
England, 3. Wales, both North and South, with the Border County of Shropshire. 
There are also a few smaller regions such as those in Yorkshire and Cornwall. In 
the large areas the strata generally strike from N. E. to S. W., but this strike swings 
round to E. and W. in South Wales. No Ordovician rocks have been found east 
of the longitude of Shropshire either at the surface or in depth. 

The rocks present two distinct facies. 1. A deepwater facies represented by 
shales and mudstones, bearing graptolites: 2. A shallow-water facies of sandstones, 
grits, and occasional limestones, usually bearing trilobites and brachiopods, but 
rarely graptolites. Between these two types correlation has been very difficult 
in the past, but the difficulties are now gradually being overcome, largely as the 
outcome of the masterly work of Charles Lapworth on the Moffat and Girvan 
facies of South Scotland. With either of these types volcanic rocks may be associ- 
ated, but there are a few areas and some parts of the succession in which important 
volcanic rocks are not known. Everywhere, however, minute volcanic dust, and 
the denudation of a freshly formed volcanic material, have provided much of the 
sediment of which the strata are made. 

Miss Elles has recently shown that there are two distinct trilobite faunas 
in the Ordovician Rocks. One, characterized by Asaphus, Calymene, and Trinucleus 
is more generally met with in Britain; the other marked by Cheirurus, Lichas, 
and Encrinurus, becomes established early in Scotland, but dominates the whole 
British area by Ashgillian time. 

The sub-division of the Ordovician Rocks now usually adopted, is as follows, 
the nomenclature being that advocated by J. E. Marr (1905. 1907): 

4. Ashgillian Series (after Ashgill in the Lake District). 

3. Caradocian Series (after Caradoc in Shropshire). 

2. Llandeilian Series (after Llandeilo in Carmarthenshire). 

1. Skiddavian Series (after the Skiddaw Slates in the Lake District). 

The Skiddavian Series has been also called the Arenig or Arenigian Series. 
Some workers prefer to place the top of the Skiddavian and the bottom of the 
Llandeilian in a Llanvirn Series. And the "Bala Series" includes at least the greater 
part of the Caradocian Series. The newer terms are, however, rather more satis- 
factorily defined and the use of them avoids certain difficulties which are the out- 
come, in part of our imperfect knowledge of the faunas of the rocks when the names 
were first given, and in part of the rocks themselves in the type localities when 
attempts were made to make the terms more precise by means of the definition 
of faunas discovered elsewhere. 

The most satisfactory subdivisions of the system as established on graptolite 
evidence, are the following: 

4. Ashgillian Series. 

c) Zone of small climacograptids. 

b) Zone of Dicellograptus anceps. 

a) Zone of Dicellograptus complanatus. 

3. Caradocian Series. 

c) Zone of Pleurograptus linearis. 

b) Zone of Dicranograptus clingani, 
a) Zone of Climacograptus wilsoni. 



58 (III. 1.) 



The British Isles. — III. Stratigraphy. — 3. Ordovician. 



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2. LIundeilian Series. 

c) Zone of Climacograptus peltifer. 

b) Zone of Nemagraptus gracilis. 

a) Zone of Didymograptus murchisoni, 
1. Skiddavian Series. 

c) Zone of Didymograptus bifidus. 

b) Zone of Didymograptus hirundo. 
a) Zone of Didymograptus extensus. 



A. Scotland. 

The discovery of the value of graptolites 
as zone fossils was made in the Southern 
Uplands of Scotland, in the Moffat district 
(Lapworth 1878), where the Middle and 
Upper Ordovician Rocks are represented by 
an attenuated succession of shales very highly 
disturbed. The succession was first worked 
out in the shale facies, and, when the se- 
quence had been independently made out in 
the shelly and trilobitic facies of Girvan it 
was found that the two facies could be 
closely correlated. The classification of 
Lapworth (1878, 1882, 1889) was later 
extended by the Geological Survey of 
Scotland (1899) and applied to the Southern 
Uplands as a whole. They found it con- 
venient to treat the area under the following 
heads: 

1. The Northern Belt, which extends S.W. 
from the Lammermuir Hills to Port 
Patrick. 

2. The Central Belt, from St. Abbs Head, 
through Moffat, to the Mull of Galloway. 

3. The Girvan Area, in Ayrshire and on its 
coast. 

The Skiddavian Series. The suc- 
cession in the Northern Belt and the Girvan 
area, the base of which is not seen, begins 
with a volcanic series of lavas and tuffs the 
"Ballantrae Rocks", from 150-460 m (500 to 
1500 ft.) thick. It is not impossible that 
part of this volcanic series may be older 
than Ordovician. This is followed by mud- 
stones with Tetragraptus, about 1.2 m. (4 ft.) 
thick, and that by radiolarian cherts 20 m. 
(70 ft.) in thickness. Similar cherts are as- 
sociated with mudstones and thin volcanic 
tuffs in the Central Belt. The lavas are dia- 
bases and spilites frequently exhibiting the 
well-known "pillow structure", the spaces 
between the spheroids being filled up with 
fine-grained shale and limestone. Sometimes 
chert fragments occur in the tuffs as though 



Watts: Great Britain. — Sedimentary and Volcanic Rocks. 



(III. 1.) 59 



the cherts had rapidly consoli- 
dated on the sea-floor. The fossils 
include Didymograptus extensus, 
Phyllograptus typus, Dichograp- 
tus, and Trigonograptus, a large 
series of hingeless brachiopods, 
and Caryocaris wrighti. 

The Llandeilian Series is 
represented by the Glenkiln Shale 
Series in the Central Belt, and 
by the Barr Series in Girvan. 
In the Central Belt the following 
divisions are present: 

4. Thin black shales : Dicrano- 

graptus zic-zac, Climacograp- 

tus peltifer; 0.6 m. (2 ft.). 
3. Orange-coloured mudstones, 

radiolarian cherts, and fine 

volcanic rocks; 1.2 m. (4 ft.). 
2. Black shales with cherty 

ribs : Nemagraptus gracilis, 

Didymograptus superstes; 2.4 

to 3.7 in. (8 to 12 ft.). 
1. RadiolSrian cherts, mud- 
stones, and volcanic tuffs. 

In the Northern Belt some of 
the shales pass into about 300 m. 
(1000 ft.) of grits and greywackes. 
In the Girvan area, the Nema- 
graptus beds are sometimes re- 
placed by the Stinchar Limestone 
Group, 20m. (60ft.) thick, and the 
Benan Conglomerate 1 50 m. ( 500 f t. ) 
thick comes in at the top of the 
series. Didymograptus murchisoni 
has not yet been found in Scot- 
land but in all probability the 
lower radiolarian cherts &c. 
(1) belong to that zone. There 
is a rich graptolite fauna in the 
black shales (2) in addition to 
the zone fossil, Nemagraptus gra- 
cilis, such as Thamnograptus, 
Dicellograptus, Leptograptus, Di- 
plograptus, and Climacograptus. 
Hingeless brachiopods are com- 
mon, with Hyalostelia. In the 
Girvan area graptolites are less 
common, but a Didymograptus 
superstes and Nemagraptus have 
been found. Corals, hinged bra- 
chiopods, gastropods, and fourteen genera of 
this horizon. 







trilobites have also been found at 



60 (III. 1.) The British Isles. — III. Stratigraphy. —3. Ordovician. 

If the zone of Dicellograptus complanatus and the "Barren Mudstones" of the 
Upper Hartfell be relegated to the Ashgillian, only the lower 12 m. (40 ft.) of the 
black, flaggy, graptolitic, Hartfell Shales is the equivalent of the Caradocian Series 
in the Central Belt. In this there are three zones: 

3. Zone of Pleurograptus linearis. 

2. Zone of Dicranograptus clingani. 

1. Zone of Climacograptus wilsoni. 

In the Northern Belt there are greywackes, calcareous conglomerates, and 
shales with Lower Hartfell graptolites, with local unconformities and volcanic 
rocks, the total thickness being over 300 m. (1000 ft.). In this area occur the 
lead-ores of the Leadhills, which are confined to the Caradocian and Ashgillian 
Bocks. In the Girvan area the Balclatchie mudstones, grits, and conglomerates, 
30 m. (100 ft.) thick, containing abundant trilobites and brachiopods, and 
Glossograptus hincksi, are followed by the Ardwell Group of flagstones and shales 
about 400 m. (1200 ft.) thick, yielding Dicranograptus ramosus. To these succeed 
the Whitehouse Group, with Pleurograptus linearis and trilobites,- about 100 m. 
(300 ft.) thick, the Barren Flagstones, 240 m. (800 ft.) thick, with Orthograptus 
truncatus, and the lower part of the Drummuck sandstones and mudstones. 

Marr (1904) has suggested that the "Starfish Bed" in the Drummuck 
green mudstones may be the equivalent of the Staurocephalus Limestone as it 
contains the zone fossil Staurocephalus globiceps. The succeeding mudstones are 
thus correlated with the Ashgill Shales. In' the Moffat region, the top of the Hartfell 
sequence consists of barren mudstones with a black bed at the base and another 
at the summit. The former yields Dicellograptus complanatus, and the latter D. an- 
ceps. In the Northern Belt, there are micaceous shales, conglomerates and lime- 
stones, with trilobites, brachiopods etc., 240 m. (800 ft.) thick. 

In the Southern Uplands the replacement of fine sediment by coarse grits, 
flags, and conglomerates, together with the greatly increased thickness of the divi- 
sions when traced in that direction, clearly indicate that the land of the period was 
situated to the north and west. The extreme thinness of the shales, combined 
with the presence of radiolarian cherts associated with the very finest sediment, all 
show that the sea of the period must have sloped very steeply downwards towards 
great depths along narrow and restricted belts. 

B. The English Lake District. 

In this area the Ordovician rocks display three lithological divisions: 

3. Coniston Limestone Series. 

2. Borrowdale Volcanic Series. 
1. Skiddaw Slates (in part). 

In certain parts of the succession the subdivisions are clearer, or have been 
more fully described, in the inlier of Ordovician rocks which occurs under (Marr, 
Nicholson 1891) Cross Fell, East of the Lake District proper; and as careful 
correlations have been made, these two areas will be, as far as possible, considered 
together. 

It has been already pointed out that part of the Skiddaw Slates includes 
the equivalent of the Tremadoc Bocks. Hence the Skiddavian Series comprises 
only the upper division of the Skiddaw Slates. The subdivisions given by (Marr 
1894, Elles 1898, 1904) Miss Elles are as follows: 

d) Ellergill Beds (probably on the horizon of D. bifidus). 

c) Upper Tetragraptus Beds. 

b) Dichograptus Beds. 

a) Lower Tetragraptus Beds. 



Watts: Great Britain. — Sedimentary and Volcanic Rocks. (III. 1 . ) 61 

The fauna includes many species of Dichograptus, Didymograptus (including 
D. extensus), Phyllograptus, and Tetragraptus in the lower part of the Skiddavian 
sequence; and Diplograptus, Climacograplus, and Glossograptus in the upper part. 
Didymograptus bifidus has been recorded from both parts. The Manx Slates of the 
Isle of Man are probably in part of Skiddavian age. 

The Llandeilian Series in the Cross Fell inlier begins with the "Millburn Beds" 
from which Didymograptus murchisoni and Glyptograptus dentatus are recorded. 
The Millburn Beds are succeeded by volcanic rocks which are correlated with the 
Borrowdale Volcanic Series of the Lake District. These volcanic rocks were 
formerly known as the "Green Slates and Porphyries". In this series it has not 
been found possible to establish divisions founded on organisms, but the following 
lithological groups have been distinguished (Harker [1902] and Marr [1900]): 

e) Shap Rhyolite and Yewdale Breccia Group. 

d) Shap Andesite Group. 

c) Scawfell Tuff and Breccia Band, with Kentmere-Coniston Slate-band. 

b) Eycott and Ullswater Basalt Group. 

a) Falcon Crag Andesite Group. 

The Falcon Crag andesites bear hypersthenc or augite: the Eycott Group 
contains no olivine but hypersthene and magnetite: the Scawfell Group has both 
basic and acid fragments and the rocks carry garnets; the Shap Andesites bear 
augite but no hypersthene: the highest beds are rhyolites and pass up into the 
volcanic rocks associated with the Coniston Limestone. Cutting the bedded vol- 
canic rocks numerous intrusive rocks occur which are described on pp. 74 — 75. 

The Coniston Limestone Series or Caradocian, has been divided by Marr 
(1892) into the following divisions: 

b) Sleddale Stage. 

5. Applethwaite Beds; 30m. (100ft.). 
4. Conglomerate; 3m. (10 ft.). 
3. Yarlside Rhyolite. 
2. Stile End Beds; 15 m. (50 ft.). 
a) Roman Fell Stage. 

1. Corona Beds; 30 m. (100 ft). 

The Corona Beds have only yielded indentifiable fossils in the Cross Fell 
inlier, the characteristic form being Trematis corona. Other fossils include Homa- 
lonotus rudis, Strophomena grandis, and Bellerophon (Protowarthia) bilobatus. 
The Stile End Beds consist of calcareous ashes with abundant, but badly preserved, 
fossils. The Applethwaite Series is made up of calcareous, very fossiliferous, shales 
with limestone bands. A white horny limestone with Orthocerata frequently occurs 
at the summit. 

The fossils of the Sleddale Stage include Beyrichia (Tetradella) complicata, 
Cheirurus bimucronatus, Harpes doranni, Illaenus bowmanni, Lichas laxatus, Remo- 
pleurides colbyi, and many species of Orthis, and Strophomena. In the north of the 
Lake District, on Caldbeck Fell, a group of shales, the "Drygill Shales", appears to 
represent the whole of the Caradocian Series. 

t 

Above the Coniston Limestone Series, there comes a thin limestone specially 
characterised by the presence of Staurocephalus globiceps, with other trilobites 
and cystideans. This is taken by Marr (1905, 1907) as the base of his Ashgillian 



62 (III. 1. 



The British Isles. — III. Stratigraphy. — 3. Ordovician. 



Series. It is followed by the Ashgill Shales, with trilobites and gastropods, and 
these by the Phyllopora Beds. Among the chief fossils confined to the Ashgillian 
Series, are the following: Encrinurus sexcostatus, Cheirurus oclolobatus, Cyphoniscus 
socialis, Remopleurides longicostatus, and Ampyx tumidus. Acaste brongniarti, and 
Phillipsinella parabola, are common in the Series, while Chasmops and Phacops 
proper are not present. 




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Watts: Great Britain. — Sedimentary and Volcanic Rocks. (III. 1.) 63 

In the Cross Fell inlier (Marr and Nicholson 1891) the Sleddale Stage is only 
represented by a shale series (the "Dufton Shales") which rests on fossiliferous 
Corona Beds. The shales appear to represent the whole of the Stage. They 
pass up into by the Keisley Limestone, the equivalent of the Staurocephalus 
Limestone, which is followed by Ashgill Shales. In the Cautley district Marr has 
recently described volcanic rocks in the Ashgillian, occurring above beds with Pha- 
cops robertsi which in the absence of a constant limestone band he takes for the 
base of the Series. In these and in the Staurocephalus Beds which follow Dicello- 
graptus anceps occurs. Inliers of Ordovician rocks crop out from beneath the 
Carboniferous of the Pennine Chain in the neighbourhood of Settle and Ingleton, 
and the "pencil slates" of Cronkley Scar in Teesdale are probably also of Ordo- 
vician age. 

From this account it will be gathered that the chief vulcanicity in the North 
of England dates to the Llandeilian Epoch, probably beginning not far from the 
time of deposition of the zone of Didymograptus murchisoni. There was, however, 
some volcanic activity both before and after this time as beds of lava and ash 
have been described in the Upper Skiddaw Slates, in the Coniston Limestone Series, 
and in the Ashgillian. 

C. Shropshire and the Borderland of Wales. 

In this region there are four distinct Ordovician areas, one on the east side 
of the Longmynd, the Caradoc area, one on the west, the Shelve area, one at the 
Breidden Hills, and one about Welshpool. Three of these areas display only the 
two higher Series, but the Shelve area gives a full succession from the Skiddavian 
to the Caradocian, and probably the Ashgillian. The succession of the subdivisions 
in the Shelve area, as given by Lapworth (1894, 1910), is the following, but 
he has not correlated any part of the succession with the Ashgillian Series: 

4. Ashgillian Series. (Upper Chirbury Series). 

? Whittery Shales. 
3. Caradocian Series. (Lower Chirbury Series). 

e) Whittery Ashes. 

d) Hagley Shales. 

c) Hagley Ashes. 

b) Aldress Shales. 

a) Spy Wood Grit. 

2. Llandeilian Series. (Middleton Series). 

d) Black Flags with Nemagraptus gracilis. 

c) Meadowtown Limestone. 

b) Betton Shales, with Didymograptus murchisoni. 

a) Weston Flags and Shales. 
1. Skiddavian Series. (Shelve Series). 

e) Stapeley Ashes. 

d) Hope Shales. 

c) Shelve Church Beds, with Dichograptidae. 

b) Mytton Flags. 

a) Stiper Stones Quartzite. 

The basal Quartzite appears to succeed the Tremadoc Shales conformably. 
It is at times conglomeratic, but for the most part is compact, with occasional shale 
bands. Only obscure traces referred to Lingula have been found in it. Following 
this is a thick series of shales and flags, made of ashy material, yielding few fossils 
among which Ogygia selwyni and Obolella (Monobolina) plumbea are conspicuous. 
Lapworth has found Didymograptus extensus and D. hirundo in these beds. 
The rocks have long been famous for the supplies of lead, zinc, and barytes 
that they yield, some mines in the district having been worked for lead by the Ro- 



64 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

mans. The highest beds of this Stage at Shelve Church are pale flags yielding abun- 
dant examples of Dendrograptus diffusus, D. flexuosus, and other Cladophora, with 
Euomphalus corndensis. The Hope Shales contain few fossils, chiefly graptolites, 
among which Didymograptus bifidus is important. In the higher beds there are 
a few intercalations of ash. But a great volcanic outburst put an end to the shale 
period, giving rise to thick beds of andesitic ash, accompanied by the outpouring of 
lava of intermediate composition. 

The Llandeilian division begins with shales and grits in which Ogygia cornd- 
ensis occurs. The shales which follow have yielded Didymograptus murchisoni 
abundantly, accompanied by Orthis (Dalmanella) testudinaria. They are followed 
by calcareous flags and limestone which, at Middleton and Meadowtown, are rich 
in fossils, especially Ogygia buchi, Asaphus tyrannus, and Trinucleus lloydi. The 
latest member of the Llandeilian is the series of black flags in which, on certain hori- 
zons, Nemagraptus gracilis and Leptograptus flaccidus occur abundantly. In the 
Llandeilian Epoch there was little vulcanicity in this area, but there are thin beds 
of ash among the sediments. 

The Caradocian Series begins with a bed of calcareous grit containing grapto- 
lites, trilobites, and brachiopods, together with abundant examples of Beyrichia 
( Tetradella) complicata. It is followed by a barren group of shales and mudstones 
containing a few diplograptidae, and in one thin band very rich in Dictyonema. 
The succession is closed by two andesitic ashes (sometimes associated with lavas), 
and two shale series with only rare and unimportant fossils. It is not certain where 
the base of the Ashgillian Series should be drawn in this region, but if the corre- 
lations to be given in the Caradoc and Welshpool areas are correct, it should come 
either at the base or at the top of the Whittery Ash. The Ordovician rocks 
are unconformably covered by the lowest beds of the Gothlandian, so that the top 
of the sequence is not known. 

While the Shelve succession is complete, so far as it goes, the lower horizons 
are not known on the eastern side of the Longmynd. In the Caradoc area, the base 
of the Caradocian Series rests unconformably on Cambrian or older rocks. The 
divisions of the rocks that are present, however, compare so closely with those 
just described, that there seems no doubt as to this remarkable overlap. A com- 
parative table is annexed: 

Shelve District. Caradoc District. 

Ashgillian Series. 

Whittery Shales. Trinucleus Shales. 

Caradocian Series. 

Whittery Ash. Acton Scott Beds. 

Hagley Shales Cheney Longville Flags. 

Hagley Ash. Soudley Sandstone. 

Aldress Shales. Harnage Shales. 

Spy Wood Grit. Hoar Edge Grit. 

In this district the rocks are rich in brachiopods and trilobites. Graptolites 
are scarce except in the Harnage Shales where they afford a close comparison with 
those of the Aldress Shales. Bastard limestones occur in the Hoar Edge division, 
and at the base of the Cheney Longville Flags there is another limestone called 
from the abundance of Orthis alternata in it, the "Alternata Limestone". The Soudley 
Sandstone is much used for building and was clearly the division that Murchison 
had in mind when he named the whole group the Caradoc Sandstones. The Acton 
Scott beds are calcareous and yield many species of corals. The Trinucleus Shales 
contain Ortkograptus truncatus and evidently compare with those to be presently 
mentioned which have been placed by Wade in the Ashgillian Series. 



Watts: Great Britain. — Sedimentary and Volcanic Rocks. — Shropshire. (III. 1.) 65 

Part of the Shelve sequence reappears on the west of the Long Mountain 
syncline in the Breidden Hills. Here a, series of barren shales comparable with 
the Aldress Shales underlies an ash which may be correlated with the Hagley Ash. 
Fossils occur in the ash and the associated beds, including Climacograptus scharen- 
bergi, Cryptograptus tricornis, and Beyrichia ( Tetradella) complicata, which establish 
the position in the Caradocian Series. According to Wade (1911), the Ashgill 
Shales make their appearance near Buttington in the south of the Breidden area. 

In the Welshpool area Wade (1911) has made out the following divisions: 

3. Ashgillian Series. 

Gwern-y-Brain Stage. 
2. Black Shales. 

1. Limestone. 

2. Caradocian Series. 

b) Gaer Fawr Stage. 

2. Limestones and ashy grits. 
1. Grits and flags. 

a) Pwll-y-Glo Stage. 

1. Llandeilian Series. (?) 

Shales of Trilobite Dingle. 

The lowest division consists of purple shales full of Trinucleus concentricus, 
with Asaphus powysi, associated with Climacograptus scharenbergi, Amplexograptus 
perexcavatus, and Mesograptus foliaceus. This stage seems to find its nearest parallel 
with the Nemagraptus flags in the Shelve District. 

Shales and mudstones follow containing some graptolites, Asaphus powysi, 
varieties of Trinucleus concentricus, and T. fimbriatus, with Orthides and lamelli- 
branchs. The Gaer Fawr Stage presents considerable resemblance to the Caradoc Rocks 
of the type area. They are over 300 m. (1000 ft.) thick and have yielded a rich harvest 
of fossils also closely related to those found in corresponding rocks in the Caradoc 
area. Among the more important are the following: Acaste alifrons, A. apiculatus, 
Trinucleus elongatus, Bellerophon ( Protowarthia) bilobatus, lamellibranchs, and 
species of Orthis, Plectambonites, Rafinesquina, Strophomena, and Triplecia. 

Wade refers the highest Ordovician Rocks in the area to the Ashgillian 
Series and correlates them with the "Trinucleus Shales" of the Caradoc district. 
There is a thin and crystalline, but unfossiliferous, limestone at the base, followed 
by about 15m. (50 ft.) of shales. The limestone may be compared with the Stauroce- 
phalus Limestone, and the shales with the Ashgill Shales. Among the fossils found 
in the shales are the following: Mesograptus modestus cf. var. parvulus, Orthograptus 
truncatus cf. var. socialis, many Entomostraca, Orthis kirnantensis, O. sagittifera, 
Siphonotreta micula, and Bollia lata. As has been pointed out, if these rocks are 
correctly referred to the Ashgillian Series, they carry with them- the "Trinucleus 
Shales" of the Caradoc district. 

No Ordovician rocks have hitherto been found in association with the Cam- 
brian or pre-Cambrian patches of the Midlands east of Shropshire. The pebbles 
in the Bunter Conglomerate, however, are sometimes fossiliferous and among the 
fossils are brachiopods and trilobites characteristic of the Gres Armoricain and the 
Gres de May, and contained in quartzites indistinguishable from those in France 
on the horizons mentioned. While it is not impossible that these pebbles may 
have drifted from the south, it is at least possible that they may have been derived 
from concealed Ordovician rocks in the Midlands themselves. 

Handbuch der regionalen Geologie. III. 1. 5 



66 (HI. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

D. North Wales. 

The Ordovician rocks of North Wales are characterised by the presence of 
vast quantities of volcanic and intrusive material which occur in thick sheets that, 
by reason of their resistance to denudation, give rise to an impressive mountain 
group, many members of which exceed 1000 metres (3,300 ft.) in height. The 
principal mountain lines are 1, the range running from Penmaenmawr to Yr Eifl 
in the Lleyn Peninsula, 2, the Carnedds, Glyders, Snowdon, and Moel Hebog 
to Llwyd Mawr, 3, the group of the Manods and Moelwyns, 4, the chain of the 
Arenigs, Arans, and Cader Idris, and 5, the Berwyn Hills. 

In many cases the Ordovician rocks are separated from the underlying Cam- 
brian by thrust planes, but where a natural junction exists there is generally a marked 
unconformity, concealing the highest part of the Cambrian sequence. In no single 
section are all the members of the sequence typically represented, so it is necessary 
to take several localities in order to get a view of all the rocks. 

W. G. Fearnsides (1905) has worked out the succession at Arenig in 
considerable detail, and this may be taken as typical of the Skiddavian Series. 
It is as follows: 

2. Llandeilian Series. 

f) Rhyolitic ashes. 

e) Massive ashes. 

d) Acid andesitic ashes. 

c) Daer Fawr Shales; (equivalent to the zone of Didymograptus murchi- 
sonij. 

b) Platy ashes. 

a) Great agglomerate. 
1. Skiddavian Series. 

f) Shales; zone of Didymograptus bifidus. 

e) Filltirgerrig or h i r u n d o beds. zone of D. hirundo. 

d) Erwent or Ogygia Limestone. 

c) Henllan or Calymene Ashes. 

b) Llyfnant or extensus flags. zone of D. extensus. 
a) Basal Grit. 

Unconformity. 

This succession brings out a very remarkable fact. The rocks which have 
come to be called Arenig, forming the lower part of the Ordovician System, are 
not those to which Sedgwick originally applied that term. He used it to signify 
the main volcanic group of the mountain, and this is now shown to occur in what 
has come to be called Llandeilian. It is for this reason mainly that the term Skid- 
davian is preferred to the older word. 

The basal grit is in places conglomeratic, and in places a quartzite. It is 
very variable in thickness and does not seem to occupy invariably the same position 
in the sequence. Sometimes it is torn into phacoids by earth-movement as seen to 
the north near Criccieth. The extensus flags yield Loganograptus logani and a 
Tetragraptus as well as the zone fossil. They are followed by beds containing ashy 
matter which increases in quantity when traced southwards. The Calymene 
of the next division is related to or identical with C. parvifrons, and it is associated 
with a few large gastropods. The most abundant trilobite in the Ogygia Lime- 
stone is O. selwyni, often of large size; Orthis carausii (O. proava) is characteristic 
of the lower, and Obolella (Monobolina) plumbea of the higher part of this stage. The 
hirundo beds are slightly ashy and contain Didymograptus patulus, Tetragraptus 
serra, with Azygograptus suecicus and Aeglina. This fauna dies out with the change 
in lithology and is replaced by one in which Didymograptus bifidus, Cryptograptus 
tricornis, and an Ogygia, like O. peltata, are important: in places the rocks 
contain pyroclastic felspars. 



Watts: Great Britain. — Sedimentary and Volcanic Rocks. — North Wales. (III. 1.) 67 

The early volcanic outbursts of the Llandeilian Epoch gave rise to platy 
ashes of intermediate composition derived from a hypersthene andesite magma. 
In these occurs a coarse agglomerate with fragments of large size. The mudstones 
that follow are very inconstant, but yield fossils such as Mesograptus foliaceus, 
Diplograptus angustifolius, and Dicellograptus mojjatensis, which suggest the higher 
part of the zone of Didymograptus murchisoni, but the zone fossil has not hitherto 
been found. The succeeding ashy beds determine the higher summits and precipices 
of the mountain: some thin lavas and agglomerates occur in them. The Massive 
Ashes are intermediate in composition and contain botryoidal pyrolusite which 
is mined. The volcanic episode closes with a series of rhyolitic ashes containing 
about 73 per cent of silica. 

The volcanic rocks terminate abruptly against a thin, richly fossiliferous, 
brachiopod, monticuliporoid, and cystoid, limestone, called the Derfel Limestone. 
The fossils include Trinucleus concentricus, Lichas laxatus, Orthis actoniae, 0. (Dal- 
manella) testudinaria, and Plectambonites sericea. The fauna is similar in aspect to that 
of the middle part of the Caradoc rocks in Shropshire. The junction with the beds 
below seems to be a natural one without fault, but it has not yet been found possible 
to assign the limestone to its exact position in the Ordovician sequence. The section 
is closed by a vast thickness of black shales or slates in which no fossils have been 
found in situ, though a species of Dicranograptus has been collected from drift 
boulders of a precisely similar rock in the black shale area. 

The intrusive rocks of this area, as of the Shropshire district and so many 
other localities in North Wales, comprise hypersthene andesites and andesitic 
dolerites. Where it is possible to ascertain the age of these intrusions they seem 
to be not later than the Upper Gothlandian. 

It is unfortunate that the above description cannot be completed by a satis- 
factory account of the rocks in the Bala district; but the strata here are very highly 
disturbed, and little recent work has been published upon them. According to Ruddy 
(1897), the section begins with ashes and fossiliferous shales, followed by the "Bala 
Limestone" containing Treplecia spiriferoides, Orthis (Herbertella) vespertilio, 0. 
( Platystrophia) biforata, and 0. actoniae, with Trinucleus concentricus, and Tenta- 
culites anglicus. These strata are followed by a considerable thiokness of barren 
shales capped by the "Hirnant Beds", including a limestone, which yield Orthis 
hirnantensis, 0. sagittifera, Lingula ovata, and Homalonotus bisulcatus. The Geo- 
logical Survey placed the limestone exposed at Rhiwlas, north-east of Bala, on the 
same horizon as the Bala Limestone, but this correlation has not met with assent. 
Marr (1907) classifies these upper beds with his Ashgillian Series, thus: 

Ashgillian Series. 

c) Hirnant Limestone, 
b) Shales. 

a) Rhiwlas Limestone. 

The Ordovician rocks dip under the syncline east of Bala Lake and reappear 
to form the Berwyn Hills, where their structure is that of an irregular and much 
broken dome. Towards the centre there are limestones and ashes with shales all 
usually correlated with the Llandeilian Series. The outer rocks have been classed 
by P. Lake and T. T. Groom (1908) as follows: 

2. Ashgillian Series. 

b) Glyn Grit, 
a) Dolhir Beds. 



68 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

1. Caradocian Series. 

e) Graptolitic Slates. 

(Gap) 
d) Bryn Beds, 
c) Craig-y-Pandy Ash. 
b) Teirw Beds, 
a) Cwm Clwyd Ash. 

The Caradocian Rocks consist mostly of sandstone and grit. In both the 
Dolhir and the Glyn beds, there are layers of nodules passing up into beds of lime- 
stone, in each case followed by shales. Trilobites, brachiopods, and lamellibranchs 
are abundant in the Ashgillian Series, but graptolites have not yet been found 
in it. The lowest beds of the Gothlandian System follow with apparent conformity. 

Ordovician Rocks similar to those described in detail extend to the south 
and west as far as Cader Idris and Towyn, and to the north and west as far as the 
Moelwyns and Snowdon, whence they pass south-west to the Lleyn peninsula and 
northeast to Conway. Near Blaenau Festiniog and the Manods and Moelwyns 
the rocks about the middle of the system are of very great importance for the 
valuable slates that they yield. In the Moelwyns also there is a Skiddavian volcanic 
series intercalated among beds with extensiform graptolites. 

In the Snowdon area it was supposed by Ramsay (1866, 1881) and the Geolo- 
gical Survey that the ashes of Arenig (now known to be of Llandeilo age) had thinned 
out, and that the Lower and Middle Ordovician divisions were reduced to a thin 
series of slates and grits in which no fossil horizons were known. On the other hand 
it was thought that the Bala Beds (Caradocian and Ashgillian) had thickened out 
enormously and included an immense series of tuffs and lavas. The basis for correl- 
ation in the Snowdon syncline was found in the fossiliferous calcareous ash at the 
summit of the Mountain, which was considered from its fossils to be the equivalent 
of the Bala Limestone. 

According to Ramsay the succession on Snowdon itself and the immediately 
adjoining mountains is the following: 

5. Columnar felspathic lava. 

[4. Andesitic lava]. 
3. Felspathic, sandy, and calcareous ashes, (with fossils like those of the Bala 
Limestone). 

2. Three beds of felspathic porphyry, which southward converge into one. 
1. Slates and fossiliferous grits. 

The andesitic lava (4) was discovered by Sir A. Geikie in 1891. When the 
slates and fossiliferous grits (1) are traced to the northward, there come in below 
them three older volcanic groups as indicated in the Geological Survey map and 
described by Harker (1889), who also points out that the main Snowdon lavas 
are thinning out rapidly in the same direction. He traces the geographical distri- 
bution of each of the five sets of Snowdonian lavas and shows that the eruptions 
shifted on the whole southwards, the final activity being probably centred some- 
where near to Mynydd Mawr. He names the lavas as follows: 

e) The Upper Snowdon lavas, (corresponding with 5. above), 
d) The main Snowdon lavas, (corresponding with 2. above), 
c) The lavas of Glyder Fach, Capel Curig, and Conway Mountain, 
b) The lavas of Pen-yr-Oleu-Wen and Carnedd Llewellyn, 
a) The lavas of Dwygyfylchi and Y Drosgl. 

The finding of Didymograptus geminus or murchisoni by Fearnsides (1903) 
as a nearly continuous zone from Criccieth northward to a point close under 
the western crags Snowdon itself, where it underlies the main Snowdoman volcanic 
group throws some doubt on the view of Ramsay as to the age of these main 



Watts: Great Britain. — Sedimentary and Volcanic Rocks. — Central Wales. (111. 1.) 69 

ashes, and makes it practically certain that the divisions a), b), and c) above, must 
come below the Caradocian Series. This view is confirmed by the work of Miss 
Elles (1909) in the Conway district, where she has found the following succession: 

3. Ashgillian Series. 

b) Deganwy Mudstones. 

a) Bodeidda Mudstones. 
2. Caradocian Series. 

Upper Cadnant or Dicranograptus Shales. 

b) Zone of D. clingani. 

a) Zone of Climacograptus ivilsoni. 
1. Llandeilian Series. 

Lower Cadnant or Dicranograptus Shales. 

b) Zone of D. brevicaulis and Mesograptus multidens. 
a) Zone of Climacograptus peltifer. 

Conway Volcanic series. 

The Conway Volcanic series would seem to be the continuation of the Main 
Snowdon lava series, (d) of the table given above, and if so, it hardly seems that 
any portion of the Snowdon volcanic rocks will come into the Caradocian Series. 
It is noteworthy that Fearnsides (1910) prefers to treat the Snowdon group 
by itself, and though he has not published his work in the Criccieth area, he remarks 
that sooty black shales like those of Conway "have recently been recognised as 
overlying the highest Snowdonian lavas in the Dwybach river west of Criccieth. 
They also appear in the quarries of black slate close to Dodwyddellan, and may be 
represented by the sooty barren shales of the Bala district." 

It therefore appears certain that if the structure of the complicated area 
of North Wales, as expressed many years ago upon the Geological Survey Map, 
is to be trusted, and if the conclusions founded upon it and given above are sound, 
considerable revision will have to be made in current ideas as to the position of 
the Snowdon Volcanic Group. 

The Cadnant Shales (Elles 1909) are only divisible into the Llandeilian and 
Caradocian Series on palseontological grounds, the lithology not affording any 
assistance. 

The Bodeidda Mudstones contain some fossiliferous bands, in which occur 
Trinucleus seticornis, var. bucklandi, var. portlocki, and var. arcuatus, Acaste brong- 
niarti ( ?), and Caiymene blumenbachi. The Deganwy or Phacops Mudstones yield 
Daimannites mucronatus, Orthograptus truncatus var. abbreviates, Orthoceras vagans, 
Chonetes laevigata, and Ctenodonta varicosa. 

Lower Skiddavian Rocks (Fearnsides 1910) belonging to the graptolitic 
facies, are found near Aberdaron, in the Lleyn Peninsula, near Carnarvon, and on 
the Menai Straits. Upper Skiddavian Rocks, with deposits of ironstone and man- 
ganese, are also found in the Lleyn, while beds with Didymograptus murchisoni 
are found near Carnarvon and on the Menai Straits. They are replaced by the 
"Neseuretus Beds" of brachiopod type, resting unconformably on the pre-Cam- 
brian Rocks in central Anglesey. At Llangwyllog, in Anglesey, the D. murchisoni 
beds occur, followed by the zone of Nemagraptus gracilis, but farther to the north- 
west, the latter overlaps on to older rocks and passes into conglomerate and pebbly 
grit. The Snowdon volcanic rocks occur in the Lleyn about Pwllheli, and Cara- 
docian shelly rocks exist in Anglesey. 

E. Central Wales and its Borders. 

The Ordovician Rocks in this tract serve to link up the facies of South Wales 
with that of North Wales on the one hand and that of Shropshire on the other. 
Skiddavian (Fearnsides 1910) rocks are met with near Builth and at Llanwrtyd 



70 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

and Llangadock. The age of the lowest rocks is unknown, but they are succeeded 
by dark graptolitic shales with Placoparia. Above these comes an andesitic series 
which would seem to occur on the same horizon as in Shropshire. The Llandeilian 
rocks are shallow-water calcareous flags with trilobites, followed by graptolitic 
shales at Pencraig. Any higher rocks which may be present are concealed by the 
Gothlandian unconformity. 

H. Lapworth (1900) records blue-black shales underlying the Valentian 
rocks of the Rhayader area; and 0. T. Jones (1909) has recognised about 
1040 m. (3400 ft.) of strata underlying the Gothlandian Rocks as probably belonging 
to the Ashgillian Series. The lowest flags and thin shales yield Dicellograptus anceps, 
and Orthograptus truncatus with other characteristic fossils, but the overlying mud- 
stones, grits, and conglomerates have so far proved unfossiliferous. 

F. South Wales. 

Ordovician Rocks occur along three main belts in South Wales: 1, north 
of the anticlinal axis of St. David's from Whitesand Bay and Ramsay Island to 
Cardigan and beyond; 2, from near St. Bride's Bay to New Quay Road south 
of that anticline; 3, from Haverfordwest through Carmarthen and Llandeilo to 
Llandovery. The chief characteristic in most of the districts is the presence of an 
important series of shales, the Dicranograptus Shales, the lower part of which 
seems to belong to the Llandeilian, and the upper part to the Caradocian, and it 
is scarcely possible to draw any line between the two series either on palseonto- 
logical or lithological evidence: consequently the lines drawn below must be only 
accepted as provisional. On the other hand, the South Wales (Hopkinson and 
Lapworth 1875; Marr and Rorerts 1885; Reed 1895; Crosfield and Skeat 
1896; Geological Survey 1907, 1909) rocks will probably in the end throw much 
new light on the Ashgillian Series. 

4. Ashgillian Series. 

c) Slade Beds. 

b) Red Hill Beds. 

a) Shoalshook Limestone. 
3. Caradocian Series. 

b) Robeston Wathen Limestone. 

' a) Mydrim Shales; (Upper Dicranograptus Shales). 
. 2. Llandeilian Series. 

e) Mydrim Limestone. 

d) Hendre Shales; (Lower Dicranograptus Shales). 

c) Llandeilo Limestones and Flags, 
b) Asaphus Ash. 

a) Didymograptus murchisoni Beds. 
1. Skiddavian Series. 

b) Didymograptus bifidus Beds, 
a) Tetragraptus Beds. 

2. Zone of D. hirundo. 
1. Zone of D. extensus. 

The lowest of the three Skiddavian divisions is conformable with the Peltura 
punctata beds previously described, and contains Ogygia selwyni, Dendrograptus, 
Callograptus, and Dictyonema, in addition to the forms mentioned above. The middle 
division yields the same genera, with Aeglina grandis, Ogygia peltata, Trinucleus 
gibbsi, and Ampyx salteri. The bifidus zone contains Barrandea homjrayi, Illaenus 
hughesi, Placoparia cambrensis, with Nemagraptus, Climacograptus, and Diplograptus. 
Some andesitic volcanic rocks occur, either in the Skiddavian Series or below it, 
near to Llangynog. 



Watts: Great Britain. — Sedimentary Rocks.' — South Wales. (III. 1.) 71 

H. H. Thomas (1911) has brought forward evidence which goes to prove 
that the great volcanic series which occurs on Skomer Island and the neighbouring 
mainland, belongs to the zone of D. extensus. At its maximum development this series 
is not less than 900 m. (2900 ft.) thick and consists for the most part of thin subaerial 
lava flows, with a few intrusive rocks, mostly basic, and a persistent band of sedi- 
ments towards the middle of the series. The igneous rocks range from soda-rhyolites 
to olivine dolerites. The soda-rhyolites, soda-trachytes, skomerites, and marloesites, 
present affinities with the alkaline rocks of Pantelleria. The mugearites, basalts, 
and dolerites, belong to the sub-alkaline class. The order of extrusion appears to 
be a succession from acid to basic and back again from basic to acid in rhythmic 
sequence. The rocks present affinities with those associated with the lowest 
Ordovician of Southern Scotland, and with those in Cornwall. 

It is in association with the zone of Didymograptus murchisoni that the 
volcanic group occurs in the neighbourhood of St. David's and about Fishguard, 
and a poorer representative of it is found near Carmarthen in the Asaphus Ash, 
and other beds on about the same horizon. The Llandeilo Limestone is a series 
of calcareous flags rather widely distributed on this horizon. It yields the well- 
known fossils Asaphus tyrannus, Calymene cambrensis, Trinucleus concentricus var. 
javus, with many species of Orthis, Rajinesquina, and Plectambonites. In the Fish- 
guard region, the Llandeilian succession is the following: ashes and tuffs associated 
with D. murchisoni, slates and flags, felsitic tuffs, beds with Siphonotreta micula, 
and graptolitic shales in ascending order. 

The Dicranograptus Shales which in the southern outcrop follow the 
Llandeilo Limestone, have been separated into the Hendre Shales and the Mydrim 
Shales, generally separated by the Mydrim Limestone. The Hendre Shales contain 
Dicellograptus sextans, Climacograptus scharenbergi, and Cyrtograptus tricornis. The 
Mydrim Limestone yields Nemagraptus gracilis, Didymograptus superstes, and 
Leptograptus validus. It seems to represent the zone of N. gracilis. 

The Mydrim Shales contain in their lower part, a mixture of Hartfell and Glen- 
kiln graptolites, but towards their summit yield forms characteristic of the zone 
of Dicranograptus clingani. In the upper part of the Shales Orthograptus truncatus 
and Climacograptus minimus have been found. The Robeston Wathen Limestone 
contains abundance of Halysites catenularia, but trilobites are few and fragmentary 
lllaenus Bowmanni has, however, been found, with Orthis actonias. This limestone 
has generally been paralleled with the Bala Limestone. 

The Shoalshook Limestone is coarser and more arenaceous than that of Ro- 
beston Wathen, and yields Staurocephalus globiceps, Calymene blumenbachi, En- 
crinurus sexcostatus, Cybele verrucosa, Cheirurus bimucronatus, Trinucleus seticornis 
var. bucklandi, Ampyx tumidus, Homalonotus rudis and Orthis actoniae. In fauna 
and character it therefore approaches the Staurocephalus Limestone in the Ash- 
gillian Series of the north of England. The Redhill Stage consists of barren olive-green 
mudstones with rare fossils occurring in isolated patches. The fossils found include 
Trinucleus concentricus, lllaenus bowmanni, Homalonotus bisulcatus, Plectambonites 
sericea, and Orthis ( Dalmanella) elegantula. The Slade Beds, the highest of the 
sequence, are similar to the last, but are varied by thin limestones. In these beds 
are found lllaenus murchisoni, Glauconome disticha, Orthis (Dalmanella) testudinaria, 
Leplaena rhomboidalis, and Phyllopora hisingeri. The two last Stages correspond 
to the Ashgill Shales. 



72 (III. 1.) 



The British Isles. — III. Stratigraphy. — 3. Ordovician. 



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(III. 1.) 73 



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74 (III. I) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

G. Cornwall. 

The so-called "killas" or clay-slates of south Cornwall have been variously 
referred to the Devonian System and to the Lower Palaeozoic Rocks ( ? "Ordo- 
vician" of the Geological Survey 1907, 1912; Ussher 1910). In the absence of 
fossils from all but a part of the rocks there found, it is impossible to be certain 
as to the age of the group as a whole, and the tectonic structure is so complicated 
that the succession of the individual members of the series has not yet been made 
out. Along tbe southern border of the clay-slates, a great series of thrusts has 
brought up "augen" of fossiliferous rocks, some of which are Gothlandian and others 
of Ordovician age. To the latter are referred the "Veryan Series" of limestones 
and radiolarian cherts, and also the "Gorran Quartzite". From the Quartzite 
the following fossils have been obtained, among others not admitting of precise 
identification: Cheirurus sedgwicki, Calymene tristani, C. cambrensis, Phacops 
mimus, P. incertus ( ?), and Asaphus powysi ( ?). These fossils seem to indicate 
a horizon about the middle of the Ordovician, a determination which finds some 
confirmation in the occurrence of radiolarian cherts and pillow lavas in the beds 
below. The beds "evidently correspond either with the Angus [ ? Angers] Slates 
or the Gres de May of Brittany and Normandy" (Survey 1907). It is interesting to 
note that fossiliferous quartzite pebbles derived from the Gres de May and the Gres 
Armoricain occur in the Budleigh Salterton conglomerate of the Devonshire Trias. 

Summary and Correlations. 

The Ordovician Rocks were deposited on narrow continental shelves, the 
flanks of a group of partly or wholly submerged volcanic islands, and on the floor 
of steep-sided troughs. As is to be expected in a volcanic area changes in depth 
occurred with remarkable suddenness, and deposition was in certain places and 
at particular times remarkably slow. A great continental area seems to have occupied 
the north Atlantic, along the southern shore of which migration between America 
and Europe could take place. At least one important island was maintained through 
out part of the period in Anglesey and to the west of it, and probably another 
where the Longmynd now is. It is not improbable that east of Shropshire much of 
England was land so that the Ordovician trough was a narrow syncline. 

Volcanoes were in action in south-east Carnarvonshire during the early part 
of the Skiddavian Epoch, but the great outburst, of which evidence remains in almost 
every area where Ordovician Rocks are exposed, was in the Llandeilian Epoch, 
and expecially in the early part of it on the horizon of Didymograptus murchisoni. 
During the Caradocian Epoch vulcanicity died down almost everywhere in Wales 
except in the Berwyns, but it continued on a small scale in Shropshire and the Lake 
District. In the last area the latest volcanic action was prolonged into the Ash- 
gillian Epoch. The Ordovician Period was brought to an end by far-reaching earth- 
movement giving rise to extensive land areas. 



II. Some Intrusive Rocks, presumably of Ordovician age 1 . 

By A. Harker. 
A. The English Lake District. 
Of the numerous igneous intrusions in the English Lake District and the 
bordering country some are anterior and others posterior to the main crust-move- 
ments of the region. This criterion of age does not give decisive results in every 
case, but it suffices to divide the intrusive rocks into an older and a younger series. 
1 Other intrusive rocks supposed to be of Ordovician age are referred to by W. W. Watts. 



Harker: GreatBritain.— IntrusiveRocks.— TheEnglishLakeDistrict.— IsleofMan. (III.l.) 75 

The older are doubtless related to the Ordovician Volcanic Series of the district, 
being of slightly later date. The younger rocks are partly of Old Red Sandstone 
age, partly Tertiary, and will be considered later. 

The Ordovician intrusive rocks show a considerable range of petrographical 
variety, but the dominant rock-types in all the larger masses are of acid com- 
position. The most important set is in the neighbourhood of Ennerdale and Butter- 
mere (Rastall 1906), where several irregularly laccolitic intrusions occur near the 
boundary of the Skiddaw Slates and the Volcanic Series. The largest mass measures 
5 x / 2 by 3 kilom. (3V 2 by 2 miles), and passes under the Volcanic Series. Here the chief 
type is an acid biotite-granophyre; but smaller masses of basic augitic rocks, of 
slightly earlier intrusion, occur on its border and in. the neighbourhood. Another 
acid rock, a microgranite, makes two boss-like intrusions near Threlkeld and the 
mouth of St. John's Vale. None of the rocks of this series have typical abyssal 
characters. The acid types are usually granophyres, the basic ones dolerites, 
while intermediate types have been styled quartz-porphyrites, augite-porphyrites, 
etc. In some cases, however, e. g. at Blea Crag in Langstrath (Walker 1904), 
intermediate varieties have been produced by admixture between a basic rock 
and an acid magma intruded slightly later. 

A special feature of many of the acid and intermediate rocks is the presence 
of garnet. This mineral is found, e.g., in a group of spherulitic quartz-porphyry 
dykes on Helvellyn and Armboth Fell and elsewhere, and in dykes and sills of 
quartz-porphyrite and andesite in various localities. It is possible that the garnet 
in these rocks is of secondary origin, as it doubtless is in the lavas and volcanic 
breccias of the district, in which it is of frequent occurrence. 

The smaller intrusions, when they have the sill- or stratiform habit, tend to 
show a certain definite distribution in the Ordovician succession, the more basic 
and heavier rock-types occurring in the lower members and the more acid and 
lighter at higher horizons. In the Skiddaw Slates a group of very basic intrusions 
is found to the north of Skiddaw and along a belt extending westwards towards 
Cockermouth. The rocks are of coarse texture, and consist principally of, horn- 
blende fhornblende-picrites' of Bonney). Numerous irregular sheets of basic doler- 
ites occur in the Skiddaw Slates and near the base of the Volcanic Series, beside 
some small boss-like masses such as that of Castle Head near Keswick. More acid 
rocks are found as sheets at higher horizons in the Volcanic Series, and the sills 
in the Coniston Limestone group are all of quartz-porphyry and allied types. 

B. The Isle of Man. 

Distinct from the Carboniferous and later igneous rocks, there is in the Isle 
of Man (Lamplugh 1903) a considerable variety of older igneous rocks, the age of 
which cannot be fixed precisely by direct evidence. They have been affected by 
the pre-Carboniferous crust-movements of the region, but in different degrees. 
This fact, together with petrographical considerations, makes it probable that 
these older igneous rocks do not all belong to one age. The earliest are probably 
Ordovician, while the later may perhaps be assigned to the Old Red Sandstone, 
but decisive criteria are not applicable in every case. 

There is considerable variety of basic dykes, with some of mean acidity, 
distributed generally but not uniformly over the Manx Slates tract. They have 
as a rule a N.E. — S.W. direction, parallel to the main axes of disturbance. They 
are later than the folding of the slates, but are affected by a second set of crust- 
movements, and are often much crushed and schistose. The rocks include diorites, 
hornblende- and mica-lamprophyres, porphyritic dolerites, and augitic lampro- 
phyres, etc. 



76 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

In addition there are acid intrusions, which are later than the majority of 
the dykes, and later than the crust-movements already mentioned, but are affected 
by a third set of movements. These intrusions occur mainly along the central belt 
of the island. The biotite-granite of Dhoon has a boss-like habit. It is accompanied 
by a set of N.E. — S.W. dykes of microgranite and quartz-porphyry. The Foxdale 
granite, which seems to have a laccolitic habit, is less crushed than that of Dhoon, 
and is probably younger. It is rich in muscovite and microcline, and sometimes 
contains garnet, being closely similar to the Dublin granites on the prolongation of 
the same axis. There is an attendant group of dykes of corresponding composition. 
A small intrusive boss at Oatland, near Santon, is very little affected by crushing, 
and is probably to be correlated with the 'Newer Granite' plutonic complexes of 
Scotland. It has a border of dark basic rock, rich in hornblende and partly uralitized 
augite, and through this there has broken an intrusion of biotite- and hornblende- 
granite. 

C. The Assynt District, Sutherland and Ross. 

In the Assynt district of the North-West Highlands of Scotland, situated 
in the western parts of the counties of Sutherland and Ross, there occurs a series 
of rocks rich in alkalies and embracing an assemblage of types not found elsewhere 
in Britain. (Horne and Teall 1902; Teall 1900, 1907; Shano 1906, 1909.) The 
age of these cannot be determined with precision; but they are younger than the 
Cambrian dolomites (Durness group) and older than the great system of overthrusts 
that has affected this region. It is possible that they are contemporaneous with 
the Ordovician igneous rocks of other parts of Britain ; but they are of very different 
nature, and constitute a small but distinct petrographical province. There is no 
indication of surface volcanic activity, but only of intrusion: the rocks comprise 
firstly a plutonic complex and secondly a series of intrusive sills and dykes. 

The plutonic complex forms Cnoc na Sroine and other low hills to the north 
and east of Loch Borolan, on the borders of Sutherland and Ross, and extends 
under the peat which covers the neighbouring low ground. The boundaries are in many 
parts concealed, but the probable area is about 7 by 5 kilom. (4 x / 2 by 3 miles), excluding 
two or three smaller detached areas. The intrusion invades dolomitic limestones, which 
have been metamorphosed near the contact and transformed to forsterite-marble, 
pencatite, etc. The igneous rocks, in common with the Cambrian strata, have 
been in part modified by crushing and shearing, and in certain places affected by 
overthrusting. Owing to this, as well as to imperfect exposure, the relations of the 
various rock-types which compose the plutonic complex are not completely revealed. 
In many places there is a gradual transition from one type to another; but in some 
places the change is a rapid one, and probably indicates that the complex has been 
built up by several distinct intrusions. The most acid type appears in the central 
part of the area, which is also the highest ground, and the most basic types on the 
border, which is lower ground. Shand supposes that the several types constitute 
the upper and lower layers of a stratified laccolitic mass, the denser and more basic 
rocks forming the base. 

Cnoc na Sroine is composed of a quartz-syenite, which extends to Alltnaceal- 
gach on Loch Borolan and for nearly 2 kilom. (D/4 mile) to the north-east. It consists 
of albite and orthoclase, either separate or in perthitic intergrowth, with quartz. This 
rock passes into a quartzless syenite, often containing some melanite. Then 
come rocks richer in the dark minerals and containing some nepheline or its alteration- 
products. One variety is a melanite-syenite: another (ledmorite), exposed in 
the Ledmore River, is rich in green pyroxene, with less melanite. A good nephe- 



Great Britain. — Bibliography. (III. 1.) 77 

line-syenite (with melanite) occurs to the north of Cnoc na Sroine, and various 
peculiar types are found as dyke-like masses on the outskirts of the area. The most 
basic, seen to the south of Ledmore, is a melanite-pyroxenite, composed of 
augite, melanite, magnetite, etc. 

The south-eastern part of the area, beyond Allt a' Mhuilinn, is not geologically 
continuous with the rest, being overthrust and much crushed. Here occurs the 
borolanite type, composed of orthoclase and melanite with green mica and altera- 
tion-products after nepheline and sodalite. It often contains ovoid white or reddish 
spots, up to 2 or 3 cm. ( 3 / 4 or 1 inch) in diameter, which Teall believed to be pseudo- 
morphs after leucite; but Shand has given reasons for regarding them as merely 
crushed porphyritic felspars. The borolanites are often severely crushed, and then 
acquire a granulitic structure, while the melanite is destroyed. 

The minor intrusions that may be attached to this series of rocks are very 
numerous. They are most developed to the north of the plutonic centre, extending 
beyond Inchnadamph, a distance of about 10 kilom. (67 4 miles). They assume mostly 
the form of intrusive sills or sheets, but dykes are also found. There is a wide range 
of petrographical types; and it is clear that, although the assemblage has unmis- 
takable affinities with the plutonic complex, some of the types must have been derived 
by further differentiation. There are hornblendic lamprophyres, which fall under 
spessartite and vogesite. A mica-porphyrite occurs on the hill Canisp and 
elsewhere, and hornblende-porphyrites are numerous in the neighbourhood 
of Inchnadamph. There are rocks consisting almost wholly of alkali-felspars, in 
particular a porphyritic albite-rock. A more acid type contains quartz in addition 
and very numerous little needles of aegirine, thus approximating closely togrorudite. 



Bibliography of the Ordovician of Great Britain. 

1896. Crosfield, Miss M. C. and Skeat, Miss E. G., Quart. Journ. Geol. Soc, vol. 52, 

pp. 523-541 (Carmarthen). 
1898. Elles, Miss G. L., Quart. Journ. Geol. Soc. vol.54, pp. 463-539 (Skiddaw Slates). 
1904. —  Geol. Mag. dec. 5, vol. 1, pp. 199-211 (Graptolite horizons in Wales). 

1909. — Quart. Journ. Geol. Soc, vol. 65, pp. 169-194 (Conway). 

1913. — Rep. Brit. Assoc, p. 400 (Shell and Graptolite Faunas of Ordovician). 
1908. Elsden, J. V., Quart. Journ. Geol. Soc, vol. 64, pp. 273-296 (Pembrokeshire 

igneous rocks). 
1906. Evans, D. C, Quart. Journ. Geol. Soc. vol. 65, pp. 597-642 (Carmarthen). 

1904. Fearnsides, W. G., Rep. Brit. Assoc, 1903, pag. 665 (Murchisoni beds). 

1905. — Quart. Journ. Geol. Soc, vol. 61, pp. 608-640 (Arenig). 

1910. — "Geology in the Field", part. 2, pp. 786-825 (Wales). 

1908. Groom, T. T. and Lake, P., Quart. Journ. Geol. Soc, vol. 64, pp. 546-595 (Berwyns). 
1889. Harker, A., "The Bala Volcanic Series of Carnarvonshire" Cambridge. 

1902. — Proc. Yorks. Geol. Soc, vol. 14, pp. 487-493 (Borrowdale Rocks). 
1875. Hicks, H., Quart. Journ. Geol. Soc, vol. 31, pp. 167-195 (Arenig Rocks). 
1875. Hopkinson, J. and Lapworth, C, Quart. Journ. Geol. Soc, vol. 31, pp. 631-672 

(Arenig Graptolites). 
1892. Horne, J. and Teall, J. J. H., Trans. Roy. Soc. Edinburgh, vol. 37, pp. 163-178 

(Borolanite). 

1909. Jones, O. T., Quart. Journ. Geol. Soc, vol. 65, pp. 463-537 (Aberystwyth). 
1878. Lapworth, C, Quart. Journ. Geol. Soc, vol. 34, pp. 240-346 (Moffat). 
1882. — Quart. Journ. Geol. Soc, vol. 38, pp. 537-666 (Girvan). 

1889. — Geol. Mag. dec. 3, vol. 6, pp. 20-24, 59-69 (Ballantrae). 

1894. — and Watts, W.W., Proc. Geol. Assoc, vol. 13, pp. 297-355 (Shropshire). 

1910. — — Geol. Assoc, Jub. Vol., Geology in the Field, pp. 739-769 (Shropshire). 
1900. Lapworth, H., Quart. Journ. Geol. Soc, vol. 56, pp. 67-137 (Central Wales). 
1885. Marr, J. E. and Roberts, T., Quart. Journ. Geol. Soc, vol. 41, pp. 476-491 (Haver- 
fordwest). 

1891. — and Nicholson, H. A., Quart. Journ. Geol. Soc, vol. 47, pp. 500-512 
(Cross Fell). 



78 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

1892. Marr, J. E., Geol. Mag. dec. 3, vol. 9, pp. 97-110 (Coniston Limestone). 

1894. — Geol. Mag. dec. 4, vol. 1, pp. 122-130 (Skiddaw Slates). 
1900. — Proc. Geol. Assoc, vol. 16, pp. 453-483 (Lake District). 

1905. — Quart. Journ. Geol. Soc, vol. 61, Proc. pp. lxxxiv-lxxxvi (Ashgillian). 
1907. — Geol. Mag. dec. 5, vol. 4, pp. 59-69 (Ashgillian). 

1881. Ramsay, A. C, Mem. Geol. Surv. The Geology of North Wales. (2nd. Edition.) 

1906. Rastall, R. H., Quart. Journ. Geol. Soc, vol. 62, pp. 253-273 (Ennerdale). 

1895. Reed, F. R. C, Quart. Journ. Geol. Soc, vol. 51, pp. 149-195 (Fishguard area). 
1879. Ruddy, T., Quart. Journ. Geol. Soc, vol. 35, pp. 200-208 (Bala). 

1906. Shand, J., Neues Jahrb. Min., Beil. Bd. 22, pp. 413-453 (Assynt). 

1909-10. — Trans Edin, Geol. Soc, vol. 9, pp. 202-215, 376-416 (Assynt). 

1900. Teall, J. J. H., Geol. Mag. dec. 4, vol. 7, pp. 385-392 (Assynt). 

1911. Thomas, H. H., Quart. Journ. Geol. Soc, vol. 67, pp. 175-214 (Skomer Island). 

1910. Ussher, W. A. E., Geol. Assoc, Jub. Vol., Geol. in the Field, vol.2, pp. 876-896 
(Cornwall). 

1911. Wade, A. Quart. Journ. Geol. Soc vol. 67, pp. 415-459 (Welshpool). 

1904. Walker, E., Quart. Journ Geol. Soc, vol. 60, pp. 70-105 (Mixed intrusions, garnets.) 

Geological Survey of England and Wales. 
Sheet Memoirs: 

229. (Carmarthen, A. Strahan, and others, 1909.) 

230. (Ammanford, A. Strahan and others, 1907.) 

351 and 358. (Land's End, C. Reid, J. S. Flett and others, 1907.) 
353. (Mevagissey, C. Reid, 1907.) 
359. (The Lizard, J. S. Flett and J. B.Hill, 1912.) 
District Memoir: 

The Geology of the Isle of Man (G. W. Lamplugh, 1903.) 

Geological Survey of Scotland. 
General Memoir: 

The Silurian Rocks of Britain, Vol. 1, Scotland (B. N. Peach and J. Horne, 1899). 
District Memoir: 

The Geological Structure of the North West Highlands of Scotland (B. N. Peach, 
J. Horne and others, 1907). 



b. Ireland. 

By G.A.J. Cole. 

At one time, the crystalline Dalradian rocks of Ireland were regarded, with 
these of Scotland, as metamorphosed Ordovician strata, a fact that must not be 
forgotten when memoirs, maps and sections by various authors are examined. Even 
at the present time, much has to be done to separate adequately the Irish Ordovician 
zones from the overlying Gothlandian, and, in the south-east, from the slaty series 
of Howth and Bray. 

On both flanks of the Leinster Chain, the foothills are formed largely of shales, 
slates, and thin beds of a more sandy character, much contorted, but with a general 
north-east and south-west strike. These are the remains of a great Caledonian 
anticline, in the midst of which the Leinster granite has arisen. Near the granite 
the slates have been altered into andalusite-mica-schist. A relic of the crest of the 
anticlinal dome rests horizontally on the summit of Lugnaquilla Mountain, in the 
highest part of the granite chain. This series of strata is possibly in part of Cam- 
brian age (Geol. Surv. 1903); but Ordovician fossils occur in the slates near Rath- 
drum, and at Ballymoney on the Wexford coast. Among the graptolites are Coeno- 
graptus gracilis, Dicranograptus ramosus, and Diplograptus foliaceus. Primitia 
m'coyi Salt, occurs near Courtown, as in the Bala beds of Portrane and the Chair of 
Kildare (see below). Arenig, Llandeilo and Bala beds are all represented on the 
east side of the Lenster chain (Geol. Surv. 1887, 1869; Elles 1910). Ordovician 
shales, with some minettes and volcanic ashes among them, occur as inliers in a 



Cole: Ireland. 



(III. 1.) 79 



Gothlandian area from Duleek to Balbriggan. Two other detached areas, at Portrane 
north of Dublin and on hilly ground north of Kildare town, include richly fossili- 
ferous limestones of Upper Ordovician age. At Portrane, andesitic lavas and ashes 
are succeeded by Middle Bala shales, above which are limestones with fossils like 



N. w. 



S.E. 




Glacial 
Gravel 



Fig. 21. Section showing relation of the Ordovician outlierof the Chair of 
Kildare to the rocks of the Central plain. Horizontal scale, one inch to 1 mile = 1:63 360; 
vertical scale, about four inches to 1 mile = 1 : 15 340. 
d* = Carboniferous Limestone 
c = Old Red Sandstone 
b* = Ordovician slates and sandstones 
b*ls= Ordovician limestone (Bala Series) 
DP = Porphyritlc andesite. 
Reproduced from the Memoirs of the Geological Survey of Ireland, No. 119, p. 4, fig. 2, 1858; with 
the permission of the Director and of H. M. Stationery Office. 



those of the Keisley Limestone in the English Lake District. Among the trilobites 
in the limestones are Stygina latifrons Portl., Trinucleus seticornis His., Cybele 
rugosa Portl., Remopleurides sp., Harpes sp., etc. Similar rocks occur in the ad- 
jacent island of Lambay. In the Kildare ridge, a large number of Middle and Upper 
Bala fossils have been discovered, including Primitia m'coyi Salt., Illaenus bow- 
manni Salt., and Sphaerexochus mirus Beyrich. These and other forms occur also 
at Portrane. The Kildare series also began with a volcanic phase, when andesites 
and basalts were erupted. Above these rocks are red and grey limestones of Keisley 
Limestone age. The grits above these may be Gothlandian. (Geol. Surv. 1858 and 
1875; Gardiner and Beynolds 1896; Seymour 1907.) 

Numerous igneous rocks, both intrusive and contemporaneous, occur along 
the strike of the Ordovician area of Leinster, notably on the south-east of the granite. 
Diorites, andesites, trachytes and rhyolites (felsites), and corresponding tuffs, form 
rougher features in a country mainly composed of shales and slates. South-west 
of Waterford town, the "felsites" cover a wide area down to the coast. Some of 
them are clearly intrusive, and have been crushed so as to resemble tuffs. These 
may be of early Devonian age. (Hatch 1889; Beed 1899, 1900; Kilroe and Mc. 
Henry 1901; Thomson 1908.) 

The strata associated with the felsites along the Waterford coast may possibly 
include some of Arenig age; but so far the fossils found belong to Llandeilo horizons. 
The limestone and shale series of Tramore contains Monticulipora petropolitana 
Pand. in nodular bands, Climacograptus bicornis Hall, Dicranograptus ramosus 
H all, Diplograptus, and Didymograptus. Numerous Ordovician trilobites are recorded. 
The fauna is somewhat specialised, and some thirty species, including the Monti- 
culipora mentioned above, have not been found elsewhere in the British Isles. 
(Jukes 1852; Geol. Surv. 1865; Beed 1899.) 

Numerous areas of Ordovician and Gothlandian shale and sandstone appear 
as inliers throughout southern Ireland in the cores of anticlinal domes. Surrounded 
by a rim of Old Bed Sandstone, which overlies them with striking unconformity, 
they often weather down into hollow lands surrounded by scarps of the more 
resisting series. Farming is carried on in these upland basins, which are reached 
across barren and forbidding hills. A good example of this structure is seen in the 



80 (III. 1.) The British Isles. — III. Stratigraphy. — 3. Ordovician. 

country south of Carrick-on-Suir, where the Devonian terraces of the Comeragh 
Mountains look down on an Ordovician and Gothlandian plateau, itself raised high 
above the sea. Another case occurs west of Galtymore, where the core of an 
Armorican upfold has been hollowed out for some 25 km. (16miles). Gothlandian 
rocks rise high in the ranges of Tipperary and round the Shannon at Lough Derg, 
and appear again in the heart of the Slieve Bloom Mountains near Maryborough. 
In recent years, these rocks have been placed by the Geological Survey in the Goth- 
landian system, on the evidence of graptolites found in certain zones; but it is 
quite possible that some Ordovician beds may ultimately be traced among them, 
in addition to those already observed by the Survey upon Slieve Bernagh. 

A complete Ordovician and Gothlandian succession can be made out in the coun- 
try round the inlet of Killary Harbour, lying partly in northern Galway, and partly in 
southern Mayo. There has been some difference of opinion in the interpretation of 
district, and much remains obscure in the moorland country northward between this 
the mountainous masses of Mweelrea (Muilrea) and Croagh Patrick. Successive 
discoveries of fossils have, however, led to the following conclusions. A true Arenig 
series was recognised by J. B. Kilroe in 1894 in a limited area of slates south 
of Bencroff, on the south side of Killary Harbour (Kilroe 1907), and Arenig grits, 
slates and cherts are now known also on the west shore of Longh Mask, where 
they include volcanic tuffs. Above the slates occur massive grits and conglomerates, 
probably of Upper Arenig age. Above these are the Mweelrea grits, some 3600 m. 
(12000 ft.) thick, with here and there Llandeilo fossils. Organic remains, however, are 
so scarce thatCARRUTHERS and Maufe have suggested a continental origin for most of 
these felspathic sandstones and pebble-beds. Llandeilo grits and ashes, with Pliomera 
(Amphion), among other trilobites, occur west of Lough Mask, pointing to a sea 
in this direction, and these are succeeded by Llandeilo limestones (once regarded 
as of Bala age). Bala beds may occur on the heights of Mweelrea and east of Killary 
Harbour (Carruthers and Maufe 1909; Gardiner and Beynolds 1909, 1910, 
1912; Beed 1909). 

In the north west of Ireland, the Ordovician and Gothlandian systems have 
been very generally removed by denudation. An interesting patch remains at 
Pomeroy, in Co. Tyrone, where Bala fossils were long ago indicated by Portlock 
(1843). Becent investigations (Fearnsides, Elles and Smith 1907), confirm the 
Upper Bala (Ashgillian) age of the sandstone and shale series containing Dicello- 
graptus anceps, Strophomena grandis, Str. siluriana, Lichas hibernicus, and Trinu- 
cleus seticornis; but a higher series of shales, from which Portlock had collec- 
ted Monograplus, corresponds with those of Birkhill in Britain, and is thus of 
Llandovery age. The whole series of strata rests towards the north against 
the old igneous and metamorphic rocks of the axis of Tyrone, already described 
as Pre-Cambrian. 

The hummocky land from the coast of Co. Down to the central Irish plain 
near Longford is formed of Ordovician strata on the north, succeeded as we go 
southward by Gothlandian beds with Ordovician inliers, much like those of the 
Scottish Southern Uplands. These shales, slates, and sandstones, into which 
the Newry granite and the Kainozoic granite of Mourne have intruded, occupy 
almost all the country southward, until we reach Balbriggan on the Dublin coast. 
The Ordovician series in Co. Down was compared with the Glenkiln shales (Llan- 
deilo) and Hartfell Shales (Bala) of southern Scotland by Swanston and Lap- 
worth (1876 — 77) and Clark (1902), and characteristic graptolites were described. 

The Irish area in Ordovician times was practically marine. The Arenig 
beds of the Killary Harbour district probably had representatives, now lost to us, 
farther south and north. Yet the highland of Dalradian rocks no doubt rose to 



Cole: Ireland. (III. 1.) 81 

westward above the sea, and furnished much of the mud in which the early grap- 
tolitic fauna is embedded. Coarse conglomerates were at times rolled down by 
rivers from the heights, and sandstones accumulated in the Mayo area, to which, 
as we have seen, a continental origin has been ascribed. Continental land must 
have long remained where the North Atlantic now spreads its waters. 

In the Ordovician limestones, which often contain corals, we see evidences 
of fairly warm waters, and the volcanic action of Bala times doubtless built up 
islands, comparable to those of the Pacific at the present day. These, however, 
must have always been subordinated to the great andesitic and rhyolitic piles 
farther to the east in what is now the mountain-land of Wales. 



Bibliography of the Ordovician of Ireland. 

1909. Carruthers, R. G. and Muff (Maufe), H. B., Irish Naturalist, vol. 18, pp. 7-11 

(Killary). 
1903. Clark, R., Rep. Brit. Assoc. 1902, pp. 599-601 (North-East Ireland). 
1902. — Geol. Mag., pp. 497-500 (North-East Ireland). 

1910. Elles, G. L., Irish Naturalist, vol. 19, p. 244 (Arenig beds). 

1907. Fearnsides, W. G., Elles, Miss G. L., and Smith, B., Proc. Roy. Irish Acad., vol.26, 
Section B, pp. 97-128 (Pomeroy). 

1896. Gardiner, C. I., and Reynolds, S. H., Quart. Journ. Geol. Soc. London, vol. 52, 

pp. 587-605 (Kildare). 

1897. — — Quart. Journ. Geol. Soc. London, vol. 53, pp. 520-535 (Portraine). 

1898. — — Quart. Journ. Geol. Soc. London, vol. 54, pp. 135-148 (Lambay Island). 

1909. — — Quart. Journ. Geol. Soc. London, vol. 65, pp. 104-140 (Tourmakeady). 

1910. — — Quart. Journ. Geol. Soc. London, vol. 66, pp. 253-270 (Glensaul). 
1912. — — Quart. Journ. Geol. Soc. London, vol. 68, pp. 75-102 (Kilbride). 
1889. Hatch, F. H., Geol. Mag. pp. 70-73, 261-265, 288 and 545-549 (Igneous). 
1853. Jukes, J. B., Journ. Geol. Soc. Dublin, vol. 5, pp. 147-159 (County Waterford). 
1907. Kilroe, J. R., Proc. Roy. Irish. Acad., vol.26, Section B, pp. 129-160 (Mayo & 

North Galway). 
1901. — and McHenry, A., Quart. Journ. Geol. Soc. London, vol. 57, pp. 479-489 

(Igneous). 
1843. Portlock, J. E. Mem. Geol. Surv., Report on the Geology of Londonderry and 

parts of Tyrone and Fermanagh. 

1899. Reed, F. R.C., Quart. Journ. Geol. Soc. London, vol. 55, pp. 718-772 (Waterford). 

1900. — Quart. Journ. Geol. Soc. London, vol. 56, pp. 657-693 (Waterford). 
1909. — Quart. Journ. Geol. Soc. London, vol. 65, pp. 141-154 (Tourmakeady). 

1907. Seymour, H. J., Irish Naturalist, vol. 16, pp. 3-13 (Lambay). 

1876 — 77. Swanston, W. and Lapworth, C, Proc. Belfast Naturalist's Field Club, 
Appendix p. 107 (County Down). 

1908. Thompson, J. A., Quart. Journ. Geol. Soc. London, vol.64, pp. 475-495 (Igneous, 

County Wexford). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets: 

102 and 112. Parts of Counties Dublin and Meath (J. B. Jukes and others) 

2nd. Ed. 1875. 
112. Dublin (G. W. Lamplugh and others). 1903. 
119. (35 N.E.) Parts of King's County, Queen's County and Kildare (J.B. Jukes 

and others). 1858. 
121, 130. Part of County Wicklow (J. B. Jukes and others). 1869. 
148, 149. Parts of Counties Carlow and Wexford (E. T. Hardman and W. H. 

Baily). 1887. 
167, 168, 178 and 179. Parts of Counties Kilkenny, Tipperary, Waterford and 

Wexford (G. V. Du Noyer and W. H. Baily). 
See also J. E. Portlock above. 



Handbuch der regionalen Geologie. III. 1. 



82 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

4. Gothlandian or Silurian. 

a. Great Britain. 

I. Sedimentary and Volcanic Rocks. 

By Owen Thomas Jones. 

The principal exposures of Silurian rocks occur in Wales, the Lake District 
and Scotland; smaller areas are found along the borders of England and Wales 
and scattered among the newer rocks in the Midland district of England. They 
have been penetrated also in deep borings in the south east of England. 

Classification. A threefold division of the rocks is generally adopted by 
British geologists but so far opinion is not unanimous in regard to the names given 
to certain of the divisions and the lines of demarcation between them. The task 
of constructing a scheme of classification which will apply to the whole of the 
British Isles is rendered exceedingly difficult by the fact that they occur in two 
radically distinct lithological and faunal developments. One facies is characterized 
by relatively coarse deposits of great aggregate thickness and containing a shelly 
fauna of brachiopods, trilobites etc.; the other is typically represented by fine- 
grained deposits of small thickness and containing a graptolite fauna almost exclu- 
sively. 

For some years therefore two schemes of classification have been in existence 
side by side — the older founded mainly by Sir Boderick Murchison having reference 
to the shelly facies; the other suggested by Charles Lapworth being based 
upon the graptolite fauna of the rocks. 

A brief history of these classifications is necessary in order to understand 
their signifiance. 

Murchison (1839) arranged the rocks in the Welsh borders into the groups 

Ludlow 

Wenlock 

Caradoc 

the last being assigned to the Lower Silurian. It was shown later by Sedgwick 
and McCoy (1853) that the Caradoc could be divided into two portions; the upper 
division, referred to by Murchison as the Horderley and May Hill rocks, was shown 
to be intimately allied to the Wenlock, and they proposed for them the name May 
Hill Sandstones. The lower division was regarded by Sedgwick as equivalent to 
his Bala group as developed in North Wales. 

This was confirmed later by Bamsay and Aveline (1854), officers of the 
Geological Survey, who remapped the Caradoc rocks of Shropshire. The upper 
Caradoc formed an impersistent base to the Wenlock rocks and consisted of a 
sandstone group with Pentameri followed by a group of purple and green shales 
almost devoid of fossils. It is to these shales that much of the confusion in the 
nomenclature at the present day is due. 

Aveline mapped these shales throughout Wales and found that near Llan- 
dovery they overlay a sandstone group with Pentameri like the upper Caradoc 
of Shropshire. Near that town there was a lower sandstone group not found in 
Shropshire but also containing species of Pentamerus. These two groups were sub- 



Jones: Great Britain. — Sedimentary and Volcanic Rocks. (III. 1.) 83 

sequently included by Murchison in a new formation (Llandovery) which he regarded 
as a transitional formation between the lower and upper Silurian; the purple 
and green shales were excluded from this formation. Aveline also traced these 
shales throughout Wales as far as Conway in North Wales ; and they were ultimately 
given the name of Tarannon shales from their marked development on an upland 
tract of that name in Central Wales. 

From his investigations among the graptolitic rocks of the South of Scotland 
(Moffat etc.) Lapworth (1882) showed that the Tarannon shales as developed 
at Conway were in the main equivalent to his Gala group in the south of Scotland 
and he considered that the groups Birkhill and Gala there established were equi- 
valent to the Llandovery and Tarannon rocks of Wales. He proposed the name 
Valentian for this series (after the Roman name of that part of the South of Scot- 
land where these rocks are well developed). 

It was established however by Mrs. Shake spear (Wood 1906) that the 
shales mapped by Aveline were of widely different ages at Tarannon and Conway. 
At the latter place they were the equivalents of the Gala group: in the former 
district although of much greater thickness they formed only the uppermost sub- 
division of the Scottish Valentian rocks, and it was proposed to redefine the term 
Tarannon to include all those rocks included in it by Aveline and thus make it 
equivalent to the Gala rocks of Scotland. This course only increased the confusion ; for 
it is certain that, where the shelly facies is in question, the upper Llandovery is largely 
equivalent to the Tarannon as thus defined and not to the upper Birkhill of South 
Scotland, as has been commonly supposed, and the overlying purple and green shales 
are probably represented by the highest (Dolgau) group of that formation. The term 
Tarannon is therefore used in two widely different senses according as it is applied 
to the shelly or the graptolitic facies. In the following article the term will be 
discarded and the more natural plan will be followed of extending the Llandovery 
to include this subsidiary and unimportant group of purple and green shales. 

The higher Silurian rocks (Wenlock and Ludlow) when traced away from the 
typical region towards the west and north-west undergo marked lithological and 
faunal changes. The massive limestones interspersed with the shales disappear 
and their place is taken by shales; also the abundant shelly fauna is gradually 
replaced by one of graptolites. It then becomes impossible to identify the original 
subdivisions of Murchison which were based to a large extent upon lithological 
characters. 

Lapworth therefore proposed as a more natural classification to include the 
beds above the Valentian in a series which he called Salopian, while for the highest 
Silurian rocks he proposed the term Downtonian. 

More recently Miss Elles (1900) and Mrs. Shakespear (Wood 1900) 
established a zonal classification of these rocks by means of graptolite species and 
were able to define with some precision the limits of Murchison's groups in terms 
of the zonal classification. Lapworth's proposal also received full justification ; 
the graptolites were found to persist though in diminished numbers throughout 
the Salopian but did not survive that period. The Downtonian series includes 
therefore all the post- graptolitic Silurian rocks and the passage beds into the Old 
Red Sandstone. 

These two classifications are set out side by side in order to show their relation 
to one another. 



84 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 



Lapwoath: 

Newer classification 



Murchison: 
Older classification 



Downtonian 



Salopian 



Valentian 



Ludlow, including the 
Passage beds 



Wenlock 



Llandovery (or Llandovery- 
Tarannon of some authors) 



Ledbury Shales (Passage beds 
into Old Red Sandstone) 

Downton Sandstone 

Upper Ludlow shales 

Aymestry Limestone impersistent 

Lower Ludlow shales 

Wenlock Limestone impersistent 

Wenlock shales 

Woolhope Limestone impersistent 

Purple and green shales (Tarannon 
of some authors) 

Upper Llandovery 

Lower Llandovery. 



1. The Valentian Series. The Valentian rocks exemplify to a marked degree 
the contrast between the shelly and the graptolitic facies, and the boundary between 
these can be traced with some precision in south Britain. South-east and south of 
this line the fauna consists of brachiopods, corals, lamellibranchs, gastropods, 
cephalopods, and trilobites, while graptolites are exceedingly rare or wanting. In 
the tract which lies west and north-west of the line the groups of organisms enumerated 
above are of rare occurrence, their place being taken by a great variety of graptolite 
forms, by means of which the rocks have been subdivided in considerable detail. 
The change of fauna is in general accompanied by a change in the lithology of the 
rocks; where shelly fossils prevail the rocks are mainly conglomerates, sandstones, 
and sandy mudstones reaching an aggregate thickness of 900-1200 m. (3000-4000 ft.). 
All the rocks are somewhat calcareous and are blue-grey in colour. 

Where the graptolitic rocks are typically developed they are of extreme tenuity 
and are composed of finely-divided sediment such as shales and mudstones. Cal- 
careous matter when present is confined to layers of nodules at certain horizons; 
Its place is taken generally by iron pyrites which occurs abundantly disseminated 
throughout the rocks. This gives the rock a prevailing dark-blue or black colour and 
causes them to become deeply ironstained on weathering. The rocks of the higher 
members, as also in the shelly facies, are lighter in colour and generally coarser in 
grain. 

The Valentian series falls naturally into two subdivisions or stages which 
vary to a certain extent independently in lithological and faunal characters 
and in certain districts there is evidence of physical discontinuity be- 
tween the upper and lower stage. Also the Upper Valentian rocks of the shelly 
facies have a far wider distribution than the lower and not uncommonly rest on 
Pre-Cambrian rocks. For these reasons it is convenient to consider separately the 
distribution and characters of these subdivisions. 

LowerValentian Stage. The rocks of this stage are known in different 
areas under a multitude of names. In the shelly facies it includes the Lower Llan- 
dovery rocks and others referred to that group such as the Haverford Group of 
Haverfordwest; the Powis Castle and Cloddiau Groups of Welshpool and the Mulloch 
Hill and Saugh Hill Groups of Girvan. In the graptolitic facies it comprises the 
Birkhill rocks of South Scotland; the Skelgill rocks of the Lake District; the 
Gwastaden and Caban groups of Rhayader; the Fachdre, Dolgadfan and 
Twymyn beds of the Tarannon district; the Pont Erwyd Stage of Central 
Wales; part of the Gyffin Shales and Castle Grits at Conway and similar shales 
with grits at Corwen and again near Llansawel in Carmarthenshire. 



Jones: Great Britain. — Sedimentary and Volcanic Rocks. — Valentian. (III. 1.) 85 

The shelly facies has long been known at Llandovery and Haverfordwest; 
at the base there are grits and conglomerates resting on Upper Bala or Ashgillian 
rocks without any evidence of unconformity. These are followed in the Haver- 
fordwest district by shales with lamellibranchs, brachiopods and trilobites and these 
in turn by sandy mudstones containing numerous characteristic fossils namely 
Nidulites favus, Lindstroemia subduplicata, var. crenulata, Atrypa marginalis,Meristina 
crassa, Orthis mullochiensis, Barrandella undata, Stricklandinia lens, Plectambonites 
duplicates, Phacops cf. elegans, numerous gastropods and other less important fossils. 
At Haverfordwest these beds are succeeded by a group of massive sandstones con- 
taining similar fossils; this group has not been identified elsewhere. The occurrence 
of Mesograptus modestus, var. parvulus and Climacograptus normaiis in the shales 
near the base is important as it enables the lowest beds of the shelly facies to be 
correlated directly with the lower horizons of the graptolitic facies. The sequence 
at Llandovery is very similar to the above. The total thickness of sediments in the 
Haverfordwest-Llandovery belt is 450 to 600 metres (1500-2000 ft.); but there is 
reason to suppose that these rocks do not extend far eastward or southward beyond 
their outcroup, having been removed over those areas before the formation of 
some part of the Upper Valentian or, alternatively, they were never deposited 
over much of this southern and eastern area. 

The graptolitic type of Lower Valentian is best developed in the Lake district 
(Marr and Nicholson 1888) (Skelgill Group) and in the Southern Uplands 
of Scotland (Lapworth 1878) (Birkhill Group). In these districts the groups 
have been subdivided minutely into zones characterised by certain species of grap- 
tolites. In the Lake District bands containing certain trilobites alternate with 
the graptolitic layers and trilobite zones have been worked out for the upper 
part of the sequence. The graptolite fauna of the rocks of these typical areas has 
since been obtained in most other regions where the facies prevails. The lithological 
characters of the rocks vary however somewhat widely in different districts ; these 
variations follow a well marked law and will be dealt with below. A general 
classification of the graptolitiferous Lower Valentian rocks may be drawn up as 
follows (the older classification being slightly rearranged in accordance with the most 
recent information): 



Lower 
Valentian 

or 

Birkhill 
Stage 


Upper Birkhill 
Sub- Stage 


Zone of Monograptus (= sedgwicki) spinigerus 
„ ,. Cephalograptus cometa 


Middle Birkhill 
Sub- Stage 


„ ,, Monograptus convolutus 
„ „ Monograptus leplotheca 
„ „ Monograptus fimbriates 


Lower Birkhill 
Sub-Stage 


., „ Monograptus cyphus 
„ „ Monograptus acinaces 
„ „ Monograptus atavus 
„ ,. Diplograptus acuminatus 



In the Lake District the two trilobite zones of Encrinurus punctalus and 
Phacops glaber intervene between the middle Birkhill graptolite zones and the zone 
of Ampyx aloniensis between the upper Birkhill zones. The zone of Rastrites 
maximus is now removed from the Lower and united with the Upper Valentian. 

The Lower Birkhill rocks of these areas consist of dark ironstained shales 
with some white seams of thin siliceous bands. 



86 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 




The Middle Birkhill is a group 
of pale greenish blue mudstones with 
dark shale bands in which most of the 
graptolites occur the mudstones having 
occasionally a scanty trilobite fauna. 

The Upper Birkhill rocks are com- 
posed mainly of thin papery shales. 

In Central Wales (H. Lapworth 
1900, Wood 1906, Jones 1909 and 
1912) the lower substage is of much 
greater thickness and contains in 
places massive grits at the base 
(Gwastaden Grits of Rhayader, Pen-y- 
Ddinas Grits of Llansawel etc.). At 
Rhayader the Upper Birkhill substage 
occurs partly in the form of massive 
grits underlain by the Caban Conglom- 
erate, which rests unconformably on 
various zones of the Lower Birkhill. 

In certain parts of the British Isles 
the distinction between the shelly and 
the graptolitic facies is not so clear as 
elsewhere. Bands of dark shale with a 
graptolite fauna alternate with calcare- 
ous sandstones, mudstones or conglo- 
merates containing a typical shelly 
fauna and thus form an intermediate 
or compound facies. The best instance 
is afforded by the Lower Valentian 
rocks of Girvan in Ayrshire (C. Lap- 
worth 1882). The Lower Valentian 
succession is as follows 

Saugh Hill Group including: 

a) Zone of Monograptus sedgwicki 

b) Saugh Hill Sandstones (unfos- 
siliferous) 

c) Zone of Diplograptus modestus 
(= Zones of M . jimbriatus, M. cy- 
phus and M. acinaces) 

d) Woodlands conglomerate, limes- 
tone and mudstone (shelly fauna) 

Mulloch Hill Group divided into: 

a) Zone of Diplograptus acuminatum 

b) Mulloch Hill Sandstones and 
conglomerate (shelly fauna). 

The representatives of these divisi- 
ons in the general scheme of classi- 
fication can be readily seen. 

A compound facies is less perfectly 
developed in more southerly districts 



Jones Great Britain. — Sedimentary and Volcanic Rocks. — Valentian. (III. 1.) 87 

in Britain, e.g. Corwen (Lake and Groom 1893, 1908) and Welshpool (Wade 1911), 
where part of the succession yields a shelly fauna while another part yields graptolites. 

Upper Valentian. The Upper Valentian may be defined as including all the 
beds between the Lower Valentian and the base of the Salopian. Two distinct facies 
can be distinguished which prevail generally over the same areas as those of the 
Lower Valentian, but the rocks of the shelly facies have a much wider distribution 
in the south and east of Wales and the Welsh borders, where they not uncommonly 
rest on Pre-Cambrian rocks. 

The Upper Valentian rocks of the shelly facies are known under various 
names. They include the "Upper Llandovery" of Llandovery together with the over- 
lying group of purple and green shales often referred to the "Tarannon", the May 
Hill Sandstone of Gloucestershire, the Millin and Rosemarket groups of South 
Pembrokeshire and the Cefn group of Welshpool. 

The Gala and Hawick rocks of south Scotland ; the Dailly Series and Camregan 
Group of Girvan; the Browgill Beds of the Lake District; the Tarannon Series of 
Tarannon and other groups correlated with the latter in Central and North Wales 
belong mainly to the graptolitic facies. It is commonly agreed at present to 
include the zone of Rastrites maximus in the base of the upper Valentian. 

Shelly Facies. The rocks of the shelly facies exhibit considerable variation 
when traced laterally but in general they consist of fossiliferous calcareous sand- 
stones and sandy mudstones followed as a rule by purple and green shales almost 
devoid of fossils. Near Tortworth in Gloucestershire (Morgan and Reynolds 1901), 
the Mendip hills in Somersetshire (Reynolds 1907) and Marloes in Pembrokeshire 
these rocks are remarkable as affording evidence of volcanic activity, the only 
instance known in the south of Great Britain of vulcanicity during the Silurian 
period. This occurrence compares however with the much greater development 
of Silurian volcanic rocks in the southwest of Ireland. Basic pyroxene-andesites, 
associated with coarse ashy conglomerates and fine tuffs are interbedded with 
fossiliferous rocks and indicate, volcanic activity at two different horizons. 

The characteristic fossils include Palaeocyclus praeacutus, Coelospira hemi- 
sphaerica, Stricklandinia lirata, Pentamerus oblongus, Barrandella globosa, Catazyga 
haswelli, Stropheodonta compressa, Illaenus aemulus, and Phacops weaveri, but some 
of these are restricted in their distribution and indicate sub-facies. In the belt 
that extends from Shropshire through Llandovery towards Pembrokeshire, Pen- 
tamerus oblongus is extremely abundant; while at Tortworth, in the Mendips and 
at Marloes in Pembrokeshire this form is exceedingly rare its place being taken 
by Stropheodonta compressa and other forms. 

Graptolitic facies. West and north-west of the areas considered above the 
graptolitic facies prevails, e. g. in North and Central Wales, the Lake District and 
the south of Scotland, but in the Girvan district of Ayrshire there is a partial return 
to a shelly facies, the Camregan group being in part a calcareous sandstone with 
brachiopods, trilobites etc. The graptolitic rocks of the Tarannon district were divided 
by Mrs. Shakespear (Wood 1906) into several distinct zones, some of which can be 
recognized over wide areas. 

These are as follows: 

Zone of Monograptus crenulatus 
„ ,, ,, griestonensis 

crispus 
„ ,, ,, turrieulatus 

,, ,, Rastrites maximus. 

The zone of Monograptus crenulatus comprises the purple and green shales 
to which the name Tarannon was originally applied by Aveline. In addition to 



88 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

the zonal graptolites Monograptas becki, M. runcinatus, M. discus, M. nodifer, M. 
nudus, M. priodon, M. exiguus, Retiolites geinitzianus, Climacograptus extremus, 
Petalograptus palmeus, var. tenuis are characteristic and commonly occurring forms. 

Conditions of deposition of the Valentian rocks. The graptolitic 
type of the Valentian appears to have been deposited in a trough which was in all 
likelihood gradually subsiding during lower Valentian times, while its margins were 
being slowly uplifted. The districts where the same facies or subfacies occurs are 
found to lie along successive belts south-eastward or north-westward of the 
axis of the trough, which ranged from N.E. to S.W. These belts are in general concave 
towards the centre of the trough and indicate shallower water or the approach to a 
shore-line away from that direction. The regions where the Valentian rocks are 
represented by the least thickness of sediments are the Lake District and North Wales ; 
in the former district the Lower Valentian is composed of 20 m. (65 ft.) and the Upper 
Valentian of about 90 m. (300 ft.) of fine graptolitiferous shales and mudstones. Farther 
south in Central Wales these subdivisions expand to 275 m. (900 ft.) and nearly 
1 100 m. (3500 ft.) respectively. Still farther south-eastward the Lower Valentian in par- 
ticular increases greatly in thickness for at Rhayader the total thickness of that sub- 
division is about 900 m. (2900 ft.). This is due however in part to a local uncon- 
formity at the base of the Caban Group of that district; the overlying rocks being 
composed of coarse boulder-beds, grits and subordinate shales. In this district 
also there is evidence of overlap at the base of the Upper Valentian. 

In the next belt, on which the Haverfordwest-Llandovery development lies, 
the lower and upper subdivisions are each represented by 450-600 m. (1500-2000 ft.) 
of sediments but there is reason to suspect a physical and paleeontological break 
between them; the total thickness of sediments is therefore less than at Rhayader 
but part of the sequence may be unrepresented. Then follows still farther east 
and south a different facies, which lies on a curved line extending from Shropshire 
to the south side of the Pembrokeshire coalfield. The Lower Valentian is absent; 
the Upper Valentian which is of comparatively small thickness, is composed of 
coarse sandstones or limestones with some shales, and rests upon older rocks generally 
Pre-Cambrian. This littoral type is fairly general over the southeast of Wales, 
May Hill, Malvern etc. and is probably prevalent over much of the Midlands where 
these rocks occur. 

Still farther east is the distinct subfacies ofTortworth and theMendips, which 
ranges to Marloes in South Pembrokeshire; it is characterized by the occurrence 
of basic volcanic rocks. 

There appears good reason for supposing therefore that while the central trough 
was subsiding during Lower Valentian times its eastern margin was being gradually 
elevated, so that in Upper Valentian times land prevailed over the eastern area. 
It is interesting to note however that in the East of England (Chilham in Kent) typical 
graptolitiferous Upper Valentian shales have been met with in a deep boring through 
the Mesozoic rocks; these probably belong to the continental province extending 
from Rrittany into the Ardennes rather than to the British province of Valentian 
rocks. 

Northwest of the centre of the trough the same general change takes 
place but it cannot be traced in so detailed a fashion. In the Moffat district about 
30 m. (100 ft.) of graptolite shales represent the Lower Valentian and 900-1200 m. 
(3000-4000 ft.) of coarse grits, conglomerates and shales the upper stage. It was shown 
by Lapworth that as the graptolite shales are traced northwestward they are 
gradually replaced by arenaceous sediments and the total thickness of the group 
increases correspondingly. In the Girvan district, still farther northwest, the 
lower subdivision is composed of 275 m. (900 ft.) of shelly sandstones and lime- 



Jones: Great Britain. — Sedimentary and Volcanic Rocks. — Salopian. (III. 1.) 89 

stones alternating with graptolite shales; there are some unconformities in the 
series indicating local earthmovements and these may also have removed an unknown 
thickness of deposits. 

On the whole the trough seems to have been gradually filling up with coarse 
sediments during Upper Valentian times; though subsidence must have continued 
pari passu, to allow of the accumulation of so great a thickness of coarse sediments 
under somewhat uniform shallow-water conditions. 

2. The Salopian Series includes the highest graptolitiferous strata, or their equi- 
valents under different facies, so far as these have been determined. There are still 
certain regions, where the upper limits of the Salopian has not been recognised 
with certainty; reference will be made to these at a later stage. 

The rocks of the series admit of a broad division into two lithological types 
or facies, but these are not so sharply marked off by their organic contents as those 
of the Valentian rocks. These two facies may be referred to as a) the calcareous 
facies, b) the non-calcareous facies. It is convenient also to subdivide the series 
into two stages which will be described as Lower and Upper Salopian; the former 
corresponds in general with the Wenlock of Murchison while the latter includes 
the Lower Ludlow and the Aymestry Limestone group of the older classification. 

a) The calcareous facies; the lithological characters and organic contents 
of the rocks of this facies were described in detail by Murchison. These rocks 
prevail in Shropshire and along the borders of England and Wales; Wenlock, Lud- 
low, Malvern, Woolhope, May Hill, Usk being well known localities, they are found 
also around Tortworth (in Gloucestershire), Cardiff and as small inliers in the neigh- 
bourhood of Birmingham, (Walsall, Dudley, Lickey). Approximately the same 
type is developed in the extreme southwest of Pembrokeshire (Marloes etc.), and 
if one may judge from the limited exposures of Silurian rocks in south Cornwall 
the calcareous facies seems to be dominant there also. Its western limit is pro- 
bably related to a peculiar belt of disturbance which forms an arc, concave to the 
northwest, and ranges from the east side of the Longmynd (Church Stretton) 
through Old Radnor towards the middle of the Pembrokeshire coalfield. This line 
is indicated on geological maps by severe post-Carboniferous disturbances and is 
probably a structural feature of great antiquity. 

Salopian rocks appear also to be somewhat sharply limited eastwards for 
they are absent in borings beneath the newer strata of the Midlands east of a line 
drawn from Birmingham to the Mendip hills in Somerset. They reappear however 
farther east as at Ware in Hertfordshire, and various localities recently discovered 
in East Kent (Cliffe etc.). Their distribution is analogous to that of the Upper 
Valentian and it is therefore possible that the subterranean Salopian rocks of the 
east of England belong to a different province from those of the west as suggested 
in connection with the preceding stage. 

b) The non-calcareous facies occupies the eastern portion of North 
and Central Wales and the border region; a large area in the Lake District and 
the surrounding tracts, a narrow belt in the southern Uplands of Scotland near the 
English borders and smaller areas near Girvan in Ayrshire, Lanarkshire and the 
Pentland Hills. 

The classification of the rocks of the calcareous facies is set out in tabular 
form on pp. 98-9. The limestone beds which intervene between the shales are relatively 
impersistent, but have acquired an importance out of all proportion to their thick- 
ness through the abundance and variety of their organic remains. Where they are well 
developed their superior hardness among the softer strata gives them great pro- 
minence in the landscape; they generally form well-wooded escarpments, while 



90 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

the intervening shales give rise to long strike valleys or low undulating tracts of 
a monotonous character. This type of scenery is strikingly exhibited along Wenlock 
Edge and around the domes of Woolhope and May Hill. The shale bands can scarcely 
be distinguished from one another by their lithology, but their fauna is somewhat 
different. The Wenlock shale usually contains numerous brachiopods and trilobites, 
the commonest being A try pa reticularis, Orthis rustica, Dalmanella elegantula, Sceni- 
dium lewisi, Plectambonites segmentum, P. transversalis, Phacops caudatus, P. stokesi, 
Calymene blumenbachi and Cardiola interrupta. The Lower Ludlow shale contains 
many of the above fossils but in addition Rhynchonella nucula, Wilsonia wilsoni, 
Choneles striatella, Phacops downingiae, Lingula lata and others are characteristic. 
In the higher portion of these shales known locally as the Leintwardine flags a thin 
band has long been known from which starfishes ( Lapworthura and Palaeocoma) have 
been obtained together with remains of Merostomata ( Pterygotus and Eurypterus). 
As indicated later these rocks have in places also yielded some graptolites by means 
of which the position of the shales and the intervening limestones were determined 
on the graptolitic scale. 

