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? t:vo JjMOIKS OF THE GEOLOGICAL SURVEY.

ENGLAND AND WALES.



THE GEOLOGY OF THE

SOUTH WALES COAL-FIELD,

PART X.
THE COUNTRY AROUND

CARMARTHEN,

BEING AN ACCOUNT OF THE REGION COMPRISED IN
SHEET 229 OF THE MAP.

BY

AUBREY STR AH AN, M.A., Sc.D., F.R.S., F.G.S.,
T. C. CANTRILL, B.Sc., F.G.S.,
E. E. L. DIXON, B.Sc., F.G.S., AND
H. H. THOMAS, M.A., B.Sc., F.G.S.

(With Notes by B. S. N. WILKINSON). /



PUBLISHED BY ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY'S TREASURY.




LONDON :

PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE,
BY DARLING & SON/LTD., 34-40, BACON STREET, E.

And to be purchased from

E. STANFORD, 12, 13, and 14, LONG- ACEE, LONDON ;
W. & A. K. JOHNSTON, LTD., 2, ST. ANDREW SQUARE, EDINBURGH ;

HODGES, FIGGIS & Co., GRAFTON STREET, DUBLIN ;

From any Agent for the sale of Ordnance Survey Maps ; or through any

Bookseller, from T. FISHER UN WIN, 1, A DELPHI TERRACE, LONDON,

W.C., who is the sole Wholesale Agent to the Trade outside the

County of London.

1909.
Price Two Shillings*



1BERKEIIY
JBRARY
JNIVERSITY OF
CALIFORNIA

EARTH

SCIENCES
LIBRARY



EXCHANGE




229.

MEMOIRS OF THE GEOLOGICAL SURVEY,

ENGLAND AND WALES.



THE GEOLOGY OF THE

SOUTH WALES COAL-FIELD,

PART X.
THE COUNTRY AROUND

CAEMARTHEN,

BEING AN ACCOUNT OF THE REGION COMPRISED IN
SHEET 229 OF THE MAP.

BY

AUBKEY STKAHAN, M.A., Sc.D., F.E.S., F.G.S.,

T. C. CANTKILL, B.Sc., F.G.S.,

E. E. L. DIXON, B.Sc., F.G.S., AND

H. H. THOMAS, M.A., B.Sc., F.G.S.

(With Notes by B. S. N. WILKINSON).



PUBLISHED BY ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY'S TREASURY.




LONDON :

PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE,
BY DARLING & SON, LTD., 34-40, BACON STREET, E.

And to be purchased from

E. STANFORD, 12, 13, and 14, LONG ACRE, LONDON ;
W. & A. K. JOHNSTON, LTD., 2, ST. ANDREW SQUARE, EDINBURGH ;

HODGES, FIGGIS & Co., GRAFTON STREET, DUBLIN ;

From any Agent for the sale of Ordnance Survey Maps ; or through any

Bookseller, from T. FISHER UN WIN, 1, ADELPHI TERRACE, LONDON,

W.C., who is the sole Wholesale Agent to the Trade outside the

County of London.

1909.
Price Two Shillings.






.10



PREFACE.



THE country around Carmarthen, which is described in the
tenth part of the Memoir on the Geology of the South Wales
Coalfield, is illustrated in Sheet 229 of the New Series One-inch
Map.

The original survey was made by Sir H. T. De la Beche,
[Sir] W. E. Logan, [Prof.] John Phillips and [Sir] A. C.
Ramsay on the Old Series One-inch Maps 37, 38, 40 and 41, and
was published in 1844-5. Some additions were made to the
Silurian areas by W. T. Aveline in 1857.

The re-survey was made on the six-inch scale under the super-
intendence of Dr. Strahan and the new edition of the one-inch
map based on this re-survey was published in 1909. The areas
surveyed by the members of the staff engaged are as follows :

Dr. A. Strahan Carm. 54 S. W. ; 53 S.W. and S.E. (part).

Mr. B. S. N. Wilkinson Carm. 44 S.E. ; 45 S.W. and

S.E. 5 46 ; 51 N.E. and 52.

Mr. T. C. Cantrill Carm. 47 N.W. and S.W. ; 45 N.E.

and N.W. ; 44 N.E. ; 38 S.W. ; 37 N.E. and S.E.

Mr. E. E. L. Dixon Carm. 53 N.W., N.E. and S.E.
(part) ; 54 N.W.

