Geology of the British Isles

359 Pages·1918·18.065 MB·English

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 (auth.), J. W. Evans (eds.)

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
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
1918
Additional material to this book can be downloaded from http://extras.springer.com
ISBN 978-94-017-5785-0 ISBN 978-94-017-6199-4 (eBook)
DOI 10.1007/978-94-017-6199-4
Softcover reprint of the hardcover 1st edition 1918
The British lsles
by
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
Iiterature 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 DAvrEs, 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. J OHN W. EvANs.
I. Morphology.
a. England and Wales.
By ARTHUR MORLEY DAVIES.
The folds and faults of England and Walesare usually grouped in four systems.,
acoording 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. TheArmorican system, withdirection varyingfrom 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 derrotes merely direction.
Handbuch der regionalen Geologie. III. 1.
2 (III. 1.) The British lsles. - Morphology.
The Charnian system is principally developed in the pre-Cambrian rocks of
Charnwood Forest (Fig. 8). As both Carboniferous and Triassie strata lap up uncon
formably against these ancient ro.;ks, 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 Laucashire 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-Ju rassic 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. Archaean Gneiss. Fa.uiC (downth~ow
8. Metamorphosed Sedimentary Rocks. on doCCed side)
E. Proc.Camb~ia.n Sedimen[a.ry Roc.l<s. Fault(throw doubCful.)
F. Cambrian and Ordovician.
P. Jurassic. Th~us[-p/a.ne with
Y. Te,.[ia.ry Volcanic Rocks. ove~ch~usC Co N.W.
Z. Ter[ia.,.y lntrusive Rocks.
F,g. 1. Te c t o n i c M a p o f t h e B r i t i s h I sIe s-Section I.-H e b r i des an d No r t h-West
High I an d s. 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 in eh.
DAVIES: England and Wales. (111. 1.) 3
Shetland
JJ:AA
IsT a.--., d s
C1
AnCicline.
Syncline.
__ ....,_ ~-~·~·-~···~· Fa.uiC (down[hroow
on doCCed s i d e..)
Dip.
8. Me.Ca.mo,.pho$ed SedimenCary Rocks.
D. Prae-Cambr"ian lnt,.usive Rocks.
J. Devonia.n (Oid Red Sandstone)
@Derived Ca.mbr"ian pebbles.
N. Triass ic.
P. Ju,.assic.
W. Pa.laeozoic Volcanic Rocks.
X. Pa.laeozoic lnCrusive Rocks.
@Creta.eeous in boulde.r clCly.
D
Fig. 2. Teetonic Map of the British Isles-Section II.-North-E ast-Scotland,
0 r k n e y s an d S h e t I an d 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 ~ound into the Caledonian direction, forming first the western boundary
fault of the North Staffordshire coalfield, and Iater the eastern boundary of the
1*
4 (III. 1.) The British Isles. - Morphology.
Longmyndian horst. Other important disturbances are c) the faults to which the
Menai Straits owe their existence; d) the Snowdon syncline; e) the Rarlech 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-Triassie 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-
8. MeCa.morphosed Sedimenfary Rocks. Antidine
D. Proe· Cambrian Jn[rusive Rocks
Syncline.
F. Ca.mbria.n.
G Ordovician. Fault, wiCh downthrow
on dotred side
H. Si/urian (Gothla.ndian)
K. Lower Carboniferous. Fau.lt wiCh doubrful
throw.
L. Upper Ca.rboniferous.
Q. C reta. ceo<.<s.
X. Palaeozoic Jn[rusive Rocks.
B DorX
F-J? 8 0 orX
KQ F-J?
K
8 D orX
F -J?
Q Dor,l(
F-J~
D?
KQ
Fig. 3. Te c t o n i c M a p o f t h e B r i t i s h I sIe s.-Section 11!.-N o r t h-West-Ire I an d.
Caiedonian system dominant. A. M. D.
DAVIES: England und Wales. (liJ. 1.) 5
B
D
D
t\N
.".
y QN ~/
H~~
1
/)
A
A.Archaea.n Gneiss. K LowerCarboniferol.ls.
H \ JK B.MeCamorphosedSed•menCa.ryRocks L. UpperCarboniferoLIS.
D.Prae-Cambrian lnCrus1ve Rocks N. Tr1assic.
E.Pme-CambrianSedimenU:try Rocks P.Jurassic.
K F.Ca.mbrian. H.Sdul'ia.n Q CreCaceous.
K 4.0rdovician J. Devonic:tn. Y. Ter-Cia,.y Volca.nic.
Fig.4. Teetonic Map of the British Isles.-Section IV.-North-East-Ireland, Scot
Iand (Grampian Highlands, Central Va!ley, Southern Uplands), England (Lake
Distri c t) an d t h e I sIe o f M an. 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-Jurassie faults into the neighho.urhood of Yeovil.
6 (III 1.) The British Isles. - Morphology.
The diagrammatic representations of the Pennirre 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 N orthumber land. 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 trcnd of the west is replaced to the
east by an east-and-west trend of folds and faults- Iiluch 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 Durharn coalfields (Fig. 5), the great Craven fault,
the post-J urassic disturbances of the Val es of Y ork and Pickering, the southern
boundary faults of the Carbonifcrous-limestone area of Derbyshire (Fig. 8) and their
post-J urassic extension eastwards, with probable unmapped disturbances determining
the position of the Wash and the north coast of East Anglia, and many minor post
Jurassie disturbances, as in the Cotteswolds and the arca north-west of Oxford.
The Armorican system is primarily post-Carboniferous in age, but includes
slight intra-Jurassie and important post-Jurassic, post-Cretaceous and post-Oligo
ccne 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, elvan-dykes, and tin- and
copper-veins were produced.
As the Palaeozoic rocks of thc 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-Liassie denudation of the Radstock district appears to be due to movement
parallel to the Mendip axes. I t is vcry 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 Ju rassic 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 Purheck and Isle of Wight, anticlines possibly continuous
with that of the Pays de Bray;
(b) the Isle of Purheck 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 prc-Cretaccous);
(g) the serics of anticlines constituting the Wealden axis, one of which is
continued into the Bas Boulonnais;
(h) the Pewsey-Kingsclere-Peasemarsh anticline accompanying the steep
southern margin of the London Basin, with associated minor folds and
faults, including a slight northwardly thrust-fault at the Hog's Back 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 und Wales. (lll. 1.) ?
AnCicline
Syncline.
Fa.ul[ with downthrow
on dotted side.
===":er"
Trough-Fa.uiC.
B. Meta.morphose.d Seclimen[a.ry Rocks.
H. Siluria.n (Gothla.ndian.)
J. Oe.vonia.n.
K. lower- Ca.r-boniferous.
L Upper- Co.r-bonifer-ous.
M. Permio.n.
N. Triassie
P. Jura.ssic.
Q. Crera.ceous.
V. Quo.terna.ry.
N
'M
p
~::-
. . p Q
~~
V
K V
V
Fig. 5. Teetonic M ap ot th e B ri tish I sl es.-Section V.-N ort h-E ast-En gla n d. A. M. D
in the centre of the basin, as shown by the Windsor inlier, but tbe very gentle angle
of dip makes determination of the nature of this disturbance very difficult. lt is
not impossible that it may be connected with the series of folds with Charnian
direction near Oxford, as the distribution of Jurassie 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