The bands of limestone are readily distinguished from one another by their 
lithological and faunal characters; they were therefore selected by Murchison to 
define the limits of his groups. 

The Woolhope Limestone is generally a blue flaglike limestone with thin 
bands of shale; occasionally it is partly represented by nodular limestone; it is 
characteristic of the southeastern portion of the calcareous area and becomes replaced 
by shales towards the north west. Its fossils are intimately related to those of the 
overlying Wenlock shale, but in some districts Stricklandinia lirata and Barrandella 
globosa survive from the Valentian. The trilobite Illaenus barriensis occurs in 
several localities and may be regarded as a characteristic fossil. 

The WenlockLimestone is, however, the best known and most distinctive 
member of the calcareous facies on account of the variety and abundance of its 
organic remains and their beautiful state of preservation. It is a bluish grey argill- 
aceous limestone in even beds of no great thickness, alternating with thin bands 
of shale. In some of the beds brachiopods and trilobites occur in profusion, while 
others are almost made up of the remains of corals and crinoids. Among the most 
characteristic fossils maybe enumerated A cervularia luxurians, Omphyma turbinatum, 
Favosites gothlandicus, Actinocrinus, Periechocrinus, Crotalocrinus, Sieberella galeata, 
Meristina tumida, Strophonella euglypha, Horiostoma discors, Phacops caudatus, 
Phacops musheni, Orthoceras, Phragmoceras, Gomphoceras. 

The calcareous material dies away rapidly and becomes replaced by shales 
in a southwesterly direction its most typical development being around Wenlock 
from which town it derives its name. 

Aymestry Limestone. The highest band of limestone attains its maximum 
development near the place after which it is called. Away from that neighbourhood 
especially towards the west and south west the massive beds of earthy limestone 
become interspersed with numerous shale bands until the group is finally reduced 
to a few thin calcareous beds or nodules. It usually contains a profusion of the 
brachiopods Conchidium knighti, and Dayia navicula, which are often associated 
with Wilsonia wilsoni, Lingula lewisi and other fossils; the first named species 
appears to be confined to this horizon. In some localities traces of graptolites have 
been found in the limestone. It has been proved recently that near Ludlow 12 to 
45 m. (40-150 ft.) of shales (Mocktree Shales) over-lying the limestone contains 
a very similar fauna including Monograptus leintwardinensis, and must therefore be 
grouped with the Aymestry limestone in the Salopian; this is the highest level at 
which graptolites have yet been recorded (Elles and Slater 1906) in Britain. 



Jones: Great Britain. — Sedimentary and Volcanic Rocks. —  Salopian. (III. 1.) 91 



The non-calcareous 
f acies. Owing to the ab- 
sence of the distinctive 
limestone bands in the west 
and northwest of the Sil- 
urian area it was for a long 
time impossible accurately 
to' identify the divisions 
established farther east by 
Murchison. This has now 
been accomplished for many 
districts by means of the 
graptolite fauna, which has 
been very completely in- 
vestigated of recent years 
by Miss Elles (1900) 
and Mrs. Shakespear 
(Wood 1900). The former 
established a detailed zonal 
classification of the Wen- 
lock (Lower Salopian) rocks 
of Wales and the border- 
land while the latter ex- 
tended the classification to 
the Lower Ludlow rocks 
and Aymestry Limestone 
(Upper Salopian). By 
means of these detailed re- 
searches and the work of 
previous observers in Wales 
(Watts, 1885 and 1890, 
Lake 1895), the Lake Di- 
strict (Marr 1892) and the 
South of Scotland (Lap- 
worth 1880) the divisions 
of the Salopian rocks esta- 
blished in these different 
districts can now be cor- 
related, and the history of 
deposition of the sediments 
and their lateral variation 
can be followed in detail. 

The Lower Salopian rocks of Builth, the Long Mountain and the Dee 
Valley in North Wales have been divided into six graptolite zones, based principally 
upon species of the genus Cyrlograptus: 

Zone of Cyrlograptus lundgre.nl 

,, rigidus 

„ Unnarssoni 

,, symmetricus 

Monograptus riccartonensis 
Cyrlograptus murchisoni. 

The zonal fossils are accompanied by species of Monograptus the most abundant 
forms being allied to Monograptus flemingi. It is the presence of these and of the 




92 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

genus Cyrtograptus, that gives to the Lower Salopian graptolite fauna its distinctive 
features. At certain horizons, where a small amount of calcareous matter is inter- 
calated among the argillaceous sediments, a few species of brachiopods, trilobites 
cephalopods etc. were obtained e. g. Atrypa reticularis, Orthis rustica, Wilsonia 
wilsoni, Chonetes minima, Phacops musheni, Acidaspis prevosti, Orthoceras primae- 
vum, Cardiola interrupta etc. An important result of this detailed zonal work 
was the detection of breaks in the succession due to repeated overlaps produced 
by irregular subsidence or tilting of the area during the deposition of sediment. 
The zones detected in the above areas can be recognized over the greater part of 
Britain where the facies prevails. 

UpperSalopian. TheUpper Salopian graptolitiferous rocks were investigated 
in the Builth and Long Mountain areas of Central Wales and Shropshire, where the 
rocks belong to the non-calcareous facies, and also in the Ludlow district, where 
the limestone bands of the Silurian are represented. Five main zones were established, 
which are characterized by various species of Monograptus, that genus together 
with certain species of Retiolites beeing the only graptolites which survive into the 
Upper Salopian. 

These zones were as follows: 

Zone of Monograptus leintwardinensis 
„ ,, „ tumescens 

,, ,, „ scanicus 

„ ,, „ nilssoni 

vulgaris 

The separation of the Upper from the Lower Salopian of these areas is in general 
arbitrary, as there is no marked change of lithological characters at the boundary 
and many of the graptolite forms are common to both stages. The distinction is 
based upon the absence of the genus Cyrtograptus and Monograptus flemingi and 
its allies from the Upper Salopian together with the presence in that stage of Mono- 
graptus colonus and its allies. Spinose forms of Monograptus are also specially 
characteristic of the upper division; this is probably due to the adverse conditions 
under which the graptolites of that period were maintaining a struggle for existence. 
Only twenty-seven forms of Monograptus and two of Retiolites were recognized. 
These have for the most part an extended vertical range and a limited geographical 
distribution. The zonal divisions are in consequence unevenly developed and some 
of the zones have been detected in only one or two areas. In the highest zone only 
the zonal graptolite and a variety of it have been found, but it happens that these 
have a wide geographical distribution so that the zone has been recognized over 
an extensive area. In addition to the graptolites various shelly fossils occur 
commonly in thin calcareous bands among the argillaceous sediments; they 
consist principally of brachiopods, together with some polyzoa, corals, trilobites 
and cephalopods. 

Relatively few species occur, but they are represented by numerous individuals. 
The brachiopod Dayia navicula is abundant in certain bands and is often associated 
with Spirifer crispus, Scenidium lewisi, crinoid stems and other remains. The 
well known form Pentamerus (Conchidium) knighti was found on one horizon on 
the same slabs of rock with Monograptus leintwardinensis, so that it is impossible 
on palaeontoiogical grounds to separate the Aymestry limestone of which this 
brachiopod is characteristic from the underlying shales. The calcareous bands 
occur less frequently as the strata are traced away from the Ludlow district towards 
the west and north-west. 

Lateral Variation and Conditions of Depositions of the Sa- 
lopian rocks. It will be convenient to trace the variation in lithological 



Jones: Great Britain. — Sedimentary and Volcanic Rock.; — Salopian. (IH. 1 ) 93 

characters and thickness of these rocks as they would present themselves in a 
general traverse from south-east to north-west across the general strike from the 
neighbourhood of Bristol to the south of Scotland. 

Near Tortworth the Salopian rocks are imperfectly rle\; iop>d and consist 
of calcareous mudstones with abundant shelly fossils; they increase in thickness 
towards the May Hill and Malvern ••egions where ?!.° limestone bands and especially 
the lower ones are clearly marked The Lower Salopian is represented by over 
300m. (1000 ft.) of calcareous mn Ties and limestones; the upper by ! Oto 210m. 
of similar rocks. Farther nor'.hw 'Si, o.cu. :• the typical calcareous deve opment of the 
Wenlock-Ludlow area: the Lower stage is composed of a thickness of 450 to 600m. 
(1500-2000 ft.) of calcareous mudstones ; the lowest ( Woolhope) limestone band is poor- 
ly represented. The Upper Salopian has increased to Over 300 m. (1000 ft.), largely 
owing to the great development of its chief calcareous member the Aymestry Lime- 
stone. A fewkilometres to the north-west of this area the calcareous facies dwindles away 
almost completely and gives place to the facies developed along the eastern borders 
of Central Wales (Builth, Long Mountain etc.). The total thickness of sediments 
remains much the same, but the strata consist of shales with arenaceous flagstones 
sometimes containing calcareous matter; some coarser gritty sediments occur 
occasionally in the higher members. Small breaks and overlaps in the succession 
have been detected, proving irregular subsidence and slight tilting of the area 
during deposition. 

This type forms a t.rp- >it>on to that developed in North Walts where the 
Salopian rocks generally have long been known under the name of the Denbigh- 
shire Series. The Lower Salopian has a thickness of about 500 m. (1700 ft.) and 
consists of slates (Pen-y-glog and Moel Ferna) with a band of grits; the slates 
contain principally a graptolite fauna while thi grit has yielded Meristina tumida 
and other shelly fossils. The Upper Salopian lias increased greatly in thickness, 
and is composed of over 900 m. (3000 ft.) of flags, mudstones and sandstones 
containing certain of the characteristic grapl : tes including the highest zonal form 
M. leintwardinensis. Certain shelly fossils Jso occur notably Dayia navienla, 
Cardiola interrupta, Rhynchonella nucula, A- idaspis hughesi, and fine examples of 
Artinocrinus pulcher. The uppermost limit of the Salopian has not been definitely 
fixed but it is believed that representatives of the highest (Downtonian) series 
may occur. 

The North Wales type is developed also in the Lake District; the Lower stage 
(Brathay Flags and possibly the Lower Coldwell Beds) is composed of fine- 
grained flags and some grits containing chiefly a graptolite fauna. The Upper 
Salopian (comprising the Middle and Upper Coldwell Beds, Coniston Grits 
and Bannisdale Slates) has however expanded greatly and attains the enormous 
thickness of nearly 3,600 m. (12,000 ft.) of flags, slates and grits. In these most of the 
zonal forms of graptolites have been observed, including Monograptus leintwardinensis 
or a variety of it; also many of the common Upper Salopian shelly fossils have 
been obtained e. g., Pterinea tenuistriata, Phacops downingiae, Cuculleal cawdori, 
Prolaster miltoni and other forms. . 

The Lake District development marks the greatest thickness of sediments 
met with in the Salopian of Britain; farther north-west Scottish rocks which may 
be referred to the Lower Salopian are developed in the southern uplands (Riccarton 
and Raeberry beds) where they consist of over 900 m. (3000 ft.) of mudstones, 
shales and marls with conglomerates, grits and some limestone nodules; they are 
sparingly fossiliferous but most of the characteristic graptolite forms have been 
obtained from them. In the Girvan district of Ayrshire the Lower Salopian consists 
of flagstones, grits and conglomerates, known as the Bargany and Straiton 



94 (HI. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

beds which attain a thickness of at least 490 m. (1600 ft.) the highest beds being 
concealed by Carboniferous rocks. 

In Lanarkshire and the Pentland Hills the division of the series into stages 
is difficult and the separation of the Salopian from higher Silurian strata has 
not been satisfactorily accomplished. The lower rocks, which may tentatively be 
referred to the Lower Salopian consist of over 600 m. (2000 ft.) of sandstones and grits 
associated with green, red, purple and grey shales and mudstones indicating peculiar 
conditions of deposition; some beds contain eurypterids and starfish. The part 
that may be attributed tentatively to the Upper Salopian consists of about 450 m. 
(1500 ft.) of red and green shales with Platyceras simulans; they have also yielded 
the scorpion Palaeophonus. These are followed by a remarkable set of deposits 
which will be described under the Downtonian. 

The Salopian rocks seem therefore to have been deposited in a trough-like 
area coinciding roughly with that in which the Valentian sediments were laid down ; 
on the margins of the trough the calcareous and argillaceous deposits with shelly 
organisms were formed while the arenaceous materials accumutated near the centre. 
As the transportation of these coarse deposits necessitated strong currents it is pro- 
bable that they were carried in the direction of the trough rather than across its 
margins, where the quiet and comparatively clear waters necessary for the formation 
of the argillaceous and calcareous deposits prevailed. The whole area of deposition 
must have been slowly sinking the central parts more quickly than the margins. 
It is probable also that the boundaries of the marine area were being uplifted con- 
currently with the subsidence of the trough. In Lanarkshire and some other parts of 
Scotland the area of deposition seems to have been at times under lagoon conditions 
with still water and rapid evaporation resulting in the formation of red and green 
shales and marls closely resembling those of the Devonian. 

3. The Downtonian Series. The rocks of this series have a relatively limited 
distribution at the surface, and are only found in certain regions, either forming 
a fringe along the base of the Old Red Sandstone, or emerging from beneath an 
unconformable cover of later deposits. They may have been deposited over much 
of the Silurian area and have since been removed; some evidence of this has been 
obtained in North Wales, where fossiliferous pebbles of undoubted Downtonian 
rocks resembling those of the Lake District were obtained in the conglomerates 
at the base of the Carboniferous rocks and appear to have been derived from the 
denudation of the highest Silurian sediments. On the other hand the some- 
what peculiar and variable characters of the rocks render it possible to 
suppose that they may have had originally a restricted distribution. The typical 
development of the series is that of the Ludlow district, where it has been exhaus- 
tively studied by Miss Elles and Miss Slater (1906). 

The classification of these rocks which immediately overlie the Aymestry 
Group is there as follows: 

Temeside Group \T QmesideShSilesv/ithLingulacornea^ Eurypterus 
[stage] JDownton-Castle Sandstones withLingula minima 

UpperLudlowGroupfUpper Whitcliffe Flags with Chonetes striatella 
[stage] JLowerWhitcliffeFlags withRhynchonella nucula 

The fossils mentioned are those which occur most abundantly, and are not 
necessarily confined to the beds with which they are linked. 

TheWhitcliffeFlags consist of highly fossiliferous calcareous blue or olive- 
green flags and shales which attain a maximum thickness of 85m. (280 ft.). In addition 
to the fossils mentioned above Orthis lunata, Spirifer elevatus, Goniophora cymbae- 



Downtonian 

Series. 



Jones: Great Britain. — Sedimentary and Volcanic Rocks. — Downtonian. (III. 1.) 95 

formis, Orthonota amygdalina, Pterinea retroflexa, Orthoceras bullatum, Homalonotus 
knighti and Beyrichia kloedeni occur abundantly; Pterygotus problematicus has also 
been obtained from these beds. At the top is the well-known Ludlow Bone-bed which, 
though only reaching a maximum thickness of about 15 cm. (6 inch.) and is frequently 
scarcely more than a centimetre, has been observed at numerous localities and appears 
to cover a wide area. It is composed of a mass of minute brown or black organic 
fragments firmly compressed together and cemented by relatively small amounts 
of calcite and ferruginous material. The organic remains are those of fishes, Crustacea, 
Brachiopoda and perhaps Annelida; they are to some extent rolled and worn. Small 
coprolites also occur. Onchus murchisoni, and other fishes are represented by 
spines, while Pterygotus, Leperditia and other Crustacea occur as small fragments. 
Besides this well-known bed, other bone-beds have been recognized in the area 
containing somewhat different fossils. 

The Downton Castle Sandstones consist of massive yellow sandstones 
associated with micaceous sandstones and shales, they have a maximum thickness of 
about 15 m. (50 ft.) and are only sparingly fossiliferous. Near the base and only sepa- 
rated from the Ludlow Bone-bed by about a metre (3 ft.) of unfossilifereous beds is a 
band containing abundant Platyschisma helicites and Modiolopsis complanata which 
passes laterally into another bone-bed (Downton Bone-bed), containing organic 
remains similar to those of the former with Thelodus parvidens and the small seed- 
like plant-remains known as Pachytheca sphaerica. At a higher level occurs another 
layer of coarsely micaceous friable sandstone full of fish fragments belonging to the 
cephalaspid species Eukeraspis pustulifera and the Acanthodian genus Climatius. 
This band may be described as another bone-bed and like the others varies much 
in texture and thickness within short distances, but it does not seem to be present 
everyhere over the area. 

The Temeside shales form the highest members of the Silurian and con- 
sist of grey, greenish and olive shales with thin sandstones; they have a maximum 
thickness of 36 m. (120 ft.). They contain small indeterminate lamellibranchs and 
Lingula cornea occurs fairly commonly. In the upper portion of these shales is the 
Temeside Bone-bed which is a grey micaceous carbonaceous grit, in which fragments 
of bone and fish-spines are disseminated; it is coarser than, and very different in 
appearance from, the Ludlow Bone-bed. It yielded two species of Pterygotus, two 
species of Onchus, and abundance of Pachytheca sphaerica. 

The uppermost bed referred to the Silurian is a grey micaceous grit at 
the top of which is a layer crowded with carbonaceous fragments but in which 
bones are rare Onchus having been recognized together with Pachytheca, Leperditia 
and Lingula cornea. The succeeding beds are purple-red sandstones with shaly 
partings, which differ in lithology from anything below and are considered to 
belong to the Old Red Sandstone. 

It is doubtful whether the detailed subdivisions established in the Ludlow 
district could be recognized far from that area though it is probable that the major 
groups will be identified approximately. 

Lateral variations and conditions of deposition of the Down- 
tonian Series. When traced to the south-west into South Wales the highest 
Silurian rocks pass into sandstones with subordinate shales. Some of the sand- 
stones are highly micaceous and split up into thin flags which have been used 
extensively in the locality for roofing, and are known as Tilestones. Many of 
the fossils of the Ludlow district occur; the prevailing forms are thick-shelled lamelli- 
branchs and certain gastropods, Orthonota amygdalina and Holopella gregaria being 
the most characteristic. The various divisions thin out gradually westward prob- 
ably due in part to repeated overlap within the series, and ultimately the highest 



96 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

members become concealed by overstep at the base of the Old Red Sandstone. 
The rocks occupying the position of the Downtonian series when the Silurian rocks 
emerge from beneath the Old Red Sandstone in South Pembrokeshire consist of 
massive greenish sandstones with very scanty organic remains, Lingula and traces 
of other horny brachiopods being the only fossils that occur. 

It is probable that Downtonian rocks fringe the Old Red Sandstone of eastern 
Wales, as a great thickness of brown shales with flagstones and sandstones succeeds 
the graptolitic deposits of the Salopian but no details are available in regard to 
their lithological and faunal characters. 

In North Wales also it is possible that the highest portion of the Denbighshire 
Series belong to the Downtonian though this has not been satisfactorily proved. 

An important development of the series occurs in the Lake District where over 
600 m. (2000 ft.) of greenish and grey sandstones and flags known as the Kirkby 
Moor Flags represent the higher Silurian rocks. The series is not complete owing 
to the overstep at the base of the unconformably overlying Carboniferous rocks. 

The thin calcareous bands among the arenaceous sediments yield abundant 
fossils such as Lingula cornea, Chonetes striatella, Orthonota amygdalina, Grammysia 
cingulata, Holopella gregaria, Orthoceras ludense, Lituites ibex and numerous others. 

These fossils make it clear that the Kirkby Moor Flags represent only the 
lower portion of the Downtonian as developed at Ludlow for not only are the above 
forms characteristic of the Whitcliffe Flags of that district but there is an entire 
absence in them of the bone-beds and Eurypterus-be&ring strata which are so 
marked a feature of the higher or Temeside stage. It is obvious that as in the 
case of the preceding series the Downtonian has expanded greatly in thickness in 
this region. 

In Scotland strata referred to the Downtonian occur at the top of the Silurian 
sequence in Lanarkshire and the Pentland Hills south of Edinburgh. They attain a 
thickness of over 600 m. (2000 ft.) and consist of red, chocolate-coloured and yellow 
sandstones, mudstones and shales with some conglomerates, the red colours predo- 
minating towards the top. On account of these characters they were at one time 
assigned to the Old Red Sandstone but they are separated by an unconformity 
from that formation. One of the bands of shale yielded some years ago numerous 
remains of fish and Merostomata; many of the genera of fish were new and of great 
interest; the genus Thelodus which occurs abundantly in the higher bone-beds of 
the Ludlow district is represented by T. scoticus. The Merostomata include species 
of Eurypterus and Stylonurus; the phyllocarids Dictyocaris and Ceratiocaris 
and the myriapod Archidesmus also occur. Sandstones and shales referred to the 
Downtonian also occur near Stonehaven, where they rest unconformably on the 
Cambrian and pass up into the Lower Old Red Sandstone; they have yielded 
Cyathaspis, Dictyocaris, Ceratiocaris, Merostomata and Archidesmus. They are 
associated with volcanic rocks. The Downtonian were formed during the final stages 
in the filling of the Silurian trough of deposition and it is possible that parts of the 
area of deposition were separated off from others or even from connection with the 
open sea and were thus converted into isolated basins where an approach to con- 
tinental conditions prevailed. This would probably account for the incoming of 
red and green sediments which are usually associated with continental conditions. 
There is in some areas evidence of earth-movements having occurred immediately 
after the deposition of these rocks and before the formation of the Old Red Sand- 
stone; it is probable also that in other regions farther south slow movements of 
uplift were in progress during the closing stages of the Silurian, leading to the 



Jones: Great Britain. — Sedimentary and Volcanic Rocks. — Downtonian. (III. 1.) 97 

great Caledonian earth-movements which closed the period in Britain. The trend 
of these movements from north-east to south-west is approximately the same as 
that of the Silurian trough of deposition. This is probably not an accidental coinci- 



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Handbuch der regionalen Geologic III. 1. 



98 (Ill.-i.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 



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Jones: Groat Britain. — Sedimentary and Volcanic Rocks. (HI. 2.) 99 




100 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

II. Intrusive Igneous Roeks. 

By Alfred Harker. 

Newer Granite group of Scotland. 

There is a great group of igneous intrusions which may be assigned to an 
epoch slightly earlier than that of the lowest Old Red Sandstone. These rocks are 
known in the Scottish Highlands by the name of the "Newer Granites", although 
they are not all of acid composition. They are younger than the great crust-move- 
ments and foliation of the region ; but, on the other hand, pebbles of some of them 
are found in the conglomerates of the Lower Old Red Sandstone. The largest masses 
occur in the neighbourhood of the Dee valley (counties of Aberdeen and Kincardine 
with parts of Forfar and Perth), but others farther north in Sutherland and Caithness 
and to the westward through the county of Inverness. Their distribution is indicated 
on the map (fig. 27). Some of the masses have a general stratiform habit, though 
with much irregularity in detail, and this seems to be true of some very large bodies, 
such as that which makes the Cairngorm Mountains. Others have apparently an 
abrupt boss or stock-form. According to Barrow, all these intrusions in the High- 
lands, breaking through strata already highly metamorphosed, have produced in 
them very little change. 

Petrographically the rocks of the "Newer Granite" group are largely biotite- 
and hornblende-granites and quartz-diorites; but there are also more acid 
granitic rocks and on the other hand numerous basic diorites and some peri do t- 
ites. At many of the centres rocks of different kinds are intimately associated in 
"plutonic complexes". There the more acid types usually prevail, and occupy 
especially the central area, while the more basic varieties occur on the border. There 
is sometimes a gradual transition, sometimes a sharp boundary, between the different 
associated rocks. Wherever a definite sequence can be detected, the more acid 
type is of later intrusion than the more basic. 

On the borders of Caithness and Sutherland intrusions belonging to this 
group range from acid to ultrabasic, including the typical 'scyelite' of Judd. In 
Sutherland masses of hornblende-granite occur also at Beinn Laoghal, Lairg, and 
elsewhere. In Nairn and the north-eastern part of Inverness there are granitic and 
other intrusions at Loch Moy, Abriachan, Stratherrick (quartz-diorite) and other 
places. In Banffshire intrusions at Ben Rinnes and elsewhere show an intimate 
association of quartz-diorite with biotite-granite, veined by muscovite-granite and 
pegmatite. A smaller boss at Netherley is of diorite with variable composition, 
more basic in the centre. In the north-eastern part of Aberdeenshire considerable 
masses of biotite-granite occur at Pitsligo and Peterhead, and numerous large intrusive 
masses, younger than the main crust-movements, are scattered along a belt of 
country extending south-westward from here nearly across Scotland. The complex 
west of Ellon includes not only diorites, but gabbros and norites, and there are ultra- 
basic as well as basic rocks in the ridge at Belhelvie. The large masses of Hill of 
Fare, Kincardineshire, Lochnagar, and Cairngorm are mainly of biotite-granite, 
sometimes graduating into quartz-diorite, and there are slightly earlier intrusions 
of basic diorites. The complex of Glen Tilt and Beinn Dearg, in Perthshire, includes 
basic diorites and granites. Near the head of Loch Linnhe is the basic diorite of 
Glen Loy, intersected by the granite (containing some muscovite) of Banavie. Other 
rocks in the West of Scotland assigned to this group are the quartz-diorite of Stron- 
tian, at the head of Loch Sunart, and the biotite-granite which makes the south- 
western promontory of the Isle of Mull. At Garabal Hill, near the head of Loch 
Lomond, is a complex including periodite, augite- and mica-diorites, tonalite, and 



Harker: Great Britain. — Intrusive Igneous Rocks. (III. 1.) 101 



hornblende- and biotite-granites (Dakyns and Teall 1892). Another plutonic com- 
plex is found at Cam Chois, N. of Comrie, in Perthshire. 




SgOTUfflS 



English Miles 



5 to zo 30 +o 

Kilometres 
o io 20 jo to so to 



Fig. 27. Map to show the distritution of tlie Newer Granitesof Scotland andof 

the volcanic and plutonic rocks of Lower Old Red Sandstone age ( Alfbed Harker). 

The plutonic intrusions are indicated in black and the volcanic districts by stippled areas. 

In the South of Scotland occurs the important set of the 'Galloway Granites', 
which break through Lower Palaeozoic strata, and have caused important meta- 



102 (III. 1.) The British Isles. — III. Stratigraphy. — 4. Gothlandian or Silurian. 

morphism. There are three chief masses: the Loch Dee intrusion of tonalite, with 
some quartz-hyperites and quartz-augite-diorites on its margin; that of Cairnsmore 
of Fleet, mainly of biotite granite ; and that of Crif fel, of the tonalite type, with 
oligoclase as the dominant felspar (Geol. Surv. 1899, pp. 607 — 25). Some smaller 
intrusions occur in other places, e. g. in the Lammermuir Hills, in the South-East 
of Scotland, but it is not possible to distinguish in every case these earlier intrusions 
from those of true Lower Old Red Sandstone age. The intrusion of Oatland, in the 
Isle of Man (p. 76), may not improbably be assigned to the 'Newer Granite' group. 

In many parts of the Scottish Highlands there are minor intrusions, mostly 
dykes, which are to be regarded as satellites of the 'Newer Granites', and similar 
dykes accompany the Galloway intrusions. They are petrographicaJly like the 
minor intrusions of the Old Red Sandstone age itself, to be noticed below, the common 
types being porphyrites, more acid felsites, and various lamprophyres 
(minette and spessartite). 

The acid volcanic rocks in the Downtonian of Stonehaven (see p. 96) and 
others of similar character found at Rhynie may possibly be connected with these 
intrusives. 



Bibliography of the Gothlandian or Silurian of Great Britain. 

1913. Campbell, R., Trans. Roy. Soc. Edinb., vol. 48, pp. 923-960 (Stonehaven). 

1892. Dakyns, J. R. and Teall, J. J. H., Quart. Journ. Geol. Soc, vol. 48, pp. 104-121 

(Garabal Hill and Meall Breac). 
1900. Elles, Miss G. L., Quart. Journ. Geol. Soc, vol. 56, pp. 370-414 (Welsh Border). 

1906. — and Slater, Miss J. L., Quart. Journ. Geol. Soc, vol. 62, pp. 195-222 

(Ludlow District). 

1908. Groom, T. T. and Lake, P., Quart. Journ. Geol. Soc„ vol. 64, pp. 546-537 (Glyn 

Ceiriog). 

1909. Jones, O. T., Quart. Journ. Geol. Soc, vol. 65, pp. 463-537 (Plynlimon and Pont 

Erwyd). 
1912. — Quart. Journ. Geol. Soc, vol. 68, pp. 328-344 (Central Wales and Adjoining 

Regions). 
1895. Lake, P., Quart. Journ. Geol. Soc, vol. 51, pp. 9-23 (South Denbighshire). 

1893. — and Groom, T. T., Quart. Journ. Geol. Soc. vol. 49, pp. 426-440 (Corwen). 
1878. Lapworth, C, Quart. Journ. Geol. Soc, vol. 34, pp. 240-346 (Moffat). 
1879-1880. — Ann. Mag. Nat. Hist., ser. 5, vol. 3, pp. 245-257, 449-455, vol. 4, pp. 333-341, 

423-431. vol. 5, pp. 45-62, 273-285, 358-369, vol.6, pp. 16-29, 185-207 (Di- 
stribution of Rhabdophora). 
1882. — Quart. Journ. Geol. Soc, vol. 38, pp. 537-666 (Girvan). 

1900. Lapworth, H., Quart. Journ. Geol. Soc vol. 56, pp. 67-137 (Rhayader). 
1892. Marr, J. E., Geol. Mag., pp. 534-541 (Lake District). 

1888. — and Nicholson, H. A., Quart. Journ. Geol. Soc, vol. 44, p. 654-732 (Stock- 
dale Shales). 

1901. Morgan, C. LI. and Reynolds, S. H., Quart. Journ. Geol. Soc, vol. 57, pp. 267-284 

(Tortworth Inlier). 
1839. Murchison, R. I., Silurian System. 
1867. — Siluria, 4 th. Ed. 

1899. Peach, B. N. and Horne, J., (with notes by J. J. H. Teall), Mem. Geol. Surv., 

Silurian Rocks of Britain, vol. 1. Scotland. 

1907. Reynolds, S. H., Quart. Journ. Geol. Soc, vol. 63, pp. 217-240 (Mendips). 
1912. — Rep. Brit. Assoc, for 1911, p. 381 (Mendips) 

1854. Salter, J. W. and Aveline, W. T., Quart. Journ. Geol. Soc, vol. 10, pp. 62-75 
(Shropshire). 

1853. Sedgwick, Quart. Journ. Geol. Soc, vol. 9, pp. 215-230 (May Hill Sandstone). 

1911. Wade, A., Quart. Journ. Geol. Soc, vol. 67, pp. 415-459 (North-Eastern Mont- 
gomeryshire). 

1885. Watts, W. W., Quart. Journ. Geol. Soc, vol. 41, pp. 532-546 (Breidden Hills) 

1900. Wood, Miss E. M. R. (Mrs. G. A. Shakespear), Quart. Journ. Geol. Soc, vol. 56 

pp. 415 — 492 (Lower Ludlow). 
1906. — Quart. Journ. Geol. Soc, 62, pp. 644-701 (Tarannon). 



Cole: Ireland. (III. 1.) 103 

b. Ireland. 
By G. A. J.Cole. 

Gothlandian rocks of the Llandovery stage have been represented on the 
Geological Survey maps of Co. Dublin and Co. Meath since 1901, occupying a consi- 
derable area between the Boyne and Skerries. C. I. Gardiner (1899) traced beds 
of Llandovery and Wenlock age, 700 m. (2300 ft.) thick, above Bala lavas and ashes, 
on the coast north of Balbriggan. The Llandovery beds contain fossils of the Mono- 
graptus gregarius and spinigerus zones of the Birkhill Shales; the age of the beds 
styled Wenlock rests on the presence of a form closely resembling Monograptus 
riccartonensis. It is believed that the grits of Dunmurry, on the south-east of the 
Kildare Ordovician inlier, may be of Llandovery age. 

The uplifted regions of Gothlandian shales, slates, and sandstones forming 
the cores of the Armorican ranges of southern and central Ireland have been already 
referred to when similar Ordovician inliers were discussed. A notable area is exposed 
in the west of the Dingle Promontory in Co. Kerry, where Llandovery, Wenlock, 
and Ludlow beds are well represented along the sea-coast, and at several points 
inland. The Llandovery and Wenlock series, which are here not easily separated 
by their fossils, contain numerous rhyolitic lava flows and ashes, and also andesitic 
tuffs. The ashes continue into the Lower Ludlow stage (Geol. Surv. 1863; Gardiner 
and Reynolds 1902). The debatable Dingle Beds have been generally held to 
succeed the Ludlow, but A. McHenry (1912) made the striking suggestion that they 
are identical with the "Smerwick Beds" of the north side of the Dingle promontory, and 
should, like those beds, be regarded as of Llandovery age (see p. 131). In the region 
round Killary Harbour, there is a local unconformity between the Ordovician and 
Gothlandian, and Bala beds may be absent; but the Owenduff series of grits and con- 
glomerates, above the Mweelrea Grits, is of Llandovery to Wenlock age. Highly 
fossiliferous sandstones, corresponding with it, and containing Pentamerus oblongus, 
occur in the lowland to the north at Cregganbaun. J. R. Kilroe found a zone of 
Wenlock ( ? Llandovery) age, rich in corals, high up on the south side of Croagh Patrick, 
among rocks previously regarded as Dalradian. South of Killary Harbour, Llan- 
dovery, Wenlock, and Ludlow sandstones and slates overstep the Dalradian schists 
(Carruthers and Maufe 1909; Kilroe 1907). 

Near Pomeroy, in Co. Tyrone, the Ordovician rocks pass up into Llandovery 
flagstones and shales, with Diplograptus vesiculosus, Dimorphograptus confertus, 
Monograptus sedgwicki, M. triangulatus and numerous other species of Monograptus 
An unf ossiferous series above may represent the Tarannon beds (Fearnsides, 
Elles and Smith 1907). Monograptus was recorded here by Portlock (1843). 

The upland country that spreads north-east from Longford to the coast of 
Co. Down is largely composed of Gothlandian shales and sandstones. The rocks 
are greatly crumpled, and Ordovician inliers appear, as in southern Scotland, on 
the crests of anticlinals here and there. Graptolites of Lower Llandovery (Birkhill 
and Gala) age have been described from Coalpit Bay near Donaghadee in Co. Down, 
and from other places (Swanston and Lapworth 1876-7). 

R. Clark (1902) has added some new localities, and has recorded the early 
plant Berwynia carruthersi from the Llandovery beds of Coalpit Bay. 

The Gothlandian sea spread somewhat farther than the Ordovician; but 
there is no evidence that it passed across the whole Dalradian land. Beach-con- 
ditions are observable in the north of Co. Galway. A volcano manifested itself 
near Dingle in the sea that covered the whole of southern Ireland, and subsidence 
seems to have continued here at the close of Ludlow times, possibly as a consequence 
of the local weakening of the crust during the Wenlock epoch. 



104 (III. 1.) The British Isles. — III. Stratigraphy — 5. Devonian. 

Economic Products. 

Slate. Though it is difficult to rival the slates of N. Wales, good green slates 
are raised from Silurian strata at Clashnamuth near Carrick-on-Suir, and at Kilmo- 
ganny in Co. Kilkenny. Quarries are also worked in the Silurian slates of Killaloe 
on the lower Shannon. 

Clay. The Ordovician shales near Waterford have been successfully crushed 
into a clay for brickmaking. 

Road-metal. The basic intrusive rocks in the Silurian areas are commonly 
used for road-metal. 

Bibliography of the Gothlandian or Silurian of Ireland. 

1909. Carruthers, R. C. and Maufe, H. B., Irish Naturalist, vol. 18, pp. 7-11 (Killary). 

1903. Clark, R., Rep. Brit. Assoc, 1902, pp. 599-601 (North-East Ireland). 

1902. — Geol. Mag., pp. 497-500 (North-East Ireland). 

1907. Fearnsides, W. G., Elles, Miss G. L., and Smith, B., Proc. Roy. Irish Acad., 

vol. 26, Section B, pp. 97-128 (Pomeroy). 
1899. Gardiner, C. I., Geol. Mag., pp. 398-402 (Balbriggan, Drogheda Bay). 
1902. — and Reynolds, S. H., Quart. Journ. Geol. Soc, London, vol. 58, pp. 226-266 

(Clogher Head District, County Kerry). 
1907. Kilroe, J. R., Proc. Roy. Irish Acad., vol. 26, Section B, pp. 129-160 (Mayo and 

North Galway). 
1912. McHenry, A., Proc. Roy. Irish Acad., vol. 29, Section B, pp. 229-234 (Dingle 

Beds). 
1843. Portlock, J. E., Mem. Geol. Surv., Report on the Geology of the County of 

Londonderry and parts of Tyrone and Fermanagh. 
1876. Swanston.W. and Lapworth, C, Proc. Belfast Nat. Field Club. Appendix, p. 107 

(County Down). 

Geological Survey. 

Explanatory Sheet Memoir to accompany Sheets: 

160, 161, 171, and part of 172. Part of County Kerry (J. B. Jukes and 
G. V. Du Noyer). 1863. 
See also Portlock, J. E. 

5. Devonian. 

a. Great Britain. 

I. Sedimentary Rocks. 

By John W. Evans. 

A. South Devon and Cornwall. 

On the south of the wide syncline that traverses the county of Devon 
the rocks have been thrown, under the influence of powerful pressure from the 
south and south-east, into numerous plications, which often pass at the apex into 
thrusts; while minute disturbances of the same character give rise to a "thrust 
cleavage" which has to a large extent obliterated the original lamination of the rock. 
The bedding is frequently difficult to discover, except when it is revealed by bands 
of different composition, or lava flows, and the apparent thickness of the rock is 
increased by its plicated state. The geological structure, and the nature of the 
succession must therefore often be inferred from a comparison with less altered 
localities, or ascertained by fossil evidence. The lithological character is however 
not sufficiently persistent to constitute a safe guide, and all traces of organisms 
are frequently destroyed by cleavage, or the metamorphic action of great masses of 
granite. Where the structure can be satisfactorily determined, it is usually found 



Evans: Great Britain. — Sedimentary Rocks. — South Devon, Cornwall. (III. 1.) 105 

that the major flexures are essentially simple, though complicated by powerful 
dip and strike faults and overthrusts. 

The lowest Devonian beds which have at present been recognised in this area 
are the Dartmouth Slates, consisting of pink, purple and green slates with grit- 
beds and more or less calcareous bands. They outcrop in an anticline crossing the 
southern projection of Devonshire in an east and west direction, and appear again at 
Rame Head in East Cornwall beyond Plymouth Sound with a west-south-west strike, 
which carries them out to sea, only to be brought back more than once within the 
coast line by powerful oblique faults. As the St. Austell granite boss is approached, 
they are faulted out of sight, but emerge to the north-west of the granite in an anti- 
clinal dome, intersected by the coast at Watergate Bay. Their relations with 
older rocks is still uncertain. 

With the exception of Bellerophon trilobatus Sow. and Loxonema, which 
are confined to the South Coast, the Dartmouth slates have yielded only a fish 
fauna of Lower Old Red Sandstone facies, including Pteraspis cornubica M'Coy, 
Cephalaspis carteri M'Coy, spines, coccostean plates and on the North Coast 
Phlyctaenaspis, Climatius and Parexus. 

The Dartmouth slates are overlain conformably by the Meadfoot Beds 1 . 

The base consists of slates with arenaceous bands, and contains no fossils, 
but the slates with sandy and siliceo-calcareous bands which succeed have yielded 
a marine fauna, though Pteraspis is still found. The fossils reported to occur in- 
clude Rhynchonella pengelliana Davidson, Rh. papilio Krantz, Spirifer hystericus 
Schloth., Sp. primaevus Stein., Sp. subcuspidatus Schnur, Rensellaeria strigiceps 
RQmer, Orthis circularis Sow., 0. personata Zeiler, 0. vulvaria Phill., Orthotetes 
umbraculum Schloth., Stropheodonta gigas M'Coy, Atrypa aspera, Schloth., 
Bellerophon trilobatus Sow., Pleurotomaria cancellata Phill., Alveolites labecheiMiLnv- 
Edwards, Pleurodictyum problematicum Goldf., Phacops ferdinandi Kayser, Neri- 
topsis cornubicus Upfield Green (a fossil of uncertain affinities) and Lodanella mira 
Kayser. These may however represent more than one horizon. 

The higher Meadfoot Beds of the Paignton and Torquay anticlines contain 
a somewhat different fauna, including Chonetes sarcinulata Schloth., Rhynchonella 
daleidensis F. Romer, Spirifer hystericus, Sp. paradoxus Schloth. and Pterinea 
costata Goldf. 

It is believed that strata of Meadfoot age are also represented in the meta- 
morphic aureole of the St. Austell granite and on the shores of St. Austell Bay, 
and extend to the north-west coast on both sides of the anticline of Dartmouth 
Slates. 

West of St. Austell Bay and south of the rocks last described is a great tract 
of almost unfossiliferous strata, known as "killas" by the miners, which have been 
mapped as the Manaccan or Grampound Grit 2 , and Portscatho, Falmouth and Mylor 
Series, but their relations and the question to what extent they are of Devonian 
age are still in dispute (Hill 1906, 1912, 1913; Green 1908, 1912, 1913). On 
the south they are in contact with rocks shattered by thrust faulting and con- 
taining Ordovician and Silurian fossils. 

The Meadfoot Beds are is succeeded by the Staddon Grits, consisting mainly 
of reddish grits and sandstones with associated shales and slates. They are usually 
placed in the Lower Devonian, but at Warberry Hill in the Torquay anticline the 
rocks attributed to this series are stated to contain Spirifer cultrijugatus F. Homer and 

1 Near Start Pont the Meadfoots are faulted against crystalline schists (see 
p. 33), believed by some authors to be of Devonian age. 

2 Recently an Orthis allied to O. personata Zeil. of the Siegener Grauwacke but 
more coarsely costate has been described from the Grampound Grit (Thomas 1912). 



106 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian, 

Orthotetes umbraculum Schloth., the former suggesting the base of the Middle 
Devonian 1 . The Staddon Grits also outcrop on the north of the anticlinal axis that 
traverses the south of Devon, reappear in the Staddon Heights on the shores of 
Plymouth Harbour, and continue through Cornwall, passing north of the St. Austell 
Granite to the North Coast, where they form the Denzil Downs and the cliffs of 
Trenance Point. 

At a higher horizon are the dark grey slates of Daddyhole near Torquay 
with Calceola sandalina Lamk., Pentamerus biplicatus Schnur, and Cyrtia whid- 
bornei Davidson. Calceola is also found in the shaly limestones overlying the 
slates in the same neighbourhood, but not in the dark slaty limestone of Hope's 
Nose, where Cyathophyllum heterophyllum Frech, Heliolites porosa Goldf., Athyris 
rugata David son, Atrypa aspera Schloth., Kayseria lens Hall, Pentamerus biplicatus 
Schnur, Productella subaculeata Murch, Rhynchonella parallelepipeda Bronn, Rh. 
procuboides Kayser, Orthotetes umbraculum Schloth., and Spirifer curvatus Sow. are 
met with. The more massive limestones in the same neighbourhood are charac- 
terized by Heliolites porosa Goldf., Cystiphyllum vesiculosum Goldf., Striatopora 
cristataBhVMEHB., and, atLummatonHill, the Upper Devonian coral, Phillipsastraea 
hennahi Lonsd. Here the upper portion is locally replaced by a shelly limestone 
containing numerous fossils, including Orthoceras robertsi Whidb., Macrochilina 
arcuata Schloth., Holopella tenuisulcata Sandb., Bellerophon lineatus Goldf., 
Conocardium clathratum d'Orb., Actinopteria texturata Phill., Stringocephalus 
burtini Defr., Merista plebeia Sow., Retzia longirostris Kayser, Spirifer ver- 
neuili Murch., Sp. undiferus F. Romer, Sp. nudus Sow., Cyrtina heteroclyta Defr., 
Atrypa aspera Schloth., A. flabellata Goldf., Pentamerus breviroslris Phill., 
Rhynchonella acuminata Martin, Rh. pugnus Martin, Rh. cuboides Sow., Orthis 
striatula Schloth., 0. eifeliensis de Vern., Orthotetes umbraculum Schloth., 
Stropheodonta interstrialis Phill., and Productella subaculeata Murch. The shells 
were probably deposited in hollows worn by marine currents in the limestones. 

Thick beds of strongly cleaved crystalline limestone also occur in the neigh- 
bourhood of Plymouth. It is largely made up of stromatoporids and corals inclu- 
ding Stromatopora concentrica Goldf., Acervularia goldfussi de Vern., Heliophyllum 
helianthoides Goldf., Cystiphyllum vesiculosum Goldf., Calamopora goldfussi d'Orb., 
Pachypora cervicornis Blainv., Heliolites porosa Goldf., Phillipsastraea hennahi 
Lonsd., Pleurodictyum problematicum Goldf., accompanied by Stringocephalus 
burtini Defr., and other brachiopods, nearly all of which are found at Lummaton. 

Though usually described as Middle Devonian, the Torquay and Plymouth 
limestones may equally well be referred to the base of the Upper Devonian. 

No continuous succession of the Upper Devonian is known, but at Saltern 
Cove near Torquay the Budesheimer Schiefer are represented by mudstones with 
nodular and lenticular limestone, which have yielded: Tornoceras auris Quenst., 
T. simplex v. Buch, T. ausavense Stein., Gephyroceras orbiculum Beyr., G. 
calculiforme Beyr., Orthoceras schlotheimi Quenst., Pleurotomaria turbinea Stein., 
and Buchiola retrostriata v. Buch; and the horizon of the Adorfer Kalk occurs at 
Petit Tor Combe, Ilsham and Lower Dunscombe (near Chudleigh) as a shaly 
limestone with Manticoceras intumescens Beyr. and Beloceras multilobatum Beyr. 
Red and green slates with Entomis serratostriala Sandb., and Posidonomya venusta 
Munst. are found in a number of localities in South Devon and appear to occupy 
a still higher position. 

The succession in Cornwall above the Staddon Grits cannot be exactly 
correlated with that in South Devon. There is, in the first place no really 



1 Other rocks in the same neighbourhood contain Meadfoot fossils though litho- 
ogically similar to the Staddon Grits. 



Evans: Great Britain. — Sedimentary Rocks. — South Devon, Cornwall. (III. 1.) 107 

satisfactory palaeontological evidence for the occurrence of Middle Devonian 
rocks in Cornwall. The slates mapped as of that age have yielded near Bedruthan 
Steps on the north coast Pteroconus mirus Hinde, of uncertain affinities, Pachy- 
pora reticulata Blainv., Palasteriscus devonicus Sturtz, Polypora ripisteria Goldf., 
Orthis arcuata Phill., Orthoceras aff. cochleiferum Sandb., as well as fish remains, 
referred by Dr. Smith Woodward to the typically Lower Devonian Pteraspis 
and Climatius; and the whole assemblage might be of that age. At Porthcothan to 
the north-east, on the other hand, the fossils include Conularia complanata Slater, 
var., Asteropyge punctata Salter non Stein., Phacops cf. granulatus Munst., Ph. 
latifrons Bronn, and, in the same neighbourhood, Orthoceras robertsi Whidb.; a 
fauna which might be Upper Devonian. The occurrence, however, of Kophinoceras 
at Cant Hill on the north of the Biver Camel suggests the occurrence of Middle 
Devonian rocks at that locality. 

Further to the north-east the Upper Devonian is well exposed in the cliffs 
on both sides of Padstow Harbour. It is strongly cleaved but lies in gentle undu- 
lations striking a little south of east. Near Tintagel it is highly metamorphosed 
by a concealed extension of the Bodmin Moor granite. The following horizons 
have been described but the succession is not in every case free from doubt. 

7. Pale greenish-grey slates of Bounds Cliff with salmon-coloured bands of thin 
grits and lenticles of lava. 

6. Purple and green slates of Daymer Bay with Posidonomya venusta Munst., 
Tentaculites, Trimerocephalus anophthalmus Frech, Phacops latifrons Bronn, 
and Entomis serratoslriata Sandb. ; metamorphosed near Tintagel into the Tredorn 
Phyllites. 

5. Thin black slate, the Trembley Cove Beds of the Tintagel area. 

4. Pillow lava. 

3. Blue black soft slate of Daymer Bay with Chonetes hardrensis Phill., Modiella 
pygmea Conr., Orthoceras commutatum C- G. Giebel and Tornoceras cf. auris 
Quenst., represended by the Barra Nose Beds near Tintagel. 

2. Grey slate of Port Quin with Allorisma concinna, I. Thomas, Buchiola retro- 
striata? v. Buch, several species of Cheiloceras including Ch. Verneuili Munst., 
Trimerocephalus pentops I. Thomas and small gastropods (= Nehdener Schiefer). 

1. Striped calcareous grey slates containing: at Dinas Head, black chert with radio- 
laria and silicified Phillipsaslraea; in Trevone Bay, Buchiola relrostriata v. Buch, 
Styliola, Tentaculites, Anarcestes lateseptatus Beyr., Tornoceras simplex v. Buch, 
Cheiloceras globosum Munst., Mimoceras compressum Beyr. and Trimerocephalus 
trinucleus Thomas = T.laevis Salter,? Munst. (= Biidesheimer Schiefer); in 
Booby's Bay, Buchiola retrostriata v. Buch, Tentaculites, Conularia complanata 
Slater var. and Anarcestes cf. noggerathi v. Buch and seams of black grit 
and phosphatic nodules enclosing Conularia, which are found also in the imme- 
diately underlying similar but less calcareous beds, south of Treyarnon Point. 

The base of the grey slates is obscured by sand, but in the metamorphosed area, 
where they are represented by the Woolgarden Phyllites, they rest on grey-green and 
blue-grey slates passing laterally into mica schist. The former yield near Delabole a 
large variety of Spirifer verneuili Murch., and fish remains resembling Psammosteus. 

Inland no continuous definite succession can be made out, but the occur- 
rence of the pillow lava affords an indication of the geological structure, the main 
outcrop extending south-eastward to similar volcanic rocks near Plymouth (vide 
p. 126), which, however, are usually considered to belong to a lower horizon. 
In the valley of the Tamar the highest strata of the North Coast are represented 
near South Petherwin by greenish calcareous slates, and limestone, succeeded by 
massive sandstone, blue slates and calcareous sandy shales. The fossils include: 
Phacops latifrons Bronn, Ph. granulatus Phill., Proetus dunhevidensis Thomas, 
Asteropyge punctata Salt., Tornoceras lineare Munst., Clymenia laevigata Munst., 
C. undulata Munst., C. striata, Muxst , Actinopteria subradiata Phill., A viculopecten 



108 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

transversus Sow., Posidonomya venustaMiinsT., Buchiolaretrostriatav. Buch, Sangui- 
nolites sulcata Mi) n st., S. elliptica Phill. (upper beds only), Murchisonia angulata 
Phill., Bellerophon trilobatus Sow., B. hiulcus Sow., Capulus compressus Goldf., 
Loxonema romeri Kayser, Athyris concentrica v. Buch, Orthis interlineata Sow, 
O. striatula Schloth., 0. resupinata Mart., Atrypa desquamata Sow., Chonetes 
hardrensis Phill., Bhynchonella acuminata Mart. var. mesagona Phill., Bh. 
ferquensis Gosselet, Spirifer verneuili Murch., Ambocoelia urei Flem., Orthotetes 
crenistria Phill. var. arachnoidea Phill., Productella productoides Murch. 

Still higher are the green and black slates of the inliers north of Petherwin 
and Launceston containing Phacops latifrons Bronn and granulatus, Entomis 
serratostriata Sandb., Sanguinolites elliptica Phill., Bellerophon hiulcus Sow, 
Clymenia sp., Ambocoelia urei Flemm., Orthis n. sp., 0. interlineata Sow., Athyris 
n. sp. and Aulocystis entalophoroides Schluter. 

The junction with the Carboniferous is usually a line of fault, often a thrust, 
bringing the Devonian above the Carboniferous. Sometimes the Carboniferous 
appears to overlie the Devonian conformably, but there is in reality a break, for 
tbe beds that cover the Devonian are high above the base of the Carboniferous, 
and the Devonian inliers represent higher horizons the further north they are found. 

B. North Devon and West Somerset. 

The strongly cleaved Devonian rocks to the north of the great syncline 
exhibit throughout a more arenaceous facies. They extend, with one break, in a 
band about 24 km. (16 miles) wide on the south of the Bristol Channel from the 
Quantock Hills on the east, to the estuary of the Taw (Etheridge 1867, 
Hamling 1909). In the north they form an anticline with a west-north-west and 
east-south-east strike but in general they dip to the south-south-west with local 
undulations and faulting. 

The lowest rocks are believed to be the Foreland Grits, which 
extend eastward along the coast from Lynmouth to Minehead. They consist of 
red and grey quartzose grits, interbedded with reddish slates, and resemble the 
arenaceous beds of the Lower Old Red Sandstone. They are faulted against the 
Lynton Slates, but are presumably of earlier date, for a small patch of the latter 
is seen resting on the grits. They are as a rule unfossiliferous, but plant remains 
recently discovered near Porlock have been rei'ered by W. N. Edwards to the 
Lower Old Red Sandstone genus Psilophyton (Evans 1914). 

The Lynton Beds consist of bluish grey irregular slates with interstratified 
grits and more or less decalcified calcareous bands. They appear to include more 
than one horizon between the Hunsruckschiefer and the summit of the Lower 
Devonian. In the immediate neighbourhood of Lynmouth, especially on the east 
they contain fish remains, among which Pteraspis has been recognised by Smith 
Woodward (1901). Further west numerous fossils have been collected, among 
which the following have been stated to occur: Spirifer primaevus Stein., Sp. 
hystericus Schloth., Sp. canaliferus Stein., Orthis arcuata Phill., O. longisulcata 
Phill., Chonetes sarcinula/a Schloth., Orthotetes umbraculum Schloth, Orthot. 
hipparionyx Vanux. (= proximus Vanux.), Pterinea spinosa Phill., Pt. fascicu- 
lar Goldf., Modiomorpha lamellosa Beush., Ctenodonta krachtae Romer, Mega- 
lodon cucullatus Sow., Bellerophon striatus Bronn, Pachypora cervicornis Blainv. 
and Alveolites suborbicularis Lam. The highest beds contain Orthis arcuata Phill. 
and Chonetes sordida Sow. (which has been identified with Ch. hardrensis Phill.). 

The Hangman Grits, which succeed the Lynton Slates and resemble the 
Foreland Grits, form the Quantock Hills and a ridge of high ground terminating 
in Hangman Point on the north coast to the west of Lynmouth. At some horizons 



Evans: Great Britain. — Sedimentary Rocks. — North Devon, Somerset. (III. 1.) 109 

casts of indeterminable lamellibranchs, gastropods and brachiopods including 
Myalina, Natica and Spirifer are found, as well as the "corduroy plant" of the 
Middle Old Red Sandstone (p. 117). They are usually placed in the Lower Devonian, 
but are probably, in great part at least, Middle Devonian. To the southward they pass 
upwards into the Combe Martin Beds, red and grey slates containing Stringo- 
cephalus burtini Defr. and lamellibranchs and gastropods. These are succeeded 
by the Ilfracombe Beds, a thick series of silver grey slates with intercalated 
limestones. The fossils reported include the following: Stromatopora concen- 
trica Goldf., Cystiphyllum vesiculosum Goldf., Cyathophyllum caespitosum Goldf., 
C. helianthoides Goldf., Pachypora cervicornis Blainv., Tentaculites, Trimero- 
cephalus trinucleus Thomas, Athyris concentrica v. Buch, Atrypa desquamata Sow., 
Cyrtia heteroclyta Defr., Merista plebeia Sow., Orihis interlineata Sow., 0. striatula 
Schloth., Rhynchonella cuboides Phill., R. pleurodon Phill., R. pugnus Sow., 
Spirifer canaliferus Stein., Sp. curvatus Schloth., Sp. verneuili Murch., Sp. nudus 
Sow., Orthotetes crenistria Phill., 0. umbraculum, Strophomena rhomboidalis W ahl. 
and Megalodon cucullatus Sow. Tuffs and possibly lavas occasionally occur. The 
absence of Calceola sandalina Lam. and Stringocephalus burtini Defr. and the 
occurrence of Spirifer verneuili Murch. at a comparatively low horizon and of 
Rhynchonella cuboides Phill. point to the conclusion that the greater part, if 
not the whole, of the Ilfracombe beds must be referred to the Upper Devonian. 

To the southward they are succeeded by the grey Morte Slates which include 
occasional calcareous nodules and arenaceous bands, the latter containing rounded 
grains. They are highly cleaved and yielded no fossils till Hicks discovered 
near Woolacombe Bay and Ilfracombe some distorted brachiopods and lamelli- 
branchs. These he believed to be characteristic of Silurian (Gothlandian) rocks, 
and accordingly contended that the slates represented a faulted inlier of that age; 
but the doubts raised by the unsatisfactory condition of the fossils, the absence 
of anything that could be accepted as graptolites and the dissimilarity to the Silurian 
of the Mendips, South Wales and South Cornwall have been justified, by the recent 
discovery of a well preserved Spirifer verneuili 1 (Evans and Pocock 1912). 

Next in order are the Pickwell Down Sandstones consisting of friable red, 
purple, brown and green grits, sandstones and shales, containing iron ore at the 
base, traces of fish remains, and fossil wood. They pass upwards into the Baggy 
and Marwood Beds, grey, green or yellowish sandstones, flags and shales, with 
a fauna consisting chiefly of lamellibranchs, including Leptodomus constricta 
M'Coy, L. semisulcata Sow. Myophoria deltoides Phill., Ctenodonta antiqua 
Sow., Cucullaea unilateralis Sow., (including var. trapezium Sow.), Ptychopteria 
damnoniensis Sow., Rellerophon subglobatus M'Coy, the myriapod Cariderpestes, 
phyllopods, Lingula squamiformis Phill. and plant remains. These are succeeded 
by the Pilton Beds, grey flags and shales with calcareous bands. The rocks in- 
cluded in this series appear to graduate upwards into the base of the Carboniferous, 
the stratigraphical break occurring at a higher level than on the south of the syncline. 
Only five forms are common to the Baggy and Marwood beds, Leptodomus constricta 
M'Coy, Sanguinolites mimusWmDB., Ptychopteria damnoniensis 2 Sow., Actinopteria 
rudis Phill. and Lingula squamiformis Phill. The lowest beds are characterized by 
Rhynchonella laticosta Phill., Rh. pleurodon Phill., and Spirifer urei Fleming. 

1 In West Somerset Hicks found at Treborough in slates usually referred to the 
Ilfracombe Beds, highly cleaved fossils, which according IoWhidborne belonged to the 
horizon of the "lowest beds" of the Rhenish Devonian; and at Oakhampton in rocks mapped 
as Morte Slates others corresponding to the higher beds of the Lower Devonian ; but at 
the latter of these localities Sp. verneuiWM.VRcn. is said to have been found (Ussher 1910). 
* Phillips however made the Pilton fossil, which only occurs in the lower beds, a 
separate species, "cancellata" . 



110 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

At a higher horizon Strophalosia producloides Murch. and Chonetes hardrensis Phill. 
are common. Among other fossils in the beds which are regarded as Devonian may 
be mentioned Phacops latifrons Bronn, Pleurotomaria gracilis Phill., Aviculo- 
pecten transversus Sow., Spirifer verneuili Murch., Sp. obliterata Phill., Spiriferina 
cristata Schloth. var. octoplicata Sow., Orthis interlineata Sow., Leplaena rhomboi- 
dalis Wilckens and Productus praelongus Sow. The plants Knorria dichotoma 
Haugh., Archaeopleris hibernica Forbes and Sagenaria veltheimiana Sternb. are 
also stated to occur. 

C. South-east of England. 

Upper Devonian rocks somewhat similar to those of North Devon, the Bou- 
lonnais and the Bassin de Namur exist below the Thames valley. The Frasnian is 
represented in a boring in London by mottled red, purple and greenish shales 
very calcareous in places, with thin seams of quartzite. They dip at 35° (probably 
to the south) and contain Spirifer verneuili Murch., Rhynchonella boloniensis d' Orb. 
( ? Rh. ferquensis Goss.). In a boring at Southall red and mottled clays and coarse 
sandstone have yielded Holoptychius and Bothriolepis, while at Turnford near 
Cheshunt dark chocolate coloured beds have been reached, with Spirifer verneuili 
Murch., Rhynchonella cuboides Sow., Leptaena rhomboidalis Wilck., Ptychopteria 
damnoniensis Sow. and Actinopteria texturata Phill., which indicate a Lower 
Pilton horizon (Whitaker1889, Proctor 1913, Smith Woodward 1913). Other 
borings have yielded similar rocks but no fossils. 

D. South Wales and the Welsh Border. 

To the northward of the Bristol Channel and its continuation in the low 
ground near Glastonbury the Devonian is represented by rocks of the Old Red 
Sandstone facies. These are exposed in the anticlines of the Mendips in north-east 
Somerset, and reappear in Gloucestershire, whence they extend northward to 
the neighbourhood of Wenlock in Shropshire, 52° 36' N., and westward through 
Wales on the north of the South Wales Coal-field into Pembrokeshire, where they 
are overlapped by the Carboniferous. They are also seen at intervals on the 
south of the Field. On the east they are bounded by a line of disturbance running 
northward from near Bristol to beyond Bridgenorth but similar rocks underlying 
the Coal Measures have been proved by boring near Northampton (Geol. Field, p. 452). 

The Old Red Sandstone of this area consists of a Lower and Upper portion, 
which are usually apparently conformable, but their organic contents are entirely 
distinct, and the palseontological break must represent a considerable interval 
of time. 

In Shropshire and Montgomery the highest beds of the Gothlandian (Silurian), 
present considerable resemblance to the Old Red Sandstone but still contain 
Lingula cornea Sow. 1 , associated with Cyathaspis banksi Huxley and Salter and 
Cephalaspis murchisoni Egert. They are succeeded conformably by the Red MarFs 
the lowest division of the Old Red Sandstone. On the south, on the other hand, 
there is usually a distinct break; the base of the Old Red consists of gritty or 
conglomerate beds, and the uppermost portion of the Gothlandian is missing. 

The Red Marls are usually about 1000 m. (over 3000 ft.) in thickness and con- 
sist of red and green argillaceous rocks, usually more or less sandy, with inter- 
calated beds of sandstone. They also contain calcareous or dolomitic material, 
known as "cornstones", which are not of organic origin. The cornstones occur 
sometimes as concretions (locally known as "race"); sometimes as conglomeratic 

1 Lingula is frequently associated with Old Red Sandstone conditions, see pp.109 
and 111 and Frech, Lethaea Geognostica vol. 2, p. 224. 



Evans: Great Britain. — Sedimentary Rocks. — South Wales. (III. 1.) Ill 

aggregates of these concretions in a gritty matrix, as if the argillaceous material 
had been washed out by a strong current, and sometimes as compact limestones. 
They are frequently found at the same horizon in distant localities. 

The fossils of the Red Marls include Pteraspis rostrata Agass., Pt. crouchi 
Lank., Cyathaspis macculloughi Smith Woodward, Palaeaspis sericea Lank., 
Eukeraspis, Cephalaspis lyelli Agass., C. salweyi Egert., Psammosteus, Clima- 
tius ( ?) ornatus Agass., Protodus, Pterygotus, Pachytheca and Nematophycus (a mass 
of apparently endless tubes). An isopod, Praearcturus gigas H. Woodward, 
has been described from the cornstones. 

On the north the Red Marls are succeeded conformably by the Senni Beds, 
green and red sandstones and marls with cornstones. They are sometimes more 
than 200 m. (650 ft.) thick. They contain Pteraspis, and Cephalaspis, and are of 
Lower Old Red Sandstone age. In the east they have not been separated from 
the Upper Old Red Sandstone Beds above. In the south-west the Gosheston 
Sandstones and the Ridgeway Conglomerate occupy a similar position. 

The lowest beds of the Upper Old Red Sandstone are the Brownstones; 
brown, red or green gritty sandstones and red marls, which contain remains of 
plants with Upper Old Red Sandstone affinities, and pass up into the conglomeratic 
Plateau Beds. Although there is no apparent discordance 1 between the Upper 
and the Lower Old Red Sandstone, the former overlap not only the Senni Beds, 
but the Red Marls and rest in the peninsula of Gower, at Tortworth, and in the 
Mendips on the Gothlandian rocks. The pebbles have been found to consist of subangular 
quartzites and red jasper, the latter being the result of the jasperization of various 
rocks, including a perlitic felsite, in a manner similar to that which is believed to 
take place under desert conditions. At the same time the sand of the finer grained 
rocks is characteristically rounded. Near Bristol the Brownstones are represented 
by strata containing a considerable amount of carbonate of lime. To the north- 
east and east of the South Wales Coal-field the highest beds consist of yellow, red 
and grey sandstones similar to the Kiltorcan beds of Ireland, and contain 
Archanodon (Amnigenia) jukesi Forbes, Holoptychius, Glyptopomus, Bothriolepis 
macrocephala Egert. (at Farlow in Shropshire), Conchodus, Ceraspis, Strepsodus, 
Sauripterus anglicus Smith Woodward and rhizodont teeth and scales*. On the 
north of the Coal-field the uppermost beds consist of grey grits or quartzites, the latter 
yielding at Penlan near Kidwelly remains of plants including Artisia approximata 
Brongn., a calamitic pith-cast, Stigmaria ficoides Sternb., and St. inaequalis Gopp. 

The Upper Old Red Sandstone of the south of Pembroke is represented by 
the Skrinkle Sandstones, quartzitic sandstones and breccias of subangular quartz 
fragments. At several places it includes marine intercalations in its upper part. 

At Sandtop Bay in Caldy Island off the south-east coast of Pembroke, there is a thin 
bed of tubular organisms described by Salter as Serpula advena, associated with cal- 
careous marls, and sandstones with lenticles of detrital limestone, made up of crinoids, 
bryozoa, and probably lamellibranchs, with palatal fish teeth similar to Carboniferous 
types. At Skrinkle Bay on the adjoining mainland greenish grey soapy shales with Modiola 
and Lingula occur. At West Angle Bay at the entrance to Milford Haven there are several 
marine bands, of which the principal is conglomeratic at the base and sharply marked off 

1 Near Milford Haven there appears to be in places considerable difference in dip 
between the Lower Old Red Sandstone and the Carboniferous, and as the Upper Old Red 
Sandstone is elsewhere conformably overlaid by the Carboniferous, an uncomformity is 
inferred between the Lower and Upper Old Red in this area, though it has never been actu- 
ally observed. 

2 I am informed by D. M. S. Watson that in the Bristol Museum there is a specimen 
of Bothriolepis, probably near hydrophila, from the calcareous rocks near Clevedon, as 
well as a Phyllolepis from the yellow sandstones. 



112 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

from the underlying rock; it consists of sandstones with plant remains, and shales and 
limestone containing marine forms, chiefly lamellibranchs. The highest marine band com- 
mences with a break indicated by borings penetrating the underlying red marl and similar 
breaks occur in the band itself. It contains a bed of dark grey shale with lenticular lime- 
stones, both crowded with lamellibranchs. Then follow grey shales, mud-stones, and sand- 
stones with marine fossils, and finally a sandstone of Old Red type, containing brachio- 
pods and crinoids, which is taken as the summit of the formation. Salter (1859) notes 
the occurrence in the Upper Old Red Sandstone of this neighbourhood of Serpula, 
Ptychopteria damnoniensis Sow. (of the Marwood type), Cucullaea unilateralis, var. trape- 
zium Sow., Rhynchonella laticosta Phill. and Bellerophon trisulcatus. 

Taking the Old Red Sandstone beds as a whole the arenaceous beds appear 
to become thicker to the north-west, as if they were derived from hills in that di- 
rection. 

The green colour which characterizes certain beds is explained by the presence of 
dark green chlorite and yellow epidote (Mem. Geol. Surv., Sh. 231, p. 6). It is character- 
istically developed in parts of the Red Marls and the Senni Reds, but is sometimes 
found in the lower part of the Rrownstones. It appears to result from the presence 
of organic matter, being associated with plants and worm borings, the latter some- 
times U-shaped like those of Arenicolites didymus of the Cambrian. 

E. North Wales, the Isle of Man and Lake District. 

Retween the South Wales area and the Cheviot Hills on the borders of England 
and Scotland, the Lower Old Red Sandstone appears to be absent, but the Upper 
Old Red Sandstone may be represented in Denbigh and Anglesey in North Wales, 
the Isle of Man and the Lake District, by red rocks consisting of conglomerates, 
sandstones and occasional marls and cornstones, underlying, in the Lake District 
with some discordance, the base of the Carboniferous, which belongs to a higher 
horizon than in South Wales. They are frequently included in that formation, 
but I prefer to retain them in the Upper Old Red until distinct evidence of their 
age is forthcoming (see also pp. 140, 143). 



F. The Scotch Border. 

In the Cheviot Hills, however, the Gothlandian is overlaid unconformably by 
volcanic rocks of Lower Old Red Sandstone age, which will be described later 
(pp. 122 — 125) and these again are covered with marked discordance by Upper Old Red 
Sandstone, which occupies a large area on the west and extends northwards to Dunbar 
and Eyemouth, resting unconformably on Ordovician, Silurian and Lower Old Red 
Sandstone. It commences with Red Conglomerates and Sandstones, (cream 
coloured and green in patches), which gradually become finer and are ultimately inter- 
stratified with marls. Rounded sand-grains frequently occur. The fossils include 
Bothriolepis obesa Traq., B. leptocheira Traq., scales of Holoptychius nobilissimus 
Agass. and fragments of Archaeopteris hibernica. The upper portion, the Cornstone 
Series is of a less pronounced red colour, and rarely yields rounded sand grains; 
it contains flakes and concretionary masses of calcareous matter, which tends to 
pass into haematite. Sun-cracks and rain-pitted surfaces are common (Goodchild 
1903). Similar beds occur at the base of the Carboniferous in Northumberland and 
are usually placed wholly or partially in that formation instead of in the Devonian. 

Fragments not only of the Lower Old Red Sandstone volcanic rocks but also 
of the granite, dykes and sills intrusive in them can be recognised in the conglomerates 
of the Upper Old Red Sandstone. 



Evans: Great Britain. — Sedimentary Rocks. — The Midland Valley. (III. I.) 113 

G. The Midland Valley of Scotland. 

The Old Red Sandstone rocks outcrop over a considerable area on both 
sides of the great north-east and south-west trough, that extends from the Firth 
of Clyde to the Firth of Forth and gives rise to the Midland Valley of Scotland. They 
are usually separated by powerful strike faults from the older rocks on the north- 
west and south-east, while in the centre they are covered by Carboniferous strata. 

The south-eastern outcrop stretches from the south of Edinburgh south- 
westward to the coast of Ayr, but is interrupted by downthrows which bring in Upper 
Old Red and Carboniferous rocks. The uppermost beds of the Gothlandian (see p. 96) 
are mostly red in colour and present considerable resemblance to the passage beds in 
the South Wales area. They are referred to by the Survey as Downtonian but 
Goodchild, who believed that they occupied a somewhat higher horizon, termed 
them Lanarkian. They were formerly included in the Lower Old Red Sandstone, 
but the base of the true Lower Old Red the "Caledonian" of Gooochild, a thick 
series of conglomeratic sandstones and volcanic rocks, rests unconformably upon 
them. 

The Lower Old Red Sandstone on the north-west margin of the Midland Valley 
is well seen on the east coast between the Firth of Tay and Downie Point, south 
of the great boundary fault of the Highlands and extends to the south-west to the 
north-east of Ireland. Hickling (1908, 1912) gives the following downward 
succession in Forfarshire: 

Edzell Shales (? 300 m. — 1000 ft.), fine sandstone, shales and marls, 

Arbroath Sandstone (365 m. — 1200ft.), coarse sometimes pebbly, with red 
flags and a band of limestones nodules. 

Auchmithie Conglomerate (240 m. — 800ft.) with well rounded quartzite 
pebbles and interstratified sandstones. 

Red Head Series (460 m. — 1500 ft.), thin bedded sandstones and shales passing 
up into thicker bedded sandstone with volcanic rocks near the base. 

Cairnconnan Grits, (610m. — 2000ft.), coarse sandstones with bands of con- 
glomerate. 

Carmyllie Series (300 m. — 1000 ft.), compact sandstones, flags and shales with 
interstratified lavas. 

Dunottar Series (1500 m. — 5000 ft.), coarse red and grey sandstones, and con- 
glomerates with large well rounded pebbles. 

The beds above the Cairnconnan Grits constitute the Strathmore Sandstones. 

The Dunottar sandstones and conglomerates are best seen south of Stonehaven 
(Campbell 1911), where they rest conformably on the Downtonian. They include 
in the higher portion basalt and andesite flows. The conglomerates consist at 
first mainly of the early Palaeozoic rocks of the Highland border and the "newer 
granites". Later on the ancient crystalline rocks of the Highlands are also repre- 
sented. The Auchmithie conglomerate consists of similar materials. The conglo- 
merates and sandstones which succeed the lava flows are made up for the most 
part of volcanic materials and pass downwards into ashes and agglomerates. The 
surface of lava flows and fragments appears to have been oxidized to a deep red 
before they were covered by succeeding flows or deposits. The hollows in the 
lavas and agglomerates are frequently filled with a greenish matrix which seems 
to consist of fine volcanic dust mixed with arenaceous material. The Carmyllie 
flags resemble this matrix in appearance and apparently also in composition 
(Hickling 1908, 1912 and Jowett 1913). 

In the lower beds the sandstones are usually dull red or grey, the shales red 
or blue and the colouring is comparatively uniform. Towards the summit of the 
Lower Old Red Sandstone red becomes the dominant colour and is of a brighter 
hue, while a curious mottling makes its appearance especially in the Edzell shales, 
which show small circular patches, or more rarely bands, of yellow, grey or green. 

Handbuch der regionalen Geologie. III. 1. 8 



114 (III. 1.) 



The British Isles. — III. Stratigraphy. — 5. Devonian. 



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Most of the fossils occur in the Carmyllie and Cairnconnan series. They include 
the Acanthodi Mesacanthus milchelli Egert., J schnacanthus gracilis Pow., Parexus 
incurvus Agass., P. falcatus Pow., Climatius reticulatus Agass., CI. macnicoli 



Evans: Great Britain. — Sedimentary Hocks. — Northern Scotland. (III. 1. ) 115 

Pow., Cephalaspis lyelli Agass., Prolodus scoticus E. T. Newton, Farnellia tuberculoid 
Traq., the Mcrostomata Pterygotus anglicus Agass., Pt. minor H. Woodw., Stylonurus 
scoticus H. Woodw., St. powriei Page, St. ensiformis H. Woodw., Eurypterus brewsteri 
H. Woodw., the myriapods Kampecaris forfarensis Page and Archidesmus macnicoli 
Peach; and the plants Parka decipiens Fleming, (Don 1913 1 ) and Zosterophyllum 
myretonianum Penhallow (Hickling 1908, 1912, 1913). 

A much higher plant horizon is stated (MacNair 1908) to occur in green- 
grey flags near the summit of the Strathmore Sandstones in the counties of Perth 
Stirling and Dumbarton and to be characterized by Psilophyton princeps Daws. 
and Arthrostigma gracile Daws., the former of which occurs in the Lower Devonian 
and the latter in the lower Middle Devonian of Canada. 

The Upper Old Red Sandstone of the Midland Valley is usually found 
on the inner borders of the Lower Old Red Sandstone, which had already been 
thrown into well marked anticlines and synclines and worn to an irregular plain, 
when the Upper Old Red, which is still nearly horizontal, was laid down upon them. 
As in the border counties, it consists of conglomerates and red or mottled sandstones, 
succeeded by the Cornstone Series consisting of less deeply coloured beds with 
intercalated calcareous material, usually at definite horizons. Everywhere there is 
evidence of conformity with the overlying Carboniferous. Holoptychius nobilissimus 
Agass. has been found below the dolerite sills of Salisbury Crags near Edin- 
burgh and in Fife and other localities, Sauripterus javosus Agass. at Clash- 
bennie in Forfar, and Bothriolepis leptocheira at the Heads of Ayr. At Dura Den 
in Fife numerous fish remains have been found in sandstones belonging to the Corn- 
stone Group including Phyllolepis concentrica Agass., Glyptopomus minor Agass., 
G. kinnairdi Huxley, Gyroptychius heddlei Traq., Holoptychius flemingi 
Agass., Phaneropleuron andersoni Huxley, and at an horizon about 15 metres 
(50 ft.) higher, Bothriolepis hydrophila Agass. 

H. The Lome Area. 

In the neighbourhood of Oban on the Firth of Lome, is a tract of rocks of 
Lower Old Red Sandstone age, extending from Loch Creran on the north to Loch 
Melfort on the south, including the islands of Seil and Lunga. Coarse breccias and 
massive conglomerates are succeeded by volcanic grits, tuffs, fine sandstones and shales 
containing Psilophyton, Pachytheca, Mesacanthus mitchelli Egert., and Cephalaspis 
lornensis Traq., and C. lyelli Agass., and these again by lavas and agglomerates. 

I. Northern Scotland. 

In the northern valleys of the Grampians, the shores of the Moray Firth, 
Caithness, and the neighbouring portion of Sutherland, the Orkneys, and Shet- 
lands, are extensive deposits which are referred to as the Middle Old Red 
Sandstone or Orcadian. They are best developed in Caithness where they are 
known as the Caithness Flags. The following downward succession is described 
in the Memoir to accompany sheets 110 and 116 of the Geological Survey of 
Scotland. The thickness attributed to the Thurso Flagstone Group is probably 
excessive. 

6. John o'Groats Sandstone Group (About 610 m., 2000 ft.) with Tristichopterus 
alatus Egert., Microbrachius dicki Traq., Diplerus macropterus Traq,, and Mesacan- 
thus peachi Egert. Yellow and red false-bedded sandstones with thin phos- 
phatic blue flags and black bituminous shales. 
(Almost complete change in the type of deposit and fish fauna). 



1 An important paper by Don and Hickling will shortly be published by the 
Geological Society. 



116 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

5. Thurso Flagstone Group (over 1830 m., 6000 ft.) with Estheria membranaceaP\cm., 
Homosteus milleri Traq., Thursius pholidotus Traq., Coccosteus minor Miller, 
C. decipiens Agass., Glyptolepis paucidens Agass., Osteolepis microlepidotus, 
Pander, Cephalaspis magnified Traq., and Dipterus valenciennesi Sedgw. and 
Murch. 1 Blue phosphatic and grey calcareous flags with pale mudstones, 
bituminous matter in bands and nodules, concretionary red and yellow sand- 
stones and "boulder" beds. 
4. Achanarras Band. (At Niand on the east coast and Achanarras south of Thurso), 
(not more than 3 m., 10 ft. in thickness) with Diplacanthus striatus Agass., D. 
tenuistriatus Traq., Glyptolepis paucidens, Osteolepis macrolepidotus Agass., 
Diplopterus Agassizi Traill, 2 Rhadinacanthus longispinus Agass., Mesacanthus, 
resembling M. pusillus Agass., Cheiracanthus murchisoni Agass., Pterichthys 
milleri Agass., Pt. productus Agass., Coccosteus decipiens Agass., Homosteus 
milleri, Dipterus valenciennesi, Cheirolepis trailli Agass., and the supposed 
marsipobranch, Palaeospondylus gunni Traq. Dark bluish-grey calcareous flag. 
(Large accession to fish fauna and further change in type of deposit). 
3. Passage Beds Group. — (including the Noss Head, Castle Sinclair, Field, and Papigoe 
Beds in descending order) (About 760 m., 2500 ft.) with Coccosteus decipiens, 
Dipterus valenciennesi and Thursius macrolepidotus Sedgw. and Murch., grey 
calcareous and dark shaly flags, hard blue and lenticular black limestone and 
sandy beds. 

(Change in type of deposits and first appearance of Coccosteus). 
2. Wick Flagstone Group (about 1830 m., 6000 ft.) with Dipterus valenciennesi, 
Thursius macrolepidotus and Osteolepis sp. ; consisting of: 

Wick Flags, Dark flags with pale grey sandstones and smooth fissile 
limestones containing fish remains. 
Red Beds, Sandstones and shales. 

Helman Head Beds, Black slates with Thursius macrolepidotus, and 
sandstones. 

Upper Conglomerate, Conglomerate, sandstone and breccia. 
(Local unconformity and change in type of deposits; first appearance of fish fauna. 
1. Basement Group (about 460 m., 1500 ft.). Purple, green, and chocolate 
mudstones, passing down into sandstones, conglomerate, arkose, and breccia. 

The Basement Beds are unfossiliferous, unless plates of Pterygotus found 
in the neighbourhood of Sarclet come from them. Local basement conglomerates 
or breccias also occur at higher horizons. The Wick flagstone group is characterized 
by the presence of Thursius macrolepidotus and absence of Coccosteus decipiens. 
The Passage beds contain both, and their lithological characters combine those of 
the Wick and Thurso group. Of the fifteen forms of fish found in the Achanarras 
bed, ten are confined to this horizon, two, Coccosteus decipiens and Dipterus valen- 
ciennesi, occur both in the Passage Beds and Thurso Group and two, Homosteus, 
milleri and Glyptolepis paucidens, are found in the latter only. The John o' Groats 
Sandstones are distinct both in fauna and lithology from the lower beds. 

At Cromarty, Lethen, Clun, Tynet Burn, Gamrie and other points on the 
shores of the Moray Firth, a coarse basement conglomerate is followed by dark 
shales with calcareous nodules containing fish, and these are covered by red sand- 
stones and shales. The fauna is closely allied to that of the Achanarras horizon 
in Caithness, for all except two — Palaeospondylus gunni, and Glyptolepis 
paucidens — of the forms constituting the latter are found in the Moray Firth, 
and of the southern forms only Glyptolepis leptopterus Agass. and Gyroptychius 
microlepidotus Agass. are definitely missing in the Achanarras fauna, though the 
identification of Mesacanthus pusillus (Agass.) is still uncertain. The only other 
horizon of the Middle Old Red Sandstone represented in the Moray Firth Area 
is that of the Thurso Group at Hillhead Quarry, Dalcross, Invernesshire, where 

1 D. M. S. Watson informs me that he has found Dipterus macropterus high in the 
Thurso Group at Brimsness, associated with Homosteus and Coccosteus decipiens. 

2 A specimen collected by Watson is in the Manchester Museum. He also found 
Estheria membranacea in the same bed. 



Evans: Great Britain. — Sedimentary Rocks. — Northern Scotland. (111. 1.) 117 

Coccosteus minor, Homosteus milleri and osteolepid scales occur in small calcareous 
nodules in shale and sandstone (Watson 1908). With the Moray Firth Middle 
Old Red Sandstone may be placed a number of outliers in the Grampians in the 
neighbourhood of Rhynie and Cabrach on the southern margin of the basin of 
the Deveron, Tomintoul on the upper waters of the Avon a tributary of the Spey, 
and Drynachan Lodge on the Findhorn. At Rhynie they consist of conglomerates 
of well rounded pebbles and sandstones with pipes and "galls" of red clay, Moray 
Firth fish and "corduroy" stems (see p. 108 and infra). 

The Middle Old Red Sandstone is nowhere seen overlying the Lower 
Old Red, but the basement conglomerates of the Moray Firth Area contain pebbles 
of granite of the Lower Old Red type. In the neighbourhood of the river Spey 
these conglomerates are in some places mainly composed of a fine gray sandstone 
which may have been derived from Lower Old Red or Downtonian rocks then subject 
to denudation in that district. The possibility of the Basement Group in Caithness 
being of Lower Old Red Age must not be overlooked, while on the other hand, 
as suggested by Hickling, the highest strata assigned to of the Lower Old Red 
sandstone in Forfarshire may conceivably be of Middle Old Red Sandstone age. 

The Middle Old Red Sandstone of the Orkney Islands corresponds to the 
higher beds of Caithness. The Stromness Flags, which are chiefly developed in 
the west of Mainland with a thickness of about 400 m. (1300 ft.), consist, except where 
there is a local conglomeratic base resting on older rocks, of either dark blue flags 
with alternations of more sandy beds, in which rounded sand grains are met with, 
or calcareous or bituminous flags. The fossils are all common either to the 
Achanarras horizon in Caithness or to the Moray Firth Area. 

The Rousay Flags, which mainly occur in the north and east and have a thick- 
ness of about 460 m. (1500 ft.), are similar in lithological characters to the Stromness 
Flags and have yielded most of the species of the latter, and in addition Coccosteus 
minor and Thursius pholidotus, which are characteristic of the Thurso group. Estheria 
membranacea is also common to the Rousay beds and the Thurso Flags. At the 
summit of the Rousay beds a specis of Asterolepis, a genus elsewhere confined to 
the Upper Old Red Sandstone, makes its appearance. 

The fossils of the Orkney flags are usually met with in thin bedded fissile 
calcareous bands. The more argillaceous beds are apt to contain concretions, which 
give the rock a fretted appearance on weathering. The flags are often ripple marked 
and sun-cracked so that they must have been laid down in very shallow water. 

The Rousay beds are covered conformably by the Eday Sandstones, 
yellow with thin fossiliferous flags below, and red and unfossiliferous above. The 
total thickness is about 150 m. (500 ft.). The fossils include Tristichopterus alatus, 
Microbrachius dicki and Dipterus macropterus, all found in the John o' Groats sand- 
stones. A single specimen of the long-lived Coccosteus decipiens has also been found. 
The red sandstones sometimes contain layers of coarse gravel and local con- 
glomerates, as well as flows of a vesicular olivine dolerite. 

A remarkable feature is the accumulation of small specimens of Osteolepis 
macrolepidotus, Dipterus valenciennesi, Glyptolepis paucidens and Coccosteus deci- 
piens at the summit of the Rousay Flags. A simular phenomenon occurs in the 
flagstone beds in the Eday sandstones. 

The Middle Old Red Sandstone is characterized by distinct plant types inclu- 
ding " Lycopodites" milleri Salter and Ptilophyton thomsoni Dawson, the stem 
of which was described as Caulopteris peachi by Salter. It appears to range from 
the Wick Group to the Thurso Group in Caithness and occurs at Gamrie in the 
Moray Firth and Stroma and Stromness in the Orkneys. "Corduroy" stems showing 



118 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

a fluted surface without nodes, similar to those found in the Hangman Grits and at 
Rhynie, occur in the Thurso group in Caithness. Plant remains in the John o' Groats 
sandstone have been compared with Sprochnus (of Stur not Kuetzing) a.nd Rhaco- 
phyllum. 

The Old Red Sandstone occurs in Shetland on both sides of the central axis 
of metamorphic rocks of Mainland. A little west of Lerwick it is faulted down 
against the crystalline rocks and there is an upward succession eastward across 
Bressay Sound to the islands of Bressay and Noss, in which the following have been 
distinguished: (Flett 1909). 

Thin flaggy sandstones and grey shales of Noss. 
Grey micaceous thin bedded sandstones with fish remains, and coarser, 
Bressay less micaceous, gritty seams, often obliquely bedded, with rounded clay galls, 
and Noss | fragments of plants and shreds of fine shale, Cullingsburgh Voe, Bressay. 
Series Brownish and grey sandstones often conglomeratic or breccia -form, 

West Bressay. 
< Grey micaceous sandstones with plant remains and Estheria mem- 

Lerwick | branacea, Nabb, south-east of Lerwick. 

Series Reddish and grey sandstones often current bedded, sometimes with 

| large rounded pebbles of quartzite, granite etc. 
Rovey Head Conglomerate. 
Red Flags of Brenista. 
Basement Breccia. 

As the Lerwick series contains Estheria membranaca and plant-remains similar 
to those of the Middle Old Red Sandstone of Caithness and Orkney, it is presumably 
of the same age. In the Bressay flags however at an horizon several thousand feet 
higher an undetermined species of Asterolepis, Holonema ornatum Traq., and a 
scale which may belong to Holoptychius have been found. Asterolepis though it 
occurs high up in the Middle Old Red of Orkney is mainly Upper Old Red, and Holo- 
nema only occurs elsewhere in the Upper Devonian Chemung Beds of North America. 
The Bressay flags may therefore be provisionally placed low down in the Upper 
Old Red. 

The only evidence of the age of the red sandstones of West Shetland is the 
identification of plant remains in rocks metamorphosed by intrusions with those 
in the Lerwick series (Peach and Horne 1884). 

The Upper Old Red Sandstone of the Moray Firth, Caithness, and the 
Orkneys, rests unconformably on the Middle Old Red, but there is not the same 
degree of discordance as between the Upper and Lower Old Red Sandstone south 
of the Grampians. The lowest palseontological horizon which has been recognized 
in the Upper Old Red Sandstone of the Moray Firth, is found in the Nairn Sandstone 
and is characterized by the fish Psammosteus tesselatusTRXQ., resembling P. paradoxus 
Agass. of Russia, Asterolepis maxima Agass. 1 , Polyplocodus leptognathus Traq., 
Coccosteus magnus Traq. and Holoptychius decoratus Eichw. A higher horizon 
occurs in the Alves or Scaat Craig Beds, south of Elgin 2 , where Bothriolepis major 
Agass. allied to B. panderi Lahus. 3 , Psammosteus pustulatus Traq., Polyplocodus 
sp., Cosmacanthus* malcolmsoni, Agass., Conchodus ostraeiformis M' Coy, Holop- 
tychius giganteus Agass., H. nobilissimus Agass. and H. decoratus Eichw. are 
found, the last of which is the only form common to the Nairn Beds. It does 



1 At a locality west of Nairn Watson found smooth osteolepid scales with 
Asterolepis maxima, suggesting a transition between Middle and Upper Old Red Sandstone. 

2 The Scaat Craig horizon appears to occur also on the Findhorn river. 

8 W. Taylor of Lhanbryde has found at Whitemire, between Alves and Nairn, 
Asterolepis maxima and Bothriolepis major together. 

4 The other species of Cosmacanthus are found in rocks in the North of Ireland, usually 
considered to be of Carboniferous age. 



Evans: GreatBritain. — SedimentaryRocks. — Climatic and topogr.Conditions. (III. 1.) 119 

not occur in the quarries, also referred to the Alves Beds, between Alves and Nairn, 
where the only fossils common to Scaat Craig are Bothriolepis major, Holoptychius 
giganteus and H. nob Hiss imus, which are here associated with Psammosteus taylori 
Traq., and Sauripterus crassidens Tbaq. similar to S. javosus, from Clashbennie. 
These may indicate a somewhat higher horizon, also represented on the north of 
the Moray Firth, where Ps. taylori and the same two species of Holoptychius are 
found. In Quarry Wood close to Elgin above beds with Ps. Taylori and S. crassidens 
is a fine grained sandstone, the Rosebrae Bed, containing a small variety of B. major 
together with B. cristata, Traq., Phyllolepis concentrica, Phaneropleuron andersoni 
and Glyptopomus minor, the three last species indicating the horizon of the lower 
and principal fish bearing beds at Dura Den. 

At Dunnet Head in the North of Caithness an unfossiliferous yellow and brown 
sandstone with grit beds is faulted against the Middle Old Red Sandstone and is 
believed to represent the Upper Old Red. In the Island of Hoy, one of the Orkneys, 
rocks of a similar character occur resting on the eroded edges of the Middle Old 
Red Sandstone. 

Climatic and topographical Conditions. 

The close of the Silurian was marked by the gradual retirement of the sea 
and the coming in of the conditions that gave rise to the Old Red Sandstone type 
of sedimentation. North of the Bristol Channel and of a line passing south of the 
Mondips and 14 miles north of London there is no evidence of a marine environment 
before the commencement of the transgression of the sea that attained its maxi- 
mum in the Lower Carboniferous Period. The prevailing red colour of the rocks is 
to be attributed to exposure to the oxidizing and desiccating effects of the atmo- 
sphere in a comparatively warm climate. The conditions under which the Red Marls 
were laid down were probably somewhat similar to those that prevail in portions of 
the Bolivian Plateau and the interior of South Australia, where a nearly level sur- 
face is covered after heavy rainfall with an expanse of shallow waters, which during 
periods of drought dry up or contract to much smaller dimensions. The Carmyllie 
Flags appear to have been laid down in a lake of somewhat more permanent character 
but of limited extent. The conglomerates and much of the sandstone are of fluviatile 
origin, but some of the latter may have been accumulated by the wind. The marls 
would seem to consist for the most part of wind-borne dust, which has been arrested 
by the water surface, damp ground or vegetation. The "race" can be paralleled by 
the concretions in the loess and by the kankar of India; and the more continuous 
cornstones by the calcareous deposits in shallow depressions in arid areas, but the 
desert conditions which prevailed may have been due more to the fact that the 
vegetation that then existed was by its nature confined to lakes and swamps, than 
to deficiency in the rainfall. 

Early in Old Red Sandstone times we have evidence of important earth 
movements resulting in the formation of a series of north-east and south-west de- 
pressions in Lome, the Midland Valley of Scotland, the Cheviots and the South 
Wales area, while the intervening tracts were elevated into mountains in which 
powerful but intermittent torrents wore out deep gorges and accumulated the debris 
in alluvial fans. (T. G. Bonne y, Rep. Brit. Assoc. 1886, p. 617; Evans, 1892 
and Geol. Mag. 1903, p. 549; Goodchild 1898 and Walther, Die Denudation 
in der Wiiste (1890) and later works). 

The time occupied by the deposition of the Lower Old Red deposits was com- 
paratively short to judge by the little change that took place in the fish fauna; 
while the fact that Pteraspis, which is so characteristic of them, occurs in the lower 



120 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

beds of the marine Lower Devonian and never in the Gothlandian leaves no doubt 
of their Devonian age. 

After the last volcanic eruptions in the Central Valley and a period of quiet 
during which the deposits became progressively finer in grain, a new series of 
earth movements appears to have commenced, which may have been connected 
with the major and minor intrusions that constituted the later stages of Lower 
Old Red Sandstone igneous activity. 

The Basement Beds of the Middle Old Red Sandstone consist mainly of torren- 
tial deposits, but sheets of water appear to have been subsequently formed, which 
were more persistent than those of the Lower Old Red Sandstone and gave rise 
to abundant vegetation, transmuted in process of time into the bitumen that is 
now characteristic of the Caithness Flags. The conditions that then prevailed may 
be compared to those of Lake Chad in Central Africa at the present day. At 
the time when the Achanarras Band were laid down, the area under water was en- 
larged so as to include the Moray Firth, the Orkneys and possibly the Shetlands, 
but the continued existence of arid conditions in the adjoining land areas is 
rendered probable by the presence in the flags of rounded sand grains. The 
southern area was soon again left dry, its fish fauna being preserved in the 
calcareous concretions that were formed as the waters evaporated. The same process 
was subsequently repeated in Caithness and the Orkneys. It is illustrated by 
an observation of J. R. Buchanan (Nature vol. 88, 1911, p. 107). 

The prolonged period that elapsed between the deposition of the Lower and 
Middle Old Red Sandstone is evidenced not only by the erosion which must have 
taken place but by the striking change in the fish fauna. There are only three families 
common to both: the Cephalaspidae, Coccosteidae and Acanthodidae and these all 
continue into the Upper Devonian or Upper Old Red Sandstone of Europe or Ame- 
rica 1 . The six remaining families of the Middle Old Red, the Asterolepidae, Osteo- 
lepidae, Rhizodontidae, Holoptychiidae, Ctenodontidae and Palaeoniscidae are also 
found in the Upper Old Red Sandstone, to which it is therefore much more closely 
linked than to the Lower. It must be nearly contemporaneous with the Russian 
Middle Old Red Sandstone of the Baltic Provinces, which overlies unconformably 
pre-Devonian rocks and is- covered conformably by marine limestone of Givetian 
age; for the forms common to the Scotch and Russian deposits include Osteolepis 
macrolepidotus, Gyroptychius microlepidotus (= angustus), Diplopterus agassizi 
(= macrocephalus), Dipterus valenciennesi and Estheria membranacea. It is also 
linked with the Middle Devonian of the Eifel by the genera Dipterus, Pterichthys 
and Osteolepis 2 . 

During the Upper Old Red times strongly arid conditions at first prevailed, 
but later there seems to have been a gradual amelioration of the climate. In the 
Moray Firth area the Nairn Sandstone can be correlated with the Wenden deposits on 
the banks of the Aa in Livonia, while the Alves or Scaat Craig Beds near Elgin 
correspond as a whole with those of the Sjass River in the Government of St. Peters- 
burg and the Psammites de Condroz in Belgium. 

1 The Middle Old Red Sandstone Acanthodidae show characters intermediate between 
those of the Lower Old Red Sandstone and later forms. 

2 The presence of these freshwater forms in marine deposits presents no difficulty, 
as at the present time many fish live both in fresh and salt water. On the other hand the 
fact that several of the Old Red Sandstone fish families extend upwards into the undoub- 
tedly fresh-water deposits of the Carboniferous is a confirmation of the view that they 
were fresh-water types. It is probable that the Old Red Sandstone fish, like their living 
allies, Polypterus, Ceratodus, Protopterus and Lepidosiren, were to a greater or less extent 
air breathers and able to live through periods of drought. Estheria still survives and is 
frequently found in more or less saline pools in arid areas, though it also occurs in fresh water. 



Harker: Great Britain. — Igneous Rocks of Devonian Age. (III. 1.) 121 

In Northumberland and the South of Scotland, where the lowest Carboni- 
ferous beds are of fresh water origin, it is not easy to define the upper limit of 
the Old Red Sandstone in the absence of fish remains; which are quite distinct 
in the two formations. 

In the south of England the relation of the Devonian to the underlying rocks 
is uncertain. There is however clear evidence that the recession of the sea extended 
to this region in early Devonian times, represented by the Dartmouth Slates and 
Foreland Grits. Afterwards the sea advanced over the whole area but retreated 
again at the close of the Lower Devonian, so that in the south the water became 
shallow and further north land conditions prevailed during most of the time 
occupied by the deposition of the Hangman Grits. Gradually the sea again ad- 
vanced but it did not extend over all the south-western area until late in the Middle 
Devonian, at the same time as the submergence of the Bassin de Namur and the 
Boulonnais. The maximum of marine conditions occurred early in the Upper 
Devonian and it was followed by a recession of which the extreme point is marked 
by the terrestrial Pickwell Down and Southall Beds, which were followed by the 
estuarine or littoral Baggy and Marwood Beds and the marine Pilton Beds 1 , only 
a portion of which can be claimed for the Devonian. The absence of the highest 
Devonian rocks in South Devon and Cornwall is probably due to their removal 
before the deposition of the Lower Culm. 

There is little to be said in reference to the economic products of the De- 
vonian rocks. The "killas", the more or less altered slates in which the Cornish 
mineral veins occur, may be of Devonian age, but the minerals date from a later 
period. The altered slates of Tintagel are extensively worked for roofing purposes; 
the Red Marls, when not too calcareous, are employed for brick making; the sand- 
stones make a useful and handsome building stone and the Carmyllie and Caith- 
ness flags are utilized for paving purposes. 



II. Igneous Rocks of Devonian Age. 
By Alfred Harker. 

Both the Old Red Sandstone and the marine Devonian formations of Great 
Britain afford evidence of contemporaneous volcanic activity, as well as igneous 
intrusion belonging to approximately the same age. We shall consider separately 
the Old Red Sandstone igneous rocks (with some older ones) of Scotland and the 
North of England and those associated with the Devonian strata of the South-West 
of England. In the intervening country, including the Old Red Sandstone of South 
Wales and the Welsh Border, there are no igneous rocks known to be of this age. 

Lower Old Red Sandstone Igneous Rocks. 