Mr. H. H. Thomas Carm. 38 N.W., N.E. and S.E. ; 39 ;
40 N.W., S.W.

In the present volume each surveyor has supplied a description,
as full as space will permit, of the ground surveyed by himself,
the whole being edited by Dr. Strahan.

On the original edition of the Old Series map the tract
occupied by the Lower Palaeozoic rocks was shown as undivided
' Lower Silurian,' but in the later edition some of the beds were
differentiated by symbols. The present re-survey has shown
that Cambrian rocks extend westward as far as the centre of the
area. The Ordoviciun rocks, which correspond to the ' Lower
Silurian,' have been divided into Arenig, Llanvirn^ Llandilo and
Bala, and the minor sub-divisions of each have beefr -separated
on lithological and palaeontological grounds. Lower Llaridovery
rocks have been distinguished on the western margin of the area.
This detailed mapping has furnished the means of unravelling
the folds and faults affecting the district, and brings out the
marked overstep at the base of the Old Red Sandstone.

The overstep of the Old Red Sandstone by the Carboniferous
rocks has become apparent, in the region described, by the dis-
appearance successively of the Brownstones and Senni Beds.
West of the Towy the Carboniferous Limestone rests on the

750 Wt 11729 12/08 D&S 37 33232.



313047



IV

Lower Old Red Sandstone. Though the existence of Upper
Old Red Sandstone is proved by the occurrence of certain plant-
remains in a quartzite near Kidwelly, some doubt still remains
as to the precise limit between it and the Lower Old Red
Sandstone.

In the Carboniferous Limestone the zones established by
Dr. A. Vaughan have been identified, and the principal grouping
indicated on the six-inch map. A remarkable break in the
sequence, however, accompanied by the formation of con-
temporaneous conglomerate, has been detected at Pendine and
elsewhere.

The part of the Coalfield represented in Sheet 229 belongs to
the south-west extremity of the anthracitic region. Of the
Pennant Series, only the lower part is present, and this contains
no seams of much value, but the Lower Coal Series is fully
developed, all the seams except some of the higher seams in the
Trimsaran district being anthracitic. Near that place a powerful
east-and-west disturbance crosses the coalfield ; south of this the
ground is imperfectly known, but it seems certain that it is cut
up by faults, ranging in an east-and-west, or west-south-west
direction, and accompanied by much overthrusting and dis-
turbance of the strata.

The disturbances to which the strata have been subjected
periodically from pre-Cambrian down to post-Carboniferous
times form one of the most interesting features in the geology
of South Wales. That many of those in the Ordovician rocks
came into existence before the deposition of the Old Red Sand-
stone is clearly proved by the manner in which that formation is
superimposed upon them. These range generally east-and-west
and are accompanied along the northern margin of the map by
cleavage having the same general direction. On the other hand
other disturbances run through the Old Red Sandstone and
Carboniferous rocks, ranging, however, in the west-south-west
direction which was observable in the post-Carboniferous
disturbances of the Neath, Tawe and Loughor Valleys.

The observations on the Glacial phenomena prove that almost
the whole region described in this volume was crossed by ice
moving in a general southerly or south-westerly direction, and
that the flow was of sufficient energy to maintain its direction
obliquely across the valleys and escarpments. In the western
part, however, there are indications of the existence of an ice-
sheet which must have travelled eastwards or south-eastwards,
the proof lying principally in the distribution of boulders from
North Pembrokeshire in the adjoining map and to a small extent
in the map under description.

In Chapter XV will be found an account of the lead-mining,
manufacture of fire-bricks, and other economic developments,
exclusive of coal.



A complete list of the fossils which have been collected is

fiven in an Appendix. The specimens are preserved in the
urvey Collection unless otherwise stated, and the exact localities
from which they were obtained are marked on a set of six -inch
maps deposited for public reference in the Survey Office.

The map is issued in two editions. On the edition for Solid
Geology the glacial deposits are omitted, while on an edition for
Superficial or Drift Geology those deposits are shown by colour,
as well as the Solid Geology where it is not concealed by them.

Our thanks for assistance rendered are due to Mr. W.
O'Connor in the Pont-Henry district, to Messrs. Llew. Jacob and
Jas. Hansard in the Carway district, and to Messrs. John
Roberts and Thos. Arnold in the neighbourhood of Trimsaran.