The Lower Old Red Sandstone age was characterized by volcanic outbreaks 
in several parts of Scotland, and also by intrusions which followed and were related 
to these. The outbreaks were distributed with reference to the N.E. — S.W. Cale- 
donian axes. Three principal areas may be distinguished: (a) the Lome and 
Glencoe district in northern Argyllshire, with Beinn Nevis a little farther north: 
(b) extensive districts along both sides of the Midi and Valley of Scotland, including 

1 The characteristic forms, Ptychopteria damnonensis and Cucullaea hardrensis are 
also found in the Psammites de Condroz of Belgium. The Pon sandstone and the rocks 
of the Grey Hook in Spitzbergen, the fauna of which has been described by Kavser, appear 
to have been laid down under similar conditions. 



122 (III. 1.) 



The British Isles. — HI. Stratigraphy. — 5. Devonian. 




Fig. 29. Sketch-map of the volcanic district of Northern Argyllshire: after 

Clough, Maufe and Bailey (from Quart. Journ. Geol. Soc, vol. 65, p. 614, 1909, with the permission of 

the Council of the Geological Society). Scale 1:633,600 or ten miles to the inch. 



on the one side the Ochil and Sidlaw Hills, with a prolongation north-eastward 
into Forfarshire, also, far to the south-west, part of Arran; on the other side the 
Pentland Hills with smaller centres extending south-westward into Ayrshire: (c) the 
Cheviot Hills, on the border of Scotland and England, to which may be added 
a district on the coast near St. Abb's Head. (See map. fig. 27, p. 101) (Geol. Survey 
maps and Memoirs; Geikie, 1897). 

In the Cheviots igneous action manifested itself in these areas under three 
successive phases (I) Volcanic, (II) Plutonic, (III) Minor Intrusions: in the 
Lome and Glencoe district the same three phases are represented, but there is a 
partial overlapping in time of the second and third: in the Midland Valley plutonic 
intrusions are wanting. 

(I) Volcanic Phase. Although the volcanic rocks here considered are of Lower 
Old Red Sandstone age, it is not possible to correlate very exactly those of the 
several areas. In Glencoe the volcanic series, with an estimated thickness of over 
1100 m. (3500 ft.), rests directly upon the old crystalline schists. Near Oban and 
elsewhere in the Lome district there is sometimes a certain thickness of sediments 
below the lavas; but the base is made by a conglomerate containing blocks derived 
from older lava-flows now destroyed. In the Midland Valley, the volcanic rocks, 



Harker: Great Britain. —  Igneous Rocks of Devonian Age. (III. 1.) 123 




Fig. 30. Geological Map and Section of Ben Nevis: after Maufe (from Summary of Progress 
L*B. for 1909, with the permission of the Director of the Geol. Survey). Scale about 1:101,000. 



more than 2000 m. (6500 ft.) thick in the Ochill Hills, overlie a considerable 
succession of stratified rocks. In general the volcanic accumulations were of sub- 
aqueous formation, but in some districts, such as Glencoe, probably subaerial. They 
alternate with ordinary sediments, but these latter are of trifling importance where 
the volcanic series is most fully developed. 

Tuffs and breccias occur interbedded with the predominant lavas, but only 
in relatively small amount; and it is evident that volcanic action here was not 
in general of the explosive type. In some districts the old volcanic vents are indica- 
ted by cylindrical "necks" of agglomerate or tuff piercing the lavas. It is possible 
that other volcanic centres are represented by some of the small boss-like intrusive 
masses which are numerous in some districts. A different type of volcanic mechanism 
is revealed in Glencoe (Clough, Maufe and Bailey, 1909). The lavas in this 
district are confined mainly to an elliptic area measuring about 14 x / 2 by 8 km. (8 by 
5 miles), which is bounded by a curved fault, and has been let down more than 
300 m. (1000 ft.) in the midst of the crystalline schists. This subsidence is believed 



124 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

to bo partly of the age of the volcanic outpourings, and it is proved to be partly 
contemporaneous with a broken ring of intrusions which follows the outer edge of 
the fault (fig. 29). 

Petrographically the Old Red Sandstone volcanic rocks have no very wide 
range of variety. The prevalent lavas are basicpyroxene-andesites (usually named 
"porphyrites" by the older geologists), graduating into olivine-basalts. In the 
Lome district the lower part of the series is of basic augite-andesites, followed by 
porphyritic hypersthene-andesites, with a few intercalations of tuffs. These are 
followed by acid tuffs interstratified with basic lavas; then less acid tuffs with 
dacites or rhyolites and some hornblende- and mica-andesite; finally 
hypersthene-andesites with some more basic andesites and andesitic agglomerates. 
In the Glencoe district again the sequence does not follow any evident law, and in- 
deed the different flows seem to have issued from different centres. Hornblende- 
andesites are here more prominent, and in the small volcanic area of Beinn Nevis 
they prevail exclusively. On the Forfarshire coast, S. of Montrose, the lavas are 
olivine-basalts, with a few enstatite-basalts (fig. 28) (Jowett, 1913); and 
farther north, in Kincardineshire, pyroxene-andesites and basalts still preponderate, 
though there are some hornblende-biotite-andesites and one flow of rhyolite, while 
all the tuffs are of acid composition. In this part of Scotland, near the Highland 
Border, vulcanicity, characterized by the same petrographical types, had already 
broken out in Upper Silurian (Downtonian) times (Campbell, 1911). In the 
Pentland Hills the rocks are usually much altered. They are chiefly andesitic, in- 
cluding pyroxene-andesites and others with hornblende and mica; but olivine-basalts 
are abundant, and on the other hand trachytes occur, besides some rhyolites. Geikie 
has remarked that the fragmental materials which fill the vents, and so represent 
the latest products, are in general of more acid composition than the lavas through 
which they have broken. The lavas of the Cheviot Hills (Teall, Geol. Mag. 1883, 
1885) are mostly hypersthene-andesites, but augite-andesites are also found, and 
one type contains abundant biotite. Some of the lavas approach dacite in com- 
position, and a trachyte is also recorded. 

(II) Plutonic Phase. Wherever the volcanic are accompanied by plutonic 
rocks, the latter are seen to break through and metamorphose the former, and 
they must therefore be assigned, in each district, to a somewhat later epoch of the 
Lower Old Red Sandstone age. 

Some of the plutonic masses have a special interest in relation to the mecha- 
nism of intrusion. The granite of Beinn Cruachan, which divides the Lome and 
Glencoe districts, and that of Beinn Nevis seem to be of cylindrical form with appro- 
ximately vertical walls, but also with a defined upper surface. It is suggested that 
in each case a cylindrical block of the country rocks has subsided, and its place 
bas been occupied by the granitic magma which rose concurrently along 
the boundary. Moreover, the intrusion has, in each case, been effected in 
two stages; for there are two distinct granites, the younger piercing the older. 
In Beinn Nevis (Maufe, 1909) the relations are even more remarkable, for the 
summit, making the highest point in the British Isles, consists of hornblende-ande- 
sites. These rest on a portion of the Highland crystalline schists, and represent a 
cylindrical plug which has subsided in the granite magma (Fig. 30). 

The Beinn Cruachan mass is part of a string of intrusions extending about 
75 km. (47 miles) in a north-easterly direction, and including Black Mount and the Moor 
of Rannoch. The dominant rock varies between hornblende -granite and quartz- 
diorite, but more basic varieties also occur. Both at Beinn Cruachan and at Beinn 
Nevis the inner granite is of more acid composition than the outer. These rocks, 



Marker: Great Britain. — Igneous Rocks of Devonian Age. (III. 1.) 125 

containing orthoclase and plagioclase felspar in fairly equal proportions, fall into 
the monzonite family, as understood by Brogger, and more basic types of this 
family are found in the same district. An olivine-monzonite (kentallenite) occurs 
associated with the acid intrusion of Ballachulish, and also makes small intrusive 
masses in Glen Orchy and elsewhere. In the Cheviot Hills there is a relatively basic 
granite with both biotite and augite. 

Finally, there are plutonic intrusions assigned to the Lower Old Red Sandstone 
age in the English Lake District (Cumberland and Westmorland). The several 
exposures of the Skiddaw granite are doubtless parts of one continuous mass, under- 
lying the metamorphosed slates. The rock is a muscovite-biotite-granite with a 
variable amount of the white mica. This mineral is wanting in the southern part; 
while on the northern border the granite passes into a quartz-mica-rock (Harker, 
1895). The Eskdale-Wastdale mass also underlies the neighbouring rocks, produ- 
cing notable metamorphism in the Ordovician volcanic series. It is a biotite-granite 
in the south, but farther north contains muscovite in addition (Dwerryhouse, 1909). 
The porphyritic biotite-granite of Shap Fell appears to have the form of a boss 
(Harker and Marr, 1891). There is no evidence of volcanic outpourings in connec- 
tion with these intrusions. 

(Ill) Phase of Minor Intrusions. The minor intrusions which occur in the 
Lower Old Red Sandstone volcanic districts, and are disposed about the plutonic 
centres, are mostly dykes of moderate dimensions, with some sills. In the Lome 
and Glencoe districts, and at the neighbouring centre of Beinn Nevis, there is a 
partial overlapping of the plutonic and dyke phases. Most of the dykes are younger 
than the outer granite and older than the inner mass, although there are also later 
dykes, younger than any plutonic intrusion. These dykes have a N.E. — S.W. direction 
and are most thickly crowded on the N.E. and S.W. sides of the plutonic centres. 
In the Cheviot district the dykes have roughly radial grouping round the granite. 
In the English Lake District the best marked set of dykes of this age is that which 
surrounds the Shap granite, with a radial arrangement. 

Petrographically these minor intrusions fall into three groups: (a) horn- 
blende- and mica-porphyrites, with allied types of intermediate acidity; (b) 
quartz-porphyries, with allied acid types; (c) hornblende- and mica-lam- 
prophyres (spessartites, minettes, etc). It is the rule, though not without excep- 
tions, that the three groups have followed this order of succession. In the Lome 
and neighbouring districts the porphyrite dykes and sheets preponderate, but the 
acid and basic rocks also occur. In the Cheviots mica-porphyrites and quartz-felsites 
are both well represented, and in the English Lake District quartz-porphyries 
and mica-lamprophyres, with transitional varieties (Harker, 1892). 



Middle Old Red Sandstone Igneous Rocks. 

In the Old Red Sandstone of the West of Shetland there is a succession of 
volcanic and plutonic rocks, followed by minor intrusions (Peach and Horne, 1884), 
which closely resembles that which has been described in the Lome District. The 
evidence of the age of these rocks is inconclusive, but they have been correlated 
with the Bressay Flags on the east coast which are apparently of late Middle Old 
Red Sandstone age. The olivine-basalt lava in the yellow sandstones of Shapin- 
say in the Orkneys (Flett, 1895) and the andesite lava of Rhynie and the Gollochy 
Burn, south of the Moray Firth, also appear to be referable to about the same 
period (Mackie, 1913). 



126 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

Upper Old Red Sandstone Igneous Rocks. 

Although the wide-spread igneous action in the Old Red Sandstone was limi- 
ted to the Lower division of that system, there was at a later time a revival of acti- 
vity on a much smaller scale and confined to isolated districts. In the island of 
Hoy, one of the Orkney Isles, a small volcanic group, consisting of bedded tuffs 
and lavas, occurs at the base of the Upper Old Red Sandstone. Another locality 
where volcanic rocks occur in the Upper Old Red Sandstone is in the island of 
Arran. They are found on the north side of North Glen Sannox, and consist of 
altered olivine-basalt lavas. Precursors of the Carboniferous lavas are also to be found 
in the Upper Old Red Sandstone of Berwickshire (Geikie, 1897). 

Devonian Igneous Rocks of S.W. England. 

The Palaeozoic igneous rocks of Cornwall and Devonshire, involved in the 
folding and faulting which have affected the strata of this region, have had their 
original geological relations partly obscured. Nevertheless it has been recognized 
that there are Devonian igneous rocks, to be distinguished from the older (Ordovi- 
cian) and the younger (Carboniferous and Permian), and that they comprise both 
contemporaneous and intrusive occurrences. 

In North Devon igneous rocks are almost wanting, but in South Devon both 
interbedded and intrusive igneous rocks of this age are found, from Torquay west- 
ward. The true volcanic rocks are in some force near Torquay and Plymouth, and 
can be followed north-westward across Cornwall to Pentire Point and Port Isaac. 
Volcanic action began in the later part of the Middle Devonian with the Ashpring- 
ton Volcanic Series, continued in the Upper Devonian, when it attained its maximum, 
and did not become extinct until the time of the Lower Culm. 

Petrographically the rocks are of basic composition, but their true nature 
is much obscured by secondary alteration and often also by crushing. The lavas 
are mainly of the spilite type, sometimes showing the peculiar "pillow" structure. 
When crushed and cleaved they resemble the " Schal stein" of German petro- 
graphers. The ferro-magnesian minerals are destroyed and the original felspars replaced 
by albite or albite-oligoclase, probably as a solfataric change (Dewey and Flett, 
1911). The associated intrusive diabases and proterobases are also albitized and 
often crushed. There are also some picrites, mostly hornblendic. The slates in 
contact with the diabase intrusions, notably in the Padstow district of North Corn- 
wall, are in places thoroughly albitized and converted to rocks of the adinole type. 



Ribliography of the Devonian and Old Red Sandstone of Great Britain. 

I. Southern Area. 

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1878. Champernowne, A., Geol, Mag., pp. 193-199 (Structure of North and South Devon). 
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1879. — and Ussher, W. A. E., Quart. Journ. Geol. Soc, vol. 35, pp. 532-548 

(West Somerset). 

1892. Collins, J. H., Trans. Roy. Geol. Soc. Cornwall, vol.11, pp. 421-479 (Cornish 

fossils). 

1893. — Trans. Roy. Geol. Soc. Cornwall, vol. 11, pp. 553-559 (Petraia). 

1894. — Trans. Roy. Geol. Soc. Cornwall, vol. 11, pp. 645-654 (Petraia). 

1900. Crick, G. C, Trans. Roy. Geol. Soc. Cornwall, vol.12, pp. 338-341 (Cephalopoda). 
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Somerset, Mem. Geol. Surv. (General). 



Bibliography of the Devonian and Old Red Sandstone of Great Britain. (III. 1.) 127 

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morphosed Devonian). 

1911. — and J. S. Flett, Geol. Mag., pp. 202-209, 241-248 (Pillow lavas and esso- 

ciatcd rocks). 
1867. Etheridge, R., Quart. Journ. Geol. Soc, vol.33, pp. 563-698 (West Somerset and 

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verneuili). 
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1895 (2). — Trans. Roy. Geol. Soc. Cornw., vol. 11, pp. 637-644 (Fossils of North 
Cornwall), ib. pp. 687-724 (Cherts and associated rocks). 

1899. — Trans. Roy. Geol. Soc. Cornw., vol. 12, pp. 278-282 (Radiolarian cherts, fossils). 
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G. J. Hinde, A. Smith Woodward, F. A. Bather and G. C. Crick). 

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1897. Gregory, J. W., Geol. Mag., pp. 59-62, 191 (Morte Slates). 

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pp. 133-134 (North Devon Fossils). 

1910. — Proc. Geol. Assoc, vol. 21, pp. 461, 466, 472 (North Devon, Geological 

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1896. Hicks, Henry, Quart. Journ. Geol. Soc, vol.52, pp. 254-272 (Morte Slates). 

1897. — Geol. Mag., pp. 105-109 (Morte Slates). 

1897. — Quart. Journ. Geol. Soc, vol.53, pp. 438-462 (Morte Slates). 
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1868. Holl, H. B., Quart. Journ. Geol. Soc, vol. 24, pp. 400-454 (South Devon and East 

Cornwall). 
1866. Jukes, J. B., Quart. Journ. Geol. Soc, vol.22, pp. 346-371 (Structure of North Devon). 

1900. Jukes-Browne, A. J., Proc. Geol. Assoc, vol. 19, pp. 291-302 (Limestones near 

Torquay). 

1913.  — Proc. Geol. Assoc, vol.24, pp. 14-32 (Limestones near Torquay). 

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and West Somerset. Mem. Geol. Surv. 
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North Cornwall). 
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1872. Symonds, W. S., Records of the Rocks, pp. 257-302. 

1909. Thomas, Ivor, Geol. Mag., pp. 167-169, 193-201 (Trilobites). 



128 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

1912. Thomas, Ivor, Geol. Mag., pp. 82-84 (Orthis in Grampound Grit). 

1881. Ussher, W. A. E., Geol. Mag., pp. 441-448 (North Devon and West Somerset). 
1885. — Proc. Geol. Assoc, vol. 8, pp. 442-450 (South Devon). 

1890. — Rep. Brit. Assoc, 1889, pp. 578-580 (General). 
1904. — Geol. Mag., pp. 587-591 (Cornwall). 

1910. — Geology in the Field (Jub. Vol., Geol. Assoc), pp. 861-862, 864-869, 

875-885 (Cornwall Devon and West Somerset). 
1889. Whitaker, William, The Geology of London, Mem. Geol. Surv., pp. 31-34 (Rocks 

under London). 
1889-1907. Whidborne, G. F., Devonian Fauna of the South of England, Palaeont. Soc, 

vols. 1 and 2 (South Devon). 
1896-1907. — Devonian Fauna of the South of England, Palaeont. Soc, vol. 3 (Marwood 

and Pilton Beds, North Devon and West Somerset). 

1899. Woodward, A. Smith, Trans. Roy. Geol. Soc. Cornw., vol. 12, pp. 229-232 (Pteraspis). 

1900. — Trans. Roy. Geol. Soc. Cornw., vol. 12, pp. 351, 356 (Fish forms, Bedruthan 

Steps and Watergate Bay). 

1901. — Trans. Roy. Geol. Soc. Cornw., vol. 12, pp. 431-433 (Fish from Looe). 

1902. — Trans. Roy. Geol. Soc. Cornw., vol. 12, p. 538 (Fish from Watergate Bay). 

1903. — Trans. Roy. Geol. Soc. Cornw., vol. 12, p. 759 (Fish from Gunwalloe). 

1913. — Quart. Journ. Geol. Soc, vol. 59, pp. 82-83 (Fish from Southall boring). 

1891. Worth, R. N., Trans. Roy. Geol. Soc. Cornw., vol.11, pp. 381-389 (Succession at 

Plymouth). 

Geological Survey. 
Memoirs illustrating sheets 295, 325, 335-339, 346-356, 358 and 359, 1", new series, of the 

Geological Survey of England and Wales, by G, Barrow, H. Dewey, J. B. 

Hill, D. A. Macalister, W. Pollard, Clement Reid, J. B. Scrivenor, 

W. A. E. Ussher, with petrological contributions by J. S. Flett and J. J. 

H. Teall. 
See also Sir H. T. De la Beche, J. Phillips and Clement Reid. 

South Wales and Welsh Border. 

1862. Egerton, Sir P. de M. G., Quart. Journ. Geol. Soc, vol.18, pp. 103-106 (Bothrio- 

lepis). 

1912. King, W. W. and Lewis, W. J., Geol. Mag., pp. 487-8, 491 (Staffordshire). 

1910. Reynolds, S. H., Geology in the Field, Jub. vol., Geol. Assoc, pp. 316-319 (Glou- 
cester and East Somerset). 

1863. Salter, J. W., Quart. Journ. Geol. Soc, vol. 19, pp. 476-478,494-496 (Upper Old 

Red Sandst. of Pembrokeshire, Somerset, Gloucestershire and Shropshire). 
1879. Sollas, W. J., Quart. Journ. Geol. Soc, vol. 35, pp. 489-495 (Neighbourhood of 

Cardiff). 
1872. Symonds, W. S., Records of the Rocks, pp. 212-256 (General). 
1894. Traquair, R. H., Ann. Mag. Nat. Hist., pp. 368-370 (Parexus, Phlyctaenaspis). 
1898. —  Ann. Mag. Nat. Hist., pp. 67-69 (Psammosteus, Protodus). 
1870. Woodward, H. Trans. Woolhope Naturalists' Field Club, -pp.266 to 270. (Prae- 

arcturus). 

Geological Survey. 
Memoirs illustrating sheets 226-232, 224-249 and 261-263, l",'new series, of the Geol. 

Survey of England and Wales, by T. C. Cantrill, J. R. Dakyns, E. E. L. 

Dixon, Walcot Gibson, Aubrey Strahan, Herbert H. Thomas, R. H. 

Tiddemann, W. W. Watts, B. S. N. Wilkinson and H.B.Woodward. 

North^Wales, Isle of Man and North of England (including the Cheviots). 

1909. Dwerryhouse, A. R., Quart. Journ. Geol. Soc, vol. 65, pp. 55-80 (Igneous rocks 
of Eskdale). 

1892. Harker, Alfred, Geol. Mag., pp. 199-206 (Lamprophyres of the North of England). 

1894. — Quart. Journ. Geol. Soc, vol. 50, pp. 311-337 (Carrock Fell Gabbro). 

1895. — Quart. Journ. Geol. Soc, vol. 51, pp. 125-148 (Carrock Fell Granophyre and 

Grainsgill Greisen). 
1891. — and Marr, J. E., Quart. Journ. Geol. Soc, vol.47, pp. 442-461 (Shap 
Granite, etc.). 

1893. — — Quart. Journ. Geol. Soc, vol. 49, pp. 359-371 (Metamorphic Rocks round 

Shap Granite). 
1903. Lamplugh, G. W., Geology of the Isle of Man. Mem. Geol. Surv., pp. 190-197 
("Basement Conglomerate"). 



Bibliography of the Devonian and Old Red Sandstone of Great Britain. (III. 1.) 129 

1900. Marr, J. E., Proc. Geol. Assoc, vol. 16, p. 471 (Lake District). 

1868. Nicholson, H. A., Trans. Edinb. Geol. Soc, vol.1, pp. 15-18 (Plants in Old Red 

Sandstone of Westmorland). 
1883. Teall, J. J. H., Geol. Mag., pp. 100-108, 145-152, 252-262 and 344-348 (Igneous 

Rocks of the Cheviots). 
1885. — Geol. Mag., pp. 106-121 (id.). 
1880. Ward, J. Clifton, Geol. Mag., p. 4 (Isle of Man). 

Geological Survey. 
North Wales, Memoirs to sheets, old series: 79 NW (Rhyl etc.), 79 SE (Flint etc.), by Aubrey 

Strahan and others. 
Isle of Man, see Lamplugh, G. W. 
North of England, Memoirs to sheets, old and new series: 108 NE = 5 (Cheviots); 108 SE=8 

(Otterburn); 101 SE = 29 (North of Lake District); 98 NE = 39 (Kendal); 

97 NW = 40 (Mallerstang); and 98 SE = 79 (Kirkby Londsdale) by W. T. 

Aveline, C. T. Clough, Hugh Miller jun., J. Clifton Ward and others. 

Scotland. 

1911. Campbell, Robert, Geol. Mag., pp. 68-69 (Kincardineshire). 

1912. — Proc. Geol. Assoc, vol. 23, pp. 291-2, 297-3 (id.) 

1909. Carruthers, R. G., Summary of Progress, Geol. Survey 1908, pp. 87-92 (Strati- 
graphical position of the Achanarras fauna). 

1909. Clough, C. T., Maufe, H. B. and Bailey, E. B., Quart. Journ. Geol. Soc, vol. 65, 
pp. 611-678 ("Cauldron-Subsidence" of Glen Coe). 

1912. Don, A. W. R., Geol. Mag., p. 469 (Parka decipiens). 

1891. Evans, J. W., The Geology of the North-East of Caithness. 

1898. Flett, J. S., Trans. Roy. Soc. Edinb., vol.39, pp. 383-424 (Orkney sediments). 

1909. — Trans. Roy. Soc Edinb., vol. 46, pp. 313-319 (Shetland). 

1879. Geikie, Sir A., Trans. Roy. Soc. Edinb., vol. 28, pp. 345-452 (North of Scotland, 

Orkney and Shetland). 
1897. — The Ancient volcanoes of Great Britain, Chapters 16-21. 
1897 Goodchild, J. G. (1)., Proc. Geol. Assoc, vol.15, pp. 125-127 (Neighbourhood of 

Edinburgh). 
1897 — (2). Trans. Edinb. Geol. Soc, vol. 7, pp. 203-222 (also in another version in 

Trans. Geol. Soc. Glasgow, vol. 11, pp. 71-104, 1898) (Desert conditions). 
1897 — (3). Proc Roy. Phys. Soc. Edinb., vol. 13, pp. 316—327 (Bituminous cement 

of Caithness Flags). 

1903. — Proc. Geol. Assoc, vol. 18, pp. 113-120 (Lower Tweedside). 

1904. — Geol. Mag., pp. 591-602 (North of England and Scotland). 
1908. Hickling, G., Geol. Mag., pp. 397-408 (Forfarshire). 

1912. — Proc. Geol. Assoc, vol. 23, pp. 299-311 (with full bibliography). 

1901. Horne, J., Geol. Mag., pp. 464-466 and Rep. Brit. Assoc, for 1901, pp. 615-631 (1902), 

(General). 

1913. Jowett, A., Quart. Journ. Geol. Soc, vol. 69, pp. 459 — 463 (volcanic, Forfarshire). 
1886. Kidston, R., Catalog. Palaeoz. Plants, British Museum, Nat. Hist., pp. 232-235, 238-9. 

1902. — The Geology of Lower Strathspey, Expl. of sheet 85. Geol. Surv. Scotland, 

p. 83 (Stratigraphical evidence of plants). 

1914. Mackie, W., Trans. Edinb. Geol. Soc, vol.10, pp. 205-236 (Rhynie). 

1908. MacNair, P., The Geology and Scenery of the Grampians and the Valley of Strath- 
more, vol.2, pp. 6-15 (Forfarshire, etc.). 

1910. Maufe, H. B., Summary of Progress, Geol. Surv., 1909, pp. 80-89 (Ben Nevis). 
1859. Murchison, Sir R. I., Quart. Journ. Geol. Surv., vol. 15, pp. 393-416 (North of 

Scotland, Orkney and Shetland). 

1892. Newton, E. T., Geol. Mag., pp. 51— 52 (Onychodus = Protodus) . 

1878. Peach, B.N. and Horne, J., Proc. Roy. Phys. Soc. Edinb., vol. 5, pp. 329-342 

(Orkneys). 

1879. — — Quart. Journ. Geol. Soc, vol. 35, pp. 783-790 (Shetland). 

1884. — — Trans. Roy. Soc. Edinb., vol. 32, pp. 359-388 (Shetland, Igneous; plant 
remains, p. 364). 

1905. — — Rep. Brit. Assoc, 1904, pp. 546-7 (Division between Old Red Sandstone 

and Carboniferous near Edinburgh). 
1858. Salter, J. W., Quart. Journ. Geol. Soc, vol. 14, pp. 72-78, including note by John 

Miller (Plants from Caithness). 
1888. Traquair, R. H. (1)., Geol. Mag., pp. 507-517 (Nomenclature of Old Red Sandstone 

fishes). 
1888. — (2). Ann. Nat. Hist. {6 th series), vol. 2, pp. 485-504 (Asterolepidae). 

Handbuch der regionalen Geologie. III. i. 9 



130 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

d890. Traquair, R. H., (1). Ann. Nat. Hist., vol. 6,4 pp. 79-486 (Achanarras and Palaeospon- 
dylus). 

d890. — (2). Proc. Roy. Soc. Edinb., vol. d7, pp. 385-400 (Dipnoi and Ganoidei). 

d892. — (1). Proc. Roy. Phys. Soc. Edinb., vol. dd, pp. 283-286 (Asterolepidae). 

d892. — (2). Ann. Scot. Nat. Hist., pp. 3d-38 (Types and figured spp. in Powrie collec- 
tion of fish). 

d892. — (3). Ann. Scot. Nat. Hist., pp. 233-235 (Gyroptychius (?) from Dura Den). 

d893. — Proc. Roy. Phys. Soc. Edinb., vol. d2, pp. 87-94 ( Palaeospondylus) and 
pp. 279-286 (Achanarras). 

1894. — (d). Ann. Scot. Nat. Hist., pp. 94-99 (Palaeospondylus). 

1894. — (2). Ann. Scot. Nat. Hist., pp. 225-226 (Psammosteus taylori). 

d894. — (3). Proc. Roy. Phys. Soc. Edinb., vol. d2, pp. 269-273 (Cephalaspis from 
Caithness Flags), pp. 279-286 (Achanarras), pp. 3d2-32d (Palaeospondylus). 

1894. — (4). Palseont. Soc, vol. 48, Monograph of the Fishes of the Old Red Sandstone 
of Britain, part 2, No. 1 (Asterolepidae), pp. 1-90. 

1896.  — The Extinct Vertebrata of the Moray Firth Area, forming part of the Verte- 

brate Fauna of the Moray Basin, pp. 235-285 (Middle and Upper Old Red 
Sandstone). 

1897. — Proc. Roy. Phys. Soc. Edinb., vol.13, pp. 376-385 (Fish of Upper Old Red 

Sandstone of the Moray Firth Area). 

1898. — Ann. Nat. Hist., 7 th series, vol.2, pp. 68— 70 (Protodus and Farnellia). 

1899. — Trans. Roy. Soc. Edinb., vol. 39, pp. 591-593 (Cephalaspis irom Oban); 

595-602 (Thelodus from Old Red Sandstone of Forfarshire). 
1902. — The Geology of Lower Strathspey. Expl. of Sheet 85, Geol. Surv. Scotl., 
pp. 81-83 (Stratigraphical Evidence of Fish). 

1904. — Palseont. Soc, vol. 58, Monogr. of the Fishes of the Old Red Sandstone of 

Britain, part 2, No. 2, pp. 91-118 (Asterolepidae). 

1905. — Rep. Brit. Assoc, 1904, pp. 547—548 (Upper Old Red Sandstone Fish of the 

Edinburgh District and of the Moray Firth Area). 

1906. — Pala?ont. Soc, vol.60, No. 3, pp. 119-130 (Asterolepidae). 

1909. — (1). Summ. Progr. Geol. Surv., 1908, pp. 92-93 (Fish fron Niand Limestone). 
1909. — (2). Trans. Roy. Soc. Edinb., vol. 46, pp. 321-329 (Fish from Shetland). 
1913. Tyrrell, G.W., Trans. Geol. Soc Glasgow, vol. 15, pp. 64—83 (Igneous, Carrick Hills). 
1908. Watson, D. M. S., Geol. Mag., p. 431 (Coccosteus minor, Homosteus milleri and 
osteolepid scales near Dalcross in Invernessshire). 

Geological Survey. 

Memoirs dealing with the following districts: Islay (19,20,27), 1907; Buteshire etc. (21), 
1903; Cowall (29, 37, 38), 1897; Edinburgh (31,32), 2 nd Ed., 19d0; East 
Lothian (33, 34, 4d), 2 nd Ed., d9d0; Seaboard of Mid Argyll (36), d909; Mid 
Argyll (37), d905; Central and Western Fife, etc. (40, etc), d900; Eastern 
Fife (4d, etc.), d902; Oban and Dalmally (45), d908; Lower Strathspey (85), 
d902; Glenelg, etc. (7d), d9d0; Beauly and Inverness (83), 1917; Caithness 
(110, 116), 1914. The numbers in parentheses are those of the sheets of the 
lin. Geological Map of Scotland now in progress. 

The Authors include R. G. Carruthers, C. T. Clough, C. B. Crampton, Sir A. Geikie, 
J. B. Hill, H. Kynaston, H. B. Maufe, and B. N. Peach. 

References to the Old Red Sandstone also occur in the explanations of other sheets and in 
the Summary of Progress (see especially contributions by R. G. Carruthers, 
H. B. Maufe and under Traquair, 1909). 



b. Ireland. 
By G. A. J. Cole. 
The Devonian system in Ireland is represented almost entirely by freshwater 
or terrestrial deposits of the Old Red Sandstone type. In the south, these resemble 
those of South Wales; but it is possible that the Dingle Beds, which appear to rest 
conformably on the Ludlow series in the Dingle Promontory, correspond with 
the passage beds of Ludlow town and the earlier part of the Welsh Old Red Sand- 
stone, while the mass of sandstones and conglomerates of Kerry, Cork, and Water- 
ford are of a somewhat later date. 

The Dingle Beds proper are known only in the Dingle Promontory, and 
are a series of grits, sandstones, and slates, 3000 m. (10000 ft.) thick, unfortunately 



Cole: Ireland. (III. 1.) 131 

devoid of contemporaneous fossils. A few fossils occurring in pebbles have been 
held to be derived from Llandovery strata, and in any case they show that 
the Lower Devonian upheaval had already begun in adjacent areas. The great 
earthfolds ultimately reached the Dingle area, and the characteristic conglomerates 
of the Old Red Sandstone overlie the Dingle Beds and the Ordovician strata with 
striking unconformity. Hence G. H. Kinahan and others relegated the Dingle 
Beds to the Gothlandian. A. McHenry (1912) has now suggested that, by reversed 
folding, their present position is misleading, and that they really underlie the 
Wenlock series, and are of Llandovery age (see p. 103). Jukes, on lithological grounds, 
connected certain grits in the lower part of the Old Red Sandstone of Glengariff 
with the Dingle Beds, under the name of Glengarriff Grits; but the unconformity 
characteristic of the Dingle Promontory has not been proved to occur within Devo- 
nian strata elsewhere in southern Ireland. The division that has been attempted 
between an upper and a lower series on Hull's general map of Ireland, since its 
first issue in 1878, and on some later editions of the maps of the Geological Survey, 
cannot be regarded as more than a suggestion (Jukes 1866, Kinahan 1878, 1879, 
Hull 1879, 1882) . It is of course possible that the base of the Old Red Sandstone 
in the Glengarriff area, which is not seen, may rest conformably on Gothlandian 
rocks; but its general unconformity on these strata is conspicuous round the 
Gothlandian exposures in the north of Co. Cork. If the Old Red Sandstone 
of southern Cork and southern Kerry is of the South Welsh type, its highest beds 
may be found overlapping the lower ones against a slope of the Caledonian land- 
surface, which descended originally from the north, while its true base may be, as 
Kinahan evidently felt to be the case, conformable on a Ludlow series down below. 
For a general account of the southern Irish Old Red Sandstone see Jukes (1866). 

The Old Red Sandstone of Ireland consists mostly of brownish to purplish 
conglomerates, with numerous pebbles of quartz-rock and quartzite, and inter- 
calated grits and sandstones. Except for a few plant-stems, it is almost devoid 
of fossil remains, until we reach its highest series. It thickens in the southern region 
from about 1000 m. (say 3000 ft.) in Co. Waterford to more than 3000 m. (10000 ft.) 
in Cork and Kerry. As shown above, it is not clear if we must add another 3000 m. 
by the inclusion of the Dingle Beds. The Old Red Sandstone overlying the Dingle 
Beds in the Dingle area is 1300 m. (4300 ft.) thick. The folds into which the country 
has been thrown by the Armorican earth-movements, together with the resistance of 
the conglomeratic beds to denudation, have caused the Old Red Sandstone to stand out 
in a fine serie of east-and-west ridges, which include in Kerry the grandest rock- 
scenery of Ireland. The unconformity of the strata on the Older Palaeozoic slates is 
well seen .on the north of of the Suir at Waterford, and in many of the inliers of 
Gothlandian or Ordovician rocks that occur within the Old Red Sandstone domes. 

These domes, produced by the Armorican folding, are a characteristic feature 
of the interior of Ireland, the Old Red Sandstone coming up in the form of some- 
what barren hills from beneath the Carboniferous Limestone Series, which overlies 
it conformably throughout the region. 

At the top of the typical Old Red Sandstone conglomerates there occurs a series 
of yellowish fine-grained sandstones, 150 to 300 m. (500 to 1000 ft.) thick, known as 
the Yellow Sandstone Series or Kiltorcan Beds. This is perfectly confor- 
mable to the Old Red Sandstone beds below, and has been styled on Geological Survey 
maps the Upper Old Red Sandstone. It has thus no similarity to the beds so 
styled in the Cheviots, except that it passes up conformably into the Lower 
Carboniferous strata. These gently deposited beds have preserved at Kiltorcan 
quarry, near Ballyhale in Kilkenny, an interesting freshwater fauna and a terre- 
strial flora of late Devonian age. The most abundant fossil is the large fern 

9* 



132 (III. 1) 



The British Isles. — III. Stratigraphy. — 5. Devonian. 



3 

to 



Bo P 

2. K » 

- ° — 

2. c a o 



O ffi ,- B* 
» S- i» 
2. o §„ 

ftS O CD Q* 

~ " ~ a 
co II .^o. 



"" o «~ 
VO o Ort- 

.>*-» so • „ 

r»- -• (o O 

o « o. ""S 
SS? II Sc 

15 t*-* 2 



2. o 3 
 o „.o- 
"■ 5 o 



is 1 - 

«+ -• rr© 



_ 1-4. 

B fd 

I. s. 

1 to 



B- o 

» B 



: 

f 



Archaeopteris hibernica. Long striated 
stems known as Filicites occur, with 
Bothrodendron, Sagenaria, Lepidoden- 
dron, and Sphenopteris. The fauna is 
composed of the earliest known fresh- 
water mollusc, Archanodon Jukesii, a 
small Belinurus (B. kiltorkensis) , a 
large isopod (Oxyuropoda UgioidesC\R- 
PENTERand Swain), fragments olEuryp- 
terus, and of a few Devonian placoganoid 
fishes, including Coccosteus disjectus 
Smith Woodward, and Glyptolepis. 
Archanodon has also been found near 
Clonmel, and a little east of Cork city, 
in the latter case with Archaeopteris, 
and the flora is represented at one or 
two places near Fermoy. (Geol. Surv., 
Lamplugh 1905, W. Baily 1861, 1869 
and 1875—7, Johnson 1911, Cole 1901, 
Carpenter and Swain 1908.) 

Considerable discussion has arisen 
over the fauna of the Coomhola 
Grits, (Jukes, 1866, p. 106, and 
1868, p. 68., Lamplugh, Geol. Surv., 
Mem. on country around Cork, 1905, 
p. 13) which are beds of sandstone oc- 
curring at various levels in the Car- 
boniferous Slate, but more abundantly 
in the lower part of it. Jukes assigns 
to them in places a thickness of 900 m. 
(3000ft.). The typical section in them is 
at Ardnaturrish, on the eastern shore of 
the approach to Glengarriff Harbour, in 
BantryBay. The lower horizon contains 
a fauna that includes Curtonotus (several 
species), Cucullaea hardingi, and Avi- 
cula damnoniensis ; and it is probable 
that we have here marine beds of 
Upper Devonian age, heralding the 
return of the sea across the Old Red 
Sandstone region. The classification of 
these beds, and, indeed, of all the 
series in Ireland between the Ludlow 
Series and the top of the Carboniferous 
Limestone, has been complicated by 
certain views of Jukes, followed by 
Kinahan, to which reference will be 
made when the Carboniferous strata 
are described (p. 172). 
Beds of the ordinary Old Red Sandstone type occur on the margin of Clew 
Bay, and on the north side of the plain along the Curlew Hills. A large outcrop of 
similar red conglomerates and sandstones stretches from Enniskillen to Pomeroy 



5 




Cole: Ireland. (III. 1.) 133 

in the county of Tyrone. These latter are the Fintona Beds, which have often 
been correlated with the Dingle Beds of Kerry (J. Nolan, 1880; E. Hull, 1882, 
p. 206). They rest, however, unconformably on the Silurian beds of Pomeroy, and 
there seems no adequate reason for cutting them off from the main Old Red 
Sandstone series of the south. A small exposure of very coarse quartzite-conglomerate 
occurs on the Antrim coast at Cushendun. Another patch lies on Dalradian rocks 
at Fanad in the county of Donegal, and is said to have been brought into its 
present position along a thrust plane. 

The igneous rocks directly associated with the Old Red Sandstone cannot 
be compared in importance with those of Scotland. Sphaerulitic and fluidal rhyolites, 
with some ashes, occur at Lough Guitane and at other points near Killarney; altered 
trachytes and andesites, also with fragmental products, in the Curlew Hills; 
and altered andesites, of the Scottish porphyrite type, in the Fintona Beds 
east of Omagh. But an immense number of "felsite" dykes, running generally north 
and south, cut the Caledonian folding throughout the northern half of Ireland, 
and do not penetrate the Carboniferous strata. These, if we may judge by the 
analogy of the Kainozoic dykes, provided passages for the outflow of trachytes and 
andesites of various types, which were denuded away before the overflow of the 
Carboniferous sea. On the Waterford coast, again, there are a number of igneous 
rocks intruded into the Silurian slates at an epoch later than the Caledonian folding 
of that area. These have been referred to the Old Red Sandstone; butF. R. C. Reed 
(1900), after careful discussion, believes that they cannot be later than Gothlandian. 
We must always remember that where Gothlandian rocks, as, for instance, in 
the county of Down, have been involved in the Caledonian folding, the great in- 
trusions of granite that are associated with the anticlinal arches must be of early 
Devonian age. 

Lakes probably gathered in the hollows of the early Devonian land, though 
it is now difficult to trace their boundaries in the Irish area. Broad fans of siliceous 
detritus accumulated on and spread across the land-surface. In the south, the 
succession and type of deposits resemble those of South Wales, though the unconfor- 
mity of these deposits on the Older Palaeozoic rocks is far more marked in Ireland. 
When the Dingle Beds became steeply uptilted, the typical Old Red Sandstone conglo- 
merate spread across their denuded edges. The mountain ranges of Dalradian rocks, 
with their characteristic Caledonian trend, must have supplied an enormous amount 
of detrital material to the hollow regions of the land. In some parts of the south, 
muds were accumulated; but on the whole the Devonian deposits indicate beaches 
and terrestrial taluses of varying coarseness, in which conglomerates predominate, 
mainly composed of the rocks best calculated to resist prolonged weathering action. 
A large part of the material consists of subangular stones (quartzite and vein-quartz 
and jasper), cemented in a sand. Where true pebbles occur, they were doubtless 
well rounded in the torrents that streamed down from the mountains, before they 
came under the influence of waves along the margins of the lakes. The Lower 
Devonian and older granites supplied some of the material ; but the stones now left to 
us must represent only a portion, naturally selected, of the waste-materials from the 
Dalradian, Ordovician and Gothlandian rocks. The Upper Old Red Sandstone of 
■the Kiltorcan and Cork type is found to underlie marine beds, which herald the 
inflow of the Carboniferous sea over a very wide area in central and southern 
Ireland; and we may be led to believe that one great estuarine flat occupied the 
region from the west of Kerry to the east of Waterford. North, however, of the 
Caledonian axis of Cavan and Newry, the Old Red Sandstone was probably laid 
down in a basin which may have been the south-westerly prolongation of that 
of the Midland Valley of Scotland. 



134 (III. 1.) 



The Rhine 



Ardennes 



Cornwall 



South Devon 



Carboniferous 



Upper Devonian 

and 

Upper Old Red 
Sandstone 



Clymenien- 
Kalk 



Pon- 
Sandstein 



Nehdener Schiefer 
Adorfer Kalk 
Budesheim. Schiefer 



Plattiger Kalk 
Kalke u. Dolomite mit 
Rhynchonella cuboides 



Calcaire d'Etroeungt 

Psammites 

de 

Condroz 



Schistes 

de 
Famenne 



(Palaeontological 
break) 



Schistes 

de 
Matagne 



Calcaires, 
Marnes et 
Schistes 



de Frasnes 



Middle Devonian 
and 



Middle Old Red 
Sandstone 



Kalke und DolomiteiCalcaire de Givet 
mit Stringocephalus 

burtini 
Crinoiden Zone | 

Calceola Mergel und, Schistes et Calcaires 

Kalke de Couvin 

Cultrijugatus Stufe 



(Palaeontological 
break) 



Green and black sla- 
tes, north of Petherwin 
South Petherwin Beds! Red and Green Slates 
(sandstones and lime- with Entomis serrato- 



stones) 
Purple and green slates 

of Daymer Bay- 
Black slates of Daymer 

Bay- 
Grey slates of Port 
Quin 



Striped calcareous sla- 
tes of Trevone Bay 
Slates of Booby's Bay 
Slates south of 

Treyarnon Point 
? Delabole Slates 
? Slates of Porth- 
cothan 



striata 
nomya 



and Posido- 
venusta 



Shaly limestone of 
Petit Tor Combe and 

Lower Dunscombe 
Mudstone with nodu- 
lar and lenticular lime- 
stone of Saltern Cove 
Lummaton Shell Bed 



Massive limestones of 
Torquay and Ply- 



Lower Devonian 
and 



Lower Old Red 
Sandstone 



Gothlandian 

or 

Silurian 



Ober-Coblenzschicht. 

Unter-Coblenzschicht. 
Hunsriick-Schiefer 

Taunus-Quarzit 



Gedinne-Schichten 



Grauwacked'Hierges I 
Poudingue de Burnot j 
Gres de Vireux 
Grauwacke de Mon- 

tigny 
Gres d'Anor 

Schistes de St. Hubert! 
Schistes d'Oignies j 



Staddon Grits 

(usually placed in the 

Lower Devonian) 



mouth 



Hope's Nose Limestone 



Shaly limest. and slates 
of Daddy Hole 

Staddon or Warberry 
Grits 



Upper Mead 
Lower Mead 



foot Beds 
foot Beds 



Dartmouth! Slates 



(including Falmouth 
Slates according to Up-! 
field Green) 



Base not seen 



Schistes de Mondre- 

puits 
Arkose d'Herbes 
Poudingue de Fepin 



| (Portscatho [and 

I'Mylor] according to 

L'pfield Green) 



Note There is considerable difficulty in correlating the Devonian rocks of the British Isles both 
among themselves and with those of the Continent of Europe and there is ample room for difference of opinion. 



(III. 1.) 135 





South Wales and border counties 




North Devon and 




Ireland 


West Somerset 








(except north) 




South-west 


North-east 


South-east 




(Palaeontological 
break) 






Cleistopora (K) zone of the Carboniferous 


Carboniferous 




(included in the Devonian by some geologists) 


Slates 


Upper Pilton Beds 








Middle and 1 Pilton 


Skrinkle | Marine 






Lower I Beds 


c..,* bands 
Sand - near 


Yellow and Red Sandstones and grits 




Baggy and Marwood 


with plant and fish remains 


Coomhola Grits 


Beds 


stones | the top 


Conglomerates 




Pickwell Down 




Brownstones (with plant remains) 




Sandstones 










Morte Slates 










(placed by some in the 










Middle Devonian, by 










Hicks in the Gothl. 








Kiltorcan Beds 

or Yellow 
Sandstone Series 

Red sandstones 


Ilfracombe 










Beds 












(Great palae- 


(Great palaeon 


tological break 


(There is no evidence 


Combe Martin Beds 


ontological break, 


but apparent conformity 


of a break in the suc- 
cession, but the Upper 


? . 


and probably 


In some places there is an 


Old Red Sandstone 
appears to overlap the 




structural 


overlap so that the Upper Old Red 


Lower to the north- 


Hangman Grits 
(usually placed in the 


discordance near 


Sandstone may rest on the 


ward) 


Lower Devonian) 


Milford Haven) 


Gothla 


ndian) 


Red 


Lynton Slates 


Ridgeway 


Senni Beds 


Sandstones 




Conglomerate 


(In some places absent; in others not yet 








separated from the Brownstones above) 


(The lowest portion of 
these sandstones in the 


Foreland Grits 


Cosheston Sand- 
stones Red Marls 

(with sandstones and cornstones) 


south - east may he 
represented in the 
south-west by the 
Dingle Beds, which are 




Basement conglomerates or grits 






(slight unconformity) 


Passage Beds from 


conformable to the 
Gothlandian, and are 






(.'■1 hi. nidi. ni 


covered unconformably 
by the Old Red Sand- 




G o t h 1 a 


n d i a n 




stone) 



In this table I have placed many of the British strata at higher horizonts relatively to 
than is usual, but in most cases similar correlations have been made by other writers. 



those of other countries 
J. W. E. 



136 





Ireland (north) 


Cheviots and adjoin- 
ing areas 


South-west of Midland 

Valley of Scotland 

and Lome 

• 


North-east of Midland 
Valley of Scotland 








(at Dura Den) 






Cement stones 


Zone of Bothrolepis 




The Upper Old Red 


Cornstone Series 


hydrophila. 
Zone of Glyptopomus 




Sandstone of the 


""""' • 


Upper Devonian 


North of Ireland is 


Red and mottled sandstones. 


and 


frequently descri- 






 


bed as the „ Base- 








Upper Old Red 


ment Beds" of the 








Sandstone 


Carboniferous, and 
the same is the case 
with the Upper 
Old Red Sandstone 
of the Isle of 
Man, North Wales, 
and the North of 
England. 
The old Red Sand- 




[There is no Upper 

Old Red Sandstone 

in Lome.] 


 




stone of the North 


(Great palaeontological and 


Middle Devonian 


of Ireland resem- 
bles that of the 


s t r u 


ctural discordai 


1 ce) 


and 


Midland Valley 
of Scotland except 








Middle Old Red 


that there is no 








Sandstone 


apparent break be- 
tween the Upper 
and Lower Old 
Red Sandstone. 


1 




Edzell Shales 


Lower Devo- 




Volcanic 
Rocks 


Strath- 
more 
Sand- 
stones 


Arbroath 

Sandstone 
Auchmithie 


nian and Lower 








Conglomerate 
Red Head 


Old Red 










Series 


Sandstone 






Sandstones and 
conglomerates 


Caimconnan Grits 
Carmyllie Series 






(unconformity) 


(unconformity) 


Dunottar Series 


Gothlandian f 
or 
Silurian [ 






Downtonian 


Downtonian 






[Ther is noDowntonian 


(unconformity) 


• 




in Lome] 







137 



Moray Firth 


Caithness 


Orkneys 


Shetland 


Russsla 










Flaggy sand- 




Rosebrae Bed with 








st. and shales 




Glyptopomus minor 








Thin bedded 




Beds with Psammo- 




Bressay 
and 


micaceous 




steus taylori 


Dunnet Head Sand- 


Sandstone of Hoy 


sandst. with 




Scaat Craig Beds with 


stone 




coarser seams, 


Sjass River Beds 


Ps. pustulatus 






Noss 


fish and plant 


Nairn Beds with Ps. 






Series 


remains Wenden deposits 


tessetatus and Aster- 








Sandst. often 


olepis maxima. 








conglomeratic Limestones with Spiri- 
with some \fer archiaci and Sp. 










shales. 


verneuili and Rhyncho- 










nella cuboides. 










Dolomite and limest. 










with Spirifer anosoffi 




John o' Groats Sand- 


Eday Sandstones 








stone Group 

(Break) 

Thurso Flagstone Gr. 


(Break) 




Grey mica- 
ceous sandst. 
with plant 


Sandstones with 


Sandstones 




Rousay Flags 




Asterolepis ( ?) 




( ? slight break) 




Lerwick 


remains and 
EsthsTia 


Osteolepis, Dipterus 


Fish Beds 


Achanarras Band 


Stromness Flags 


Series 


membranacea. 


and Estheria. 


Conglomerate 


Passage Beds Group 
Wick Flagstone Group 






Sandstones 

with rounded 

pebbles. 






Upper Conglomerate 




Rovey 


Head Conglo- 






(Break) 




merate 






Mudstones 




Red Hags of Brenista 






Basement Conglom. 


/ 


Basement Breccia 


Red Sandstones of the 
Dniester and of Poland 
with Pteraspis pass- 
ing down into the 












Gothlandian. 



J.W.E. 



138 (III. 1.) The British Isles. — III. Stratigraphy. — 5. Devonian. 

The volcanic action of Devonian times has left few lava-flows in the Irish 
region; but the immense number of dykes (p. 133) of various compact types found in 
the exposed Dalradian and Silurian areas of the north, cutting the Caledonian folds, 
but not the Carboniferous strata, shows how extensive in reality was the igneous 
basin down below. At least an equal number of these dykes must be concealed by 
the mantle of Lower Carboniferous strata; and we may assume that any lava-flows 
to which they gave rise outside the margins of the Old Red Sandstone basins became 
denuded away before the Carboniferous sea invaded the district. The Caledonian 
continent, towards the close of Devonian times, had suffered greatly from conti- 
nuous denudation. The enormous accumulations of material in the lowlands and lake- 
basins sufficiently indicate the lowering of its surface. The passage from conglomerates 
and grits to the Yellow Sandstone type of deposit, which was no doubt laid down in 
shallows by sluggish streams, suggests that the surrounding country had assumed 
the character of a peneplain. The torrents of earlier times were now replaced 
by meandering streams, moving this way and that over the surface of a land that 
was ready to admit the sea. Subsidence of the lake-floors commenced early 
in the period, and thus allowed a great thickness of deposits to accumulate; 
and this subsidence affected at the same time the adjacent land, and combined 
with denudation in bringing the Caledonian ranges nearer to the sea-level. To 
this day, in the south of Mayo, where the Lower Carboniferous beds have only 
recently been removed from the crests of the Dalradian hills, we may trace in 
the level tops of these hills the last relics of the Devonian peneplain. 

Economic Products. 

Granite. A number of Irish granites in the Dalradian areas may represent in- 
trusions that accompanied the Armorican folds; and on the east of the country, 
a definite early Devonian age can be assigned to the granites of the Leinster Chain and 
of the Newry Axis. The former is a muscovite-granite, which becomes charged with 
biotite near its junctions with the Ordovician rocks. It is extensively used for building 
in Dublin, most of the stone coming from Ballyknockan in Co. Wicklow. The Newry 
granite is rich in biotite; it is fine-grained, with occasional patches of schistose 
rocks which have been only partially absorbed, and it forms a good grey ornamental 
stone. 

Slate. Massive slate and roofing slate have been raised from the Devonian 
strata of Valencia Id., Co. Kerry. 



Bibliography of the Devonian of Ireland. 

1870. Baily, W. H., Rep. Brit. Assoc, 1869, pp. 73-75 (Kiltorcan). 
1875-1877. — Proc. Roy. Irish Acad., ser. 2, vol.2, pp. 45-48 (Kiltorcan). 

1908. Carpenter, G. H. and Swain, I., Proc. Roy. Irish Acad., vol. 27, Section B, pp. 61-67 

(Isopod from Kiltorcan). 
1901. Cole, G. A. J., Geol. Mag., pp. 52-54 (Belinurus kiltorkensis). 
1879. Hull, E., Quart. Journ. Geol. Soc. London, vol.35, pp. 699-723 (Dingle Beds, 

Glengarriff Grits & Shales). 
1882. — Quart. Journ. Geol. Soc. London, vol.38, pp. 205-206 (Dingle Beds, Glengarriff 

Grits & Shales). 
1911-1912. Johnson, T., Sci. Proc. Roy. Dublin Soc, vol. 13, pp. 114-136, 137-141, 247-252 

(Archaeopteris etc.). 

1866. Jukes, J. B., Quart. Journ. Geol. Soc. London, vol. 22, pp. 320-371 (South Ireland). 

1867. — Journ. Roy. Geol. Soc. Ireland, vol.1, pp. 103-138 (South-west Ireland, 

North Devon, Rhine). 

1871. — Journ. Roy. Geol. Soc Ireland, vol.2, pp. 67-69 (South Ireland). 



6. Carboniferous. — Kendall: Great Britain. — Sedimentary Rocks. (III. 1.) 139 

1878. Kinahan, G. H., Manual of the Geology of Ireland, pp. 52-62 (Dingle Beds & Glen- 
garriff Grits). 

1880. — Journ. Roy. Geol. Soc. Ireland, vol. 5, pp. 165-169 (Dingle Beds & Glengarriff 
Grits). 

1912. McHenry, A., Proc. Roy. Irish Acad., vol. 29, Sel. 36B, pp. 229-234 (Dingle Beds). 

1880. Nolan, J., Quart. Journ. Geol. Soc. London, vol. 36, pp. 529-535 (Old Red Sand- 
stone, North Ireland). 

1900. Reed, F. R. C, Quart. Journ. Geol. Soc. London, vol. 56, pp. 690-691 (County 
Waterford). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets : 

147, 157. Parts of Counties Kilkenny, Carlow, & Wexford ( J. B. Jukes & W. H. 

Baily), 1861. 
186, 187, 194, 195 (Parts of sheets). Cork (G. W. Lamplugh & others), 1905. 



6. Carboniferous. 

a. Great Britain (including the Isle of Man). 

I. Sedimentary Rocks. 

By Percy F. Kendall. 

The Carboniferous rocks are the most important of all the British strata, 
not only from the thickness that they attain and the great area that they occupy, 
but from the fact that they form the greatest repository of minerals of economic 
value. Coal, oil, ironstone, building-stone, limestone, brick- and pottery- 
clays or shales, fire-clay, alum shale, lead veins, chert and other valuable sub- 
stances of lesser importance are obtained from this great formation. 

The geological interest of these rocks is not inferior to their economic value, as 
they present a nearly continuous record of avast lapse of geological time during which 
great variations of physiographical and climatic conditions affected the British area. 
Marine conditions varied from the clear-water reef-conditions of some of the lime- 
stones to frequently recurring lagoon-phases. Estuarine conditions are thought 
to be represented at some stages, while the "Millstone Grit" was laid down 
mainly as a series of deltaic flats at or near the debouchure of great rivers. Terrestrial 
or swamp conditions are indicated by coal-seams and their seat-earths. In the 
early stages the region from the Tyne northward seems to have experienced condi- 
tions of desiccation that recurred at a late stage in the Coal Measure period over 
the greater part of Britain. 

The lithology varies very greatly, not only in the vertical sequence, but also 
when the rocks are followed from south to north. Thus the massive marine lime- 
stones of the Bristol area and the southern Pennines become interstratified with 
shales and sandstones with coal-seams in the North of England, and in Scotland 
their equivalents constitute the most important coal-bearing division. The old 
lithological classification into 1. Carboniferous Limestone with Yoredale 
Series, 2. Millstone Grit, and 3. Coal Measures is applicable only to a portion 
of the Pennine Region, and attempts to press into these compartments the strata 
outside that area have led to the greatest confusion. The Ybredale phase of deposi- 
tion descends to lower and lower horizons as the series is traced to the northward 
from the titular region, while to the southward its homotaxial equivalents are 
rocks whose contemporaneity is on palseontological grounds steadfastly denied by 
authorities of acknowledged competence. The Millstone Grit, another characteristic 
Pennine type, almostly completely loses its identity in Northumberland by reason 
of the occurrence of similar rocks both higher and lower in the sequence, while, in 



140 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

a southerly direction, it dwindles and disappears in the Midlands. The rocks called 
Millstone Grit in the South West Province differ from the type lithologically and 
are not restricted to a specific horizon but appear both below and above the position 
assigned to it in the classification referred to. 

Two broad palseontological divisions are recognised. An 

Upper Carboniferous comprising the Coal Measures and Millstone Grit, 
and 

Lower Carboniferous including the Pendleside Series, the Yoredale 
Rocks, Carboniferous Limestone and, locally, some Basement beds. 

The fish fauna furnishes no evidence for further subdivision though two cate- 
gories of fishes — estuarine and marine — may occur. Fresh-water lamellibranchs 
show in many areas a definite vertical succession in the Upper Carboniferous. 
Lee however suggests that the distribution is affected by local conditions and 
hence that a fauna may reappear above its proper horizon, but Hind and Stobbs 
regard the order as invariable. Only one departure from the sequence they establish 
is known to the writer, viz: in the West of Scotland (Geol. Surv. Mem. Glasgow 1911, 
p. 72, 92) and this exception can hardly be regarded as invalidating the rule. 

The marine Invertebrata are of paramount importance in the Lower Carboni- 
ferous or Avonian where they furnish materials for zonal discriminations of the 
greatest value, whereas, in the Upper division they are of little value except in 
their relation to other criteria. 

Palaeobotany on the other hand is of comparatively little value in subdivid- 
ing the Lower Carboniferous, but the Upper can be divided into four more or 
less sharply defined stages by means of the succession of plants. 

Relation of the Carboniferous Rocks to the subjacent strata. 

The Upper Devonian rocks of Devon and Cornwall and the London area 
were largely of marine origin. Elsewhere in Britain continental conditions with 
terrestrial surfaces and inland waters mainly prevailed. The wide spread submergence 
that had commenced before the close of the Devonian Period brought about a gene- 
ral transgression of the Carboniferous deposits over a diversified suite of rocks. 
In North Devon the Upper Pilton Beds, — a very early, perhaps the earliest, phase 
of the marine Carboniferous — succeed in apparent conformity the latest Devonian. 
In the Mendips, South Wales and Scotland, the Carboniferous is probably conform- 
able on the Upper Old Red Sandstone. Elsewhere the Carboniferous rests in strong 
unconformity on rocks of various earlier geological dates. 

Even before the recognition of a zonal sequence it became clear that the 
surface of pre-Carboniferous rocks was not a plain, but a country of fairly high 
relief, and though tectonic movements during the deposition of the Carboniferous 
rocks — in some cases with an amplitude of thousands of feet — make exact measure- 
ment difficult, if not impossible, it is certain that inequalities of great magnitude 
must have existed. 

The study of the zonal distribution of the Invertebrate fossils in which Gar- 
wood, Mark, Hind and Vaughan have achieved great success, and the palaeo- 
botanical work of Kidston and Arber enable the progressive submersion of old 
land features to be studied in greater detail. The broad results of these investigations 
show that at an early stage a great insular, or peninsular, mass occupied a large 
part of Central and North Wales, much of the Irish Sea, and theWicklow mountains, 
with a narrow isthmus extending to the eastward across the Midlands, which was 
not finally overwhelmed until a late stage of Coal Measure time. The region to the 



Kendall: Great Britain. — Sedimentary Rocks. — Avonian. (III. 1.) 141 

north was very irregular in relief so that while some parts succumbed to the earliest 
marine invasion, others, e. g. the Isle of Man, and the northern moiety of the Pennine 
Chain, remained above water until the Visean stage 1 . 

Lower Carboniferous Palaeontology. 

The first definite attempt to establish a zonal succession was that of Gar- 
wood and Marr (1895) who recognised six zones in the Lower Carboniferous of 
the Northern Pennines. They were followed by Hind and Howe (1901) who 
defined a series of zones characterised by species of Goniatites in a group of shales 
black limestones and sandstones to which they gave the name of the Pendleside 
Series. They found strata with the Pendelside fauna only in the country South 
of the Craven faults. In 1904 Vaughan presented the results of a minute examin- 
ation of the Lower Carboniferous Series of Bristol; but this important paper 
was not published till the succeeding year. The distinctive feature of his work 
was the recognition of an evolutionary sequence of corals and brachiopoda in which, 
not merely varietal or specific, but even generic limits were overpassed. 

In the appended table (p. 142) Vaughan's zones 2 are placed in sequence 
with those of Hind and Howe, while Garwood's recent amplification of his early 
work is brought into parallelism. 

In the Pendleside Series of Hind and Howe reliance is placed on the invariable 
sequence of the Cephalopod fauna, but the occurrence of these animals seems to 
have been entirely dependent upon special conditions of sedimentation, that were 
on the other hand inimical to the coral fauna upon which Vaughan mainly relied. 
Consequently the task of bringing the two series of zones into sequence is one of 
great difficulty, but, as in Ireland and in Derbyshire, the two faunas alternate, 
the Pendleside in the shales, and the uppermost Avonian in the limestones, it seems 
probable that they were contemporary rather than successive. The Pendleside 
phase has a wide geographical development in the West of Ireland, the Isle 
of Man, North Wales, the Pennine Chain south of the Craven faults, South Wales, 
and North and South Devon and Cornwall. It is not recognisable as such in Scot- 
land, the Northern Pennines, or in the Bristol-Mendip area. 

A. Avonian (Carboniferous Limestone). 

Stratigraphical details. 

In considering the development of the Avonian Series and its equivalents 
it is convenient to divide the area of Great Britain into six Regions: 

1. The Southern including Devon and Cornwall 

2. The South-West Province of Vaughan including the Mendip and 
Bristol areas, the Forest of Dean, Clee Hills and South Wales. 

3. The Midland comprising Derbyshire, North Staffordshire, Shropshire, 
North Wales, Anglesey and the Isle of Man. 

4. The Mid Pennine Region, including the country between Pendle and 
Clitheroe (53° 52' N.) in Lancashire, and the Craven faults. 

5. The Northern region extending from the Craven faults northward 
to the Tweed Valley. 

6. Finally the region of the Scottish Midlands extending from Dunbar 
to the Clyde. 

1 The term Tournaisian and Vis6an are here used as aquivalent to Vaughan's 
Clevedonian and Kidwellian and therefore not strictly in the sense in which they are 
employed in Belgium. 

2 For the most authoritative account of these zones see Vaughan 1910. 



142 (III. 1. 



The British Isles. — III. Stratigraphy. — 6. Carboniferous. 



■= _. N 



3~ 



oQa 



5> Ism 
c -2 u 

« a" 



(Hind and Howe) 

5. Glyphioceras bilingue 
4. Glyphioceras spirale 
3. Glyphioceras reticu- 

latum 
2. Posidonomya becheri 
1. Prolecanites com- 

pressus 

(Vaughan) 

D 3 Subzone of Cyatha- 
xonia 

D 2 Subzone of Lonsdalia 
floriformis (Lonsdalia 
subzone) 

Dj Subzone of Dibuno- 

phyllum 8 and <p 

(6<p subzone) 



5 c 
: to 



. o 
° 8 

§ a 



c « 



p. passage to Zj 






K 2 Subzone of Spiriferina 
cf. octoplicata 

Kj Subzone of Productus 
bassus 

K m Phase of Madiola lata 



Garwood (1912) 

In the North West 
Province 

D 3 ? 1 3. Botany Beds with\ k. 
Dy Phillipsastraea | 

(12. Saccammina carteri\  
I) 2 11. Girvanella Nodular L 
Bed 



Dibunophyllum 
muirheadi 

Lonsdalia flori- 
formis 



iv 



S 2 Subzone of Productus 
cora mut. S, 



10. Chonetes aff. como- 
des and Cyrtina 
septosa 
9. Davisiella llangoll- 
ensis 



8. Bryor.oa Band 



Sj Subzone of Productus 
semireticulatus mut. 

C 2 Upper Caninia Zone 



Cj Lower Caninia Zone 

Z 2 Subzone of Zaphrentis 
aff. cornucopiae (Mat- 
ley and Vaughan 1906 
[Ireland], p. 301). 

Zj Subzone of Spirifer aff. 
clathratus 



8, 



Cyathophyllum \ | 
murchisoni\ ^ 



Nemalophyllum } a. 
minus /b 

Q 

Cyrtina carbo- ]S 
nariai~ 

' A 
U 

Gastropod Bed | 



>. 
•* 
a. 

a 



C, 



7. Clisiophyllum \d. 

multiseptatum |c. 

6. Spirifer furcatus 

5. BrownberPebbleBd 

with Si/ring, cuspidata 

4. Thysanophyllum 

pseudovermiculare 

3. Productus globosus 

and Algal Band 
2. Camarotoechia 

proava 



Chonetes carinata 
Camarophoria 

isorhyncha 

Seminula 

gregaria 



1. Vaughania cleisto- 
poroides 
Z 2 ? Shap Conglomerate 

[ Pinskey Gill Beds 
Z! ?| with Spirifer pins- 
keyensis 



a. Solenopora 



1 

a 



»S 



•5 s 






tr. O 



« 



■2 



3 
o 



P5 






Kendall: Great Britain. — Sedimentary Rocks. — Avonian. (III. 1.) 143 



1. The Southern region includes the country South 
and West of Sedgemoor (51° 10' N.). Two areas of 
Lower Carboniferous exist respectively in North and 
South Devon. The severe folding, crushing and thrusting, 
to which the rocks have been subjected in the develop- 
ment of the Hercynian chain, render the elucidation 
of the succession extremely difficult. 

In North Devon the black slates of the Upper 
Pilton have yielded to Vaughan a fauna suggesting 
a low horizon in the Zaphrentis zone and recalling the 
horizon of Z. delepini (Hor. (3) in Belgium. These are 
separated by a considerable break, represented elsewhere by 
the greater part of the Carboniferous Limestone 1 , from the 
Codden Hill Cherts containing radiolaria with Prolecanites 
compressus and Cyathaxonia and belonging to the 
Cyathaxonia or D 3 Subzone. These cherts are closely 
allied to those described by Dixon and Vaughan (1911) 
in South Wales. They are followed by black shales and 
limestones with the following "Pendleside" zone-fossils (1) 
Posidonomya beckeri and N omismoceras rotiforme, (2) 
Glyphioceras reticulatum and (3) Glyphioceras spirale. 
These are followed by Gastrioceras listeri of the Millstone 
Grit, but the earlier Millstone Grit zone-fossil G.bilingue 
has .not been found. These are succeeded by the grits 
and shales of the Middle Culm. A similar succession 
and most of the same fossils are found in South Devon, 
but there are no representatives of the Pilton Beds. 
(Hinde and Fox 1895, Hamling and Rogers 1910). 

2. South-Western Province (of Vaughan) furnishes 
perhaps the only complete sequence of marine Avonian. 
The rocks are prevailingly calcareous, though shales 
sandstones and grits or conglomerates appear at dif- 
ferent horizons in various parts of the district, but 
especially along the northern margins. 

The limestones seem without exception to have been 
formed in shallow water and many of the shales, especially 
such as are characterised by the Modiola fauna, 
to have accumulated under lagoon conditions, i. e. in 
shallow salt water with incomplete connexion with the 
sea. The dolomitic condition is very frequent, especially 
at the "laminosa" horizon. The dolomitization is generally 
considered to have been in the main contemporaneous, 
but in some cases it has clearly been due to percolation 
after consolidation, as the dolomitic changes traverse 
blocks, so that one end may have 23 °/ of Magnesium 
Carbonate and the other only 1,7 %. 

Oolitic structure is present at certain horizons, 
especially at C and S 2 . A remarkable type of "pseudo- 
breccias" in C 2 occurs in the Gower Peninsula. 

1 The nearest point at which typical Carboniferous 
Limestone has been found is at Cannington Park in West 
Somerset Lat. 51° 9' N and Long. 3° 5' W, where 8, occurs. 



w 
o 

oi 
o 
o 

z 
o 

> 
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144 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

They have been carefully described and discussed by Dixon (1911). They appear 
from the descriptions to bear considerable resemblance to beds on the C 2 S t horizon 
at Ingleton, and Dixon suggests that they have originated by the partial early 
recrystallisation of a calcareous mud. Some of them have undergone subsequent 
dolomitization. 

Chert appears in the Mendips at the passage y from Z 2 to C x , as well as in S x . 

In the Gower Peninsula, where alone D 2 3 is represented in this Province, chert 

also appears, and it is interesting, and possibly significant, that the horizon D 2 — 3 
is cherty in North Wales, Derbyshire, Wensleydale, and Northumberland. 

The variation in thickness of the Avonian in this region is very remarkable, 
the general tendency is to increase of thickness from north to south and east to 
west. This is in part due to the invasion of the upper zones by sheets of coarse 
grit or sandstone, the so called "Millstone Grit", that appear at lower and 
lower horizons pari passu with the reduction of thickness; in part, again, it is due 
to attenuation of the zones; and probably, as to the remainder, to intraformational 
unconformity. Dixon and Vaughan have shown that in the Tenby area from West 
Williamston to Pendine a plane of unconformity, succeeded by a lagoon-phase, cuts 
in a west to east direction from the top of C to the top of Z, and is succeeded by over- 
lapping lagoon-phases that, at Pendine,' bring S with an intervening conglomerate, 
on to Z 2 . 

The following thicknesses have been estimated 

Abergavenny 
30 m. (100 ft.) 

Mitcheldean 
180 m. (600 ft.) 
Bristol 
685 m. (2250 ft.) 
Tenby SW. Gower Mendips 

365 m. (1200 ft.) 1130 m. (3700 ft.) 920 m. (3020 ft.) 

Dixon ascribes these variations in a series of essentially shallow water deposits 
to earth movements of depression towards the south or south-west and elevation 
in a northerly direction, but the direction of the axes of movement changed, so that, 
whereas in the movements during the deposition of K m to C the axis of tilting 
was roughly N.W. — S.E., the later movements were parallel to an axis roughly 
S.W.— N.E. 

3. The Midland Province. This region is characterized in the Pennine area 
by the enormous development of the Dibunophyllum zone in all its three divisions, 
and, consequently, though the deep valleys that trench the anticlinal axis of Derby- 
shire expose about 460 m. of Upper Avonian Limestone, it is composed wholly of 
the Dx—3 divisions. Black limestones occur near the base of the visible portion, 
and again in the upper part of D 2 and lower part of D 3 , where also chert, chiefly in 
nodules, is largely developed. 

On the reappearance of the series in North Wales it is found, to include, be- 
sides all the subzones of the Dibunophyllum zone, a representative of S 2 , with a 
basal layer containing Daviesiella (Chonetes) llangollensis resting on a red conglo- 
merate 1 90 m. (300 ft.) thick that in some localities is charged with pebbles of 
Downtonian rock of a type that is not known in Wales. Lomas (1908) gives 
a revised correlation of the beds that does not materially alter the classification. 

1 These and other red rocks at the base of the Carboniferous are referred by some 
authors to the Upper Old Red Sandstone, see p. 112. 



Kendall: Great Britain. — Sedimentary Rocks. — Avonian. (III. 1.) 145 



From this it appears that the Visean subzones "j 
comprised almost entirely by the D x 3 have a thick- 



ness of 390 m. (1275 ft.). The local interruption of 
the lower beds by a ridge 180 m. (600 ft.) high of the 
floor of pre-Carboniferous rocks was illustrated by 
Lomas who pointed to its coincidence with the 
axis of the Berwyn anticline. 

The upper part of the Dibunophyllum series, 
D 3 , is often sandy and even somewhat conglomeratic. 
A most notable feature of this horizon is the ex- 
tensive and valuable beds of chert that occur at the 
top. At Pentre near Gronant (53° 20' N.) 21 m. 
(70 ft.) of these black chert is exposed, but this is 
not the full thickness. It is extensively worked for 
use in the Potteries (Stoke-on-Trent) for grinding 
calcined flints. The close general resemblance of 
the development just described to that found in 
Derbyshire has prompted the inference, that not 
only do the two areas belong to one province, but 
the Southern Pennine development would, like 
that of North Wales, commence with the Visean. 
This does not seem a justifiable inference, as North 
Wales may have been much nearer to the shore-line 
and we shall see later that Tournaisian rocks are 
present at the next emergence of the Lower Car- 
boniferous in the Pennine anticline. 

Anglesey is considered to be within the 
Midland Province. Here a great basal series of 
sandstones and conglomerates (180 m., 600 ft., 
thick) are exposed in Lligwy Bay. They are suc- 
ceeded by 210 m. (700 ft.) of limestone with inter- 
calations of conglomerate and sandstone. Greenly 
has recognised in this series the whole of the Dibuno- 
phyllum subzones. In a southerly direction the 
limestones, reduced to 140 m. (450 ft.), overlap the 
sandstones and rest on Archaean rocks. 

A remarkable feature recorded by I. E. George, 
and confirmed and explained by Greenly, is the 
occurrence in the top of the limestone of "potholes" 
filled with tough yellow sandstone. They are re- 
garded as infilled solution-hollows produced under 
contemporaneous subaerial conditions. 

Similar "potholes" 12 m. (40 ft.) deep are found 
at Ifton near Newport, Monmouthshire (Dixon and 
Vaughan). They are filled with "MillstoneGrit". 
Others have been noted by Professor O. T. Jones 
at Haverford-west (1906) and evidences of uncon- 
formity at or about the same horizon are noted 
by Sibly and by Wedd (1908) in Derbyshire. 

The Carboniferous Series in the Isle of Man 
is generally attributed to the facies of the Midland 
Province. In the south of the Island a massive 



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146 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

conglomerate rests in striking unconformity upon the Manx Slates. Upon this succeeds 
about 60 m. (200 ft.) of white limestone with a D 2 fauna 1 passing up into D 8 with abun- 
dant Cyathaxonia, and this division is followed by Pendleside shales and limestones. 
At Poolvash a remarkable variant occurs; the "top of D 2 is represented by knoll-like 
masses without any definite bedding planes." The knolls are of various sizes, some 
being diminutive, and when unaltered by metasomatic changes are crowded with 
fossils" (Hind 1907). They appear to protrude through the bedded D 3 lime- 
stones and are surmounted directly by normal Pendleside beds. The Peel 
Sandstones in the north of the island have been referred to the lower part of the 
Carboniferous series. They rest upon the ancient rocks, but their relations to the 
Carboniferous Limestone are not seen in any section. Bands of calcareous con- 
glomerate have yielded remanie fossils attributed by Dawkins to the Carboniferous, 
but Gill (1903) identifies well-known Ordovician species and his determinations 
are confirmed by the fact that the matrix precisely resembles the peculiar Keisley 
Limestone that contains the fauna described. 

4. The Mid Pennine Region. This is the area where the Avonian reappears 
between Pendle Hill (53° 51' N.) and the Craven Faults (54° 1'— 11' N.). 

The district is much folded, the strata on some axes being vertical or even 
slightly overturned, and this, together with the fact of an extensive cov< r of Glacial 
deposits, would suffice to make the task of correlation difficult; but, beside this, the 
rocks vary greatly in lithology and fossil-contents even when traced along the 
strike. 

The base is nowhere visible. Wilmore states (1907, 1910) that the series 
extends from zones at least as low as Z, up to the junction of D a or D 3 with the 
Pendlesides. 

The most remarkable feature of this region is the occurrence of the "reef- 
knolls" of Tiddeman (1891). These are semi-ovoid or hemispherical masses of 
limestone forming rows or irregular groups of hills up to 60 m. (200 ft.) or more, 
in height. They are commonly crowded with well-preserved shells, especially 
brachiopods, and in some knolls examples may be found' still retaining the 
colour markings. Tiddeman describes the structure of the knolls as quaquaversal 2 , 
and supposes that they were shell-banks accumulating upon a sinking sea-floor, 
hence that their form is an original feature. Dakyns (1899) supported this opinion. 

These views have been opposed by Marr, Hind and Wilmore. Marr (1899) 
denies the abundance of fossils, holding that the rock is abnormally crystalline 
and that the fossils are thereby rendered conspicuous. He attributes the mounds 
and their structure to thrusting movements breaking up thin layers of limestone 
embedded in shales and piling them together in a kind of "Schuppen-struktur". 
He traces a connexion between their distribution and lines of over-thrust. Wil- 
more cite's examples of minor thrust-planes and folds in knolls, and, mentions 
that in certain cases, e. g. Gerna near Downham (53° 52' N.), the shales lying at the 
foot on one side are of Pendleside age, while those on the other are on a lower strati- 
graphical horizon. 

Vaughan has recognised a special fauna in these knolls, as well as in 
equivalent beds at Wetton (Staffordshire) and Rush (Ireland). He states that 



1 Garwood has, however, found a C faum, at Derbyhaven. 

2 According to Vaughan, this does not extend to the interior of the knolls, which 
is structureless. 



Kendall: Great Britain. — Sedimentary Rocks. — Avonian. (III. 1.) 147 

those "Brachiopod Bods" with the "knoll" phase appear, in part, to represent D 3 , 
and that D y is not typically developed in the localities exhibiting this peculiar 
phase. He believes that a knoll phase occurs at more than one horizon. 

The present writer, after examination of many of the knoll-areas, is inclined 
to favour the reef theory of Tiddeman, perhaps with modification, and to regard 
smli a case as that of Gerna as a strike-section of a lenticular mass. The abnormal 
abundance of fossils is beyond dispute. In some places, e.g. in Mill Gill, Wensleydale 
(the type section of the Yoredales of Phillips) miniature knolls rise about 1 m. (4 ft.) 
from the surface of the Great Scar Limestone, which here contains Cyathaxonia, 
and black shales with Posidonomya becheri are bedded round about and over the 
knolls. The difference between these and the typical knolls is one of scale, which 
may of course be most material. 

The Mid Pennine Province extends in a westerly direction to Kendal and 
Arnside where the series may include a part of the Tournaisian. 

5. The Northern Region presents three types or Sub-regions, (a) The Kirkby 
Stephen and Shap escarpment on the Western Side of the Vale of Eden. In 
this area limestones greatly predominate. At Pinskey Gill near Ravenstonedale 
(54* 30' N.L.) a Tournaisian fauna, perhaps older than any in the South West Region, 




Fis. 35. Section across Ingleboro and the Craven Faults (A. R. Dweeryhouse). 

5 = Coal Measures; 4 = Millstone Grit; 3 = Yoredale 
Series; 2 = Carboniferous Limestone; 1 = Older Primary. 

Reproduced from the Proceedings of the Geologists' Association, vol.22, 1911, p. 38, with the permission 

of the Council and of the author. 

shows some doubtful Devonian affinities. An important datum in this area is pro- 
vided by the Fell Sandstones in the Sj zone, (b) The Northumbrian fault-block 
(Kendall 1911). This is a block of country walled by a system of faults exten- 
ding from the North Sea at the mouth of the Tyne (55° 1' N.) round to the sea 
again at Filey (54° 10' N.), the whole series forming a figure like a reversed 3 (s). 
Within the fault-blocks no marine horizons below C 2 Sj have been recognised but 
extensive Basement beds of sandstone and conglomerate, expanding on Roman 
Fell (54° 34'/ 2 ' N, 2» 23' W) to 150 m. (500 ft.) thick, occur. The upper part of this 
series contains materials entirely of local origin and is referred by all observers to 
the Carboniferous series. The lower part contains a great diversity of derived frag- 
ments (hence styled polygenetic) and is by many geologists referred to the Upper 
Old Red Sandstone. These pebbles are different from any rocks exposed in the 
adjacent pre-Carboniferous areas, and the writer suggests that they may have 
derived from a Pre-Cambrian series lying to the North of the Ingletonian rocks of 
Ribblesdale. These lower beds also contain thin bands of dolomitic limestone a 
fact of some significance when the series is compared with the succession further 
north. 



10* 



Yoredale Rocks 280 m. (930 ft.) 



148 (III. 1. The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

A typical section is seen on Ingleborough (54° 10' N.). 

Coarse Pebbly Grit Millstone Grit 18 m. (60ft.) 

Shale 

Main Limestone 

Sandstone with some Shale 

Limestone with Shale . . . 

Shale and sandstone .... 

Middle Limestone .... 

Sandstone and Shale . . . , 

Simonstone Limestone . , 

Sandstone and Shale ... 

Hardraw Scar Limestone. 

Shales and Limestone .... 

Great Scar Limestone . . Carboniferous Limestone . 180 m. (600ft. 

Basement Bed (impersistent) 

Silurian and older rocks 

The rocks are displayed in magnificent sections that have been studied by 
generations of geologists, but the palaeontological succession has not yet been 
fully worked out and much difference of opinion exists as to the zones represented. 
Thus Hind in 1909 placed the Great Scar Limestone in S 2 and the whole of the 
Yoredales in D v Garwood (1907) carried D x up to and including the Hardraw 
Scar Limestone. D 2 is made to embrace the strata between this horizon and the 
Main Limestone. The Main Limestone and strata up to the Millstone Grit he refers to 
D 3 . S. Smith (1911) in a review of the succession north of the Tyne places the Hardraw 
Scar Limestone in D 2 , the strata up to the Main Limestone in D 2 _ 3 and the Main 
Limestone D 3 . All the remaining beds are designated by the symbol D y . Johns 
in 1908 referred the upper part of Great Scar Limestone to D 2 in which subzone 
he also included the Main Limestone, but later, in 1910, he announced the occurrence 
of Cyathaxonia in the top of the Great Scar Limestone of Wensleydale and pro- 
nounced the fauna of the Main Limestone to "indicate a higher level than any- 
thing recorded from Bristol or South Wales". This was before the recognition of 
Dj5_ 3 in Gower. Until researches now in progress are completed it would be pre- 
mature to express any definite opinion upon this question of correlation. 

Since the foregoing was written Garwood's full statement has appeared 
(1912). Some of his results are embodied here. 

The Yoredale Rocks though containing many important beds of limestone 
are predominantly sandstones and shales. Some coal-seams, even of workable di- 
mensions, occur, each with its seat-earth, and these increase in number and impor- 
tance northward. The number of limestones also increases, but whether, as some 
think, these are intercalary in the shales or whether they are due to penetrations 
of shale into the limestones has not yet been determined, but the latter, in view 
of the other changes noted seems the more probable. 

6. Northumberland and the Tweed Valley. This sub-region lying to the north 
of the fault block exhibits a great contrast to the areas just described as will 
be seen from the following table adapted by Smith (1911) from the works of Lehour 
and Gunn. The terms Tuedian and Bernician are adopted by Lebour for the 
Lower Carboniferous series: 

Bernician 

Calcareous division . . 

Carbonaceous division. 
Tuedian 

Fell Sandstone Series 

Cement Stone Series . 



Tyne and 


Rede 


Tweed 


. 1200 m. 
. 760 m. 


(4000 ft.) 
(2500 ft.) 


520 m. (1700ft.) 
275 m. (900 ft.) 


. 180 m. 
. 180 m. 


(600 ft.) 
(600 ft.) 


180 m. (600 ft.) 
760 m. (2500 ft.) 



Kendall: Great Britain. — Sedimentary Rocks. — Avonian. (III. 1.) 149 



The correlation of this succession with that of the fault-block and with 
Vaughan's system of zones is shown in the following compilation from the works of 
Gunn, Garwood and Smith: 

Northumberland (Garwood) 

(Smith, 1911) 



Wensleydale 
(Gunn, 1898) 



Main Limestone 
Undersett Lmst. 

Acre Limestone 
Hardraw Scar L. 



Dy 



D, 



Di 



Fell Top Limestone 



Robsheugh , 
Thornbrough , 
Corbridge , 




Little 

('.real , 




Four Fathom , 

Acre , 
Eelwell 




Oxford , 




Fourlaws , 
Redesdale 





Redesdale Ironstone 



Botany Beds .... 
Fell Top Limestone 



Dryburn or Great „ 
Lowdean 

or 4 Fath. 
Acre 
Eelwell 
Oxford 
Fourlaws 
Redesdale 
Carbonaceous . . . 

Division .... 
Fell Sandstones . . 
Cement Stones and 
Lower Freestone 



(1910) (1912) 
D 8 



D, 



!>:, 



D, 



Dy 



D 2 



D, 


}D, 


s. 


B, 




s, 


B, 


c, 


c{ 


Cj Y 


Z(?) 



Apart from the question of zones there is a general agreement in correlating 
the Hardraw Scar with the Oxford Limestone, so that only the comparatively small 
Redesdale and Fourlaws limestones, if even these, can be regarded as calcareous 
equivalents of the massive Great Scar Limestone of Ingleborough. The limestone 
beds are separated by shales and sandstones with occasional coal-seams some of 
which are of workable thickness, especially the Lickar Coals between the Great 
and Little Limestones. The Acre limestone is packed with Saccammina carteri, 
a fossil that also characterizes a bed near the top of the Great Scar Limestone in 
Wensleydale. 

The Carbonaceous division of the Bernician may represent a phase 
of which a mere trace is developed at Ingleton in the form of an eroded fragment 
of a coal-seam with its underclay, that is intercalated in the Great Scar Limestone. 
In Northumberland this Carbonaceous division, also known as the Scremerston 
Series, consists of sandstones, shales, and thin limestones with thin impure lime- 
stones. The coal-seams are of considerable importance, 16 seams exceed one foot 
in thickness and of these six are of workable dimensions. Most of the seams have 
a limestone roof and two contain a thin parting of limestone. 

The Fell Sandstones contain minor beds of shale and some small coal-seams 
and besides plant remains they yield the interesting lamellibranch Archanodon 
jukesi. The Cement Stone Series consists of "reddish and white sandstones and 
green and dark-coloured shales and thin magnesian limestones (Cement Stones)". 
The fauna in the Tweed Valley where they attain their maximum consists, accor- 
ding to Garwood, mainly of land and fresh water lamellibranchs, gastropods and 
fishes, with a varied assemblage of arthropods, including Arachnida und Crustacea. 
No brachiopods or corals occur but an Orthoceras is recorded. According to 
Garwood the most characteristic fossil is Spirorbis helicteres, he also notes the 
occurrence of Syringothyris cuspidata and Orthotetes crenistria, either at the summit 
of this series, or at the base of the Fell Sandstone. It is in either case clear 
that occasional irruptions of the sea came into this area. Mitcheldeania gregaria 
has been found in limestones in many places and Athyris glabristria Phill. (royssii 



150 (III. 1.) 



The British Isles. — III. Stratigraphy. — 6. Carboniferous. 



auct.) occurs near the borders of Cumberland in beds referred by Garwood 
to some part of the G. zone. 

A digression may now be conveniently made to consider briefly the relation 
of the Yoredale Rocks to the Pendleside series. Hind insists that the two 
are quite independent, the Pendleside series being the newer. Correlation is 
difficult because the two types have never been found in clear succession but Johns 
holds that the Pendleside Limestone is the same as the Main Limestone, and points 
out that in Mill Gill, Wensleydale, the top of the Great Scar Limestone with a 
Cyathaxonia fauna (whether the true D 3 fauna or not has not been made clear) 
is directly succeeded by shales crowded with Posidonomya becheri which he considers 
to mark the incoming of the Pendleside fauna. The characteristic goniatites have not 
been found and until this defect is supplied the question cannot be decisively settled. 
Hind's contention involves great stratigraphical anomalies, for example, on Ingle- 
boro, 284 m. (930 ft.) of Yoredale Rocks intervene between the Great Scar Limestone 
and the Millstone Grit, and in full view, 32 miles away, stands Pendle with 450 m. 
(1500 ft.) of Pendleside Beds occupying a precisely similar homotaxial position. 
The palseontological argument for difference of age is much weakened by the dis- 
covery in Ireland (Matley and Vaughan 1908, Ireland) of rocks with a Pendleside 
fauna interbedded with typical D 3 beds. Similar relations appear to hold in parts 
of Derbyshire (Sibly 1908), and the present writer inclines to the opinion ex- 
pressed by Vaughan that the faunal differences depend more upon differences 
of conditions than of age. It has long been believed by Tiddeman and others that 
the Craven faults, that constitute the boundary between the Yoredale country and 
area within which the Pendleside Series occurs, were moving in Carboniferous times 
with consequent marked effects upon deposition. Many observers, e. g. Wilmore 
(1910), Garwood and Carruthers have commented upon the great palaeontolo- 
gical contrasts presented upon the two sides of this great system of dislocations, 
and it seems more probable that the two series of strata were contemporaneously 
deposited than that, without perceptible unconformity, the whole Pendleside series 
should be absent from the Northern area and all the Yoredale Rocks from the 
Southern one. 

Hind's argument that, as the Yoredale fishes differ from those of the Pendle- 
side Series, the rocks must be of different ages, is neutralized by the fact that Traqu air 
can find no significant differences between the fish faunas of different parts of the 
Lower Carboniferous Series. 

7. The Scottish Lowlands. This region is enclosed between great trough-faults 
forming the "Rift", or Midland, Valley of Scotland. It is the general opinion that 
these faults were in operation in Old Red Sandstone time and that the movement 
continued at least during the deposition of the Carboniferous strata. The succession 
of Lower Carboniferous rocks is in all essentials the same as in Northumberland as 
will be seen from the following table: 

Scotland 
Upper Limestone Group 
Edge Coal Group (Coal and 
Ironstone Group of Glasgow) 
Lower Limestone Group 
Carbonaceous Group 
and Midlothian Oil-shale 

Upper Series 
with Fell sandstones near 
Dunbar 
Cement Stone Group (in- 
cluding the Ballagan Group 
of Glasgow) 



Bernician 



Northumberland 

Calcareous division 
with Lickar Coals 

Carbonaceous 

division 
(Scremerston Coals) 



Tuedian . 



Fell Sandstones 



i Cement Stone Series 



Carboniferous 
Limestone 

Series 



Calciferous 
Sandstones 



Kendall: Great Britain. — Sedimentary Rocks. — Avonian. (III. 1.) 151 



The sections near Dunbar approximate most closely to the Northumbrian 
type, and towards Glasgow the lithology changes so greatly that without the connect- 
ing links, furnished by the intervening area of Midlothian, correlation would be 
difficult, if not impossible. 

The Calciferous sandstones consist mainly of green clays and shales 
with bands and nodules of argillaceous dolomite (Cement Stones) and some sand- 
stones, especially in the upper part near Dunbar, where they clearly correspond 
with the Fell Sandstones. 

The occurrence of dolomitic limestones and gypsum in the Ballagan beds 
have by many writers, particularly Goodchild, been regarded as affording indi- 
cations of an arid climate. 

Beds of limestone containing a marine fauna occur in the upper part of 
the series, and in the Glasgow area the Hollybush Limestone, about 90 m. (300 ft.) 
below the summit of the Calciferous Sandstones has yielded a considerable suite of 
fossils including Productus giganteus and P. latissimus characteristic members 
of the D. fauna. 

The Carbonaceous group, contrary to the general practice, is in the table 
attached to the Carboniferous Limestone series in order to make clear its relation to 
the Bernician series of Northumberland. It contains several small coal-seams near 
Dunbar that may correspond with the Scremerston Coals of Northumberland and 
the group is considered to be represented in Midlothian by the very important 
Oil Shales. 

On lithological grounds it just as ill-deserves the name, for, while limestones 
do occur, they are few in number and very thin, rarely attaining a thickness of 
6 m. (20 ft.) and in the upper division seldom so much as 1,5 m. (5 ft.). The great bulk 
of the formation consists of sedimentary materials — shales and sandstones with 
coal-seams. 

The Lower Limestone Group includes six principal limestones on the East 
Coast near Dunbar and three limestone horizons in the Glasgow area. The corre- 
lation .of these two districts is somewhat difficult. The following scheme exhibits 
the probable relation to Northumberland. 



Lickar Coals 



Northumberland 



Acre Limestone 

Eelwell Limestone 

Woodend (or Fourlaws) Limestone 
Dun (or Redesdale) Limestone 



East Lothian 
Edge Coals 
Barness Limestone 
Chapel Point „ 
Skateraw ,, 

Longcraig Upper Limestone 

„ Middle „ 

,, Lower ,, 

Linkhead or Cove Upper Limestone 
Cove Lower Limestone 



The Skateraw Limestone contains a persistent band of Saccammina carteri. 
Several coal-seams occur in this series. 

The Edge Coals of Midlothian, the equivalents of the Coal and Ironstone Series 
of Glasgow, constitute an important series, with seams varying in thickness up to 
about 1,5 m. (5 ft.) in the east, but much thinner in the west. In Midlothian there 
is a general tendency for the seams to become thinner from north to south. Cannel 
occurs throughout this region, and in the Glasgow area a valuable seam of 
anthracite is worked. Its formation is attributed to the proximity of a dolerite 
sill. Valuable ironstones also occur. 

The Upper Limestones constitute a series bearing a strong general resemblance 
to the Lower Limestones and like them containing workable coal-seams, but the 



152 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

limestone bands themselves are very thin, despite which, however, they are very 
constant, the Index Limestone, which is taken as the base of the series, and the 
Castle Cary Limestone that marks the summit, extend quite across from the 
East Coast to Glasgow. The abundance of Productus latissimus characterizes 
the lower part of this series. 

Though not included in the Carboniferous Limestone in any scheme of classi- 
fication, the lower part of the Roslin Sandstone must find a place, either there or 
in the Pendleside Series, and in the absence of any specific evidence it seems more 
appropriate to group it on stratigraphical grounds with the former, for, as we have 
seen, the term Pendleside Series probably connotes rather a special palaeontological 
phase than a specific and constant stratigraphical horizon. 

The palaeontological succession in the Carboniferous rocks of Scotland has 
long engaged the attention of geologists, and a broad division into an upper, and a 
lower, series was put upon a satisfactory basis by the labours of Kidston upon the 
plants and of Traquair upon the Fishes. These two workers found themselves 
in close agreement in drawing a line of separation at some distance above the base 
of the Roslin Sandstone or Millstone Grit. Below this line no further subdivision 
has been found practicable by them. The invertebrate fossils, until the publication 
of the results obtained by Garwood, Hind and Vaughan in England, were almost 
equally unproductive of bases for subdivision or of correlation with the sequence 
of Lower Carboniferous in other parts of Britain. It is now found however that the 
general zonal distribution applies, with some modification to the Scottish rocks. 
The true horizon of the Calciferous Sandstone is still uncertain but the occurrence 
of the Hollybush Limestone with a D 2 fauna about 73 m. (240 ft.) from the top 
of the upper division affords a valuable datum. It shows further that as already 
remarked the name "Carboniferous Limestone" must bear a different connotation 
in Scotland and in England, the entire Scottish series so designated, as well as 
a large part of the Calciferous Sandstone, lying on the horizon of the Yoredale 
Series of Yorkshire 1 . 

G. W. Lee (1912, pp. 95 — 6) refers the whole series from this limestone up 
to the top of the Upper Limestones to D 2 . He remarks that "this D 2 phase in 
Central Scotland appears to have persisted during a longer period than in England. 
Our Upper Limestones therefore, though from stratigraphical evidence known to be 
higher up in the sequence than the top part of the English D 2 zone, still contain a 
fauna which, in our present knowledge, has D 2 affinities." With reference to sub- 
zones D 3 and P he states that "species characterizing these sub-zones have 
not yet been met with in Scotland as distinct assemblages, though marine beds 
of the same age are doubtless present." It may be remarked however that 
mutation D of Zaphrentis delanouei found by Carruthers in the Lower Lime- 
stones and Z. omaliusi car. ambigua mut. a from the same series were found by 
Vaughan (1908, Ireland) to be confined respectively to the P. and D 3b horizons 
at Loughshinny in Ireland. The lower part of the Roslin sandstone may be 
the stratigraphical equivalent of the highest Yoredales and Pendlesides. 

Outlying occurrences of Lower Carboniferous rocks in the West of Scotland 
are of interest as aiding any attempt to reconstruct the geographical conditions 
of the period. Judd records the occurrence of Carboniferous plants (Lepidodendron 
aculeatum) from Ardtornish in Argyllshire and similar evidence has been obtained 
from Bridge of Awe in the same district. The occurrence of a Modiola related to, 
if not identical with, M. macadami is also noted. 

1 Syringothyris has been found by Peach and Horne in Liddisdale at the base of the 
Fell Sandstones. The Cement Stone group below must therefore be of Tournaisian age. 



Kendall: Great Britain. — Sedimentary Rocks. — The Millstone Grit. (III. 1.) 153 

B. The Millstone Grit. 

This is, of all the members of the Carboniferous series, the most difficult to 
reduce to any systematic arrangement. 

Many causes conspire to complicate the task. In the first place palaeonto- 
logy gives little aid in the endeavour, except so far as the definition of a base, cutting 
across the lithological lines, may be said to be an assistance ; but, even with this 
reservation, it must be admitted that the presence of well-preserved fossils of 
diagnostic value is exceptional. Lithology, again, is often a source of error, rather 
than a helpful guide; and finally, the stratigraphy is confused by the wedging 
out of massive beds of sandstone as might be expected in deltaic accumulations 
laid down in areas undergoing a general movement of depression varied by long 
periods of quiescence or even of elevation. 

To all this must be added the fact that the Grit formations of Scotland and the 
Pennine Region are of an origin and provenance absolutely distinct from the Fare- 
well Rock of the South-Western Province, and in large measure also from each other. 

The grits of the Northern area extending from Charnwood (52° 43' N.) and 
the neighbourhood of Birmingham to the Midland Valley of Scotland are essential- 
ly arkoses, derived from the waste of crystalline rocks lying to the north, north-west or 
north-east. "The Farewell Rocks" of the South- Western Province, on the other hand, 
are quartzose grits and conglomerates whose materials have come from an entirely 
different source, at present not definitely ascertained, though probably to be sought 
in Central Wales. To the first of these alone the name Millstone Grit should be applied. 

The grits of the southern portion of the Pennine range were classified by Hull 
and Green (1864) into four main arenaceous groups with intervening shales, and they 
numbered them, very oddly, by ordinals commencing with a First Grit or Rough 
Rock at the top and concluding with a Fourth Grit or Kinderscout Grit. To this 
series is added an additional lower member Farey's or the Shale Grit formerly 
grouped with the Yoredale Series. 

The grits are well-defined as separate beds or groups of beds of sandstone or 
more or less conglomeratic grit, composed of sharp and generally subangular grains 
of quartz with felspar, mostly microcline, often in a very fresh and little altered 
condition, though -upon exposure the felspar may be reduced to a kaolin mud, 
with the concurrent production of crystal-terminations upon the quartz grains 
as well as a hackle of minute facets upon the pebbles. Sorby (1847, 1858 — 59) 
studied the current bedding of the grits in an area near Sheffield and found that, 
while the direction varied considerably, the predominant direction indicated that 
the materials were distributed by currents coming from the north or north-east. 
His studies of the contained stones supported this conclusion. Recent researches 
by Albert Gilligan (1912), of the Leeds University, have resulted in the identi- 
fication of pebbles conforming to types well-known in the Highlands of Scotland, 
thus confirming in some measure Sorby's conclusion that the materials were of 
northern, probably of Scandinavian, derivation. He finds that the main substance of 
the grits consists of quartz and microcline — other felspars rarely being present. 
The constitution of the rock thus resembles in a remarkable way the pre-Cambrian 
Torridon Sandstone of the North-West Highlands of Scotland, but the extremely 
fresh condition of the felspar, and the angularity of the particles, coarse as well as 
fine, no less than the common occurrence of fragments of pegmatite, forbid the 
inference that the Millstone Grit was derived from that source, but favours the 
opinion that both rocks, separated though they are by so wide an interval 
of time, came from a common source. No area of pegmatite of adequate magnitude 
to be the source of this immense mass of material exists in North Western Europe 
and the conclusion appears to be unavoidable that some tract of crystalline rocks 



154 (III. 1.) The British Isles.  — III. Stratigraphy. — 6. Carboniferous. 

at present submerged beneath the waters of the Atlantic provided both the Torridon 
Sandstone and the Millstone Grit. Gilligan considers that the fresh and un- 
altered condition of the felspar and the distribution of the sheets of Millstone Grit 
indicate that it was borne by a large river from an area of low rainfall lying in the 
direction named. The shales intervening between the grit beds appear to be 
mainly of fresh water origin, though fresh water shells have been discovered at 
only two or three localities. There are, however, true marine shales distinguished 
both by their fauna and by lithological peculiarities. It is probable that one such 
marine band occurs in each main bed of shale. The most notable of these occur 
above the Kinderscout Grit (Sabden Shales of the Geological Survey), beneath 
the Rough Rock, and in unassigned positions near the middle of the series. 

At Eccup near Leeds, in the Middle Series, blue shales occur crowded with 
marine lamellibranchs, gastropods, cephalopods, brachiopods, crinoids and crusta- 
ceans. Brachymetopus ouralicus, the last of the Rritish trilobites, occurs in these 
beds. At a slightly lower horizon is an arenaceous limestone, the Cayton Gill Red, 
extending from Harrogate (54 ° N.) up the Nidd Valley. Its fauna has been 
discussed by Hind (1907) who comments upon the reapparition of a brachiopod 
fauna of Lower Carboniferous aspect 300 m. (1000 ft.) above the base of the Grits. 
He assigns it to "a late Dibunophylluni" stage. Garwood seems to have over- 
looked these two beds, when expressing the opinion (1912) that his Rotany Reds, 
occupying an undefined position in rocks referred to the Millstone Grit in Tees- 
dale, yield "the highest truly marine fauna yet met with in the North of England". 
In some sections, e. g. at Marsden (53 ° 35' N.), each bed of Grit is surmounted 
by a coal-seam with its seat-earth. The coals in the Millstone Grit have been mined 
in some of the more remote valleys of the Pennine Chain, where transport from the 
regular coalfields is difficult and costly. 

The Grit series varies not only in thickness but in its constituent members 
as it is traced from north to south. 

In Scotland it is represented by a portion of the Roslin Sandstone, which 
near Edinburgh consists of shales, marls, fireclays and pebbly sandstones attain- 
ing a total thickness of 225 m. (740 ft.) of which, however, on the evidence of the 
plants, the lower 72 m. (235 ft.) is assigned to the Lower Carboniferous. Two beds 
of pebbly grit occur in the portion assigned to the Millstone Grit and a similar 
one in the lower division, besides which the same type appears in the Lower Car- 
boniferous and recurs in the Lower Coal Measures. The pebbles are mostly of 
vein-quartz, a notable difference from the grits of the Pennine area, but in some 
sections conglomeratic beds contain fragments of Carboniferous Sandstone and, at 
one place, angular fragments of volcanic rock. 

In the Glasgow area fireclays of a remarkable character occur in the lower 
part of the series, that at the famous Glenboig works consists of about four-fifths 
of kaolin, some quartz, felspar, hornblende and biotite. A rhombohedral carbonate 
occurs in minute crystals identified by Gregory as sideroplesite. 

A very notable pal«ontological feature of the beds in the Glasgow area attri- 
buted to the Millstone Grit is the apparition, near the base of the series, of a marine 
fauna, of which fully 50 per cent of the forms (e. g. Meekella) were until recently un- 
known elsewhere in Rritain, though they had been previously recognised in the 
Upper Carboniferous of Nebraska and some of the species had been found in Russia 
and China. Many of the typical lamellibranchs have since been found in a limestone, 
presumably belonging to the Carboniferous Limestone, in a bore at Stirling, and 
others at various horizons in the Carboniferous Limestone Series and Calciferous 
Sandstone Series. It should, however, be noted that the plant evidence would place 



Kendall: Great Britain. — Sedimentary Rocks: —  The Millstone Grit. (III. 1.) 155 

the division between Upper and Lower Carboniferous above the horizon of the 
Marine Bed in the Millstone Grit. 

In Northumberland the series consists of alternations of grits and shales 
with a total thickness of 150 m. (500 ft.). Grits lithologically indistinguishable occur 
both in the Lower Carboniferous and in the Coal Measures. Garwood (1912) assigns 
some of the beds mapped as Millstone Grit in Teesdale to a horizon below his 
"Botany Beds", which contain a D 3 fauna. 

In North Yorkshire a coarse typical Millstone Grit appears below the high- 
est Yoredale limestone (the Main Limestone) on Ingleborough, while the summit 
of the mountain is formed of the Kinderscout Grit. Further south the full Mill- 
stone Grit series attains great magnitude, but the correlation with the typical 
development is at present impracticable, for instead of the four or five grits of the 
southern extremity of the Pennine Chain, ten or twelve beds of grit are found, 
separated by larger or smaller beds of shale. 

This multiplication of the grit-beds has been ascribed to the intercalation 
of wedges of shale penetrating from the north. In view, however, of the proofs that 
the grit materials were derived from a northerly source, it seems much more likely 
that the sheets of grit were of the nature of deltaic sand-flats spread out by a river 
flowing from the north and dwindling to a free edge in a southerly direction. 

In South Derbyshire the interpretations of the geological surveyors do 
not support this view, but in Staffordshire the grits die out as they are traced to the 
south and west. The Second Grit does not penetrate beyond Cheshire and the 
Fourth and Fifth next disappear, then the First Grit or Rough Rock, so that, 
when the Millstone Grit is last seen, only the Third Grit separates the Pendle- 
side Series from the Coal Measures, and no palseontological evidence is available to 
determine how much of the over-and under-lying shales should be attributed to 
the Grit Series. A little further south the series dies out altogether and the Coal 
Measures rest upon pre-Carboniferous rocks. 

The physiographical conditions attending the deposition of the Mill- 
stone Grit appear to have been estuarine or deltaic. A great river seems to have 
entered the area of the North of England from the north or north-east bearing the 
detritus of some large area of crystalline rocks, most probably from a district of 
mountainous land lying beyond Scandinavia and the Highlands of Scotland. The 
fresh and unweathered condition of the felspar suggests that the chief agent in 
the disintegration of the parent-rock was change of temperature and not ordinary 
pluvial denudation. The Scottish area was probably in a different drainage system. 
The area of deposition was undergoing a general movement of subsidence during 
which dark, frequently carbonaceous and micaceous, shales with drifted plant- 
remains were laid down. At times a more rapid subsidence brought in marine 
conditions, and at others, more stable conditions permitted the gradual encroach- 
ment of the sandbanks cumbering the actual channel. These spread out over broad 
stretches and grew by deposition upon their margins so as to form great flat ex- 
panses of grit. As Barrow (1905, p. 30) remarks "The First and the Third Grit are 
not single beds but a series of interlacing lenticles of grit, which together build up 
a minor sub-formation which is just as regular in its thickness as is any one of the 
sub-divisions of many other formations." 

At other times a complete equilibrium was established when vegetation crept 
out over the sandy flats and formed the thin coals that frequently occur as a capping 
to a bed of grit. These coals invariably, in the writer's experience, rest upon a bed 
of fire-clay or gannister crowded with rootlets. Sometimes the vegetable matter 
was insufficient in quantity to form a coal-seam or it underwent contemporaneous 



156 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

decay and only the rootlet bed remained. All these features in miniature can be 
observed in a reservoir that is being silted up. 

The thickness of the Millstone Grit series in the Pennine area varies very greatly. 
In the neighbourhood of the Burnley Coalfield it reaches its maximum 838 m. 
(2770 ft.), it diminishes to 365 m. (1200 ft.) at Axe Edge (53° 12' N.) and in the next 
32 km. (20 miles) is further reduced to about 122 m. (400 ft.). This however takes no 
account of that portion of the shales below the Third Grit assignable to the Grit 
Series. In North Wales the series attains a thickness of about 200 m. (650 ft.) 
and includes cherty beds with Productus and other marine forms. 

Extensive local movements caused unequal depression of the area of depos- 
ition, and into these as catch-pits the grit materials would be poured and the 
wide-spread uniformity of character of the Rough Rock shows that the hollows 
were quite filled up and levelled by deposition. 

The Millstone Grit of the Bristol-South Wales area is quite distinct litho- 
logically and stratigraphically from that of the Pennine region. It consists, where 
most complete, of two beds of course siliceous grit with pebbles of vein-quartz, 
and an intermediate shaly division with occasional sandstones. These rocks are 
overlain by Coal Measures with a flora characteristic of the Middle Division while 
they are underlain in the Gower Peninsula by rocks with a Pendleside fauna. 
The value of these stratigraphical landmarks is however diminished by the fact 
that in Gower the grits have given place to shales, and Strahan (1910) states 
that "no line, stratigraphical or palaeontological, save of the most arbitrary des- 
cription can be drawn for the top of the Pendleside." Furthermore, grits of an 
exactly similar character occur both in the Carboniferous Limestone and at various 
horizons in the Coal Measures. 

In the Bristol-Mendip area the Avonian D t zone is succeeded by 30 m. 
(100 ft.) of limestone containing a late D fauna, followed by 300 m. (980 ft.) of 
"Millstone Grit" in the upper part of which a fauna and flora suggestive of Coal 
Measures is found, and above this the undoubted Coal Measures referred by Newell 
Arber to the Middle division. The equivalence of this grit is thus quite uncer- 
tain and, as in South Wales, the same lithological type occurs both below and above 
the series. 

C. The Coal Measures. 

This great series, the chief repository of coal in Britain, is also locally the 
greatest in respect of thickness of the Carboniferous rocks, attaining in South Wales, 
where it reaches its maximum, a thickness computed to be 2500 m. (8200 ft.) 
(Strahan and Pollard 1908). Lithologically the Coal Measures are essentially 
shales, but in most areas, there is also a notable amount of sandstone. Ironstones 
though of small thickness and local in distribution are economically of great 
importance. Limestones are rarely developed, except the peculiar Spirorbis lime- 
stones that characterize some of the unproductive higher measures. Coal seams 
range at varying intervals throughout the succession except in the highest 
members of the series. Finally, in a category by themselves, are the various types 
of "seat-earth" known as underclay, fireclay and gannister. 

The whole Coal Measure series may be regarded as characteristically a fresh- 
water formation, but occasional marine bands occur in the Lower and Middle 
parts, and these have proved of great service in determining the horizon of rocks 
found in deep bore-holes. Marine faunas are not, however, sufficiently clearly in- 
dividualized, as a rule, to furnish intrinsic evidence of age, and it is only when their 
associations are observed that they yield decisive evidence. The marine bands, 
which rarely amount to 6 m. (20 ft.) thick are usually fine blue shales of a soapy 
texture, readily distinguishable, even in the absence of fossils, from the normal 



Kendall: Great Britain. — Sedimentary Rocks. — Coal Measures. (III. 1.) 157 

shales of the Coal Measures, and this difference of texture furnishes an additional 
argument in favour of, fresh-water origin of the bulk of the strata, which is still 
further supported by the fact, insisted upon by Green (1878), that the assumed 
fresh-water shells (Carbonicola, Anthracomya &c.) never occur in the same layer as 
the unquestioned marine forms, even though the layers may be in contact. One 
exception to this rule is known in the Yorkshire Coal-field where Culpin has found 
a single example of Lingula mytiloides on a surface bearing Carbonicolse. 

Strahan has argued that Carbonicola is not a fresh-water shell. He says: 
"the Coal Measures [ ? of South Wales] were almost certainly not fresh-water. 
The Anthracomya is known to have lived by side with true marine molluscs, and 
the Carbonicola, though allied to a great fresh-water family, is always found in close 
attendance upon the Anthracomya.' 1 '' 

This opinion is not shared however by those palaeontologists such as Ward, 
Hind, Stobbs and Lee who have studied closely the genera mentioned. 

Coal seams and their seat-earths present many interesting problems that 
can in general be merely hinted at here. 

The mineral character of the seams shows every variation from the extreme 
of bituminous to a very pronounced type of anthracite. 

In the Scottish coal-fields the blazing Coals are the dominant types, but 
anthracite occurs in the Glasgow district as a consequence of the proximity of an 
igneous intrusion (sill), and in Arran three anthracitic seams are known. 

The seams in the English coal-fields vary from extremely bituminous 
to hard steam and coking coal; the South Wales coalfield, on the other hand, is 
distinguished by the occurrence of anthracite, besides other types. Cannel (or 
parrot) coal occurs in all areas. 

The seams vary in thickness from mere films of no economic use or importance 
up to 2 or 3 m. (7 or 10 ft.) and in only one instance is the latter greatly exceeded, 
namely, by the famous Thick Coal of South Staffordshire. This seam known also as 
the Ten Yard Seam attains a maximum thickness of 12 m. (40 ft). 

The question of the mode of origin of coal seams has been much discussed and 
the present is not the place for entering at length into controversial matters, but 
as the subject has been reopened by recent writers, a brief statement may be given 
here of the reasons, admirably arrayed by Bowman (1841), Binney (1846) Green 
(1878) and never yet categorically answered, that have induced the writer to 
adopt the in situ or growth-in-place theory of the origin of the coal in all the 
British coal-fields with which he has a personal familiarity. 

Green's summary argument may be briefly stated as follows: 1. The 
quantity of ash is very small. 2. The seams are constant in character and thickness 
over wide areas. 3. They are often of great extent. 4. Bemains of aquatic animals 
are entirely absent from the coal. 5. Each seam rests upon a seat-earth of some 
kind, which he considers to be an ancient soil. 

The reasons for this last opinion are as follows: 1. It is not a laminated or 
bedded deposit. 2. It is crowded with roots and rootlets. 3. Other fossils are only 
in rare instances found in it. 4. It has the chemical characters of an exhausted soil. 
Some beds of a coal-like substance, viz. cannel, display the exact opposite of the 
features detailed above, being of limited extent; show great variations of thickness; 
yield a high percentage of ash; are only in fortuitous and exceptional relation to 
a seat-earth; and, finally, as an almost invariable character, contain remains of 
aquatic animals e. g. ostracods, molluscs, and fishes. The fact that cannel is in every 
respect the reverse of true coal constitutes at the same time evidence of its sedi- 
mentary origin and against the "drift" origin of ordinary coal. 



158 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

As an illustration of the constancy of some seams it may be mentioned that, 
while it is highly probable that the chief seams in the Yorkshire coalfield are re- 
presented in Lancashire, North Staffordshire, and North Wales, one small seam 
near the base of the series is so clearly characterized that the correlation is quite 
certain. This is the seam known in Yorkshire as the Halifax Hard Bed, in Notting- 
hamshire as the Alton Coal, in North Staffordshire as the Crabtree, and in Lan- 
cashire as the Gannister Seam, or Mountain Mine. Its maximum thickness is less 
than four feet and it declines to about one and a half feet near Leeds. 

The seam has a floor of gannister (i. e. a siliceous seat-earth), a roof of black 
shale with a rich marine fauna, and in the area adjacent to the Pennine Chain, in 
Yorkshire and Lancashire, it contains the remarkable nodules known as "coal-balls" 
that constitute the principal source of our knowledge of the structure of the coal flora. 

It is not absolutely certain that the seam can be identified in the coal-fields 
near Chester, though it is highly probable that it extends there. If this identification 
is correct the seam must have had an area of between 13 000 and 15 000 qkm. 
(5000 and 6000 sq. m.). The difficulty of explaining so equable a distribution of 
drifted vegetation over so vast an area, applies, though in less degree, to the gannister 
floor upon which the seam rests. 

Spore-coals, as Huxley pointed out, are of very common occurence, and Lomax 
(1912) has made further studies that confirm and extend the application of his 
observation, but more exhaustive investigation is still needed, for many seams 
can, even without the aid of the microscope, be seen to contain layers mainly or 
perhaps entirely constituted of macrospores. 

These spore-coal layers are usually an inch or less in thickness, of a dull aspect, 
and are very tough. The Beeston Bed of the neighbourhood of Leeds contains two such 
layers of a distinct brown colour, and at one colliery the portion of the seam containing 
them is hand-picked for sale as steam-coal. Another seam, the Haigh Moor, has a spore- 
band about half an inch thick, known as the "dull-streak", that can be traced over many 
square-miles. 

The splitting of coal seams, i. e. the separation of a seam by a wedge or lens 
of sedimentary material, is a phenomenon of common occurrence in nearly all the 
British coalfields. An excellent explanation of its cause was given by Bowman 
(1840), though he failed to take accoumt of the effects of the compression of 
the peaty mother-substance. 

The Gannister Coal is a case in point. At Todmorden (53 ° 42' N.) it consists 
of two elements in direct superposition, but near Halifax and elsewhere in York- 
shire they are separated by a considerable interval, while in the south of the same 
coalfield, in South Derbyshire, the two seams again coalesce. 

The most famous example however, is that of the Thick Coal of South Stafford- 
shire. This seam subdivides on the north of a large fault crossing the coalfield, and 
by successive splits is resolved into 14 seams in a distance of 7 km. (4'/ 2 miles), the 
intervening strata attaining a thickness of about 150 m. (500ft.) (see Geol. Surv., 
Coalfield Mem., South Staffordshire). 

Another feature commonly observed in most of the British coalfields is the 
occurrence of "washes", the name usually given to areas in which the coal seam 
is replaced by shales, sandstones, or conglomerates. Sometimes these have the form 
of a regular river-system with meanders and tributaries. Another species of "wash" 
is broad and irregular, resembling more an area over which a river has operated 
by shifting meanders. This type can be shown in certain areas to be in such relation 
to the major faults as to indicate that movement of the faults was the cause or 
accompaniment of the washes. The Haigh Moor Seam of the Yorkshire coalfield is 
much subject to washes and in a series of Collieries ranging for 8 km. (5 miles) 



Kendall: Great Britain. — Sedimentary Rocks. — The Coal Measures. (III. 1.) 159 

in a south-west and nord-east direction the seam is extensively "washed" on the 
down-throw side of a fault, almost even up to the line of dislocation, while it is 
quite intact up to the brink of the fault on the upthrow side. 

Another evidence of' contemporary earth-movement is afforded by the thicken- 
ing of the Coal Measure strata in synclinal areas, as in the North Staffordshire Coal- 
field where a certain group of strata thickens from 600 m. (2000 ft.) on an anticline 
to 1200 m. (4000 ft.) in the adjacent syncline. 

The anthracitic character of much of the coal of the South Wales Coalfield 
is of immense economic importance and of great geological interest: it was formerly 
ascribed to the internal heat of the earth, because, as a general rule, the seams 
in the deeper portions of the great basin are more anthracitic than those above 
llirm. The whole subject are been carefully considered by the geologists who have 
recently resurveyed the field (Strahan and Pollard 1908, pp. 66, 70). Their 
conclusions are as follows: 

"1. The seams are not all similarly anthracitic, and though each seam is generally 
more anthracitic than the one above it; there are many exceptions to this rule". 

"2. The anthracitic character was not due to faults, but existed before the 
faults were formed." Faults with a throw of hundreds of feet throw anthracitic 
against non-anthracitic seams. 

It may be remarked that this statement is not quite conclusive, as the faults 
may have been produced by successive movements and the anthracitization have 
affected at an early stage of the faulting only certain of the lower seams. 

"3. The anthracite existed as such before the coalfield was reduced by denu- 
dation to its present dimensions." Some seams are anthracitic right up to the 
outcrop. This may be taken to prove that the change was pre-Triassic, for the 
disturbances and denudation took place before the deposition of the Trias; more- 
over, pebbles of bright coal, neither crushed nor deformed, occur in the Pennant Grit. 

"4. The percentage of ash diminishes pari passu with the decrease of 
bituminous matter," whereas, had the normal percentage been present originally, it 
might be expected that the anthracite, having lost more volatile matter, would 
show a higher proportion of ash. 

The following extremes of composition (excluding cases of probable error) 
are noted: 

Bituminous Coal Anthracite 

Ash Carbon Ash Carbon 

11,0 — 87,19 6,6 — 92,64 

0,9 — 87,93 0,7 — 93,20 

The inverse ratio, which may be said in general terms to exist between the degree 
of anthracitization and the quantity of ash present, though apparently contradicted 
by these figures, is however borne out decisively by a more comprehensive review 
and it lends some support to the view that the anthracitic change is due to an 
original difference of conposition; but a much more extended study of the nature 
of the ash is needed before a plenary acceptance of this hypothesis is permissible. 
The mineral nature of coal-ash is very imperfectly known. Some of it may be, 
no doubt, attributed to the original plants, while other parts may be mere mineral 
detritus, and others again may occur in the form of veins of calcite, iron pyrites etc. 
filling-in joints that, occur much more abundantly in bituminous than in anthracitic 
coal. Thorpe (1878) found that careful separation of the bright from the dull or 
'"mineral charcoal" layers in two typical bituminous coals disclosed great differences 
in the percentages of ash respectively characterizing the two types, bright coal 
giving 2,8 and 2,2 %, against 9,5 and 6,3 in the dull layers. It may further be noted 
that the alkalies constitute the principal ingredients in the ash of most plants, while 



160 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

they are almost entirely absent from coal. On the other hand salts of calcium and 
magnesium, relatively rare in modern plants, are predominant elements of coal-ash. 

It appears to the present writer probable that the degree of anthracitization 
depends rather upon physical conditions set up at an early stage of conversion 
of the vegetable matter into coal than to "original" differences in the chemical 
compositions of the mother-substance. In the case of the Halifax Hard Seam 
the presence in it of petrifactions of the undistorted plant structures in the form 
of coal-balls shows beyond question that the mineralizing materials were intro- 
duced by percolation from an overlying shell-bed. 

The distribution of the anthracitic seams in South Wales throws little light 
upon the problem. The degree of anthracitization increases in general from south 
to north and at both ends of the coal-field it becomes ' more pronounced as the 
thickness of the measure diminishes, but the anthracitic area does not by any 
means coincide with the region of least thickness. 

Strahan (1901) has described a case in which a seam of coal passed gradually 
into dolomite. 

One other interesting feature of the coal seams remains to be mentioned. Well 
rounded blocks of foreign rock occasionally occur embedded in the seams, or, more 
rarely, in roof or floor. They are most frequently of a hard grey quartzite and 
the largest blocks weigh several hundredweights each. Such masses can not have 
been rolled into the position in which they are found and some agent of flotation 
such as ice, or entanglement in tree-roots, must have operated. As to the latter, 
it may be observed that the only roots of arborescent vegetation found in asso- 
ciation with these seams are the divergent rhizophores (Stigmaria) of the giant 
lycopods and these are entirely unsuited to the involution of large stones. It is 
a remarkable circumstance that no boulders at all comparable are noted from 
the sedimentary elements of the Coal Measures, such as the sandstones, where, if 
any where, far-transported blocks might be expected. This may be due to lack 
of observation rather than to non-existence, for the mass of sandstone and other 
sedimentary materials excavated is but a small fraction of the tonnage of coal 
raised; moreover, the occurrence of a boulder in a coal seam is much more likely 
to attract attention than the like occurrence in a quarry. 

The classification and correlation of the Goal Measures is attended 
with considerable difficulties, the first of which arises from the fact that, in the 
absence of any pateontological guide, the strata were subdivided at well-marked 
lithological changes, or according to the character or frequence of coal seams, the 
nature of their seat-earths, or other, more or less arbitrary, criteria. 

The application of palseobotany to the problem has brought about a much 
needed change by enabling lines to be drawn at the horizons at which notable 
changes of the flora take place. The study of the animal remains has also yielded 
results of great value in exploration, but, as might be expected from the con- 
ditions attending the deposition of the Coal Measures, the animals are much more 
affected by local influences than the plants. 

In North Staffordshire Hind has found the lamellibranch mollusca to be 
distributed with such constancy that they can be used as indices with much con- 
fidence, the succession in ascending order being as follows: 1. Carbonicola robusta, 
2. Anihracomya williamsoni, 3. A. adamsi, i.A.wardi, 5. A. phillipsi, 6. A. calcifera. 
In Scotland however the distribution is not constant, and it is suggested by Lee 
(1912) that the distribution of these species is determined more by suitability of 
conditions than by time. In East Lothian the molluscan sequence appears to be 
the same as in North Staffordshire but a marked divergence may be noted in 
the Glasgow area. 



Kendall: Great Britain. — Sedimentary Rocks. — The Coal Measures. (III. 1.) 161 

The classification by plant evidence is in large measure due to the labours 
of Kidston who divides the Coal Measures into four horizons as follows: 

4. Radstockian Series = Upper Coal Measures. 

3. Staffordian „ = Transition Series. 

2. Westphalian „ = Middle Coal Measures. 

1. Lanarkian „ = Lower Coal Measures (including the Millstone Grit). 

The necessity for adopting a new terminology is apparent from a consideration 
of the confusion that would arise when correlations were attempted of areas in 
which a palaeontological classification had been effected with others in which the 
terms Upper, Middle and Lower Coal Measures had merely a stratigraphical and 
local foundation. 

The zoological indices are more irregular in their distribution and are less 
frequent in their occurrence than the plants, and to the present writer it seems 
better to employ Kidston's terminology and to use the evidence of the mollusca 
as a useful or even an indispensable supplement. 

A few broad features of the floral sequence may be summarized from data 
kindly furnished by Kidston: 

Radstockian (= Stephanian, or true Upper Coal Measures). Pecopteris arborescens and 

P. polymorpha. 
Staffordian. A flora transitional from the Westphalian to the Radstockian. 
Westphalian Great abundance of Sigillaria especially S. boblayi. 
Lanarkian. Chiefly characterised by rarity of Sigillaria the flora being much poorer than 

that of the Westphalian and many species common in the latter being absent. 

While upon this subject the floral characteristics of the Lower Carboniferous may 
fitly be mentioned. The Lower Carboniferous is characterized by the great rarity 
of Sigillaria, and the abundance of Lepidodendron especially L. rachiopteris. Sphenop- 
teroid species are also very characteristic. The Calciferous Sandstones of 
Scotland have the same general features and are specially notable for the occurrence 
of Telangium affine Lind. and Hutt. sp., and Adiantites antiquus. 

A brief mention may now be made of the distribution in the various coal-fields 
of Great Britain, so far as has been ascertained, of the floras, as thus defined, Kid- 
ston's views being adopted, except in certain specified instances. 

The CulmMeasures of Devon are separable into a lower division presenting 
a well-marked Pendleside fauna and surmounted by a series containing a West- 
phalian flora. 

The Somersetshire Coal Measures present anomalous stratigraphical 
relations due to severe tectonic disturbances. They include a lower Farrington and 
an upper Radstock Series both referable to Kidston's Radstockian. 

The Bristol Coal-field is still under consideration. No Lanarkian represen- 
tatives have been definitely recognised, but a series of measures below the lowest 
workable seam may belong to that horizon. The Westphalian, according to Arber, 
includes all the workable coals. 

The great South Wales Coal-field is provisionally classified by Kidston 
as follows: 

Upper Pennant = Radstockian. 

Lower Pennant = Staffordian. 

White Ash = Westphalian. 

Basal Sandstones and Grits = Probably Lanarkian. 

The Forest of Dean contains representatives only of the Farington subdivision. 
The little Dover Coal-field is referred by Arber to the Staffordian, all the 
three divisions recognized in Staffordshire, being according to him, present. 

Handbuch der regionalen Geologie III. 1. 11 



162 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

The South Staffordshire Coal-field shows the overlap of Westphalian 
on to Lower Palaeozoic rocks. It is succeeded by Staffordian. 

North Wales. All the seams at present worked are in the Westphalian, 
but Kidston fully endorses Walcot Gibson's ascription of an upper unproductive 
series to the Staffordian. 

North Staffordshire furnishes a full sequence from the Lanarkian up to 
the Keele Series, the equivalent of the basal Radstockian. 

In Lancashire a similar sequence is found up to the Ardwick Series, which 
is referable to the Staffordian. The Whitehaven Coal-field has yielded evidence 
of Westphalian and Staffordian (probably Lower) measures. And the equivalents 
of the Keele Series occur at Jockey's Sike in Cumberland. 

Turning now to the Eastern Coal-fields, we find that though South Leicester- 
shire is very imperfectly known at present the presence of Westphalian is certain. 

The great Coal-field of Yorkshire, Derbyshire and Nottinghamshire 
is mainly constituted of Lanarkian and Westphalian, but traces of Staffordian 
have survived pre-Permian denudation at Conisboro in Yorkshire, and explo- 
rations through the newer rocks at Gedling and Thurgarton show that at the former 
place the Staffordian is present and at the latter the full Staffordian and Lower 
Radstockian (the Keele Series). 

The Coalfield of Northumberland and Durham has not yet been fully 
studied. The Westphalian and Lanarkian certainly occur and Stobbs (1906) has 
found a fauna suggestive of Staffordian. 

In all the Scottish Coal-fields the Lanarkian isworked; and the Westphalian, 
also, is found in Fife and in the little Border Coalfield of Canonbie, where in addition 
a representative of the Keele Series (Lower Radstockian) has been identified. 
It is probable that the Staffordian will be detected by closer investigation. 

Lithological Characters. The Lanarkian and Westphalian divisions present 
no marked characters beyond those due to the development of a Millstone Grit 
facies, to the prevalence of gannister seat-earths in the coalfields of the Pennine 
Region and North Wales, and to the Pennant Series of sandy and gritty rocks 
that forms a parting, inconstant in position, between Higher and Lower Productive 
Measures in South Wales. 

In South Wales this Pennant series mounts higher in the sequence as it is traced 
from west to east, but its approximate position is within the Staffordian, whereas in the 
Bristol and Somerset field it lies between the S taffordian and Radstockian. 

The Staffordian and Radstockian present great abnormalities in the strong 
colouration and the generally barren character of the rocks and the occurrence of 
peculiar fine-grained limestones, often crowded with Spirorbis and Ostracoda, that 
are commonly, though (as Gibson points out) erroneously, designated by the term 
Spirorbis limestones. Such limestones are by no means restricted to this series 
but are found in the Lower Carboniferous of Scotland. 

Throughout the Midland area, and North Wales these Measures were for a 
long time confounded with the Permian rocks, but the recognition of plants of 
Carboniferous type in some of them led to a revision of the whole series, and the 
recent resurvey of the North Staffordshire Coal-field by De Rance, Gibson and 
others has afforded a welcome opportunity for a close investigation of the whole 
series. The area was peculiarly well fitted for the purpose as, though the rocks 
are almost destitute of workable coal-seams, they are largely exploited for ironstone, 
and the clays are employed for "seggars" in the great pottery industries that have 
flourished in the district for more than two centuries. 



Kendali: Great Britain. — Sedimentary Rocks. — The Coal Measures. (III. 1.) 163 

Gibson classifies the rocks as follows 

Keele Group. 210 m. (700 ft.). Red and purple sandstones and marls with occasional coal- 
seams and thin black grey or limestones. 

Newcastle under Lyme Group. 90 — 105 m. (300 — 350 ft.). Grey sandstones and shales with 
four thin seams of coal and at the base an entomostracan limestone. 

Etruria Marl Group. 245— 335 m. (800— 1100 ft.). Chiefly mottled red and purple marls 
and clays. Thin bands of green grit very characteristic. Limestone bands occur 
near the summit and near the base one thin coal-seam with a laminated ironstone. 

Black Band Group. 90 — 120 m. (300 — 400 ft.). Grey sandstones, marls and clays. Numerous 
thin coal seams and Black-Band ironstone. Thin bands of limestone throughout. 

Kidston refers the Keele Group to the Lower Radstockian and the remaining 
three divisious constitute the type of his Staffordian. 

An exactly similar series has been identified by Gibson in North Wales, 
and at Thurgarton in Nottinghamshire. Cantrill (1895) has recognised a portion 
of the series in the Forest of Wyre and at other localities in Shropshire, Warwick- 
shire and South Staffordshire. In the Warwickshire Coalfield Vernon (1912) 
has found a series comparable to that of North Staffordshire. 

In the coal-field of South Lancashire occur the Ardwick Series described 
long ago by Binney and later, with sections coloured as in nature, by Brockbank 
and De Rance. They consist of marls brilliantly coloured red and green with 
many beds of Spirorbis limestone, which were formerly extracted by mining. They 
probably represent the Etruria Marls, and they attain a thickness of at least 250 m. 
(800 ft). At Bradford Colliery near Manchester the Black Band Group is well 
represented. 

In Scotland a great series of barren measures generally of a red colour sur- 
mount the Productive Coal Measures and probably represent some part of the 
Staffordian or Radstockian, but palaeontological proof of the occurrence of rocks 
of this age is lacking, except in Ayrshire where the Radstockian flora seems to 
be represented. 

The relations of the Red and Gray Rocks of Central England to the West- 
phalian on the one hand and the Permian on the other are not always clear, as 
sections showing the contacts are seldom available and the outcrops are often 
concealed by Drift. In general it may be said that the whole Coal Measure sequence 
from the lowest to the highest is in strict conformity. The notable cases of dis- 
cordance are found in the Flintshire Coal-field and in the Coalbrookdale Coal-field 
near Shrewsbury, the so-called Simon Fault. This was interpreted by some of the 
earlier observers as a "wash", i. e. a great trough eroded in the "Middle" Coal 
Measures and filled in with "Upper" Coal Measures. Clarke however has shown 
that the older beds were folded and denuded, and the newer series laid across the 
plain of erosion. 

While the Coal-Measure sequence is in general uninterrupted, it is becoming 
more and more clear that in the Midlands and on the South side of the great central 
barrier a basal unconformity is by no means infrequent, and the failure to detect 
the Lanarkian flora in any part of the South Western, and Southern regions is prob- 
ably due to a break in the succession. Thus, Vaughan considers that there is an uncon- 
formity at the base of the Coal-Measures in the Clevedon area, Dixon has shown 
that at Titterstone Clee the Coal-Measures rest on Lower Carboniferous rocks; 
and Sibly has ascertained that the Radstockian of the Forest of Dean lies in strong 
unconformity upon "Millstone Grit", which is of Lower Carboniferous age, and over- 
laps the underlying Tournaisian so as to come on to the Old Red Sandstone. 

The Permian rocks are usually in strong discordance upon the Carboni- 
ferous no matter what division they may rest upon, most examples quoted of the 



164 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

contrary, being cases in which stained Carboniferous rocks have been mistaken 
for Permian. Cantrill however speaks of a gradual passage into the Trias. 

The deposition of the Coal Measures above the Westphalian in Central England 
probably took place under conditions markedly different from those of the earlier 
series. The general poverty of the fauna and flora, the entire absence of distinct- 
ively marine forms, and the strong colouration with peroxidized iron, point to 
climatic conditions of a desert or semi-desert type, as Green observed. He 
concluded that these strongly coloured rocks were probably laid down in lakes 
having no overflow to the sea. The Spirorbis or ostracod (entomostracan 
of Ward) limestones commonly contain a high percentage of magnesia and 
in some cases, eg. in the Ardwick Limestone, the iron content is high enough to 
give them the character of ores of Iron of sufficiently high grade to have justified 
their extraction, if the mode of their occurrence had been favourable to mining. 

These rocks are usually of a compact smooth texture and reddish or grey 
colour. They sometimes show a curious brecciated structure, with fragments and 
matrix almost identical in colour and texture. Spirorbis pusillus is not an 
invariable component of these limestone, some beds being found from which it 
is practically absent, but Carbonia is much more general. The habits of the Spi- 
rorbis must have been markedly different from those of the modern animal attributed 
to the same genus. The latter is exclusively of marine habitat, its favorite position 
being on the fronds of Fucus and Laminaria, whereas the Carboniferous examples 
have not been recorded as associates of marine animals. A common mode of occurrence 
is attached to ferns. The fauna of the Spirorbis limestones includes, besides Car- 
bonia, the small lamellibranchs Anthracomya phillipsi and A.calcifera. Fish remains 
are of rare occurrence. These associations seem to negative decisively any idea 
that the Spirorbis of the Coal Measures was a marine form. 

It is interesting to observe that the conditions, whatever they were, that induced 
the formation of these limestones, were not confined to the period of the Staffordian 
and Radstockian: one occurrence is noted below the position assigned to the top 
of the Westphalian in North Staffordshire. In the Midland Valley of Scotland lime- 
stones with the colour and texture of the typical Spirorbis limestones occur in 
the Upper Red Rarren Measures, and in the Ayrshire basin the characteristic anne- 
lids are found. 

The Calciferous Sandstone Series of Northumberland and of the Midland Valley 
of Scotland contains many beds of "cement-stone", for the most part fine-grained 
dolomites (see Mem. Geol. Surv., Glasgow, for analyses), without recognisable fossils, 
but in East Lothian Spirorbis helicteres occurs in profusion in certain bands. The Lower 
Carboniferous rocks of this area in their strong colouration and the frequent occur- 
rence of gypsum suggest deposition in an area of desiccation. The climatic condition 
of the later Coal Measure times was a recurrence of a perhaps equally wide-spread 
phase. 

The Coal-fields and their Economic Resources. 

The resources of the Rritish coal-fields have been exhaustively considered by 
a Royal Commission to whose Final report in 1905 reference should be made, as 
well as to the works of Hull, and Gibson that embody much of the geological 
information. 

The Kent Coal-field or Coal-fields, lying beneath an unconformable 
cover of secondary rocks, is known from one colliery that has just commenced 
operations and from a small number of borings; the data are altogether inadequate 
for the correlation of seams even between adjacent bores. Any estimate of either 
the area or productiveness is therefore premature. It is not certain that the measures 



Kendall: Great Britain. — Sedimentary Rocks. — Economic Resources. (III. 1.) 165 

proved lie in a single basin. Arber recognises the equivalents of the Staffordian 
series "and of the Keele Beds. 

Cornwall and Devon. The Upper Culm Measures in these two counties 
are mainly shaly, of unknown thickness, and contain thin beds of inferior coal (locally 
called "culm"). So far as the plants have been studied the flora appears to be 
Westphalian. 

The Bristol and Somerset Coal-fields. The group of coalfields lying 
between the Mendip Hills and the Severn are arranged roughly as an inverted 
J_ in consequence of the interference of two systems of folds — the E.-W., Armorican 
and the N.-S., Malvernian. The general succession is: 

d„j„*„„i,i f Radstock Series 

Radstockian f Farrington |§ 

Pennant Sandstone Series 
Staffordian { Jew Rock Series 

A large part of the known coal-fields is under an unconformable cover of Triassic 
and Jurassic rocks and it is probable that other detached basins yet remain to be 
discovered. The Upper Series about 914 m. (3000 It.) thick, contain 22 seams, the 
Pennant Sandstone 525 m. (1725 ft.) contains 5 seams and the Staffordian, 660 m. 
(2000 ft.) thick, 36 seams. 

The output in 1903 amounted to 14 million tons. The estimated quantity of 
available coal (after allowance for waste in working etc.) in seams of one foot and 
upward at a depth not exceeding 1220 m. (4000 ft.) is 4 000 000 000 tons. 

The South Wales Coal-field is practically all exposed, except where covered 
by the sea, and where, in South Glamorgan, a small area is concealed under secon- 
dary rocks. 

The succession varies progressively in a west to east direction. The general 
sequence is, as already statet, according Kidston: 

Upper Pennant (Supra-Pennant) Radstockian 

Lower Pennant (Pennant and Red Ash) . Staffordian 

White Ash or Lower Coal Series .... Westphalian 

Basal Sandstones and Grits ? Lanarkian 

A lithological classification and correlation is rendered extremely difficult by the 
fact already mentioned that the Pennant phase runs athwart the stratigraphy, 
its base and summit being on lower horizons in the west than in the east. 

The area of the field is 2600 qkm. (1000 sq.m.). The maximum thickness of the 
Coal Measures is upwards of 2500 m. (8400 ft.) (Strahan 1910). The number of 
seams varies from place to place, in Pembrokshire 10 seams with 8.4 m. (28 ft.) of 
coal, Carmarthen 18 to 34 with 14.2 to 26.5 m. (47 to 88 ft.); Glamorgan 24 to 48 
with 20 to 38 m. (66 to 124 ft.) and Monmouth 11 to 21 with 11.8 to 14.3 m. (38 to 
47 ft.). The total available coal remaining in 1905 was 26 470 000 000 tons. Of this 
quantity 30°/o is bituminous, 22°/ Anthracite, 47% Steam Coal. The output in 
1903 was 42 millions of tons. 

The Forest of Dean Coal-field has an area of 88 qkm. (34 sq. miles), 
wholly exposed. 

A threefold division has been adopted, but the whole of the Measures, 843 m. 
(3765 ft.) in thickness, belong to the Radstockian. A thick sandstone, suggestive of 
the Pennant of South Wales but of course on a higher horizon occurs in the Lower 
division. 

Sibly has shown (1912) that the so-called Millstone Grit in this area is of 
Avonian (probably Tournaisian) age and that the Coal Measures rest unconformably 
upon it and pass transgressively on to the Old Red Sandstone. 



166 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

The available coal remaining in 1905 was 258 533 000 tons. The output, which 
appears to be declining, is less than one million tons per annum. 

Coal-fields of the Midlands. These coalfields, in which for the most part 
the Coal Measures rest unconformably upon pre-Carboniferous rocks, are the subjects 
of a report to the Royal Commission by Lapworth. They are only partially exposed, 
the greater part being concealed beneath Triassic and small tracts of Liassic rocks. 
On the West occur the little isolated fields of 1. Coalbrookdale, 2. the Forest 
of Wyre, 3. the Clee Hills, 4. Shrewsbury, 5. Le Botwood, 6. Dryton. 
Except at Coalbrookdale and the Clee Hills, no Lower Carboniferous rocks are 
present. In most of these the Measures belong exclusively to the Staffordian and 
Radstockian, the latter in unconformable relation to various divisons of the Carboni- 
ferous. Dixon has shown that at Titterstone Clee they rest on Avonian. This 
group of coalfields is estimated to contain 275 000 000 tons of available coal in the 
visible and 46 000 000 tons in the concealed parts. 

The Warwickshire Coal-field is exposed to the extent of about 245 qkm. 
(62 sq. m.) but there is, concealed beneath newer rocks, a considerable area that 
can not be computed. Vernon (1912) recognises Westphalian, Staffordian and 
Radstockian (Keele Beds) with a maximum thickness of 850m. (2800 ft.). The meas- 
ures thin towards the south and the seams come closer together. Nine workable 
seams are known. The available coal remaining in 1903 was 375 000 000 tons in 
the visible field and 751 600 000 tons in the concealed extension. 

The South Staffordshire Coal-field. The succession is substantially the 
same as in the Warwickshire Coalfield. The total proved area is3875qkm. (1495 sq.m.) 
but it is probable that it will be considerably extended by further exploration. 
The available coal remaining amounts to 1 400 000 000 tons. 

The Leicestershire and South Derbyshire. The Measures in this field 
are very difficult to correlate with those in adjacent areas and even between one 
part of the field and another. A Westphalian flora has been recognised, and an un- 
productive series succeeding Millstone Grit is probably of Lanarkian age. The 
visible coal-field extends to about 78 qkm. (30 sq. m.) and the concealed portion 
to 140 qkm. (54 sq.m.). The available coal in the visible field is estimated at 
433 800 000 tons and in the concealed portion 1391 000 tons. 

The North Staffordshire Coal-field. The stratigraphy has already been 
described. The Coal Measures in three separate areas, the Potteries, Cheadle and 
Shaffalong fields, respectively 208 qkm. (80 sq.m.), 47 qkm. (18 sq.m.) and 5 qkm. 
(2 sq.m.) in area. The southern portion is concealed beneath a cover of Triassic rocks 
and the whole area is cut off on the west by a great fault with a downthrow of 
640 m. (2100 ft.). The total available coal in 1905 is estimated at 4368000000 tons. 

The Cheshire Coal-fields. Two small coalfields have been proved in this 
county, one on the Pennine side near Stockport, and the other on the shore of the 
Dee estuary. The available coal is estimated at 291 080 000 tons. 

The North Wales Coal-field. This is situated in the counties of Flint 
and Denbigh on the shores of the Dee estuary. The full Coal Measure sequence 
is doubtless present. The available coal is estimated at 1 736 000 tons. 

The Lancashire Coal-field. This field contains representatives of every 
division of the Coal Measures up to the Etruria Marl. It abuts on the west upon the 
Pennine Chain, on the north it surrounds the anticline of Rossendale, and on the 
south and west it descends below the great unconformable cover of Permian and 
Trias of the Cheshire Plain, beneath which, but at a depth prohibitive of profitable 
working, the coal measures extend from all the surrounding Coalfields. In the 
Burnley area the Coal Measures probably attain their maximum thickness in Eng- 
land, though lacking the Ardwick series (= Etruria Marls). 



Kendall: Great Britain. — Sedimentary Rocks. — Economic Resources. (III. 1.) 167 

The available coal is estimated at 4 238 500 000 tons. The total area of the 
Coalfield is about 564 qkm. (217 sq.m.). 

Ingleton Goal -field. This little field forms a shallow basin lying against 
the South Craven fault. It is partly covered by Permian rocks. Several coal seams 
occur and two collieries have recently been started but no reliable estimate of its 
productiveness can be made. 

The Yorkshire, Derbyshire and Nottinghamshire Coal-field. This 
is by far the largest and most productive Coal-field in Britain. The visible coal-field 
has an area of 1980 qkm. (760 sq.m.), but Coal Measures have now been proved as 
far East as the Trent at Scunthorpe. The further extension is conjectural but the 
present writer in a report to the Royal Commission gave his grounds for the belief 
that the true boundaries would coincide on the north with a remarkable post- 
humous fold running through Market Weighton, on the south with a similar fold 
extending in a southeasterly direction from Charnwood towards Cambridge, while 
on the east the basin would either terminate on the flanks of a low anticline whose 
axis runs through Willoughby and Louth in Lincolnshire, or would extend under 
the North Sea. The nature and position of this boundary he regarded as immaterial, 
as in either case no Coal Measures at workable depth would be found to the east of 
the assumed boundary. The Commissioners include in the "proved" coalfield not 
only the uncovered portion but also that part of the concealed field enclosed within 
lines joining the north-east and south-east corners with Haxey (11 miles east of 
the visible coalfield). 

The estimate of available coal in this area is 26 500 000 000 tons. The area 
of "unproved" coalfield beyond this is computed by the writer at 10 100 qkm. 
(3885 sq. m.) with a possible 35 000 000 000 tons of available coal. The Commissioners 
regarded the south-eastern extension as too hypothetical to be included in the 
area for which they considered an estimate possible; they therefore reduced the area 
to 6630 qkm. (2550 sq. m.) and the estimate of available coal to 23 000 000 000 tons. 
Even thus reduced it is clear that this gigantic field must constitute the principal 
coal reserve of Great Britain ; it is indeed the only British coalfield that is capable 
of any very large increase of its output; all the other coalfields have practically 
reached their limit or are actually declining; on the other hand new collieries are 
starting here, generally on the expectation of an annual output of one to two millions 
of tons. The full sequence of Coal Measures from the Lanarkian to the Radstockian 
is present, but the higher divisions (Upper Staffordian and Keele Series) only 
in bore holes. 

The Northumberland and Durham Coal-field. This great coal-field 
is fully exposed save for the belt on the east and south covered by the Magnesian 
Limestone. The Coal Measures include Lanarkian and Westphalian with some 
representative of the lower part of the Staffordian in the south-east. Regarded 
as a coalfield however, the Lickar and Scremerston series in the Lower Carboni- 
ferous must be included. The estimates of the Royal Commission also include 
the extension of the field out to the three mile limit beneath the sea. The total 
available coal is estimated to be 5 271 000 000 tons. 

The Whitehaven Coal-field. This coal-field is divisible, like the last, into 
three tracts — the exposed area, the undersea area, and the sub-Permian area. 
Workings now extend at Whitehaven to a distance of four miles under the sea. 
The Coal Measures include Staffordian and Westphalian but no Lanarkian has 
yet been identified. The total available coal to a distance of 5 miles under the 
sea is estimated to be 1 527 700 000 tons. 

The Scottish Coal-fields. In all the coal-fields of Scotland the Lower Carboni- 
ferous contains a notable percentage of workable coals and the term coal-field in 



168 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

this region does not connote merely Coal Measures. The general development 
of the members of the Coal Measure Series in Scotland has already been mentioned a 
propos Kidston's classification and need not be repeated here. 

In the absence from the Report of the Royal Commission of separate estimates 
of area and productiveness of the Scottish Coal Measures and the Lower Carboni- 
ferous rocks respectively it is impossible to give any detailed treatment field by 
field as was done in England and Wales. The gross available coal from all divisions 
is computed to be 14 681 000 000 tons. The increase of output is extremely slow 
in several areas, e. g. Lanarkshire; the thicker seams are practically exhausted, so 
that in the near future the output will begin to decline. The concealed or partially 
proved coalfields are of small extent. 

II. Igneous Rocks. 

By Alfred Harker. 

During Lower Carboniferous times igneous activity broke out in numerous 
districts in the southern half of Scotland and also, on a more restricted scale, at 
certain isolated centres in England. The course of events was in some respects dif- 
ferent from that which was followed in the Ordovician and Old Red Sandstone 
times, and subsequently in the Tertiary, in so far that there are in Britain no large 
plutonic intrusions of Carboniferous age. Here igneous action was represented only 
by lavas and fragmental volcanic accumulations and by intrusions of moderate 
dimensions in the form of plugs, sills, and dykes. On a broad view it appears that 
the more important groups of intrusions succeeded the surface volcanic outbursts: 
but the sequence is a complicated one, and there were also intrusions accessory 
to the volcanic eruptions themselves. Moreover the visible evidence sometimes 
admits of ambiguity, or at least of difference of opinion, as regards the extrusive 
or intrusive nature of particular sheet-formed bodies of rock. 

A. Carboniferous Igneous Rocks of Scotland. 

We shall begin with the Scottish area as in every respect the most important. 
Volcanic action was mostly confined, except in the west, to the Lower Carboniferous, 
and was most energetic in the earlier division, represented by the Calciferous Sand- 
Stone Series. Sir A. Geikie remarks that the earlier eruptions were of the "plateau" 
type, in which continous tracts of volcanic materials were built up by discharges 
from numerous vents; while the later eruptions were of the "puy" type, in which 
the accumulations lie round isolated vents, and are sometimes exclusively fragmental. 
At no stage is there any indication of fissure-eruptions: the actual sites of the vol- 
canoes can often be identified, and many of them are of small size. 

The region, affected consists of a broad belt of country along the "Midland 
Valley" of Scotland (Forth and Clyde) and a narrower and more scattered belt 
near the border of Scotland against England (see map, fig. 36). The eruptions were 
not always synchronous in different districts : as a rule they began earlier, and ceased 
earlier, in the eastern and south-eastern part of the region than in the western. Some 
of the fragmental volcanic deposits are of submarine origin; but in general the vol- 
canoes appear to have stood above water until they were gradually submerged. 

Petrographically the volcanic rocks, and those intrusive rocks which are 
intimately connected with them, are predominantly basic in composition, and they 
possess decided, but not very strongly marked, alkaline affinities. Analcime and 
nepheline occur in some types, but the latter mineral is seldom more than an unim- 
portant accessory constituent. The basalts, which are the prevalent rocks, have 



Harker: Great Britain. — Igneous Rocks. — Scotland. (III. 1.) 169 




Fig. 36. Sketch-map showing the distribution of the Carboniferous and Permian 

volcanic rocks of Southern Scotland. (Alfred Harkbb.) 

The Permian, or supposed Permian, are found chiefly in two districts: M = Mauchline (Ayrshire), 

and D = Dumfriesshire. 

Volcanic rocks black. The principal E. — W. dykes of quartz-dolerite are also indicated. 



as a whole a composition between gabbroitic and essexitic. They are often conspicu 
ously porphyritic, with large crystals of augite, olivine, or labradorite. Associated 
with the basalts is the more alkaline type mugearite, rich in oligoclase and some- 
times in orthoclase. The more felspathic types which have been styled trachytes 
(but are mostly orthophyres) are not so generally abundant. They consist of a 
soda-orthoclase with green augite and sometimes doubtfully a little nepheline. 

(I) In the Calciferous Sandstone Series. The igneous rocks in the Calciferous 
Sandstone Series of southern Scotland include, besides fragmental deposits, a suc- 
cession of sheets which are partly lava-flows, partly intrusive sills. The distinction 
between extrusions and intrusions is here perhaps not of great importance, for there 
is evidence that the sills were intruded near the surface of the ground at an epoch 
little later than that of the lavas. 

The Midland Valley belt begins in the county of Haddington or East Lothian. 
The earliest volcanic accumulation in the neighbourhood of North Berwick is a 
green ash enclosing large blocks. Above is a series of sheets of porphyritic olivine- 
basalts of several types, becoming generally less basic upwards, and having sheets 
of mugearite intercalated among them. Farther west these rocks are overlain by 
thick sheets of so-called trachytes, which build the Garlton Hills. The whole covers 
an area of more than 100 qkm. (40 sq.m.). About Dunbar the sites of numerous 



170 (III. I.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

volcanic vents are marked by "necks" of agglomerate, sometimes invaded by 
intrusions of basalt. Elsewhere are intrusive stocks which probably mark the 
sources of both lavas and sills. Some are of basic nature, while North Berwick Law 
and the Bass rock are trachytic stocks, and Traprain Law is a laccolite of like 
composition. 

In Midlothian similar lavas and tuffs occur, but only as scattered outliers. 
Both at Edinburgh and in the Mid-Calder district porphyritic olivine-basalts are 
overlain by mugearites. There are old volcanic vents at Arthur's Seat and other 
places near Edinburgh, and some of the basic intrusions in the neighbourhood are 
referable to the same age. On the north side of the Forth a series of lavas and tuffs 
occurs in the upper part of the Calciferous Sandstone Series about Kirkcaldy and 
Burntisland in Fife. The lavas are basic, mostly porphyritic olivine-basalts, while 
numerous volcanic necks occur as before. 

In the west of Scotland are much larger tracts of volcanic rocks, representing 
collectively a broken and eroded plateau which has probably had an original area 
of 5000 to 7500 qkm. (2000-3000 sq.m.). It extends on both sides of the Clyde, 
covering a considerable part of the counties of Stirling, Dunbarton, and Renfrew, 
with the west of Lanarkshire and the north of Ayrshire. In addition there are out- 
lying relics in the islands of Cumbrae, Bute, and Arran, and near the southern 
end of the Cantyre peninsula. The succession is well displayed in the Campsie 
Fells in Stirlingshire, where the maximum thickness is probably 600 to 900 m. 
(1800-2700 ft.). It is made up of porphyritic olivine-basalts and mugearites of 
types found also in the eastern area, underlain by another type of olivine-basalt, 
only micro-porphyritic. The sequence, however, varies in different localities, owing 
to the overlapping of flows from different centres of eruption. There are numerous 
volcanic necks, some of agglomerate, others of basalt and trachydolerite, and at 
Fintry is an intrusion, probably a laccolite, of a trachytic phonolite. A similar suc- 
cession is met with in the neighbouring Kilpatrick Hills, in Dunbartonshire, where 
the more felspathic basalts are often amygdaloidal, and contain various zeolites. 
In the Cathkin Hills, south of Glasgow, the succession shows non-porphyritic olivine- 
basalts succeeded by others with porphyritic felspar. 

The volcanic rocks of the Scottish border belt are less fully known. There is 
a considerable development in the lower part of the Calciferous Sandstone Series 
in the Tweed Valley district of Berwickshire and Roxburghshire. The lavas are 
basalts, including both porphyritic and micro-porphyritic types. The western limit 
of the volcanic plateau is determined by erosion, and beyond it the older strata are 
pierced by basaltic plugs and agglomerate necks, which probably represent the 
-vents of Carboniferous volcanoes. Some other intrusions in the neighbourhood 
are possibly to be related to this volcanic epoch. The most interesting is the sheet 
which makes the Eildon Hills, near Melrose, consisting of trachytic rocks contain- 
ing riebeckite (McRobert, 1914). 

A similar but thinner volcanic group makes a belt running south-westward 
through the southern parts of Roxburgshire and Dumfriesshire, along Liddesdale 
and across lower Annandale, and is seen again on the Solway coast south of Criffell. 

(II) Of Carboniferous Limestone and Later Age. In much of the Scottish Car- 
boniferous tract true volcanic action did not outlast the Calciferous Sandstone 
Series, and later igneous activity took the form of intrusion only. There are, however, 
certain areas where superficial vulcanicity was prolonged into the Carboniferous 
Limestone age. 

One of these areas includes Linlithgowshire (or West Lothian) with parts 
of eastern Stirlingshire and western Fife. The chief volcanic district is found in 



IIarker: Great Britain. — Igneous Rocks. — Scotland. (III. 1.) 171 

the Bathgate Hills and the neighbourhood of Linlithgow and Bo'ness. The group 
begins with tuffs in the upper part of the Calciferous Sandstones, and these are 
followed by a series of olivine-basalt lavas (with intercalated later sills) in the Lower 
Limestone Group of the Bathgate Hills. Corresponding lavas occur in the Kinghorn 
district of Fife. A higher group of lavas and tuffs is found in the Upper Limestones 
of the Bo'ness district and elsewhere, and this also is represented on the north side 
of the Forth in the Saline Hills. To the east of the Bathgate Hills the lower members 
of the Carboniferous Limestone Series are pierced by volcanic necks of agglomerate 
and basalt, which may be assigned to this age. 

In some of the western districts of Scotland vulcanicity continued, not only 
throughout the Carboniferous Limestone Series, but even into part of the Coal 
Measures. This is seen in northern Ayrshire. The volcanic rocks are basalt lavas 
and tuffs, but we have no detailed account of their petrography. 

The intrusive rocks, excluding those already mentioned as being intimately 
associated with the volcanic outpourings, fall into three groups: 

a) Analcime-basalts, monchiquites, limburgites, etc. 

b) Analcime-dolerites, teschenites, picrites, etc. 

c) Quartz-dolerites and tholeiites. 

The first two groups have alkaline affinities which serve to link them with the 
volcanic rocks, but they are of distinctly later age, being mostly intruded into the 
Carboniferous Limestone. In the eastern districts (from East Lothian and Fife to 
eastern Stirlingshire, and perhaps as far as Glasgow) these alkaline intrusions are 
probably to be referred to the age of the Carboniferous Limestone Series, since they 
do not penetrate higher strata. In Ayrshire and Renfrew rocks of similar petrogra- 
phical nature must be of later age, for they are intruded into the Coal Measures 
and even into strata which have been assigned to the Permian. The quartz-dolerites 
(c) are younger than the alkaline intrusions, in the eastern districts at least. They 
are intrusive in strata up to the Coal Measures, and their geological relations 
connect them with the crust-movements at the close of Carboniferous times. 

(a) A number of sheets and irregular intrusions of analcime-basalt and 
monchiquite occur near North Berwick and elsewhere in East Lothian. In a plug 
at Kidlaw the analcime is in crystals of 3 mm. ('/g inch) diameter. A sill at Chesters, 
near Haddington, between monchiquite and limburgite, contains doubtful nephe- 
line. In West Lothian again there are sills of analcime-basalt in the Bathgate Hills. 
The dykes and sheets of monchiquite found in some parts of western Scotland belong 
probably to a later date. 

(b) The coarser-grained intrusions of alkaline rocks have a wider distribution 
than the preceding group, and form sheets up to 65 m. (200 ft.) in thickness. They 
include ophitic analcime-dolerites, teschenites (with hornblende), and pi- 
crites. Analcime-dolerites with olivine occur near Anstruther in eastern Fife, at 
Gosford Bay and elsewhere in East Lothian, at several places in Mid-Lothian, and 
at Mochrie's Crag in West Lothian. Teschenite sills are seen at Gullane in East 
Lothian, at Salisbury Crags, Carcraig, Mons Hill, and other places near Edinburgh, 
in the Bathgate Hills, and at Necropolis Hill, Paisley, and Cathcart near Glasgow. 
Rocks which may be termed essexite-dolerites occur on the islet Craigleith 
at the mouth of the Forth, at Corstorphine near Edinburgh, and in a boss at Lennox- 
town in Stirlingshire. Picrites are less abundant, and are found usually in intimate 
association with the teschenites. On the islet Inchcolm, near Edinburgh, a picritc 
sill, 20 m. (60 ft.) thick, is bordered above and below by teschenite, and a like associ- 
ation is seen at Bathgate in West Lothian. 



172 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

(c) The third group includes doleritic rocks, free from olivine, having inter- 
stitial micropegmatite or sometimes glass. They may be termed quartz-dolerites 
and sometimes tholeiites. The intrusions take the form partly of sills, partly of 
dykes with an E.-W. direction (see fig. 36). The sills are found chiefly in the Midland 
Valley of Scotland. There is a complex of them about Stirling, and they reappear 
in the Kilsyth and Croy district of Dumbartonshire. In Linlithgowshire (West 
Lothian) sills occur at Cocklerue and in the Bathgate Hills, and again along a belt 
extending from Torphichen into the northern part of Lanarkshire. Others are found 
near Old Cumnock and elsewhere in Ayrshire. The dykes are developed in the same 
districts as the sills, where they attain widths of 40 or 50 m. (120 or 150 ft.) but 
they have a somewhat wider distribution, being found northward as far as Loch 
Etive in Argyllshire and Loch Tay in Perthshire. Westward scattered examples 
are known in Bute, Cantyre, Islay, and Jura. Eastward the belt widens, for 
dykes of this group are found as far north as Forfarshire and Kincardineshire and 
as far south as the English border of Berwickshire. The distribution therefore 
does not correspond with that of the alkaline Carboniferous rocks. 

The quartz-dolerite group further passes into the north of England. It includes 
probably one or two dykes, such as that at Hett in Durham, and also the "Great 
Whin Sill". This latter can be followed for 120 km. (75 miles), from the Fame Is- 
lands off the coast of Northumberland to the escarpment of the Eden Valley in West- 
morland, and has a maximum thickness of 50 m. (150 ft.). A still further extension 
is possible, though not proved, for quartz-bearing basic intrusions of doubtful age are 
known at several places even as far as St. David's Head in South Wales (Elsden, 1908). 

B. Carboniferous Igneous Bocks of England. 

(I) In the Carboniferous Limestone. Evidence of a marine volcanic episode 
in the Carboniferous Limestone is found in three isolated districts: (a) Isle of Man, 
(b) Derbyshire, (c) Somerset (see fig. 37). All the rocks are of basic composition. 
Those of the second district at least show no sign of alkaline affinities, and it is 
probable that we are to recognize here a petrographical province distinct from that 
which occupied the southern half of Scotland. 

(a) Isle of Man. The volcanic rocks occur on the coast near Castletown, 
at the southern end of the island. They consist of basaltic tuffs and agglomerates 
and porphyritic olivine-basalts, resembling certain Scottish types. They have 
been greatly disturbed by subsequent crust-movements. The confused relations 
of the tuffs and agglomerates to the limestone can be explained only by overthrusting. 
The same explanation is applicable to certain dyke-like ribs of basalt in the midst 
of the agglomerate, sometimes in a highly inclined posture: these appear to be, 
not dykes, but broken portions of lava-flows. 

(b) Derbyshire. The igneous rocks of Derbyshire attain no great develop- 
ment. The volcanic group consists of basalts and spilites, with basaltic tuffs 
and ashy limestones, and there are also volcanic necks composed of agglomerate. 
The rocks occur about three centres. — Miller's Dale, Matlock, and Tissington. 
In this last place volcanic action continued from the Carboniferous Limestone into 
the Yoredale Series. Closely related to the volcanic centres are a number of intrusive 
sills of olivine-dolerite. 

(c) Somerset. Spilites and spilitic tuffs are found in the Carboni- 
ferous Limestone at several places in the neighbourhood of Weston-super-Mare 
in northern Somersetshire, and give evidence of contemporaneous volcanic action 
of a sporadic kind. The spilites are lava-flows, but it is possible that certain coarser 
doleritic rocks may be intrusive sills. This district is probably to be connected 
with that next to be mentioned. 



Harker: Great Britain. — Igneous Rocks. — England. (III. 1.) 173 




Fig. 37. Sketch-map showing the distribution of Carboniferous and Permian 

igneous rocks in England. 

M = Isle of Man; Db = Derbyshire; S = Somerset; the three volcanic districts of Carboniferous Lime- 
stone age. W = Whin Sill (quartz-dolerite) ; C and D = Cornwall and Devonshire granites; E = Per- 
mian volcanic rocks of the Exeter district; Z = intrusions in the Coal-Measures of the Midlands, perhaps 

to be referred to a Tertiary age. 

(II) In the Culm Measures of Cornwall and Devon. Although the stratigraphy 
is in some places not free from doubt, it seems to be established that in certain 
parts of the south-western counties volcanic action was prolonged from the Upper 
Devonian into the Lower Culm. The lavas resemble the Devonian spilitic types, and 
tuffs are also represented. 

(III) Intrusions in the Coal Measures of the Midland Counties. No contempo- 
raneous volcanic rocks are found in the Carboniferous between Derbyshire and 
Somerset; but there are numerous basic sills and laccolites, which are intruded 
mostly in the Coal-Measures, and have sometimes been assigned to a late Carboni- 
ferous age. Most of them are olivine-dolerites. These occur especially in the South 
Staffordshire coal-field, but also in the neighbouring counties, Shropshire and 
Leicestershire (fig. 37). Some of these rocks have a decided suggestion of alkaline 
affinities in the occurrence of some orthoclase or interstitial analcime and a purplish 
pleochroic augite. There is no direct evidence of their Palaeozoic age, and it is 
possible that they are Tertiary. In Warwickshire is found a group of hornblendic 
sills of variable characters, some being diorites and others of a camptonitic variety. 



174 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

Other rocks of doubtful age may be mentioned in this connection: viz. a dyke 
of analcime-dolerite near Hereford, one of monchiquite near Chepstow in Monmonth- 
shire, and one of nepheline-basanite at Butterton in Staffordshire. The first two 
occur in Old Red Sandstone, but the last intersects the Trias, which points with 
much probability to a Tertiary age. 



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176 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous 

Geological Survey of England and Wales. 
Coal-field Memoirs: 

1859. South Staffordshire (J. B. Jukes). 

1859. Warwickshire (H. H. Howell). 

1860. Leicestershire (E. Hull). 

1875. Burnley (E. Hull & others). 

1876. Somerset & Bristol (H. B. Woodward & others). 
1878. Yorkshire (A. H. Green & others). 

1899-1912. South Wales (A. Strahan & others). Parts I-X. 

1903. Cheadle (G.Barrow). 

1905. North Staffordshire (W. Gibson & others). 

1907. Leicestershire & South Derbyshire (C. Fox-Strangways). 

1908. Coals of South Wales (A. Strahan & W. Pollard). 

Geological Survey of Scotland. 
The Geology of the Neighbourhood of Edinburgh (Second Edition), (B. N. Peach & others), 

pp. 47-323, 337-361, 369-405, 1910. 
The Geology of East Lothian (Second Edition), (C. T. Clough & others), pp. 37-161, 

196-198, 207-217, 1910. 
The Geology of the Glasgow district (C. T. Clough & others), pp. 9-165, 203-233, 1911. 
See also Geikie, Sir Archibald, Jones, O. T., and Lamplugh, G. W. 



b. Ireland. 
By Grenville A. J. Cole. 

The Carboniferous System assumes great importance in Ireland, since Meso- 
zoic strata were either not laid down upon its surface, or have been stripped away 
by denudation to a degree unknown in England. The valuable coal-seams of the 
Upper Carboniferous have, however, suffered severely by this denudation, and the 
Carboniferous Limestone now forms the most characteristic rock exposed. 

South of a line from Queenstown to Glengariff, the lower series are argillaceous, 
and the Armorican folding has converted them into dark slates known as the Car- 
boniferous Slate. These rocks follow conformably on the Old Red Sandstone, 
and include at their base the Coomhola Grits with their marine fossils, which have 
already been referred to under the Devonian System. While it is clear that the 
Carboniferous Slate represents the "Lower Limestone Shales" of other areas, 
it is uncertain how far into the Carboniferous period this muddy type of deposit 
continued. It seems probable that the Carboniferous Slate includes fairly high 
zones of the Limestone series, as Jukes always maintained (1864). In reading 
some of the Irish literature on the correlation of these strata and of the Old Red 
Sandstone, we must bear in mind the views held by Jukes (1866 — 68) towards the 
close of his career as to the contemporaneity of the systems styled Devonian and 
Carboniferous by other geologists. These views, which proved to be entirely unsus- 
tainable, were too faithfully repeated by G. H. Kinahan (1878), who ignored the 
existence of a Devonian system. JutfEs, in the first of the papers here referred to, 
gives an excellent and comprehensive account of the Lower Carboniferous rocks of 
southern Ireland. The Carboniferous Slate is from 900 m. to 1500 m. (3000 to 
5000 ft.) thick in the south of Co. Cork. It contains Productus semireticulatus, Spirifer 
pinguis, Spirifer striatus, Sanguinolites plicatus, Bellerophon striatus, Phillipsia pustu- 
lata, and other species characteristic of Carboniferous Limestone horizons; but zonal 
determinations in it are still much to be desired. The ordinary grey Carboni- 
ferous Limestone, resting on Lower Limestone Shale, as it does in South Wales, 
appears in the synclinals near Cork city. In places the rock has been altered into 
a red or pink marble. 

The succession from this point throughout central Ireland as far north as the 
Curlew Hills and the Newry axis is as follows (Hull 1877): 



Cole: Ireland. 



(III. 1.) 177 



Upper 
Carboniferous 



Lower 

Carboniferous 

(Avonian) 



8 



W 



o Jog 



Ohl 



So 



r — 
"C  

O ii 

W II 



.5 o 



5. Coal-Measures. 

4. Sandstone and shale series, representing the Millstone 

Grit and Pendleside series of England. 
3. Sandstone, shale, and limestone series, of Yoredale or 

Upper Limestone Shale age. 
2. Carboniferous Limestone, which may be 900 m. (3000 ft. ) 

thick. 
1. Lower Limestone Shale. 

The fossils of the Lower Carboniferous series a: 
have been recorded by Kelly (1855 — 7), Griffith 
(1844—60) and M'Coy (1844); M'Coy's brachio- 
poda have been revised by Davidson (1864 — 8), 
and the cephalopoda have been carefully investi- 
gated by A. H. Foord (1897). But the establish- 
ment of palseontological zones has not as yet 
been carried far. The clayey limestone, or "calp" 
type (Jukes 1857), has been generally assumed 
to include middle horizons of the main Carboni- 
ferous Limestone ; and it is true that the limestone 
above it is often far more pure, and weathers out 
in scarps and plateaus in the western areas, in 
contrast to the gentler slopes formed by the under- 
lying series. The calpy beds are probably, how- 
ever, local developments of a type that recurred 
throughout Lower Carboniferous times, wherever 
portions of the Caledonian land rose above sea-level, 
and sent down detritus into the ocean. A detailed 
study has recently been made of the Lower Carboni- 
ferous succession between Rush and Skerries on 
the Dublin coast (C. A. Matley and A.Vaughan 
1906 — 9). There is a general agreement here with 
the succession established by Vaughan for the 
Bristol area in England, even to the occurrence 
of shallow water conditions following on the 
Zaphrentis beds. 



5. Limestones and shales, passing up into 
shales, with Posidonomya becheri. 

4. Argillaceous limestones and shales, with Cya- 
thaxonia rushiana and C. contorta (Vaughan). 

3. Limestones (Dibunophyllum zone). 

2. Sands, shales, and conglomerates. 

1. Slates with Zaphrentis cf. phillipsi (Upper 
Zaphrentis zone). 

Thus, while the lowest orCleistopora zone 
of the Lower Carboniferous series is not seen in 
this area, the succession is a satisfactory one, 
through strata some 600 m. (2000 ft.) thick, up into 
the Upper Carboniferous Pendleside Series, represen- 
ted by No. 5 above (W. Hind and J. A. Howe 1901.) 

The bare plateaus of almost horizontal lime- 
stone in north-western Clare have similarly been 
compared with the English and Belgian sequence 
(Douglas 1909). Brachiopods of the Cleistopora 
zone occur in sandy shales at the base, following 

Handbuch der regionalen Geologie. III. 1. 



« 



OO 



o" 
Z-5 









o£ 



'3 a = 

1 <« U f/3*- 






og 



o 

"8 

— 
< 

t-, 

§5 



5* 
— - 

am 



h 
J2 



178 (III. 1.) 



The British Isles. — III. Stratigraphy. — 6. Carboniferous. 



on the Old Red Sandstone. The Zaphrentis zone 
is followed by a shallow-water Syringothyris 
zone, with abundant large cephalopods. The Lower 
Carboniferous is here complete, closing with the top 
of the Dibunophyllum zone, in which Caninia 
and other zaphrentids are abundant. Beds or 
nodular layers of chert are a common accompani- 
ment of the Carboniferous Limestone, especially 
above the lower zones. The limestone has been 
locally modified into a brownish dolomite in many 
places. The Carboniferous Limestone has been 
much worn away by prolonged denudation, since 
the material passes into solution, and is also of in- 
ferior hardness when compared with many other 
rocks. In the Sligo area, and in the terraced highland 
of the Burren in northern Clare, scarps of Carboni- 
ferous Limestone remain some 450 m. (1500 ft.) above 
the sea. But in the great part of Ireland, and 
even among the steep Armorican folds of the 
south, the limestone has given rise to lowland 
and fairly level country. The great peneplain of 
central Ireland owes its uniform character to the 
presence of the limestone, and a series of very 
shallow synclinals may be traced in it, with Old Red 
Sandstone and Silurian ranges protruding along the 
anticlines. This level country rises in plateaus, but is 
covered in many places with drift, on which broad 
bogs have established themselves. In other places, 
the solvent action of the rivers has formed the 
shallow lakes that are so characteristic a feature 
of the plain. Subterranean water-ways and dis- 
appearing or emerging streams are frequent, 
especially in the west, and their exploration gives 
rise to an increasing literature. 

In the north of Ireland generally, the basal 
Carboniferous beds include much sandstone, which 
is often of a red colour and which forms bleak 
uplands where it is lifted on the slopes of the 
Dalradian country. At Ballycastle, on the north 
coast of Co. Antrim, seams of coal are in- 
cluded in this series, accompanied by one thin 
band of limestone. The beds of the Ballycastle 
Coal-field, some 400 m. (1300 ft.) thick, were de- 
posited in a hollow of the Dalradian schists, and have been broken through 
and faulted by Kainozoic dykes of basalt. The laccolitic dolerite of Fair Head 
separates the field into an eastern and a western division. The highest strata are 
probably of the age of the "Carboniferous Limestone" of the basins of the Forth 
and Clyde, and the series should be compared with the Lower Carboniferous of 
Scotland, rather than with that of any other part of Ireland (Hull and Baily 
1871, Arber 1912). Among the marine fossils are Lingula squamiformis, Rhyn- 
chonella pleurodon, Productus giganteus, Murchisonia angulata, Bellerophon uri, 
and Orthoceras steinhaueri. The Lower Carboniferous Sandstone of the north 




Cole: Ireland. (III.l.) 179 

has been compared with the Yellow Sandstone series of Devonian age in the south 
(Nolan 1880); but its fossils ally it rather with the Avonian Series and, as above 
observed, sandy beds occur in the northern area, both near the base and much 
higher in the Carboniferous series. The Carboniferous Limestone facies is, however, 
well developed in the mountainous country round the source of the Shannon, and 
as an "Upper Limestone" above a series of shales and sandstones near Lough 
Melvin and Lough Erne. Hence the region in which Lower Carboniferous coal seams 
are likely to occur is very limited. A boring has failed to detect coal in the sand- 
stones of Dungiven, only 17 km. (11 miles) south of the latitude of Ballycastle. 

Unless, as previously hinted, some beds of the Carboniferous Slate represent 
high Avonian zones, the Yoredale and Upper Limestone Shale Series of central 
England are preserved in the south of Ireland only in the neighbourhood of the 
coal-fields. In the area of the Leinster Coal-field we have these horizons represented 
by a cherty "Upper Limestone", and Wheelton Hind (1905) urges that in some 
western districts what are called "Upper Limestone Shales" belong to the Upper 
Carboniferous Series. This view is borne out by the work of Douglas in Clare, 
previously quoted. 

In the counties of Leitrim and Fermanagh, there are considerable beds of 
sandstone below the horizon of the Millstone Grit, sometimes 300 m. (1000 ft.) 
thick, and probably representing part of the Carboniferous Limestone series of 
the south. A few thin coal-seams, not good enough to work, occur in these 
shore-deposits (W. B. Wright 1912). 

The Upper Carboniferous strata include the Pendleside series of Wheel- 
ton Hind, which was traced by him in several parts of Ireland (1905 and Hull 
1877, Kinahan 1878). A large part of the areas formerly mapped as Coal Measures 
have been in later years referred to Millstone Grit and Pendleside horizons. Wheel- 
ton Hind regards the Pendleside Series in Co. Clare as 24m. (80 ft.) thick, and as 
deposited in the western end of a basin which deepened across central England. 
These beds have been styled Upper Limestone Shales, but are succeeded above by a 
generally marine Millstone Grit, with Glyphioceras reticulatum. The following fossils 
are among those regarded as characteristic, and as proving here the presence of 
the Pendleside Series above the Carboniferous Limestone : Glyphioceras diadema, 
Dimorphoceras gilbertsoni, Pterinopecten papyraceus, Posidoniella laevis. The 
Millstone Grit Series contains workable coals at Dungannon, round Lough Allen, 
and perhaps in the Leinster Coal-field. The Skehana anthracite seam, 60 cm. (2 ft.) 
thick, appears round the margin of the high Leinster Coal-field, and seems to 
underlie a large part of it. Thinner seams occur in still lower beds. The fauna 
associated with this horizon is marine and egtuarine. The same beds recur in the 
Slieve Ardagh Coal-field in Co. Tipperary. Poor coals have also been found in them 
over a wide area in northern Kerry and in western Limerick and Clare. The lower 
coal-seam worked at Arigna near Lough Allen is probably on a Millstone Grit hori- 
zon. The Dungannon coals of the Tyrone Coal-field, which have still to be 
developed, lie in shales and sandstones with marine fossils. 

The true Coal Measures, representing on the whole terrestrial and freshwater 
conditions in the Irish area, remain, as has been pointed out, only in a few favoured 
localities 1 . The coals in them are anthracitic south of the line connecting Dublin and 
Galway, and of ordinary household typhes north of this line. In the Leinster Coal- 
field the Jarrow coal was in parts 2 m. (6 ft.) thick. Its disposition has been accounted 
for by the suggestion that it was laid down in a curving channel, excavated by 

1 The plants are described in several memoirs of the Geological Survey on the 
coalfields. See also T. Johnson. 

12* 



180 (III. 1.) The British Isles. — III. Stratigraphy. — 6. Carboniferous. 

river-action in lower strata. This coal-field is preserved as a high synclinal basin, 
the margin of which is formed by a series of scarped sandstones. Some 600 m. 
(2000 ft.) of coal-bearing strata are here recorded. 

Attention was called in 1865 by W. B. Brownrigg to a very interesting 
series of amphibian remains from the Coal Measures of the Jarrow colliery in the 
Leinster Coal-field. These were described by T. H. Huxley and E. P. Wright 
(1866), and include the genera Urocordylus, Ophiderpeton, Dolichosoma, Ichthyer- 
peton (shown by Lydekker to include Erpetocephalus) , Keraterpeton, and Lepter- 
peton, all of which were then new to science; also Anthracosaurus, which was already 
known from Scotland. Ichthyerpeton hibernicum was added by Lydekker in 1891. 
Small mines also extract anthracite on the adjacent plateau of Slieve Ardagh, 
where Coal Measures overlie the Millstone Grit horizons. The outlier near Carrick- 
macross is unimportant. The upper coal at Arigna in the Connaught Coal-field lies 
in true Coal Measures, which here remain only as a capping to the highest hills. 
The mining is carried on at about 300 m. (1000 ft.) above the sea. 

At Coalisland, north of Dungannon in the Tyrone Coal-field, Coal Measures occur 
in a small triangular exposure; the Annaghone seam here is nearly 3 m. (9 ft.) thick. 
(Geol. Surv. Mem. and Hardman 1875 — 7). A number of other coals occur, and the 
dip of the strata, combined with their downthrow by faulting to the east, leads 
one to suppose that they may ultimately be traced under the Triassic sandstones 
to the east. The form of the boundary of the Coal-field, however, which was deter- 
mined by denudation soon after the Armorican uplift, does not leave hope for any 
very large extension in this direction. Excellent fire-clay is obtained from the 
Carboniferous shales of this area, and the coal raised is mostly consumed in the 
furnaces connected with this industry. 

While many of the dykes that traverse Carboniferous strata in  northern 
Ireland are evidently connected with the Kainozoic volcanic activity, there are 
evidences in two or three places of contemporaneous volcanic action. The chief 
of these lies east of Limerick city, where lavas, ashes, and intrusive sheets occur 
in the Carboniferous Limestone (Mc Henry and Watts 1895 and Mem. Geol. 
Survey). Activity probably continued into Upper Carboniferous times. The lower 
series of lavas was poured out about the middle of the Carboniferous Limestone 
epoch. The igneous rocks include pinkish trachytic types (orthophyres), andesites, 
and olivine-basalts, passing into limburgites. They form a number of low hills, 
on several of which picturesque feudal castles stand. 

North of Philipstown in King's County there is a second but smaller volcanic 
area of Carboniferous Limestone age, where basalts and limburgites are associated 
with volcanic tuffs. Andalusite-schist has been brought up in these tuffs from some 
unseen mass below (Haigh, 1914). 

The invasion of the Irish area by the Carboniferous sea was remarkably 
complete. We can realise, by the sandy nature of its first deposits in the north 
and west, that land lay not far off in the Atlantic area. The presence of coal-seams 
at Ballycastle, and the virtual absence of the limestone, indicate in this one place 
the actual shore-line. But Carboniferous outliers occur on the crest of Slieve League 
in the far west of Donegal, and on the great flat-topped hills near Killary 
Harbour. Even if the Connemara mass was not completely submerged, the 
rocks that have been dredged up so abundantly from the Atlantic off the western 
Irish coast show that we cannot mark out a limit to the Carboniferous overflow 
in that direction. A considerable region of Caledonian land must have remained 
for a long time in about latitude 51° N., to furnish the muddy material now known 
as the Carboniferous Slate. The Leinster Chain and the Newry axis stood out for a 
while as bold promontories; but the higher strata of the Carboniferous Limestone 



Cole: Ireland. (III. 1.) 181 

series now conceal the earlier shore-deposits at most points, by overlap as the sub- 
sidence went on. In the Dublin district, however, copious admixtures of mud, and 
even coarse conglomerates formed of older Palaeozoic rocks, occur at various levels in 
the limestone, and we may conclude that the topography was much what it would 
be at the present day, were a subsidence of 150 m. (500 ft.) to let in the sea over 
lowlands. The addition of mud to the sea does not seem to have appreciably limited 
the marine fauna, and even such delicate forms as crinoids continued to flourish. 
The so called "calp" beds are, indeed, limestones rather than shales. The Leinster 
Chain had already been so far worn down as to expose its core of granite, fragments 
from which are found in the Carboniferous Limestone south of Dublin. Detrital 
mica occurs freely here in many places, and masses of the metamorphic Ordovician . 
schist also remain just as they were washed down. A "calpy" or argillaceous type 
of limestone occurs very frequently through Ireland, and the handsome pure grey 
limestone must be mainly looked for in what has been styled the Upper Limestone 
series. 

Gradually, as the sea spread, very few islands remained above its sur- 
face. Then came the first intimation of the Armorican movements, in the upward 
swing of the whole area, giving rise to an epoch in which shales and sandstones 
were the predominant deposits, while the once abundant brachiopods and molluscs 
moved elsewhere, and perhaps far eastward, into purer waters. The forests began to 
manifest themselves about the horizon of the Millstone Grit, and the type of coal- 
field known in Scotland and northern England, with good seams in the Lower 
Carboniferous series, is found in Ireland only in the north at Ballycastle. But in 
true Coal Measure times land was so far prevalent that we may regard the whole 
Irish area as clothed with forests of Carboniferous trees. 

By the close of the Carboniferous period, denudation had already acted on the 
uplifted land. A depression appears to have arisen in the north of the area., where- 
by the region of accumulation in later periods remained in the north, and especial- 
ly in the north-east, while that of exposure and denudation lay in the south and 
west. The continental character given to the region by the Upper Carboniferous 
uplift, and soon after by the Armorican movements, seems to have been remarkably 
preserved through succeeding periods ; and consequently the Mesozoic and Kainozoic 
deposits have none of the rich variety of those of France and England. 

The Armorican folding probably produced a far less mountainous country 
than that of Lower Devonian times. The old crumpled Caledonian hill-barriers 
were still effective down below, with their schistose boundaries and granite cores, and 
checked the free rise of the Armorican folds. In an endeavour to wrinkle them- 
selves over the older topographic features, the Armorican folds became greatly 
influenced by the Caledonian trend. A general highland, however, was produced, 
the surface of which was almost everywhere composed of Carboniferous strata. 
It must have been a long time before denudation began to reveal the domes of Old 
Red Sandstone with Silurian cores that are now such conspicuous features in the 
limestone plain. As Jukes long ago pointed out, these did not appear through the 
Carboniferous covering until the present river-systems had begun to establish 
themselves on a plain of denudation, which was tilted somewhat to the south. 
We know that the main streams of these systems are pre-Glacial. Is it possible 
that any of them have descended to us from the conformation of the country in 
Permian times ? The answer to this question depends on what view we take of the 
westward development of the Cretaceous ocean. If much of Ireland can be shown 
to have sunk below the Senonian sea-level, the river-systems at once become limited 
in antiquity to Kainozoic times. 



182 (III. 1.) The British Isfles. — III. Stratigraphy. — 6. Carboniferous. 

Economic Products. 

Coal. Ordinary Coal for household purposes occurs in the high Upper Car- 
boniferous outliers round Lough Allen; at Ballycastle, in Lower Carboniferous 
shales and sandstones; and in Upper Carboniferous beds at Dungannon and Coalis- 
land west of Lough Neagh. In the last-named locality, it is possible that a good 
deal of coal, including the continuation of a seam nearly 3 m. (9 ft.) thick, remains 
to be discovered beneath the Pliocene clays and Triassic sandstones between 
Coalisland and the lake. The Dungannon coals still remain unexplored. 

In southern Ireland, the coal is anthracitic. The great outlier of Upper Carbo- 
niferous beds forming the Leinster coal-field contained several good seams which 
have been almost worked out. An almost untouched seam 0,6 m. (2 ft.) thick 
underlies, however, part of the field, and promises well for the future. Coal is also 
worked to the south-west on the plateau of Slieve Ardagh. 

The large area of Upper Carboniferous strata in the counties of Limerick and 
Clare yields only a few occasional small seams of anthracite. 

Iron-Ore. Concretionary iron-carbonate is common in the Upper Carboni- 
ferous shales, as round Lough Allen; but it is not easily worked, owing to the amount 
of material that must be removed during its extraction. There are numerous iron 
ore zones at Lough Allen, below that in which the coal occurs. 

Fireclay is worked at Coalisland in Co. Tyrone from Upper Carboniferous 
strata, and a variety rich in silica occurs near Ballycastle in Co. Antrim. 

Barytes is mined near Clonakilty in Carboniferous strata, and at other places 
in the south-west of Co. Cork; also near Glencar in Co. Sligo. 

Limestone and Marble. The common grey Carboniferous limestone is very 
largely used for building, as well as for conversion into lime. Owing to its cheapness, 
it is too generally employed as a road-metal. Excellent stone of uniform grain, 
for buildings in which carved work is required, comes from the country near Ballinasloe 
in the central plain. 

A crushed and iron-stained variety from Little Island, Cork, makes a hand- 
some red marble when polished. Grey marble, with pink and red calcite veins, is 
quarried at Midleton, Co. Cork. Black varieties, coloured by carbon, are quarried 
at Kilkenny city and at Menlo near Galway. 

Sandstone. The Lower Carboniferous beds of Mount Charles, west of Donegal 
town, and of other places in the northern counties, provide good yellowish sandstone 
for building. The very hard well bedded sandstones of the Upper Carboniferous 
series in the west of Clare, and similar stones from the Kilkenny Coal-field, have 
been used as paving-stones. The casts of animal tracks on their surfaces are an 
advantage in preventing their becoming slippery. They also make good slabs for 
steps and landings. 

Slate is worked in the Carboniferous Slate series near Clonakilty, Co. Cork. 



Bibliography of the Carboniferous of Ireland. 

1912. Arber, E. A. N., Sci. Proc. Roy. Dublin Soc, N. S., vol.13, pp. 162-176 (Bally- 
castle Flora). 

1867. Brownrigg, W. B., Journ. Roy. Geol. Soc. Ireland, vol. 1, pp. 145-147 (Fossil 
Amphibians). 

1857-1862. Davidson, T., Mon. Pal. Soc, British Fossil Brachiopoda, vol. 2, and Supple- 
ment, 1874-1882. 

1909. Douglas, J. A., Quart. Journ. Geol. Soc. London, vol.65, pp. 538-586 (Carboni- 
ferous Limestone of Co. Clare). 



7. Permian. — Kendall: Great Britain. — I. Sedimentary Rocks. (III. 1.) 183 

1897-1903. Foord, A. H., Mon. Pal. Soc, Carboniferous Cephalopoda of Ireland. 
1857. Griffith, R., Journ. Geol. Soc. Dublin, vol. 7, pp. 267-277 (Notes explaining 

Divisions of his Map). 
1862. — Journ. Geol. Soc. Dublin, vol.9, pp. 21-155 (List of Fossils and Localities). 
1844. — and M'Coy, F., Synopsis of the Characters of the Carboniferous Limestone 

Fossils of Ireland. 
1914. Haigh, W. D., Proc. Roy. Irish Acad., vol. 32, sect. B, pp. 17—33 (Phillipstown 

volcano). 
1875-1877. Hardman, C, Proc. Roy. Irish Acad., ser. 2, vol.2, pp. 529-538 (Coal and 

Ironstone analyses). 

1905. Hind, W., Proc. Roy. Irish Acad., vol. 25, Section B, pp. 93-116 (West Ireland). 
1901. — and Hohve, J. A., Quart. Journ. Geol. Soc. London, vol. 57, p. 375 (Pendleside 

Series). 

1877. Hull, E., Quart. Journ. Geol. Soc. London, vol. 33, pp. 616-626 (Classification). 
1871. — and Baily, W. H., Journ. Roy. Geol. Soc. Ireland, vol. 2, pp. 260-275 (Bally- 
castle Coalfield). 

1871. Huxley, T. H., and Wright, E. P., Trans. Roy. Irish Acad., vol. 24, pp. 351-369 
(Fossil Amphibians). 

1911. Johnson, T., Sci. Proc. Roy. Dub. Soc, N. S., vol.13, pp. 1-11 (Plants). 

1912. — Sci. Proc. Roy. Dublin Soc, N. S., vol. 13, pp. 177-183 (Plants). 
1857. Jukes, J. B., Journ. Geol. Soc. Dublin, vol.7, pp. 277-281 (On "Calp"). 

1866. — Quart. Journ. Geol. Soc. London, vol. 22, pp. 320-371 (Carboniferous &0. R. S. 

of South Ireland &c). 

1867. — Journ. Roy. Geol. Soc. Ireland, vol. 1, pp. 138-143 (Carboniferous and O. R. S. 

of South Ireland &c). 
1871. — Journ. Roy. Geol. Soc. Ireland, vol. 2, pp. 67-107 (Carboniferous and O. R. S. 

of South Ireland &c). 
1857. Kelly, J., Journ. Geol. Soc. Dublin, vol. 7, pp. 1-61 (Fossil localities). 

1878. Kinahan, G. H., Manual of Geology of Ireland, pp. 50, 95-129. 

1891. Lydekker, R., Quart. Journ. Geol. Soc. London, vol. 47, pp. 343-347 (Labyrinth- 
odonts). 

1906. Matley, C. A. and Vaughan, A., Quart. Journ. Geol. Soc. London, vol. 62, pp. 275 

to 323 (Rush, County Dublin). 

1908. — — Quart. Journ. Geol. Soc. London, vol. 64, pp. 413-474 (Loughshinny, 

County Dublin). 

1895. McHenry, A. and Watts, W. W., Geol. Surv. General Memoir. Guide to the Collec- 
tions of Rocks and Fossils belonging to the Geological Survey of Ireland, 
pp. 63-65. 

1880. Nolan, J., Quart. Journ. Geol. Soc. London, vol.36, pp. 529-535 (Old Red Sand- 
stone of North Ireland). 

1909. Vaughan, A., Rep. Brit. Assoc, 1908, pp. 267-269 (Avonian Succession). 
1897. Woodward, A. S., Geol. Mag., pp. 293-298 (Fossil Amphibia). 

1913. Wright, W. B., Proc. Geol. Assoc, vol. 24, pp. 70-77 (South Donegal). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets: 

35. Parts of Counties Antrim, Armagh & Tyrone (E. T. Hardman & W. H. Baily), 

1877. 
143&144 (in part). Limerick (G. W. Lamplugh & others). 1907, p. 20, 102. 
187, 195 & 196. Part of County Cork (J. B. Jukes & W. H. Baily). 1864, p. 32. 
186, 187, 194 & 195 (in parts). Cork (G. W. Lamplugh & others). 1905, p. 18-33. 
See also McHenry, A. above. 



7. Permian. 
a. Great Britain, including the Isle of Man. 

I. Sedimentary Rocks. 

By Percy F. Kendall. 
The Permian rocks of Britain present two strongly contrasted lithological 
facies that may be broadly described as the Eastern, or Magnesian Limestone, and the 
Western, or Red Rock facies. 



184 (III. 1.) The British Isles. — III. Stratigraphy. — 7. Permian. 

The first of these characterized by the great predominance of limestone, gene- 
rally magnesian, and by pale yellow sands when arenaceous members are present 
extends in a continuous outcrop from Cullercoats on the east coast 2 km. (I 1 /* miles) 
north of the Tyne to the neighbourhood of Nottingham. 

The western type consists of bright red sandstones, marls and breccias or 
conglomerates, with a local development round the Irish Sea of thin magnesian 
limestone. This type extends from Arran and the south-western peninsula of Scot- 
land to Ireland the Vale of Eden, Cheshire and the Midlands. 

No rocks of Permian age appear in South Wales or the Mendip area, nor have 
any been met with in borings in the east or south-east of England, but the western 
facies is in doubt represented by certain of the Red Rocks of Somerset, Devon and 
Cornwall, which, though yielding no unequivocally significant fossils, are yet con- 
nected with the Permian by their association with volcanic rocks as well as by their 
stratigraphical relations with the Carboniferous and Triassic rocks. 

The interval between the Carboniferous and Permian periods in Britain was 
marked, as elsewhere, by vast earth movements producing in the south the great 
foldings of the Armorican Chain and further north folds, though of less amplitude 
still of large dimensions, (Hull 1868). These, so far as affects the present discussion, 
may be briefly outlined. The great boundary faults of the Scottish "rift valley", 
usually referred to as the Midland Valley, had made a large further movement, 
whereby the Central Highlands and the Southern Uplands were raised above it. In 
England an anticline of great magnitude and nearly E. to W. in direction, the Howgill 
anticline of Marr (1910), extended from the neighbourhood of Richmond (Yorkshire) 
to near St. Bees Head (Cumberland) and perhaps to the Isle of Man and County 
Down Ireland, while, in the opposite direction, the post- Jurassic folds of Cleveland 
indicate its continuance to the North Sea. The Pennine fold was initiated at 
this period, as well as a great S.W. — N.E. set of undulations that crosses the Pennine 
system about its centre. At the southern end the Pennine fold gives place to a 
diverging series of disturbances, for the most part posthumous movements of 
much earlier systems, such as the Charnian folding. 

Faulting accompanied the folding, and, while some of these faults cannot 
be proved to have had any prior existence, some were renewals of the activity of 
earlier dislocations and in a few cases the disturbances continued to operate down 
to much later geological periods — even, as earthquake records show, to the present 
time. 

Denudation went on concurrently with these crust movements, and anti- 
clines and fault-features of great magnitude were worn down prior to the deposition 
of the Permian rocks upon their sites. 

Near Clitheroe in the Ribble Valley red rocks, presumably of Permian age, 
rest upon the Visean, and Hull (1868) has argued from the great thickness of the 
Yoredale (Pendleside) rocks, the Millstone Grit, and Coal Measures of the adjacent 
area, that no less than 6000 m. (20000 ft.) of Carboniferous rocks were removed 
prior to the deposition of the Permian rocks at this place. This is probably an 
overestimate but denudation even more drastic has affected other areas; thus the 
Permian rocks of the western side of the Lake District rest upon pre-Carboniferous 
rocks, as do those of Belfast Lough, of Dumfries, and of some parts of the Midlands, 
while the Upper Permian rocks of the Vale of Eden and the Ingleton area contain 
fragments of pre-Carboniferous rocks that must have been exposed to denudation 
by movements of the adjacent faults. The Permian rocks in different parts of 
Britain can be found to rest upon every rock of older date back to the Archaean. 

Local details and succession. It will be convenient to consider first the eastern 
type of Permian, both because the continuity of the outcrops and the general 



Kendall: Great Britain. — I. Sedimentary Rocks. 



(III. 1.) 185 



uniformity of characters permit a simple and comprehensive treatment, and also 
because the similarity to the development in Germany brings the eastern Per- 
mians into clear relation, to the continental sequence. 

Throughout their range the Eastern Permians rest with marked unconfor- 
mity upon different members of the Carboniferous series. The most constant member 
of the series, the Magnesian Limestone, is selected for first consideration. This 
division, despite local variations, especially of its upper division, ranges completely 
through from Cullercoats (55° 2' N.), to Nottingham (52° 57' N.) a distance of 
233 km. (145 miles). 

This rock was admirably described by Sedgwick (1836) and further descrip- 
tions and correlations have been given by Howse (1857), Kirkby (1861), Binney 
(1855, 1857), Woolacott (1909), Garwood (1910) and others. 

The chemical constitution of the rock varies from nearly pure carbonate of 
lime as at Knottingley (Yorkshire) Roker and Fulwell near Sunderland (54° 55' 
N.) to a true dolomite at Hartlepool (54° 39' N.). The subjoined table by Kirkby 
(1861), somewhat abbreviated, gives a general correlation and description of the strata. 



Subdivisions 


Durham 


South Yorkshire 


1. Bunter Schiefer 


(Howse) 

Red Sandstone overlying the 

Magnesian Limestone in the 

S.E. portion of the County 

Thickness 15m. (50 ft.] 