Miss G. L. Elles, D.Sc., visited some of the principal sections
and by means of her intimate knowledge of graptolites was able
to render much assistance in determining the sequence of zones
in the Dicranograptus Shales.

Acknowledgment must also be made of the assistance received
from specialists in naming the fossils mentioned in this memoir.
Mrs. Shakespear is responsible for the determination of the
graptolites, Mr. P. Lake has named the trilobites, and Dr. C. A.
Matley has dealt with the brachiopods from the Lower Palaeozoic
rocks. Nearly all the remainder of the fossils mentioned in the
following pages have been named in the Palaeontological Depart-
ment, principally by Dr. Ivor Thomas. The few exceptions are
some specimens from the Carboniferous Limestone, not in the
Survey Collection, the names of which have been supplied by
Dr. A. Vaughan, and the remains of plants which were
examined by Dr. K. Kidston. A large proportion of the fossils
was collected by Mr. John Pringle, Assistant for Survey
Collections.



J. J. H. TEALL,

Director.



Geological Survey Office,
28, Jermyn Street,

London.
19th January, 1909.



Vll



TABLE OF CONTENTS.



Page
PREFACE BY THE DIRECTOR ... iii

CHAPTER I. INTRODUCTION 1

CHAPTER II. CAMBRIAN ROCKS. TREMADOC SERIES, PELTURA

PUNCTATA BEDS : Introduction. Local Details. ... ... 5

CHAPTER III. ORDOVICIAN ROCKS. ARENIG SERIES (TETRAGRAPTUS
BEDS) : Introduction. Local Details. Igneous Rocks. LLANVIRN

SERIES : LOWER LLANVIRN (DIDYMOGRAPTUS BIFIDUS BEDS).

Introduction. Local Details. UPPER LLANVIRN (DIDYMOGRAP-

TUS MURCHISONI BEDS) : Introduction. Local Details 9

CHAPTER IV. ORDOVICIAN ROCKS continued. LLANDILO SERIES :
Introduction. The Asaphus Ash. Flags and Limestones.
DICRANOGRAPTUS SHALES i Introduction. Hendre Shales.
Mydrim Limestone. Mydrim Shales. BALA SERIES : Intro-
duction. Local Details. Bala Limestones. Redliill and Slade
Beds , 39

CHAPTER V. SILURIAN ROCKS. LOWER LLANDOVERY SERIES ... 62

CHAPTER VI. OLD RED SANDSTONE : Introduction. East of the Towy.

Between the Towy and the Tdf. West of the Tdf ... ... 63

CHAPTER VII. CARBONIFEROUS ROCKS. CARBONIFEROUS LIMESTONE

SERIES. Introduction. Local Details ... 76

CHAPTER VIII. CARBONIFEROUS ROCKS continued. MILLSTONE

GRIT 83

CHAPTER IX. CARBONIFEROUS ROCKS continued. COAL MEASURES :
Introduction. LOWER COAL SERIES : North of the Trimsaran
Fault: (1) Pontylerem and Pont-Henry, (2) Pont Yates ... F6

CHAPTER X. CARBONIFEROUS ROCKS. COAL MEASURES (LOWER

COAL SERIES) continued. South of the Trimsaran Fault ... 122

CHAPTER XI. CARBONIFEROUS ROCKS, COAL MEASURES continued.

PENNANT SERIES 136

CHAPTER XII. FAULTS AND DISTURBANCES : WEST-SOUTH-
WESTERLY DISTURBANCES. NORTH-NORTH-WESTERLY FAULTS 138

CHAPTER XIII. SUPERFICIAL GEOLOGY. RAISED BEACH. GLACIAL

DEPOSITS. COEGEN (COYGAN) BONE-CAVE 143

CHAPTER XIV. SUPERFICIAL GEOLOGY continued. POST-GLACIAL

AND RECENT DEPOSITS : Terraces and Deltas. Peat. Blown Sand 150

CHAPTER XV. ECONOMIC PRODUCTS. LEAD-ORE. COPPER-ORE.

IRONSTONE. LIME AND LIMESTONE. ROTTENSTONE AND PLASTIC
CLAY. SAND, DINAS FIREBRICKS. POLISHING POWDER.
BUILDING STONES. WATER SUPPLY 152

APPENDIX I. LIST OF FOSSIL LOCALITIES IN THE PALAEOZOIC ROCKS

OF SHEET 229 159

APPENDIX II. PALEOZOIC FOSSILS, FROM SHEET 229, IN THE

SURVEY COLLECTIONS 163

INDEX.. 168



viii



LIST OF ILLUSTRATIONS.