(Geol. Survey) 
Red Sandstone and Marl near 
Doncaster and Tickhill. 

Thickness ? 15 m. (50 ft.) 


2. Upper Limestone 


Yellow, concretionary, and 
Crystalline Limestone of Mar- 
sden, Roker etc. 

Thickness 75 m. (250 ft.) 


Brotherton Limestone and 
Lower Red Marl and Gypsum 
of Brotherton, Knottingley 
etc. Thickness 37 m. (120 ft.) 


3. Middle Limestone 


Shell- and cellular Limestone 
(Fossiliferous and Pseudo- 
brecciated Limestone of King) 
of Tunstall and Humbleton 
Hills. Claxheugh etc.. 

Thickness 45 m. (150 ft.) 


Small-grained dolomite of 
Vale of Went, Roche Abbey, 
Warmsworth etc. 

Thickness 60 m. (200 ft.) 


4. Lower Limestone 


Compact Limestone of Ferry 
Hill, Whitley etc. 

Thickness 60 m. (200 ft.) 


Lower Limestone of Ponte- 
fract, Hampole, Micklefield 
etc. Thickness 37 m. (120 ft.) 


5. Kupfer-Schiefer 


Marl Slate of Claxheugh, 
Ferry Hill etc. 

Thickness 3 m. (10 ft.) 


6. Rotliegendes 


Lower Red and Yellow Sand- 
stone of Tynemonth, Clax- 
heugh etc. 

Thickness 30 m. (100 ft.) 


Lower Red, Yellowjand Varie- 
gated Sandstone of Ponte- 
fract, Hickleton etc. Thick- 
ness 0— 30 m. (0— 100 ft.) 



Lebour (1886) gives for Durham the following scheme: 

Red Marly Sandstones and Marls, with lenticular beds of anhy- ] 
drite, gypsum and salt, and fetid limestone in variable bands 
towards the base 

Thick Magnesian Limestone 

Marl Slate, with Fish Bed 

Yellow Sands 



Upper iPermian 
(Rauchwacke) 

Middle Permian 



Lower Permian 



186 (Iir. 1.) The British Isles. — III. Stratigraphy. — 7. Permian. 

The limestone varies in texture from a fine close-grained rock, to deposits 
with the cavities lined with crystals of dolomite. Concretionary structures of great 
diversity occur — especially in the non-magnesian rock at Roker and Fulwell in 
Durham. Brecciated structures are described in detail by Lebour (1884) and 
Woolacott (1909). These are found in some places in the form of bedded masses 
when they are in great part at least the products of fault thrusts and in others of 
vertical sheets and wedge-shaped masses filling fissures in the rocks described by 
Lebour under the name of "breccia-gashes" and ascribed to the falling in of 
solution hollows. 

Garwood considers that "both the lime and magnesia in the Durham beds 
appear to have existed in the original deposit". Green (1882) attributes the con- 
cretionary structures, as well as the cavernous condition of much of the Magnesian 
Limestone, and the contortions of the bedding, to the readjustments that would 
take place when calcium was replaced by magnesium. Much of the cavernous 
structure observed, especially in the Lower Limestone of Yorkshire, has been shown 
by Ernest Guy (1911) to be due to the solution of irregular inclusions of gypsum, 
anhydrite and barytes that are found in the limestone in deep borings. "Suture- 
lines" are very common in the porous limestones. They are alway accompanied 
by a thin film of marl and are regarded by the present writer (1907) as the effects 
of irregular solution, the marl being the insoluble residue. 

While the Magnesian Limestone maintains a general constancy of litholo- 
gical character through its range from north to south there are significant local 
modifications. About the mouth of the Tees there are extensive intercalations 
of anhydrite and gypsum, and in the neighbourhood of Mansfield (53° 2' — 53° 
8' N.) a sandy facies of the Upper and Middle beds is developed (Sherlock 1911) 
that has been mistakenly attributed to the Bunter and hence has led to the assump- 
tion of an unconformity between the Permian and Trias there. Sherlock's inference 
that the Upper Limestone and Marl of the northern part of the outcrop are the 
time-equivalent of the Bunter of South Nottinghamshire does not follow as a neces- 
sary corollary and is not likely to be admitted. 

The Yellow Sands that form the base of the Permian in Durham are fine 
pale yellow or sometimes red sands and are believed by Lebour (1884, 1905) and 
others to be of aeolian origin and to exhibit dune-bedding. 

Throughout Yorkshire sandy basal beds are often absent but to the' west 
of Leeds they are well developed as well as near Doncaster. 

From Conisborough (53° 25' N.) to Nottingham the Lowest-Permian rock, 
resting directly on the Carboniferous is commonly a breccia ("Poxon-stone"). 

In Durham the Marl Slate is very generally present, even when the Yellow 
Sands are missing. It yields in some places well-preserved fishes and some plant 
remains. In Yorkshire, in the same position, are found occasional small patches 
of chocolate-coloured marl, sometimes containing gypsum etc., as at Knaresboro' (54° 
1' N.). This marl appears to have no connexion with the Marl Slate. Borings in 
Southern Yorkshire show the occasional presence of dark marly limestone regarded 
by Gibson (1907) as Marl Slate. It has not yielded any trace of the fish fauna of the 
Marl Slate. Near Nottingham shales and flaggy sandstones with plant-remains 
and mollusca have been referred to the Marl Slate. 

Above the Middle Magnesian Limestone of the table there occurs with great 
constancy through the greater part of Yorkshire a series of red and blue marls with 
gypsum and anhydrite and at Barlow (53° 42' N.) a bed of rock salt. No definite 
parting appears in the sequence in Durham, but about the mouth of the Tees many 
intercalations of marl with gypsum and anhydrite occur in the upper part of th e 
Magnesian Limestone. 



Kendall: Great Britain. — I. Sedimentary Rocks. (III. 1.) 187 

The Magnesian Limestone is almost everywhere surmounted by a series of 
Marls with gypsum, and sometimes anhydrite, besides, in a few localities, rock- 
salt. The classification of these Marls has led to great divergence of opinion — in 
Yorkshire, where, atthe outcrop, they contain few if any intercalations of sandstone, 
they have been classed by the Geological Survey with the Permian but the great 
series of Marls and Sandstones with gypsum, anhydrite and rocksalt round the 
estuary of the Tees have from the impossibility of drawing any line of separation 
been referred by the Surveyors to the Upper Trias, and herein they have been 
supported by Wilson (1876). The testimony of recent borings in South Yorkshire, 
and in Lincolnshire supports the opinion of Lebour (1886) that the Tees beds are 
of Permian age and in any case not Up per Trias. The gradual passage in the White- 
house boring from Magnesian Limestone with intercalations of red and blue marl, 
anhydrite and gypsum, upward through red marl with anhydrite and gypsum to 
red marl with red sandstone renders any attempt to divide the series purely 
arbitrary and in a boring at Scunthorpe the difficulty was increased by the fact 
that red sandstones with very rare pebbles passed down into sandy marls, sand- 
stones and gypseous marls with recurrences of sandstones having the exact litho- 
logical features of those above the marl series, and thence into red gypseous marls 
with a thick bed of anhydrite, that is constant over several hundreds of square 
miles, and traces of rock salt. 

There is on the eastern side of the Pennine Chain in the judgment of the 
writer, a perfect passage from the Permian into the Trias, and the Bunter division 
of the Trias does not, as commonly supposed, come to an end near Tadcaster (53° 
50' N.) but continues to the Tees. 

The Permian series appears to thicken continuously in an easterly direction. 
In Yorkshire the increase is about 4.7 m. per kilometre (25 ft. per mile). 

The Eastern Permians have yielded a large fauna including Fenestella reti- 
formis, Lingula credneri, Productus horridus, Camarophoria schlotheimi, Spirifer 
alatus, Bakewellia antiqua, Schizodus obscurus, Nautilus, Palaeoniscus; and plants 
such as Sphenopteris naumanni, Alethopteris goepperti and Ulmannia selaginoides. 

The Western Type. Borings in the northern end of the Isle of Man penetrated 
St. Bees Sandstone — here regarded as Trias — "passing down into red marls 
with intercalations of sandstone (Permian), brown coarse-grained sandstone with 
partings of marls, and fine "brockram" (conglomerate) at the base (Permian)". 
These rest upon highly inclined Lower Carboniferous rocks. (Lamplugh 1903). 
The evidence here of passage from the Trias down into the Permian is interesting. 
Across the Southern Uplands of Scotland there are several belts of red sandstone, 
sometimes with associated conglomerates, that have with much probability been 
assigned to the Permian series. They lie unconformably on Palaeozoic rocks, cither 
Carboniferous or older, and in several cases, as for example in Loch Ryan, and 
Nithsdale, occupy deep valleys eroded in the complex of the Southern Uplands. 
The only fossils found are reptilian or amphibian foot prints, and these are considered 
by Hickling (1909) to be of Permian types. In the Nith valley these rocks are 
associated with basic lavas similar to those found in other areas of supposed Permian 
rocks. In the Island of Arran, similar rocks have been observed, but the red rocks 
of Arran are probably referable to several geological periods, the Upper Old Red 
Sandstone of the Western side of the island being closely similar in character to the 
supposed Permian. Geikie (1897) regards the volcanic vents that pierce the 
Coal Measures of Fifeshire as of Permian age (pp. 192—193), and Watson (1909) 
attributes the Red Sandstones of Elgin with the reptiles Gordonia and Elginia 
to the Permian, as these reptiles have close affinities with those found in the Upper 
Permian of other areas. Hickling (1909) corroborates this reading on the ground of 



188 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Permian. 

the resemblance of fossil footprints in these rocks to those found at Mansfield and 
elsewhere in undoubted Permian rocks. 

In Cumberland and Westmorland the Permian series attains its maximum 
development in Britain. The succession in the Vale of Eden is of particular interest 
from the evidence that it furnishes of the physical conditions of the period and their 
changes. This valley is bounded on the east by the Pennine escarpment which 
owes its existence to a tremendous series of faults truncating the Permian and later 
rocks. The succession from west to east is: Carboniferous Limestone and Mill- 
stone Grit, covered unconformably by massive calcareous conglomerates, "Lower 
Brockram", usually dolomitized; bright-red Penrith Sandstone about 300 m. 
(1000ft.) ; "Upper Brockram" interbedded in the upper part of the Penrith sandstone; 
Hilton Plant Beds with Noeggerathia 45 m. (150 ft.); Magnesian Limestone — 6 m. 
(0 — 20 ft.) ; Marls with gypsum, having locally, a basal conglomerate, 90 m. (300 ft.) ; 
St. Bees Sandstone (Trias) 600 m. (2000 ft.). (Goodchild 1893). The succession 
here, save for the Brockrams and Penrith Sandstone, is fairly comparable with 
the succession in Durham, but the great thickness of bright-red sandstone has no 
parallel in the Yellow Sands. 

The Penrith Sandstone is strongly current-bedded and its sand-grains are 
coarse, extremely well rounded and often most accurately "graded" into minor 
beds of equal sized grains. These are characteristics of wind-sorting and support 
the view that the rock is an seolian accumulation. The large size of the sand-grains, 
and the inclusion of a large proportion of felspar grains suggested to the writer (1910) 
that the materials had been derived from the Millstone Grit of the Pennine Chain. 
Marr observes that the current bedding inclines from east to west. 

The materials of the Lower and Upper Brockrams respectively furnish evidence 
of contemporaneous movements of the adjacent fault zone. The Lower Brockram 
consists exclusively of fragments of Carboniferous Limestone and the writer infers 
that it represents gravel-fans washed by torrential rains from the uplifted fault 
country, when the displacement had exposed only that division of the Carboniferous 
series. The Upper Brockrams were laid down after the deposition of 300 m. (1000 ft.) 
of Penrith Sandstone, which should have covered up an equivalent portion 
of the faulted area, yet these Brockrams consist in large measure of the Basement 
Conglomerate of the Carboniferous series, with occasional pebbles of the under- 
lying Ordovician rocks. This is interpreted to mean that between the formation 
of the two Brockrams a great further movement of the faults took place bringing 
the base of the Carboniferous up within the action of surface erosion. 

In this region the "Marls with Gypsum" extend unconformably across the 
beds below and in places rest upon the Penrith Sandstone. Whether this is to be 
regarded as evidence of a limiting unconformity or merely as a local consequence 
of further movement of the faults cannot be decided without a wider survey. 

The western side of the Lake District furnishes one admirable section of the 
Permians at Barrowmouth (54° 30' N.) figured by Murchison and Harkness 
(1864) who show Magnesian Limestone with a basal breccia resting upon an eroded 
surface of Carboniferous sandstone. The limestone contains a few fossils and is 
succeeded by red and green marls with gypsum, covered by St. Bees Sandstone (Trias). 

To the south of this point the St. Bees Sandstone overlaps on to Ordovician 
rocks and when the Permian rocks reappear, the lithological type is repeated near 
Furness Abbey (54° 8' N.) and again at Skillaw Clough (53° 43' N.), beyond 
which the limestone phase is no doubt represented by the fossiliferous marls with 
septaria that occur in parts of Lancashire and Cheshire. 

On the little Ingleton Coal-field, at the foot of the Craven fault-block (54° 
7' N.) a succession is found, having the same general significance as the series 



Kendall: Great Britain. — I. Sedimentary Rocks. (III. 1.) 189 

in the Vale of Eden. A Lower Brockram rests on Coal Measures, and the pebbles 
include many fragments of Carboniferous Limestone and a few of a Spirorbis lime- 
stone, no doubt from the Upper Coal Measures, a type that is not known to occur 
nearer than Manchester. In another section an Upper Brockram is seen which 
contains pebbles of Millstone Grit., Carboniferous Limestone, and pre-Carboniferous 
slate. This has been interpreted, in accordance with the Brockrams of the Vale 
of Eden, as indicating that while the Lower Conglomerate was being deposited only 
the Carboniferous rocks were exposed along the fault-scarp, and that a further 
movement of the faults brought up the platform of older rocks before the Upper 
Brockram was deposited. 

At Clitheroe, in the Ribble valley (53° 49* N.), red rocks attributed to the 
Permian rest upon the Carboniferous Limestone on the crown of a denuded anticline. 
As this outcrop is overlooked by heights capped by Millstone Grit it seems probable 
that, as Sir A. Geikie suggested in the case of the Nith valley, the deposits had been 
laid down in a kind of fiord. The Coalfield of Lancashire is fringed on the north 
and east by Permian rocks of a distinctive type, described by Binney (1845). 
A thin Basal Breccia is overlaid by the Collyhurst Sandstone, a bright- 
red sandstone, identical in appearance with the Penrith Sandstone except for the 
paucity of felspar. This is succeeded by chocolate-coloured marls, the Collyhurst 
Marls, with calcareous bands and concretions and many fossils such as Schizodus 
and Bakewellia. Often an Upper Breccia intervenes between the Sandstone and the 
Marls and on the South Side of Manchester a few feet of Marl come below this 
breccia. 

At Stockport (53° 22' N.), a few miles further south, two thick beds of 
marl with an intervening sandstone are seen below the Upper Breccia in some sec- 
tions, while in others the Upper Breccia rests in bold unconformity upon the Colly- 
hurst Sandstone. The movement, of which this is the record, appears to synchronise 
with those of the faults in the Vale of Eden and at Ingleton. 

In the neighbourhood of the Mersey estuary marls have been encountered 
in boreholes, and in some cases a red sandstone exactly like the Collyhurst 
Sandstone has served as the type of the "Lower Mottled Sandstone" formerly attri- 
buted to the Trias; it now, however, appears certain that it is of Permian age. 

On the Welsh border, e. g. near Wrexham (53° 3' N.) and Oswestry (52° 52' N.), 
red sandstones and marls, perhaps in part of Permian age, crop out (Gibson 1901). 
The Permian rocks of the Midlands, including the country from the Welsh border 
to Charnwood and from Staffordshire to the Malvern Range, present a most 
perplexing problem on account of the rarity of fossils and the presence of red rocks 
of various geological ages. The difficulty of classification is increased by the fact 
that similar conditions seem to have persisted, or to have recurred at intervals, 
from the time of the Upper Coal Measures to that of the Trias, and that throughout 
that time the Archaean and Older Palaeozoic rocks were exposed to denudation, so 
that the constituents of conglomerates do not always form a safe criterion of age. 
To add to the difficulty, the older rocks have been very largely stained with iron 
by percolating water and hence many Carboniferous rocks have been ascribed 
to the Permian. Fossils are extremely rare, and no invertebrates have yet been 
discovered; moreover no volcanic rocks occur in the Permian rocks here as they 
do in Scotland and Devon. 

The western portion of the area has been described by Wickham King (1899), 
the Malvern area by Groom (1910) and Leicestershire by H. T. Brown (1889) 
and the Geological Survey in a recent memoir (Fox-Strangways 1907). Wickham 
King accepts a classification into Lower, Middle, and Upper Permian. 



190 (III. 1.) The British Isles. — III. Stratigraphy. — 7. Permian. 

The Lower Permian consists of red sandstones interstratified with red marls 
260 m. (850 ft.) 1 . These are succeeded, probably unconformably, by Middle Permian 
conglomerates, calcareous sandstones and marls, and those in turn by the Upper 
Permian marls and breccias (the "Trappoid Breccias" of some authors). The Trias 
(Bunter) lies unconformably upon the Permian. 

The conglomerates and breccias exhibit a general tendency to thin out, and 
pass into sandstones from south-east to north-west. The pebbles in the Middle 
Permian include rocks from the Archaean, Cambrian, Gothlandian, Old Red Sand- 
stone, Carboniferous and Lower Permian. The Upper Permian "Trappoid Breccia" 
is composed mainly of Archaean rocks and a general review of the Permian rocks 
of this area favours the suggestion that they are the degradation products of a 
series of anticlines from which first the Palaeozoic rocks were stripped and later 
the Archaean cores were exposed. The transport of the materials was mainly from 
south-east to north-west. The total absence of Ordovician rocks is significant, 
especially in view of the fact that the Gres de May, with Ordovician fossils, consti- 
tutes a conspicuous element in the overlying Bunter. 

Ramsey supposed that these Permian breccias and conglomerates were 
of Glacial origin but this view is no longer entertained by local workers, and the 
striations often found upon the stones are ascribed to friction during earth-move- 
ments. It may be remarked that one single striated stone has been recorded from 
the Lower Brockram of the Vale' of Eden but diligent search has failed to yield a 
second. 

In Leicestershire, on the south west side of the Archaean massif of Charnwood, 
rocks referred to the Permian have been mapped. At Swadlincote bright red sand- 
stone covered by mar] rests unconformably upon Coal Measures and is succeeded 
by an unconformable cover of Trias. The Charnwood axis is an example of post- 
humous folding; its latest movements appear to be of Cretaceous date. 

At Exhall (52° 28' N.) a sandstone attributed to the Permian has yielded 
fragments of Lepidodendron, Calamites and casts of a shell "considered to be of Per- 
mian type and more allied to Strophalosia than to any other genus" (Howell 1859). 
The latter is of importance as the only example of an invertebrate fossil from the 
Permian of the Midlands, but great doubt must attach to the record from the im- 
probability of Permian beds yielding such an association of plants. The Calamites 
was identified by Forbes as C. mougeotii but Salter considered it to be C.suckovi. 
Both are Carboniferous species. 

The great Armorican folds of the Mendip area separate the Permian area of 
the Midlands from that of Somerset and Devon, but it must, not be assumed that 
the two regions were discontinuous in Permian times. Probably a connexion 
existed to the East of the Mendips, as was almost certainly the case in the Bunter 
period. 

The interval between the southernmost Permian exposure in Worcestershire (at 
Haffield) and the most northerly in Somersetshire is 113 km. (70 miles). The Permian 
outcrops in Somerset and Devon extend from north to south parallel to that of the 
Trias and send offshots along some of the synclinal folds of the Armorican system. 
The whole series of the "New Red Sandstone" has undergone recent revision by 
the Geological Survey with the result that the Permian is held to include only 
two divisions — the Lower Sandstone and Breccia, and the Lower Marls. 



x ) Lapworth and Watts (1910) refer this division to the Keele Series of the Upper 
Coal Measures and Cantrill (1895) would unite King's three divisions as "Coal Measure 
Passage Beds". 



Kendall: Great Britain. — I. Sedimentary Rocks. (III. 1.) 191 

The former consist of red sandstones with breccias and conglomerates, some- 
times becoming mere incoherent sands and gravels. The pebbles are of quartz, 
grit chert, and limestone, with occasional fragments of slate. 

The Lower Marls are dark-red green-spotted marls with intercalations of sand- 
stone, the whole reaching a thickness of perhaps 150 m. (500 ft.) or more. Igneous 
rocks are associated with the Permian in the neighbourhood of Exeter (see p. 190). 
The relations with the Trias cannot often be discerned, the junctions being fre- 
quently faulted, but in some places, e. g. in the Quantock Hills, conformable junction 
has been observed, it should however be borne in mind that the lowest division of 
the overlying Trias is the famous Budleigh Salterton Pebble Beds in which the 
sudden influx of fossiliferous pebbles of the Gres de May, and Gres Armoricain 
attest a great physiographical change. 

In any attempt to reconstruct the physiography of Britain during the Permian 
period much will depend upon the correctness of the correlation of the strata. The 
eastern type of Permian forms a continuous outcrop and it is therefore compara- 
tively safe to carry the stratigraphical lines through the whole outcrop. On the 
west however the great variation in lithology and general paucity of fossils makes 
the synchronism much more problematical. One important guiding line is, however, 
available: the Magnesian Limestone of Cultra in Ireland contains the brachiopod 
Productus horridus which according to all authorities is quite characteristic of the 
Lower Magnesian Limestone of Yorkshire. This, then, is a datum — and the present 
writer ventures to refer to the same line the Magnesian Limestone of Barrowmouth 
and of the Vale of Eden and, with much doubt, the Collyhurst Marls of the Manchester 
district. The temptation is great to carry the parallel further and correlate the 
Penrith Sandstone with the Yellow Sands, and the Plant bed with the Marl Slate 
(vide Goodchild). The Marls above the Magnesian Limestone in the Vale of Eden 
would then represent the Saliferous Marls of the Tees. The writer prefers to limit 
himself to the single correspondence of the Lower Magnesian Limestone. 

The earliest phase of the Permian physiographical development was represented 
by an arid country traversed by the denuded folds of Carboniferous rocks 
of the Armorican system and with protrusions of older rocks in the western area, 
the Scottish Highlands and Southern Uplands, Ireland, Wales, the Midlands and 
Devon. Into the deep valleys that intersected the country, gravel fans were swept 
by occasional torrential rains. These formed the brockrams and non-calcareous 
conglomerates and breccias. Meanwhile the wind bore hither and thither the finer 
rock debris disintegrated chiefly by sun and chill; thus the detritus of the Millstone 
Grit, a true arkose, with its felspar still undecomposed was worn down to the smooth, 
polished grains of large size, that characterise the red Permian sandstones of the 
western area. The fault scarps of the northern Pennine, and of Ingleton overlooked 
the sandy tracts and contemporary movements brought up the fault-blocks more 
swiftly than accumulation could bury their bases. Whether the sands were actual 
dry land deposits or were blown into lacustrine areas cannot with certainty be 
determined, but the marly layers in which the vertebrates left their footprints must 
have been deposited in water. The Plant-beds of the Vale of Eden, and the Marl 
Slate, must have been water-deposited. The frequent current or cross bedding 
may be sand-dune bedding or may have been effected by water. It is note- 
worthy that the Permian Rocks contain no mica and no doubt this soft mineral 
would be reduced to indistinguishable flour by wind action. The Magnesian 
Limestone and the Collyhurst Marls bear unequivocal witness to the influx of salt- 
water, the general impoverished character of the fauna telling of unfavourable 
conditions, probably of super-salinity. The western area must have had some 
waterway joining it to the eastern sea and though it is not clear where it was 



192 (HI. 1.) The British Isles. — III. Stratigraphy. — 7. Permian. 

situated it may be supposed to have been a narrow strait incapable of equalising 
the loss by evaporation, so that the conditions were progressively less favourable 
from north to south in the western region. 

The concentration in the east increased till it reached at the time of the Middle 
Marls of Yorkshire, the stage of precipitation of calcium sulphate. When the 
temperature was low, gypsum was deposited, but at times it rose to or above 30° C 
(86° F) and anhydrite was thrown down. The culmination of this phase was reached 
with the formation of a bed of rock-salt at Barlow. The waters sweetened again after 
this so that a fresh influx of marine life came in and the Upper Magnesian Lime- 
stone was formed, but it is noticeable that the fauna shows signs of further im- 
poverishment in the absence of those elements of the Permian fauna least tolerant 
of abnormal salinity such as Productus and other brachiopods, and cephalopods. 
This recurrence of phase continued through the deposition of the Upper Marls with 
gypsum, anhydrite and rocksalt. 

The area about the mouth of the Tees was through the greater part of the 
Permian period experiencing exceptional conditions, attested by the enormous depo- 
sits of anhydrite interbedded with the Magnesian Limestone, and by the great 
bed of rock salt. This completed the phase and the Triassic period brought new 
conditions that will be discussed by another pen. 

The economic products of the British Permian are of interest and of great 
value. The Penrith Sandstone is a building stone of much beauty but generally 
too soft to command a market in competition with the Triassic sandstones that 
accompany it. The old castle of Penrith at Penrith is built of the Permian stone 
which shows beautifully the recfystallization of the quartz grains at the expense 
of silica from the decomposition of grains of felspar. 

The Magnesian Limestone yields a fine durable stone that has been employed 
for many famous buildings both ancient and modern. 

The Permian gypsum is used to a small extent for Plaster of Paris, and the 
salt at Tees mouth is also worked. 

By far the most valuable mineral product of Permian age is the Cumberland 
haematite. This occurs as enormous ore-bodies filling partially or completely huge 
cavities in the Carboniferous limestone, where that rock has been traversed by water 
percolating through from the Permian strata or by the ferriferous waters from which 
these were deposited. 

Many minerals occur in the Magnesium Limestone, for example, barytes, 
strontianite, zincblende and ores of copper, but they are not present in work- 
able quantities. 

The Magnesian Limestone is distinguished, where not covered with Boulder- 
clay, by a bright-red clayey-soil, the insoluble residue derived from the solution 
of the limestone. This suggested to William Smith the name "Bedlands Lime- 
stone" which he gave to this rock in his famous "Table of the Strata". 

II. Igneous rocks. 

By Alfred Harker. 

A. Permian (or Late Carboniferous) Igneous Rocks of South-Western Scotland. 

It has been remarked above that igneous action was prolonged in general to 
a later stage of the Carboniferous in the west than in the east of Scotland ; and further 
that there occur in the west numerous intrusions of alkaline igneous rocks, compa- 
rable with types found in the east but of later age. These late Palaeozoic igneous 
intrusions are found mostly in Ayrshire. In the middle of that county, in the district 



Harker: Great Britain. — II. Igneous Rocks. (III. 1.) 193 

of Mauchline, there occurs also a volcanic group of strongly alkaline character and 
of late age. It is associated with red sandstones, which Sir A. Geikie has assigned 
to the Permian, while others have regarded them as the uppermost part of the 
Coal Measures. Since the alkaline intrusions of Ayrshire break through all strata 
up to and including the Mauchline lavas, they may be referred to the same cycle 
of igneous activity as that volcanic group. 

The volcanic group of Mauchline (fig. 36) presents a ring-shaped outcrop mea- 
suring about 12 by 8 km. (7'/2 by 5 miles), and has a thickness of 90 m. (280 ft.), 
including numerous thin lava-flows associated with tuffs. Volcanic action at this 
epoch was doubtless more extensive than is indicated in this small area. Sir 
A. Geikie (1897) supposes that the rocks continued into Dumfriesshire, where again 
lavas are found in association with strata believed to be Permian. Moreover, he 
assigns to this age numerous volcanic necks, which pierce the Carboniferous strata, 
not only in the south-western districts but also in Eastern Fife (Geikie 
1902). Near Mauchline (Tyrrell 1912) the lavas present some variety of inte- 
resting types: olivine-basalts, analcime-basalts (including some with 
nepheline), nepheline-basalts, monchiquites, and limburgites. 

The intrusions, which have a somewhat wider distribution, have the form of 
sills and small bosses. They are found about Old Cumnock, Lugar, Patna, Dal- 
mellington, Ardrossan, Troon, etc. The rocks are teschenites, picrites, thera- 
lites, essexites, and allied types, with one occurrence of analcime-syenite, 
at Howford Bridge near Mauchline, and some monchiquites. 

In this place may be mentioned certain basic dykes, with more or less marked 
alkaline affinities, which are found in large numbers in some parts of the south- 
west of Scotland. They are most abundant in Argyllshire and in the islands of 
Jura, Islay, and Colonsay. They cut the quartz-dolerite dykes where they encounter 
them, but are sometimes cut by Tertiary dykes of basalt and andesite. Owing 
chiefly to their general N.W. — S.E. direction, these Argyllshire dykes have often 
been supposed to be of Tertiary age, but they differ from the known Tertiary dykes 
in petrographical characters, and resemble rather the late Palaeozoic intrusions. 
The majority of them are olivine-dolerites, often with purplish pleochroic 
augite, and analcime-dolerites (crinanites), but more specialized types are 
found in the outlying districts. Monchiquite dykes occur in Colonsay, and both 
monchiquites and camptonites in the S.W. of Mull and in the Ardmucknish 
peninsula, north of Loch Etive. 

Another district of dykes having pronounced alkaline characters, and of 
doubtful age, is the Orkney Isles (Flett 1900, 1914), in the far north of Scotland. 
These dykes intersect the Old Red Sandstone, and have a general E.N.E. — W.S.W. 
direction. They are camptonites, with some monchiquites and alnoites and 
one bostonite. 

B. Granites of Cornwall and Devonshire and their associated Dykes. 

The granites of Cornwall and Devon (see fig. 37, p. 173) are the largest intrusive 
masses of igneous rocks in England. The principal distinct bodies, enumerated from 
east to west, are those of Dartmoor (Devonshire), Bodmin Moor or Brown Willy, St. 
Austell or Hensbarrow, Cam Menelez (near Camborne), Land's End, and the Scilly 
Isles. Smaller masses occur elsewhere in Cornwall, and there is one making Lundy 
Island, lying N.W. of Devonshire. These granites break through and metamor- 
phose the Devonian and Culm strata. They are related to the Armorican system 
of crust-movements, and may be assigned to a late Carboniferous or Permian age. 
Some of the granite masses seem to underlie the bordering strata in a manner sug- 

Handbuch der regionalen Geologie. III. 1. 13 



194 (III. 1.) The British Isles. — III. Stratigraphy. — 1. Permian. 

gestive of a dome-shaped upper surface, but the junction is sometimes rather steeply 
inclined. 

The rock is in general a muscovite-biotite-granite with large porphyritic 
crystals of orthoclase, and very much of it contains tourmaline. Pinite pseudo- 
morphs after cordierite, andalusite, and other special minerals are found locally. 
The tourmaline is in great part connected with pneumatolytic action, and as a last 
stage the granite may be converted to a tourmaline-quartz-rock. A different kind 
of pneumatolysis has in some districts converted the granite along joint-planes 
into greisen, and to this kind of action belong the tinstone- veins. Still another 
pneumatolytic change is that which has resulted in the formation of kaolin. 

The slates bordering the granite have been metamorphosed to hornfels and 
mica-schist, often with andalusite or cordierite, and the impure calcareous bands 
have become lime-silicate-rocks ("calc-flintas"). A pneumatolytic action, involving 
boric acid, has often given rise to tourmaline in the metamorphosed slates, and in 
some places to axinite in the more calcareous beds. 

The important metalliferous, ores of Cornwall are connected with the granite, 
and occur near the borders of the several intrusions (see various Mem. Geol. Survey). 
The tin and copper lodes run mostly E.N.E. — W.S.W. Silver and lead ores were 
deposited subsequently in the same lodes, but more especially in the "cross- 
courses", which intersect and displace the principal set of lodes. 

Two groups of dykes occur in this region, and must be supposed related to the 
granite: (a) quartz-porphyries and (b) mica-lamprophyres. 

(a) The quartz-porphyries, locally termed "elvans", are probably slightly 
posterior to the granite, which some of them intersect. The dykes are very numerous 
in the south-western part of Cornwall, near the granite masses of Land's End and 
Carn Menelez, and have there a general E.N.E. — W.S.W. direction. Near the gra- 
nites of St. Austell and Bodmin Moor the direction is more nearly E.— W. Other 
dykes of this group occur near the Dartmoor granite in Devonshire. The rocks 
are often partly sericitized, and some contain tourmaline or pinite pseudomorphs 
after cordierite. 

(b) The mica-lamprophyre dykes are probably of slightly later age, and 
are much less numerous, but a number of them are known about Falmouth and 
Truro, and they occur again near Newquay in North Cornwall. They tend generally 
to have a N. — S. direction. 

C. Permian Volcanic Rocks of Devonshire. 

In the Permian of England intercalated igneous rocks are found only in the 
south-west, and there only in feeble development. They occur in the Exeter district 
(fig. 5), to the N. and N.W. of the city, and represent, at least in part, contemporaneous 
lava-flows. The rocks, which are mostly much decomposed, show some variety. 
They are apparently the effusive equivalents of lamprophyric magmas, and some 
of them are very rich in potash. They have been described (Teall 1902, Ussher 
1902) as basic trachytes or orthophyres ; viz. biotite-trachyte (approximating 
to minette), augite-trachyte, olivine-trachyte, and transitional forms 
between these and basalts. 

At Cawsand, on the west side of Plymouth Sound, a rhyolite is found asso- 
ciated with Permian breccia, probably as an intrusion (Flett 1907, Ussher 1907). 
It may be related to the lavas of the Exeter district. 



Bibliography of the Permian of Great Britain. (III. 1.) 195 

Bibliography of the Permian of Great Britain. 

1845. Binney, E. W., Quart. Journ. Geol. Soc, vol. 2, pp. 12-26 (Lancashire and Cheshire). 
1855. — Mem. Manchester Lit. and Phil. Soc, ser. 2, vol. 12, pp. 209-269 (North-West 
of England). 

1889. Brown, H. T., Quart. Journ. Geol. Soc, vol. 45, pp. 1-40 (Leicestershire). 

1895. Cantrill, T. C, Quart. Journ. Geol. Soc, vol.51, pp. 528-548 (Wyre Forest, 

Staffordshire). 
1900. Flett, J. S., Trans. Roy. Soc Edinburgh, vol. 39, pp. 865-905 (Intrusive Rocks of 

the Orkneys). 
1907. — Mem. Geol. Surv., Expl. Sheet 348 N. S., The Geology of the country around 

Plymouth and Liskeard, pp. 114-115 (Cawsand 'Porphyry'). 
1914. — Mem. Geol. Surv., Caithness, pp. 107 — 117 (the Intrusive rocks). 

1907. Fox-Strangways, C, Mem. Geol. Surv. The Geology of the Leicestershire and 

South Derbyshire Coalfield, pp. 56-62. 

1910. Garwood, E. J., Geol. Assoc. Jubilee Vol., Geology in the Field, pp. 685-687 (North- 
umberland and Durham). 

1897. Geikie, Sir Archibald, Ancient Volcanoes of Great Britain, vol. 2, pp. 53-106. 

1902. — Mem. Geol. Surv. Scotland. The Geology of Eastern Fife, pp. 197-198, 200-238 

(Volcanic necks). 

1863. Geinitz, H. B., Trans. Manchester Geol. Soc, vol. 4, pp. 120-145 (England; trans- 

lated from "Dyas oder die Zechsteinformation und das Rothliegende", Heft 2). 

1890. — Trans. Manchester Geol. Soc, vol.20, pp. 535-554 (Upper Permian of Man- 

chester; translation of "Uber die roten und bunten Mergel der oberen Dyas 
bei Manchester"). 

1908. Gibson, W., Geol. Surv., Summary of Progress, 1907, p. 16 (Nottinghamshire). 

1913. — Mem. Geol. Surv. The Concealed Coalfield of Yorkshire &' Nottinghamshire. 
1893. Goodchild, J. G., Trans. Cumberland and Westmorland Assoc, no. 17, pp. 1-24 

(St. Bees Sandstone etc.). 
1882. Green, A. H., Physical Geology, 3 rd Ed., pp. 299-301 (Magnesian Limestone). 

1914. Gregory, J. W., Trans. Geol. Soc. Glasgow, vol. 15, pp. 174—187 (Arran). 

1910. Groom, T. T., Geol. Assoc. Jubilee Vol., Geology in the Field, pp. 725, 734-735 

(Haffield Breccia near Malvern). 

1911. Guy, E., Trans. Leeds Geol. Assoc, part. 16, pp. 10-15 (Cavities in Magnesian 

Limestone). 

1912. Hardaker, W. H., Quart. Journ. Geol. Soc, vol.68, pp. 639— 683 (Plants and 

footprints). 
1862. Harkness, R., Quart. Journ. Geol. Soc, vol. 18, pp. 205-218 (Cumberland and 
Dumfries). 

1864. — Quart. Journ. Geol. Soc, vol. 20, pp. 429-443 (North-East of Scotland). 

1909. Hickling, G., Mem. and Proc Manchester Lit. and Phil. Soc, vol. 53, Mem. 22, 

pp. 1-23 (Footprints). 
1859. Howell, H. H., Mem.Geol.Surv. The Geology of the Warwickshire Coalfield, pp. 30-34. 
1857. Howse, R., Ann. Mag. Nat. Hist., ser. 2, vol. 19, pp. 33-58, 304-312, 463-473 (Durham 

and Northumberland). 

1868. Hull, E., Quart. Journ. Geol. Soc, vol. 24, pp. 319-335 (Post-Carboniferous Folding). 

1869. — Mem. Geol. Surv. The Triassic and Permian Rocks of the Midland Counties 

of England, pp. 1-29. 
1882. Irving, A., Geol. Mag., pp. 158-164, 219-223, 272-278, 316-322 (Subdivisions of the 

Permian). 
1907. Kendall, P. F., Victoria History of the Counties of England. Yorkshire, vol. 1, 

pp. 25-32. 
1911. — Proc Geol. Assoc, vol. 22, pp. 44-49 (Rocks near Settle and Harrogate). 
1850. King, William, Palaeojit. Soc, Monograph on the Permian Fossils of England. 
1899. King, W. Wickham, Quart. Journ. Geol. Soc, vol.55, pp. 97-128 (Conglomerates 

of the Lower Severn Basin). 
1861. Kirkby, J.W., Quart. Journ. Geol. Soc, vol.17, pp. 287-325 (South Yorkshire). 

1903. Lamplugh, G. W., Mem. Geol. Surv. Geology of the Isle of Man, pp. 263-295. 

1910. Lapworth, C. and Watts, W. W., Geol. Assoc. Jubilee Vol., Geology in the Field, 

pp. 762-763 (Shropshire). 
1884. Lebour, G. A., Trans. North of England Inst. M. and M. E., vol.33, pp. 165-177 

(Breccia-gashes in Magnesian Limestone). 
1886. — Outlines of the Geology of Northumberland and Durham, 2 nd Ed., pp. 28-38. 

1904. — Trans. Inst. M. E., vol. 24, pp. 370-391 (Marl Slate and Yellow Sands of North- 

umberland and Durham). 

13* 



196 (III. 1.) The British Isles. — III. Stratigraphy. — 7. Permian. 

1905. Lebour, Victoria History of the Counties of England. Durham, vol.1, pp. 16-21. 

1906. Marr, J. E., Quart. Journ. Geol. Soc., vol. 62, pp. Ixxxiii-lxxxv (Lake District). 

1907. — Proc. Geol. Assoc, vol. 20, pp. 136-138 (Westmorland). 

1910. — Geol. Assoc. Jubilee Vol., Geology in the Field, pp. 650-655 (Lake District). 
1864. Murchison, Sir R. I. and Harkness, R., Quart. Journ. Geol. Soc, vol. 20, pp. 144 

to 165 (North-West of England and South of Scotland). 

1829. Sedgwick, A., Trans. Geol. Soc, ser. 2, vol. 3, pp. 37-124 (Nottingham to North- 
umberland). 

1836. — Trans. Geol. Soc, ser. 2, vol. 4, pp. 383-407 (Eden Valley). 

1908. Sherlock, R. L., Mem. Geol. Surv., Expl. Sheet 125 n. s., The Geology of the 

Southern part of the Derbyshire and Nottinghamshire Coalfield, pp. 103-112. 

1911.  — Quart. Journ. Geol. Soc, vol. 67, pp. 75-117 (Nottinghamshire). 

1904. Strahan, A., Geol. Mag., pp. 449-462 (Earth movements between Carboniferous 

and Permian). 

1905. — Rep. Brit. Assoc, 1904, pp. 532-541 (Earth Movements between Carboniferous 

and Permian). 
1892. Tate, T., Quart. Journ. Geol. Soc, vol. 48, pp. 488-495 (Borings in Tees District). 
1902. Teall, J. J. H., Mem. Geol. Surv., Expl. Sheet 325, n. s. The Geology of the Country 

around Exeter, pp. 76-85 (Igneous rocks near Exeter). 

1912. Tyrrell, G. W., Geol. Mag., pp. 69—80, 120-131 (Mauchline lavas &c). 

1902. Ussher, W. A. E., Mem. Geol. Surv., Expl. Sheet 325, n. s. The Geology of the 
Country around Exeter, pp. 17-47 and 55-76 (Sedimentary and igneous rocks 
near Exeter). 

1907. — Mem. Geol. Surv., Expl. Sheet 348, n. s. The Geology of the Country around 
Plymouth and Liskeard, pp. 111-113. 

1909. Watson, D. M. S., Geol. Mag., pp. 102-107 ("Trias" of Moray). 

1876. Wilson, E., Quart. Journ. Geol. Soc, vol. 32, pp. 533-537 (North-East of England). 
1909. Woolacott, D., Mem. Univ. Durham Phil. Soc, No. 7, pp. 16 (Thrusting of Permian 
of Durham). 

1913. — Proc. Geol. Assoc, vol. 24, pp. 92-100, 104-105 (Durham and Northumberland). 

Geological Survey of England and Wales. 
Memoirs to accompany sheets (new series): 

30 (old series 102 S. W.). Appleby, Ullswater and Haweswater (J. R. Dakyns 

& others). 1897. 
40 (old series 97 N. W.). Mallerstang ( J. R. Dakyns). 1891. 
42&52 (old series 96 N. W. & 96 S. W.). Northallerton and Thirsk (C. Fox- 

Strangways & others). 1886. 
58 (old series 91 N. W.). Furness (W. T. Aveline). 1873. 
62 (old series 93 N. W.). Harrogate (C. Fox-Strangways). 1873. 2nd Ed. 1908. 
70 (old series 93 N. W.). Leeds and Tadcaster (W. T. Aveline). 1870. 
113. Ollerton (G. W. Lamplugh & others). 1911. 

125. Derbyshire and Nottinghamshire Coalfield (W. Gibson & others). 1908. 

126. Newark and Nottingham (G. W. Lamplugh & others). 1908. 
141. Derby, Burton-on-Trent, etc. (C. Fox-Strangways). 1905. 

155. Atherstone and Charnwood Forest (C. Fox-Strangways, with notes by W. 

W. Watts). 1900. 
295. Quantock Hills (W. A. E. Ussher). 1908. 
311. Wellington and Chard (W. A. E. Ussher & others). 1906. 
326. Sidmouth and Lyme Regis (H. B. Woodward & others). 1906. 2nd Ed. 1911. 
339. Newton Abbot (W. A. E. Ussher & others). 1913. 
See also Flett, J.; Fox-Strangways, C; Geikie, Sir Archibald; Gibson, W. ; Howell, 
H. H.; Hull, E.; Lamplugh, G. W.; Sherlock, R. L.; Teall J. J. H.; 
Ussher, W. A. E. 



b. Ireland. 
By G. A. J. Cole. 
The first invasion of the eastern sea into the land that was depressed in the 
Irish area at the close of Carboniferous times is traceable in three small tracts of 
Permian strata in a limited district of the north. Magnesian limestone, like that 
of north east England, occurs on the shore near Holywood in Co. Down. It con- 
tains, among other fossils, Productus korridus, Bakewellia antiqua, and Schizodus 



Cole: Ireland. — Economic Products. (III. 1.) 197 

Schlotheimi (W. King 1852 and Mem. Geol. Surv. 1871). Certain shales, with inter- 
calated unfossiliferous magnesian limestone bands, rest on Silurian rocks near Moira, 
in the Lagan valley. These are also probably Permian. Fossiliferous yellowish 
dolomitic limestones, now much concealed by vegetation, occur in three or four 
places between Carboniferous and Triassic strata near Tullyconnell, not far from 
Stewartstown, west of Lough Neagh (King 1851). E. Hull (1873) has described 
boulder beds, formed of blocks of Carboniferous limestone in a reddish sandy ground, 
near and underlying the city of Armagh. He compares these with the Permian 
"brockram" .beds of north-west England, and suggests for them a glacial origin. 
They are overlain by red Triassic sandstone 

The proposed correlation of the lower beds of marl and sandstone in the Lagan 
valley south-west of Belfast with the St. Bees Sandstone of Cumberland, which is 
sometimes regarded as Permian, makes it possible that part of these beds is of Per- 
mian age (Mem. Geol. Survey 1904) ; and in any case it is probable that the Triassic 
strata of northern Ireland still conceal several relics of the Permian terrestrial 
and marine sedimentary series. 

The Armagh "breccia" shows how the Carboniferous Limestone was exposed 
to denudation in the land area to the south. 

Economic Products. 

There is no direct evidence of the age of the metalliferous lodes of Ireland, 
which are very possibly of Devonian age; but, as those of Cornwall have been 
discussed with the Permian igneous rocks with which they are believed to be 
connected, it will be convenient to consider here the Irish ores of the same 
general character. 

Copper. In the middle of the nineteenth century, the mining of copper was 
an important Irish industry. Large quantities of copper pyrites were raised annually 
from lodes in the Vale of Ovoca in Co. Wicklow, and in the south of Co. Waterford. 
One Mine in Co. Wicklow yielded 7500 tons of copper ore in 1842; and the joint 
Waterford mines raised 9000 tons in 1843. Other mines were worked in the west 
of Co. Cork beyond Castletown Berehaven. Attempts are being made to reopen 
some of these lodes, which were formerly so highly profitable. A mine has also been 
recently worked at Beauparc on the River Boyne. 

Lead and Zinc. Small mines of galena have been opened from time to time 
in many parts of the country, and zinc-blende commonly occurs with the lead- 
ore. At Silvermines, in Co. Tipperary, at the junction of the Old Red Sandstone 
and the Carboniferous Limestone, a considerable lode of zinc carbonate occurs, 
with argentiferous galena and iron pyrites. Mining has now ceased in this locality. 
Galena, associated with cerussite, is occasionally worked at the junction of the 
mica-schist and granite above Laragh in central Wicklow. 

Gold. The abundance of prehistoric gold ornaments in Ireland points to the 
working of local alluvial gold. Though the quartz veins and other rocks that have 
been examined are not by any means rich in gold (Lyburn, 1901), a good deal of 
gold has been procured by the washing of river-gravels between the hill of Croaghan 
Kinshelagh and Shillelagh in Co. Wicklow. These deposits were worked by the 
Government from 1796 to 1803, but without much profit. Traces of gold have 
been reported from the Dalradian areas of eastern Londonderry and Donegal. 



198 (III. 1.) The British Isles. — III. Stratigraphy. — 8. Trias. 

Bibliography of the Permian of Ireland. 

1873. Hull, E., Quart. Journ. Geol. Soc. London, vol. 29, pp. 402-407 (Armagh breccias). 

1853. King, W., Rep. Brit. Assoc, 1852, p. 53 (Fossils from Cultra). 

1857. — Journ. Geol. Soc. Dublin, vol. 7, pp. 67-81 (Magnesian limestone, County 

Tyrone). 
1901. Lyburn, E. St. J., Sci. Proc. Roy. Dublin Soc, new series, vol. 9, pp. 422-427 (Gold 

and Silver in Wicklow). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets: 

21, 28 & part, of 29. Part of County Antrim (E. Hull & W. H. Baily). 1876. 

37, 38. Part of County Down (E. Hull & others). 1871. 

Memoir on country round Belfast (G. W. Lamplugh & others). 1904. 



8. Trias. 



a. England and Wales. 

By Linsdall Richardson. 

In England the Triassic rocks belong to the Bunter and Keuper divisions: 
no representative of the German Muschelkalk has as yet been identified. 

The outcrop of the Trias in England is comparatively narrow in the South- 
western District, but expands in the Midland Counties and bifurcates at the 
southern end of the Pennine Range — one extension projecting into Yorkshire, 
and the other (considerably dissected) into Lancashire, Westmorland and Cumber- 
land. 

The landscape where the Bunter Sandstones and Pebble-Beds prevail is usually 
diversified; but where the Keuper Beds occur it is relatively tame, being 
generally lowland. This lowland, however, is rich agricultural ground and usually 
pleasingly undulating — particularly if the "Arden Sandstone", is present. 

Bunter. — The Bunter Beds have a more restricted geographical extent than the 
overlying Keuper Beds. Their subterranean limits are fairly well known owing to 
numerous deep borings. Generally speaking, the lower the subdivision, the more 
limited its extent. This is because the earliest deposits were accumulated in the 
deepest hollows and the later deposits generally successively overlapped the pre- 
ceding. 

In England there were two distinct areas in which Bunter rocks accumulated. 
The one was situated in portions of the counties of Dorset, Devon and Somerset, 
and the other in the Midlands and on both sides of the Pennine Hills. 

South-Western Area. — In this area the Permian marls are succeeded 
at once by a pebble-bed, about 24m. (80ft.) thick, called the "Budleigh-Salterton 
Pebble-Bed". Between Budleigh and Burlescombe the pebbles are mostly of 
quartzite; but between the latter place and Williton, near Watchet, mainly of 
Carboniferous Limestone. 

The pebbles of the Pebble-Bed at Budleigh Salterton have been examined by 
Salter and Vicary, Davidson, Bonney and O. A. Shrubsole (1903), and while 
some may be matched in Devon and Cornwall rocks, the majority of the now well- 
rounded fragments must have been derived from Ordovician rocks similar to 
those of "Normandy and Brittanv or the south of Cornwall" (Jukes-Browne, 
1911). 

The precise manner in which the pebbles were .transported and distributed is 
a little obscure, but the most generally held view is that they were brought by a 
river flowing northwards from the Calvados district of Normandy. H. H. Thomas 



Richardson: England and Wales. — Bunter. (III. 1.) 199 

found, after an examination of the sandy matrix of the Pebble-Bed, that its 
constituents supported such a conclusion (1902). 

The Carboniferous-Limestone pebbles of the other section of the Pebble-Bed, 
that situated between Burlescombe and Williton, must have come from the opposite 
direction. E. C. Martin (1908) suggests that two rivers conjoined near Burles- 
combe — the one coming from a northerly direction and the other from a southerly 
direction. Further investigation, however, appears desirable. 

Above the Budleigh Pebble-Bed are sandstones, pebbly in the lower portion, 
but less so in the upper. 

Midland and North of England Area. In the Midland District, 
Cheshire, South Lancashire and South Yorkshire, the lowest subdivision of the 
Bunter is known as the "Lower Mottled Sandstone". This sandstone is usually 
of a reddish-brown colour, but is sometimes bright red, yellow, striped or variegated. 
In thickness it varies greatly, attaining its maximum at Bridgnorth, where it 
measures some 190 m. (650 ft.). It is absent — except at Polesworth — from 
around the Warwickshire Coal-field; under Market Bosworth, in Leicestershire, a 
deep boring proved it to be represented by merely a thin pebble-bed, but near 
Nottingham it is represented by some 8 to 30 m. (25 to 100 ft.) of orange-coloured 
sandstone. Near Selby this sandstone, together, with the overlying Pebbly Sand- 
stone (see table p. 202), is said to be 189 m. (620 ft.) thick; but in North York- 
shire the Pebbly Sandstone has disappeared, and the stratigraphical position of 
the orange-coloured sandstone is occupied by red clays and shales with layers of 
gypsum and rock-salt between 60 and 120 m. (200 and 400 ft.) thick. On the other 
side of the Pennines the Lower Mottled Sandstone is continuous into Lancashire, 
but under Carlisle its place is taken by clays and shales with gypsum and rock- 
salt, similar to those in North Yorkshire. 

In the Midland District, Cheshire and South Lancashire the middle division 
of the Bunter is very pebbly, and, what is very interesting, pebbles of rock similar 
to the Ordovician quartzite of the Budleigh-Salterton Pebble-Bed occasionally 
occur. The Pebble-Beds are finely exposed at Kinver Edge, near Kidderminster, 
where most of the pebbles are curiously pitted (Reade 1895); but as regards actual 
quantity the pebbles are most abundant in Staffordshire, where a great mass of 
them occurs banked up against the Palaeozoic rocks. In Cheshire and South Lan- 
cashire the middle division (pebbly portion) is thicker, 180 to 210 m. (600 to 700 ft.), 
but the pebbles are fewer in number and the quantity of associated sand greater. 
In the parts of North Lancashire, Westmorland and Cumberland, where the 
Triassic rocks occur, the equivalents to the Pebble-Beds of the Midlands are sand- 
stones, inseparable as regards lithology from the equivalent of the overlying Upper 
Mottled Sandstone. On the other side of the Pennines the equivalent of the Pebble- 
Beds is seen as a pebbly sandstone in the cliff below Nottingham Castle 
(Lamplugh and Gibson, 1910); but it does not appear to continue further 
north than Knaresborough, being unrecognisable in the northern part of Yorkshire. 

The Upper Mottled Sandstone varies in thickness in the Midland District, 
Cheshire and South Lancashire from 90 to 150 m. (300 to 500 ft.). It has a wider 
geographical extent than either of the underlying subdivisions, extending as far 
south as the Bromesberrow district of Gloucestershire. On the west side of the 
Pennines, the equivalent to the Upper Mottled Sandstone cannot be separated 
from the sandstone which is the time-equivalent of the Pebble-Beds of the Midlands 
The whole mass is called the St. Bees or Garstang Sandstone — usually the former. 
In this district footprints of reptilian animals, ripple-marks and dessication- 
cracks have been observed. In Nottinghamshire and South Yorkshire the Upper 



200 (III. 1.) The British Isles. — III. Stratigraphy. — 8. Trias. 

Mottled Sandstone is not represented; but in North Yorkshire, red and white 
sandstone, some 120 to 150 m. (400 to 500 ft.) thick, has been paralleled therewith. 

The Bunter Beds do not contain any building-stone of repute; but they are 
important in connexion with questions of water-supply, for their yield is consi- 
derable. 

Keuper. — From the table on p. 203 it will be seen that the Keuper Series is 
divisible into two parts: a Lower in which sandstone predominates and an Upper 
in which marl preponderates. 

The Keuper rocks are finely exposed in the cliff-sections between Sidmouth 
and Seaton on the English Channel. Thence they extend inland, giving rise to the 
rich vale-land around Taunton. In Somerset, Glamorganshire, and South Gloucester- 
shire the portions of the Keuper, which are near to or rest upon the Palaeozoic 
rocks, are usually conglomeratic. The constituent rock-fragments — mainly of Carboni- 
ferous Limestone • — vary much in size, being sometimes between 0.6 and 0.9 m. (2 to 
3 ft.) in diameter. The majority are well-rounded, but many are best described as sub- 
angular, and it may be that a considerable quantity of the material accumulated as 
screes before being reached by the waters of the Keuper sea. The cementing material 
is generally calcareous and usually dolomitic, on which account the rock is locally 
known as the "Dolomitic Conglomerate". This conglomerate is well seen in many 
places in the Mendip country and particularly by the side of the Bridge Valley 
Road at Clifton. In this neighbourhood it has yielded the remains of Thecodonto- 
saurus and Palaeosaurus and has been considerably used for building-purposes. 
The Conglomerate is essentially a marginal deposit of the Keuper and this is partly 
shown by the fact that the Tea-green Marls become "Dolomitic Conglomerate" when 
in contact with the Palaeozoic rocks. Also, if Old Red Sandstone is the neighbouring 
Palaeozoic rock, then the "Dolomitic Conglomerate" is very arenaceous. 

The Keuper Marls are for the most part red, but in places are variegated with 
greenish spots and have greenish layers traversing their upper portion. Attempts 
have been made, especially by G. Maw (1868) and G. T. Moody (1905) to account 
for the several colours. Thus the latter author writes: — "The ease with which 
iron is deposited from solution in exchange for calcium and magnesium, affords 
strong evidence in favour of the view that variegation in rocks has in many cases 
resulted primarily from the passage of chalybeate water through calcareous strata. 
Subsequently, when conditions were favourable, owing to subsidence of water, air 
has been introduced and the ferrous carbonate has been converted into ferric oxide." 
In Gloucestershire and counties to the north, the uppermost 3 to 10 m. (11 to 35 ft.) 
of rock is of a more uniform greenish colour, and this portion is called the "Tea- 
green Marls". It is interesting to note that if the overlying Rhaetic Black Shales 
are thick, so are — relatively speaking — the Tea-green Marls and vice versa. In 
parts of Somerset and Glamorgan above the Tea-green Marls are Grey Marls which 
pass downwards into the Tea-green Marls and upwards into the Sully Beds (Rhaetic). 

The upper portion of the Keuper is magnificently exposed in the cliffs of 
Aust, Sedbury, Garden andWainlode on the banks of the Severn, and at Glen Parva 
in Leicestershire. 

At various distances between 35 and 65 m. (110 to 215 ft.) below the top of the 
Keuper in Gloucestershire, Worcestershire and Warwickshire, is a prominent bed of 
sandstone called the "Arden Sandstone" by C. A. Matley (1912). It is well exposed 
in the neighbourhoods of Pendock (near Tewkesbury) (Richardson 1905) and Ink- 
berrow and at many places in Warwickshire. Murchison and Strickland (1840), 
the Rev. P. B. Brodie, and subsequently others, have obtained a considerable 
number of animal and plant-remains from this Arden Sandstone, such as Estheria 
minuta, Hybodus, Acrodus, labyrinthodont remains, Equisetites, Voltzia, etc. 



• Richardson: England and Wales. — Keuper. (III. 1.) 201 

The lower or sandstone-portion of the Keuper Series is composed of beds 
of usually red sandstones, which are important from a water-supply standpoint. 

These sandstones have yielded many interesting remains of the animal and 
plant life of the period, notably near Bromsgrove in Worcestershire, whence L. 
J. Wills (1910) has obtained and described a most interesting collection, including 
Schizoneura, Yuccites, Voltzia, Equisetites, teeth of Ceratodus, the scorpions Meso- 
phonus perornatus gen. and sp. nov., M. bromsgroviensis gen. and sp. nov., Meso- 
phomis sp. and Mytilus-likc shells; and in the neigbourhood of Birkenhead, where 
the footprints of reptiles abound. 

The neighbourhood of Charnwood Forest and Mount Sorrel is most interesting 
because in the numerous quarries that have been opened in search of slate and road- 
metal frequent views are afforded of the junction of the Keuper with the older 
rocks (Watts 1902). In one of the Mount- Sorrel quarries the granite rock beneath 
some recently-removed marl exhibited groving which it is thought could only have 
been accomplished by the wind-driven sand of the desert. 

The Upper Keuper Marls of Worcestershire and Cheshire contain vast quanti- 
ties of salt, the brine-springs of Droitwich and Stoke in Worcestershire, and the 
salt-workings at Nantwich and other places in Cheshire, being well-known. Gypsum 
occurs in the Watchet district of Somerset, at Penarth (near Cardiff), Aust Cliff 
in Gloucestershire, and abundantly in the Midland Counties, where masses are 
often obtained sufficiently pure to be of use to the sculptor. In the Bristol district, 
as at Yate, celestine (strontium sulphate) occurs and is largely dug for export to 
Germany to be used in connexion with the process of beet sugar refining. The marl 
itself is extensively ground for brick-making purposes, and in a few places — • as at 
Emborough to the north of the Mendip Hills — certain portions are worked for 
fullers' earth. 

The abundant occurrence of footprints in the sandstone of the Birkenhead 
district has stimulated the search for them in other parts, and the discovery of 
the sand-grooved rocks at Mount Sorrel has given added interest to the attempt to 
discover the precise conditions under which the British Triassic rocks, and, of recent 
years, particularly the Keuper, were formed. 

In England, at the time of formation of the Lower Mottled Sandstone there 
were apparently three distinct areas of accumulation of rock-forming material. Two 
were situated on either side of the Pennine Range, namely, in the Carlisle and North 
Yorkshire districts, and were lakes in which red clays and shales with layers of gypsum 
and rock-salt were formed. The surrounding conditions were most likely those of a 
desert, for the Lower Mottled Sandstone, which was presumably being accumulated 
contemporaneously in the Midland district, Cheshire, South Lancashire and parts 
of Nottingham and South Yorkshire, contains beds of "Millet-seed Sandstone", 
whose grains were doubtless rounded by the action of desert winds. If any rock 
were formed in the South-Western district, its amount appears to be a negligible 
quantity. 

The pebble-beds, pebbly sandstone and sandstones of the Midlands also 
suggest the action and therefore presence of water. The pebbles must have been 
introduced thereby and the footprints and dessication-cracks in the St. Bees Sand- 
stone point in the same direction. 

T. G. Bonney (1900) holds that the pebbles of the Western-Midland 
pebble-beds, and particularly the predominant quartzites, were brought by a river 
which flowed from the direction of the present western side of Scotland; but it 
may be that, as our knowledge of the buried Archaean and Palaeozoic rocks of the 
Midland and South-eastern Counties increases, a nearer source of origin will be 
discovered. 



202 (III.l.) 



The British Isles. — III. Stratigraphy. — 8. Trias. 



co 
W 

PC 

w 

CO 

PC 

p 

.03 
W 

a 
o 

co 

O 

co 



Q 
co 



.is 

1 

8 . 

o 
Z 


Sandstone, 
red and white : 
120 to 150 m. (400 
to 500 ft.). 


(The pebbly sand- 
stone of the Notting- 
hamshire and South 
Yorkshire district has 
disappeared.) 


Red clays etc., 
as in the N. W. Dis- 
trict: 

60 to 140 m. (200 
to 450 ft.). 


•o 

§ 

u u 
■3 £ 

| 


(Upper Mottled 
Sandstone said to 
be unrepresented). 


Pebbly Sandstone, 
white. 

(Near Nottingham this 
deposit and the under- 
lying sandstone are 
only 90 m. (300 ft.) 
thick, but near Selby 
190 m. (620 ft.). The 
pebbly sandstone dies 
out between Selby and 
Knaresborough.) 


Lower Mottled 

Sandstone, 

orange-coloured : 

8 to 30 m. (25 to 

100 ft.). 


I 

Q 

BE 

Z 


St. Bees 

or 

Garstang 

Sandstone 

with 

occasional 

pebble-beds. 

(Footprints of re- 
tilian animals, rip- 
ple - marks and 
dessication cracks.) 

300 to 450 m. (1000 
to 1500 ft.). 


Red clays 
and shales with beds 
of gypsum and 
rock-salt : 

30 to 90 m. (100 to 
300 ft.). 


■a 

g 

6 

 

V 

J3 . 

O « 

M 

££ 
« s 

a -> 

.2 <n 

Q 

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9 

rt 


Upper Mottled Sandstone 
Sandstone, generally soft bright-red, 
yellow, white and variegated. 90 to 
150 m. (300 to 500 ft.). No fossils dis- 
covered as yet 

(This subdivision has the widest geo- 
graphical extent of the three compo- 
sing the Bunter, extending through 
Lancashire, Cheshire, Shropshire and 
Worcestershire into Gloucestershire.) 


Pebble-Beds and pebbly sandstones: 
90 to 120 m. (300 to 400 ft.). [Extend 
over a large area with an average thick- 
ness of 90 m. (300 ft.), thinning out in 
Warwickshire, but thickening in Cheshire 
and S. Lancashire, 180 to 210 m. (600 to 
700 ft.). In this district the pebbles are 
smaller and the quantity of associated 
sand greater]. 


Lower Mottled Sandstone. 
Sandstone, reddish-brown but some 
times bright-red, yellow and striped or 
variegated, much current-bedded. Thick- 
est at Bridgnorth 200 m. (650 ft.). 

(Practically limited to Staffordshire, 
Shropshire, Cheshire, South Lancashire 
and the Vale of Clwyd, being overlapped 
by the Pebble-Beds to the northward, 
eastward and southward.) 


'5 

 

S 

1 

1 


Sandstone 
coarse, current - 
bedded, red, with 
pebbles :91m. (300 ft.) 
Conglomerate or 
"pebble-beds" : 
25 m. (80 ft.) 


Budleigh-Salter- 
ton Pebble-Bed: 
21 to 24 m. (70 to 
80 ft.) 


(Presumably not 

represented.) 






sainas HaiNfia 



Richardson: England and Wales. 



(III. 1.) 203 



CO 

W 

M 

w 

CO 

w 

Oh 

w 
w 

o 

Z 

o 

I— ( 
CO 



Q 

D 

CO 



l 


Tea-green 
Marls. 
Red marls 
with gvpsum: 
290m. (1000ft.). 


Kirklin- 

ton 

Sandstone: 

150 m. (400 ft.). 


a 
.is 

 
u 


Tea-green Marls. 

Red and variegated 
marls: 120m. (400ft.). 


Sandstones, red and 
white passing down 
into the Bunter 
Sandstone: 60 to 
90 m. (200 to 300 ft.). 


•a 
IS 

01 

1 

i 

i 

c 
9 

o 

a 


Tea-green Marls. 

Red and variegated 
marls with gypsum 
passing down into 
the sandstones men- 
tioned below. 


Sandstones soft, 
brown with dessica- 
tion - cracks, ripple- 
marks and conglo- 
merate at base resting 
sometimes upon 
White Sand with occa- 
sional pebbles and at 
others directly and 
unconformably upon 
an eroded surface of 
the Bunter. 


Cheshire and 
Lancashire. 


Tea-green Marls. 

Marls with layers 
of gypsum and beds 
of rocksalt 20 to 
30 m. (70 to 100 ft.), 
worked at North- 
wich: over 600 m. 
(2000 ft.). 


a. Waterstones. 
Brown micaceous 
sandstones with red 
and grey shales at 
the base (at Liver- 
pool 60 m. — 200 ft.). 

b. Sandstone, red white 
and yellow quarried 
for building-stone. 
Rich in foot-prints: 
60 m. (200 ft.). 

c. Conglomerate : 120m. 
(400 ft.). 


S 

S 

•o 
1 

s 


Teagreen Marls 
red and variega- 
ted marls. 

Arden Sandstone 

Estheria minuta 
6 to 9m. (20to30ft.) 

Red and variega- 
ted marls with gyp- 
sum and rock-salt. 
Total thickness in 
Shropshire, 450 to 
550 m. (1500 to 
1800ft.); Stafford- 
shire, 210 to 240 m. 
(700 to 800 ft,); War- 
wickshire and Lei- 
cestershire 180 m. 
(600 ft.) and less. 


Where fully deve- 
loped : 

a. Sandstone locally 
called "Water- 
stones" and con- 
taining Labyrinth- 
odont remains. 

b. Sandstone, fine- 
grained, useful for 
building - purposes, 

c. Sandstone, coarse 
with breccias and 
corns tones: 

total 180 m. (300 ft.) 


ti 

C 

■s 
3 

B 

w 
4) 

B 
3 
O 

CO 


r Grey and Tea-green 
Marls. Red and 
variegated marls 
with gypsum and 
pseudomorphs of 
salt, and thin sand- 
stone layers in the 
lower 45 m. (150 ft.); 
350 in. (1150 ft.). 

(At Lyme Regis a 
boring proved 400 m. 
(1300 ft.) without 
reaching the base.) 


Red and grey sand- 
stone with seams 
of marl, and brec- 
cia 0.6 m. (2 ft.) 
thick at the base: 
23 m. (75 ft.). 






•saiuas Haanax 



204 (III. 1.) 



The British Isles. — III. Stratigraphy. — 8. Trias. 



The geographical distribution of the Upper Mottled Sandstone indicates the 
steady extension of the Bunter area of accumulation. 

In Nottingham a slight uplift appears to have taken place in closing Bunter 
times, for the Upper Mottled Sandstone is said to be lacking and the irregular 
development of the basal Keuper rocks also points to a non-sequential relationship 
between Keuper and Bunter. 

The geographical distribution of the Keuper Sandstone testifies to the continued 
extension of the Triassic area of accumulation and the Keuper Marls to a still greater. 

At present opinions are divided as to whether the Keuper Marls were formed 
mainly under inland sea or mainly under desert conditions (Beasley 1906; Bos- 
worth 1908, 1912; Lomas 1907); but probably the nearest present-day parallel 
is to be found in the Salt-Lake district of Utah. 

b. Scotland. 

By P. G. H. Boswell. 

The Triassic rocks, which are probably of Keuper age, occur in three areas of 
Scotland. In the southern part seven small tracts are met with, (Dumfriesshire, 
Wigtownshire, Ayrshire, and Isle of Arran) lying unconformably upon older rocks. 
The supposed Triassic rocks consist chiefly of unfossiliferous red sandstones, in 
early times referred to the Trias, later to the Permian, but now once more by general 
opinion to the Trias. The table compares the general succession of the beds here 
with that in the northern Scottish localities. 



Southern Division. 



Eastern Division. 



Western Division. 



Thin bedded sandstones 
with beds of clay 90m. (300 ft. ) 

Massive breccias and 
conglomerates 90 m. (300 ft.) 

Soft red current bedded 
sandstones, and brec- 
cias 150 m. (500 ft.) 



Concretionary cream co- 
loured limestones passing 
into chert etc. (=cherty 
rock of Elgin) 4 m. (13 ft.) 

Yellow and light coloured 
sandstone, lacustrine 
? (= Elgin reptiliferous 
sandstone) 15 m. (50 ft.) 



Soft reddish argillaceous 
and sandy beds, conglo- 
merates and cornstones, 
with gypsum 60 m. (200 ft.) 

Red and variegated 
clays and marls, with 
cornstones 60 m. (200 ft.) 

Coarse breccias and 
conglomerates, matrix 
calcareous 150 m. (500 ft. ) 

It is possible that only the upper breccias and sandstones are of Triassic age, 
the lower beds perhaps representing the Penrith sandstone of Permian age. In 
the southern part of the Island of Arran a considerable area of these red sandstones 
is found, they are underlain by conglomerates, and are succeeded by red shales and 
marls. A clue to their age was given by the investigation of an agglomerate filling 
a Tertiary volcanic neck here, large masses of the sedimentary rocks surrounding 
the volcano at the time being preserved in the tuff, while denudation destroyed the 
upper portion of the rocks. One such mass showed a succession of strata from the 
red marl through RhaHic shales to Lower Lias. 

On the western coast of Scotland small exposures of Triassic rocks occur at 
the base of the Jurassic in the islands of Skye, Raasay, and Mull, and on the main- 
land at Morvern and Ardnamurchan (Argyleshire) and at Gruinard Bay in Rosshire. 
The general succession according to J. W. Judd (1878) is indicated in the table. 
The beds of this area are of rather a different type, being characterised by the cal- 
careous element present. The occurrence of gypsum in occasional layers of marl 



Boswell: Scotland. — Bibliography of the Trias of Great Britain. (III. 1.) 205 

associated with concretionary limestones in Mull is noteworthy, but no rock-salt 
has yet been found. Some casts of Cyrena (?) have been met with in sandstones 
in Morvern. 

On the eastern coast of Scotland two small patches of Trias are found, on 
each side of the Moray Firth, one in Sutherland, near Dunrobin Castle, and the 
other in Elginshire. The series is similar at each locality but the sandstones of the 
latter locality, first thought to be part of the Upper Old Red Sandstone upon which 
they rest, have acquired considerable importance on account of the reptilian fauna 
yielded by them. The fauna of the lower portion is most nearly allied to that 
of the Karroo Beds of South Africa, Texas and Russia. The upper beds (Lossiemouth 
Beds) contain an undeniably Triassic fauna, e. g. Telerpeton elginense, Hyperodapedon 
gordoni, Stagonolepis robertsoni, Ornithosuchus woodwardi etc. (Huxley 1859, 
Newton 1877, 1893, 1894, Watson 1909). The deposits of this eastern area 
were probably laid down in a fresh-water lake, and Jukes-Browne (1911) con- 
siders it likely that its outlet was by way of an outflowing stream entering the 
western basin, which probably became saline in later Keuper times. The age of 
the southern deposits is too doubtful to permit speculation upon the Triassic 
geography of the area. 

Bibliography of the Trias of Great Britain. 

1906. Beasley, H. C, Proc. Liverpool Geol. Soc, vol. 10, pp. 79-97 (Upper Keuper Marls). 
1900. Bonney, T. G., Quart. Journ. Geol. Soc, vol. 56, pp. 287-306 (Bunter of Midlands). 
1908. Bosworth, T. O., Trans. Leicester Lit. and Phil. Soc, vol. 12, pp. 28-34 (Upper 

Keuper of Leicestershire). 
1912.  — Quart. Journ. Geol. Soc, vol.68, pp. 281-294 (Keuper of Leicestershire). 
1903-1911. British Association Reports (Fauna and Flora of the Trias). 
1914. Gregory, J. W., Trans. Geol. Soc. Glasgow, vol. 15, pp. 174 — 187 (Arran). 
1869. Hull, E., Mem. Geol. Surv. The Triassic and Permian Rocks of the Midland Counties 

of England. 
1873. Judd, J. W., Quart. Journ. Geol. Soc, vol. 29, pp. 98-195 (Scotland, Eastern area). 
1878. — Quart. Journ. Geol. Soc, vol. 34, pp. 660-743 (Scotland, Western area). 

1911. Jukes-Browne, A. J., The Building of the British Isles, 3 rd Ed., pp. 213-255 

(British Trias). 

1910. Lamplugh, G. W. and Gibson, W., Mem. Geol. Surv., The Geology of the Country 

around Nottingham, pp. 29-45. 

1907. Lomas, J., Proc. Liverpool Geol. Soc, vol. 10, pp. 172-197 (Origin of British Trias). 

1908. Martin, F. C, Geol. Mag., pp. 150-157 (Bunter, Devonshire). 

1912. Matley.C. A., Quart. Journ. Geol. Soc, vol. 68, pp. 252-280 (Keuper of Warwickshire). 
1868. Maw, G., Quart. Journ. Geol. Soc, vol.24, pp. 351-400 (Iron stained strata). 
1905. Moody, G. T., Quart. Journ. Geol. Soc, vol.61, pp. 431-439 (Keuper Marls). 
1840. Murchison, R. I. and Strickland, H. E., Trans. Geol. Soc, ser. 2, vol. 5, pp. 331-348 

(Gloucestershire, Worcestershire, Warwickshire). 
1895. Reade, T. M., Geol. Mag., pp. 341-345 (Bunter Pitted Pebbles). 
1905. Richardson, L., Proc. Cotteswold Nat. Field Club, vol. 15, pp. 93-100 (Keuper of 

Eldersfield). 

1911. Sherlock, R. L., Quart. Journ. Geol. Soc, vol. 67, pp. 75-117 (Permian and Trias 

of Nottinghamshire, with bibliography). 
1903. Shrubsole, O. A., Quart. Journ. Geol. Soc, vol. 59, pp. 311-333 (Bunter of Midlands 

and Devon). 
1902. Thomas, Herbert H., Quart. Journ. Geol. Sos., vol. 58, pp. 620-632 (Bunter of 

West of England). 
1914. Tyrrell, G. W., Trans. Geol. Soc. Glasgow, vol. 15, pp. 188—199 (Arran). 
1910. Ussher, W. A. E., Geol. Assoc. Jubilee Vol., Geology in the Field, pp. 888-890 

(Cornwall, Devon and West Somerset). 

1909. Watson, D. M. S., Geol. Mag., pp. 102-107 (The 'Trias' of Moray). 

1902. Watts, W. W., Proc. Geol. Assoc, vol. 17, pp. 373-381 (Charnwood Forest). 

1910. Wills, L. J., Proc. Geol. Assoc, vol. 21, pp. 249-331 (Worcestershire Keuper, with 

valuable bibliography, principally palaeontological). 
1887. Woodward, H. B., The Geology of England and Wales, 2 nd Ed., pp. 221-252. 



206 (III. 1.) The British Isles. — III. Stratigraphy. — 8. Trias. — Cole: Ireland. 

c. Ireland. 
By G. A. J. Cole. 

The continental type of Trias, common in England, must have prevailed 
over a large part of Ireland; but long-continued denudation has removed the depo- 
sits from all but the north-east area. An important outlier, capped in part by basalt, 
and resting on Upper and Lower Carboniferous strata, occurs between Carrick- 
macross and Kingscourt near the Monaghan border. Here both the Bunter sandstone 
type and the Keuper marls are represented. At the southern end of this outlier, 
the latter contain a bed of gypsum nearly 20m (65 ft.) thick, which bas been worked 
from time to time commercially. 

Red Triassic sandstone, with thin greenish partings of clay, have been pro- 
tected by basalt at Scrabo Hill, west of Newtownards in Co. Down. The rock has 
been quarried as building-stone, though it is rather friable. Great Kainozoic dykes 
and sheets of basalt penetrate the strata, and a cap of basalt occurs, which may 
be part of a former sheet (Mem. Geol. Survey 1904). Throughout northern 
Ireland, indeed, the easily denuded Triassic deposits probably owe, their preser- 
vation to a covering of basalt, even though this has now in some cases disappeared. 
At Scrabo, the bedding of the sandstones is very distinct, the parting of the strata 
being assisted by the occasional layers of clay. In these layers, ripple marks, sun- 
cracks, and rain-prints are abundantly preserved; but no fossils have been found. 

From Scrabo, a thin strip of sandstone runs westward, to connect the out- 
lying mass with a considerable area in the Lagan valley. The lowest beds near 
Belfast, found only in borings, are marls; and above them are sandstones which 
have been correlated with the St. Bees Sandstone of north-west England (Mem. 
Geol. Survey Ireland, 1904). 

Hence the marly part of the lower series, at any rate, may be of Permian age. 
The Bunter is represented by sandstones with a few pebble-beds ; and the overlying 
red and greenish grey marls and shales often contain gypsum, and are no doubt of 
Keuper age. At Carrickfergus and Kilroot, north-east of Belfast, beds of rock- 
salt occur in the marls, one bed being 30 m. (100 ft.) thick. 

Red Triassic strata appear frequently on the margins of the basaltic plateaus 
of Antrim and Londonderry, and are therefore presumed to underlie a very large tract 
of country. They were denuded away before Cretaceous times in the Dalradian area 
south of Ballycastle, but are conspicuous on the steep slopes of Murlough Bay, 
where they rest on Lower Carboniferous sandstones. East of Limavady and Dungiven, 
they form, as they do near Belfast, gentler and sloping country at the foot of for- 
bidding basaltic cliffs. Farther south, at Moneymore and Cookstown, the red soils 
formed from their broad outcrop are a feature of the lowland under Slieve Gallion. 
A considerable outcrop remains south of Dungannon, stretching towards Caledon. 
In this area, Estheria minuta (= portlocki) and the fish Palaeoniscus have been 
found (Baily 1877). 

The continental type of Triassic deposits is the only one found in Ireland. 
Arid conditions probably prevailed through part of each year, while copious 
but merely seasonal rains spread pebbles at intervals over the plains. The lakes 
and pools of the "vlei" type, that were established here and there, were liable to 
sudden extensions over their low shores, and then shrank back again in times of 
desiccation. The stratification and ripple-marking of the Scrabo Hill sandstones 
and muds, associated with sun-cracked surfaces, point to these alternations of 
overflow and retreat. The deposits of gypsum and rock-salt indicate the general 
dryness of the climate. 



9. Rhsetic. — Richardson: England and Wales. (III. 1.) 207 

Economic Products. 

Rock-Salt. Beds of rock-salt are mined in the Triassic marls near Carrick- 
fergus on Belfast Lough. At the Duncrue mine, one bed is 25 m. in thickness. 

Gypsum. Gypsum occurs in small layers and veins in the Triassic marls near 
Belfast, and in a considerable bed in similar strata in an outlier near Carrickmacross 
in Co. Monaghan (p. 206). 

Clays. The Triassic clays are used for brickmaking near Carrickmacross and 
Belfast. 

Bibliography of the Trias of Ireland. 

Geological Survey. 
Explanatory Memoir to accompany Sheet : 

35. Parts of Counties 'Antrim, Armagh & Tyrone (E. T. Hardman & W. H". Baily). 

1877. 
Also Memoir on country round Belfast (G. W. Lamplugh & others). 1904. 



9. Rhsetic. 



a. England and Wales. 
By Linsdall Richardson. 

The Rhaetic Series extends all across England from the Devonshire to the 
Yorkshire Coast. The beds crop out at or near the top of a small ridge, which is, 
however, very well-marked except in the neighbourhood of Chard, where their out- 
crop is concealed by the Cretaceous rocks, in the neighbourhood of the Mendip Hills, 
where they frequently assume a littoral facies, and in portions of certain Midland 
Counties, where they are buried beneath a thick accumulation of Drift. In advance 
of the main escarpment are several others, notably atBerrowHill, near Tewkesbury, 
(Richardson 1905); Rnowle near Birmingham; Needwood Forest and north of 
Abbots Bromley, near Burton-on-Trent; Whitchurch, near Market Drayton; and 
probably near Carlisle. 

In Gloucestershire and counties further north the Tea-green Marls are succeeded 
at once by the well known black Pteria contorta Shales. The line of demar- 
cation between them is very sharply-defined and not infrequently there are signs 
that the top-portion of the Tea-green Marls was eroded previous to the deposition 
of the succeeding Black Shales. The reason for this sudden change in the lithic 
characters is apparent when the Upper Keuper and Rha3tic Beds of the south- 
western Counties and Glamorganshire are studied. There the Tea-green Marls are 
succeeded by what Robert Etheridge, Sen. (Woodward 1904), called the "Grey 
Marls" — marls and marlstones of various shades and combinations of the colours 
green, grey, brown and black. 

Sully Beds. — On the Bristol-Channel littoral, on the Somerset side in the 
neighbourhood of Lilstock and Watchet and on the Glamorgan side around Sully, 
the uppermost 4 m. (14 ft.) of these Grey Marls contain fossils that link them with the 
succeeding Contorta Shales. To these rocks the term "Sully Beds" has been applied 
and while for cartographical purposes they may be associated with the Keuper, 
for scientific purposes they must be regarded as Rhaetic. It was from these beds 
near Watchet that Boyd Dawkins obtained teeth, which proved to belong to the 
oldest known British mammal, Microlestes, along with specimens of Chlamys 
valoniensis, Protocardia rhaetica, etc. (Dawkins 1864.) 



208 (III. 1.) The British Isles. — III. Stratigraphy. — 9. Rhaetic. 

Lilstock, near Watchet, is an excellent place for studying these Sully Beds; 
while at the type-locality, Sully, they contain in abundance Ostrea bristovi Richard- 
son and specimens of Pteria (Avicula) contorta Portlock, the teeth of Sargodon, 
Lepidotus, etc. 

But although the gap between the Tea-green Marls and the Rhaetic Black 
Shales is to a considerable extent bridged over on the Bristol-Channel littoral, there 
is still a non-sequence between the Sully Beds and Black Shales. The surface of 
the former was considerably channelled previous to the deposition of the latter, 
and in places, as at Goldcliff, near Newport, sand with vertebrate-remains was washed 
down into holes which were possibly made by percolating water (Richardson 1905). 

Westbury Beds. — These beds, or the Contorta Shales, extend all across Eng- 
land; but they vary considerably in thickness from place to place. Between the 
English Channel and Stratford-on-Avon hard bands are of common occurrence in 
the shales; but between that town and the Yorkshire Coast they are the exception. At 
Lilstock, in West Somerset, the Westbury Beds are 9.6m (32 ft.) thick (Richardson 
1911) in the railway-cutting at Chilcompton, near Radstock, 2 m. (6 ft. 6 inch.) ; while 
in places near the Mendips they are represented in part by conglomerates only a 
few inches thick. Interesting deposits, teeming with vertebrate-remains, lie hori- 
zontally upon the upturned Carboniferous Limestone near the viaduct north of 
Shepton Mallet, fill up fissures in the Limestone in the picturesque neighbourhood 
of Holwell, and, markedly conglomeratic, crop out in the sides of the lanes near 
Butcombe — a locality between the Mendip Hills and Broadfield Down. In Vallis 
Vale, near Frome, some of the thin layers of black shale are rich in the remains 
of Pollicipes and Chiton (Moore 1861) and most of the limestone-pebbles in a thin 
conglomerate are bored by a species of Polydora (Bather 1909). In the Bridgend- 
Pyle district of Glamorganshire the Westbury Beds are largely replaced by sandstone, 
which is extensively worked at the Quarella Quarries for building-stone, and at 
Pyle is rich in specimens of Natica pylensis Tawney (Tawney 1865). 

The Contorta Shales in this country are separable into two portions : an upper, 
in which mollusks predominate, being particulary noticeable in two impure lime- 
stone-beds called " Pecten-Beds" ; and a lower, in which vertebrate-remains prepon- 
derate, occurring principally in layers called "bone-beds". In the neighbourhood 
of the junction-line between these two subdivisions in the South-West of England 
is a thin layer which is particularly rich in specimens of Pleurophorus elongatusMooRE 
and small gastropods. It is probably the bed that was pierced in the making of. 
the canal near Beer Crocombe, pieces of which rock yielded to Moore so unique 
a series of fossils. Moore(1861) called the bed the "Flinty Bed". It occurs at between 
0.3 and 0.6 m (1 and 2 ft.) above the layer which is richest in vertebrate-remains, in- 
cluding Ceratodus teeth — the layer which is known as the Bone-Bed. In certain 
parts of Gloucestershire (Richardson 1903) and Worcestershire (Richardson 1904), 
however, this Bone-Bed has passed laterally into a non-vertebratiferous sand- 
stone, which has relatively speaking, greatly increased in thickness (Richardson 
1903). In West Somerset and Monmouthshire Cardium cloacinum is a useful 
zonal fossil, particularly fine specimens occurring in a limestone-bed near the top 
of the Black Shales. 

It has been found that, while the component layers of the Westbury Beds 
above the Bone-Bed are persistent over large areas, the same cannot be said of 
those b e 1 ow. They appear and disappear in an at first sight inexplicable matter. Thus 
at Blue-Anchor Point there is 6.6 m. (22 ft.) of deposit between the Bone-Bed and 
Sully. Beds. They contain hard beds, some of which are rich in a number of rare 
lamellibranchs — Pteromya crowcombeia Moore, for example. The Wedmore Stone 
is one of these sub-Bone-Bed Rhaetic limestones, which, near the historic country- 



Richardson: England and Wales. (III. 1.) 209 

town whence it derives its name, is sufficiently thick and hard to have been worked 
for building-purposes. At Aust Cliff, the Bone-Bed — which contains rolled pieces 
of Tea-green Marl — rests directly and non-sequentially upon the Tea-green Marls; 
at Garden Cliff 2m. (6ft. 5 inch.) of deposit intervenes; at Denny Hill, near Glou- 
cester, it reposes directly on the Tea-green Marls again (Paris 1904); at Dunhamp- 
stead, in Worcestershire, 1.25m. (4 ft. 1 inch.) of deposit intervenes; at Marl Cliff 
on the borders of Worcestershire and Warwickshire, 0.6m. (2 ft.) (Richardson 1903, 
1904); while at Wigston in Leicestershire, Bone-Bed and Tea-green Marls are again 
in apposition (Richardson 1909). 

It has been suggested that this irregular geographic distribution of the sub- 
Bone-Bed Rhaetic deposits is due to the surface of the marl having been flexured 
in closing Keuper times and deposition being subsequently made in the hollows 
so that each successive bed has an increasingly wide extent (Richardson 1904). 

A detailed study of the Westbury Beds suggests that their accumulation was 
slow and that the aggregation of vertebrate-remains was due, not to any sudden 
killing-off of countless fish and reptiles, but rather to paucity of sediment. 

Cotham Beds. — The top-beds of the Contorta Shales in places exhibit features 
indicative of incipient crust-oscillations. These crust-oscillations rapidly produced 
conditions suitable for the formation of beds totally distinct from the Black 
Shales, namely, to a series of greenish-yellow marls and limestones with the curious 
but well-known Cotham Marble, with its arborescent markings, at or near the top. 
Ostracods abound in the marly beds that immediately underlie a limestone which 
is locally rich in Estheriae (E. minuta var. brodieana Jones, and plant-remains 
(Lycopodites), (Sollas 1901); while the Cotham Marble or its equivalent is locally 
prolific in specimens of Pseudomonotis fallax auct. and insect-remains — the "Insect 
Bed" of Brodie (1845). 

The Cotham Beds, like the underlying Westbury Beds extend all across the 
country and are quite distinct from the Langport Beds or White Lias proper. The 
Cotham Beds were formed slowly. The Cotham Marble has a curiously irregular 
surface, is occasionally bored by Lithophagi, and at Aust and Sedbury Cliffs was 
broken up and its tabular fragments enclosed in a very similar matrix to that of the 
fragments themselves (Vaughan 1903). This conglomeratic marble has been called 
"False Cotham" (Short 1904). 

Langport Beds. — These beds, or the White Lias proper, are an interesting series 
of white, pale-grey and cream-coloured limestones with decidedly subordinate part- 
ings of marl. The top-bed is often of sufficient thickness and hardness to have 
gained a distinctive appellation — generally the "Sun-Bed" in Somerset north 
of the Mendip Hills and "Jew Stone" to the south. The beds are particularly rich 
in specimens of Dimyodon intus-striatus „Emmr. (Gronwall 1906) and in the south- 
western counties, in Volsella minima Moore non Sow., and Lima praecursor Quen- 
stedt. In the railway-cutting at Charlton Mackrell, Somerset, they are 6 m. (20 ft.) 
thick; but even here, where the subdivision is so thick, the individual limestone- 
beds are often irregularly channelled, sometimes bored, and not uncommonly have 
oysters and Plicatulae adherent to their surfaces. Ostracods are not infrequent, 
and in the neighbourhood of Charlton Mackrell a branching coral is abundant near 
the middle of the subdivision. 

The White Lias is well-developed at Culverhole in Devonshire (Richardson 
1906), and in Mid and East Somerset (Wright 1860) ; but in West Somerset and 
Glamorganshire it has attenuated and in South Gloucestershire died out altogether 
— the Cotham Marble and Ostrea Beds being in apposition near Wickwar. Near 
Stratford-on-Avon, however, the White Lias reappears (Richardson 1912) and is 
continuous northwards to somewhere between Church Lawford and Wigston in 

Handbuch der regionalen Geologie. III. 1. 14 



210 (III. 1.) 



The British Isles. — III. Stratigraphy. — 9. Rhaetic. 



Leicestershire, apparently then disappearing not to reappear in the more northern 
counties (Wilson 1882). In times past, in Warwickshire, the stone has been ex- 
tensively worked for road-metal and for burning for lime. The subdivision in this 
county does not exceed 3 m. (10ft.) in thickness and is characterized by an abundance 
of specimens of Dimyodon intus-striatus and radioles of the echinoid Diademopsis 
tomesi Wright. The surface of its top-bed is often very ferruginous, waterworn 
and sometimes bored and is immediatily succeeded by the Lower Lias. 

Watchet Beds. — In West Somerset and Glamorganshire, above the true 
White Lias are certain marly beds to which the term "Watchet Beds" has been 
applied. They are immediately succeeded by the Lower Lias. 



Table. — Rhaetic Series. 



Series Stage 



Deposits 



Lias Lower Paper Shales (and occasional 

limestone at base) 



Approximate 

thickness in 

England 



Sequence of the maxima 

of the principal fossils of 

the Rhaetic 



0.3 m. (1ft.) Volsella 



RhaHic 



Upper 



I. Watchet Beds ('Marly Beds \ 2.31m. (7 ft 
of the White Lias') . . J 7 inch.) 



II. Langport Beds (White 
Lias proper) . . . , 



\° 



to 7.5m. 

(25 ft.) 



III. 



Cotham 
Beds 



Cotham Marble 



f 5a 

5b. Cardiu m 
cloaci num Bed 1 

6 

7. Pecten Bed 2 



Lower 



IV. West- 
bury Beds 
(Black 
Shales) 



9 

10 

11. 

12 

13. PI eur oph o - 
rus Bed . . 

14 

15. Bone-Bed . . 

Infra-Bone-Bed 
deposits . . 



Sully Beds (Fossiliferous 
Grey Marls) 



0.83 m. (2ft. 

9 inch.) to 

5.8m. (19ft.) 



I Volsella & Ostrea liassica 

\Ostrea liassica 
J Volsella minima 

(Moore non Sow.) 
Dimyodon intus-striatus 
Pseudomonotis jallax 
Ostracoda 

Estheriae & Lycopodites 
Ostracoda common below 
Bed 3 



Cardium cloacinum 
Actaeonina & Natica oppeli 

Chlamys valoniensis 
Ophiolepis damesi 



0.3 m. (1ft.) 

to 
14m. (47ft.) 



Keuper Upper {g^ Te.-green Marls 



to 4.3 m. 

(14ft.) 

\ about 3.3 m. (lift.) 
j to 35 m. (115 ft.) 



{Pleuropkorus elongatus, 
'Chemnitzia' spp., Heter- 
astraea rhaetica 
Relatively barren 

ICeratodus latissimus 
Mytilus cloacinus 
Vertebrate-remains 
(Acrodus minimus, etc.) 

Ostrea bristovi 



1 Or Upper Pecten Bed. 
* Or Lower Pecten Bed. 



Boswell: Scotland. (III. 1.) 211 

The Ostrea-Beds of the Lower Lias extend right across England. At Culverhole, 
near Lyme Regis, they rest upon the White Lias; in Mid and East Somerset generally 
upon the White Lias, whose top-bed — Sun Bed or Jew Stone • — is often waterworn 
and considerably bored; in West Somerset and Glamorganshire upon the Watchet 
Beds; at Sedbury and Aust Cliffs and in North Gloucerstershire and Worcestershire 
upon the Cotham Beds; in Warwickshire upon the White Lias, and in counties to 
the north upon the Cotham Beds — the subdivision, certain layers of which, contain 
Estkeriae. 

Except for the road-metal, lime and local building-stone yielded by the true 
White Lias and the Quarella Sandstone of Bridgend, the Rhsetic Beds are not 
productive of anything of commercial value. 



The principal sections of the Rhsetic Beds in England are: Culverhole, near 
Lyme Regis; Blue Anchor and Lilstock in West Somerset; Dunball railway-cutting, 
near Bridgewater; quarries near Queen Camel; Milton Lane, Wells; Holwell and 
Vallis Vale, near Frome; railway-cutting, Chilcompton ; Aust, Sedbury (Richardson 
1903), Garden and Wainlode Cliffs on the Severn; Crowle and Dunhampstead 
railway-cutting, in Worcestershire; quarry in the White Lias near Ettington, War- 
wickshire; and Wigston, near Leicester. In Glamorganshire there is the fine and 
very accessible section at Lavemock Point, the exposure of the Sully Beds at St. 
Mary's Well Bay, Sully; and the interesting sections in the sandstones on Stormy 
Down and at Pyle. 

b. Scotland. 
By P. G. H. Boswell. 

Except for the masses of Rhsetic and Lower Lias rocks found in the volcanic 
agglomerates of Arran (mentioned under Scottish Triassic Rocks), the occurrence 
of these beds is confined to small areas on the east and west coasts of Scotland. 
The table on p. 237 gives a general comparison of the two areas with one another 
and with the corresponding deposits in England. 

Undoubted Rhsetic black fossiliferous shales occur in association with Keuper 
Marls and Lower Lias beds in the neck of a Tertiary volcano in Arran. 

On the eastern coast of Scotland, near Dunrobin Castle in Sutherlandshire, 
coarse sandstones and conglomerates lie upon rocks similar to the Elgin sandstones 
and cherts (Trias), and contain fragments and pebbles of the latter. Judd 
regards these as probably of Rhsetic age, and it is noteworthy that masses included 
in the Boulder Clay on the South side of Moray Firth contain fossils similar to those 
of the Scanian Rhaetic. In the Western area (islands of Skye, Mull, etc.) it is not 
possible at present to separate the Rhsetic from the Lower Lias (zone of A. planorbis). 
In the Summary of Progress of the Geol . Survey for 1910, a section on the mainland at 
Morvern is recorded where nearly 100 m. (320 ft.) of Triassic sandstones and pebble 
beds, with marls and cornstones near the top, pass into white calcareous sandstones, 
which in turn pass into Lower Lias of the b u c k 1 a n d i zone. Thus there is a complete 
transition through the Rhaetic, but such fossils as occur are not zonally determinative. 

Lying above the Triassic strata of Skye and Mull Judd (1878) describes 
120 m. (400 ft.) of oolitic limestones, calcareous grits and conglomerates, with seams 
of coal, as Infra-Lias, the upper part of this series being equivalent to the 
planorbis zone of the Lower Lias. The western facies then shows a prevalence 
of littoral and brackish-water conditions, a distinctly transitional phase. 

14* 



212 (III. 1.) The British Isles. — III. Stratigraphy. — 9. Rhsetic — Cole: Ireland. 

Bibliography of the Rfiaetic of Great Britain. 

1909. Bather, F. A., Geol. Mag., pp. 108-110; and 1910, pp. 114-116 (Lithodomous worm, 

Polydora).. 
1845. Bhodie, P. B., History of Fossil Insects of the Secondary Rocks of England, pp. 51-104. 

1864. Dawkins, W. B., Quart. Journ. Geol. Soc, vol.20, pp. 396-412 (Somerset). 
1906. Gronwall, K. A., Geol. Mag., pp. 202-205 (Genus Dimyodon), 

1873. Judd, J. W., Quart. Journ. Geol. Soc, vol. 29, pp. 145-149 (Scotland, Eastern area). 
1878. — Quart. Journ. Geol. Soc, vol. 34, pp. 696-701 (Scotland, Western area). 
1861. Moore, Chas., Quart. Journ. Geol. Soc, vol. 17, pp. 483-516 (Avicula-contorta 

zone). 
1906. Paris, E. T., Proc Gotteswold Nat. Field Club, vol. 15, pp. 263-266 (Gloucestershire). 
1904. Reynolds, S. H. and Vaughan, A., Quart. Journ. Geol. Soc, vol. 60, pp. 194-214 

(South Wales). 

1903. Richardson, L., Quart. Journ. Geol. Soc, vol. 59, pp. 390-395 (Chepstow). 

1904. — Trans. Worcester Nat. Field Club, vol. 3, pp. 92-101 (Worcestershire). 

1903. — Proc. Cotteswold Nat. Field Club, vol. 14, pp. 127-174 and 251-256 (Gloucester- 

shire). 

1904. — Quart. Journ. Geol. Soc, vol. 60, pp. 349-358 (Gloucestershire & Worcester- 

shire). 

1904. — Proc Cotteswold Nat. Field Club, vol. 15, pp. 19-44 (Worcestershire). 

1905. — Quart. Journ. Geol. Soc, vol. 61, pp. 374-384 (Monmouthshire); pp. 385-424 

(Glamorganshire); pp. 425-430 (Berrow Hill, Tewkesbury). 

1906. — Trans. Worcester Nat. Field Club, vol. 3, pp. 206-209 (Worcestershire). 
1906. — Proc. Geol. Assoc, vol.19, pp. 401-409 (Devon and Dorset). 

1909. — Geol. Mag., pp. 366-370 (Leicestershire). 

1911. — Quart. Journ. Geol. Soc, vol.67, pp. 1-74 (Somerset). 

1912. — Geol. Mag., pp. 24-33 (Warwickshire). 

1904. Short, A. R., Quart. Journ. Geol. Soc, vol. 60, pp. 170-193 (Bristol district). 
1901. Sollas, I. B. J., Quart. Journ. Geol. Soc, vol. 57, pp. 307-312 (Rhastic plant 
Naiadita). 

1865. Tawney, E. B., Quart. Journ. Geol. Soc, vol. 22, pp. 69-93 (South Wales). 

1903. Vaughan, A., Quart. Journ. Geol. Soc, vol. 59, pp. 396-402 (Lowest Beds of Lower 

Lias of Sedbury Cliff). 
1882. Wilson, E., Quart. Journ. Geol. Soc, vol. 38, pp. 451-456 (Nottinghamshire). 

1904. Woodward, H. B., Proc. Bristol Nat. Soc, n. s., vol. 10, pp. 175-187 (A Memoir 

of Robert Etheridge). 

Geological Survey, Summaries of Progress, 1909-1911. 



c. Ireland. 

By G. A. J.Cole. 
The beds of the Rhsetic stage, have been preserved in several places, connecting 
with perfect conformity theTriassic and the Lower Jurassic strata (Tate 1863, 1864). 
It is probable however, that the Rhaetic overflow, which heralded the arrival of 
the Jurassic sea, did not spread far westward of Lough Foyle. The Rhsetic series 
in Co. Londonderry is not completely seen, and its thickness is uncertain. Avicula 
contorta marks these beds throughout north-eastern Ireland. At Larne they contain 
concretionary spheroids which resemble an oolitic structure. There is also a well 
known section at Collin Glen four miles south-west of Belfast, now somewhat ob- 
scured. Pteria (Avicula) contorta, Protocardia rhaetica, Modiola minima, and several 
fish, are among the fossils recorded. With the Rhaetic subsidence, and the spread of 
the sea as far west as Londonderry, a more humid climate doubtless set in; but the 
conditions on the land must have depended greatly on whether the prevalent winds 
blew from the north-western continent or from the great sea that had now asserted 
itself across central Europe. 

Bibliography of the Rhsetic of Ireland. 

1864. Tate, R., Quart. Journ., Geol. Soc. London, vol. 20, pp. 103-111 (Rhsetic near Belfast). 

1865. — Quart. Journ. Geol. Soc. London, vol.21, p. 17 (Rhsetic near Belfast). 



10. Jurassic. — Davies: England and Wales. — I. The Lias. (III. 1.) 213 

10. Jurassic. 

a. England and Wales. 
By A. M. Davies. 

I. The Lower Jurassic or Lias. 

The term "Lias", so familiar to geologists as the name of the Lower Jurassic 
series, is an old quarryman's term for a hard limestone, still applied locally to beds 
of various ages. The presence of thick beds of "white Lias" and "blue Lias" in Glou- 
cestershire and adjacent counties led William Smith and other early stratigraphers 
to adopt "Lias" as the name of that geological horizon, and gradually the term 
was stretched to cover higher and higher beds. First, the clays overlying the Blue 
Lias were included, the strata next above these being for a time confused with 
the Inferior Oolite. When this mistake was rectified, it was done by throwing into 
the Lias all the beds below the true Inferior Oolite, the limestones and ironstones 
that had been mistaken for the latter receiving the inappropriate name of Marlstone. 
Thus came about the triple division of the Lias still recognized on the Geological 
Survey map — Lower Lias limestones and clays (g 1) Middle Lias or Marlstone (g 2) 
and Upper Lias clays (g 3). 

The recognition of the Rhaetic stage (fg) below led to the removal of the 
White Lias from the "Lias" as extended; while at the top a series of sandy beds 
were taken as a transition series between Lias and Inferior Oolite, and mapped as 
Midford Sands (g 4). 

Zonal work, initiated by Williamson in 1834, extended by Oppel, Wright, 
Tate and Blake, Beeby Thompson, S. S. Buckman and others, has led to modi- 
fications of the above scheme. The zonal palaeontologists drew the base-line of the 
Middle Lias below the armatum-zone; but this being an unmappable line in the 
midst of a clay-series the Survey extended the Lower Lias to the top of the capri- 
cornus-zone, their Middle Lias being thus equivalent to the Domerian stage of 
the Italians, while their Lower Lias is equivalent to Hettangian, Sinemurian and 
Pliensbachian or Charmouthian (in the restricted sense, after deducting Domerian). 
The zonal work of Buckman showed that the change from Upper Lias Clay to 
"Midford Sands" was not contemporaneous in different places, and he therefore 
insisted on the necessity for using distinct local names for these sands. The Upper 
Lias and Midford Sands proper correspond to the Toarcian stage, though locally 
the sandy facies extends upwards into the Aalenian. Owing to the large number 
of zones in the Toarcian, Buckman has lately (1910) proposed to divide it into a 
lower Whitbian stage, corresponding approximately to Upper Lias clays, and an 
upper Yeovilian, answering approximately to Midford Sands. A list of zones is 
given in the accompanying tables (p. 235—237). 

A. Lower Lias (Hettangian, Sinemurian and Charmouthian). 

These formations crop out along a band from the coast of Dorset at Lyme 
Regis and Charmouth, to the coast of Yorkshire at Whitby, and through the greater 
part of this course they show very uniform characters — excepting only in the 
neighbourhood of the anticlinorium of the Mendip Hills. They consist of alternating 
beds of grey argillaceous limestone and grey shale, below, and of grey shale with 
only occasional bands of limestone above. The Blue Lias, in which limestone 
is as common as shale or predominates over it, corresponds to the Hettangian and 
bucklandi-zone of the Sinemurian. The limestones are largely worked for hydraulic 
cement, both on the coast, as at Lyme Regis and Aberthaw in South Wales, and 



214 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

inland, as at Harbury and Rugby in Warwickshire, Barrow-on-Soar in Leicestershire, 
and many other places. Northwards, however, the limestone becomes very much 
less in amount, and in Yorkshire these beds are of no value for hydraulic cement. 
In addition to the zonal ammonites, many fossils are obtained from the Blue 
Lias, particularly Gryphaea arcuata Lamarck, Plagiostoma giganteum J. Sowerby, 
Cardinia listeri J. Sowerby and other species, Plearotomaria anglica Sowerby, 
Belemnites acutus Miller, Pentacrinus basaltiformis Miller, Ichthyosaurus com- 
munis Conybeare etc. Brachiopoda are not abundant, but Rhynchonella calcicosta 
Quenstedt is found in the marmorea-zone and Spiriferina walcotti Sowerby 
abounds in the gmuendense zone of Radstock. 

The semicostatum or turneri zone at the top of the Blue Lias is not usually 
distinguished from the zones above and below, but from the Vale of Belvoir in 
Leicestershire northwards to the Humber, it has the character of a very ferruginous 
limestone passing into an ironstone which supports large iron and steel works at 
Frodingham in Lincolnshire. 

The clays and shales from the oxynotus zone up to the capricornu zone 
are fairly uniform in character, except that the oxynotus zone is generally more 
pyritic. These clays make good bricks and there are many openings into them at 
intervals along the outcrop, but the workings are much shallower than those into 
the Blue Lias below; hence their thickness and characters are less known, except 
on the sea-coast. Among the fossils characteristic of the Sinemurian clays are 
Pentacrinus briareus Miller, Cardinia spp., Hippopodium ponderosum Sowerby, (a 
senile form of Cardinia) and Plearotomaria anglica Sowerby. In addition to the 
zonal ammonites, there may be mentioned Xipheroceras planicosta J. Sowerby, enor- 
mous numbers of which, along with a few examples of Asteroceras smithi J. de C. 
Sowerby make up a bed of limestone in the obtusum zone. A separate stellare- 
zone can be recognized at Lyme Regis, with Asteroceras stellare Sowerby; 
while at the base of the same zone, one characterized by Microderoceras birchi 
J. Sowerby can be distinguished; but these zones are not traceable inland. 
The Charmouthian clays contain more abundant brachiopods than the beds 
below, Cincta numismalis Lamarck and other species of Cincta, along with 
Rhynchonella rimosa von Buch and Spiriferina verrucosa von Buch being 
common in the jamesoni zone: it is in the abnormal facies of the Radstock 
area that brachiopods are most abundant, however. Other Charmouthian fossils 
are Crenatula ventricosa Sowerby, Goniomya hybrida Munster, Leda spp., and 
Belemnites clavatus Blainville. In the neighbourhood of the series of anticlinal 
folds of Armorican direction which form the southern margin of the South Wales 
coalfield, the Lower Lias undergoes a very remarkable change, being reduced locally 
to less than one-tenth of its normal thickness. The zones become thinner and also 
more calcareous, and at the same time many breaks in the sequence of zones ("non- 
sequences") are found locally. Thus in South Wales, near Dunraven Castle, the 
Hettangian loses its argillaceous character and passes into massive and in part con- 
glomeratic limestones, composed of material derived from the wear and tear of 
the Carboniferous Limestone. The upper part (Southerndown beds) is about 15 m. 
(50 ft.) the lower (Sutton beds) about 12 m. (40 ft.) thick, so that in this case there is 
little diminution of thickness. The Sutton beds include the only good building- 
stone in the Lower Lias: the fossils include nine species of corals. A very similar 
facies is found near Shepton Mallet in Somerset, close to the Carboniferous Lime- 
stone of the Mendip Hills. 

It is in the neighbourhood of Radstock in Somerset that the most remarkable 
attenuation of the Lower Lias is seen. The folding movements of the Mendip Hills 



Davies: England and Wales. — I. The Lias. (III. 1.) 215 

must still have been in progress, since the imperfections in the sequence are so 
many and so local. Thus either the ar ma turn-zone (with remanie fossils from the 
raricostatum-zone) or the raricostatum zone rests upon obtusum or semi- 
co statu m-zone at Radstock, and directly upon Palaeozoic at Vobster. The arma- 
tum or jamesoni-zone upon Palaeozoic atMells; the spinatum-zone upon Palaeo- 
zoic at Whatley, though elsewhere Toarcian rests upon Charmouthian without 
any Domerian between 1 . At Nunney again, the whole of the Lias is missing, the 
garantiana-zone (Vesulian) resting directly on Rhaetic or Palaeozoic. Resides 
the absence of zones, individual zones in this district are thin, often from a few 
centimetres to a metre only in thickness; and they are mainly limestones and marls. 

B. Middle Lias (Domerian). 

The Middle Lias is fairly constant in character throughout England. The 
lower part (algovianum and margaritatus zones) consists of sandy micaceous 
clays; the upper part (spinatum zone) is a rockbed, usually forming a well-marked 
escarpment, and in several areas constituting a most valuable iron-ore. Among 
the fossils of the two lower zones are various species of Amaltheus. At the top of 
the clays, which perhaps represent the algovianum zone on the Dorset coast 
there is a starfish-bed with Ophioderma egertoni Rroderip and 0. milleri Phillips. 
The spinatum zone is richly fossiliferous. Ammonites of the genus Paltopleuro- 
ceras occur, though not abundantly — P. spinatum Rruguiere etc. Terebratula 
punctata J. Sowerby and Rhynchonella tetraedra Sowerby occur in "nests" in 
enormous numbers. Other fossils include Gryphaea gigantea Sowerby, Pseudopecten 
aequivalvis Sowerby, Rhynchonella acuta J. Sowerby, R. media J. Sowerby, 
Zeilleria cornuta J. de C. Sowerby and Z. subquadrifida Oppel. 

The spinatum-zone or "Marlstone" yields the iron-ore of Cleveland in North 
Yorkshire, of which 6 million tons are raised annually, and that of Leicestershire and 
North Oxfordshire. Elsewhere it forms a good building stone, particularly in 
the fine escarpment of Edge Hill on the border of Oxfordshire and Warwickshire 
(Hornton Stone). 

Resting upon the top of the Marlstone, in the district around Ranbury only, 
js an extremely thin layer containing a very special fauna of which Tiltoni- 
c eras acutum Tate and Dactylioceras holandrei Wright (non d'Orbigny) are 
t he two chief species. This is known as the Transition-bed or acutum zone, and 
t he only other representative of it known in England is in the bottom portion of 
.he thin "Junction-bed" of Down Cliffs, Dorset, described below. 

C. Upper Lias (Lower Toarcian). 

This formation consists of grey shale or clay, with frequent septarian and 
other nodules. It is particularly well-exposed on the Yorkshire coast near Whitby, 
where the upper portion is very pyritous and, on decomposition, yields alum, while 
the lower portion contains beds with the hard, anthracitic form of lignite known 
as jet; hence the terms Alum-Shale and Jet-rock. Roth these were of economic 
value for many years, but alum is now made more cheaply from Coal-Measure shales, 
or the by-products of coal-gas, while carved jet ornaments are no longer fashionable. 
Inland, the lower beds are often exposed in open workings for the marlstone iron- 
ore, and the top beds are dug for brick-clay, but the middle portion is rarely seen. 
On the Dorset coast, the whole of the Lower Toarcian and some of the zones above 
and below are represented by a remarkable junction-bed, less than lm. thick, in which 
four very distinct layers can be recognized: a brown layer with pebbles of lower 
beds (spinatum and in places acutum zone), a greenish layer (falciferum zone), 

1 Unpublished information from J. W. Tutcher, Bristol. 



216 (III. 1.) 



The British Isles. — III. Stratigraphy. — 10. Jurassic. 



a pink layer (bifrons zone) and a white layer (striatulum zone). All these are 
not always present, and the state of preservation of the fossils shows that throughout 
the whole period represented the small amount of sediment deposited was subject 
to erosion and reconstruction. 

Among the characteristic fossils of the lower part of the Upper Lias (tenui- 
costatum to falciferum zone) are various species of Dactylioceras and Harpoceras, 
Phylloceras heterophyllum J. Sowerby, Nautilus astacoides Young and Bird, 
Belemnites vulgaris Young and Bird, Inoceramus dubius Sowerby, and Posi- 
donomya bronni Voltz. The "Leptaena beds" of Somerset and Gloucestershire 
have yielded small species of the brachiopods Cadomella and Koninckella. The 
upper beds of the Upper Lias (the old bifrons zone) yield species of Hildoceras, 
Dactylioceras, Peronoceras, Lytoceras and Phylloceras, Belemnites ilminstrensis, 
Phillips, and Leda ovum Sowerby. 



II. Middle Jurassic. 

A. The Bridport, Yeovil, Midford and Cotteswold Sands and associated beds 

(Upper Toarcian). 

Above the clays of the Upper Lias there usually come, in the South of England 
a series of fine yellow sands with bands and nodules of calcareous sandstone. These 
are mapped as Midford Sands (g 4), but as they begin and end at very different 
palaeontological horizons in different areas, local names are very desirable. As the 
table (p. 235) shows, the change from clay to sand began earlier and earlier north- 
wards. On the Dorset coast, the Bridport sands are partly Upper Toarcian and partly 
Aalenian. Inland, the Yeovil sands begin at the same horizon, but, owing to a non- 
sequence, only the Toarcian portion is present. The upper part of the Yeovil Sand 
passes locally into thick beds of shelly limestone, which include the much-valued 
and beautiful building-stone of Ham Hill. 



Stinchcombe 
Hill 



S. by 15°E. 




Railway (MR.) 



Ordnance-Datum 



Fig. 40. Section across the escarpment at Stinchcombe, South Cotteswolds 

(L.Richardson). Vertical scale, 1 inch = 400 feet; horizontal scale, 3 inches = 1 mile. 
Reproduced from the Proceedings of the Geologists' Association, vol. 20, p. 528, pi. XXVIII, 1908; 

with the permission of the Council. 

The principal division of the Inferior Oolite shown is the Lower Freestone; the greater part of 

what is indicated as Upper Lias is the Cotteswold Sands. 



The Yeovil and other sands are easily eroded, but like other calcareous sands, 
they stand in good vertical faces; consequently their outcrop is marked by deeply- 
worn steep-sided lanes of very picturesque appearance. 

Farther north, in the Bath district, the Midford Sands proper begin two 
zones earlier than the Yeovil sands and are likewise followed non-sequentially by 
much later beds (Vesulian — garantian a zone). Below the sands, is a thin "Cepha- 
lopod-bed", containing ammonites of four distinct zones: struckmanni, stria- 



Davies: England and Wales. — II. Middle Jurassic. (III. 1.) 217 

tulum, lilli and bifrons. The Cotteswold Sands of Gloucestershire are of still 
earlier date than the Midford Sands (Lower Toarcian), and are overlain by thin 
beds of iron-shot limestone and marl (Cephalopoda-bed), which contain the whole 
Upper Toarcian in the thickness of little over 1 metre. These thin beds contain 
an abundant fauna of ammonites, lamellibranchs and brachiopods. It will be noticed 
that the term "Cephalopod-bed" refers to deposits of different age in different 
areas. 

Beyond the Cotteswold Hills, no deposit of Upper Toarcian age is known 
until Yorkshire is reached. There the Alum Shale is succeeded by the striatulum- 
shales and the grey and yellow sands of BleaWyke. The striatulum-shales contain 
Grammoceras striatulum Sow., Belemnites voltzii Phillips, Trigonia literata Young 
and Bird, etc. The lower part of the grey sands contain nodules with Lingula 
beani Phillips and Orbiculoidea reflexa Sow., while the upper part abounds in 
Serpula deplexa Bean. The yellow sands are noted for the casts of Terebratulae 
generally known as T. trilineata Young and Bird. A very remarkable fact is the 
sudden disappearance of the whole of the Upper Toarcian on crossing the im- 
portant Peak Fault from south-east to north-west. The probable explanation of 
this is that the fault was in process of growth during later Toarcian time, so that 
there was less deposition and more erosion on the upthrow side than on the 
downthrow. 

B. The Lower Inferior Oolite, Northampton Sands and Lower Estuarine beds 

(Aalenian). 

On the Dorset coast the lower zones of the Aalenian are represented on the 
coast by the upper part of the Bridport Sands; inland, they are altogether wanting. 
The upper zones consist of a thin and variable series of limestones, some beds of 
which are locally very fossiliferous and have for many years been famous for their 
ammonites. The same statement applies to the Bajocian and Vesulian beds above. 
Owing to the rapid local variation in thickness, in lithic character and in abundance 
of fossils, these strata were long united together under the general name of Inferior 
Oolite, with little attempt at distinction of zones, until the minute palseontological 
and stratigraphical work of Buckman revealed the highly condensed character of 
the sequence (Buckman, 1893, 1910). These characters are the result partly of paucity of 
sedimentation, partly of almost contemporaneous erosion. The variations in thickness 
of the zones are indicated in the table. In the Sherborne district there is a marked 
eastwardly thickening of the zones. Among the most characteristic fossils may 
be mentioned for the opaliniforme zone: Rhynchonella stephensi Dav., Aula- 
cothyris blakei Walker, Zeilleria whaddonensis S. Buckman, Canavariella spp. 
For the Scissum-zone: Lioceras opalinum Reinecke, Volsella sowerbyana 
d'Orb. For the Ancolioceras zone: Amusium personatum Goldf. For the 
murchisonae zone: Zeilleria anglica Oppel and many ammonites of the 
family Hildoceratidae (sub-families Hyatteinae and Graphoceratinae of Buck- 
man). For the bradf ordensis zone: Rhynchonella ringens Dav. and other ammoni- 
tes of the same subfamilies. For the concava zone: Ludwigella concava Sow., 
and Lucya marginata S. Buckm. 

The concava zone is intimately associated with the overlying discites- 
zone, being in places welded on to it in the same block of stone. Nevertheless the 
boundary between Aalenian and Bajocian is drawn here by Buckman, because, 
although Hildoceratids do not die out until the discites zone (and are still abun- 
dant in it), that zone contains the first representatives of the new ammonite fauna 
of the Sonniniae. 



218 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

Thin calcareous representatives of the Aalenian are also known at Dundry 
Hill, near Bristol, but it is in Gloucestershire that the beds of this stags attain their 
greatest development, and here they include the valuable building-stones of the 
Stroud and Cheltenham district. Above the Cotteswold Cephalopod-bed come 
successively ferruginous oolite, sandy limestone, oolitic limestone (not of much 
value as building-stone) and "Pea-Grit". The last is a coarse pisolite with Hemi- 
pedina bakeri Wright, Acrosalenia lycetti Wright and other Echinids, Tere- 
bratula pisolithica S. Buckman, Rhynchonella oolithica Davidson and other brachio- 
pods, lamellibranchs and gastropods; at the top is a Coral-bed. 

Next above comes the Lower Freestone, a thick mass of oolitic limestone 
which includes the principal Cotteswold building-stones. This is followed by the 
Oolite Marl, characterized by Terebratula fimbria Sow., and also with a coral-bed 
at top; and this by the Upper Freestone, with Rhynchonella tatei Dav., not so ex- 
tensively quarried as the Lower Freestone. 




Fig. 41. Boulby alum-works, eastern quarry. (R. H. Rastall.) 

6 = Shale of the Estuarine Series 3 = Impure coal; 

5 = Sandstone of the Estuarine Series; 2 = Ironstone; 

4 = Conglomerate; 1, 1, 1 = Alum Shale. 

Reproduced from the Quarterly Journal of the Geological Society vol.61, p. 452, 1905; with the 
permission of the Council and of the author. 

The brachiopod fauna of the Cotteswold Aalenian is strikingly different 
from that of Dorset — a fact that, in conjunction with the very imperfect develop- 
ment of the Aalenian in the intervening region, shows that movements of upheaval 
along the Mendip axis were still in progress, with the result that the northern and 
southern areas were separated. Dundry Hill, although on the northern side of the 
visible Mendip Hills, belongs to the Dorset province. 

Eastwards from the Cotteswolds the Aalenian is also feebly developed, only 
the gcis sum-beds having any wide extension. In Oxfordshire, locally, scissum- 
beds are intercalated between the Vesulian Clypeus-grit and the Upper Lias 
(fibulatum-zone); but in Northamptonshire the marine Scissum-beds (North- 
ampton Sands) are followed sequentially by an estuarine series of sands which 
represent gome part of the upper Aalenian. 

The Northampton Sands are divided into a lower Ironstone series, from 
which is obtained the valuable ironstone for the blast-furnaces of Kettering, Welling- 
borough and other places, and an upper variable series of sands and limestones. 
The Ironstone series has yielded many fossils, including Lytoceras wrighti S. Buck- 
man (Amm. jurensis auct.), Lioceras opalinum Reinecke, Tmetoceras scissum 
Benecke, Astarte elegans Sow., etc. The variable series is but slightly fossiliferous. 

The Lower Estuarine beds consist of very fine white or lightly-coloured sands, 
including beds full of vertical carbonized plant impressions, with some clayey beds 
used for terra-cotta manufacture. 

In the Stamford district these beds are overlain by beds of highly-fissile 
sandy limestone, known as the Collyweston Slate, which is still much prized as 
a beautiful roofing-stone, being even exported to America. This represents the 






Davies: England and Wales. — II. Middle Jurassic. 



(III. 1.) 219 




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highest zone of the 
Aalenian, contains 
many fossils, includ- 
ing Malaptera bentleyi 
Mor. and Lyc, Ger- 
villia acuta Sow., and 
Trigonia pulla Sow. 
Estuarine beds with 
marine sands below 
continue onwards 
through Lincolnshire, 
but little detail is 
known about them, 
until the Yorkshire 
coast is reached. 
There both the Estu- 
arine beds and marine 
sands, though in the 
same relative po- 
sition, appear to be- 
long to higher zones 
than in Northampton- 
shire. The marine 
sands are known as 
the "Dogger", a term 
having reference to 
the concretionary 
masses of sandstone 
which they contain. 

Nerinea cingenda 
Phillips and other 
gastropods, Astarte 
elegans Sow. and 
other lamellibranchs 
are found in the Dog- 
ger. The Dogger is 
much thinner on the 
west (upthrow) side 
of the Peak Fault 
than on the East, and 
rests directly on an 
eroded surface of the 
Alum Shale (Leda 
o v u m beds) (see Figs. 

41 and 42). The Dogger contains locally a bed of magnetic ore, formerly 
mined extensively at Rosedale, but now worked out. 



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Above the Dogger come the Lower Estuarine beds — sandstones with up- 
right Equisetum columnare Brongniart, shales, and occasional coal-seams. In 
part of Yorkshire they contain a marine intercalation, the Eller Beck bed, with 
Astarte minima Phil., and Gervillia acuta Sow. 



1 



220 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

C. Middle Inferior Oolite and Middle Estuarine beds (Bajocian). 

The Bajocian strata of Dorset resemble the Aalenian in their thinness and 
want of continuity. The uppermost zones in particular are largely wanting through 
late Bajocian denudation. In one famous quarry, long closed, a single bed, only 
0.5 m. (2 ft.) thick, contained three zones, each with a distinct and abundant fauna, 
viz. sauzei, Witchellia and Shirbuirnia; and the fauna of the last-named 
is scarcely known from any other locality in England. Like the Aalenian, the 
Bajocian strata of the Sherborne district thicken to the east. 

Characteristic of the discites zone are the earliest species of Sonninia, e. g. 
S. (Euhoploceras) spinifera S. Buckman and the last of the Hildoceratidae, e. g. 
Hyperlioceras discites Waagen; also Belemnites blainv <illei Voltz, Trigonia striata 
Sow., Rhynchonella forbesi Dav., and Terebratula cortonensis S. Buckm.; of the 
post-discites zone, Sonninia ovalis Quenst. and Astarte excavata Sow.; of the 
Shirbuirnia zone, Sonninia fissilobata Waagen and many other of the Gingen 
ammonites; of the Witchellia zone, besides species of the index genus, Emileia 
brocchii Sow., and Lima proboscidea Sow.; of the sauzei-zone, Otoites sauzei d'Orb., 
Sonninia propinquans Bayle, Astarte excavata Sow.; of the blagdeni zone, 
Poecilomorphus cycloides d'Orb., Sphaeroceras brongniarti Sow., and Teloceras 
blagdeni Sow.; and of the niortense zone, Strenoceras niortense d'Orb., Nor- 
mannites braikenridgei Sow., Terebratula phillipsi Morris and Glossothyris curvi- 
concha Oppel. 

Owing to the late Bajocian denudation and consequent overstep of the garan- 
tiana zone, Bajocian beds are not again found until Dundry Hill, near Bristol, a 
famous fossil-locality. Here the discites and post-discites zones are represen- 
ted by grey limestones, 0.4 m. (1 ft. 4 in.) thick, and the Shirbuirnia, 
Witchellia and sauzei-zones by ironshot oolites, respectively 0.475 m. (1 ft. 7 in.), 
0.35 m. (1 ft. 2 in.), and 0.3 m. (1 ft.) thick. Higher Bajocian zones are wanting. 

In the Cotteswolds, the Bajocian strata are limestones, for the most part 
inferior as building-stones to the Aalenian "freestones", and known as "ragstones", 
with some sandy beds. The several "grits" in this and the Vesulian series are mis- 
named, being fragmental limestones, not arenaceous. The Lower Trigonia grit 
receives its name from the abundance of Trigoniae, such as T. sculpta Lycett and 
T. striata Sow. The Gryphite Grit is marked by the presence of Gryphaea 
sublobata (auct. non Deshayes). The beds higher than the Gryphite Grit are 
restricted in geographical distribution, and indeed the whole of the Bajocian strata 
may be locally absent, for they were thrown into a series of gentle folds and planed 
down to a level surface before the deposition of the basal beds of the Vesulian.. 
The separation of the Cotteswold and Dorset areas, as shown by the distinctness 
of the brachiopod-faunas, continued through the Bajocian age as in the Aalenian. 

From the Cotteswolds, no Bajocian strata are found until Northamptonshire 
and Lincolnshire, where the beautifully oolitic Lincolnshire limestone is found, 
yielding famous building-stones at Ketton, Stamford, and elsewhere. The limestone 
attains considerable thickness, only some beds being suitable for building-stone, 
while others make good lime. Probably several zones, from discites upwards, 
are present, but fossils are not abundant, and ammonites and brachiopods are 
very scarce, so that much zonal research remains to be done. Nerinaea cingenda 
Phillips, Ceromya bajociana d'Orb., Pholadomya fidicula Sow. and Pygaster 
semisulcatus Phillips are among the fossils recorded. The Lincolnshire limestone 
forms the very straight and well-jnarked escarpment running north and south 
through the county, breached at Lincoln in a wide gap by the river Witham. 



Davies: England and Wales. — II. Middle Jurassic. 



(III. 1.) 221 



Between Lincolnshire and North Yorkshire 
the overstep of Cretaceous beds conceals the con- 
tinuation of the Bajocian, and in the latter area 
they have an estuarine facies. They constitute 
the Middle Estuarine Series, with marine strata 
at bottom (Millepore Oolite) and top (Scarborough 
Grey Limestone). The "Millepore" Oolite is so 
named, inaccurately, from the abundance of a 
bryozoon, Cricopora straminea Phillips. Lima 
duplicata Sow., and Pygaster semisulcatus Phillips 
are among the other recorded fossils. 

The Middle Estuarine Series are massive 
sandstones and shales, which have yielded an 
abundant flora of ferns and cycads, including 
Pecopteris dentata Lindley and Hutton, Taenio- 
pteris major Lindley and Hutton, Nilssoniacompta 
Phills. , andOtozamites beani Lindley and Hutton. 

The Scarborough Grey Limestone has yielded 
ammonites attributed to the species blagdeni and 
humphriesianum, and though more exact identi- 
fications are desirable, they appear to indicate a 
high Bajocian horizon. Other fossils include 
Belemnites giganteus Schlot., Trigonia costala 
Sow. etc. 



D. Upper Inferior Oolite, Lower Fuller's Earth, 
and Upper Estuarine beds (Vesulian). 

With the beginning of the Vesulian age, a 
widespread depression occurred, and free com- 
munication was once more established between 
the Cotteswold and Dorset areas. The garan- 
tiana beds therefore transgress widely over the 
various divisions of the Bajocian, Aalenian and 
Toarcian and even rest upon the Carboniferous 
limestone at Nunney in the Mendips (Fig. 43). At 
Vallis at the eastern end of the Mendip Hills, the 
truelli zone overlaps the Garantiana zone 
and rests directly upon Carboniferous Limestone, 
while in a few places, the still higher schloen- 
bachi-zone overlaps the garantiana and truelli * 

zones (Chideock and Stoke Knap in Dorset; Chipping Norton in Gloucestershire 
and adjacent parts of Oxfordshire). 

On the Dorset coast, the garantiana beds are thin, richly fossiliferous lime- 
stones, with Astarte (Crassinella) obliqua Deshayes, flat evolute species of Parkin- 
sonia, Garantiana spp., Terebratula sphaeroidalis, auctt., 0.1 m. (4 inch.). On this 
rests the truelli zone, 0.55 m. (2 ft.) of grey limestone, the home of the well-known 
and well-preserved Parkinsonia parkinsoni Sow. and P. dorsetensis S. Buckman; 
Astarte obliqua and Terebratula sphaeroidalis also occur here. The schloenbachi 
zone consists of 1.4 m. (4^2 ft.) of limestone with Parkinsonia schloenbachi 




" " i>; 






MP 






222 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

Schlippe, Terebratula phillipsi Morris, Aulacothyris carinata Lam., Acanthothyris 
spinosa d'Orb., and Echinids such as Collyrites ringens Agassiz and Stomechinus 
bigranularis Lam. Above this are 1.5 m. (5 ft.) of limestone belonging to the zigzag 
zone, with species of Zigzagiceras and Morphoceras. Then a lithological change 
takes place, and the clayey series known as Fullers Earth begins with the fusca- 
zone. At an uncertain height above the base is the 6 — 9 m. (20—30 ft.) thick zone 
of Ostrea acuminata Sowerby, well-exposed at Langton Herring. 

Inland in Dorset, the Upper Inferior Oolite is exposed in the Sherborne 
district, where the lower zones, like those of the Aalenian and Bajocian, thicken 
towards the East. The change from limestone to clay begins some way up in the 
fusca zone; but the evidence of a deep boring at Stowell, farther east, appears 
to show that in that direction this change begins several zones lower. Over a very 
large area, extending from Doulting (south of the Mendips) to the Cotteswolds 
the Upper Trigonia Grit is deposited upon the bored and otherwise eroded surface 
of beds of very various earlier dates. This bed takes its name from the abundance 
of Trigonia duplicata Sow., T. producta Lyc. and other species. It also yields 
Terebratula globata auctt., and Holectypus depressus Leske. 

The higher part of this zone yields a good building-stone (freestone) at Dundry. 
At the base of the truelli zone comes the uppermost of the four Coral-beds of the 
Cotteswolds, with Spiriferina (?) oolithica Moore, Thecidella triangularis d'Orbign y, 
Zellania davidsoni Moore and other microzoa. This bed is found at intervals from 
Stroud to the Mendips. Above this bed, in Somersetshire, comes the valuable build- 
ing-stone of Doulting; but in the Cotteswolds and thence eastwards to Oxfordshire, 
its place is taken by the Clypeus Grit, with finely-preserved specimens of Clypeus 
ploti Klein, also Terebratula tumida Dav., T. cheltensis S. Buckm., T. cotteswold- 
ensis S. Buckm., Nerinaea guisei Witchell. 

From Dorset to Gloucestershire the calcareous beds of the Vesulian are over- 
lain by the clays known as the "Fullers Earth". The true Fullers Earth of economic 
value — a soapy, non-plastic clay, which falls to pieces in water — is limited to a 
small area around Bath. The upper part of the Fullers Earth Clay of Dorset belongs 
to the Bathonian (Bradfordian or Bathian) stage; but only the lower part (fusca- 
zigzag zones) appears to be represented by clay in the Bath and Gloucester district. 
The characteristic fossils of this clay are Rhynchonella smithi Walker, Tere- 
bratula globata auctt., Aulacothyris cucullata S. Buckman, and Ostrea Knorri Voltz. 
Ostrea acuminata Sowerby characterizes a higher horizon — the highest Vesulian 

In passing from the Cotteswolds towards Oxfordshire the Fullers Earth clay 
thins away and is replaced by a sandy limestone, the Chipping Norton Limestone, 
and other sandy beds characterized by Trigonia signata Ac At the same time 
there come in above the limestone a thick series of marly beds characterized by 
Neaera ibbetsoni Morris, Kilvertia (Exelissa) pulchra Lycett, and many other special 
forms. These are the "Neaeran beds" of Walford (1906), and resemble 
those described from l'lndre, France, by Cossmann and Benoist. These beds 
extend into Northamptonshire and Lincolnshire where they directly overlie the 
Lincolnshire Limestone and are the sole representatives of the Vesulian: they 
are known here as the Upper Estuarine beds, and contain in addition to the special 
marine fauna a few freshwater shells such as Cyrena cunninghami Forbes, and 
plant-remains. In Yorkshire the Upper Estuarine series reappears, after being 
hidden by Cretaceous overstep; but here they consist of shales and thick sandstones, 
with ill-preserved plant-remains and freshwater shells only. 



Davies: England and Wales. — II. Middle Jurassic. (III. 1.) 223 

E. The Groat Oolite Series (Upper Bathonian, Bradfordian or Bathian). 

On the Dorset coast a thick, undivided mass of clay, the "Fullers Earth" 
45 m. (150 ft.) intervenes between the thin limestones of the Inferior Ooolite and the 
Forest Marble. The portion of this clay below and including the zone of Ostrea 
acuminata Sowerby, has already been described under the Vesulian stage. The 
overlying clay (Upper Fullers Earth) belongs to the Bradfordian stage and is about 
8 m. (26 ft.) thick. 

About 16 km. (10 miles) inland, an earthy limestone makes its appearance im- 
mediately above the acuminata zone, and forms the base of the Bradfordian. This 
is called the Fullers Earth Rock, and can be traced to the Mendip district; coming 
between two thick clays, it generally forms a distinct feature on the ground. Among its 
fossils are Ornithella ornithocephala J. Sowerby, Ostrea sowerbyi Morris and Lycett, 
0. subrugulosa Mor. and Lyc. Macrocephaliles morrisi Oppel and Teloceras sub- 
contractum Mor. and Lyc. As it is traced northwards, the clay below becomes 
thinner, while that above thickens; it is possible therefore that the Fullers Earth 
rock is not a constant palffiontological horizon, and that the "Upper Fullers Earth 
Clay" of Bath, in which the economic Fullers Earth occurs, may really bo of the same 
age as the Lower Fullers Earth Clay of Dorset: the fossils found in it appear to 
indicate this. Again, ammonites apparently identical with those of the Fullers 
Earth Rock are found in the Great Oolite of Minchinhampton, which has 25 m. 
(83 ft.) of Fullers Earth Clay below it. 

The Great Oolite proper is a mass of oolitic and shelly limestones, in part false- 
bedded, which at Bath attains a thickness of 16m. (50ft.), but in 9.5km. (6miles) to 
the south disappears completely. The exact mode of disappearance is not clear, but it 
is probably due in part to the lateral change of the lower beds into Fullers Earth, 
and in part to the denudation of the upper beds. The limestones include the famous 
Bath stone, a very valuable freestone. Fossils are not very abundant in the Bath 
district, but some beds yield corals such as C alamo phy Ilia, and others Bryozoa and 
small gastropods. Farther north, at Minchinhampton near Stroud, the upper 
beds of the Great Oolite are richly fossiliferous, yielding Purpuroidea morrisi 
Buv., Patella rugosa Sow. and other gastropods, and Teloceras subcontractum 
Mor. and Lyc, and other ammonites, but these last are very rare. In the same 
district the lowest beds begin to take on the character of "Stonesfield Slate", that 
is of fissile, sandy, thin-bedded limestones. This facies is best developed at Stones- 
field in Oxfordshire, where the beds have been worked for roofing purposes from 
the time of the Roman occupation. The presence at Stonesfield of a single ammonite, 
Perisphinctes gracilis J. Buckman, not known elsewhere suggests that a lower zone 
may here be represented. Other fossils include the famous mandibles of small, 
primitive mammalia, Phascolotherium bucklandi Brod. and others; remains of 
Ornilhosauria, Dinosauria and Crocodilian fish teeth — various forms of Ganodus, 
Hybodus, Strophodus, etc.; Belemnites aripistillum Lhwyo, B. bessinus d'Orb.; 
Nerinaea stricklandi Mor. and Lyc. and many other gastropods; Trigonia impressa 
Sow., and many other lamellibranchs; insect-remains and plant-remains. The 
Stonesfield Slate at Stonesfield immediately overlies the Neaeran beds. 

The Stonesfield Slate is not recognisable far north-eastwards from Stonesfield; 
but beds of oolitic and shelly limestone corresponding to the Great Oolite occur 
along the outcrop to Lincolnshire, resting upon the Upper Estuarine beds. They 
are locally quarried for lime or building-stone, but nowhere attain the thickness 
or excellence of quality of the Bath stone. 



224 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

F. Bradford Clay, Forest Marble, Blisworth Clay and Cornbrash. 

On the Dorset Coast, the Upper Fullers Earth Clay is overlain by a very fossili- 
ferous band with Rhynchonella boueti Dav., Ornithella digona Sow. and Dictyothyris 
coarctata Park. This is the equivalent of the Bradford Clay, a zone only seen else- 
where at Bradford-on-Avon in Wiltshire, where it is 3 m. (10 ft.) thick and imme- 
diately overlies the Great Oolite, attached to the surface of which are abundant 
fine specimens of Apiocrinus parkinsoni Schlot. 

Above the Bradford Clay in both places and extending continuously between 
and northwards to Buckingham are beds of thin-bedded, often false-bedded lime- 
stones, sometimes oolitic, alternating with beds of clay. These constitute the "Forest 
Marble", the latter name referring to the fact that some of the limestones are often 
hard and blue and capable of taking a polish, so that they were formerly used as 
ornamental stones, while the first part of the name is taken from the Forest of 
Wychwood in Oxfordshire where this formation is well shown. From among the 
abundant fossils may be mentioned Ostrea sowerbyi Lyc, Chlamys vagans Sowerby, 
Epithyris (Terebratula) marmorea Oppel, and Acrosalenia spinosa Ac In North 
Oxfordshire the lower half of the Forest Marble is all clay and includes a band of 
bright green clay of striking appearance. Marble has been worked at Buckingham, 
but east of that place the whole formation becomes clayey, and is known as the 
Blisworth Clay or Great Oolite clay. This continues along the outcrop into 
Lincolnshire. 

In Yorkshire the Bradfordian appears to be entirely absent, unless represented 
by part of the Upper Estuarine Series, or by the lower part of the Cornbrash. 

The Cornbrash is a clayey limestone, never oolitic, weathering to a brown or 
yellow colour and a very rubbly consistency. It varies from 1 to 9 m. (3 to 30 ft.) in 
thickness, and is easily recognized in the field by its difference from the underlying 
marbles and oolitic limestones of the Great Oolite Series, and the clays and calcareous 
sandstones above. The character of its outcrop depends in large measure on the 
nature of the overlying Kellaways beds: where these are soft clays and sands the 
Cornbrash has a wide extension along the dip-slope of the Great Oolite escarpment, 
and in these cases it weathers down into the rich corn-growing soil, from which 
it takes its name. Where the true Kellaways Bock lies above it, its outcrop is narrow 
and inconspicuous. 

Fossils are abundant. Pholadomya deltoidea Sow., Pseudomonotis echinata 
Sow., Chlamys vagans Sow., Rhynchonella concinna Sow., Waldheimia (Ornithella) 
obovata Sow., Waldheimia lagenalis Schloth., Nucleolites clunicularis Lhwyd, 
and Anabacia complanata Defr. are the commonest. From Yorkshire to Bedford- 
shire and Northamptonshire, Maerocephalites macrocephalus Schlotheim is recorded, 
but not from farther south, while Clydoniceras discus Sow. is found from Dorset 
to Lincolnshire but not from farther north. It is probable therefore that the Corn- 
brash is a deposit the period of formation of which came gradually later in time 
from south to north. 

III. Upper Jurassic. 

Unlike the Middle Jurassic rocks below, which consist mainly of shallow- 
water limestones and sands, and the Upper Cretaceous rocks above, consisting 
mainly of pelagic limestone (chalk), the Upper Jurassic and Lower Cretaceous rocks 
are mainly argillaceous. Between the Cornbrash and the Cenomanian there is 
scarcely any portion of the series that is not represented somewhere in England 
by a deposit of clay. In no place, however, is the whole clayey; everywhere there 
are intercalations of limestone and sandstone, and upon these alternations in lithic 



Davies: England and Wales. — III. Upper Jurassic. (III. 1.) 225 

character was based the original classification of these rocks, which is still adopted 
in England although its imperfections are generally recognized. Since the actual dura- 
tion of each interruption of the general argillaceous deposit varied from place to place, 
the divisions usually recognized have not a fixed time-value, and do not correspond 
strictly to palaeontological zones. On a geological time-scale the terms Kellaways 
Rock, Oxford Clay, Corallian, Kimmeridge Clay, Portland Sand and Stone, Lower 
Greensand and Gault have a different value in different parts of England, and must 
not be equated with such terms as Callovian, Oxfordian, etc., as defined palseonto- 
logically. Thus much of the English Oxford Clay is Callovian, and much of the York- 
shire Corallian is Oxfordian in the sense in which those terms are understood out 
of England. 

In the accompanying table p. 240 — 243, an attempt has been made to correlate 
the Upper Jurassic and Lower Cretaceous strata throughout Great Britain, and I 
must gratefully acknowledge the kind help given to me by S. S. Buckman in the 
preparation of this table. At the present time, however, any such correlation must 
be provisional. In the near future, the number of zones will probably be much 
increased, and many alterations in the correlation made 1 . 

The Upper Jurassic and Lower Cretaceous strata have in general a gentle 
dip to the south-east, and their main outcrop extends in a broad band across Eng- 
land from the coast of Dorset to that of Yorkshire. This general disposition is 
broken across by folds in an east-and-west direction, of which the two most important 
are the anticlines of the Weald and of the Isle of Wight and Purbeck peninsula. 

Considered from the point of view of the conditions of deposition, three areas 
may be distinguished in England  — (1) North Yorkshire, where there is an almost 
unbroken marine sequence from the Cornbrash up to the Chalk; (2) the Weald 
of Kent, Surrey and Sussex, where there is also an unbroken sequence, but where 
the transitional strata from Jurassic to Cretaceous are of fresh-water origin; (3) 
the rest of the outcrop and most of the area where these strata are concealed beneath 
newer systems: here there was a land-area during the time of transition from the 
Jurassic to the Cretaceous period, and consequently there is an unconformity between 
the Lower Cretaceous and Upper Jurassic. This unconformity reaches its extreme 
in Devonshire and under the London area, where Lower Cretaceous strata rest 
upon rocks of Palaeozoic age, the Jurassic strata having been entirely denuded away 
before the Gault transgression. The Upper Jurassic and Lower Cretaceous strata, 
as here described, are thus defined palasontologically: — They begin with the 
re-appearance of an abundant ammonite-fauna, after the very scanty representa- 
tives of the ammonites that characterize the Bathonian; starting with Macro- 
cephalites, soon followed by Cadoceras and Kepplerites, and the typical Cardio- 
ceratids and Cosmoceratids. In the south of England this palaeontological boundary 
corresponds with the top of the Cornbrash, but farther north it gradually splits up 
that formation, until in Yorkshire it appears to be at the base of it. 

At the top, the end of the Lower Cretaceous period ought, on palaeontological 
grounds, to coincide with the almost complete disappearance of the Hoplitidae 
and the incoming of the genus Mortoniceras; but this would involve the splitting 
up of the thin band of Red Chalk, and the separation of the Upper Gault of south- 
east England from the Lower Gault — a separation which no one has attempted 
to express on the map. For convenience, therefore the zone of Mortoniceras ros- 
tratum Sow. is included in the Lower Cretaceous. 



1 While this part is passing through the press an important contribution to the zoning 
has been made by H. Salfeld (1914). Some of his results have been incorporated 
in the text and table of correlation, but it has not been possible to do so fully. 

Handbuch der regionalen Geologie. III. 1. 15 



226 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

The boundary between Jurassic and Cretaceous has been the subject of much 
dispute. In the South of England it is usual to draw it at the level where the more 
calcareous freshwater Purbeck beds are followed by the more arenaceous fresh- 
water Wealden beds, but the flora, the fishes and the reptiles of the Wealden all 
have a Jurassic character. In Yorkshire the line must be drawn somewhere in a 
continuous series of clays, and it has been drawn by Pavlow at the level where the 
Jurassic Olcostephani are replaced by the Cretaceous Hoplitidae — a level not 
marked by any lithic change, and one which splits into unequal parts a well-marked 
belemnite zone. 

A. Kellaways Rock and Oxford Clay. 

The term Kellaways Rock is applied to beds of calcareous sandstone, either 
resting directly upon the Cornbrash or separated from it by a variable thickness 
of clay (Kellaways Clay). It receives its name from a village in Wiltshire, where it 
was quarried for road-metal in the early years of the nineteenth century and which 
became famous for its fossils. Now these quarries are abandoned, as are the equally 
fossiliferous exposures at Scarborough, and it is only exceptionally that any exposures 
of the rock are found. In Yorkshire the rock-facies extends upwards into higher 
zones than in the more southern localities. Along large parts of the outcrop the 
stone passes into soft sands (in which large rounded masses or "doggers" of concre- 
tonary sandstone may be developed), or thins away altogether. 

The typical Kellaways Rock is highly fossiliferous, some of the most charac- 
teristic species being Cadoceras sublaeve Sow., and other species, Proplanulites 
koenigi Sow., Sigaloceras calloviense Sow., Patoceras calloviense Morris, Gryphaea 
bilobata Sow., Goniomya v-scripta Sow., Ostrea flabelloides Lam., Rhynchonella 
varians Schlotheim. 

The "Kellaways Rock" of Yorkshire includes also the d u nc a n i and a t h 1 e t a 
zones, but elsewhere these are represented by part of the Oxford Clay. Shaley clays 
with compressed nacreous fossils (as at the famous railway-sections, long over- 
grown, at Christian Malford, Wilts.) constitute the jason zone; stiff blue clays with 
pyritic fossils (as at Oxford and Peterborough), constitute the dun can i zone. These 
make up the Lower Oxford Clay. In these clays occur many species of Cosmoceras: C. 
duncani Sow., C. elizabethae Pratt, C. jason Reinecke, &c. At Christian Malford 
remains of Belemnoteuthis antiquus Pearce, were found in which the outline of 
the body is preserved with the ink-bag, arms with horny hooks, eyes, fins, 
funnel etc. 

The middle Oxford Clay is of very uniform character, dark bluish-grey clay 
with some gypsum and many pyritic fossils. Two zones can be recognised; the 
lower, of Peltoceras athleta contains few fossils: Aulacothyris bernardina d'ORB., 
and Gryphaea bilobata Sow.; in the higher, species of Quenstedticeras are the most 
characteristic ammonites: Q. lamberti Sow., Q. mariae d'Orb., and Q. suther- 
landiae Sow., with Creniceras renggeri Oppel, Hecticoceras hecticum Rein., and 
Belemnites hastatus Blv. Recent work shows that these beds contain the characteristic 
fauna of the renggeri-zone of the Jura Mountains. 

The upper Oxford Clay is of similar appearance, but more shaly in places, 
less pyritic and gypseous, the actual shells of the Ammonites being more frequently 
preserved. It contains species of Cardioceras, s. str., but not C. cordatum Sow., 
Perhaps the most characteristic fossil is Gryphaea dilatata auctt., (non Sow.), of very 
large size. Others are Pleuromya recurca Phill, and Modiola bipartita Sow. 

In Yorkshire, only this last zone is represented by clay in the] coast-section, 
though the records of fossils suggest that other zones may take on the Oxford 
Clay facies in some places. 



Davies: England and Wales. — III. Upper Jurassic. (III. 1.) 227 

Occasional bands of septaria, or beds of argillaceous limestone occur throughout 
the Oxford Clay. In the Weymouth district the septaria are of a bright red colour 
with white calcite-veins : they are polished for ornamental purposes. The clays are 
much used for brick-making throughout their outcrop, but especially in the Peter- 
borough district, where the presence of bituminous matter in certain beds was found 
to facilitate greatly the process of burning, and where easy access to London has 
led to the development of an enormous brick-making industry. 

B. Corallian Rocks and Ampthill Clay. 

The Jurassic strata higher than the Oxford Clay have a discontinuous outcrop 
owing to the overstep of Cretaceous beds. From Weymouth to Oxford, wherever 
the next succeeding series is seen, it consists of very variable limestones, sands 
and sandstones, with occasional clays, collectively called the Corallian rocks. 
In the lower portion sands usually predominate, and to this have very generally 
been given the names: "Lower Calcareous Grit" (taken from the Yorkshire se- 
quence) and "zone of Ammonites perarmatus" ; but the ammonites found, usually 
as internal casts, belong to other species of Aspidoceras, such as A. catena Sowerby 1 . 
Among other common fossils of the Lower Corallian are Cardioceras vertebrate Sow. 
Belemnites abbreviates Miller, Ostrea gregaria Sow. 

The Upper Corallian is more calcareous in general character, and at many 
places, such as Steeple Ashton in Wiltshire, corals are very abundant, the limestone 
then being termed "Coral Rag", a term which is often loosely applied to the whole 
Upper Corallian. Other beds are of oolitic limestone, "Coralline oolite", another 
term often used in an equally wide sense. The occurrence of local unconformities, 
pebbles derived from Palaeozoic rocks, and false-bedding, indicate shallow-water 
conditions of deposit. To these strata the term "zone of Ammonites plicatilis" is 
commonly applied, but many species have been included under that name, and 
more careful study is needed. At least the zone of Perisphinctes martelli can 
be recognised. 

Among the most characteristic corals are Thecosmilia annularis Fleming, 
and Thamnastraea arachnoides Parkinson. Echinoids are locally abundant, Calne 
in Wiltshire being a famous locality: Cidaris florigemma Phillips, Hemicidaris 
intermedia Fleming, and Nucleolites scutatus Lam. are common species. Gas- 
tropods also abound locally, such as Pseudomelania heddingtonensis Sow., and 
Nerinaea goodhalli Sow. Lamellibranchs are represented by Pecten articulatus 
Schloth. and Trigonia clavellata, Sow. — the latter especially characterising the 
Trigonia-beds of Weymouth. Exogyra nana Sowerby is enormously abundant 
in some beds. 

At two localities — Abbotsbury near Weymouth (Fig. 44), and Westbury in 
Wiltshire — there occur deposits of oolitic iron-ore which appear to belong to a higher 
horizon than any other Corallian rocks. They are characterised by Waldheimia 
lampas Sow. and contain other species with Kimmeridgian affinities*. 

A few miles east of Oxford, the typical Corallian facies ends abruptly, and 
from thence — except for a local reappearance at Upware in Cambridgeshire 
(Fig. 45) — it is seen no more until Yorkshire. Along the intervening outcrop, the 
Oxford Clay is followed by a grey or black clay with much gypsum, the Ampthill 
Clay. The most characteristic fossil is Ostrea discoidea Kitchin. Usually, as at 
Elsworth and St. Ives, there is a rock-bed with ferruginous oolite-grains at its base, 
and in such cases there are clear indications of a non-sequence. This Elsworth 

1 From information by S. S. Buckman. 

* According to H. Salfeld's recent results, the Abbotsbury ore belongs to the 
cymodoce zone of the Kimmeridgian. 

15* 



228 (III. 1.) 



The British Isles. — III. Stratigraphy. — 10. Jurassic. 



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Davies: England and Wales. — III. Upper Jurassic. (III. 1.) 229 

Rock also underlies the Coralline Oolite of Upware (Fig. 45). It is the base of the 
mart ell i zone, and rests on varying zones of the Upper Oxford Clay. 

Until the ammonites of the Corallian rocks and Ampthill clay have been more 
fully worked out, any correlation, such as that in the accompanying table, must be 
taken as provisional. 

In Yorkshire, the Corallian facies reappears, and a great thickness of strata 
is exposed on the coast and inland. They represent here a longer period of time 
than anywhere else in England: including as they do the whole of the cordatus 
zone below, and probably a part of the serratum zone x at the top. A large number 
of divisions can be recognized, but broadly it may be stated that there are three 
masses mainly of sandstone (the Lower, Middle and Upper Calcareous Grits) sepa- 
rated by two masses mainly of limestone. Both limestones take on a Coral facies 
locally, but more particularly the upper; the usual Coral Rag species being found. 

Oolitic limestones also occur, a famous fossil-bed being that at the base of 
the Upper Limestone at Malton, from which many fine gastropods and lamelli- 
branchs have come. 

C. Kimmeridge Clay. 

In everything except thickness, the Kimmeridge Clay is remarkably uniform 
in character from one end of England to the other. The lower beds are dark 
clays, often gypseous, with occasional phosphatic nodules and septaria and 
bands of argillaceous limestone. The upper beds are distinctly shaly and bitumi- 
nous, often contain lignite, and also contain septaria. On the Dorset coast, a band 
of oil-shale or "Kimmeridge Coal" in these higher beds has been worked, and yielded 
from 30 to 60 litres (85 to 170 gallons) of crude oil per ton, with various by-products; 
but the workings are now abandoned. 

At the base of the Kimmeridge Clay, Rhynchonella inconstansT) A.v.nonSow., 
is abundant. In the next beds above, Ostrea deltoidea, Sow. is the most characte- 
ristic fossil, with Belemnites nitidus Dollfus, and Amoeboceras serratum Sow. 

About the middle, Exogyra virgula Defrance is extremely abundant, though 
it ranges below less plentifully. In the highest portion, Orbiculoidea latissima David- 
son, occurs with ammonites of the pallasianus type. Where Portlandian beds 
of the South-of-England type are present, the upper Kimmeridgian becomes sandy 
and glauconitic and passes upwards gradually into the Portland sands. 

The thickness of the Kimmeridge Clay varies enormously. It is thinnest in 
the Midlands where it probably does not exceed 30 m. (100 ft.) In Yorkshire it is 
three times, on the Dorset coast ten times as thick, while in the Sub-Wealden boring 
near Hastings it attained a thickness of about 380 m. (1250 ft.). 



D. Portlandian of the South of England. 

The Kimmeridge Clay of the Dorset Coast becomes sandy at the top and 
passes up into a series of fine, glauconitic sands, the Portland Sands, among which 
occur beds of calcareous sandstone or sandy limestone. Fossils are not abundant 
in these beds, but Exogyra bruntrutana Thurmann, Trigonia pellati Munier- 
Chalmas, Mytilus autissiodorensis Cotteau etc. may be found. 



1 This is usually called the alternans zone, but Amoeboceras alternans v. Buch 
really belongs to a lower horizon according to Salfeld. 



230 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

Above the Portland Sands comes the Portland Stone series, famous for its 
building-stones; but the actual valuable oolitic freestone layers only amount to 
a thickness of from 3 to 6 m. (10 to 20 ft.), while beneath them are about 9 m. 
(30 ft.) of limestone containing many bands and nodules of black chert. Above 
the freestones is about 1 metre of "roach" — an oolitic limestone full of casts of 
Cerithium portlandicum SowERBYand Trigonia gibbosa Sowerby, used for rougher 
building work. Ammonites attaining a great size characterize the Portland Stone 
series — Perisphinctes giganteus Sowerby, the Freestone beds and P. pseudogigas 
Blake, the cherty series. 

• Inland, in the Vale of Wardour, and the Swindon and Aylesbury districts, 
there are indications of an unconformity between the Lower and Upper Portland 
beds, in the occurrence of a bed of lydite pebbles with phosphatic casts of Portlan- 
dian and Kimmeridgian ammonites and other fossils. At Swindon and Aylesbury 
the Portland sands below this lydite-bed are replaced by a glauconitic sandy clay 
the Hartwell Clay, containing a fauna of distinct character including ammonites 
(Perisphinctes or Virgatites?) of the pallasianus group, Astarte hartwellensis Sow., 
A. saemanni de Loriol, Perna bouchardi Oppel, Waldheimia boloniensis Sauvage 
and Rigaux and others. 

Above the lydite-bed in the Vale of Wardour come the sandy glauconitic 
building-stones of Chilmark, above which come the cherty beds and a diminished 
representation of the freestones of the coast. Farther inland the Upper Portland 
beds become thinner and disappear altogether a few miles north-west of Aylesbury. 



E. Purbeck-Beds. 

This series, mainly of freshwater calcareous strata, is magnificently developed 
on the coast of the so called Isle, more correctly a peninsula, from which it takes 
its name. It is as much as 120 m. (400 ft.) thick, and is divided into three divisions, 
of which the Lower and Upper are purely freshwater and terrestrial in origin, while 
the Middle contains two marine horizons. The presence of the strictly Jurassic 
echinid Hemicidaris in these marine intercalations justifies the reference of the 
whole series to the Jurassic system. 

The Lower Purbeck beds consist of marls and limestones, with many ostracods, 
such as Cypris purbeckensis Forbes, the isopod Archaeoniscus brodiei Milne Ed- 
wards, and freshwater Mollusca including Planorbis fisheri Forbes. At the base 
resting directly on Portland limestone is a "dirt-bed", or ancient soil from which 
rise up the stumps of the fossil cycads which grew in it. A second and more important 
dirt-bed occurs from 2 to 5 m. (6 to 17 ft.) higher. 

These dirt-beds vary much in thickness, never exceeding 0.3 m. (1 ft.), and 
not being present everywhere. Where the basal dirt-bed is wanting, Purbeck and 
Portland limestones may be united in a single block. 

The Middle Purbeck beds also begin with a dirt-bed, which in Durlston Bay 
has yielded jawbones of 24 species of small mammals, including species of Plagiaulax 
and Triconodon. Above come limestones (Lower Building Stones) and cherty beds 
with Chara, insects, ostracods and freshwater Mollusca, followed by the "Cinder- 
bed", an impure limestone composed chiefly of shells of Ostrea distorta Sow., with 
Trigonia gibbosa Sow., and Hemicidaris purbeckensis Forbes. There follow more 
freshwater limestones (Upper Building Stones), after which is a second marine 
intercalation, the Corbula beds, with Corbula alata Sow. and a mixture of marine 



Davies: England and Wales. — III. Upper Jurassic and Lower Cretaceous. (III. 1.) 231 

and freshwater Mollusca. The Middle Purbeck series ends with the "Beef beds", 
dark shales with bands of fibrous calcite ("beef"). Cypridea granulosa Sow., is 
an ostracod strictly confined to the Middle series. 

The Upper Purbeck beds are entirely of freshwater origin, consisting of 
limestones and clays, in which Unio valdensis Mantell and U. compressus Sow., 
are very characteristic stells. Cypridea punctata Forbes, is a very characteristic 
ostracod, though not absolutely confined to the Upper series. An important feature 
is the occurrence of beds of Paludina-limestone or Purbeck marble, with Vivipara 
carinifera Sow. These were extensively worked in the Middle Ages as an ornamental 
stone. The Middle Purbeck limestones are very extensively mined near Swanage. 

The three series, greatly reduced in thickness, re-appear inland in the Vale 
of Wardour, with such characteristic features as the main dirt-bed and the Cinder- 
bed; but in the Swindon and Aylesbury districts the beds are very greatly reduced 
in thickness and neither dirt-beds nor marine intercalations are found. Possibly 
only Lower Purbeck beds are present, but the occurrence at Aylesbury of an uncon- 
formity or contemporaneous erosion within the series, as well as the presence of 
Cypridea punctata Forbes, suggests the possibility of the Middle or Upper beds 
being also represented. A little gypsum occurs in the Upper Purbeck beds of Dorset, 
and in the centre of the Wealden anticline, valuable gypsum deposits have been 
found in the uppermost beds. 



F. Speeton Clay. 

On the Yorkshire coast, the Kimmeridge Clay is followed by another series 
of clays which pass up conformably into the Upper Cretaceous beds. Inland these 
clays rapidly disappear by reason of the Upper Cretaceous overstep, and in Speeton 
Cliff the sequence is greatly obscured by drift and slipping. The fauna also differs 
greatly from any comparable fauna in the south of England. Consequently the 
relations of the Speeton Clay were long imperfectly understood. 

At the base is a thin bed of phosphatic nodules (so called "Coprolite-Bed"), 
in which occur phosphatic casts of Virgatites cf. scythicus Vischniakov, and 
various Olcostephani, with Belemnites magnificus d'Orb, and B. cf. absolutus, 
Fischer. This bed is thus comparable to the virgatus-zone at the base of the Russian 
Volgian. 

Above it come about 10 metres of clay, with several fossil-beds, the whole 
characterized by Belemnites lateralis, Phillips. These are followed by a second 
layer of phosphatic nodules, the "Compound Nodular Band", in which appear for 
the first time ammonites of the family Hopliditae, particularly Neocomites regalis 
Pavlov (Bean MS), and Hoplites amblygonius Neum. and Uhl. With these are 
Olcostephanus gravesiformis Pavlov, Holcodiscus rotula Sow., and Pecten cinctus, 
Sow. Bel. lateralis Phill. still occurs. 

The imperfect understanding of the Speeton section was largely due to con- 
fusion between the two phosphatic bands, coupled with the belief that the nodules 
were derived fossils indicating an unconformity. It appears more probable that 
they only indicate two prolonged phases of non-deposition. The "Coprolite-Bed" 
may thus represent the whole or a large part of the Portlandian age. The clays 
between the two nodule-bands are correlated by Pavlov with the catenulatus- 
nodiger and riasanensis zones of the Volgian of Russia, and the stenom- 
phalus and gravesiformis zones of the Petchorian, which he includes in the 



232 (III. 1.) 



The British Isles.  — III. Stratigraphy. —  10. Jurassic. 



Lower Cretaceous. For the purposes of English stratigraphy it appears more 
convenient at present to take the "Compound Nodular Band" with its new 
hoplitid fauna as the lowest zone of the Lower Cretaceous system, although even 
this, in respect of its belemnites, shows close affinity with the beds below. 



6. Spilsby Sandstone. 

In Lincolnshire the Kimmeridge Clay is surmounted by a bed of phosphatic 
nodules similar to the Lower nodule-bed of Speeton, but upon this rests a sandstone 
(Spilsby Sandstone), which has yielded Belemnites lateralis Phillips, and allied 
species, Craspedites subditus Trautschold, Aucella volgensis Lahusen, and many 
other lamellibranchs. 

Above this Spilsby Sandstone comes the Claxby Ironstone, which will be 
described among the Lower Cretaceous beds later. 



H. The Underground Extension of the Jurassic Rocks in Eastern England. 

(Fig. 46.) 

The exploration of the east and south-east of England by deep borings has 
shown that that area was more or less occupied by land during large portions of 




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Fig. 46. Sketch-map to illustrate the underground distribution of Upper 

Jurassic and Lower Cretaceous rocks inSouth-East England. 

All localities marked are the sites of deep borings (SOU = Southall; RICH = Richmond; 

STR= Streatham; CL = Cliffe). 



the Jurassic period. Thus, nowhere at any great distance from the outcrop are 
Rhaetic, Hettangian or Sinemurian strata known. At Calvert in North Bucking- 
hamshire and Brabourne and Dover in Kent, the oldest Jurassic deposits areChar- 
mouthian (j am e son i zone in the two former places, capricornu zone in the 



Boswell: Scotland. — Lower and Middle Jurassic. (III.l.) 233 

third). Above these Charmouthian beds the sequence is very incomplete. 
Thus at Calvert the lowest zone of the Domerian is at once overlain by a 
high zone of the Vesulian (Chipping Norton Limestone). At Brabourne the 
Domerian is perhaps complete, but only the bifrons and striatulum zones of 
the Toarcian have been recognized, and only 13 m. (43 ft.) of oolitic lime- 
stone intervene between them and the Bathonian. At Dover the sequence is 
perhaps complete up to the falcifer zone but that is at once followed by 8m. 
(27 ft.) of sands, above which come Bathonian limestones. 

In the London district, Bathonian strata (apparently bathonica and 
digona zones) rest directly upon the Old Red Sandstone, and are overlain 
by Cretaceous rocks. 

The Oxford Clay has been found at Dover and Brabourne, and northwards 
to Chatham, but under the London Basin it has been removed by pre-Cretaceous 
denudation. Southwards, higher and higher Jurassic strata come in, the top- 
most member everywhere being incomplete through denudation. Thus at Fred- 
ville Corallian rocks appear, and attain a thickness of over 100 m. (342 ft.) at 
Brabourne. A little north of Dover the Kimmeridge Clay comes in and becomes 
more complete to the south-west, where Portland and Purbeck beds are also 
found. 

Quite apart from this southerly increase in completeness of the sequence, 
there is a marked thickening of the strata from east to west, due to the ori- 
ginal conditions of deposit. Thus the Lower Kimmeridge Clay thickens from 
60 to 100 m. (200 to 340 ft.) in the 16 km. (10 miles) between Brabourne and 
Pluckley; and there is evidence of similar thickening in the other beds. This 
is explained by Lamplugh and Kitchin as due to the accumulation of sediment 
in an area which underwent great depression about a N.W.-S.E. axis to the east 
of Dover. At Dover itself shallow-water, current-influenced conditions persisted 
through a large part of the Jurassic period, indicating that the axis of de- 
pression was approximately coincident with a shore-line. 



b. Scotland. 

I. Lower and Middle Jurassic. 
By P. G. H. Boswell. 

The Jurassic rocks of Scotland occur only in isolated masses on the west 
coast (Skye, Raasay, Mull, Morvern etc.) and on the borders of the Moray Firth 
(Sutherland, Ross, Cromarty and Elgin), and are but the vestiges of the former 
wide extent of the beds. They are usually faulted in among the older rocks, with 
intense crumpling along the junctions, and their preservation is often due to the 
covering of Tertiary lavas. Nearly all the chief zones of the Lias are represented 
on the west coast, where the formation reaches a thickness of 360 m. (1200 ft.), but 
on the east no certain Upper Lias has been identified, though some of the Estuarine 
sandstones and shales of the lower part of the Oolites may belong to this division 
(Judd, 1873, 1878). The chief zones recognized are shown in the table, but recent 
surveying of Mull and the adjacent mainland (Summaries of Progress of the Geo- 
logical Survey 1909 — 1911) has resulted in the recognition of the smaller divisions 
of the system present in England. In the Lower Lias of the Morvern area, which 
consists of 30 m. (100 ft.) of very fossiliferous limestones and shales, surmounted 
by shaly sandstones, bucklandi and obtusus zones have been recognized, 
while in that of Mull, resting on unfossiliferous quartz conglomerate (probably 



234 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

Triassic), the following beds were found: hard shelly limestones, 18 m. (60 ft.) of 
bucklandi zone, rusty micaceous sandstones of semicostatus zone, thick cal- 
careous sandstones representing armatus and capricornu zones, thick white 
sandstones (? margaritatus or algovianum zone), dark shale, 9 m. (30ft.), 
of tenuicostatum and bifrons zones, yielding also D. commune. It is pro- 
bable that much of the Upper Lias is here denuded away, for sandy limestones, 
21 m. (70 ft.), belonging to the Lower Oolites rest upon an eroded surface of the 
former. Index ammonites are sporadic but the following zones are indicated; 
bradfordensis, concava, discites and blagdeni zones, with suggestions 
of sauzei and Dumortieria zones. Ammonites characteristic of scissum zone 
were found in the coast section and Ardnadrochet Glen. 

The lithological characters of the strata are indicated in the table, the "roof 
bed" of the Brora coal being a calcareous sandstone of the age of the Kellaways 
Rock. There are indications of the proximity of a shore line and it seems likely that 
these marine and estuarine deposits of the eastern and western areas were laid down 
in a gulf of the Jurassic sea connected with the English basin by way of North 
Ireland and the North Channel (Jukes Browne, 1911). 

II. Upper Jurassic. 

By A. M. Davies. 

The alternation of marine and estuarine conditions that characterize the 
Middle Jurassic strata of Yorkshire are found in Scotland in the Upper Jurassic 
also. Strata of this age occur along both the east and west coasts, but a much fuller 
sequence is seen on the east coast. Their position on the present coast-line is in no 
way connected with their original littoral character, but is due to the powerful 
faults which have both determined the position of the present coast-line and preserved 
on their downthrow side Mesozoic rocks removed by denudation from the rest of 
the country. The Jurassic land lay to the north, not to the west, of the area of 
deposition. 

On the east coast, the Bathonian coal of Brora is immediately followed by 
a representative of the Kellaways Rock, with many characteristic fossils of the 
koenigi zone. The calloviensis zone, is represented by black shales with 
crushed bivalves such as Nucula nuda Phill. Marine conditions continue through 
the ornatus and renggeri zones. The former is clayey with the usual fossils but 
with an admixture of shallow water forms, the latter sandy and containing plant- 
remains in addition to marine fossils. Among the latter may be mentioned Quen- 
stedticeras sutherlandiae Murch., of which the type comes from Braamberry Hill 
in this area. 

With the cordatus zone estuarine conditions set in, and there is a 
great thickness of sandstones with some seams of coal, but with several marine 
intercalations. 

These appear to be followed non-sequentially by alternations of estuarine and 
marine beds of Kimmeridgian age (serratum and pseudomutabilis zones). 
These include, along with finely laminated argillaceous strata, the so-called "brecciated 
beds", full of angular blocks of Old Red Sandstone often of very large size. Accor- 
ding to Judd, who has given the fullest account of these beds, they indicate the 
occasional occurrence of violent floods, and possibly river-ice was the agent by 
which the large blocks were carried out to sea. 

The highest strata of all are unfossiliferous estuarine sandstones. 

On the west coast of Scotland, only the cordatus-renggeri zones appear to be 
present, represented by dark blue clays with septarian nodules. 



Great Britain. 



Lower Jurassic. 



(III. 1.) 235 



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236 (III. l.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

LOWER JURASSIC 



Stages 


Older 
Zones 


Modern Zones 


Northamptonshire 


Lincolnshire 


Next overlying Stage and Zone 


Aalenian-scissum 




c 
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a 2 

u o 

at 

3 


jurensis 


Dumortieria moorei 


absent 


absent 


Dumortieria sp. 


Phlyseogr. dispansum 


Pseudogr. struckmanni 


Grammoc. striatulum 


B 
« .2 


bifrons 

or 

communis 


Haugia variabilis 


Lillia lilli 


Upper Leda ovum Beds 
4— 7 m. (13— 23 It.) 


Shales with septaria 
11,5 m. (38 ft.) 


Collina brauniana 


Lower and Middle Leda ovum 
Beds 22 m. (72 It.) 


Peronoceras fibulatum 


Unf ossiferous Beds 23 m. 
(75 ft.) 


Shales 
2,5 m. (8 ft.) 


Cymbites subcarinatus 


Upper Cephal.B.(Argill.limest.) 

2 m. (67i ft ) 


serpentinus 


Harpoceras falciferum 


Lower Cephal. Bed 1 m. (3 ft.) 


Shales with septaria 
12 m. (40 ft.) 


Harpoceras exaratum 


Fish Bed (shale and limest. 
0,6 m. (2 ft.) 


annulatus 


Dactyl, tenuicostatum 


absent ? 


Shales with fish and insect- 
limestone 2,5 m. (8 ft.) 


c 
3 

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6 

S 

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aculus 


Tiltoniceras acutum 


Transition-bed 


absent ? 


spinatus 


Paltopleur. spinatum 


Marlstone rock-bed 
0,2 m. (8 in.) 


Marlstone rock-bed 
2—6 m. (6—20 ft.) 


margari- 
talus 


Amaltheus margaritatus 


Clays and limestones 
6— 12 m. (20— 40 ft.) 


Blue and grey micaceous 

sh. w. cementstones-2 — 11 m. 

(6— 36 ft. 


Seguenzic. algovianum 


Sandy micaceous shales 
18— 24 m. (60— 80 ft.) 


a 

3 

s 

■** 
3 

q 
6 
§ 
a 
5 


capricornus 


Aegoceras capricornu 


Clay- 
thickness 
uncertain 


Clays with septaria 18 m. 
(60 ft.) 


henleyi 


Liparoceras striatum 


Ironstone (Pecten bed) 
1,2 m. (4 ft.) 


ibex 


Acanthopleur. valdani 


Clay 
27— 42 m. (90— 140 ft.) 


jamesoni 


Uptonia jamesoni 


armatus 


Deroceras armatum 


raricostatus 


Echioceras raricostatum 


Clay 1 m. 


a 

a 

'C 

3 
S 

fi 


oxynotus 


Oxynoticeras oxynotum 


Clay 6 m. (20 ft.) 


obtusus 


Asteroceras obtusum 


Clay 6 m. (20 ft.) 


turneri 


Arnioc. semicostatum 


Clay 


Frodingham Iron-Ore 
1,5— 9 m. (5— 30 ft.) 


bucklandi 


Coronic. gmuendense 


Argillaceous limestone 
and shales 




Coroniceras rotiforme 


S 

9 

B 
« 

G 
X 


angulatus 


Schlotheimia marmorea 


Waehneroc. megastoma 


Argillaceous limestone 
and shales 50 m. (160 ft.) 


planorbis 


Psiloceras planorbe 


Osirea beds 


1 Shales 6 m. (20 ft.) 


Clays with limestone 
bands 6 m. (20 ft.) 


Pleuromya beds 



Great Britain. — Lower Jurassic. 
ROCKS OF BRITAIN. 



(III. 1.) 237 



Yorkshire 


Scotland 
East Coast West Coast 


Aalenian-murchisonae ? 


Vesulian? 


Aalenian-scissum ? 


absent ? 


absent 


probably present 


Blea Wyke\ Yellow sands 8 m. (26 ft.) 
beds j Grey sands 12 m. (40 ft.) 


absent ? 


absent ? 


Striatulus-sbales 20 m. (65 ft.) 


Shales- 4 m. (13 ft.) + 


absent 


Blue shales with 
nodules, jet and py- 
rites in places 
18— 30 m. (60— 100 ft.) 


Alum Shale 
(grey shale with much 

disseminated 
marcasite27 m. (90 ft.) 


Hard-dark shale 20 m. (65 ft.) 


Jet-rock 7 m. (23 ft.) 


Grey shale 9 m. (30 ft.) 


absent 




absent ? 


Scalpa beds: 
sandy 
limestones 
and calcare- 
ous grits with 
Raasay iron- 
ore 


150m. 
(500 ft.) 


Clevel. Ironstone and Upper Kettleness beds 
9—16 m. (30— 52 ft.) 


Lower Kettleness beds (micaceous sandy shales) 
19 m. (62 ft.) 


Staithes beds (sandy shales) 14 m. (46 ft.) 


Shale with ironstone-doggers 36 m. (120 ft.) 


(Upper zones absent?) 

Dark blue 

micaceous shales 

24 m. (80 ft.) + 


Pabba beds 
sandy 
micaceous , 
shales 


Shales with ironstone-doggers 
40 m. (130 ft.) 


Blue shale with ironstone-doggers 
27 m. (90 ft.) 




Blue shale with sandy bands 13 m. (42 ft.) 


absent ? 


absent 


Shale with limest. bands 2,5 m. (8 ft.) 






Shale with some limestone-bands 17 m. (56 ft.) 


absent ? 


absent 








Shale with thin bands of earth and shelly limestone 
54 m. (180 ft.) 


alternations of sandst. 
a. micaceous shale 27 m. 

(90 ft.) 


limestones and shales 
120 m. (400 ft.) 




Blue shale with limestone-bands 
9 m. (30 ft.) 


Estuarinebeds: sandst. 

shales and thin coals 

120— 150 m. (400-500 ft.) 


Calcareous sandston. with 
coral-bands. 
Ostrea irregularis 
60 m. (200 ft.) 




Blue Clay with limestone-bands 
? 17 m. (56 ft.) 









238 (III. 1.) 



The British Isles. — III. Stratigraphy. — 10. Jurassic. 



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Great Britain. — Middle Jurassic. 



(III. 1.) 239 



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240 (III. 1.) 



The British Isles. — III. Stratigraphy. — 10. Jurassic. 



UPPER JURASSIC AND LOWER 



OQ 

£> 

o 
m 

u 
< 

E- 

H 

o 
PS 

o 

■J 



u 

GO 
GQ 

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SERIES 



ZONES 



Albian 



Aptian 



issi 

0Q £ 



Neocomian 



Purbeckian 
(Aquilonian) 



SSm 



no 



60 



I 3 

s ■» 

5 5 



e 

S » rt 

g-60 

M 



E » 

i 



E 5 = 

05 



•■=•2 o. 
Ill 

05~ 



Mortoniceras 
rostratum 
Sowerby 



Hoplites lautus 
Sowerby 



Hoplites interruptus 
Bruguiere 



Douvilliiceras mammil- 
latum Schlotheim 



Hoplites deshayesi 
Leymerie 

Simbirskites speetonen 
sis Young and Bird 



YORKSHIRE 



LINCOLNSHIRE 



Red Chalk 
9 m. (30 ft.) 



Speeton Clay, A 
(Passage Marls) 2 m. 



Simbirskites subin- 

versus M. Pavlow 

Neocomites regalis 

Pavlow 



Speeton 

Clay, B 

44 m. (145 ft.) 



Red Chalk 
4 m. (13 ft.) 



Carstone 
6—12 m. (20—40 ft.) 



Speeton Clay, 
C 1— 6;24 in. (8u ft.) 

Speeton Clay, 

C 6— 7;5m, (16 ft.) 

Speeton Clay, C8 — 11 



Tealby Limestone 4 m 
(13 ft.) passing south- 
ward into Roach Iron- 
stone It m. (36 ft.) 



NORFOLK 
&c. 



Red Chalk 
1,5 m. (5 ft.) 



21- 



Dl(part), 7,5m. (25 ft.) 1,5—4,5 m. (5—15 ft.) 



Olcostephanus 

gravesiformis 

Pavlow 



Craspedites jragilis 
Trautschold 



Perisphinctes 

giganteus 

Sowerby 

Perisphinctes 

pseudogigas 

Blake 



Perisph. eastlecottensis 

Salfeld 

Perisph. pectinatus 
Phillips 



Speeton Clay, 
D 1—3, 

3 m. (10 ft.) 



Speeton Clay, 

D 4—8, 
8 m. (26 ft.) 



Olcostephanus palla- 
s ianus d'Orbigny_ 
Aulacostephanus 
pseudomutabilis 

de Loriol 

Rasenia cymodoce 
d'Orbfgny 



Coprolite-bed, 
E 0,1 m. (4 in.) 



Kimmeridge 
Clay 

150 m. (500 ft.) + 



Amceboceras serra- 
tum Sowerby 



Upper Calcareous 
Grit 9-14 m. (30-46 ft. 



Tealby Clay 
-25 m. (70—80 ft.) 

Claxby Ironstone - 



Carstone [ferru- 
ginous sandstone] 
12 m. (40 ft.) 
Snettisham Clay 
[marine fossils and 
ferns]0-9m.(0:30ft.) 
Sandringham Sands 
30 m. (100 ft.) 



Spilsby Sandstone 
2—14 m. (6—46 ft.) 



Phosphatic 
nodule-band 



Kimmeridge Clay 
90 m. (300 ft.) 
phosphatic nodules 
at base 



absent 



Kimmeridge 
Clay 



a — 

7*. bO 

5 a 
c 

O 3 



Perisphinctes martelli 
Oppel 



Upper Limestone and 

Coral Rag 
12—15 m. (40— 50 ft.) 

Middle Calcareous 
Grit 5-25m. (16-80 ft.) 



Ampthill Clay 

(selenitic clay) 

7 m. (23 ft.) 



Ampthill 

Clay 
(selenitic 

clay) 



Aspidoceras catena 
Sowerby 



Cardioceras cordatum 
Sowerby 



Lower Limestone 
0—18 m. (0— 60 ft.) 

Passage beds 
0— 12 m. (0— 40 ft.) 

Lower Calcareous 
Grit 15-40m(50-130ft.) 



absent 



absent 



Cardioceras sp. 



Oxford Clay 
6—45 m. (20— 150 ft.) 



£ v bo 
O rt 



Crenic. renggeri Op. 



Peltoc. athleta Phill. 



Cosmocera's duncani 
Sowerby 



*3o 

= 60 
rt tfi H 



Sigaloceras caltoviense 

Sow. 

Propl. koenigi Sow. 



Kellaways 

Rock 

3—30 m 

(10— 100 ft.) 



Oxford Clay 
90 m. (300 ft.) 



Oxford 
Clay 



Macrocephalites 

macrocephalus 

Schlotheim 



Dark Shales 2-3 m.(6-10ft.) 
Hard ferruginous lime- 
stone and calcareous 
shales- 1-3 m. (3-10 ft.) 



Kellaways Rock 

0—1 m 

Kellaways Clay 

6 m. (20 ft.) 

Cornbrash 

1—2 m. (3—6 ft.) 



Kellaways 
Rock 

Cornbrash 

2—6 m. 

(6—20 ft.) 



Great Britain. — Upper Jurassic and Lower Cretaceous. 



(III. 1.) 241 



CRETACEOUS ROCKS OF BRITAIN. 




CAMBRIDGE- BEDFORD- c J^K'NGHAM- WILTSHIRE ' VALE OF WAR- 
SHIRE SHIRE SH1RE SH1RE & BERKSHIRE DOUR. &c. 


Partly absent from 
denudation 

Gault Clay 

30—55 m. 

(100-180 ft.) 


Upper Gault, in 

part removed by 

denudation 

Gault Clay 

45—55 m 

(150— 180 ft.) 


Gault Clay with 

phosphatic nodules 

50—60 m. 

(160— 200 ft.) 


Malmstone and mica- 
ceous sands 37 m. (120 ft.) 


Malmstone and mi- 
caceous sands- Exo- 
gyra columba 
32-36 m. (105-120 ft.) 


Grey Gault Clay 
27— 52 m. (90— 170 ft.) 


Grey sandy mica- 
ceous Gault Clay 
12 m. (40 ft.) 


Brown, yellow and WoburnSands [with rare 
white sands with phos- | Brachiopod limestone] 


Thin basement bed 
0,1 m. (4 In.) 


Thin basement bed 
0.1 m. (4 in.) 


Sands 

10 m. (33 ft.) 


phatie nodules at base. 

H, deshayesi and 

derived Jurassic and 

Lower Cretaceous 

fossils 4-20m (13-65 ft). 


Earth 4m. (I3ft.) in 
middle portion: phosph 
nodules with derived 
Jurassic fossils at base 


Variable sands 0-15m. 
(0-50 ft.) + resting on 
Purbeck, Portland or 

Kimmeridge series 


Faringdon beds (Sponge- 
gravels and sands) 0-30 m. 
(0-100 ft.) Bel.speeionensis, 

resting on Kimm. Clay 


absent 


absent 


Freshwater (Wealden) 
Ironsands of Shotover 
and Brill 15 m. (50 ft.) 
resting on Purbeck or 
. Portland beds 


Purbeck marls and 
thin-bedded lime- 
stone 6 m. (20 ft.) 


Wealden 
Clays 
10 m. (33 ft.) 


Middle and Lower 

Purbeck beds (marls 

and thin-bedded 

limestones) 

4—5 m. (13— 16 ft.) 


Upper Purbeck clays 

and marls 

6 m. (20 ft.) 


Middle Purbeck 

marls and sandstones 

Archaeoniscus 4 m. 


Low. I'urb. limest. shal. 
and dirt-beds 16.5 m. 


Creamy limest. 3,5m. 
(117, rt.) 


Chalky limestone 1 — 2 m 

Oolitic limestone with 

Tri'gom'a-casts 2 m 


Upp. build, stone 3-5m. 
Chalky series, Isastraea 
of>/onga(silicified)2-8m. 
Ragstones2.5 m Lower 
Build, stones (oolitic 
and sandy limest. )5. 5m. 


Sands 1,5 m. (5 ft.) 

Rubbly limest. 2,5 m. (8 ft.) 

Glauconitic sands3m.(10ft.) 

Pebble-bed with 

derived Kimmeridge 

ammonites 


Sands and calcareous 
sandst. 8 m. (26 ft. ) Lime- 
stone ("cockly bed") 2,5 m. 
Pebble-bed with derived 

phosphatic casts 
SwindonClay~4-6 m. (13-20 ft.) 
Marly Sandst. ,E.Bruntrutana 

1-3 m. (3-10 ft.) 
Sands with doggers 12m.(40ft.) 


Pebble-bed 

Portland 

Sands 

12 m. (40 ft.] 


Hartwell Clay [sandy 
glauc] 4 m. (13ft.) + ? 


Upper Kimmeridge 
Clay (bituminous 
shale)Or(>icufoidea 
latissima Exogyra 

virgula 5 in. (16 ft.) 


Upper Kimmeridge 

Clay (shaley, with 

lignite) 15 m. (50 ft.) 

Lower Kinimeridge 
Clay (selenitic) Ostrea 
deltoidea. 15 m. (50 ft.) 


Kimmeridge 
Clay 

90 m. (300 ft.) 


Kimmeridge 

Clay 
(thickness 
uncertain) 


Lower Kiinm. Clay 

black clays, phosphatic 

nodules at base 

Ostrea deltoidea 

38 in. (125 ft.) 


Westbury Iron-Ore 
3 m. (10 ft.) 


Coral Rag 3 m. (10 ft.) 
Oolitic Limestone 
6 m. (20 ft.) + 
Elsworth Rock 
(limestone with 
ferruginous oolite 
grains) 3 m. (10 ft.) 


Ampthill Clay 

18 m. (60 ft.) 

Elsworth Rock 

(inconstant) at 

base 


Ampthill Clay, with 
Elsworth Rock at 

base, passing west- 
wards into Coral 
Rag and Oolite 


Coral Rag, falsebedded 
sands, loamy clay and 

oolitic limestone 
(variable) 10 m. (33 ft.) 


Sandsfoot Clay 7 m. 

Sandy, shelly and 

oolitic limestones 

18 m. (60 ft.) 


absent 


absent 


absent 


Sands and calcareous 
sandstones 5 m. (16 ft.) 


Clays and sands with 

doggers 

8 m. (26 ft.) 


Arni,'roveStone(R/iaxe/(a- 
chert) locally 2 m. (6 ft.) 


Oxford Clay dark 
blue and grey 

clays with bands 

of septaria ; occa- 
sionally with 
much selenite) 

? 150 m. (500 ft.) 


Oxford 
Clay 


Oxford Clay 

120 m 
(400 ft.) 


Upper Oxford Clay 
90 m. (300 ft.) 


Oxford Clay 
125 m. (400 ft.) ? 


Middle Oxford Clay 
30 m. (100 ft.) 


Lower Oxford Clay 
34 m. (110 ft.) 




Kellaways Rock (Cal- 
careous sandst. and 
sands) 3 m. (10 ft.) 


Sands 2 m. (6 ft.) 


Shelly clay 

and 

calcareous sandstone 

19 m. (62 ft.) 




I.'ppi-r part of 

Cornbrash-less 

than 2 — 5 in. 

(6— 16 ft.) 


Kellaways Clay (se- 

enitic) 3 m. (10 ft.) 

Upper part of 

Cornbrash 1 m. 


Clay 0-4 m. (0-13 ft.) 
Upper part of Corn- 
brash less than 4 m. 
(13 ft.) 



Handbuch der regionalen Geologic III. 1. 



16 



242 (III. 1.) The British Isles. — III. Stratigraphy. — 10. Jurassic. 

UPPER JURASSIC AND LOWER 





SERIES 


ZONES 


DEVONSHIRE 


DORSET COAST 


GO 
& 
O 

H 
U 

< 
E-> 
H 
03 
O 

03 
H 

O 
J 


Albian 


fa 

W ■*-» 
Hi rA 

|3 

I| 

E 


Aforfon/ceras 
rostratum 
Sowerby 


Glauconitic Sands with layers 

of chert- 37 m. (120 It.) 

Exogyra conica, Neithea 

i-costata (resting on Lias, 

Trias or Permian) 


Glauconitic Sands with 

layers of stone Ex. conica, 

Neithea i-costata 24 m. (80 ft.) 


Hoplites lautus 

Sowerby 


Sandy Gault 

Clay 

with few fossils 

20 m. (65 ft.) 


Hoplites interruptus 
Bruguiere 




Belemnttes 

bruns- 

vicensls 

Strombeck 


Douvilliiceras mammil- 
latum Scblotbeim 


White and ferruginous 

sands 45 in. (150 ft.) 

Atherfield Clay 

15 m. (50 ft.) 


Aptian 


Hoplites deshayesi 
Leymerie 


Neocomian 


■** £ en 

£ a* 
laS 

a, .O ft 
CO 


Simbirskites speetonen- 
sis Young and Bird 
Simbirskites subin- 
versus M. Pavlow 


Wealden Shales 

Wealden Sands with lignite 

60—600 m. (200— 2000 ft.) 


Neocomites regalis 
Pavlow 


o 

02 
02 
«U 

03 

1-5 

03 
W 
CM 
Oh 

& 


Purbeckian 
(Aquilonian) 


CO 

C a-- 

m 


Olcostephanus 

gravesiformis 

Pavlow 


Upper Purbeck freshwater 
shales and limest., Vivipara, 
Unio, etc 8— 19 m. (26— 62 ft.) 


Middle I'urheck marine and 
freshwater limestones Hemici- 

daris purbeckensis, Ostrea 
distorta.etc. 16-51 m.(52-170ft.) 


Craspedites fragilis 
Trautscbold 


Lower I'urheck marls and 
dirt-beds 27-52 m. (90-170 ft.) 


c 

« 3 © 

o rt 

CM 


© 

rt tin 
O en 

tn 




Perisphinctes 
giganteus 
Sowerby 


Freestones (oolitic lime- 
stones) Perisph. giganteus 

9 iii. (30 ft.) 


Perisphinctes 

pseudogigas 

Blake 


Cherty series (limestones 
with nodules and bands of 

chert) '?u m. (65 ft.) 


Perisph. eastlecottensis 
Salfeld 


Portland Sands (glauconitic) 


Perisph. pectinat. PhiU 


e o 
.2 — 

j? 60 

2 c 
S3 « 

S 3 

•S c 

B0 






Olcostephanus palla- 
sianus d'Orbigny 






Upper Kimmeridge Clay 
(dark bituminous shales 

with cementstones) 
Orb. latissima, Exogyra 
virgula 195 m. (640 ft.) 


M 

a) C ^ 
5 w «5 

3 




Aulacostephanus 

pseudomutabilis 

de Loriol 


Lower Kimmeridge Clay 
Ostrea deltoidea, Rhynch. 
inconstans 120 m. (400 ft.) 




Rasenia cymodoce 
d'Orbigny 


Sandsfoot Grits 
5— 6 m. (16— 20 ft.) 


Amceboceras serra- 
tum Sowerby 


Sandsfoot Clay 8 m. (26 ft.) 

Trigonia beds T. clavellaia 

4,5 m. (15 ft.) 

Osmington Oolite 18 m. (60 ft.) 


© 

;= c 

O 3 

a 

CD 
CO 


o 

o 

g » 

BO 




Perisphinctes martelli 
Oppel 




Aspidoceras catena 
Sowerby 


Bencliff Grits 3 m. (10 ft.) 
Nothe Clay 12 m. (40 ft.) 
Nothe Grits G. dilatata 
auctt. 11 m. (36 ft.) 




Cardioceras cordatum 
Sowerby 


a! 3 O 

|-£ 




Cardioceras sp. 


Upper Oxford Clay (bluish- 
grey clay with red septaria) 
75 m. (250 ft.) 


o 

e - 

o t» 

t) 




Crenic. renggeri Opp. 


Middle Oxford Clay with 

pyritized fossils Bel. hastatus. 
25 m. (80 ft.) ? 




Peltoc. athleta PhiU. 




Cosmoceras duncani 
Sowerby 


Lower Oxford Clav (thin shales with 
fragile fossils) 25 m. (80 ft.) ? 


Is? 

; ■» " 

rt to c 




Sigaloceras calloviense 

Sow. 

Propl. koenigi Sow. 


Clays with occasional calcar. 
sandst. Cadoceras sublaeve, Pro- 
planulites koenigi 25 m. (80ft.) ? 




Macrocephalites 

macrocephalus 

Schlotheim 


? 



Great Britain. — Upper Jurassic and Lower Cretaceous. (III. 1.) 243 



CRETACEOUS ROCKS OF BRITAIN. 



ISLE OF WIGHT 



WEST WEALD 



EAST WEALD 



WEST COAST 

OF 

SCOTLAND 



EAST COAST OF 
SCOTLAND 



Sandstones 18-25 m. 
(60-80 ft.) Sandy mica- 
ceous clay 13-16 m. 
(43-52 ft.) 



Upper Gault Clay 
20— 25 m. (65— 80 ft.) 



Lower Gault Clay 
6 m. (20 ft.) 



Carat. 22 m. (72 ft.) Sand- 
rock Ser.25-57m.(80-190ft.) 
Ferugin. Sands ("Crackers" 
at base) 75-157 m. (250 to 
515 ft.) Atherlield Clay 
(Perna Bed at base) 
18-25 m. (60-80 ft.) 



Fernig.SandsC'Folkestone 
Sands") 30 m. (100 ft.) Bar- 
gate Stone and Pebble-beds 
15 m. (50 ft.)? Sands and 
chert-beds 90 m. (300 ft.) 
AtherfieldClayl8m.(60ft.) 



Wealden Shales 

150 m. (500 ft.) 

Wealden Sandstone 

140 m. (460 ft.) 



Weald Clay 270 m. (900ft.) 

Tunbridge Wells Sands 

115 m. (380 ft.) Wadhurst 

Clay 48 m. (160 ft.) 

Ashdown Sands 150 m. 

(500 ft.) 



Malmstone 40 m. (130 ft.) 
Sandy marls 15 m. (50 ft.) 



Upper Gault Clay 

(pale grey marl, phos- 

phatic nodules at 

base) 24 in. (80 ft.) 



Gault Clay 
30 m. (100 ft.) 



Lower Gault Clay 
(d ark clay) 8 m. (26 ft. ) 

Low. Gaull Clay (dark 
clay, phosph. nodules 
at base) 3,5 m. (lift .) 



Creensand with phosphatic 

nodules 2jn. (6 ft.) 
FolkestT beds 18,5 m. 

(60 ft.) Sandgatebeds 
24,5 m. (80 ft.) Hythe 

beds 18,5 m. (60 ft.) 
Atherfield Clay 8 m. (26 ft.) 



Weald Clay 115 m. 
(38 ft) Tunbridge Wells 

Sands 45 m. (150 ft.) 
Wadhurst Clay 30 m. 

(100ft.) Ashdown 
Sands 120 m. (400 ft.) 



Purbeck beds 
(limestones and shales 

with gypsum) 
up to 170 in. (560 ft.) 



Portland Stone and 
Sand (known only in 
borings) 40 m. (130 ft.) 



Kimmeridge Clay 
(known only in 

borings) 
380 in. (125 ft.) ? 



Corallian rocks 
(known only in 

borings) 
100 m. (330 ft.) 



Oxford Clay 
(known only in 

borings) 
50 m. (160 ft.) 



Dark blue 
clays with 
sectarian 
nodules 
thickness 
uncertain 



Glauconitic sand- 
stone (in glacial drift) 



Estuarine sandstones 
(unfossiliferous) 
35 m. (115 ft.) 



Brecciated beds" coarse 
shelly limestones and ear 
bonaceous shales 170 m. 

(560 ft.) 
Marine and estuarine sand 

stones 130 m. (430 ft.)? 



Limestones, clays and sand- 
stone 60 m. (200 ft.) ? 
Estuarine sandst. with ma- 
rine bands 150 m. (500 ft.) 



Fine grained sandst. 

with plants and marine 

fossils 8 m. (26 ft.) 

Sandy shales 75 m. (250 ft.) 



laminated black 
shales 23 m. (75 ft.) 
calcareous sand- 
stone 2 m. (6 ft.) 



244 (III. 1.) 



The British Isles. — III. Stratigraphy. — 10. Jurassic. 



Zonal Position of the principal Iron- Ores and Building- Stones of the Jurassic Rocks 

of Great Britain. 



Or°e n s: Zone - 


Building- 
Stones. 


Iron- 
Ores. 


Zones. 


Building- 
Stones. 


Upper Purbeck 


/ Purbeck 
\ Marble 


Eller Beck 


concava 
bradfordensis 


Colly weston* 
Painswick 


Middle Purbeck 


Swanage 


Rosedale 


murchisonae 


Cheltenham 


Lower Purbeck 

giganteus 


Portland 


Northampton-| scissum 


Duston 


peudogigas 


Chilmark 




opaliniforme 




pectinatus 






aalensis 




pallasianus 






moorei 


Ham Hill 


pseudomutabilis 






Dumortieria 




Abbotsbury cymodoce 






dispansum 




Westbury pseudocordatus 






struckmanni 




serratum 






striatulum 




martelli 


Oxford 




variabilis 




catena 






mil 




cordatum 






braunianum 




renggeri 






fibulatum 




athleta 






subcarinatus 




o rna t um 






falciferum 




calloviense 






exaratum 




koenigi 






tenuicostatum 




m acrocephal us 




Raasay 


-.acutum 
i ispinatum 




discus 




Cleveland 




marmorea 


Frome.etc. 


Leicestershir 


Hornton 


digona 




Banbury 




bathonica 1 
subcontractum / 


Bath, 




margaritatus 




Corsham etc. 




algovianum 




gracilis 


Stonesfield* 




capricornu 




acuminata 






striatum 




fusca 


BradfordAbbas 




valdani 




zigzag 






jamesoni 




schloenbachi 






armatum 




trueliii 


Doulting, Dun- 




raricostatum 




garantiana 


Cdry 




oxynotum 




niortense 






obtusum 




blagdeni 

sauzei 

Witchellia 


Cotteswolds 


Frodingham 


semicostatum 
gmuendense 1 
rot if or m e 


Hydraulic 
limestone, 
Dorset to 
Nottingham 


Shirbuirnia 
post-discites 






marmorea 


d isci t es 


Lincolnshire 




megastoma 
planorbis 


Sutton Stone 



Bibliography of the Jurassic Rocks of Great Britain. 

1880. Blake, J. F., Quart. Journ. Geol. Soc, vol. 36, pp. 189-236 (Portland Rocks of 
England). 

1877. — and Hudleston, W. H., Quart. Journ. Geol. Soc, vol. 33, pp. 260-405 

(Corallian Rocks of England). 
1887-1907. Buckman, S. S., Mon. Pal. Soc, The Inferior Oolite Ammonites. 
1893. — Quart. Journ. Geol. Soc, vol. 49, pp. 479-522 (Bajocian of the Sherborne 

District). 

1909. — Yorkshire Type Ammonites (in progress). 