Page

Pig. 1. Generalised Section along the Abbey Farm Dingle 6

2. Map of Nant-y-caws Dingle 12

3. Section along Cwm-Crymlyn 19

4. Section across Coomb Dingle 22

(Reproduced by permission from the Quart. Journ. Geol. Soc.,
vol. Ixii, p. 232).

5. Map of Capel-Dewi Hill 26

6. Section from Mydrim to Plas-parciau 29

7. Section across Tre-Vaughan Hill 37

8. Map of Clog-y-fran and Forest 42

9. Section through C16g-y-fran along line A-B of Fig. 8 ... 43

10. The Llandilo-Bala Succession 47

11. Map of Llandowror and Faynor 54

12. Section at Llandowror along line A-B of Fig. 11 55

Figs. 13 and 14. Sections across the Bryn-yr-odyn Disturbance at

Llandyfaelog and near Llanstephan 66

Fig. 15. Section north of Nantgaredig 138

16. Map to illustrate Distribution of Cleavage 139

17. Map of Overflow Valley at Merthyr 148

18. Map of Lead-mining District near Carmarthen 153



CHAPTER I.

INTRODUCTION.

Sheet 229 includes that part of the western margin of the
Carmarthenshire Coalfield which lies between Pontyberem
and Llandyry, and the tract of Old Red Sandstone which
separates the Carmarthenshire and the Pembrokeshire Coalfields.
The northern part of it is occupied by the Lower Palaeozoic
rocks which crop up on both sides of a great anticline.

In the space between the two coalfields the Rivers Gwen-
draeth-fach, Towy and Taf break through the Old Red Sandstone
and reach the sea in Carmarthen Bay. Generally speaking, the
rivers disregard the geological structure of the country and
maintain a southerly direction across folds, faults, and escarp-
ments, but the Gwendraeth, the Towy above Carmarthen,
and the Taf above St. Clears, form exceptions to this rule and
follow the strike for several miles. A tendency of the south-
ward-flowing drainage to concentrate on Carmarthen Bay
suggests that there was a weakness in the Old Red and Car-
boniferous escarpments somewhere between Kidwelly and
Laugharne, and that it was in consequence of this that the
two coalfields were separated by denudation. The detection of
certain disturbances belonging to the W.S.W. system, and
cutting obliquely across the head of the bay, lends support to
this view.

The highest ground is formed by the Pennant rocks, which
rise to 760 feet near Brondini. The Millstone rrit and Car-
boniferous Limestone make a bold escarpment which reaches but
rarely exceeds 600 feet, while the Old Red Sandstone seldom
rises to 500 feet, and touches 600 feet in one spot only. The
Lower Palaeozoic rocks form a tract diversified by countless
undulations and little im per sis tent scarps, but generally keeping
at a low level. Most of it lies below 300 feet and it rarely
reaches 500 feet. The outcrop of the oldest rocks is followed
by a more or less continuous valley, such as that of the Towy
above Carmarthen, or a depression such as that of which
advantage has been taken for the Great Western Railway from
Carmarthen westwards. This low tract is crossed, and not
followed, by the various rivers which* are collected by the Taf.

The mining is wholly confined to the working of coal along
the Gwendraeth Valley, the few metalliferous mines which have
been opened in the Ordovician rocks being now at a standstill.
The lower coals are anthracitic, but begin to show the change by
which they pass southwards into bituminous coals. 1 The highest

' The Coals of South Wales, with special reference to the Origin and
Distribution of Anthracite ' (Mem. Geol. Surv.), 1908.



; s x i 5



2 INTRODUCTION.

seams existing in the tract under description are in the inter-
mediate condition of steam-coal. The quarrying of the purely
quartzitic basal sandstone of the Millstone Grit for the manu-
facture of fire-bricks is an important industry. The 'silica-
sand,' as it is called, is got upon Mynydd-y-Gareg and made
into bricks at Kidwelly.

Limestone was energetically quarried in former days at Fan
and on Mynydd-y-Gareg for lime-burning. The industry is
locally almost extinct. The Coygan limestone is much worked
for road-metal and other purposes.

Lead-ores, and to a very small extent copper-ores, were
formerly raised, but the mines are now all inactive.