1910. — Quart. Journ. Geol. Soc, vol. 66, pp. 52-89 (Certain Jurassic (Lias-Oolite 

Strata of South Dorset), with bibliography of this author's other works. 
1892. Fox-Strangways, C, Mem. Geol. Surv., The Jurassic Rocks of Britain, vols. 1 & 2, 

Yorkshire. 
1873. Judd, J. W., Quart. Journ. Geol. Soc, vol.29, pp. 97-195 (Secondary Rocks of 

Scotland). 

1878. — Quart. Journ. Geol. Soc, vol. 34, pp. 660-743 (Secondary Rocks of Scotland). 

1884. — Quart. Journ. Geol. Soc, vol.40, pp. 724-764 (Jurassic Deposits which 

underlie London). 

1885.  — and Homersham, C, Quart. Journ. Geol. Soc, vol. 41, pp. 523-528 (Deep 

Boring at Richmond, Surrey). 
1889. Lamplugh, G. W., Quart. Journ. Geol. Soc, vol.45, pp. 575-618 (Subdivisions of 

the Speeton Clay). 
1896. — Quart. Journ. Geol. Soc, vol. 52, pp. 179-220 (Speeton Series in Yorkshire & 

Lincolnshire). 

1911. - — and Kitchin, F. L., Mem. Geol. Surv. Mesozoic Rocks in some of the Coal 

Explorations in Kent. 

* Collyweston and Stonesfield yield roofing "slates". 



Bibliography of the Jurassic Rocks of Great Britain. — Cole: Ireland. (III. 1.) 245 

1914. Lang, W. D., Proc. Geol. Assoc, vol. 25, pp. 293-360 (Charmouth). 

1867. Moore, C, Proc. Somerset Archaeol. & Nat. Hist. Soc, vol. 13, pp. 119-244 (Middle 

and Upper Lias of South West of England). 
1856-1858. Oppel, A., Die Juraformation Englands, Frankreichs und des siidwestlichen 

Deutschlands. 
1896. Pavlov, A. P., Quart. Journ. Geol. Soc, vol. 52, pp. 542-555 (Strata between 
. Kimeridgian and Aptian). 

1892. — and Lamplugh, G. W., Bull. Soc. Imp. Nat. Moscow, n. s., vol. 5, pp. 181-276, 

455-570 (Argiles de Speeton et leurs equivalents). 
1908. Pocock, T. I., Woodward, H. B. & Lamplugh, G. W., Mem. Geol. Surv., The 

Geology of the Country around Oxford. 
1904. Richardson, L., A Handbook to the Geology of Cheltenham and Neighbourhood. 
1907. — Quart. Journ. Geol. Soc, vol. 63, pp. 383-436 (Inferior Oolite and Contiguous 

Deposits of the Bath-Doulting District). 
1911. — Proc. Cotteswold Field Club, vol.17, pp. 195-235 (Inferior Oolite and Con- 
tiguous Deposits of the Chipping Norton District). 
1889. Roberts, T., Quart. Journ. Geol. Soc, vol. 45, pp. 545-560 (Upper Jurassic of 

Lincolnshire). 
1914. Salfeld, H., Neues Jahrbuch fiir Min., Beil. Bd. 37, pp. 125-246 (Die Gliederung 

des oberen Jura in Nordwesteuropa). 
1898. Strahan, A., Mem. Geol. Surv., The Geology of the Isle of Purbeck and Weymouth. 
1876. Tate, R. and Blake, J. F., The Yorkshire Lias. 
1902-1905. Thompson, B., Journ. Northampton Nat. Hist. Soc, vol. 13, pp. 55-56, 93-105 

(Junction Beds of the Upper Lias and Inferior Oolite in Northamptonshire). 
1906. Walford, E. A., On some New Oolitic Strata in North Oxfordshire, pp. 1—32, 

Buckingham. 

1893. Woodward, H. B., Mem. Geol. Surv., The Jurassic Rocks of Britain, vol. 3. The 

Lias of England and Wales. 

1894. — Mem. Geol. Surv. The Jurassk; Rocks of Britain, vol. 4. The Lower Oolitic 

Rocks of England (Yorkshire excepted). 

1895. — Mem. Geol. Surv. The Jurassic Rocks of Britain, vol. 5. The Middle and 

Upper Oolitic Rocks of England (Yorkshire excepted). [These Memoirs 

contain complete bibliographies.] 
1857-1878. Wright, T., Mon. Palaeont. Soc. British Fossil Echinodermata from the 

Oolitic Formations. 
1878-1886. — Mon. Palasont. Soc. Lias Ammonites of the British Islands. 



c. Ireland. 

By G. A. J. Cole. 

The only Jurassic strata in Ireland are of Lower Liassic age. Middle Liassic 
fossils bave been found in the boulder-clays of Co. Antrim and even of Co. Dublin. 
In Co. Dublin Hildoceras bifrons of the Upper Lias is also recorded (Tate 1870, 
Sollas and Praeger 1895). These drifted specimens may, however, have come 
from Scottish sources or from the Irish Channel. The Irish beds are all closely 
connected with the protective covering formed by the north-eastern basaltic plateaus; 
but even here only a part of the Lower Lias remains preserved. The epoch of denu- 
dation that prevailed also in parts of England before the Cretaceous strata were 
laid down has destroyed any higher Jurassic beds in Ireland. Lower Liassic 
limestones and shales are well seen on the coast just north of Larne in 
Co. Antrim. The zones that remain are those of Psiloceras planorbis, Schlotheimia 
angulata, and Arietites bucklandi. The lowest beds graduate conformably into 
the Rhaetic marls. At Collin Glen, south-west of Belfast, shales and limestones 
occur under the Cretaceous glauconitic sands, and contain Aegoceras intermedium, 
Gryphaea arcuata, Lima gigantea, and Modiola minima. The zone of Psiloceras 
planorbis is traceable on Cave Hill, and small patches of Lower Lias, much 



246 (III. 1.) The British Isles. — III. Stratig raphy. — 11. Lower Cretaceous. 

squeezed in places by landslide movements, occur at various points round the 
basalt and chalk escarpment (Tate 1863 and 1870). The occurrence of Liassic 
beds near Lough Foyle shows that the Jurassic sea spread as far westward as 
that of Rhsetic days. 

The highly altered calcareous shales of the Lias at Portrush, into which a 
sheet of Kainozoic dolerite has intruded from below, formed the subject of a historic 
controversy between the vulcanists and the Wernerian school. The history of this 
is well summarised by Portlock, 1843. Impressions of ammonites are clearly seen 
at Portrush on the surface of a black flinty rock, which is the product of contact 
metamorphism of the shales. The mineral characters of this rock have been studied 
in detail by Portlock 1843 and others (Lacroix 1893, Cole 1906, Thomson 1907). 

The Jurassic period was mostly marked by elevation in Ireland, and the 
Scottish deposits of the same age again and again suggest the nearness of a shore- 
line. We must not, however, forget the large area over which marine Jurassic strata 
at one time existed in England, and from which they have now entirely disappeared. 
It is very doubful, however, if marine conditions prevailed in the Jurassic period 
in any part of Ireland later than Upper Liassic times. 



Bibliography of the Jurassic of Ireland. 

1906. Cole, G. A. J., Proc. Roy. Irish Acad., vol. 26, Section B, pp. 56-66 (Junction of 

Lias & Dolerite at Portrush). 

1864. Etheridge, R., Quart. Journ. Geol. Soc. London, vol. 20, pp. 112-114 (Lias fossils). 

1893. Lacroix, F. A., Les Enclaves des Roches Volcaniques, pp. 64-65 (Portrush). 

1843. Portlock, J. E., Mem. Ordn. Surv., Report on the Geology of the County of London- 
derry, and parts of Tyrone and Fermanagh. 

1895. Sollas, W. J. and Praeger, R. Ll., Irish Naturalist, vol. 4, p. 326 (Lias fossils 
in Glacial Deposits). 

1864. Tate, R., Quart. Journ. Geol. Soc. London, vol. 20, pp. 103-111 (Lias near Belfast). 

1870. — Quart. Journ. Geol. Soc. London, vol. 26, pp. 324-325 (Middle Lias, North 
East Ireland). 

1907. Thomson, J. A., Geol. Mag., pp. 493-496 (Inclusions in Dolerite of Portrush). 



11. Lower Cretaceous. 
Great Britain. 

By A. M. Davies. 

A. Speeton Clay. 

Above the "compound nodular band", which is taken as the base of the Lower 
Cretaceous at Speeton (Fig. 47) are 36 m. (120 ft.) of clays with Belemnites jaculum 
Phillips and other belemnites of more southerly type than those in the zones 
above and below. Associated with these are boreal ammonites of the genus Sim- 
birskites, by means of which finer zonal divisions have been recognized. In the 
highest zone occurs the southern echinid Echinospatagus cordiiformis Breyn. 
(Toxaster complanatus Ac). Other fossils of the jaculum zone are Exogyra 
sinuata Sow. and Terebratula sella Sow. 



Davies: Great Britain. 



(III. 1.) 247 




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Above the jaculum-zone come 30 m. (100ft.) of clays, 15 m. (50ft.) of 
"Cement-beds" and perhaps 15 m. (50 ft.) of black clay, in all of which Bel. bruns- 
vicensis Stromb., and allied boreal species occur. Hoplites deshayesi Leym., Exo- 
gyra sinuata Sow., Syncyclonema orbicularis Sow. are also recorded from this zone. 
A slightly higher horizon seems to be indicated by a bed of marly clay with Bel. 
fusiformis Voltz, which is followed by marls with Bel. minimus Lister, which in 
turn pass up into the Red Chalk, to be described later. 

The probable correlation of these several divisions of the Speeton Clay is 
shown in the table given on pp. 240 — 243. 



248 (III. 1.) The British Isles. — III. Stratigraphy. — 11. Lower Cretaceous. 

B. Neocomian of Lincolnshire. 

Resting conformably on the Spilsby Sandstone is the highly fossiliferous 
Claxby Ironstone, formerly worked as an iron-ore. Although its lower part is closely 
linked to the underlying beds by having belemnites of the lateralis-gro\i]>, the 
upper part contains Belemnites jaculum Philipps, and ammonites such as Poly- 
ptychites blakei Pavlov, and P. beani Pavlov occur throughout, while Neoco- 
mites regalis Pavlov occurs at least in the upper portion. It is therefore necessary 
to draw the line between Jurassic and Cretaceous either within the thickness of 
this formation or at the base of it. The most abundant fossils are Lamellibranchs, 
e. g. Area raulini Leym., Exogyra sinuata Sow., Pecten cinctus Sow. and Trigonia 
ingens Lycett. Other species are Pleurotomaria neocomiensis, Rhynchonella walkeri 
Dav., Terebratula praelonga Sow., Waldheimia Jamarindus Sow., W. faba d'Orb. 

Above the Claxby Ironstone lies the Tealby Clay, a sandy clay with pyritic 
fossils, which include Belemnites jaculum Phill., Simbirskites umbonatus Lahusen, 
Exogyra sinuata Sow., and Perna mulleti Desh. Not much is known of this clay, 
owing to the infrequency of exposures. 

Above it lies the Tealhy Limestone (replaced to the south by Clay and iron- 
stone). This yields Belemnites brunsvicensis Strombeck, and allied species, Am- 
monites cf. carteroni d'Orb., Pecten (Camptonectes) cinctus Sow., Ostrea (Alectry- 
onia) frons Park., and Exogyra sinuata Sow. 

C. Wealden Beds. 

In the South of England, the lithic change from the limestones and marls of 
the Purbeck to the sandstones of the Wealden beds is very striking, and makes a 
very convenient level for the division-line between Jurassic and Cretaceous. There 
is, however no palaaontological justification for the separation, the freshwater 
fauna and land-flora of the two series being very closely related and having many 
species in common; while there are no marine intercalations in the Wealden by 
which it can be correlated with the typical marine Lower Cretaceous. 

NorthDowns. Lower Greensand Forest. Southern Valley- South Downs. 
N. Escarpment.- - ' — - _____ 3, 




Fig.48. Diagrammatic Section of the Weald. 



h5 = Chalk 

h4 = Upper Greensand 

h3 = Gault 



h2 = Lower Greensand 

hi = Weald clay 

h"' = Tunbridge Wells Sands 



h" = Wadhurst Clay 
h' = Ashdown Sands 
g!4 = Purbeck Beds 



Reproduced from Geology in the Field, the Jubilee Volume of the Geologists' Association 1910, 
p. 435 with the permission of the Council. 

The Wealden beds (Fig. 48) are thickest in the western part of the Weald or 
the concealed area farther west, and thin away in all directions. The lower division 
is mainly sandy, the upper mainly argillaceous. In the typical area, the lower or 
Hastings Sands series is divided into three divisions. The lowest consists of soft 
sandstones or sands (Ashdown sands) with plant remains, including Endogenites 
erosa Mantell. 



Davies: Great Britain. 



(III. 1.) 249 



The middle division of the Lower Wealden is 
the Wadhurst Clay, in which are beds of fossili- 
ferous calcareous sandstone (Tilgate Stone), with 
Iguanodon mantelli Meyer, Hylaeosaurus oweni 
Mantell, Goniopholis crassidens Owen, Lepidotus 
mantelli Ac, and freshwater shells, particularly 
Cyrena media- Sow., and Vivipara fluviorum Sow. 

Towards the base of the Wadhurst Clay occur 
nodules and seams of clay ironstone, which were 
for many centuries worked as iron-ore — the Weald 
of Sussex having long been the chief iron-producing 
district in England, until the utilization of coal in 
iron-smelting led to the migration of that industry 
to the coal-fields. 

The upper division consists of sands in part 
consolidated into sandstones, which often weather 
into very remarkable shapes (Tunbridge Wells 
sands). 

The Upper Wealden or Weald Clay, consists 
of clays and shales with beds of limestone very 
similar to the Paludina limestones of the Purbeck 
beds but with other species of Vivipara — V. sus- 
sexiensis Sow. and V. fluviorum Sow. The more 
shaley beds are full of Ostracods. Other freshwater 
fossils are Vicarya lujana and Unio valdensis Mantell. 

In the Isle of Wight, only the upper portion 
of the Wealden beds is exposed, the lowest visible 
horizon being full of drifted trunks of conifers — the 
"Pine-raft". On the Dorset coast, sandstones are 
the principal rock-type, and they contain much 
lignite. The sandstones become thinner westwards 
and at the same time coarser and more conglo- 
meratic. 

Inland, Wealden beds are exposed in the Vale 
of Wardour (Fig. 49) and again on Shotover and 
Brill Hills near Oxford, where they consist of 
variable sands and clays with rare fossils. 



D. Lower Greensand. 



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The beds which intervene between the Wealden 
and the Gault are still almost universally known in 
England by the unfortunate name of "Lower Green- w 
sand", relic of a time when the importance of the 

Gault was not recognized and it was only looked upon as an intercalation in a 
"Greensand formation". Although sandy facies predominates in these Aptian strata, 
glauconite (the presence of which is implied in the prefix "green") is absent from 
the greater portion. With the beginning of this series marine conditions are again found 
over a large area of south-east England, and at scattered points in the Midlands. 



250 (III. 1.) The British Isles. — III. Stratigraphy. — 11. Lower Cretaceous. 

In the typical locality, near Folkestone, these strata are usually divided into 
four divisions. At the base is the Atherfield Clay, constant over the whole region 
south of the London basin. It yields Perna mulleti Deshayes, as well as many 
fossils common to the next overlying beds. 

The Hythe beds are glauconitic limestones and sandstones with Hoplites 
deshayesii Leym., Trigonia alaeformis Forbes, Exogyra sinuata Sow., and 
Terebratula sella Sow., as their most distinctive fossils. The Sandgate beds are 
glauconitic clays, not separable palseontologically from the Hythe beds. The 
top division, or Folkestone beds consist of light greenish sands with beds of calcareous 
sandstone and chert full of sponge-spicules. The fossils include Avicula pectinata 
Sow., and Waldheimia pseudojurensis Leymerie. 

Traced inland, the Atherfield Clay alone remains constant in lithic character. 
The Hythe beds take the form, now of massive glauconitic limestone (Kentish rag), 
now of thick beds of sponge-spicule-chert, now of unfossiliferous ferruginous sands. 
The Sandgate beds only maintain their distinctness from the Hythe beds here and 
there, particularly near Nutfield, where they include valuable deposits of Fuller's 
earth. The Folkestone beds most frequently take the form of red or white, non- 
glauconitic, unfossiliferous sands, with bands and irregular masses of hard ferru- 
ginous sandstone (carstone). 

In the Isle of Wight, the Atherfield Clay is again found with a very fossili- 
ferous Perna-bed (P. mulleti DeshJ at the base. Above the clay is another highly 
fossiliferous bed, the "Crackers", yielding Gervillia sublanceolata d'Orb., Panopaea 
plicata Sow., Trigonia daedalea Forbes, and Hoplites deshayesii Leym. 

The overlying beds are nearly all sandy, and different fossil-beds are found in 
them characterised respectively by Exogyra sinuata Sow., Macroscapkites gigas Sow., 
Crioceras bowerbanki Sow., and the macrurous decapod Meyeria vectensis Bell. In 
Dorset, the Atherfield Clay is succeeded by white and ferruginous sands, not 
divisible. 

Inland, beds of Aptian age have a very discontinuous outcrop, being over 
wide areas overlapped by the Gault. Thus at Seend, in Wiltshire, ferruginous 
sands occur which have been worked for iron-ore, and contain casts of fossils among 
which Toucasia lonsdalei Sow. is most notable. At Faringdon, in Berkshire, there 
are deposits famous for calcareous sponges, Raphidonema faringdonense Sharpe, 
Peronidella ramosa Roemer, Barroisia anastomans Mantell, Brachiopods, Tere- 
bratella menardi Lam., Waldheimia tamarindus Sow., Terebratula tornacensis 
d'Archiac, Rhynchonella latissima Sow., and Echinids Peltastes wrighti Desor, 
with Belemnites speetonensis Pavlow, and many derived Jurassic fossils. In Bed- 
fordshire, the Aptian sands suddenly attain a great thickness and include valuable 
fuller's earth deposits; and near the base the Faringdon fauna is found with phos- 
phatised Jurassic fossils. The greater part of the overlying sands is quite unfossili- 
ferous, but at one place near Leighton Buzzard there occurs a bed of limestone 
with a much later Brachiopod fauna having Cenomanian affinities. 

These sands, frequently passing into ferruginous sandstone (carstone) and 
having often at the base a bed of phosphatic nodules with derived Jurassic fossils, 
have an almost continuous outcrop from Bedfordshire to Lincolnshire, where there 
underlie them the Neocomian beds already described. As a transition to these, in 
Norfolk, the Snettisham Clay which comes below the Carstone, contains an associa- 
tion of marine fossils and plant-remains that indicates the nearness of a land-surface. 



letres 


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Davies : Great Britain. (III. 1.) 251 

E. Gault. 

The typical locality for the Gault is Folkestone on the Coast of Kent, where its whole 
thickness is clearly exposed in cliff-sections, and minute zoning is possible, as follows 

Upper I zone of Morloniceras rostratum Sow. 
Gault ,, „ Kingena lima Defr. 
(24m.) I ,, ,. Inoceramus sulcatus Park. 
Junction-bed — (clay with nodules) 

zone of Hoplites auritus Sow. (Dark bed) 
„ „ H. denarius Sow. (Mottled Bed) 
Lower „ „ H. lautus Sow. (Coral bed- Smilotrochus) 
Gault „ ,, Dipoloceras delaruei d'Orb. 
(8 m.) Crab bed Palaeocorystes stokesi Mant. 
zone of H. auritus Sow., var. 
„ ,, H. interruptus Brug. 
zone of DouviUiiceras mammillatum Schloth. 

In most of the zones of the Lower Gault, the index-species is not confined 
to its zone but only very abundant in it, and for general zonal purposes only the 
zones given in the table are of value. The mammillatum-zone, consisting of a grit 
with phosphatic nodules, is usually considered as part of the Lower Greensand. 

Fossils, beautifully preserved and often iridescent, are very abundant. From 
the interruptus zone may be mentioned Desmoceras beudanti Brongn., Hamites 
rotundus Sow., and Nautilus bouchardianus d'Orb.; from the lautus zone (in the 
broad sense) various Hoplites, Hamites intermedius Sow., Turrilites hugardianus 
d'Orb., and Nucula gaultina Gard.; from the Upper Gault, Inoceramus sulcatus 
Park., Turrilites bergeri d'Orb.; while Nucula pectinata Sow., and Belemnites 
minimus Lister occur all through. 

Traced inland from Folkestone the Gault varies little in character for a great 
distance, but increases in thickness. With the opening of the Albian epoch, uniform 
marine conditions were re-established over a wide area as they had not been since 
the Kimmeridgian. In all the deep borings under the London district, while the 
beds below the Gault are very inconstant, the Gault maintains itself, only showing 
a tendency to thin away towards the east. Nevertheless when traced far enough, 
either northwards or westwards, it undergoes at last marked lithic changes. 

Northwards, in Norfolk it passes into a very remarkable thin bed, the Red 
Chalk, which separates the white Chalk from the Carstone. This is a foraminiferal 
limestone, with much of the structure of white chalk, but with coarse quartz-grains 
and a brick-red colour. This persists without very great modification as far as 
Speeton. 

Westwards, the Gault overlaps the Lower Greensand in Dorset and rests 
unconformably on Jurassic strata (Fig. 50). At the same time, the "Upper Greensand" 
facies of the strata above the Gault passes downwards through that formation 
itself, so that in Wiltshire, the rostratum zone is a fine sandy, micaceous and 
glauconitic limestone; while in Somerset and Devon, the Blackdown Beds with 
their chert may represent perhaps the whole of the Gault. If not, the Upper Gault 
has here overlapped the Lower. 

F. Lower Cretaceous of Scotland. 

No strata comparable to the Speeton Clay are known in situ anywhere farther 
north than Yorkshire; but in the glacial drift of Moreseat, on the east coast of 
Aberdeenshire, there are abundant remains of a fine glauconitic sandstone with sponge- 
spicules and many other fossils, which indicate the speetonensis zone and 
possibly higher zones also. Among the fossils are Simbirskites aff. speetonensis Young 



252 (III. 1.) The British Isles. — III. Stratigraphy. — 11. Lower Cretaceous. 

and Bird, Crioceras duvalii Lev., Cardium raulinianum d'Orb., Plicalula placunea 
Lam., Rhynchonella sulcata Park., and Galerites castanea Brong. The last- 
named fossil, though in the same matrix as the rest appears to indicate an Upper 
Cretaceous horizon. It is possible that the Upper Jurassic strata of Sutherland 
may, in their submarine extension, be followed by Lower Cretaceous. Upper 
Cretaceous erratics have also been found in the glacial drift of Caithness. 



6. Underground Extension of Lower Cretaceous Rocks. 

Many borings in search of water or coal have been made in the London Basin 
and the Weald, and much is now known of the underground extension of these strata. 

Gault. This has been proved to be everywhere present under the London basin, 
but to thin rapidly eastwards in the Harwich district. In the absence of zonal obser- 
vations it is not possible to say whether this thinning is due to overlap of the higher 
zones, or to thinning of all the zones. Over a large area north of the Thames, the 
Gault rests directly on the Palaeozoic rocks which formed the land surface in Port- 
landian and Neocomian times. 

Aptian. In view of the continuity of outcrop from Leighton Buzzard to the 
Wash, and all round the Weald, it was at one time anticipated that it would be 
found to be continuous under London and was looked to for a supplementary water- 
supply to that from the Chalk. This expectation was disappointed, and the occur- 
rence of Aptian beds under the London basin is as sporadic and variable in thickness 
as in the area to the west. 

Wealden. These beds thin out and disappear with startling rapidity to the north 
of their outcrop. They have not been met with in any one boring in the London 
basin. They also become thin under the Chalk of north-east Kent, being only 
11 m. (36 ft.) thick at Fredville and only 5 m (16 ft.) at Ropersole (see Fig. 46, 
p. 232.) 



Bibliography of the Lower Cretaceous Rocks of Great Britain. 

1910. Herries, R. S., Geol. Assoc. Jubilee Vol., Geology in the Field, pp. 433-449 (The 

Weald). 

1900. Jukes-Browne, A. J. (with contributions by W. Hill), Mem. Geol. Surv. Cre- 
taceous Rocks of Britain. Vol. I. The Gault and Upper Greensand of England. 

1883. Keeping, W., The Fossils & Palaeontological affinities of the Neocomian Deposits 
of Upware and Brickhill. 

1889. Lamplugh, G. W., Quart. Journ. Geol. Soc, vol.45, pp. 576-618 (Speeton series 
in Yorkshire and Lincolnshire). 

1911. — and Kitchin, F. L., Mem. Geol. Surv. Mesozoic Rocks in some of the Coal 

Explorations in Kent. 
1913. Seward, A. C-, Quart. Journ. Geol. Soc, vol. 69, pp. 85—116 (Wealden Plants). 
1898. Strahan, A., Mem. Geol. Surv. The Geology of the Isle of Purbeck and Weymouth, 

pp. 122-142. 
1889. — and Reid, C, Mem. Geol. Surv. Geology of the Isle of Wight. 2 n< l Ed. 
1875. Topley, W., Mem. Geol. Surv. The Geology of the Weald. 
1907. Treacher, Ll., Proc. Geol. Assoc, vol. 20, pp. 115-121 (Excursion to Faringdon). 

1910. White, H. J. O., Geol. Assoc. Jubilee Vol., Geology in the Field, pp. 215-224 (Berk- 

shire, Faringdon beds, etc.). 

1911. Woodward, A. S., Quart. Journ. Geol. Soc, vol. 67, pp. 278 — 281 (Wealden 

Mammals). 



12. Upper Cretaceous. — White: Great Britain. — England. (III. 1.) 253 



12. Upper Cretaceous. 

a. Great Britain. 

By H. J. Osborne White. 

By British geologists the Upper Cretaceous strata of the United Kingdom are 
usually taken to comprise those beds of Cretaceous age which lie above the base 
of the zone of Douvilleiceras mammillatum, that is to say, the Selbornian (Gault 
and Upper Greensand) and Chalk formations. In the following article however, 
we adopt the Continental usage, and place the lower limit of the Upper Cretaceous 
at the base of the Cenomanian stage, including in that stage the ill-defined and 
impersistent zone of Pecten asper. The several divisions and sub-divisions of the 
Upper Cretaceous, as thus limited, and their salient lithological features in divers 
parts of Great Britain, are shown in the accompanying comparative table 
(pp. 262—263). 

The Upper Cretaceous series has its chief development in the south of England, 
where, by surface outcrop and underground extension, it occupies the greater part 
of the country that lies to the south-east of a line drawn from West Dorsetshire 
to the inlet of the Wash. A second tract, separated from the first by the Wash, 
occupies the area of the Lincolnshire and Yorkshire Wolds; and other tracts, of 
smaller dimensions, are found in Argyllshire, in the West of Scotland. 



A. England. 

In this country the prevailing dip of the Cretaceous rocks is to the east, at low 
angles, but the general inclination is interrupted by a series of late Tertiary folds, 
whose axes have a roughly westward trend. These disturbances are most pro- 
nounced to the south of the River Thames, and there the Upper Cretaceous beds 
in many places have been removed from the anticlines, exposing the Lower Cre- 
taceous and older strata as inliers, or as embayments of the Upper Cretaceous 
boundary line. The largest of these denuded areas is that of the Weald of Kent 
and Sussex, while the principal embayments occur in the Vales of Wardour, War- 
minster, and Pewsey. 

Cenomanian. The zone of Pecten asper and Cardiaster fossarius (3 to 18 m., 10 to 
60 ft. thick) comprises a group of sandy beds, sometimes termed the "Warminster 
Beds", from their markedly fossiliferous character in the Vale of Warminster, in 
Wiltshire. In that locality they are about 5.5 m (18 ft.) thick, and consist of 
glauconitic sands with chert and siliceous rock (cherty sandstone) composed 
largely of sponge spicules. 

The Pecten asper Beds are confined to the south-western and south-central 
counties, from the Isle of Wight to Buckinghamshire. They are doubtfully represented 
at the south-western angle of the Weald, but are absent in Kent and eastern Sussex. 
In Wiltshire and the Isle of Wight they pass up into the glauconitic marl ("Chloritic 
Marl") of the Schloenbachia varians zone, but in Devonshire and Dorsetshire their 
upper limit is an erosion-surface, by which they are clearly marked off from the 
overlying Chalk. 



254 (III. 1.) The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 







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White: Great Britain. — England. (HI. 1.) 255 

1 

Among the common or characteristic fossils are Doryderma benetli Hinde, 

Hallirhoa costata Lam., Pachypoterion robuslum Hinde, Cardiaster fossarius Benett, 

Epiaster lorioli Wright, Discoidea subucula Klein, Rhynchonella dimidiata Sow., 

Pecten asper Lam., P. galliennei d'Orb., Exogyra columba Lam. E. digitata J. Sow. 

The zone of Schloenbachia varians (1 to 50 m., 3 to 160 ft.) varies in litho- 
logical character but consists generally of grey, fissile marls, alternating with 
layers of hard grey chalk. In the northern counties (Yorks. and Lincolnshire) 
the marls occur only in thin seams. Beds of compact siliceous chalk with nodules 
of impure flint occur in Wiltshire and Berkshire, and similar nodules, with nuclei 
of pure black flint, are present in light-grey homogeneous chalk on this horizon 
in Dorsetshire. 








Fig. 52. View of a coprolite pit near Horningsea (now closed) 

a = Gault; b = Cambridge Greensand; c = Chalk Marl. 

Reproduced from the Memoirs of the Geological Survey of the United Kingdom. 

Cretaceous Rocks of Britain, vol.2, p. 194, 1903; with the permission of the 

Director and of H. M. Stationery Office. 



At the base of this zone, and included in the range of S. varians J. Sow., is 
the sub-zone of Stauronema carteri, an arenaceous, glauconitic chalk, ranging up 
to 5 m. (17 ft.) in thickness, and commonly termed "ChloriticMarl". The distinctive 
siliceous sponge is of sporadic occurrence in the southern counties and has not been 
recorded north of the River Thames. Tb^> well-known "Cambridge Greensand", 
on this horizon, contains many derived fossils (Albian) in a phosphatized condition 
and pebbles of older rocks, and rests on an eroded surface of the Gault. The 
derived fossils here comprise upwards of 200 species of Invertebrata, about one- 
third of which have not been recognized elsewhere in England. Among the com- 
moner Albian forms are Terebratula biplicata J. Sow., Plicatula gurgitis Pict. and 
Roux, Hoplites auritus G. Sow., Mortoniceras rostratum, J. Sow. Bones and teeth 
of many reptiles (Ornithosauria, Dinosauria, Ichthyopterygia, Crocodilia, Chelonia), 
and of a few birds also occur, the great majority being derivative. (Rastall 1909, 
Jukes-Browne, 1900 — 04 and Mem. Surv. 1880.) In Devonshire the zones of S. 
varians and Holaster sub-globosus are represented by a quartziferous limestone 
(1 to 12 m., 3 to 40 ft.) which has been termed the zone of Mantelliceras mantelli 
J. Sow. The fossils of the S. varians zone include: Plocoscyphia labrosa T. Smith, 
Stauronema carteri Sollas, Rhynchonella grasiana d'Orb, R. mantelliana J. de C.Sow., 
R. martini Mant., Pecten elongatus Lam., Aucellina gryphaeoides J. de C.Sow., 
Metacanlhopliles rotomogensis Brong., Schloenbachia coupei Brong., S. varians 
J. Sow., Baculites baculoides Mant., Scaphites aequalis J. Sow., Turrilites costatus 
Lam., Nautilus deslongchampsianus d'Orb. 

The zone of Holaster subglobosus (12 to 36 m., 40 to 120 ft.) is of a more constant 
lithological type than the zone below. From Yorkshire southward to the valley of the 
Thames its base is marked by a bed of hard gritty chalk known as Totternhoe Stone. 



256 (III. 1.) The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 

Farther south,where this stone is absent, the lower limit of the zone is rather indefinite, 
the marly beds with S. varians passing up into a firmer and more massive grey 
chalk in which S. varians becomes rare. The grey chalk is succeeded by firm chalk 
of a lighter tint, often almost white ; and this arrangement holds good over most of 
south-eastern England, though with much variation in the thickness of the grey 
and white beds. In the Isle of Wight and Dorsetshire, however, the grey beds are 
wanting, and the zone consists of massive white chalk; while in Lincolnshire and 
Yorkshire the lower parts consist of rough greyish chalk, in regular beds separated 
by seams of grey marl. 

Throughout the English Chalk-country the highest beds of the zone are laminated 
grey marls (1 to 5m., 3 to 16ft.), which, from the frequent presence of Actinocamax 
plenus be Blain., have been termed the Act. plenus or "Belemnite" Marls. Intercalated 
in the marls there is often a definite bed of hard white chalk. Characteristic fossils 
of the Hoi. subglobosus zone are: Cidaris bowerbanki Forbes., Discoidea cylindrica 
Lam., Holaster subglobosus Leske, H. trecensis Leym., Of f aster sphaericus Schlut., 
Haploceras austeni Sharpe, Actinocamax plenus de Blainv. Holaster trecensis Lehm. 
is especially characteristic of the upper beds (Bower and Farmery 1910). 

Turonian. By most British geologists this stage in England is considered to 
comprise the zones of Rhynchonella cuvieri and Terebratulina gracilis var. lata only. 
In the present article we follow the Continental geologists and include in this stage 
the zone of Holaster planus. 

Zone of Rhynchonella cuvieri and Inoceramus labiatus (3 to 25 m., 10 to 80 ft.). 
This is typically a hard white or cream-coloured chalk, largely nodular. Thin 
partings of grey marl are a common feature. The nodular character is most marked 
at the base of the zone, and the lowest beds, over the greater part of the Chalk 
country, form a band of hard nodular limestone (1,5 to 9 m., 5 to 30 ft.) known 
as Melbourn Rock. This rock is thickest in Kent and Sussex and has there been 
described as the "Grit Bed". In north-western Norfolk, Lincolnshire, and York- 
shire it is indistinguishable from the rest of the zone. Scattered flints occur in the 
higher beds of this zone, but are seldom abundant. The thickness of the Rh. 
cuvieri beds is usually about 18 to 25 m. (60 to 80ft.), but decreases northward 
to about 3 m. (10 ft.) in Yorkshire. A noteworthy instance of local thinning is seen 
at Hooken Cliff, near Beer, in Devonshire, where the zone dwindles from 8 m. (25 ft.) 
to nothing in a distance of about 100 m. (330 ft.). Fossils: Serpula avita J. de C. 
Sow., (habitually attached to shell of Inoceramus labiatus). Cardiaster pygmaeus 
Forbes, Discoidea dixoni Forbes (= D. minima Ac), Rhynch. cuvieri d'Orb., 
Inoceramus labiatus Schloth., Acanthoceras cunningtoni Sharpe, Pachydiscus 
peramplus Mant. 

The zone of Terebratulina lata (9 to 65 m., 30 to 210 ft.) possesses a fairly uniform 
character in the southern counties. It consists of rather soft, white to greyish-white, 
massive chalk, with occasional thin layers of grey marl. Flints occur in the 
upper beds but are thinly disseminated, except in Devonshire where they are 
abundant. From Cambridgeshire northward they are of common occurrence, and 
in Lincolnshire and Yorkshire, where the chalk is very hard, they are found in well- 
marked beds. The upper limit of the Terebratulina lata zone is marked by no 
persistent feature, though in parts of Southern England it coincides with, or closely 
approaches, the base of the Chalk Rock (described below). Fossils: — Conulus 
subrotundus Mant., Discoidea dixoni Forbes, Hemiaster minimus Agas., Micraster 
cor-bovis Forbes, Terebratulina lata Ether., Inoceramus brongniarti J. de C. Sow., 
Ostrea vesicularis Lam., Prionotropis woolgari Mant. 



White: Great Britain. — England. 



(III. 1.) 257 



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Zone of Holaster 
planus. In recent me- 
moirs of the Geological 
Survey of England and 
Wales this zone, as lately 
defined by A. W. Rowe 
(1900), is described as 
the lowest member of 
the "Upper Chalk" — a 
division which includes 
the Upper and Lower 
Senonian stages. Its 
thickness ranges from 5 
to 37 m. (16 to 120 ft.). 
Save in the counties of 
Norfolk, Lincoln, and 
York (where it is usually 
a homogeneous, hard, 
white chalk) it is marked- 
ly nodular or lumpy. 
Flints are everywhere 
present, in the upper 
half, at least, and in 
Lines, and Yorks. these 
chalcedonic concretions 
occur in tabular masses, 
some exceeding 0,3 m. 
(1 ft.) in thickness. Along 
the main outcrop bet- 
ween North Dorsetshire 
and Cambridgeshire the 
zone contains, at or near 
its base, a hard cream- 
coloured limestone (0,3 
to 3,5 m., 1 to HVsft.) 
with green phosphatic 
nodules and grains of 
glauconite. This hard 
bed — the Chalk Rock 
— is best developed in 
the counties of Berks 
and Oxford. Where the 
Chalk Rock is present the 
peculiar faunule of the 
Heteroceras reus- 
s i a n u m subzone is con- 
fined to it. Where the 
rock is absent this fau- 
nule has a greater ver- 
tical range, but is usually 
limited to the lower half 
ofthe Hoi. planus zone 



o coo m m < 




Handbuch der regionalen Geologie. III. 1. 



17 



258 (III. 1.) The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 

(e. g. Hampshire, Kent). In most of the southern counties, however, and in Lincolnshire 
and Yorkshire, the Reussianum fauna is either absent or very poorly represented. 
The upper limit of the Hoi. planus zone is occasionally marked by a thin layer of 
hard yellowish chalk, with or without green nodules. At Southerham, near Lewes 
(Sussex), the lower beds of the zone are strongly phosphatic (Strahan 1896). 

Characteristic fossils of the Hoi. planus zone are Ventriculites mammillaris 
T. Smith, Pentacrinus agassizi v. Hag., Cyphosoma radiatum Sorig., Echinocorys 
(Ananchytes) scutatus Leske, (gibbous form), Holaster placenta Ac, H. planus 
Mant., Micraster cor-bovis Forbes, M. leskei Desm., M. praecursor Rowe (a group- 
form including M. beonensis, normannia, cayeusi, Rowe 1899), Terebratula carnea 
J. Sow., T. semiglobosa J. Sow., Spondylus spinosus J. Sow., Ostrea proboscidea 
d'Arch. (in Yorkshire), Pleurotomaria perspectiva Mant., Solariella (Turbo) gem- 
mata J. Sow. 

The subzone of Heteroceras reussianum contains the above-named fossils with 
the following additional forms; — Arctica quadrata d'Orb., Trapezium trapezoidale 
F. A. Roemer, Cuspidaria caudata Nilss., Emarginulina sanctae-catharinae Passy, 
Avellana cf. humboldti Muller, Natica vulgaris v. Reuss., Turbo geinitzi Woods, 
Baculites bohemicus Fritsch., Crioceras ellipticum Mant., Heteroceras reussianum 
d'Orb., Scaphites geinitzi d'Orb., etc. (Woods 1896 — 7). 

Lower Senonian. The zone of Micraster cor-testudinarium (12 to 36 m., 40 
to 115 ft.) is a white to yellowish chalk, with nodular layers which are frequently 
conspicuous in the south of England but are wanting in the north-eastern counties. 
Rands of flint-nodules and continuous layers or veins of flint are abundant. 

Fossils: — Serpula cincta Goldf., S. ilium Goldf., Echinocorys scutatus Leske 
(gibbous forms), Holaster placenta Ac, Micraster cor-testudinarium Goldf., M. 
praecursor Rowe (of a characteristic form), Cidaris serrifera Forbes, Cardiaster 
cotteauanus d'Orb., Rhynchonella reedensis Eth., Inoceramus lamarcki Park. 

The zone of Micraster cor-anguinum (50 to 95 m., 165 to 320 ft.) is typically a 
white, soft chalk with regular bands of nodular flint. In Yorkshire, however, the 
lower third of the zone alone contains flints. Fossils: Cidaris clavigera Koenig, 
C. sceptrifera Mant., C. perornata Forbes, Conulus albogalerus Leske, Echinocorys 
scutatus Leske (ovate forms), Epiaster gibbus Lam., Hagenowia rostrata Forbes, 
(usually rare, but abundant in Yorkshire), Micraster cor-anguinum Leske, 
Thecideum wetherelli Morris, Crania ignabergensis Retz, Inoceramus cuvieri J. de 
C. Sow., /. digitatus J. de C. Sow., /. involutus J. de C. Sow (in lower part 
of zone), Exogyra sigmoidea v. Reuss (rare), Lima (Plagiostoma) hoperi Mant., 
Ostrea normaniana d'Orb., Actinocamax westphalicus Schlut. 

Zone of Marsupites testudinarius (12 to 64 m., 40 to 210 ft.). In the pure white 
chalk of this zone flints are relatively scarce in the South of England, and are absent 
in Yorkshire. Marsupites testudinarius v. Schloth. (— M. ornatus, etc.) is con- 
fined to the upper half (approximately) of the zone, the lower half being characterized 
by remains of Uintacrinus sp. Phosphatic chalk occurs on these horizons at Taplow 
(Buckinghamshire) and Winterbourne (Berkshire), the abnormal lithological con- 
dition accompanying a decrease in the thickness of the zone and certain modifi- 
cations in its fauna (White and Treacher 1905, 1906). Fossils: Porosphaera 
globularis Phill. (large), Caryophyllia cylindracea v. Reuss, Echinocorys scutatus 
Leske, special forms (Brydone 1911/12), Bourgueticrinus ellipticus Miller (nipple- 
shaped calyx), Marsupites testudinarius v. Schloth., Uintacrinus sp., Terebratulina 
rowei Kitchen, Ostrea semiplana Mant., O. wegmanniana d'Orb., Actinocamax 
granulatus de Blainv. (upper beds), A. verus Miller (lower beds). 



White: Great Britain. — England. 



(III. I.) 259 



The zone of Actinocamax quadratus and Offaster pilula (60 to 122 m., 200 to 
400 ft.) is usually a soft white chalk in which flints are more numerous than in the 
zone below, save in Yorkshire where, like the Marsupites zone, it is flintless. The 
base of the A. quadratus zone is phosphatic at Winterbourne (Berkshire). It is 
probable that the highest part of the phosphatic chalk of Taplow belongs to this 
division. 

Fossils : Coeloptychium 
agaricoides Goldf. and many 
other sponges in Yorkshire, 
Coelosmilia laxa Ed w. , Echino- 
corys scutatusLESKE, (gibbous 
and other forms, Brydone 
1911/12), Offaster pilula Lam., 
Inoceramus lingua Goldf. (in 
Yorkshire), Ostrea lateralis 
Nilss. (striate form), Actino- 
camax granulatus deBlainv., 
A. quadratus Defr., Pachydis- 
cus leptophyllus Sharpe, Sca- 
phites binodosus Roem. (upper 
beds in Yorkshire). 

Upper Senonian. Zone of 
Belemnitellamucronata (144m., 
480 ft., Isle of Wight.) This 
zone appears to be confined 
to the southern parts of Dor- 
setshire, Wiltshire, Hamp- 
shire, and the south-western 
end of Sussex ( ?), in the south 
of England, and to Norfolk and 
Suffolk in the east. It is nor- 
mally a soft white chalk with 
numerous flints which often 
attain great dimensions. Verti- 
cal columns and vase-shaped 
concretions of flint, termed 
"pot-stones" and "paramoud- 
ras", are a notable feature 
of this zone in Norfolk. Fossils: 
Terebratula carnea J. Sow., 

Rhynchonella limbata 
Schlot., R. plicatilis var. 
octoplicata J. Sow., Crania co- 
stata G. B. Sow., Magas pumi- 
lus J. Sow., Cidaris pleracantha Ac, C. serrata Desor., Cardiaster ananchytis Leske, 
Echinocorys scutatus Leske var. pyramidatus (and other characteristic forms), 
Belemnitella lanceolata Schlot., B. mucronata Schlot. 

The zone of Ostrea lunata (33 m., 110 ft.?) is found only at Trimingham near 
Cromer, on the coast of Norfolk. On the shore at Trimingham R.M. Brydone (1908) 

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260 (III. 1.) 



The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 




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recognises five distinct beds, 
which are, in ascending order, 
— (a) Lower grey chalk, 3.5 m. 
(12 ft.); (b) Lower white 
chalk, with 0. lunata Nilss., 
6 m. (20 ft.); (c) White chalk 
without 0. lunata, 2.5 m. 
(8 ft.) ; (d) Upper white chalk 
with 0. lunata, 3 m. (10 ft.); 
(e) Upper grey chalk, 7.5 m. 
(25 ft.). There is a discordance 
between beds (d) and (e) which 
may be due to faulting. The 
exposures are small and the 
beds are much disturbed, 
largely, if not entirely, by 
glacial agencies in post-Plio- 
cene times. Characteristic 
fossils are : Pentacrinus bronni 
Hag., Serpula canteriata 
Hag. (quadrangular form), 

Thecideum vermiculare 
Schloth. , Terebratulina 

gisei Hag.. T. gracilis 
Schoth. (type), Ostrea lu- 
nata Nilss., Nautilus bellero- 
phon? Lindgr. 

B. Scotland. 

Small relics of Upper 
Cretaceous strata, of the Irish 
type, are preserved under 
Tertiary lavas in the Morvern 
District of Argyllshire and 
the adjacent island of Mull. 
On the shores of the inlet 
called Loch Aline, and on the 
lower slopes of the hills Beinn- 
y-Hun and Beinn-y-Hattan, 
J.W. Judd (1878) made out 
the succession shown in the 
last column of the table p. 
261. The glauconitic sands at 
the base of the section 
contain Pecten asper Lam., 
P. orbicularis J. Sow., Exo- 
gyra conica J. de C. Sow., 
Nautilus deslongchampsianus 
d'Orb., etc. They probably 
represent the zones of Pecten 
asper and Schl. varians. The 



White: Great Britain. — Scotland. (III. 1.) 261 

succeeding White Sandstones with coal are unfossiliferous. A. J. Jukes-Browne 
(1902) suggests that they are homotaxial with the zone of Ostrea (Exogyra) 
columba in Ireland. The Turonian and Lower Senonian seem to be unrepresented. 
In the White Chalk above are Belemnitella mucronata and Inoceramus sp. The 
highest sandstones, etc., may be of either Cretaceous or Eocene age. 

Detached masses of hard chalk occur in an agglomerate occupying a Tertiary 
volcanic neck in the Island of Arran. They contain Porosphaera globularis, Ino- 
ceramus, Bryozoa, and other remains, and are most probably of post-Turonian age 
(Peach, Gunn, and Newton, 1901). Pebbles of chalk, and flints containing Seno- 
nian fossils, occur in the Pleistocene deposits of Aberdeenshire, and have been 
dredged from the Moray Firth. 

C. Physiographical Conditions. 

Little is known concerning the geography of the British area in Upper Creta- 
ceous times. The wide-spread transgression which commenced in Albian or earlier 
ages was continued, without important interruption, in the Cenomanian, and by the 
close of that age the greater part of England, north-eastern Ireland, and Western 
Scotland were submerged. Cornwall and western Devonshire, and part of the 
Welsh upland, probably were promontories of a western land which included the 
south of Ireland ; while the Pennine uplands, together with much of Scotland, may 
have been a peninsula connected with a westward extension of the Scandinavian 
massif. The Irish and Scotch sediments of the time were laid down in shallower 
water than the English, but they contain no truly littoral deposits. 

The Turonian chalks mark an increase in the depth of the sea, so far at least 
as the English area is concerned, though both the lithology and fauna of the 
Heteroc. reussianum beds suggest a temporary shallowing of the water 
towards the close of this stage. 

The submergence reached its maximum in Lower Senonian times, when it 
is probable that almost all the British area was under water. Except in Scotland, 
where the highest beds are sandstones, there are few indications of the great regres- 
sion with which the Cretaceous period came to an end. The record is everywhere 
abrupty broken off with the Senonian, the thoroughly marine Cretaceous beds being 
covered unconformably by the fluvio-marine sediments of the Eocene in England, 
and by the lava-flows of that period in Scotland and Ireland. 

D. Economic Products. 

The building material most extensively employed is flint. The nodules 
of this substance are much used in construction of churches, small dwellings, and 
garden walls, and are usually only roughly faced or left untrimmed. Architectural 
flint-work is seen at its best in Norfolk, where the art of "flint-knapping" has been 
practised from time immemorial. The hard grey chalk known as Totternhoe Stone 
is worked in Bedfordshire, Hertfordshire, and Cambridgeshire. Beer Stone, from 
the Rhyn. cuvieri zone of Beer and Sutton in Devonshire, has been much used 
in the west of England. In Berkshire and Buckinghamshire the soft, regularly- 
jointed beds of the Tereb. lata zone have been employed, to a small extent. 

The lime made from the Turonian and superior chalks is usually of the com- 
mon or "light" kind; stronger, "hydraulic" limes are got from the more argilla- 
ceous Cenomanian beds. "Portland" cement is manufactured from the latter beds 
in Hertfordshire, Bedfordshire, and Cambridgeshire, and from mixtures of Turonian 
and younger chalks with alluvial clays in Kent and Sussex. Whiting or whitening 
is made by levigating the soft Senonian chalks. 



262 (III. 1) 



The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 



COMPARATIVE TABLE OF THE 

England 



Stages 


Zones 


Sub-zones 


Kent 


Isle of Wight 


South Dorset 


q 


Ostrea lunata 










Belemnitella 
mucronata 






White chalk with 
flints, 
144 m. 
(480 ft.) 


White chalk with 

flints, 

76 m. 

(250 ft.) 


q 

'£ 
o 
a 

<o 

u 
O 

►5 


Actinocamax 

quadratus 

and 

Offaster pilula 






White chalk with White chalk with 

flints and veins flints and veins 

of marl, of marl, 

122 m. H7 m. 

(400 ft.) (385 ft.) 


Marsupites 
testudinarius 


Marsupites 


White chalk with 

few flints, 

15 m. (50 ft.) 


White chalk with 

flints, 

14 m. (46 ft.) 


White chalk with 

flints, 

9 m. (30 ft.) 


Uintacrinus 


ditto, 

9-25 m. 

(30 to 82 ft.) 


ditto, 
11 m. (36 ft.) 


ditto, 
24 m. (80 ft.) 


Micraster 
cor-anguinum 




White chalk 

with flints, 

85 m. 

(278 ft.) 


White chalk, no- White chalk, no- 
dular at base, dular at base, 
with flints, with flints, 
94 m. 51-73 m. 
(308 ft.) (170-240 ft.) 


Micraster 
cor-testudinarium 




White and yel- 
lowish chalk with 
flints, 
17 m. (56 ft.) 


White and light whit nodular 
red nodular chalk cha ii , v iUi fM Us 
with flints, Chdlk 15 ^ , 3 h n ^ lnts ' 

(52V, n.) < 50 - 110 «W 


c 
flj 
c 
o 
E 
3 
P 


Holaster planus 




Nodular chalk 
with flints 




Heteroceras 
reussianum 


ditto (with reus - 
"i an u m fauna) 


dular chalk with lar chalk with 
flints, flints, 
18 m. 6-17 m. 
(60 ft.) (20-56 ft.) 




Nodular chalk, 

flints, total 10.5 m. 

(35 ft.) 


Terebratulinalata(T. 

g. var. lata) and 

Inoceramus 

brongniarti 




White chalk, 

partly nodular, 

with marl seams 

and few flints, 

50 m. (164 ft.) 


White nodular 
chalk with marl 
veins. (Green no- 
dules and few 
flints near top), 
19 m. (62 ft.) 


White chalk with 
marl seams and 

few flints, 
9-17 m. 

(30-56 ft.) 


Rhynchonella cuvieri 

and 
Inoceramus labiatus 




White chalk with 

nodular beds: 
"Grit-bed" (10 m) 

at base, 21 m. 
(70 ft.) 


White nodular 
chalk, 
27 in. 

(90 ft.) 


White nodular 

chalk, with few 

flints at top, 

13-22 m. 

(42-72 ft.) 




c 

s 

o 
a 
S 



Holaster 
sub-globosus 

and 
H. trecensis 


Actinocamax 
plenus 


Yellow-grey marl, 
1.8 m.-(6 ft.) 


Grey marl, Grey marl, 
2 m. (6'/i ft.) , 2 m. (6 ft.) 




White and grey 

chalk, 
36 m. (120 ft.) 


White and grey Grey marly chalk, 
marly chalk, 15-30 m. 
30 m. (100 ft.) (50-100 ft.) 


Schloenbachia 
varians 




Grey marl and 

marly chalk, 
20 m. (65 ft.) 


Grey marly obaik. £g SttlS? 

(80-1 on ft 1 flints ' 8 " 12 ■"• 
(80-120 ft.) (26 _ 4() f , j 


Stauronema 
carteri 


Glauconitic 

("Chloritic")marl, 

to 5 m. (16 ft.) 


Glauconitic marl, 
3 m. (10 ft.) 


Glauconitic marl, 
1 m. (3 ft.) 


Pecten asper 

and 

Cardiaster fossarius 




(wanting) 


Glauconitic marly 

sand with chert, 

7 m. (23 ft.) 


Glauconitic sand 

and calcareous 

sandstone, 

8 m. (26 ft.) 




Underlying strata 




Gault clay 
(Albian) 


Sandstone 
(Albian) 


Green sands 
(Albian) 



White: Great Britain. 



(III. 1.) 263 



BRITISH UPPER CRETACEOUS STRATA. 

England 



Scotland 



Devonshire 



Wiltshire 



Berksh.&Oxfordsh. 



Norfolk 



White chalk with 

flints, 

30 m? 

(100 ft.) 



White chalk with 

flints, 

90 m? 

(300 ft.) 



White chalk with 

flints, 

15 m? (50 ft.) 



ditto, 
15 m? (50 ft.) 



White chalk with 

flints, 

60 m? 

(200 ft.) 



White chalk with 

few flints 

(Berkshire), 

15 m. (50 ft.) 



White chalk with 
few flints (Berk- 
shire), 10 m. 
(33 ft.) 



ditto, 
10 m. (33 ft.) 



White chalk with 

flints, 

60 m. 

(200 ft.) 



White and grey 
chalk with flints 
(of Trimingham), 
33 m? (110 ft.) 



White chalk with 
big flints C'para- 

moudras"), 
76 m? (250 ft.) 



White 
chalk 
with 
flints, 

125 m? 

(410 ft.) 



Yorkshire 



White chalk with 

seams of marl 

("Zone of Ino- 

ceramus lingua"), 

100 m? 

(330 ft.) 




White chalk with 
marl seams, 
36 m. (120 ft.) 



ditto, 
26 m. (85 ft.) 



White chalk with 
nodular beds, marl 
seams, and flints, 
15 m. (50 ft.) 



Grey-white nodu- 
lar chalk with 
flints, 
12-18 m. 

(40-60 ft.) 



White chalk, no- 
dular in lower 

part, with flints, 
15 m. (50 ft.) 



Greyish nodular 
chalk with flints. 
Chalk Rock (with 
reussianum- 
fauna) near base, 
total 9 m. 
(30 ft.) 



White chalk, no- 
dular at base, 
with flints, 
15 m. (50 ft.) 



White 
chalk 
with 
flints, 

105 m? 

(350 ft.) 



Nodular chalk. 

Chalk Rock (with 

reussi an u m- 

fauna) at base, 

total 5-6 m. 

(16-20 ft.) 



White and greyish 

chalk with marl 

seams, 

6-46 m. 

(20-150 ft.) 

White chalk, part- 
ly nodular, with 
flints in places, 
0-24 m. 
(0-80 ft.) 



White and greyish 

chalk (nodular at 

top) with marl 

seams and few 

flints, 

15-30 m? 

(50-100 ft.) 



Grey marl (local), 
1 m. (3 ft.) 



White nodular 

chalk, 

Melbourn Rock 

at base, 

15-20 m. 

(50-65 ft.) 

Grey marl, 
30 cm. (1 ft.) 



White and greyish 

chalk, with marl 

seams and few 

flints near top, 

30 m. (100 ft.) 



White chalk with 
flints, 
15 m? 
(50 ft.) 



Glauconitic sand 

and calcareous 

sandstone ("Zone 

of Acanthoceras 

mantelli), 

1-12 m. 

(3-40 ft.) 



White and grey 

chalk, 
24 m. (80 ft.) 



White nodular 

chalk. 

Melbourn Rock 

at base, 

18 m. (60 ft.) 



Grey marl and 
white chalk, 
1.5 m. (5 ft.) 



Grey marly and 
siliceous chalk, 
48 m. (160 ft.) 



Glauconitic marl, 
2 m. (6 ft.) 



calcareous sand- 
stone and sand 
with chert, 
21 m. (70 ft.) 



Green sand and 

sandstone with 

chert, 

6 m. (20 ft.) 



White and grey 

chalk, Tottern- 

hoe Stone at base, 

24 m. (80 ft.) 



White chalk with 

marl seams and 

few flints near 

top, passing down 

intonodularchalk 

with Melbourn 

Rock at base, 

30 m? 

(100 ft.) 



"Zone of Hage- 
novia rostrata", 
comprising white 
chalk with flints 
49 m. (160 ft.) 
overlying white 
flintless chalk, 
30 m. (100 ft.) 

White chalk with 
marl seams and 

flints, 
36 m. (120 ft.) 



White chalk with 

flints, 

37 m. (120 ft.) 



White chalk with 

flints, 

64 m. (210 ft.) 



Grey marl, thin. 



Grey marly chalk, 
42 m. (140 ft.) 



Glauconitic marl, 
1 m. (3 ft.) 



Glauconitic marl 
and sand, 

5-8 m. 
(16-26 ft.) 



Grey and white 

chalk, Tottern- 

hoe Stone at base, 

10-15 in. 

(30-50 ft.) 



Yellowish chalk 
with marl seams, 
3.5 m. (117. ft.) 



Grey marl 
("Black-band"), 
0.5 m. (1 ft. 6 in.) 



Grey marly chalk. 

glauconitic 

at base, 

6-23 m. 

(20-75 ft.) 



White marly no- 
dular chalk, Tot- 
ternhoe Stone at 
base, 12 m. 
(40 ft.) 



Grey nodular 
chalk with white 
or yellow lime- 
stone at base, 
7-20 m. 
(23-65 ft.) 



(wanting) 



(wanting) 



White 
sandst. 

with 
seam of 

coal, 
9-30 m. 
(30 to 
100 ft.) 

Glauco- 
nitic 
sands 
and 
calca- 
reous 
sand- 
stone, 
6-18 m. 
(20 to 
60 ft.) 



Sand or clay 
(Albian) 



Green sands 
(Albian) 



Gault clay 
(Albian) 



Gault or "Red 
Chalk" (Albian) 



"Red Chalk" 
(Albian) 



Jurassic 



264 (III. 1.) The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 

For manuring or "dressing" soils deficient in calcium carbonate, all the softer 
kinds of chalk, the Chloritic Marl, and the calcareous sands of the Pecten asper 
zone, are freely used, though not to so large an extent as in former times. Phos- 
phatic nodules have been dug for agricultural purposes from the Chloritic Marl 
in Cambridgeshire and Surrey, but the few local phosphatic beds of Turonian and 
Lower Senonian age have as yet been put to no economic use. 

For road-making, flints from the Chalk and cherts from the P. asper zone 
are commonly used : also the limestones known as Melbourn Rock and Chalk Rock, 
and other hard chalks of more local occurrence. 



Bibliography of the Upper Cretaceous of Great Britain. 

1910. Bower, C. R. and Farmery, J. R., Proc. Geol. Assoc, vol. 21, pp. 333-359 (Lincoln- 

shire). 

1908. Brydone, R. M., Quart. Journ. Geol. Soc, vol. 64, pp. 401-412 (Trimingham). 
1912. — The Stratigraphy of the Chalk of Hants. 

1911. — and Griffith, C, The Zones of the Chalk in Hants. 

1878. Judd, J.W., Quart. Journ. Geol. Soc, vol.34, pp. 660-743 (West Scotland). 
1900-1904. Jukes-Browne, A. J. (with contributions by W. Hill). Mem. Geol. Surv. 
The Cretaceous Rocks of Britain, vols. 1-3. 

1909. — Student's Handbook of Stratigraphical Geology, Second Ed., pp. 491-525. 

1911. — Building of the British Isles, Third Ed., pp. 291-335. 

1901. Peach, B. N., Gunn, W. and Newton, E. T., Quart. Journ. Geol. Soc, vol.57, 
pp. 228-229, 238-243 (Rocks in neck of volcano in Arran, South-West Scotland). 

1881. Penning, W. H. and Jukes-Browne, A. J., Mem. Geol. Surv. The Geology of the 
Neighbourhood of Cambridge, pp. 11-72. 

1909. Rastall, R. H., Geol. Assoc, Jub. Vol., Geol. in the Field pp. 153—158 (Cam- 
bridge Greensand). 

1899. Rowe, A. W., Quart. Journ. Geol. Soc, vol.55, pp. 494-545 (Evolution of Mi- 
craster). 

1900-1908. — Proc. Geol. Assoc, vol.16, pp. 289-367; vol.17, pp. 1-76; vol.18, 
pp. 1-51; vol.19, pp. 193-296; vol.20, pp. 209-328, 336-339 (Chalk Zones). 

1900-1908. Sherborn, C. D., Proc. Geol. Assoc, vol. 16, p. 368; pis. 9-10; vol. 17, pis. 1-10; 
vol. 18, pis. 1-13; vol. 19, pis. 17-40; vol. 20, pp. 328-335, 340-352, pis. 8-23, 
Maps A-F (Cliff sections). 

1896. Strahan, A., Quart. Journ. Geol. Soc, vol. 52, pp. 463-473 (Phosphatic Chalk, Lewes.) 

1905. White, H. J. O. and Treacher, Ll., Quart. Journ. Geol. Soc, vol. 61, pp. 461-494 

(Phosphatic Chalk, Taplow). 

1906. — — Quart. Journ. Geol. Soc, vol. 62, pp. 499-522 (Phosphatic Chalk, Winter- 

bourne and Boxford). 
1896-1897. Woods, H., Quart. Journ. Geol. Soc, vol. 52, pp. 68-98, vol. 53, pp. 377-404 
(Chalk Rock Fauna). 

1912. — Quart. Journ. Geol. Soc, vol. 68, pp. 1-20 (Evolution of Inoceramus). 

Geological Survey of England and Wales. 
District Memoirs: 

Isle of Wight (C. Reid & A. Strahan), 2 nd Ed. 1889. 
Isle of Purbeck & Weymouth (A. Strahan). 1898. 
Explanations of Sheet Memoirs, New Series: 

254. Henley-on-Thames and Wallingford (A. J. Jukes-Browne & H. J. Osborne 
White). 1908. 

267. Hungerford and Newbury (H. J. Osborne White). 1907. 

268. Reading (J. H. Blake and H. W. Monckton). 1903. 

282. Devizes (A. J. Jukes-Browne). 1905. 

283. Andover (A. J. Jukes-Browne). 1908. 

284. Basingstoke (H. J. Osborne White). 1909. 

298. Salisbury (C. Reid & others). 1903. 

299. Winchester and Stockbridge (H. J. Osborne White). 1912. 

300. Alresford (H. J. Osborne White). 1910. 

311. Wellington & Chard (W. A. E. Ussher & others). 1906. 

314. Ringwood (C. Reid & others). 1902. 

315. Southampton (C. Reid). 1902. 



Cole: Ireland. (III. 1.) 265 

316. Fareham and Havant (H. J. Osborne White). 1913. 

317. Chichester (C. Reid & others). 1913). 

326. Sidmouth & Lyme Regis (H. B. Woodward & others). 1906, 2 nd Ed., 1911. 

328. Dorchester (C. Reid). 1899. 

329. Bournemouth (C. Reid). 1898. 
332. Bognor (C. Reid). 1897. 

334. Eastbourne (C. Reid). 1898. 
See also Jukes-Browne, A. J., Penning, W. H. 



b. Ireland. 
By G.A.J. Cole. 



The Cretaceous rocks of Ireland possibly include at their base some represen- 
tative of the Albian stage; but they are practically all of Upper Cretaceous age. 
It is impossible to say how far they once spread over the Irish area. A high outlier 
remains on Slieve Gallion in Co. Londonderry, and the eastern escarpment of the 
beds is traceable, under basalt, southward into the north of Co. Down. But the 
Cretaceous strata clearly owe their preservation to the capping of Kainozoic lavas, 
and at one time must have covered a far wider stretch of country (Jukes-Browne, 
1911 p. 333). The abundant flints in the superficial deposits of south-eastern Ireland 
(Mem. Geol. Surv. 1879), and those on the west coast, as on Inishbofin, probably 
represent the waste of Senonian strata. Dredgings have shown, moreover, the 
presence of chalk, as well as flint, in depths of about 1000 m. (500 fathoms) off 
the coast of Kerry (Cole and Crook 1908 — 9). 

A large part of the flints that occur so freely in the gravels of Co. Wexford 
were probably derived from the western extension of the strata which once lay 
over Devon and Cornwall. 

In the north-east, the beds rest on an eroded land-surface of Middle Cretaceous 
times, so that Lower Jurassic, Triassic, Carboniferous, and Dalradian rocks are 
found in various places immediately underlying the deposits of the Cretaceous sea. 
The general succession in Co. Antrim is as follows (Tate 1865; Barrois 1876; 
Hume 1897; Jukes-Browne and Hill 1900): 

5. White Limestones (hard chalk) with flints; sometimes 
conglomeratic at base, with quartzite pebbles ("Mulatto 
stone"). 30 m. (1 00 ft.), where thickest. Belemnitella mucronata 
abundant. 

4. Glauconitic white or pinkish limestone, with numerous 
sponge-remains (= "Chloritic Chalk"). About 3 m. (10 ft.) 
Actinocamax verus, Echinocorys gibbus. 

nian in upper part" 3 " Yeuow glauconitic sands (= "Chloritic Sandstones"). 

Mainly Cenomanian:! About 3 m " (10ft > £ *W™ columba. 

Cenomanian ' 2- Yeuow Sandstones, often cherty. About 8m. (26ft.) Alec- 

{ tryonia carinata. 

Cenomanian. Possibly II. Glauconitic Sands, of a deep green colour. About 3m. 

Albian in lower part. \ (10 ft.) Exogyra conica. 

The Glauconitic Sands at the base are often very largely composed of glauco- 
nite. They contain Pecten asper, Pecten orbicularis, Janira quinquecostata, Exogyra 
conica, Thetis sowerbyi, Belemnites ultimus. 

The Yellow Sandstones above are somewhat barren in fossils; Alectryonia 
carinata, Janira quadricostata and Acanthoceras rothomagense are recorded. The over- 
lying sands, which contain more glauconite (formerly regarded as chlorite), are 
characterized by Rhynchonella schloenbachi, Exogyra columba, Pecten asper, 
Janira quinquecostata, and the crustacean Callianassa. The upper beds of these 



Senonian 



266 (III. 1.) The British Isles. — III. Stratigraphy. — 12. Upper Cretaceous. 

"Glauconitic Sands" are often more calcareous, and contain numerous fragments 
of Inoceramus. They seem to be of Upper Turonian or Lower Senonian age, and 
to have been laid down on the underlying beds after an elevation of the district. 

The Glauconitic Chalk is clearly Lower Senonian (Emscherian), containing 
numerous sponges, Terebratula carnea, Spondylus spinosus, Actinocamax varus, 
Aclinocamax quadratus, Echinocorys gibbus, and Micraster coranguinnm. The White 
Limestone above, with its numerous bands of flint, is the most conspicuous Creta- 
ceous rock in Ireland, being largely quarried for the production of lime. Rivers seem 
to have often brought down pebbles of vein-quartz and quartzite from the exposed 
Dalradian promontories into the Senonian sea, while it was still shallow in this area. 
The resulting Senonian conglomerate or "Mulatto Stone" is about 30 cm. (1 ft.) 
thick at Murlough Bay east of Fair Head, where it rests directly on Triassic sand- 
stone. This pebbly zone indicates that the western limit of the great chalk sea of 
Europe was not very far away. The White Limestone is especially characterised 
by Belemnitella mucronata. Terebratula carnea, Rhynchonella octoplicata, and Ostrea 
vesicularis occur. 

Though the complete Upper Cretaceous Series is nowhere present, and rarely 
more than 30 m. (100 ft.) can be seen at any one point, there is evidence of a prevalence 
of Cenomanian beach-deposits in the country near Belfast (Geol. Surv. Mem. 1904), 
while north-east of this the sea was generally deeper. After a brief epoch of ele- 
vation, by which an unconformity occurred at the top of the Cenomanian deposits, 
the sea in Senonian times spread northward, southward, and westward, over a wide 
area, until Senonian conglomerates and white limestone were deposited from Moira 
to Lough Foyle. By far the larger part of these deposits is now concealed by the 
Kainozoic basalts of the plateaus. 

The Cenomanian overflow was marked by deposits very rich in glau- 
conite. The frequent occurrence of pebbles of fair size in beds of glauconitic 
chalk of early Senonian age shows that a deposit of the white limestone type 
could be formed in shallow water. The true white limestone, with its residue 
of fine grains of quartz, and only minute quantities of heavy minerals, certainly 
suggests (Hume 1897) conditions of greater depth, but it is difficult to believe that 
the absence of coarse detrital material in the upper zones of the chalk of Co. Lon- 
donderry is entirely due to the remoteness of the shore. If a large part of the uplifted 
Irish area were at this epoch covered by Carboniferous Limestone, karst-con- 
ditions may have arisen, and any rivers that flowed into the sea in this region may 
have been almost devoid of material in suspension. 

Economic Products. 

The white limestone (compact chalk) of the north-east of Ireland is extensively 
used for lime-burning. 

Bibliography of the Cretaceous of Ireland. 

1876. Barrois, C, Mem. Soc. Geol. du Nord, vol. 1, Recherches sur le Cretace sup. de 

PAngleterre et de l'lrlande. 
1908. Cole, G. A. J., Geol. Mag., pp. 333-334 (Dredged Rocks). 

1910.  — and Crook, T., Mem. Geol. Surv., On Rock Specimens dredged from the floor 

of the Atlantic and their bearing on Submarine Geology. 
1897. Hume, W. F., Quarl. Journ. Geol. Soc. London, vol.53, pp. 540-606 (Antrim). 

1911. Jukes-Browne, A., Building of the British Isles, 3rd. ed. 

1900 — and Hill, W., Mem. Geol. Surv, Cretaceous Rocks of Britain, vol. 1. 
1865. Tate, R., Quart. Journ. Geol. Soc. London, 21, pp. 15-44 (North-east Ireland). 

Geological Survey. 
Explanatory Memoirs to accompany Sheets: 

169, 170, 180 & 181. Part of County Wexford (G.H. Kinahan & W. H. Baily). 1879. 

28, 29, 36&37 (in parts). Belfast (G. W. Lamplugh & others). 1904. 
See also Cole, G. A. J. and Jukes-Browne and Hill, W. 



Great Britain. — White: Sedimentary Rocks. — Eocene. (III. 1.) 267 



13. Tertiary. 

a. Great Britain. 
By H. J. Osborne White. 

I. Sedimentary Rocks. 

A. Palaeogene. 

1. Eocene. 

As in the case of the Upper Cretaceous beds, the principal masses of Eocene 
strata in Great Britain are situated in the south-east of England, where they occupy 
the broad tectonic depressions known as the London and Hampshire Basins. In 
the northern part of Britain, thin sediments of this age are intercalated in the lavas 
of the islands of the Inner Hebrides (Mull, Skye), off the west coast of Scotland. 

The British Eocene beds consist mainly of sands and clays of marine, estuarine, and 
fresh-water origin, and they rest on Upper Cretaceous and older rocks with a more or 
less marked unconformity. Their principal divisions are shown in the subjoined table. 



Comparative Table of British Eocene Strata. 

England 



Scotland 





Stages 


London Basin 


Hampshire Basin 


Isle of Mull 




Marin6sian 




Headon Beds 




Upper 
Eocene 


Barton or 
Headon Hill Sands 






Barton Clay 






Auversian 


Upper Bagshot Beds 


Upper Bracklesham Beds 




Middle 
Eocene J 


Lutetian 


Middle Bagshot Beds 


Lower Bracklesham Beds 






Cuisian 


Lower Bagshot Beds 


Alum Bay Sands 






London Clay 


Bognor Beds 
or London Clay 




Lower 

Eocene 


Oldhaven and 
Blackheath Beds 


(wanting) 






Sparnacian 


Woolwich and 
Reading Beds 


Reading Beds 






Thanetian 


Thanet Beds 


(wanting) 


? 




Montian 


(wanting) 


(wanting) 


Leaf beds 



a. England. 

Although the formation of the Eocene basins of the South of England 
is due to earth-movements which took place in post-Eocene times, and there is no 
good reason to doubt that the contemporaneous beds in each were once continuous 
across the intervening country, it will be convenient to consider the stratigraphical 
succession in each basin separately. 

1. The London Basin. 

This basin has the form of a triangle, with the town of Marlborough (Wilts) at the 
apex, on the west, and the base on the east coast between Deal (Kent) and Southwold 
(Suffolk). Its length is about 200 km. (125 miles), and its width at the coast is about 
120 km. (75 miles). The region is bounded on the north by the Chalk uplands of the 
Berkshire Downs and Chiltern Hills, and on the south by the Sydmonton Hills and 
the North Downs. 

The Thanet Beds (24 to 27 m., 80 to 90ft.), which are the oldest of the English 
Eocene strata, consist of white and yellow sands, clayey and glauconitic in the lower part 
and having at the base a thin, persistent layer of unworn, green-stained flints. In East Kent 



268 (III. I.) 



The British Isles. — III. Stratigraphy. — 13. Tertiary. 



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the beds are made up of green sandy marl (15 to 18 m., 50 to 60 ft.) overlain by grey and 
green sand (9 to 12 m., 30 to 40 ft.), both being fossiliferous. The best exposure is in the cliffs 
of Pegwell Bay, south of Ramsgate. The sandy marl passes westward into fine green and 
buff sand, the upper beds thinning out, so that at Woolwich and Charlton, in west Kent, the 
whole formation is not more then 15 m. (50 ft.) thick. It dies out westward in Surrey 
and northward in Essex. The Thanetian fauna comprises about 70 known species, all 
marine, including Astarte tenera Mor., Corbula regulbiensis Mor., Cyprina Scutellaria Lam., 



Great Britain. — White: Sedimentary Rocks. — Eocene. (III. 1.) 269 

Cucullea crassatina Lam., Ostrea bellovacina Lam., Sanguinolaria edwardsi Mor., Phola- 
domya cuneata Sow., P. konincki Nyst, Aporrhais sowerbyi Mor., Natica subdepressa 
Mor., Scalaria bowerbanki Mor., and fish-remains. 

Woolwich and Reading Beds (15 to 25m., 50 to 80ft.). These are a variable 
series and present three distinct facies as they are followed from east to west. In East Kent, 
and confined to that district, is a marine facies consisting of grey sands with marine mollusca. 
The second or Woolwich type, composed of laminated clays and sands full of estuarine shells, 
is best developed in West Kent and East Surrey, but has thin, local representatives as far 
westward as Guildford and Reading. The third, and more widespread, Reading facies, 
found in the western and northern parts of the London Basin, includes unfossiliferous or 
sparingly-fossiliferous, varicoloured (mottled), plastic clays and brightly tinted sands, 
with local beds of flint-pebbles and (on the north-west) occasional inclusions of flint and 
quartz gravel. The Reading Beds proper appear to be mainly of freshwater origin; they 
contain impersistent seams of clay with impressions of leaves ("leaf-beds"), which occur 
in the Estuarine (Woolwich) beds also, but their basal layers, whether in contact with the 
Chalk or the Thanet Beds, consist of glauconitic sand and loam with green-stained flints and re- 
mains of oysters [Ostrea bellovacina h am., O. tenera J. Sow., and sharks-teeth (Odontaspis, etc.). 

The flora of the leaf-beds has a temperate aspect: it includes Acacia, Anemia sub- 
cretacea Sap., Aralia, Corylus, Ficus, Grevillea, Laurus jovis de la Harpe, Liriodendron, 
Platanus, Populus, etc. Among the molluscan forms present in the Woolwich Beds are 
Corbicula cordata Mor., C. cuneiformis J. Sow., C. tellinella Fer., Cyprina morrisi J. de 
C. Sow., Unio sub-parallela S. Wood, Melania (Melanatria) inquinata Defr., Melanopsis 
buccinoides Fer., Natica labellata Lam., Neritina globulus Defr., Pitharella rickmani Edw. 
Vertebrates are represented by Odontaspis, Gastornis, Coryphodon, etc. 

The Oldhaven and Blackheath Beds (3tol5m., 10 to 50 ft.) are of limited 
stratigraphical extent, and though in places very fossiliforous they are hardly of sufficient 
importance to rank as a primary division. They consist partly of sands, partly of well 
worn flint-pebbles in a matrix of light-coloured sand. Cross-bedding is usually a very 
marked feature. In places the pebbles are cemented by calcareous matter derived from 
the associated shells. Near Reculvers in east Kent, where the beds consist mainly of sand 
(Oldhaven type), they appear to be conformable with the Woolwich Beds: south of London, 
where they are very pebbly (Blackheath facies), they rest on an eroded surface of the same and 
older Eocene strata, and even come in contact with the Chalk. Their small flora (including 
Cinnamomum and Ficus) suggests a warmer climate than that of the Woolwich epoch. The 
fauna is partly estuarine, but mainly marine (gastropoda being especially abundant), and in- 
cludes Calyptraea trochiformis Lam., Potamides funatus J. Sow., Melanatria inquinata Defr., 
Natica labellata Lam., Protocardia plumstediense J. de C. Sow., Pectunculus terebratularis Lam. 

London Clay (to 150 m., 500ft.). This is a deposit of more uniform character 
than the beds below. It consists of stiff, blue-grey clay (weathering brown) with layers of 
septarian nodules of argillaceous limestone. Its lowest or "Basement" bed (2 to 4 m., 67 2 to 
13 ft.) is a glauconitic sandy clay with seams of impure limestone and flint-pebbles. The 
formation as a whole attains its greatest thickness (150 m., 500 ft.) in Essex, and thins 
westward to about 90 m. (300 ft.) near Windsor, 15 m. (50 ft.) near Newbury, and 0,3 (1 ft.) 
or less near Bedwyn in Wilts. Most of the clay is poorly fossiliferous or barren, but at 
certain horizons it has yielded a rich fauna. J. Prestwich 1854, recognized four ill- 
defined zones, the lowest (including the basement bed) indicating, in the eastern part of 
the area of deposition, a maximum depth of water; while a progressive shallowing is in- 
dicated by the higher zones, the uppermost of which contains (at Sheppey in Kent) 
abundant remains of terrestrial vegetation, and of fish and reptiles. The plants are of sub- 
tropical character and include the genera Amygdalus, Cupania, Diospyros, Gingko, Laurus, 
Musa, Nipa, Pinus, Quercus, Victoria, Magnolia, Liquidambar, etc. Of the fauna, mention 
may be made of Hemiaster forbesi Greg., Ditrupa plana J. Sow., Vermicularia bognoriensis 
J. Sow., Lingula tenuis J. Sow., Terebratulina striatula Mant., Axinaea brevirostris J. 
de C. Sow., Cyprina Scutellaria Lam., Modiola elegans J. Sow., Nucula bowerbanki J. de 
C. Sow., Pholadomya margaritacea J. Sow., Pinna affinis J. Sow., Panopaea intermedia 
J. Sow., Aporrhais sowerbyiMxNT., Cassis striata J. Sow., C. ambigua Sol., Pyrula smithi 
J. Sow., Nautilus imperialis J. Sow. 

The fish, of which nearly 100 species have been recorded, include Carcharodon, Lamna, 
Myliobatis,Odontaspis, etc.; the reptiles Chelone,Crocodilus, and Polaeophis;ttiebirdsDasornis, 
Lithornis, Odontopteryx, and the mammals Coryphodon, Didelphys, Hyracotherium, Lophiodon. 

Lower Bagshot Beds (15 to 45 m., 50 to 150ft.). The London Clay passes up, 
gradually or abruptly, into light-coloured, cross-bedded sands, with subordinate beds of 
grey and white clay, and lenses of flint-pebbles. Save for lignite and occasional im- 
pressions of leaves the Lower Bagshot Beds are usually unfossiliferous, but have yielded 
a few casts of marine mollusca in Surrey and Essex. 



270 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

The Middle Bagshot Beds (12 to 18 m., 40 to 60 ft.) are usually regarded as the 
equivalent of the Bracklesham Beds (of the Hampshire Basin), and are now generally known 
by the latter name, but this correlation is open to question. J. S. Gardner 1879 — 1888 
and G. F. Dollfus 1909 regard them as equivalent to the lower part only of the true marine 
Bracklesham Beds of Hampshire. They consist of laminated sandy clays, in two groups, 
between which lies a dark-green, glauconitic, clayey sand (3 to 6 m. 10 to 20 ft.) in which 
fossils are plentiful locally. Some of the forms present are Nummulites laevigatus Brug., 
Cardita planicosta Lam., Corbula gallica Lam., Ostrea flabellula Lam., Pecten corneus 
Sow., Fusus (Clavalithes) longaevus Lam., Turritella imbricataria Lam., and many fish-teeth 
— Aetobatis, Galeocerdo minor Agas., Myliobatis, Lamna, Odontaspis macrota Agas., etc. 

Upper Bagshot Beds (70 m., 230 ft.). These are the youngest Eocene strata in the 
London Basin. They are composed of yellow and white sands, argillaceous near the base, 
which is marked by a thin pebble-bed. Their precise age is uncertain, some authors 
correlating them with the Barton Clay (Marinesian) of Southern Hampshire, others with 
the upper part of the Bracklesham Beds (Auversian) of that district. Organic remains are 
rare, and take the form of casts in ironstone. About 50 species have been recorded from 
Pirbright in Surrey. The Upper Bagshot fossils include — Nummulites varioiarius Lam., 
Cardita sulcata Brand., Corbula pisum 3. Sow., Ostrea flabellula Lam., Pecten reconditus 
Brand., Tellina scalaroides Lam., Natica patula Desh., Turritella imbricataria Lam. 

2. Hampshire Basin. 

This area is limited on the north by the anticlines of Wardour, Winchester, 
and the Weald, and on the south by those of Purbeck and the Isle of Wight; the 
Tertiary tract having a maximum width of 45 km. (28 miles), and a length, from 
Dorchester to Worthing, of about 135 km. (84 miles), with small outlying tracts 
near Newhaven 40 km. (25 miles) farther east. 



HeadonHill. High Down. 




Fig. 59. Section across the west side of the Isle oi Wight (after H. W. Bristow). 

a = Chalk; b = Reading Beds; c = London Clay (Bognor Beds), d = Alum Bay Sands 

(Lower Bagshot Beds); e = Bracklesham Beds; f = Barton Clay; g= Barton Sands;" 

h = HeadonBeds; i = Osborne Beds; k = Bembridge Beds; 1 = Gravel and Sand (Pleistocene). 

Horizontal and vertical scale about 1:14,500 or abont 4,3 inches to one mile. 

In this basin the Thanet Beds are unrepresented, the oldest of the Eocene rocks 
being the Reading Beds (18 to 49 m., 60 to 160ft.). As in the London Basin, these 
Sparnacian strata are mainly mottled clays and sands, with a glauconitic bed at the 
bottom. Near Dorchester they contain gravel of fluviatile aspect. They have yielded 
few fossils, except in Sussex, where thin estuarine shell-beds of the Woolwich type occur 
on the coast between Worthing and Seaford. The average thickness of the Reading 
Beds in the Hampshire Basin is probably between 20 and 25 m. (65 and 82 ft.). The 
maximum (49 m., 160 ft.) is reached at the eastern end of the Isle of Wight. 

Unfossiliferous pebble-beds occur in the upper part of this formation near Romsey 
(Hampshire), and in other places. 

Bognor Beds or London Clay (91 to 122 m., 300 to 400 ft.). Excepting a thin 
outlier at Newhaven in Sussex the easternmost sections of Cuisian beds are at Bognor (in the 
same county), where beds of clay and richly-fossiliferous calcareous sandstone, forming 
part of a series of sands and clays with occasional pebble-beds, are exposed on the shore. 
The formation contains sands with Lingula near Chichester, and at Portsmouth it is 
divisible into three lithological series, the highest of which consists chiefly of clays con- 
taining Cyprina Scutellaria 3. Sow., Pholadomya margaritacea 3. Sow., Rostellaria lucida 
3. Sow., etc. (Meyer 1871). 

In the Isle of Wight the junction with the Reading Beds is sharply marked by a 
layer of flint-pebbles. About 11 m. (36 ft.) above this layer, at Whitecliff Bay, there is 
a fossiliferous zone with Panopaea intermedia 3. Sow. and Pholadomya margaritacea 
3. Sow.; at 15 m. (50 ft.), a band of Ditrupa plana 3. Sow.; at 36 m. (120 ft.) an oyster- 
bed, above which come brown clays with Panopaea intermedia 3. Sow., Cyprina Scutellaria 
3. Sow., Cytherea tenuistriata 3. Sow.. Pinna af finis 3. Sow., succeeded by laminated 
sandy clays. 



Great Britain. — White: Sedimentary Rocks. — Eocene. (III. 1.) 271 

In Dorsetshire the London Clay is mainly sandy clay or loam, with seams of ironstone 
and the usual pebble-bed at the base. Near Wareham it is 20 to 24 m. (65 to 80 ft.), but 
it thins westward, and is overlapped by the succeeding Alum Bay Sands. 

Alum Bay Sands ("Bagshot" or "Lower Bagshot Beds"), 10 to 30 m. (33 to 100 ft.) 
These are red, yellow, and white sands with intercalations of grey laminated clay and, 
near the middle, layers of white pipe-clay, containing plant-remains in places. This is their 
character in the Isle of Wight and in East Dorset, but near Dorchester they pass into coarse 
pebblysands with irregular beds of pipe-clay and of gravel,and overlap both the London Clay 
and the Reading Beds. The gravel, though mainly flint-stones, contains fragments of 
pre-Cretaceous Mesozoic and of Palaeozoic rocks of the types found farther west, and are 
most probably of fluviatile origin. Some of the hill-gravels and masses of pudding-stone 
found in West Dorsetshire and East Devonshire have been referred to these Upper Cuisian 
beds. Most of the plant-remains recorded from Alum Bay in the Isle of Wight were found 
in a lenticular thickening of a seam of pipe-clay near the middle of the series. The most 
typical and conspicuous forms are referred by J. S. Gardner 1879 — 1888 to Aralia pri- 
migenia Heer., Cassia ungeri Heer., Comptonia acutilobata Sternb., Caesalpina, Dry- 
andra bunburyi de la Harpe, Ficus bowerbanki de la Harpe. Leaves of palm, and pods 
of Acacia and Cassia, have been found near Corfe on the mainland. 

Bracklesham Beds (Lutetian and Auversian). These comprise a set of estuarine 
and marine sands and clays (to 179 m., 587 ft.) which vary so markedly in their character 
from place to place that the correlation of their parts in the several sections in Sussex, 
Hampshire, and the Isle of Wight is a task presenting considerable difficulty. At Brack- 
lesham Bay (Sussex) and in Whitecliff Bay (I. of W.) they are wholly or largely marine. The 
descending succession shown in the cliff at the latter spot is as follows — 

m. ft. 

7one of f Green an d ^\ue c l avs > with a little sand 55 180 

A7 • , I Nummulites variolarius Lam., Corbula pisum Sow., Pecten 

Numm. variolar- \ ia„ n, . i-.t 

,. , corneus J. Sow., Fleurotoma plicata Lam. 

ius(Auversian) ( Yellow sands and sandy clays 8,5 28 

Sandy clays and green sands, with lignite 37,5 123 

Nummulites laevigatus BRVG.,Sanguinolariahollowayst J. Sow., 
VolutilithesspinosusLiNN., V. cithara Lam. Laminated clays 
and calcareous sands and sandy clays with pebble-bed at base 76 250 
Nummulites laevigatus Brug., Ostrea jlabellula Lam., Calyp- 

traea trochiiormis Lam., in upper part 

The lower 30 m. (100 ft.) of these beds is unfossiliferous 177 581 

At Alum Bay, at the western end of the Isle of Wight, the series is represented mninly 
by sandy clays and lignites, marine fossils being restricted to the highest beds (Numm. 
variolarius zone). Farther west, between Poole Harbour and Highcliff on the mainland, 
the descending succession made out on the coast by J. S. Gardner (1882) is: 

6. Dark sandy clays with pebbles at base 

5. Highcliff sands, unfossiliferous 

4. Hengistbury clays with septaria 

3. Boscombe sands 

2. Bournemouth marine beds with plants and mollusca .... 

1. Bournemouth freshwater beds with plants ?122,0 

The thickness of the series is here about 179 m. (587 ft.) 

The freshwater beds (1) consist of sand with beds of clay in which plant remains 
are numerous — notably Acrostichum, Osmunda, Polypodium, Araucaria, Eucalyptus, 
Priartea, Salix, Sequoia. The Bournemouth marine beds (2) are referred to the N. laevigatus 
zone, and the succeeding beds (3 to 6) to the zone of N. variolarius. 

Barton Clay (28 to 48 m., 90 to 160ft.). This formation is well exposed on the 
Hampshire coast at Barton and Hordle, and in the Isle of Wight. It is composed of grey 
clays and light coloured sand, and is celebrated for the abundance and good preservation 
of its fossils, especially marine mollusca, of which some 500 species have been collected. 
The lower beds ("Lower Barton" of Gardner, Keeping, and Monckton 1888, (15 to 
16.5 m., 49 to 55 ft.), consist of green sandy clay — in which Nummulites wemmelensis 
de la Harpe [=N. elegans var. presttvichianus T. R. Jones) is of common occurrence — 
with a thin pebble-bed at the base, and of grey clays and sands containing Schizaster 
d'urbani Forbes, Cassis ambigua Brand., Volutilithes athleta Brand., V. nodosa J. Sow. 

The higher beds or Barton Clay proper ("Middle Barton" of the above-named writers) 
are composed of grey and brown clays (16 to 28 m., 53 to 92 ft.) with layers of septarian 



Zone of 

Numm. laevigatus 

(Lutetian) 



m. 


It. 


4,2 


14 


9,2 


30 


17,3 


57 


42,1 


138 


15,2 


50 


22,0 


400 



Upper 
Headon 

Beds 
(15 m., 
50 ft.) 



Lower 

Headon 

Beds(20m., 

65 ft.) 



272 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

concretions, and Crassatella sulcata J. Sow., Clavalites longaevus Lam., Murex minax 
Brand., Rostellaria ampla Brand., Volutilithes ambiguus Brand., V. luctatrix Brand. 
Barton Sands (otherwise "Upper Barton", "Headon Hill Sands") 27 to 67m. 
(90 to 220 ft.) These are white, grey, and yellow, argillaceous at the base, and charac- 
terised in the lower part ('Chama-bed') by Chama squamosa Brand., Terebratula bisinuata 
Lam., Conus scabriculus Sol., Voluta costata Sol., V. humerosa Edw., V. solandri Edw., 
and in the upper part by Cerithium (Potamides) concavum J. Sow., C. pleurotomoides 
Lam., Oliva branderi J. Sow. These are the "Becton Bunny" and "Long Mead End Beds" 
of the Hampshire mainland section, and are well shown in the cliffs north of the pier at 
Alum Bay in the Isle of Wight. 

Headon Beds (44 to 45 m., 144 to 148 ft.). By most British geologists this series 
is regarded as the lowest division of the Oligocene system. A recent comparison of the 
English Palaeogene rocks with those of the Paris Basin and Belgium, however, has led 
G. F. Dollfus (1909) to the conclusion that this series belongs rather to the Marinfcian stage 
of the Upper Eocene, and is approximately on the horizon of the Calcaire de St. Ouen. The 
Headon Beds underlie the northern part of the Isle of Wight and are shown in the cliffs 
between Headon Hill and Cliff End, and at Whitecliff Bay. On the Hampshire mainland 
they occupy part of the New Forest area, and their lower beds are exposed on the coast 
at Hordle. Three divisions are recognized — an upper and a lower freshwater group, 
and a middle group containing marine and estuarine mollusca. In the typical section at 
Headon Hill the descending succession is: 

m. ft. 

Variegated clays with Erodona gregaria J. Sow 6.15 20 

Limestone with Limnaea long iscata J. Sow. and Planorbis euomphalus 

J. Sow 2.4 8 

Blue clays with similar fossils 1.5 5 

Limestone, with similar fossils 3.0 10 

Sand 0.6 2 

Middle . Clays with Potamides concavus J. Sow., Cyrena obovata J. Sow., etc. 2.1 7 

Headon I Limestone with Limnaea and Planorbis 0.3 1 

Beds(10m., | Sandy clay with marine fossils 4.5 15 

33 ft.) I Sand and clay with Neritina, Cyrena, Cerithium, etc 3.0 10 

Limestone with Limnaea and Planorbis 0.9 3 

Sand and clay with lignite 6.1 20 

Clay sand sands with two beds of limestone containing Viviparus 
angulosus J. Sow., NematuraparvulaDESu., Limnaea, Planorbis, etc. 7.6 25 
Sands and clays with Erodona plana J. Sow., etc 6.0 20 

In Whitecliff Bay, at the opposite (eastern) and of the Isle, the Lower Headon Beds 
are only 8,5 m. (28 ft.) thick. At Hordle on the mainland they are 26 m. (85 ft.), and have 
yielded many reptilian and mammalian remains. The middle beds, which are exposed 
to 37 m. (120 ft.) at Whitecliff Bay, and are well represented about Brockenhurst and Lynd- 
hurst on the mainland, contain about 150 known species, including the anthozoa Sole- 
nastraea granulata Dune, and other spp., Axopora michelini Dunc, Lobopsammia cariosa 
Dunc, Litharea cf. deshayesi Michelin, Madrepora solanderi Dunc; the mollusca 
Meretrix (Cytherea) incrassata Desh., Ostrea flabellula Lam., O. velata Wood, Potamides 
concavus J. Sow., Melanopsis jusiformis J. Sow., Pisania, Melania muricata Wood, Ancilla 
buccinoides Lam., Neritina aperta J. Sow., and the cirripede Balanus unguiformis Sow. 

Evidence of the presence of Eocene strata off the coast of Cornwall has been 
brought forward by C. Reid (1904). 

p. Scotland. 

Mull Leaf-Beds. Thin sedimentary beds are intercalated in the Tertiary 

lava-flows of the islands of Mull, Skye, and Eigg, off the west coast of Scotland. 

In the promontory of Ardtun Head, Mull, many plant-remains have been obtained 

from bands of gravel, sand, and shale. The descending sequence seen in one of the quarries 

on the coast here is: 

m. ft. in. 

Columnar basalt 3.0 10 

Stratified sandstone 2.4 8 

Indurated gravel of flints and lava-fragments 2.1 7 

Indurated dark mud with ferns 0.3 1 

Soft black shale full of leaves 0.7 2 6 

Hard gravelly sand 0.6 2 

Basalt — 



Great Britain. — White: Sedimentary Rocks. — Oligocene. (III. 1.) 273 

Among the plants are Equisetum, Onoclea hebridica Forbes, Gingko, Podocarpus, Taxus, 
Sequoia, Populus arcticus Heer, Cornus, Boehmeria antiqua Gard., Corylus?, Laurus?, 
Rham.nus ? 

These beds were first examined by the late Duke of Argyll (1851) and were long 
thought to be of Miocene age. J. S.Gardner (1887), who has studied them more 
recently, points out the late Cretaceous character of their flora, but is inclined to regard 
the deposits as of earliest Eocene age, and not younger than the Thanetian. 

2. Oligocene. 

The British Oligocene rocks — so far as known — are confined to three small 
areas, situated in tectonic troughs, and disposed along a line running approximately 
westward through the Isle of Wight, and the southern part of Dorset, to Bovey 
Tracey in Devonshire. 

1. Isle of Wight. The largest of the three areas just mentioned occupies the northern 
part of this island, where the following stratigraphical divisions are recognized: 

Upper Oligocene, Stampian [ H 7 m S e) Beds 

(Hamstead Beds (freshwater and brackish). 
Bembridge Beds. 
Osborne Beds. 

The Osborne Beds (24 to 33 m., 80 to 110ft.). At Headon Hill and Colwell Bay 
these consist of white and coloured marls, and concretionary limestones with siliceous 
nodules. They contain Limnaea longiscata Brand, var., Planorbis discus Edw., Vivi- 
parus lentus Brand., and other freshwater shells. At Whitecliff Bay they are green 
clays and sands, but between Osborne and Nettlestone they consist of marls with beds 
of sandy and shelly limestone full of Viviparus lentus Brand., and Melania acuta, var. 
excavata Morris (Nettlestone Beds), overlain by coloured sands, marls, and clays 
(St. Helens Beds) with Limnaea longiscata Brand., Planorbis obtusus J. Sow., and 
Cypridae. At King's Quay near Osborne, and other places, the lower beds contain the fish 
Clupea vectensis E. T. Newt., in remarkably good preservation, and remains of Lepidosteus, 
Diplocynodon, Emys, Trionyx, Chelone, Palaeoiherium, Theryodomys. Nucules of Chara 
are plentiful. Other plants have been found at Cliff End and near Ryde, but have not 
been much studied. 

The Bembridge Beds (27 to 39 m., 90 to 130ft.) comprise the Bembridge 
Limestone and overlying Bembridge Marls. The Limestone (4,5 to 8 m., 15 to 26 ft.) 
is the most constant of the fluvio-marine strata in the Isle of Wight, and is everywhere 
readily recognizable. It is a cream-coloured stone, partly homogenous, partly tufaceous 
and concretionary, and contains bands of marl. The base is sharply marked, and the 
upper surface frequently shows signs of having been eroded before the deposition of the 
succeeding Bembridge marls. The highest limestone of the Headon Hill and Sconce 
sections, and the limestone of Hamstead and Gurnard Ledges, of Cowes, and of New- 
bridge are on this horizon. Its fauna is terrestrial and freshwater, the mollusca including 
Amphidromus ellipticus J. Sow., Glandina costellata J. Sow., Helix d'urbani Edw. and 
other species, Limnaea elongata M. de Serres, Planorbis oligyratus Edw.; the mammalia 
Palaeoiherium magnum Cuv., P. medium Cuv., P. crassum Cuv., Plagiolophus minax Cuv., 
Pterodon dasyuroides de Blainv., Chamaeropotamus gypsorum Desm., Anoplotherium 
commune Cuv., A. secundarium Cuv., Hyopotamus porcinus Gerv., Dichobune leporina 
Cuv., all found also in the Sannoisian of the Paris Basin. 

At Hamstead, the Bembridge Marls (21 to 36m., 70 to 120ft.) consist entirely 
of freshwater marls and clays, of grey or greenish tints, and contain the plants Chara lyelli 
Forbes, Chrysodium, Carpolilhes, Cinnamomum, Ficus, Pinus, Sabal, Zizyphus, and the 
mollusca Cerithium plicatum Brug., Cyrena convexa Brong. (= semistriata Desh.), 
Melania (Striatella) muricata S. Wood, Melanopsis carinata J. Sow., Nystia duchasteli 
Nyst, Viviparus lentus Brand. At Whitecliff Bay there is, near the base of these marls, 
a thin, sandy marine bed with Cytherea incrassata Desh., Mytilus affinis J. Sow., 
Nucula similis J. Sow., Ostrea vectensis Forbes. This is succeeded by clays with Cyrena 
convexa Brong., and Viviparus lentus Brand., in which clays there is a bed of sandy lime- 
stone containing Amphidromus ellipticus Sow., Glandina costellata Sow., Limnaea longiscata 
Brand., var. The highest beds contain abundant Potamides turritissima Forbes. In 
places, as at Cowes, the marls contain, about 3 m. (10 ft.) above their base, a thin seam 
of bluish limestone, like lithographic stone, in which are occasional leaves and insects. 
About 20 genera of insects have been identified, belonging to 8 orders. 

Handbuch der regionalen Geologic III. 1. 18 



274 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

The Hamstead (Freshwater and Estuarine) Beds (60 to 70 m., 200 to 
225 ft.), which G. F. Dollfus (1909) refers to the same (Sannoisian) stage as the Osborne 
and Bembridge Beds, are black and green clays. They occur at the surface over a 
large area of the northern part of the Isle of Wight, between Hamstead (or Hempstead) 
on the west and Brading on the east. Near Hamstead they show the following des- 
cending succession: 

m. ft. in. 
Cerithium Beds . . Clay with Cerithium plicatum Lam., Cyrena semistriala 

Desh., Nystia duchasteli Nyst 10,5 35 

Leaf and Seed Beds . Green and red clays with lignitic layers containing remains 

of Andromeda, Sequoia, Carpolithes, Chara, Neiumbium 46,0 150 

White Band .... Green clay with white shell-marls 2,0 68 

Nematura Beds . . Green and black clays with Nematura pupa Desh., Me- 

lania jasciata J. Sow., Mya minor Forbes, Nystia 

duchasteli Nyst, Melanopsis carinata J. Sow 19,5 64 

Black Band .... Black clay with Viviparus lentus Brand 0,5 18 

The vertebrate remains include Pterornis, Anthracotherium, Coryphodon, Entelodon 
(= Elotherium), Hyopotamus. 

The Hamstead (Marine) Beds (6 m., 20ft. ?). At Hamstead these consist of 
blue and bluish-green clays, abounding in Corbula pisum J. Sow., Cyrena semistriata 
Desh., Ostrea callifera Lam., Natica labellata? Lam., Voluta rathieri Herb., Strebloceras 
sp., Balanus. According to Dollfus 1909, they belong to the Lower and Middle parts of 
the Stampian stage. 

2. Dorset. A little outlier of Lower Oligocene beds, including a representative 
of the Bembridge Limestone of the Isle of Wight, has recently been identified in 
the so-called 'Isle' of Purbeck (H. Keeping, 1910). It forms the upper part of the 
isolated, conical hill of Creechbarrow, between the villages of Corfe and Lulworth. 
Among the few Bembridge Limestone fossils so far lecorded are Amphidromus 
ellipticus Sow., Helix occlusa Edw. Clausilia striatula Edw., Glandina costellata 
Sow. A tooth of Palaeotherium was found at a lower horizon. 

3. Devon. At Bovey Tracey, near Newton Abbot, an interesting series of 
freshwater clays, sands, and lignites occupies a small basin, about 14.5 km. (9 miles) 
in longest diameter and surrounded by hills of Carboniferous and Devonian rocks. 

In 1863 this series was referred, on the evidence of the flora of the lignites, to the 
Miocene period, by Oswald Heer (1863), who correlated it with the Aquitanian of France, 
and with the Hamstead Beds of the Isle of Wight. J. S. Gardner, writing in 1879, con- 
sidered that the plant-remains collected by Heer and Pengelly were the same as those 
yielded by the Bournemouth leaf-beds (Lower Bracklesham, Lutetian), and on the strength 
of this opinion the Bovey Beds have since then been generally classed as Eocene. Recently, 
however, C. and E. M. Reid (1910) have shown that the flora, so far from having an 
Eocene facies, is almost identical with that of the lignites of the Wetterau (Rhine valley), 
which are referred to the close of the Oligocene, or beginning of the Miocene. Heer's cor- 
relation would seem, therefore, to be approximately correct. 

The following is a generalized description of the strata found in a pit and boring 
at Heathfield (Jukes-Browne 1909) near the middle of the Bovey basin: 

m. ft. 

Superficial deposits, about 6 20 

Beds of clay and sand with occasional beds of lignite 76 250 

Beds of lignite and clay, with one of sand 16 50 

Beds of lignite, with thin layers of clay 67 220 

165 540 

The base of the series was not reached in the boring, but the beds traversed all appear 
to belong to a single formation. 

The plants in the lignitic beds include  —  Magnolia attenuata Weber, Nyssa europaea 
Unger, N. obovata O. Weber, N. ornithobroma Unger, N. vertumni Unger, Sequoia 
eouttsiae Heer, Palmacites daemonorops Unger, Carpolithes boveyana Heer. 

"The Bovey flora, so far as examined, seems to be essentially the flora of the granite- 
ravines, with the admixture of a very few aquatic forms ". The mingling in it of 

"the outgoing warm-temperate with incoming northern forms is probably due to the proxi- 
mity of Dartmoor, which rises sharply above the Bovey basin, but is also a characteristic 



Great Britain. — White: Sedimentary Rocks. — Palaeogene. (III. 1.) 275 

of the close of the Oligocene period. The absence, or great scarcity of sedges, grasses and 
mosses make it difficult to call the Bovey Beds Miocene, in the modern sense of the term" 
(C. and E. M. Reid, 1909). 

It may be noted that there is a smaller basin, containing lignites and clays of uncer- 
tain age, near Marland, in the northern part of Devonshire. 

3. Physiographical Conditions. 

At the close of the Cretaceous period the British area emerged from the sea 
and the Cretaceous rocks underwent considerable erosion. So far as the English 
area is concerned this marine regression appears to have been caused, in part at 
least, by a geocratic movement of a differential character, the elevation being 
greater on the north-west than on the south-east; for the Lower Eocene beds 
overstep the Upper Cretaceous in a northward direction in Dorsetshire, Hampshire, 
and Berkshire, and in a north-westward to westward direction in Essex and Suffolk. 

The Thanet Beds of the London Basin mark the beginning of the Eocene trans- 
gression which, approaching from the east, probably extended, in early Spar- 
nacian times, over the whole area now occupied by Cretaceous and Oolitic rocks 
in England. Relics of the glauconitic pebble-bed withOstrea and teeth olOdontaspis, 
forming the base of the Woolwich and Reading Series, are found all over the Chalk 
country, up to the edge of the escarpments which mark the present inland limits of 
the Turonian and Senonian strata. Though wide spread, the early Sparnacian sub- 
mergence was of small depth, and marine conditions soon gave place to the fluvio- 
marine and fluviatile conditions under which the greater part of the Woolwich and 
Reading series was accumulated. The London Clay, however, registers a more decided 
encroachment of the sea upon the southern English area, an encroachment followed, 
in late Cuisian and early Lutetian times, by a notable shallowing of the water over the 
country between Berkshire and Essex (Lower Bagshot Beds), and by a return 
of fluviatile conditions in the region of Dorsetshire and Hampshire (Alum Bay Sands, 
Bournemouth Beds). The succeeding Bracklesham Beds of BrackleshamandWhitecliff 
Bay, and the Barton Clay and Sands, together with the Middle and Upper Bagshot Beds 
of the London district, indicate a renewed submergence, probably not less widespread, 
though less deep, than that of the Cuisian age; but towards the close of the Eocene 
period there came another pronounced regression, and the small remnants of Oligocene 
strata preserved in the Isle of Wight and Dorset record alternations of marine or 
brackish and freshwater conditions, such as usually obtain in the deltas of large rivers. 

With the lignitic freshwater beds of Bovey Tracey the Palaeogene record comes 
to an end, and the oldest of the succeeding fossiliferous deposits in the British area 
are of Pliocene age. 

4. Economic Producti. 
Of the building materials obtained from the Palaeogene rocks the most 
important are the brick and tile clays, which occur in many of the constituent for- 
mations —  notably the Reading Beds, London Clay (sandy beds), Lower and Middle 
Bagshot Beds, and Barton Clay. The scattered blocks of hard sandstone and flint- 
conglomerate (known as Sarsens and Greywethers), which occur in the superficial 
deposits of Surrey, Bucks., Wilts., etc., and are believed to have been derived from 
beds of Eocene age (e. g. Reading Beds, Upper Bagshot Beds), are used for buil- 
ding, as in Windsor Castle. These stones were much favoured by the builders of 
prehistoric stone circles, e. g. Stonehenge and Avebury, Wilts.) and dolmens (e. g. 
Kit's Cotty, Kent). In the Isle of Wight the Bembridge Limestone has been largely 
quarried for local dwellings. Septarian concretions from the London Clay and 
Bognor Beds were formerly burned for cement; fire-bricks for furnaces are occa- 
sionally made from a silty clay in the Reading Beds; glass sand and foundry sand 
are got from the Thanet, Reading, and Barton Beds. 

18* 



276 mi. 1.) 



The British Isles. — III. Stratigraphy. — 13. Tertiary. 



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Great Britain. — White: Sedimentary Rocks. — Neogene. (HI. 1.) 277 

For fuel, the lignites or "brown coal" of Bovey Tracey and Alum Bay have been 
worked on a small scale and to little profit. The principal minerals are pipe-clay 
and alum. The latter has been made from Eocene clays at Alum Bay, and pipe- 
clay is extensively dug atCorfe (Alum Bay Beds or 'Lower Bagshot') in Dorsetshire, 
and at Bovey Tracey. The Lower Headon marls are used as manure in the Isle 
of Wight. For road-mending the Eocene pebble-beds and gravels are dug wherever 
they occur in quantity. 

B. Neogene. 

a) Pliocene. 

The British rocks known to be of Pliocene age comprise certain more or less 
ferruginous and shelly sands with frequent pebble-beds and occasional beds of 
sandy clay. They are, for the most part, of marine origin, and are confined to three 
small areas in southern and south-eastern parts of England, viz. — 1, the low country 
of the coastward parts of East Anglia, including Essex, Suffolk, and Norfolk; 2, the 
North Downs in Kent (and, probably, in Surrey), and 3, the vicinity of St. Erth, 
near Hayle, in Cornwall. Considerable diversity of opinion exists among British 
authorities in regard to the proper grouping of these deposits. The classification 
here adopted is, in the main, that of F. W. Harmer, (1898, 1900). 

1. East Anglia and the North Downs. 

Older Plioce ne. 

The Boxstones. — The oldest of the Pliocene deposits occurs only in a remanie or 
derivative form, in a thin conglomeratic nodule-bed at the base of the Coralline and Red 
Crag divisions of the Newer Pliocene group, in East Anglia. The nodule-bed in question 
contains (besides flints, septarian concretions, pebbles of quartz, granite etc., phosphatic 
nodules, Jurassic fossils, bones of terrestrial and marine mammals, and other material) 
some rounded lumps of hard brown sandstone ("box-stones"), containing casts of marine 
shells, and evidently derived from a definite bed which has not been found in situ. The 
included shells comprise some 16 species, most of which are common British Pliocene 
forms, except Conus dujardini Desh., Voluta auris-leporis Grat., and one or two besides, 
which occur in the Older Pliocene and Miocene of the Continent. 

Lenham Beds (tol5m., 50 ft.?). These are thin and irregular patches of ferruginous, 
slightly glauconitic sand and iron-stone which occur at intervals along the higher parts of the 
chalk downs of East Kent, between Folkestone and Maidstone. They rise to about 
190 m. (623 ft.) above sea-level near Lenham, and everywhere rest on a north-eastward 
sloping surface, which truncates the Chalk (Turonian to Lower Senonian), and has become 
deeply indented by differential solution since Lenhamian times. Generally unfossiliferous, 
these iron sands here and there contain casts of marine mollusca sufficiently preserved 
to admit of identification, and examinations of these remains, undertaken by J. Pre st- 
wich, C. Reid (1890) and others, have shown that the sands themselves are of the same 
(Diestian) age as the similar deposits which cap the hills of Belgian Flanders, and form 
continuous strata in Holland. 

Near Lenham and Harrietsham about 67 species have been obtained from ironstone 
contained in "pipes" (solution-hollows) in the Chalk. Most of these forms are found in the 
Coralline Crag of Suffolk, but the following are characteristic Lenhamian species: Area 
diluvii Lam., Cardium papillosum Poli, Gastrana fragilis Linn., Terebra acuminata Bors., 
Pleurotoma consobrina Bellardi, P. jouanneti Desm. The presence of Pyrula, Xenophora, 
Lotorium, and Avicula gives the fauna a meridional aspect. 

Sands which may be of Lenham age occur on the North Downs in Surrey, farther 
west. They have yielded a few casts of marine shells at Netley Heath, near Guildford, but 
none that can be definitely referred to the Pliocene. 

Newer Pliocene. 
The Coralline Crag (otherwise White or Suffolk Crag), 10 to 20 m. (33 to 66 ft.) 
consists mainly of calcareous sands composed of broken shells and bryozoa. It is restricted 
to the county of Suffolk, where it occurs in a small tract around Gedgrave nearAldeburgh, 



278 (III. 1.) 



The British Isles. — III. Stratigraphy. — 13. Tertiary. 







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and in other smaller areas at Tattingstone, Ramsholt, and Sutton. It rests on an eroded 
surface of London Clay, and contains, at its base, the interesting nodule-bed with box- 
stones, already noticed. Above the nodule bed are yellow marly sands (10 to 12 m., 33 to 
40 ft.), with seams of broken shells, succeeded by about 10 m. (33 ft.) of soft brown, cal- 
careous rock, made up of fragmentary bryozan and molluscan shells, and displaying a very 
irregular bedding. The mollusca (over 400 species) include many southern genera, such 
as Voluta, Cassidaria, Chama, Mitra, Ovula, Pyrula, Ringicula. Characteristic species are 
Lingula dumortieri Nyst, Terebratula grandis Blum., Astarte omalii Laj., Cardita corbis 
Phil., C. senilis Lam., Pecten opercularis Link., Pholadomya histerna J. Sow., Pyrula 
reticulata Lam., Ringicula buccinea Broc, Voluta lamberti J. Sow. Of the abundant 



Great Britain. — White: Sedimentary Rocks. — Neogene. (III. 1.) 279 



Bryozoa or "corallines" about 120 have been named, 
of which 76 appear to be extinct. The large forms 
Celkpora and Theonoa (Fascicularia) are particularly 
characteristic. Fish-teeth and drifted land-shells also 
occur. In his memoir on Pliocene Mollusca (1914), 
F. W. Harmer divides the Coralline Crag into a lower 
or Gedgravian stage and an upper or Boytonian stage 
(of Boyton and Ramsholt). The latter is distinguished 
by the presence of certain Red Crag species, e. g., 
Nassa reticosa J. Sow., and appears to be interme- 
diate between the Gedgravian (of Gedgrave and Sutton) 
and the Waltonian. 



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Red Crag (8 to 12 m., 25 to 40ft.). The beds 
long grouped under this title consist mostly of fer- 
ruginous shelly sands, which are separated by a con- 
siderable break from the Coralline Beds. They lie on 
an eroded surface of the Gedgravian, and overlap it, so 
as to rest upon London Clay, Reading Beds, and the 
Chalk. The Red Crag covers a larger area than the 
Coralline, but, owing to the covering of glacial de- 
posits, is seldom exposed except on the sides of the 
river valleys which cut through the Pleistocene beds. 

From the variation in its fossils from place to 
place, it is inferred that the Red Crag includes sedi- 
ments of diverse ages and having an imbricate ar- 
rangement, the younger deposits overlapping the older 
towards the north. F. W. Harmer (1898, 1900) re- 
cognizes four distinct stages, the oldest of which 
contains the largest percentage of extinct and southern 
forms, the newest the largest proportion of recent and 
northern species. 

The oldest or Walton Crag, of Essex, is especi- 
ally distinguished by the prevalence of Neptunea 
(Jussus) contraria Linn. Other characteristic mollusca 
are Cardita corbis Phil., Astarte obliquata J. Sow., 
Cypraea avellana J. Sow., Nassa labiosa J. Sow., Natica 
hemiclausa J. Sow., Pleurotoma milrula J. Sow., Tro- 
chus cineroides S. Wood, Turritella incrassata J. Sow. 
The recent species common in the succeeding sub- 
stages or zones are rare at Walton-on-the-Naze. 

The Oakley Crag, or zone of Mactra (Spisula) 
obtruncata, exposed to the north-west of Walton, con- 
tains a fauna of more than 350 species, including 
a group of northern shells, such as Astarte compressa 
Mont., Tellina obliqua i. Sow., Scalaria groenlandica 
Chem., Trophon islandicus Gmel., T. scalariformis 
Gould. The Crag of Bentley and Tattingstone is 
thought to be rather younger than the Waltonian. In a 
section formerly visible near Bentley it was seen abutt- 
ing against a reef of Coralline Crag. 

The Newbourn Crag, or zone of Mactra (Spisula) 
constricta, is developed in Suffolk on the north side of 
the river Stour, and is distinguished by a scarcity of 
southern mollusca and by the presence of Cardium an- 
gustatumi. Sow., Mactra ovalis J. Sow., Tellina obliqua 
J. Sow., T. praetenuis Leath., Nucula cobboldiae J. Sow., Purpura lapillus Linn., etc. 
At Sutton this division of the Red Crag surrounds an island of Coralline Crag, on whose 
sides two strand-lines of Newbournian age, 3 m. (10 ft.) apart, have been traced. 

The Butley Crag (zone of Cardium groenlandicum) occurs yet farther north, and 
is marked by a further diminution of southern, and increase of northern, types. The 
species Tellina (Macoma) obliqua 1. Sow., T. praetenuis Leath. Mactra constricta S. Wood, 
and Cardium. angustatum J. Sow., together form a great part of the deposit; while the 
northern forms Cardium groenlandicum Chemn., Buccinum groenlandicum Chem., Natica 




fcoO 



280 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

groenlandica Beck, and Tritonofusus altus S.Wood, are more conspicuous than in the 
older crags. 

The Norwich Crag (Icenian of F. W. Harmer), to 55 m. (180 ft.) or more, 
occupies a larger area than any of the preceding deposits. It extends through East 
Suffolk from Aldeburg northwards, by Beccles, to the Bure Valley in Norfolk, a 
distance of about 64 km. (40 miles). It cuts off the Coralline Crag abruptly near 
Aldeburgh, and thickens rapidly northward, to 41 m. (135 ft.) at Leiston, and 55m. (180ft.) 
at Lowestoft. It is only 5 to 9 m. (16 to 30 ft.) thick in the Yare Valley, however, 
and 2.5 m. (8 ft.) at Aylsham, beyond which place it has not been traced. The Nor- 
wich Crag forms a variable group of sands, laminated clays, and pebbly gravels with oc- 
casional seams of shells; the whole group being more evenly stratified than the beds of 
the Red Crag, and containing a fauna of more recent character than they. The extinct 
and southern molluscan species are few in number and of rare occurrence, while northern 
forms not found in the Red Crag make their appearance, notably Astarte borealis Chem., 
A. elliptica Brown, Mactra subtruncata Da Costa, Eumargarita groenlandica Chem., 
Velutina undata Pen. The marine fauna is relatively small (about 150 species) and most 
of the more abundant species are common living British forms. Of the 30 species of drifted 
non-marine mollusca, only three are extinct. In a conglomeratic bed ("Stone-bed") at the 
base of the Norwich Crag mammalian remains are locally abundant, whence the old name 
"Mammaliferous Crag" applied to this group. These remains are of Lutra reevei Newton, 
Gazella anglica Newton, Cervus carnutorum Lang, Equus stenonis Cocchi, Mastodon 
arvernensis Cr. and Joub., Elephas antiquus Falc, Microtus intermedins Newt., Trogon- 
therium cuvieri Owen, and the marine mammals Delphinus delphis Linn, and Trichechus 
huxleyi Lank. 

The Chillesford Beds (5 to 6 m., 16 to 20 ft.) are a series of micaceous sands with 
an overlying estuarine clay. They rest indifferently on the older crags, and are traceable 
along a sinuous belt of country from Walton-on-the-Naze to Mundesley in Norfolk. 
Characteristic fossils are Cardium edule Linn., Tellina (Macoma) calcarea Chem., T. 
obliqua J. Sow., Mya truncata Linn., Mactra ovalis 3. Sow., Leda oblongoides S. Wood, 
Nucula cobboldiae J. Sow. 

Weybourn Crag (to 4 m., 13 ft.). At Chillesford in Suffolk the Chillesford Beds 
pass upward into fine micaceous sand and sandy clay with Buccinum undatum Linn., 
Purpura lapillus Linn. etc. Farther north they appear to pass laterally into green and 
blue clay with loamy sand, well seen on the Norfolk coast, west of Cromer. These have 
yielded over 50 species of marine shells, of which five are extinct and nine are Arctic forms. 
Among the species present are, Astarte borealis Chem., Cyprina islandica Linn., Mya 
arenaria Linn., Saxicava arctica Linn., Tellina (Macoma) baltica Linn., Littorina littorea 
Linn., Buccinum undatum Linn., Neptunea antiqua Linn. 

The Cromer Beds (to 10m., 33ft.), which outcrop from beneath boulder clay 
on the Norfolk coast, form the highest recognized member of the East Anglian Pliocene 
deposits. They comprise: 

m. ft. 

3. Upper Freshwater Bed : Sand and blue clay containing plants and 

non-marine mollusca — Succineaputris Lin n. , 
Sphaerium corneum Linn., Valvata piscinalis 
Mull., Pisidium amnicum Mull., etc. . . 0.6 to 2,1 2 to 7 
2. Forest Bed : Laminated estuarine clays and lignite alter- 

nating with gravels and sands with masses 
of peat, stools and branches of trees, mam- 
malian bones and teeth ........ to 7,0 to 23 

1. Lower Freshwater Bed: Carbonaceous, green, silty clays with seeds, 

lignite, etc to 1,5 to 5 

The plants contained in the above group include about 60 species of flowering forms, 
nearly all still living in Norfolk. The land and freshwater mollusca belong to about 60 
species, of which Limax modioliformis Sandb., Nematura runtoniana Sandb., Viviparus 
glacialis S. Wood, V. media Woodw., Pisidium astartoides Sandb., appear to be extinct, 
and five others, including Corbicula fluminalis Mull., are no longer living in Britain. The 
marine species are all Weybournian forms, and probably in part derived. 

Of the fish, Platax woodwardi Ac, and Gadus morhua Linn., may be named, and 
there are 12 other kinds, marine and freshwater. There are also a few reptiles (e. g. Vipera 
berus Linn), amphibians (e. g. Bana temporaria Linn., Triton cristatus Laur.), and birds 
(e. g. Anser, Mergulus, Bubo ignavus Forster). Mammals are well represented — nearly 
60 species, mostly terrestrial and riparian. They include Canis lupus Linn., C. vulpes 



Great Britain. — -White: Sedimentary Rocks. — Neogene. (III. 1.) 281 

Linn., Machaerodus, Hyaena crocuta Erxl., Ursus spelaeus Blum., Mustela martes Linn., 
Lutra vulgaris Erxl., Ovibos moschatus Zimm., Cervus (9 spp.), Hippopotamus, Sus scrofa 
Linn., Equus stenonis Coccm, Rhinoceros etruscus Falc, Elephas antiquus Falc, E. meri- 
dionalis Nesti., Microtus arvalis Pal., Castor fiber Linn., Trogontherium cuvieri Owen, 
Talpa, Sorex, Myogales moschata Linn. 

The sandy clay with Yoldia (Leda) myalis Couth., and succeeding "Arctic Fresh- 
water Bed" with Betula nana Linn., which overlie the Cromer Beds, are now regarded 
as Pleistocene deposits. 

2. Cornwall. 

St. Erth Beds (6 m., 20 ft.?). These occur at St. Erth in western Cornwall, on the 
neck of land between St. Ives and Mounts Bays. They form small patches of sands and clays, 
30 to 45 m. (100 to 150 ft.) above sea-level, occupying hollows in Palaeozoic slates. The 
clays have yielded between 80 and 90 species of marine mollusca, most of the forms being 
such as occur in the lower part of the Red Crag beds of East Anglia. Some southern 
species, however, such as Cardium papillosum Poli, Cardita aculeata Poli, Fusus corneus 
Linn., Nassa mutabilis Linn., N. reticostata Bellardi, are not known in the Pliocene 
of East Anglia, while the northern and arctic forms, so abundant in the higher part of 
the Red Crag, are absent. 

A raised beach or strand-line, probably of about the same age as the St. Erth Beds, 
contours the hill of St. Agnes Beacon, at a height of 113 m. (370 ft.) above sea-level. 
Two older erosion-platforms, at about 228 m. (750 ft.) and 300 m. (1000 f(.), occur in the 
neighbourhood of Camelford and Bodmin (Barrow 1908). 

' 3. Other Localities. 

Remains of Pliocene mammals have been found in limestone fissures in Dorset and 
Derbyshire. At Dewlish, in the former county, bones and teeth of Elephas meridionalis 
Nesti and E. antiquus Falc. occur in fine sand with some polished pebbles, filling a trench- 
like hollow, of artificial aspect, on the top of a Chalk ridge (Reid 1899, Fisher 1905). 

The reddish ossiferous deposit, containing relics of E. meridionalis Nesti, Mastodon 
arvernensis Croiz. and Joub., Rhinoceros etruscus Falc, observed in the Victory quarry near 
Doveholes, Derbyshire, occupied a fissure of more normal type; and there were indications, 
in this case, that the bones (some of them gnawed by carnivora) had been washed in from 
above. (Dawkins 1903.) 

Indications of the existence of Pliocene deposits on the sea-bed off the British coasts 
are afforded by the Pleistocene drifts of the Isle of Man and the north-east of Scotland. 

Deposits of Uncer tain Age. 

Besides the foregoing there are, in the south of England, many unfossiliferous accu- 
mulations, possibly or probably of Pliocene age. 

Such are the apparently-marine pebble-beds (Westleton Beds) which underlie the 
Pleistocene boulder clay and other glacial deposits in Suffolk and Norfolk; also parts of 
the probably-fluviatile, inland, high-level gravels ("Clay with flints", "Pebble gravel", 
"Plateau gravel", "Southern Drift") which range from 30 to 150 m. (100 to 500 ft.) about 
the level of the principal rivers in their neighbourhood. 

b) Physiographical Conditions. 

Concerning the condition of the British region in the Miocene period, nothing 
is positively known. From the entire absence of recognizable deposits of this 
epoch ; from the small areal range and character of the Oligocene beds in the South 
of England ; and from the nature and geographical position of the Miocene strata in 
north-western Europe, it is inferred that Britain was then dry land. 

The east-and-west folds of the Weald, of Kingsclere, Wardour, the Isle of 
Wight, South Dorset, &c, which have played so important a part in determining 
the existing physiography of the south of England, are believed to be mainly of 
Miocene age. Certain it is, that the principal movements affecting the rocks of the 
Isle of Wight are of more recent date than the local Oligocene strata. These 
'posthumus Armorican' folds are disposed en echelon, and have a markedly 
asymmetrical form, their northern limbs being, as a rule, more strongly inclined 



282 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

than their southern. In most cases the flexing is of a gentle order, but locally, 
e. g. in the Isle of Wight, South Dorset, and Surrey (west of Guildford), the distur- 
bances have been more violent, and — in the second and third of these localities — 
the stresses have found relief in over-thrust faulting. The broad tectonic depres- 
sions of the London and Hampshire basins appear to be in part of more recent 
development than the better-defined folds just mentioned. 

The Boxstones and Lenham Beds record the encroachment of the Messinian 
sea upon English territory. The extent of this transgression can only be surmised, 
but it probably was considerable, for the fauna of the Lenham iron-sands is not of a 
littoral type: it indicates, according to C. Reid 1890, a depth of not less than 73m. 
(240 ft.) — and the sands themselves, as well as their (Diestian) equivalents in Belgium 
and Holland, rest on a peneplain of erosion for which it is hard to assign any prob- 
able western limit. It seems that much of the topographical relief arising from the 
development of the Miocene folds had already been obliterated when the early 
Pliocene transgression took place. At or about the close of the Messinian epoch 
the sea retired from the south-eastern angle of England, apparently as a result of 
the earth-movements which elevated the crete de l'Artois and its continuation 
north-west of Dover Straits; and the Coralline Crag (Gedgravian) of Suffolk, though 
lying at a lower level than the Lenhamian of Kent by some 150 m. (500 ft.), seems 
to have accumulated, as a current-built shell-bank, in a depth of water no greater 
than that indicated by the Lenham fauna. 

The Red and Norwich Crags are clearly shore deposits, comparable, in a large 
measure, to the beaches and shell-banks formed on the coast of Holland at the present 
day, and pointing to the prevalence of easterly winds over the eastern part of the 
English area in Newer Pliocene times. The northward to north-eastward overlap 
of the younger zones of the Red Crag upon the older, and the overlap or overstep 
of the Norwich Crag upon the Red Crag, are taken to imply the continued north- 
ward retreat of the shore-line, proceeding pari passu with an elevation of the 
land to the south and south-west, and a depression of the sea floor over parts of the 
North Sea area and of Holland, to the north and north-east. 

In the Chillesford Beds F. W. Harmer sees the sediment of a western distri- 
butary of the Rhine, and other indications of a large river flowing from the south- 
east are presented in the constituents of the estuarine gravels of the Cromer Beds. 

c) Economic Products. 
The shelly sands, or "crags", of East Anglia have been extensively dug for 
agricultural purposes, chiefly as manure for the heavy soils on the Eocene and Glacial 
clays. They are used also for paths, e. g. in the London parks. The pebble-beds are 
dug for road-mending, and the sands for general purposes. Phosphatic nodules and 
phosphatised bones, from the conglomeratic beds (Bone-bed, Stone-bed) at the base of 
the Coralline and newer Crags of East Anglia, were formerly much used in the manu- 
facture of chemical manure. 

II. Igneous Rocks. 

By A. Harker. 

Igneous action during early Tertiary time affected in greater or less degree a 
large part of the British area, but was most developed in the West of Scotland, 
including the Inner Hebrides, and the North-East of Ireland. In these tracts, where 
the record is most complete, we can distinguish three successive phases of activity: 
1. Volcanic, 2. Plutonic-, and 3. Minor Intrusions; and each phase includes 
distinct episodes, which followed one another in a definite sequence, and are marked 
by district groups of igneous rocks. In the outlying tracts only the last phase has 
left its evidence. 



Great Britain. — Harker: Igneous Rocks. 



(III. 1.) 283 



In the succession thus 
indicated we have further to 
recognize two different cate- 
gories of events, Regional and 
Local. The regional groups 
of rocks have a wide dis- 
tribution, in some cases per- 
haps almost coextensive with 
the whole region affected. 
Their intrusion and extrusion 
were related to crust-move- 
ments of a broad type, in- 
volving faulting and differen- 
tial subsidence over consider- 
able areas. In this way, in 
particular, the tract including 
the Inner Hebrides has been 
let down between the Outer 
Hebrides on one side and the 
mainland of Scotland on the 
other. The local groups of 
rocks occur within more re- 
stricted districts, each sur- 
rounding a certain centre 
which was marked out from 
an early stage as a special 
focus of activity. About 
these centres there were crust- 
movements of a more localized 
and accentuated kind, in- 
volving a certain degree of 
lateral thrust and in some 
cases strong anticlinal folding. 
Excluding Ireland, the chief 
centres of special activity 
were: a. St. Kilda, a small 
island group about 80 km. 
(50 miles) west of the Outer 
Hebrides; b. Central Skye; 
c. Southern Rum; d. the 
peninsula of Ardnamurch- 
an; e. South-eastern Mull; f. Northern and Central Arran. It is 
possible that we ought to add Carrock Fell, on the north-eastern border of the English 
Lake District, but the Tertiary age of the igneous intrusions at this centre cannot 
be proved. The situations of the several centres are shown on the sketch- 
map (fig. 62). 

Owing to the absence of the Tertiary sedimentary formations in the northern 
parts of Britain, the age of the igneous outbreaks cannot be fixed with precision. 
The volcanic series contains in some intercalated deposits a flora referred to the 
Eocene, but it is possible that the later phases of igneous activity were prolonged 
into subsequent divisions of Tertiary time. On the other hand, the igneous rocks 
of the Inner Hebrides have been affected by profound erosion, which has left the 




Fig. 62. Sketch-map to show the distribution of 

the British Tertiary igneous rocks (A. Harker). 

Scala 1 inch to 150 miles, or 1 : 10 000 000. 

The broken curves enclose the two areas In which basalt lavas 
are preserved, viz. the Inner Hebrides and the plateau of Antrim. 
The situations of the principal plutonic centres are indicated 
by letters: K = St. Kilda; S = Skye; R = Rum; A = Ard- 
namurchan ; M = Mull ; Ar = Arran ; Mo and C = Mourne Mts. 

and Carlingford district; X = Carrock Fell. 
A dotted curve marks the southern limit of known Tertiary 
dykes of basalt and augite-andesite. Z is the area of distri- 
bution of dolerites, diorites, etc., of possibly Tertiary age, in 
the Midlands of England. W is the situation of the Wolf Rock 
phonolite. Rockal, lies about 300 km. (190 miles) west of St. Kilda. 
Redrawn with modifications from the Memoirs of the Geological 
Survey of the United Kingdom. The Tertiary Igneous Rocks 
of Skye, p. 3, 1904, with the permission of the Director and 
of H. M. Stationery Office. 



284 (III. l.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

plutonic masses standing out as mountains, and almost the whole of this erosion was 
accomplished before the Glacial epoch. 

Petrographically the regional and the local groups of rocks present a marked 
contrast. The regional rocks are, with relatively few exceptions, of basic nature, 
and they appear to have alkaline affinities (Harker, 1912), though not very pronoun- 
ced. The local groups show a much wider range, from ultrabasic to thoroughly 
acid, and belong in general to types of the calcic branch. The North British Ter- 
tiary igneous area forms part of the 'Brito-Icelandic' petrographical province of 
Judd, and its relations are with the Arctic regions. Only in certain localities remote 
from the principal theatre of activity are found some rocks of highly alkaline nature, 
which suggest a relation with the Mid-Atlantic region. On Rockall, about 380 km. 
(240 miles) west of the Outer Hebrides, is a rock composed of aegirine, albite, and 
quartz; and the Wolf Rock, situated 30 km. (20 miles) south-west of the Land's End 
of Cornwall, consists of phonolite (Allport 1871, 1874, Teall 1888). The nephe- 
line-basanite dyke of Butterton hag already been mentioned (p. 170). 

1. Volcanic Phase. 

Basaltic lavas. — The principal event of the volcanic phase was the outpouring 
of basaltic lavas on a regional scale. These basalts make the greater part of the 
islands of Skye, Canna, Eigg, Muck, and Mull, with parts of Morven and Ardna- 
murchan on the Scottish mainland. These areas are merely relics left by erosion, 
and may be fragments of a continuous lava-field which once extended from 
Ireland to the Arctic regions, a. distance of more than 3000 km. (2000 miles) 
There is rto accumulation about particular centres, and, as Sir A. Geikie has 
shown, the lavas were not poured out from great volcanoes, but from innumerable 
small fissures distributed over the region. The thickness left by erosion amounts 
in places to over 1000 m. (3000 ft.), built up by many overlapping flows. The lavas were 
erupted subaerially, and the land stood relatively higher than at the present day. 
The courses of rivers of the volcanic epoch are indicated by fluviatile conglomerates, 
which at the eastern end of Canna reach a thickness of nearly 100m. (300 ft.) and are also 
found, intercalated among the basalts, in Skye, Rum, Eigg, and Mull. The material 
of these conglomerates is of basalt together with pebbles of the underlying pre- 
Tertiary strata, derived from volcanic agglomerates. At many horizons in the basalt 
succession old land-surfaces are indicated by the weathered crusts of lava-flows, 
and there are occasionally small lacustrine deposits with the remains of land-plants. 
Beds of tuff and agglomerate are exceptional and of small importance, apart from 
the local accumulations to be mentioned below. 

The lavas are mostly olivine-basalts, and are very commonly amygdaloidal, 
the chief contents of the cavities being minerals of the zeolite group. These minerals 
must be regarded as essential constituents of the rocks, and the frequent abundance 
of analcime and natrolite thus implies a noteworthy richness in soda. In certain 
of the lavas analcime occurs as a primary constituent of the ground-mass. Among 
the less frequent types are basalts very rich in olivine, while olivine-free lavas are also 
found. Where the basalts have been metamorphosed by subsequent plutonic intrusions, 
the zeolites are converted to felspars, the augite usually to hornblende and biotite. 

The basaltic districts are broken by faults and divided into separate plateaux, 
the general arrangement being monoclinal, with gentle inclination. This faulting 
occurred during the phase of minor intrusions. 

The important local episodes of the volcanic phase are two, and we will notice 
these in turn. 

Volcanic agglomerates and tuffs of basaltic nature. — Among the basalts 
generally there is little evidence of explosive action; but at certain places vulcanicity 



Great Britain. —  Harker: Igneous Rocks. (III. 1.) 285 

took this form episodically and at an early stage. This is proved by accumulations of 
volcanic agglomerate and tuff in the lower part of the basalt series. They are of 
lenticular form, reaching a thickness sometimes of 300 or 400 m. (1000 to 1250 ft.) 
but rapidly thinning out in a lateral direction. There is more direct evidence of the 
existence at this early epoch of large volcanoes, for the actual vents are sometimes 
marked by cylindrical 'necks' of coarse agglomerate. The two largest and most 
remarkable of these old vents are at Kilchrist in Skye and in the centre of Arran: 
each has a diameter of over 3'/2km. (2 miles). The blocks in these agglomerates are 
often of large size, and are partly of basalt, partly of non-volcanic rocks. There 
are also large masses which have been engulfed in the vent from neighbouring 
stratified formations; and in this way the Arran vent has preserved evidence of 
the former existence in this district of Rhaetic, Liassic and Cretaceous strata 
(Peach and Gunn). 

In the island of Mull, which at present has been only partly surveyed, the 
succession of events is more complex than elsewhere, and there occurs a very peculiar 
breccia. It was formed after the basalt lavas had been sharply folded, invaded 
by plutonic intrusions, and deeply eroded. It thus rests unconformably upon the 
older igneous rocks and upon the Moine gneisses, which here lie at the base of all. 
Subsequently the breccia has been itself folded and penetrated by newer plutonic 
intrusions (Bailey 1912). 

Trachytic and rhyolitic rocks. — Among the great spread of basalts there occur 
locally a few volcanic rocks of more felspathic and acid nature. In Mull certain 
volcanic 'necks' composed of trachytic agglomerate break through the basalts, 
and are pierced by plugs of trachyte. These may belong to a late epoch of the 
volcanic succession, but no corresponding lava-flows have been detected. There 
is however, a rhyolite associated with the peculiar breccia already mentioned. 
In Skye, on the northern border of the Cuillin Hills, a trachytic and rhyolitic group 
is intercalated in the midst of the basalts. It has a total thickness of about 
700 m. (2000 ft.), but each member of the group thins away rapidly. The lower 
part consists chiefly of trachyte lavas, and these are succeeded by rhyolitic tuffs 
and lavas. Trachytes occur again near Bracadale, about 20 km. (12 miles) north- 
west of the Cuillin Hills. 

2. Plutonic Phase. 

Igneous action in the plutonic phase was localized wholly at the special centres 
already enumerated (Fig. 62). At each of these centres there were successive intrusions 
of different magmas, constituting distinct episodes; and the order of succession 
of these is always the same, although they are not all represented at any one centre. 
A partial exception is found in Mull, where two plutonic phases may be recognized, 
divided by a period of erosion with some revival of volcanic action. 

The geological relations of the plutonic masses are not always the same. Most 
of the larger masses have something of the sheet-like or laccolitic habit, though with 
much irregularity in detail (Fig. 63). Such a mass has been built up, not by a single 
act of intrusion, but by repeated injections, not always identical in petrographical 
characters. Often there is a general parallel disposition of the parts, and this is 
very pronounced in the most basic rocks. On the other hand, there are boss-like 
masses and these are usually of more uniform composition. 

The order of succession of the several groups of plutonic rocks was that of 
decreasing basicity: peridotites and other ultrabasic types, eucrites, gabbros, 
and finally granites, normal rocks of mean acidity being unrepresented. In some 
cases there was a marked interval between one group and that following; in other 
cases the interval was very brief. We shall notice the several groups in chrono- 
ogical order. 



286 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

Peridotites and allied rocks. — This ultrabasic group is seen in Skye, on the 
south-west side of the main plutonic tract, but it attains a much greater development 
in Rum. The characteristic types are on the one hand dunite and other very 
olivine-rich varieties and on the other hand allivalites, consisting of olivine and 
anorthite in various relative proportions. Enstatite and augite are less abundant 
constituents. The intrusions usually show a stratiform appearance, due to alter- 
nating layers of olivine-rich and felspar-rich rocks, and a parallel arrangement of 
the crystals is also a common feature. 

Eucrites.  — These rocks are well developed in Rum, where they have been 
intruded partly beneath and partly into the ultrabasic group, and there is another 
large intrusion forming the headland of Ardnamurchan. The eucrites consist of 
a basic felspar (anorthite or bytownite) and pyroxene (often both monoclinic and 
rhombic), with or without olivine. Some varieties rich in olivine and poor in pyroxene 
graduate into the allivalite type. 

Gabbros and norites. — Basic intrusions occur at most of the plutonic centres, 
and they are usually of gabbro, consisting of labradorite, augite, usually olivine, 
and some titaniferous iron-ore. Rhombic pyroxene is uncommon, norite and 
hyperite being almost restricted to Central Arran. The intrusive masses are often 
variable and heterogeneous in petrographical characters, but a pronounced banding 
is much less common here than in the ultrabasic rocks and eucrites. 

Gars-bheinn UlfhartPoint 

N.byW. ^<^p „...- 



^j^T^SmtM^^-^i- 



faAwJJ Torridon Sandstone \-~~t--A Basaltic Lavas | JGabbro 

Fig. 63. Section through Gars-bheinn, Skye, to illustrate alternations of 

basaltic lavas and gabbro, due to the successive intrusions of the latter 

rock having followed different bedding-planes in the lavas. 

Scale: 2 inches to 1 mile or 1:126,720. 

Reproduced from the Memoirs of the Geological Survey, The Tertiary Igneous Rocks of 

Skye, p. 89, 1904; with the permission of the Director and of H. M. Stationery Office. 

Olivine-gabbro occurs as a composite stratiform mass on St. Kilda. In Skye 
a like rock makes a complex laccolitic body, 13 km. (8 miles) in diameter and pro- 
bably 1000 m. (3000 ft.) thick, from which the Cuillin Hills are carved out. This in- 
trusion is in the lower part of the volcanic series, and it has invaded and enveloped 
the earlier-intruded peridotite (Fig. 64). Farther east an olivine-free gabbro breaks 
vertically through the Cambrian dolomites N. W. of Broadford. There are small in- 
trusions of gabbro in Rum, and a dyke-like mass occurs on Muck. In Mull the earlier 
gabbro, which is not extensively exposed, is of a felspar-rich variety. The later gabbro, 
of a more normal type, makes a number of intrusions of no great size, the largest con- 
stituting Beinn Buidhe in the south-east of the island. In Central Arran a broken ring of 
plutonic intrusions round the great volcanic vent comprises gabbros (with and without 
olivine) and norites, these basic rocks being often metamorphosed and injected by sub- 
sequent acid intrusions. Finally we may mention Carrock Fell, in Cumberland, where 
occur laccolitic intrusions of olivine-free gabbro (Harker, 1894) possibly but not 
demonstrably of this age. 




Great Britain. — Harker: Igneous Rocks. 

Granites, with granophyres. — The 

acid plutonic rocks have sometimes the 
granitoid, sometimes the granophyric 
structure, and these may be found in 
different parts of the same mass. In 
other respects these rocks are much less 
variable than the basic rocks, and band- 
ed structures are rarely seen. In some 
places the margin of a mass becomes 
porphyritic, felsitic, or spherulitic. In 
other places there is no indication of 
rapid chilling, and it is sometimes 
evident that the acid rock has been 
intruded only a little later than a basic 
rock with which it is in contact. In 
this latter case there have been mutual 
reactions between the two, with the 
production of hybrid or mixed rocks. 
The admixture has been effected both 
by impregnation and partial fusion of 
the basic rock-masses and by inclusion 
and partial dissolution of basic material 
in the acid magma (Harker, 1904). 

Petrographically the acid rocks 
may be divided into three sub-groups: 
a. less acid, silica-percentage 70 — 72, 
with hornblende or augite, seldom bio- 
tite; b. more acid, silica-percentage 
75 — 77, with less of the ferro-magnesian 
element, often biotite; c. relatively 
alkaline, with riebeckite. 

a. To the less acid sub-group 
belongs the large tract of the Red 
Hills in Skye (Fig. 65). It has some- 
thing of the habit of a very irregular 
sheet, but is often transgressive in its 
behaviour, and to the east there is a 
distinct boss forming Beinn na Caillich 
and the adjacent Hills. To the west the 
granite is intruded beneath and into the 
gabbro of the Cuillin Hills (Fig. 64), and 
on Marsco occur some interesting hybrid 
rocks, where strips of gabbro have 
been enveloped by the acid magma. 
A remarkable granophyre enclosing 
half-digested gabbro material is in- 
truded along the border of the vol- 
canic vent of Kilchrist. There is a 
considerable mass of granite, usually 
granophyric, in the West of Rum, and 
peculiar hybrid rocks have been pro- 
duced by the admixture of granite and 






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The British Isles. — III. Stratigraphy. — 13. Tertiary. 



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southern part of Raasay, near Skye, 
and granophyre containing riebeckite, 



i eucrite. In the valley of Fiadh-innis 

* and elsewhere such admixture, in con- 
3 junction with contemporaneous move- 
5 ment, has given rise to well-banded 

gneisses. At Glendrian and elsewhere 
3 in Ardnamurchan a hornblende-biotite- 

granite breaks through the eucrite, and 
m again various hybrid products have 
^ been formed. Granites and granophyres, 
«,- mostly augitic, occur in Mull. There 

* is a large mass about Loch Ba, while 
■« another crosses Glen More and invades 
» the gabbro of Beinn Buie. These 

belong to the later epoch; the earlier 
M granophyre, seen on Sgurr Dearg, is 
not essentially different. Hornblende- 
£8 granite, sometimes with biotite, makes 
£o part of the complex surrounding the 
3fc volcanic vent of Central Arran, and 
|>g has there invaded the gabbros and 
«•§ norites. The so-called 'diorites' are 
fj*™ gabbros uralitized by metamorphism, 
g S . and the 'quartz-diorite' of Zirkel is 
.§* really a hybrid product. The augite- 
.2^ granophyre of Carrock Fell has also 
*5, entered into reactions at its junction 
Jo with the neighbouring gabbro. (Har- 
g| ker, 1895). 

go b. The granite of St. Kilda belongs 

Zja probably to the second sub-group. The 
>,»3 hornblende-biotite-granite of Beinn an 
>g Dubhaich in Skye is also one of the 
ma more acid kind. It makes an elongated 
<*£ boss, 2 1 / 2 km. (l 1 ^ mile) long, in a 
% curved anticline of the Cambrian dolo- 
mites, which are highly metamorphosed. 
Finally there is the large mass of bio- 
2 tite-granite which occupies most of 
° the northern half of Arran, making a 
is nearly circular area with a diameter 
of 11 — 13 km. (7 — 8 miles). The man- 
S ner in which the surrounding strata 
J} dip away from the mass seems to indi- 
E cate a laccolitic habit. The prevalent 
2 coarse granite is pierced by a more 
■a fine-textured rock, otherwise similar, 
c. Although the acid plutonic 
rocks are in general distinctively 
of calcic affinities, alkaline types 
are not wholly wanting. In the 
occur thick sheets of microperthitic granite 
and there is a limited occurrence also at Meall 






Great Britain. — Harker: Igneous Rocks. (III. 1.) 289 

Dearg in the Red Hills of Skye. At the southern end of the principal belt of igneous 
action alkaline rocks are again found, the islet of Ailsa Craig, south of Arran, being 
composed of a riebeckite-microgranite (paisanite). 

More remarkable is an isolated occurrence of syenite, which forms a small 
island opposite Carsaig, on the south coast of Mull. It has lO 1 /^ per cent, of 
alkalies, and contains aegirine and arfvedsonite. 

3. Phage of Minor Intrusions. 

In this final phase regional igneous activity was resumed with great energy 
and over an extensive area. The intruded magmas took the habit first of regular 
sills and later of innumerable dykes. This change of behaviour was related to 
changes in the mechanical conditions affecting the region, and especially to 
the plateau-faulting. Sheet-formed intrusions posterior to the faulting are mostly 
of small size and of irregular habit. The rocks of this regional suite are, as a rule, 
of consistently basic composition, often with indications of alkaline affinities, but 
exceptions are found in certain subsidiary groups, which seem to belong to a late 
epoch. It appears that progressive differentiation of the parent-magmas attained 
an advanced stage before the cessation of activity, and probably subsidiary centres 
of differentiation were established, distinct from the special centres which had been 
operative from the beginning. 

In addition to these regional groups of minor intrusions, there are others connec- 
ted with the special centres at which activity had been localized during the plutonic 
phase. Where the record is most complete, as in Skye, these local groups fall under 
three heads: — acid, basic, ultrabasic; the order being the reverse of that found in 
the plutonic rocks. 

a) Regional minor intrusions. 

Basic sills. — Regular sill-intrusions are very numerous both in the basalt 
lava group and in the underlying Jurassic strata of Skye, Eigg, Mull, and other 
parts of the region. Where the volcanic rocks have been removed by erosion, the 
sills are still numerous in well-bedded strata, such as the Trias of Southern Arran, 
but not in massive formations such as the older rocks of South-eastern Skye and the 
Torridon Sandstone of Rum. The thickness of the individual sills ranges usually 
from 1 to 30 m. (3 to 100 ft.). 

The prevalent petrographical type in most districts is an ophitic olivine- 
dolerite, and sills of this kind are widely distributed in Skye, Eigg, Muck, Mull, etc. 
A variety with conspicuous porphyritic crystals of labradorite is more common on 
Canna and Sanday. The rarer mugearite type is represented by a few sills in Skye, 
Eigg and Muck, and allied rocks occur in Rum and Canna. At certain localities 
in Skye there are double sills, consisting of an upper member of porphyritic olivine- 
dolerite and a lower member of mugearite. Some of the olivine-dolerite sills of 
Raasay, Northern Skye, and the Shiant Isles, 20 km. (12 miles) north of Skye 
approximate to picrite, being rich in olivine and containing a purplish pleochroic 
augite. A great sill, 160 m. (500 ft.) thick, in the Shiant Isles is of coarse 
texture and variable nature, becoming ultrabasic in its lower part. In Southern 
Arran there are some sills of analcime-dolerite, and others of a type very rich 
in magnetite. On the other hand quartz-dolerite sills are found exceptionally 
in Arran and Ardnamurchan. 

Basic dykes. — One of the most striking features of Tertiary igneous action 
in Britain is the immense number of basic dykes, usually running in a N.W. or 
N.N.W. direction. They are most abundant in the Inner Hebrides and on the 
west coast of Scotland, but extend southward to the Isle of Man and Anglesey 

Handbuch der regionalen Geologie. III. 1. 19 



290 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

(Greenly, 1900) and south-eastward across southern Scotland to the counties of 
Northumberland and Durham (Teall, 1884) (Fig. 62). In this last area the direction 
of the dykes is W. N. W. The width of the dykes probably averages 1 — 17 2 rn. 
(3-4 ft.), but some are 30—40 m. (100-120 ft.) wide. Where they are most 
numerous, it is common to find a number of distinct dykes intruded side by side 
in the same fissure. 

Basic dykes have been intruded at various times during the Tertiary igneous 
history. Some belong to the volcanic phase, and represent the feeders of fissure- 
eruptions of basalt; others doubtless fed the sill-intrusions; but the majority are 
posterior to the sill epoch. They belong certainly to various subsequent epochs, 
but the chronological sequence of the different groups is not easily made out. 

The larger dykes consist of dolerites of various kinds, with or without olivine 
and with or without porphyritic crystals of felspar and less often of augite. The 
smaller dykes have commonly a finer texture, and may be termed basalts. The 
dykes very generally become finer-textured towards the edges, and some of them 
have a thin skin of tachylyte. On certain less common varieties, which approach 
mugearite in composition, there is a thicker glassy crust. In the more outlying 
districts the dolerite dykes contain a purplish pleochroic augite and sometimes 
interstitial analcime. More decidedly alkaline types are found in Argyllshire (in- 
cluding its islands), such as camptonite and monchiquite; but these dykes, though 
they have been claimed as Tertiary, may be referred more probably to a late Paleo- 
zoic age (p. 189). 

Subsidiary groups. — In all cases in which evidence of relative age can be 
obtained, these belong to the later episodes of the phase of minor intrusions, and 
some of them indicate considerable petrographical divergence. They assume the 
form sometimes of dykes, sometimes of sheets, but the latter have not the regularity 
or extent of the sills noticed above. 

Here belong certain sheets of small thickness and irregular behaviour, which 
are often noticeable as presenting tachyly tic surfaces. These occur at numerous 
localities in south-eastern Skye, Eigg, Mull, and elsewhere. Some of the rocks are 
basalts, while others are rather to be regarded as basic augite-andesites. 

Another well characterized group is that of the augite-andesite dykes 
(with some sheets). They are found in Skye and other parts of the Inner Hebrides, 
though much inferior in number to the basalt dykes. They are more abundant in 
the more southern districts, viz. Arran, Bute, the Cumbrae Isles, and parts of Argyll- 
shire, and similar rocks become the predominant type among the Tertiary dykes 
in Anglesey, Northumberland, and Durham. The rocks vary in character from 
basic augite-andesites to dacites, the more acid varieties containing much inter- 
stitial glass. 

Related to the preceding group are the dykes and sheets of pitchstone. These 
are rare in most parts of the Inner Hebrides; but in Eigg, besides some dykes, there 
is a great sheet, 130 m. (400 ft.) thick, forming the prominent Sgurr. A similar 
rock makes the little island of Oigh-sgeir or Hyskeir, about 29 km. (18 miles) 
farther west. In Arran alone dykes and sheets of pitchstone are numerous. These 
rocks vary in composition, subacid types being more common than acid. Augite- 
andesites and pitchstones are often associated, and at certain places in Arran the 
two occur together in the form of composite dykes. It is possible that some of the 
more acid pitchstones should be separated from the rest and attached to the 
local series of intrusions. 

Dykes of trachyte and allied rocks have a limited distribution. A group 
of such dykes, with pronounced fissile weathering, occurs about Drynoch, on the 



Great Britain. — Harker: Igneous Rocks. (III. 1.) 291 

west side of Skyo. Another group is found in the south-eastern part of Skye, and 
here the margins often show a quasi-spherulitic structure along lines following 
the direction of flow. Trachyte dykes are also represented in the Lome and Cowal 
districts of Argyllshire and elsewhere. 

On the other hand, the regional series includes some sheets and dykes of ultra- 
basic composition, or verging on ultrabasic. These likewise have only a limited distri- 
bution: they are known in the south-eastern part of Skye and a few other localities. 

b) Local minor intrusions. 

Acid group. — This, the earliest group of minor intrusions connected with the 
special centres, belongs to an epoch anterior to the regional faulting but in general 
posterior to the regional group of basic sills. Some of the acid intrusions, however, 
were closely connected with intrusions of basic magma, and form with them com- 
posite sills and dykes. In these the acid magma has been intruded, after only a 
short interval, along the middle of a basic sill or dyke, and there have been mutual 
reactions between the two. 

In general the minor acid intrusions occur within distinct areas, each surround- 
ing a granitic centre. In Skye the area has a greatest diameter of 36 km. (22 1 j i miles), 
in a N.W. — S.E. direction, with the granite of the Red Hills in the centre. Compo- 
site sills and dykes occur along a curved belt within the boundary of this area, 
on the northern and eastern sides of the granite. In most districts the acid intrusions 
are quite inferior in numbers to the (regional) basic ones, but in the southern half 
of Arran they are very numerous, and some of the sills attain a great thickness. 
Some of these are composite sills, and another is found in the southern part of Bute. 
Two sheets of acid rock occur in Eigg, where there is possibly a plutonic centre 
concealed below; while there are also acid dykes in the Lome district of Argyllshire, 
remote from any plutonic centre of Tertiary age. 

Most of the rocks of this group belong to simple petrographical types. The 
larger masses are usually of granophyre and the smaller of quartz -porphyry, 
often spherulitic. Exceptionally there are more felspathic rocks, orthophyres 
and bostonites. In Skye these occur sparingly on the border of the area, and 
others are found in the Arran district. 

Basic group. — Basic dykes belonging to local centres are not always easily 
separable from those of the regional series. It is found, however, that such dykes 
become extremely numerous about some of the plutonic centres, and may occur 
in great number intersecting the plutonic rock itself: the gabbro area of the Cuillin 
Hills in Skye is the most striking example. In some cases the dykes have a radiate 
disposition about the centres. This is only partially realised in Skye, but is well 
displayed in Rum. 

More remarkable are the inclined sheets, which are found in great numbers 
about some of the plutonic centres, dipping always towards the special centre to 
which they belong. The main gabbro mass of Skye is intersected by a vast number 
of sheets of dolerite with this arrangement. In Rum they are less developed. They 
are very numerous round the eucrite mass of Ardnamurchan, and in this case 
they do not occur in the plutonic mass itself but outside its border. In south-eastern 
Mull intrusions of this kind attain an enormous development and complexity. They 
belong to more than one epoch of injection, and are not all of basic nature. 

Ultrabasic group. — Minor intrusions of ultrabasic nature are only sparingly 
found. They intersect all other rocks which they encounter, and must represent 
the youngest intrusions connected with the local centres. They resemble in com- 
position the plutonic ultrabasic rocks, but often show porphyritic and other struc- 
tures indicative of their hypabyssal habit. 

19* 



292 (III. 1.) The British Isles. — HI. Stratigraphy. — 13. Tertiary. 

There is a group of ultrabasic dykes in the Cuillin Hills of Skye and the neigh- 
bouring district of Strathaird. They have a regular radiate arrangement, but repre- 
sent only the south-western half of the complete circle. Some larger and less regular 
intrusive masses occur in the same area, and in the neighbouring island of Soay 
there are irregular sills or sheets intruded in the Torridonian strata. Elsewhere 
ultrabasic dykes are known only in the south of Rum. 



Bibliography of the Tertiary of Great Britain. 

1871. Allport, S., Geol. Mag., pp. 247—250 (Phonolite, Wolf Rock). 

1874. — Geol. Mag., pp. 462—463 (id.). 

1851. Argyll, Duke of, Quart. Journ. Geol. Soc, vol. 7, pp. 89-103 (Leaf beds in Isle 

of Mull). 
1912. Bailey, E. B., Geol. Mag. p. 517 (Breccia in Mull). 

1908. Barrow, G., Quart. Journ. Geol. Soc, vol. 64, pp. 384-400 (High level platform, 

Bodmin Moor). 
1903. Dawkins, W. Boyd, Quart. Journ. Geol. Soc, vol. 59, pp. 105-132 (Pliocene Cavern, 
Derbyshire). 

1909. Dollfuss, G. F., Proc. Geol. Assoc, vol. 21, pp. 24, 101-118 (Classification of beds 

of Paris Basin). 
1905. Fisher, O., Quart. Journ. Geol. Soc, vol. 61, pp. 35-38 (Elephant trench, Dorset). 
1879. Gardner, J. S., Quart. Journ. Geol. Soc, vol. 35, pp. 209-228; 1882. Ibid., vol. 38, 

pp. 1-15 (Bournemouth Beds). 
1887. — Quart. Journ. Geol. Soc, vol. 43, pp. 270-300 (Leaf beds and Gravels of 

Ardtun, etc., Mull). 
1879-1886.  — and Ettinghausen, C. v.,Palaeont. Soc, Mon. British Eocene Flora, 2 vols. 
.1888. — , Keeping, H., and Monckton, W. H., Quart. Journ. Geol. Soc, vol. 44, 

pp. 578-635 (Barton and Bagshot Beds). 

1889. Geikie, Sir Archibald, Trans. Roy. Soc. Edinburgh, vol. 35, pp. 21-184 (Tertiary 

volcanic action). 

1897. — Ancient Volcanoes of Great Britain, vol. 2, pp. 107-465. 

1903. — Text Book of Geology, 4" 1 Ed., pp. 1229-1233, 1249-1252, 1280-1289. 
1900. Greenly, E., Geol. Mag., pp. 160-164 (Basic dykes of Anglesey). 

1894. Harker, A., Quart. Journ. Geol. Soc, vol. 50, pp. 311-337 (Carrock Fell Gabbro). 

1895. — Quart. Journ. Geol. Soc, vol. 51, pp. 125-148 (Carrock Fell Granophyre and 

Grainsgill Greisen). 

1904. — (with notes by C. T. Clough), Mem. Geol. Surv., The Tertiary Igneous Rocks 

of Skye. 

1912. — Rep. Brit. Assoc, 1911, pp. 370-381 (Some Aspects of Modern Petrology). 

1898. Harmer, F. W., Quart. Journ. Geol. Soc, vol. 54, pp. 308-356 (Lenham Beds and 

the Coralline Crag). 

1900.  — (with appendix by J. Lomas), Quart. Journ. Geol. Soc, vol. 56, pp. 705-744 

(Crag of Essex and its relation to that of Suffolk). 
1914. — Palaeont. Soc, 1913, in progress (Pliocene Mollusca). 
1863. Heer, O., Phil. Trans. Roy. Soc, vol. 152, pp. 1039-1086 (Bovey Tracey flora). 
1897. Judd, J. W., Trans. Roy. Irish Acad., vol. 31, pp. 48 — 58 (Rockall). 
1902. Jukes-Browne, A. J., Stratigraphical Geology, pp. 467-469, 494-497, 522-531. 

1909. — Geol. Mag., pp. 257-265 (Bovey lignite deposits). 
1911. — Building of the British Isles, 3 rd Ed., pp. 336-428. 

1910. Keeping, H., Geol. Mag., pp. 436-439 (Bembridge fossils from the Isle of Purbeck). 
1871. Meyer, C. J. A., Quart. Journ. Geol. Soc, vol. 27, pp. 74 — 89 (Lower Tertiary 

of Portsmouth). 
1891. Newton, R. B., Systematic List of the F. E. Edwards Collection of the British Oligo- 
cene and Eocene Mollusca in the British Museum (Natural History), London. 

1901. Peach, B. N., Gunn, W., and Newton, E. T., Quart. Journ. Geol. Soc, vol. 57, 

pp. 228 — 241 (Arran, volcanic vent). ; 

1854.' Prestwich, J., Quart. Journ. Geol. Soc, vol. 10, pp. 401-419 (London Clay, etc.). 

1890. Reid, C, Mem. Geol. Surv., The Pliocene Deposits of Britain. 

1899. — Mem. Geol. Surv. Expl. Sheet 328, N. S. The Geology of the Country around 

Dorchester, pp. 33-36 (Elephant Trench). 
1904. — Quart. Journ. Geol. Soc, vol. 60, pp. 113-119 (Eocene in Mounts Bay, Cornwall). 

1913. — Mem. Geol. Surv. Expl. Sheet 339. The Geology of the Country around 

Newton Abbot, pp. 102-117 (Bovey Beds). 



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1910. Reid C. and Reid, E. M., Phil. Trans. Roy. Soc, ser. B, vol. 201, pp. 161-178 (Bovey 

Beds). 
1913. Scott, A., Trans. Geol. Soc. Glasgow, vol. 15, pp. 16 — 37(Arran, pitchstones.) 
1884. Teall, J. J. H., Quart. Journ. Geol. Soc, vol. 40, pp. 209-247 (Basic Dykes, N. of 

England). 

1888. — British Petrography, p. 67 (Phonolite of Wolf Rock). 

1913. Tyrrell, G. W., Geol. Mag., pp. 305—309 (Soda-rocks in Arran). 

1914. Washington, H. S., Quart. Journ. Geol. Soc, vol. 70, pp. 294—301 (Rockall). 
1898. Watts, W. W., Proc Geol. Assoc, vol. 15, pp. 397-400 (Dolerites and Basalts of the 

South Staffordshire Coal Field). 
1872. Whitaker, W. (parts by H. W. Bristow and T. McK. Hughes), Mem. Geol. 
Surv., vol. 4. Geology of the London Basin, pp. 55-343, 368-377. 

1889. — Mem. Geol. Surv. The Geology of London and of part of the Thames Valley, 

vol. 1, pp. 86-280. 
1848 — 1882. Wood, Searles V., PaLseont. Soc. (Crag Mollusca). 

1859.' — Quart. Journ. Geol. Soc, vol. 15, pp. 32 — 45 (Extraneous fossils of Red Crag). 
1909. Woodward, H. B., Mem. Geol. Surv. The Geology of London District, pp. 20-44. 

Also contributions to the Geologists' Association Jubilee Volume, Geology in the Field, 
by Elsden, J. V.; Harmer, F.W.; Holmes, T. V.; Hopkinson, J.; Leach, 
A. L.; Monckton, H. W.; White, H. J. O.; & Young, G. W. 

Geological Survey of England and Wales. 
District Memoirs: 

Isle of Wight (C. Reid & A. Strahan), 2 n d Ed., 1889. 
Explanations of Sheet Memoirs, New Series: 

267. Hungerford and Newbury (H. J. Osborne White). 1907. 

268. Reading (J.H.Blake). 1903. 

282. Devizes (A. J. Jukes-Browne). 1905. 

283. Andover (A. J. Jukes-Browne). 1908. 

284. Basingstoke (H. J. Osborne White). 1909. 

298. Salisbury (C. Reid & others). 1903. 

299. Winchester & Stockbridge (H.J.Osborne White). 1912. 

300. Alresford (H.J.Osborne White). 1910. 

311. Wellington and Chard (W. A. E. Ussher & others). 1906. 

314. Ringwood (C. Reid & others). 1902. 

315. Southampton (C. Reid). 1902. 

316. Fareham and Havant (H. J. Osborne White). 1913. 

317. Chichester (C. Reid & others). 1903. 

328. Dorchester (C. Reid). 1899. 

329. Bournemouth (C. Reid). 1898. 

330. 331. Lymington and Portsmouth (H. J. Osborne White, 1915). 
332. Bognor (C. Reid). 1897. 

334. Eastbourne (C. Reid). 1898. 

339. Newton Abbot (W. A. Ussher & others). 1913. 

346. Newquay (C. Reid & others). 1906. 

347. Bodmin and St. Austell (W. A. E. Ussher & others). 1909. 
351, 358. Land's End District (C. Reid & others). 1907. 

359. Lizard and Meneage ( J. S. Flett & J. B. Hill). 1912. 

Geological Survey of Scotland. 
District Memoirs: 

Cowal, Argyllshire (W. Gunn & others). 1897. 

Islay (S. B. Wilkinson & others). 1907. 

Glasgow District (C. T. Clough & others). 1911. 
Sheet Memoirs: 

21. Buteshire (Sir A. Geikie & others). 1903. 

28. Knapdale, Jura & North Kintyre (B. N. Peach & others). 1911. 

35. Colonsay and Oronsay (E. H. Cunningham Craig & others). 1911 

36. Mid-Argyll (B. N. Peach & others). 1909. 

37. Mid- Argyll (J. B. Hill & others). 1905. 

45. Oban and Dalmally (H. Kynaston & others). 1908. 

60. Small Isles of Inverness-shire (A. Harker & G. Barrow). 1908. 

70. West Central Skye (C. T. Clough & A. Harker). 1904. 

See also Harker, A., Reid, C, Whitaker, W. & Woodward, H. B. 



294 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

b. Ireland. 
By G. A. J. Cole. 

Owing to the perpetuation of the uplift that took place in the Irish area at 
the close of Cretaceous times, the Kainozoic deposits have none of the interest 
that they possess in the south-east of England. Milioline limestone, like that of the 
Paris Basin, has been dredged up from two localities off the coast of Kerry (G. A. J. 
Cole, 1908); but there is no evidence of Eocene marine deposits in Ireland. On the 
other hand, the north of Ireland formed part of the great volcanic region which 
became flooded by basaltic lavas during early Kainozoic times. An immense number 
of dykes, running north-west and south-east, mark the fissures up which the lava 
rose. The flint-gravels that had already formed on the denuded surface of the chalk 
are still seen as a reddened band, sometimes associated with lignite, buried beneath 
the earliest igneous flows. These first lavas were somewhat thin individually; but 
the long-continued activity obliterated the former features of the surface and con- 
verted the country into a region of high volcanic plateaus. A pause then occurred, 
and the accumulation of stems and leaves in a few places in pools on the surface 
of decomposing lava gives us the only evidence by which the geological horizon of 
the eruptions in the Kainozoic era can be ascertained. For a long time they were 
assigned to the Miocene period; but a revision of the evidence in Ireland and in 
Mull by J. Starkie Gardner (1885) has led to their being regarded as early Eocene. 
The vegetation is held to by Starkie Gardner correspond with that of the Lower 
Eocene (Heersian) beds of Gelinden in Belgium, and to be earlier than that of 
the plant beds of Mull. Even now,' we know too little about Kainozoic floras to 
base very wide conclusions on such fragmentary material (Baily 1869, 1879 — 83), 
and the main part of the eruptive series may prove to be of Oligocene age. 
The early Kainozoic climate was a fairly warm one; and interesting support is given 
to this by the presence of a conspicuous zone of laterite on the surface of the Lower 
Basaltic series. The interbasaltic red iron ores of the counties of Antrim and Lon- 
donderry have a considerable literature of their own, and Tate and Holden (1870), 
with some earlier authors, maintained that they were formed at the expense of the 
basalt immediately underlying them. Other writers, however, have described the 
red zone, with its residual cores of unaltered basalt, as a band of tuffs, and have 
suggested that the materials were accumulated in lakes. The rich pisolitic ore that 
occurs, notably in eastern Antrim, at the summit of the zone, may have been 
formed in temporary pools; but Maufe has recently shown how such ores may 
develop in Uganda on a land-surface under the drip of rain from tropical forests. 
The lower basalts of northern Ireland remained, in fact exposed sufficiently long 
and sufficiently generally for lateritic decomposition to penetrate them for a consi- 
derable depth, often for 7 to 10 m. Purple lithomarge, red bole, and crumbling red 
and yellow masses retaining traces of the spheroidal structure of the basalt, were 
produced from the lava-flows in place; silica was lost during the process, as now 
happens in the tropics, and the residual clays approach in composition ferruginous 
bauxites (Tate and Holden 1870, Cole' 1908— 1912). 

A true pale-grey bauxite occurs in places as a thin seam above the pisolitic 
iron-ore, and contains detrital bipyramidal crystals of quartz. Pebbles of rhyolite 
occur on this horizon at Glenarm, and there is little doubt that the tropical type 
of decomposition that produced the red zone in the Lower Basalts led to the forma- 
tion of pale bauxite wherever rhyolites had been erupted. Rhyolites, in fact appeared 
sporadically during the interval between the basaltic outpourings. They are now 
best seen, in a variety of glassy and stony types, round about the volcanic neck of 
Tardree mountain, some 12 km. (7Vi miles) north of Antrim town. McHENRYhas 



Cole: Ireland. 



(III. 1.) 295 



well pointed out that the granitic mass of the Mourne Mountains cuts a typical 
north-west and south-east series of basaltic dykes and is itself cut by a later 
series. Hence the epoch of its intrusion is very probably the same as that of the 
extrusion of the Antrim rhyolites, which correspond with it in composition. 
(McHenry 1895; Cole 1896.) 

The plant-beds form, after all, the most interesting feature of the interbasaltic 
zone. They occur at Ballintoy, Glenarm (Libbert mine), and Ballypalady east 
of Antrim town. The last-named locality is the only one at present exposed for 
study; the leaves are here found in a brown volcanic tuff, with fragments of basalt 
and rhyolite. Silicified lignite (with Cupressus) has been found on the eastern shore of 
Longh Neagh, and no doubt comes from the interbasaltic beds. W. Swanston 
(1879) and J. S. Gardner have sought to include the Lough Neagh clays, covering 
a large prea at the south-west end of the lake, in the Eocene series. These pale 
pipe-clays rest on an eroded surface of Lower Basalt and Trias, and are at least 
100 m. (330 ft.) thick. They contain plant-remains; but these appear to be merely 
derived from the destruction of interbasaltic plant-zones a little to the north. The chief 
difficulty in accepting for them an Eocene age is the evidence of considerable erosion 
of the Lower Basalts in the neighbourhood, before they were laid down. If, however, 
no Upper Basalt was poured out in this area, they may be contemporary with the 
higher volcanic series of the country to the north. Following the suggestions of 
Hull and Hardman (1876), the Lough Neagh clays have generally been referred 
to the Pliocene Period, as products of the subsidence in the basalt plateaus which 
ultimately resulted in the formation of Lough Neagh (Swanston 1879; Mem. Geol. 
Survey Ireland, Interbasaltic Bocks, pp. 100 and 121). 

Basaltic eruptions were resumed after the interval above described, and the 
Upper Basalts were poured out. The dolerite necks of Slemish, Tiveragh and Carn- 
money (fig. 66), and the explosive vent of Carrick-a-rede in the extreme north, belong 




Fig. 66. Kainozoic volcanic neck of basalt: Cammoney, Co. Antrim. 

T = Basaltic lavas; C = Cretaceous; L = Lower Lias; K = Keuper Marls. 

Reproduced from the Memoirs of the Geological Survey of Ireland, Country round Belfast, p. 43, 1904; 
with the permission of the Director and of H. M. Stationery Office. 



to this stage. The lavas were mostly more massive and columnar than the Lower 
Basalts, and a fine example forms the Giants Causeway where it has been brought 
down by earth-movements to sea-level, and there denuded of its upper and more 
rubbly layer by the waves. The dolerite of Fair Head, forming a sea-front of co- 
lumns 100m. (330 ft.) high, above a huge block-talus, is a laccolitic mass intruded into 
Carboniferous sandstone, but clearly connected with the later upwellings of basic 
rock. The volcanic history of th* whole area, which attracted J. H. Berger, Cony- 
beare, and other writers early in the nineteenth century, has been fully dealt with 
by Sir A. Geikie (1897). The flora associated with the basalts may prove to be 
of later date than the Lower Eocene; but the Upper Basalts are hardly likely 
to be of younger age than Oligocene. 

A considerable mass of olivine-gabbro, which was first correctly appreciated 
by A. von Lasaulx (1878), is intrusive in Silurian and Carboniferous strata on the 



296 (III. 1.) The British Isles. — III. Stratigraphy. — 13. Tertiary. 

south side of Carlingford Lough. Granite of the Mourne type has risen through its 
centre, producing in its basal portions an intricate network of veins (Sollas 1894). 
As has been already stated, there is every reason to believe that the Mourne granite 
(granophyre of Rosenbusch) is of Eocene or Oligocene age. This granite, more- 
over, is of the same type as those which invade the basic series of Skye, Mull, and 
St. Kilda, and which are undoubtedly connected as parts of the Kainozoic magma- 
basin. Hence the rugged crest of Carlingford Mountain, and the bold granite domes 
of Mourne, must be regarded as the latest additions to the mountain-scenery of 
Ireland. 

Except for the problematic Lough Neagh clays, which are possibly Miocene or 
Pliocene, and one or two areas of quartzose clay near Gahir in Tipperary, left as 
residues from the solution of the Carboniferous Limestone, Ireland can produce 
no Kainozoic deposits between the Upper Basalts and the Glacial drift. The Wex- 
ford Gravels, which will be discussed under Pleistocene deposits, cannot be put 
back into the Pliocene period. It is, however, very probable that subsidence admitted 
the Pliocene sea into many parts of southern Ireland. 

The history of the volcanic area may be thus summarized. The general 
uplift of the area of the British Isles that took place while the Danian sea 
still covered part of western Europe brought Ireland as a whole above sea-level. 
Her Eocene deposits were formed on a land-surface, and there are no indu- 
bitable traces of any subsequent submergence. Considerable denudation had 
taken place on the surface of the raised plateau of chalk before it became broken 
by the vents and fissures from which the first Kainozoic lavas poured. Flint-gravels 
had gathered in the hollows of the round-backed hills, and here and there taluses 
of blocks of chalk had formed against the steeper slopes. Then the ground over the 
whole northern half of Ireland cracked open in that remarkable series of parallel 
fissures which characterise the region from eastern Yorkshire to western Donegal. 
The surface-rocks over which the subaerial products of volcanic action spread must 
have been widely different from those in which we can trace the dykes to-day. 
The olivine-gabbro of Carlingford Mountain, followed by the granite of the Mourne 
Mountains, must have collected in subterranean cauldrons beneath considerable thick- 
nesses of Older Palaeozoic slate and probably of basaltic lava-flows. It is difficult, 
moreover, to believe that basaltic plateaus were not formed across the country 
which is marked by Kainozoic dykes in the county of Donegal and several of the 
adjacent counties. The denudation that removed the basalts must have also remo- 
ved considerable thicknesses of the underlying rocks. It is only where the basaltic 
lavas remain that we can realise the true nature of the surface over which they 
flowed. In a very large part of the area we find that the eruptions took place before 
the Cretaceous limestone, which is only 30 m. (100 ft.) in thickness, had been cut 
through by denudation. 

Here and there , the surface of a lava-flow remained exposed sufficiently long 
for a red earth to accumulate upon it; and a succeding flow has preserved this 
layer. But a fortunate pause in the eruptions of basalt occurred, and the decay 
of the lavas gave rise to thick lateritic soils and subsoils. Vegetation flourished, 
the types being suggestive of warm conditions, and the plants were washed down 
here and there into pools, and were preserved by the detrital material that accom- 
panied them. The mode of decomposition of the basaltic surfaces, and the deep 
rotting of the rock, points to tropical conditions, such as now occur in India and in 
central Africa. During this comparatively quiet interval, a few small cones erupted 
rhyolitic lavas and tuffs, and these products were also seized on by agents of decay 
acting under tropical influences. Pale bauxitic clays and true bauxites, including 
crystals of quartz from the rhyolites, were thus spread locally over the red zone 



Cole: Ireland. (III. 1.) 297 

of the basaltic series. All these features were buried under a second series of basalts, 
which rose along fissures broken through the older lavas, and the country again 
assumed the monotonous character of a lava-covered plain. 

It is difficult to reconcile the comparative tranquillity of Antrim in the epoch 
of the rhyolitic cones with the intrusion of a great mass of granite beneath the sur- 
face in the country immediately to the south. The Mourne granite occupies a caul- 
dron excavated, as it were, in the Older Palaeozoic rocks. Even if the strata on the 
crest of Thomas Mountain suggest a laccolitic mode of intrusion, there is no general 
evidence of arching of the strata, and the granite magma seems to have moved 
upwards in virtue of its own energy, perhaps aided by pressures originating some- 
where else, rather than in response to orogenic movements in the Irish area. In this 
respect it presents a marked contrast to the core of Lower Devonian granite that 
lies so near to it on the north-west. 

Since no organic remains are known among the basalts later than those in the 
red zone of iron-ores, it is impossible to say how long the volcanic outpourings con- 
tinued. The upstanding dolerite neck of Slemish, and the exposure of the laccolitic 
mass at Fair Head, show how large an amount of superincumbent material must 
have been removed in later times by denudation. We may fairly presume that the 
later eruptions extended into the Oligocene period, but ceased before the well known 
outbreak of Miocene volcanoes in Auvergne. The activity in the Hebridean and Irish 
area may thus be regarded as the herald of the Alpine epoch of disturbance. 

The crust-movements that gave us our modern mountain-system in Europe, 
though they are manifested by folding in the south-east of England, were probably 
accompanied by the falling in of the basaltic plateaus of the north Atlantic basin. 
Numerous faults, probably of late Miocene and Pliocene age, broke up the region, 
and admitted the ocean over an important area between Greenland, Iceland, 
and the British Isles (A. Geikie 1896 and Hard man 1875 — 76). The great extrusion 
of volcanic material was no doubt responsible for the general subsidence of this 
area. When the River Bann began to flow through a depression formed by the 
lowering of the basalt-surface, it denuded away the lavas along its course, and still 
further prepared a hollow, into which the sea penetrated in Glacial times. The post- 
Glacial uplift, marked by the raised beaches along the coast, probably drove out 
the sea again, but left the ground warped southward so as to allow of the accumu- 
lation of the 1 waters now known as Lough Neagh. 

Economie Products. 

The Kainozoic granite and dolerite of Carlingford and the Mourne area afford 
materials for setts and road-metal. The cavities of the Mourne granite often contain 
colourless topaz, and sometimes aquamarine. 

Basalt. The jointed columnar basalt of the Portrush area in Co. Antrim 
is now used, like that from the Rhine district, for the construction of sea walls 
and dykes. 

Iron-ores. The most profitable iron-ores of Ireland are the bedded lateritic ores 
in the Kainozoic basaltic series of Co. Antrim. These red masses have arisen from 
the weathering of the Lower Basalts in Eocene times under tropical conditions. 
The upper part of the bed is often pisolitic; but a similar structure occurs in the 
decomposing basalt itself, where it has passed into the condition of bole. As is now 
recognised in India and elsewhere, these lateritic ores are rich in aluminium 
hydrate, and in parts are ferruginous bauxites. They are used as a flux for the 
haematite ores of Cumberland, and form the only iron-ores regularly mined at 
present in Ireland. 



298 (III. 1.) The British Isles. — III. Stratigraphy. — 14. Quaternary Period. 

Bauxite. Pale bauxites occur as beds above the pisolitic iron-ore in 
several parts of Co. Antrim, and have been protected by the flows of later basalt. 
They often contain grains of quartz, and are probably derived from the dis- 
integration of rhyolites, which are known to have been poured out locally in the 
interval between the two basaltic series. At present they are only used for the 
production of alum, and French bauxite is imported for the aluminium works 
established at Larne. 



Bibliography of the Tertiary of Ireland. 

1869. Baily, W. H., Quart. Journ. Geol. Soc. London, vol. 25, pp. 357-362 (Plants from 

Basalts, County Antrim). 
1879-1883. — Reports British Assoc. (Plants from Basalts, &c.). 

1896. Cole, G. A. J., Sci. Trans. Roy. Dublin Soc, ser. 2, vol.6, pp. 77-114 (Antrim 

Rhyolites). 

1908. — Geol. Mag., pp. 341-344 (Basaltic laterites). 

1909. — Rep. Brit. Assoc, 1908, pp. 697-698 (Dredged Rocks off Coast of Kerry). 
1885. Gardner, J. S., Quart. Journ. Geol. Soc. London, vol.41, pp. 82-92 (Eocene 

plants). 

1897. Geikie, Sir Archibald, Ancient Volcanoes of Great Britain, vol. 2, pp. 107-465. 
1877. Hardman, E. T., Journ. Roy. Geol. Soc. Ireland, vol. 4, pp. 170-199 (Age and mode 

of formation of Lough Neagh). 
1880. Lasaulx, A. v., Journ. Roy. Geol. Soc. Ireland, vol. 5, pp. 30-38 (Igneous rocks). 
1895. McHenry, A., Geol. Mag., pp. 260-264 (Antrim Rhyolites). 
1894. Sollas, W. J., Trans. Roy. Irish Acad., vol. 30, pp. 477-510 (Carlingford granite 

and gabbro). 
1879. Swanston, W., Geol. Mag., pp. 62-64 (Lough Neagh clays). 

1870. Tate, R. and Holden, J. S., Quart. Journ. Geol. Soc London, vol. 26, pp. 151-165 

(Iron-ores). 

Geological Survey. 
Memoir on the country round Belfast (G. W. Lamplugh and others) 1904. 
Memoir on the Interbasaltic Rocks of North-East Ireland (G. A. J. Cole & others). 1912. 
(Contains numerous references.) 



14. Quaternary Period. 

a. Great Britain. 
By Percy Fry Kendall. 

The Quaternary deposits and phenomena of Great Britain present a very 
complete record of geological time from the close of the Pliocene period up to the 
present. The conditions indicated are also singularly varied:— ground moraine, 
and terminal and lateral moraines of great ice-sheets, deposits of glacier-lakes, sea- 
beaches, and other marine deposits, estuarine clays, river-gravels, flood-loams, 
peats, seolian sands, and rain-wash furnish valuable details of the state both of 
the glaciated and the unglaciated areas during the Pleistocene stages. Relics of 
contemporary man and the Pleistocene mammalia are preserved in river gravels 
and cave deposits. 

The post-Glacial conditions are, in consequence of fluctuations of sea level, 
chronicled with equal fullness and clearness. Raised beaches and submerged forests 
tell of these changes, while lake-deposits, peat-mosses and river-terraces, as well as 
the upper layers of the cave deposits yield data for the completion of the parallel 
history of the land surface. 



Kendall: Great Britain. — Pre-Glacial land-level. (III. 1.) 299 

The literature of the subject is of such enormous volume that no general reader 
can attempt to master it, but there are certain contributions of paramount interest 
and importance that should on no account be neglected. Among these may be 
cited Sir Archibald Geikie's paper on the Glacial phenomena of Scotland (1863) 
and his Scenery of Scotland (1901); Prof. J. Geikie's invaluable Great Ice Age 
1894) and his Prehistoric Europe (1880); Croll, Climate and Time (1875). Nothing 
comparable to these has been written from the point of view of English geology, 
but two classical papers by Tiddemann (1872) and Goodchild (1875) deal in the 
finest spirit with adjacent areas of the Northwest of England. Searles Wood 
Junior's summary of Newer Pliocene Geology (1880) and Harmer's many valuable 
contributions should be read. The posthumous work "Glacial Geology of Gt. Britain 
and Ireland" of Carvill Lewis (1894) contains much that is valuable especially 
in bibliography and a short summary of the knowledge of glacial geology then 
current can be obtained from G. F. Wright's "Man and the Glacial Period" (1892). • 

A. Pre-Glacial land-level. 

It has long been known that a raised beach of Pleistocene age extends along 
the shores of the English Channel from Brighton westward but it is very fragmentary 
and its exact geological date is not easily or definitely ascertainable. Near Flam- 
borough Head in Yorkshire however a beach and old cliff -line were found to be buried 
beneath the oldest glacial tills or boulder-clays of the district. 

It yielded moreover to Lamplugh (1889) an assemblage of mammalia including 
Elephas antiquus and Hippopotamus that declared it to be of early Pleistocene 
age. The next important clue was obtained by Tiddeman (1900) in the Gower 
Peninsula, where a raised beach and cliff-line perforated by caves with an early 
Pleistocene fauna was found to be in places overlain by glacial deposits. Later, 
Maufe and Wright (1904), traced along the South Coast of Ireland and up to 
near Dublin a rock-shelf at times supporting beach materials and backed by a 
cliff. This they, no doubt correctly, inferred to be a raised beach though it has 
yielded no marine organisms. It is in some localities overlain by glacial deposits, 
and the sea-worn platform is sometimes re-dressed by glacial striae. 

The height of this beach is remarkably uniform, at the maximum about 3.7 
m. (12 ft.) above sea-level. Traces of it have been recognised in Carnarvon- 
shire (Fearnsides 1910) and in the Isle of Man (Lamplugh 1903). Until 
recently no evidence of a similar phase was known from Scotland but Wright 
(1911) found a strongly marked beach-platform of characteristic form covered by 
glacial deposits and at times partly obliterated by glacial erosion. It stands at 
about 30 to 37 m. (100—120 ft.) above existing high water mark and has been 
traced in Colonsay and other islands of the Inner Hebrides. No corresponding fea- 
ture on the East Coast of Scotland has been recorded but the present writer has 
observed a rock platform of composite geological structure, upon which the greater 
part of the town of Dunbar stands, at 15 to 18 m. (50 to 60 ft.) above sea-level. 
It appears to be pre-glacial. Wright (1914) considers that the discrepancy between 
the respective levels of the Scottish and the Anglo-Irish beaches may be due to 
block-faulting. 

The Flamborougli Head beach is separated from the boulder clay by blown 
sand and land wash, showing that the sea must have withdrawn before the 
advent of the ice, and as these deposits extend to at least 7 m. (23 ft.) below 
high water mark it is inferred that an actual rise of the land took place in the 

1 W. B. Wright's "Quaternary Ice Age" has appeared since this contribution was 
written. It is particularly valuable for the chapters relating to the pre- and post-Glacial 
a nd levels. 



300 (III. 1.) The British Isles. — III. Stratigraphy. — 14. Quaternary Period. 

interval. The cliff backing the beach extends behind and beneath the glacial 
deposits, and the present writer has, by the study of borings, traced it round by 
Nafferton and Beverley to Hessle on the Humber, where the beach and cliff were 
exposed in a railway cutting. The same features are traceable along the edge of the 
Chalk Wolds of Lincolnshire. 

This cliff is confronted by the broad Drift-covered belt of Holderness under 
which the present writer has traced a Chalk-floor falling with a gradient of about 
1 : 480 (11 ft. per mile) to the existing coast. 

A marine deposit with Pholas crispata of exceptional size occurs at Selsey 
Bill on the Sussex coast and above it are large erratics of crystalline rocks 
probably from Brittany or the Channel Islands. Reid (1897) appears to regard 
this succession as marking an interglacial and glacial sequence. 

At Goodwood, some 16 km, (10 miles) to the north at about 40 m. (130 ft.) 
above sea-level there is an upraised marine deposit described by Reid (1903). It 
contains a limited molluscan fauna and the allocation of a unique example such 
as this to a place in the Pleistocene sequence presents a problem of great difficulty 
of which no satisfactory solution has been offered. 

In apparent conflict with the evidence of pre-Glacial raised beaches is that 
of a deep-sunken series of river-valleys found in many parts of the glaciated regions, 
of which a few examples must suffice. The most detailed description of any such 
system is that of the country about Glasgow (Geol. Surv. Mem., 1911). The study 
of many bores in this district has enabled the surveyors to contour the rock-floor 
beneath the Drift and it is seen that valleys exist beneath the Clyde and its tribu- 
taries, the White and the Black Cart, extending to 30 to 45 m. (100 to 150 ft.) below 
sea-level. These are shown to fall abruptly into the valley of the Kelvin with a 
descent of more than 15 in 180 m. (50 ft. in 200 yards), or perhaps even twice as 
much. Now the Clyde has a catchment roughly 10 times the area of that of 
the Kelvin and it is inexplicable why a main stream should "hang" to one of its 
minor tributaries. 

Hollows of comparable depth exist below the Drift at Grangemouth in the Forth 
basin but on the same line as the Kelvin. The rivers Tyne, Wear, Tees, Ouse, 
Humber and Lower Trent, on the east coast, show similar relations, as does the 
Mersey on the west. A feature common to many of these is the fact that, so far 
as can be ascertained, the concealed valleys are shallower at the seaward end than 
further inland. It is in some instances possible that the borings have failed to hit 
the deepest part of the trough, but, in the case of the Mersey, all uncertainty was 
removed by the construction of a tunnel from Liverpool to Birkenhead the floor 
of which is entirely in rock, while a groove filled with boulder-clay just touches the 
roof at about 30 m. (100 ft.) below sea-level. There are large areas of country 
within the Mersey basin wherein the rock-floor is below sea-level even as far in- 
land as Nantwich (1 m., 3 ft.) and Crewe. The deepest hollows are at Widnes 
(45 m., 147 ft.) and near Crewe in Cheshire, about (60 m., 200 ft.) (Annual Report 
Geol. Survey 1894, p. 274, 1895). 

Three explanations of this common phenomenon may be offered — 1. That 
there was another outlet for the pre-Glacial drainage — this is highly improbable 
in the case of the Mersey and impossible in those of the Tyne and the Humber. 
2. That there has been a depression of the interior of the country in consequence 
of the imposition of the ice-load, from which the recovery is not yet complete — 
this is highly improbable, for in the cases of the Tyne, Humber, and Mersey the 
greater load was at the seaward end and therefore the depression should have been 
greater there. 3. The last js that the interior regions have suffered great glacial 
erosion. This view, to which the writer has been brought with some reluctance, 



Kendall: Great Britain. — Marine Shells in Glacial deposits. (III. 1.) 301 

has much to commend it. The existence of thick deposits of boulder-clay consisting 
very largely of the ground-up materials of the subjacent rock-floor is proof of very 
drastic local erosion. 

The floor of the Vale of York is a good illustration of this fact. It consists of 
the soft sandstones and marls of the Trias, and, not only do these materials occur 
in recognisable fragments in the Drift, but the Boulder-clays owe their strong red 
colouration to triturated marl and to the presence of large quantities of Triassic 
sand-grains still retaining the characteristic pellicle of iron-oxide. 

Applying these principles to the case of the Clyde, we should attribute the 
"super-deepening" of the Kelvin to glacial erosion, and in support of this explanation 
it should be remarked that the Kelvin Valley runs directly in the line of the ice- 
flow. The magnitude of the glacial erosion in the district is commented upon in the 
Glasgow memoir a propos the dispersion of blocks of essexite from a small outcrop. 

The sunken valleys are generally excavated in soft rocks, but hard beds have 
also suffered in the Kelvin trough. 

A few of the deepest drift-filled hollows may be cited. At Newport in the north- 
east of Essex, the rock-floor is more than 43 m. (140 ft.) below sea-level; at Boston, 
Lincolnshire, near the Wash, 49 m. (160 ft.); Barnby on Don, Yorkshire, north- 
east of Doncaster, 52 m. (170 ft.); Gateshead, Durham, on the Tyne, 43 m. (141ft.). 
At the northern point of the Isle of Man drift occurs to a depth of 137 m. (448 ft.), 
starting from very near sea-level, and at Crewe, Cheshire, 60 m. (200 ft.). The 
maximum thickness reached is probably at Glemsford in the valley of the Stour 
in south-west Suffolk, where the thickness is 145 m. (477 ft.). 

B. Marine Shells in Glacial deposits. 

It may be convenient at this stage to consider the occurrence of fragmentary 
and, in a few instances, complete shells in the glacial deposits. 

It is the nearly unanimous opinion of British geologists that where other 
indications, such as the transport of erratics, and striations upon rock surfaces, 
indicate a movement of ice onto the land after traversing some part of the sea- 
floor, shells have been brought in from the sea-bed as erratics. Thus, wherever 
ice out of the Irish Sea invaded the land, as in the neighbourhood of Dublin, the 
Isle of Man, the coastal regions of North Wales, South Lancashire and Cheshire, 
fragmentary and, very rarely, entire shells occur in the Drift even up to great 
altitudes, e. g. 366m. (1200 ft.) on Three Bock Mountain, Dublin, 412m. (1350 ft.) 
on Moel Tryfaen near Snowdon, 427 m. (1400 ft.) at Frondeg near Buabon and 
390 m. (1280 ft.) near Macclesfield. 

From the North Sea they were carried into Caithness, Aberdeenshire, Northum- 
berland, Durham, Yorkshire, and probably East Anglia. 

It is of interest to observe that in the Irish sea-basin this fauna shows Arctic, 
British, and Southern, deep- and shallow-water types, all confusedly intermingled, 
and the same species are found at the highest levels as at the lowest, and the same 
in boulder-clays as in sands or gravels. In the Isle of Man, and in Wexford they 
are accompanied by many extinct species of Mollusca of Pliocene provenance; 
such as Nassa monensis, Nassa reticosa and Columbella sulcata. Fusus contrarius is 
of frequent occurrence, not only at these two localities but all through South 
Lancashire and Cheshire. Occasionally a pure fauna generally of high arctic type 
is found, e. g. in the Isle of Man (Kendall 1894) and at Bridlington (Lamplugh 1881), 
in both instances probably in masses of sea-bottom transported bodily. 

This evidence enables us to say that the Irish Sea and the North Sea, 
as well as some of the larger inflections of their margins, were already in 
existence at the beginning of the Ice Ag\ 



302 (III. 1.) The British Isles. — III. Stratigraphy. — 14. Quaternary Period. 

One very important problem is left unsolved — the question whether the 
Straits of Dover existed prior to the Ice Age, but the consideration of this must 
be reserved for consideration later. 



C. The Ice-sheets. 

The initial stages of the glaciation have left little or no trace, any early 
effects being obliterated by subsequent action, but it may be inferred that by 
the time the later Red Crag was deposited small glaciers had come into existence 
in the mountains of Wales, the Lake District and Scotland. These grew, coalesced 
so as to fill the larger valleys, and deployed out on the plains, even invading the sea 
itself. Croll (1865) seems to have been the first to observe that all down the East 
Coast of Great Britain the native ice-streams were opposed by some extraneous 
obstacle, that forced them to take a course to North or South or even to turn back 
upon the land. Croll (1875) developed this view, especially as regards the north- 
east corner of Scotland, Caithness, showing that ice that came down Loch Ness 
into the Moray Firth was turned northward onto the land and brought with it Jurassic 
and Cretaceous rocks from the coast and sea-bottom, together with fragmentary 
marine shells, and deposited them, along with other matter, in the boulder-clays 
of the invaded country. Croll definitely attributed this deflection to the influence 
of the Scandinavian ice-sheet bearing down upon Britain. Since the promulgation 
of this daring hypothesis his explanation has been found to apply to the whole 
tract from the Shetlands, which were completely overridden from the south-east 
(Peach and Horne), to Norfolk, Suffolk and Essex. 

There must have been a place where a cleavage or divergence of the conflicting 
ice-flows took place, some going to the north and the rest to the south. Croll shows 
this point as lying opposite the Yorkshire Coast. The present writer has suggested that 
it must have oscillated between very wide limits dependent upon the variations of 
alimentation of the components of the ice-sheets. The transport of erratics throws 
some light on the question. Rocks from the central Highlands of Scotland are rare in 
the Drift of the East of England, but examples have been recognised, especially one 
might cite a quartz-porphyry from Buchan Ness (57° 28' N.) which in a not very 
characteristic form is relatively common on the Yorkshire Coast and has been 
recognised in Cambridgeshire (Rastall and Romanes 1909). 

All authorities however agree that there was at one stage a movement from 
south to north along the coast of Aberdeenshire beginning at least 32 kilometres 
(20 miles) to the south of Buchan Ness, and some would extend it as far as the 
mouth of the Tay (Bell 1895 and Ann. Rep. Geol. Surv. 1895, p. 32 and Summary 
of Progress 1902, p. 103) and Professor J. Geikie places the point of cleavage at the 
Firth of Forth, following in this Peach and Horne (1879). 

The late Angus Peach (1909) found that the trail of boulders from an out- 
crop of essexite near Lennoxtown was so narrow and definite as to imply great 
constancy of direction of the ice-movement, and hence to oppose the views here 
set forth. 

The Scandinavian ice-sheet affected the British ice in another way. By ob- 
structing a free escape to the east, it caused a shifting of the line of ice-shedding 
to the east of the natural water-parting in the North of Scotland ; thus, as in Scandi- 
navia, rocks of the eastern slope were carried as boulders over to the West Coast. 

The glaciation of Scotland at its maximum stage covered all except the highest 
mountains with a moving sheet of ice. The Hebrides were almost completely 
overridden and the ice must have terminated out in the Atlantic in a free, and 
perhaps floating, edge comparable to that of Ross's Barrier in the Antarctic. The 



Kendall: Great Britain. — The Ice-sheets. (III. 1.) 303 

mountains up to altitudes of over 1100 m. (3600 ft.) show signs of severe glaciation. 
The southern slopes of the Grampians poured a flood of ice into the great Midland 
Valley of Scotland that, encountering the hills of the Southern Uplands which at first 
were independent centres of glaciation, in part overflowed them, and the lower portions 
of the ice deviated to the right (west) into the Clyde and to the left (east) along 
the Forth basin and so into the North sea. The western element gradually surmoun- 
ted the high grounds of Ayrshire and swept across the hills of Galloway into the 
Irish Sea carrying with it many characteristic rocks, such as the granites of the 
Cairnsmores and the riebeckite-eurite (see p. 304) of Ailsa Craig, a lofty islet 
335 m. (1114 ft.) high in the Firth of Clyde (55° 15' N.). 

We may leave the later stages of the glaciation of Scotland for subsequent 
description, and now consider the country further south. 

The Lake District, a dissected mountainous dome, no doubt passed through 
the same early phases as we have suggested for Scotland. The northern Ponnines 
and the mountains of both North and South Wales, nourished valley glaciers 
whose continued growth produced very complex interactions especially upon the west. 

The Irish Sea, never of any great depth, formed a pool into which Scottish 
ice poured from the north, Irish ice from the west. Radial flow from the Lake 
District centre contributed on the north-east, and from North Wales glaciers radiated 
in a similar manner, as well as from South Wales. 

From this congested area only three outlets were available, n