The great tidal flats laid dry at low water off the mouth of
the Gwendraeth, Towy and Taf rivers yield an abundance of
cockles, the gathering of which gives employment to a number
of women. For the rest the population is engaged in
agriculture.

The water-supply is obtained chiefly by the impounding of
streams, or from springs and shallow wells, in no case from deep
wells.



The following formations are distinguished by colour upon the
Map :

^ Recent and Post-Glacial
Gravels (Deltas | \- Superficial

} Glacial



Blown Sand
Alluvium
Peat
River

and Terraces)
Boulder Clajt
Sand and Gravel



Pennant Series with the^
Brondini or Gyscwm
Vein at its base

Lower Coal Series with }-
Cockshot and other
sandstones, and the |
principal coal-seams J

Farewell Rock, imperO

sistent

Shales with sandstones [
Basal Grit J

Upper Limestone Shales \
Main Limestone



Coal Measures



Millstone Grit



Lower Limestone Shales | donianj



T^-J 11- 1 Carboni-
Kidwelhan I feroug

I Limestone
Series



- Carboniferous



Penlan Quartzite
Brownstones

Senni Beds ^

Red Marls with Green ^
Beds at base J



Upper Old Red Sandstone ")

I Old Red Sand-
Sand- | stone

J



Lower Old
stone



Red



INTRODUCTION.



3



Mudstones, grits, and \
conglomerate /

Slade and Redhiil Beds
Shoalshook Limestone "1
Robeston Wathen Lime- >

stone

Mydrim Shales
Mydrim Limestone
Hendre Shales 1

Llandilo limestone and !

flags.

Asaphus Ash J

Didymograptus murchi- \

soni Beds J

Didymograptus

Beds
Didymograptus

Beds*
Didymograptus extensus f

Beds* J

Peltura punctata Beds
Dolerite \

Porphyry J

Andesite
Rhyolite



Lower Llandovery

Upper Bala "]

Bala lime- j
stones J- Bala

"] Dicrano-

}- graptus

J Shales

Llandilo



Silurian



> Llandilo



Ordovician



bifidus \

J

hirundo 1






Llanvirn J



Intrusive
Extrusive



Tremadoc Cambrian



Igneous Rocks



The identification in the western end of the coalfield of the seam
known as No. 2 Rhondda in Glamorganshire has proved difficult.
The Brondini Vein has been taken to be the same as a vein which,
under the names of Garnswllt and Ynjsarwed, ranges eastward
along the north crop to a point where its identity with the No. 2
Rhondda Seam becomes fairly certain. So far as regards the
southern side, the Gyscwm is regarded as being the same as the
Penlan Vein of Gower, the Dyvatty Vein of Swansea, and the
Wernddu Vein of Neath. This further east becomes the Rock-
fa wr, which is believed to correspond to the No. 2 Rhondda
Seam. That the Gyscwm corresponds to the Brondini Vein is
highly probable, and consequently the tracing of this horizon
from the eastern end of the coalfield along the north and south
crops has resulted in a fairly satisfactory reunion in the western
end. The seam, however, no longer forms the downward limit of
massive sandstones. Rocks not differing from Pennant sand-
stone appear below it, with a tendency to expand westwards.
These, which have to be included in the Lower Coal Series, are
distinguished under various local names, such as Llynfi,
Tormynydd, or Cenrhos Rock.

The Coal Measures pass down into the Millstone Grit here as
elsewhere. Some sandstones in the top of the latter may repre-
sent the Farewell Rock but are impersistent, and in their absence
the lowest seam, the Rhas-fach, forms an arbitrary base to the
Coal Measures. The Millstone Grit belongs to the type which
prevails along the north side of the coalfield rather than to that
which is developed in Gower. Quartzitic sandstones predominate
in the lower part.

* Not separated on the Map for the reasons given on p. 10.



INTRODUCTION.

The Old Red Sandstone here begins to show that diminution
through which, further west, it disappears. The Brownstones
and Senni Beds are present in the eastern part, but in the
western part of the map the Carboniferous Limestone Series
oversteps them and rests on the Red Marls, though no dis-
cordance is visible. Near Kidwelly some outliers of quartzite
have yielded plants of Carboniferous affinities. The relation of
the quartzite to the Limestone Series above and to the Lower Old
Red below is obscure, but the plants show that it cannot be older
than Upper Old Red Sandstone. The unconformity at the base
of the Old Red Sandstone is most pronounced.

The faults and disturbances belong chiefly to the west-south-
west system which passes down the Yale of Towy. Movement was
renewed along the same general line of country at more than one
period, for while the majority of the faults by which the Ordovician
rocks are sliced up pass under the Old Red Sandstone without
affecting it, a certain number shift also the Old Red and the
Carboniferous rocks most conspicuously. Among these may be
noticed a number of faults at Kidwelly, the remarkable faulted
monocline of Llandyfaelog, the faults which repeat the Old Red
outcrops near Llanddarog, and the crush which cuts through the
Old Red marls south-west of St. Clears. These later movements
differ in no way from the earlier. Their age is unknown further
than that they are post-Carboniferous, but their effect upon the
physiography of the region suggests that they are, in part at
least, of quite a late date. To some of them may be attributed
the existence of Carmarthen Bay, as before mentioned. The
west-south-west disturbances are accompanied by cleavage, which
sets in along the northern margin of the map.

The glaciation of the region shows proof of the existence of
two ice-systems. One, of which we had evidence in the adjoining
area on the east (Sheet '230), moved from a little east of north,
and was sufficiently powerful to scour Mynydd-y-Gareg to its
summit, carrying boulders from it to the shore near Kidwelly.
The other, which just reached this region, introduced boulders
the source of which lav to the west or north-west.



CHAPTEE II.

CAMBEIAN EOCKS.

TREMADOC SERIES.
PELTURA PUNCTATA BEDS.

INTRODUCTION.

The Tremadoc rocks, which are brought to the surface near
Llanarthnej 1 by a series of anticlinal folds, continue their westerly
course into the area represented by the map under description.
They were first recognised and mapped in the Carmarthen
district by the Misses Crosfield and Skeat, 2 who relegated them
to the stage 3a of Brogger 3 and suggested their possible correla-
tion with the Shineton Shales. Mr. Fearnsides 4 , however,
remarked that he was unable to correlate them with any known
deposits of Tremadoc age.

Collection by the Survey has resulted in the discovery of the
two well-known Scandinavian forms DikelocepTialus serratus
Boeck and Pambolinella rugosa Brog. These are confined to
the Ceratopyge Limestone of the Christiania district and are
referred by Brogger 5 to his stage 3a^ or the uppermost member
of the Tremadoc series.

In the memoir on the Country around Ammanford it was
shown that the Tremadoc rocks of Carmarthenshire occupy a
high position in the series insomuch 'as they appear to pass
gradually into the Arenig rocks and contain in common with the
Arenig certain fossils such as Ogygia selwyni (Salt.) [0. mar-
yinata? Crosfield and Skeat].

The Tremadoc series of this distict is characterised by Peltura
punctata Crosfield and Skeat. Other fossils are rare but include
Orthoceras, several lamellibranchs, and species of the genera
DikelocephaliiS) Ogygia^ Parabolinella, and Erinnys.

The lower part of this series is nowhere exposed, but the
upward passage into the overlying Arenig rocks may be studied
at several localities. Where fossils are scarce the line of separa-
tion is most indefinite. We include in the Tremadoc series all
beds in which Peltura punctata has been detected, for with the
disappearance of this form Ogygia selwyni becomes more
abundant and the Arenig genera Pkyllograptus and Tetragraptus
with extensiform species of Didymograptus appear for the first
time.

1 H. H. Thomas in * The Country around Ammanford ' (Mem. Geol. Surv )
1907, pp. 6 and 7.

2 Quart. Journ. Geol. Soc. vol. lii, 1896, p. 523.

5 ' Die Silurischen Etagen 2 und 3 Kristianiagebiete,' 1882.

4 Geol. Mag., 1907, p. 203.

5 Op. cit. pp. 14-18.

6 ' The Country around Ammanford/ footnote on p. 7.



6



CAMBRIAN ROCKS.



Lithologically the Tremadoc beds are dark blue-grey shales
and mudstones, with occasional dark-blue conglomeratic grits
and thin sandstones. The harder beds preponderate upwards,
but reach their maximum development in the lower part of the
Arenig deposits.

LOCAL DETAILS.

The most easterly Tremadoc rocks form two almost parallel
outcrops, continuations of those shewn on Sheet 230. The
northern band is faulted on the south, but passes naturally
under the Arenig rocks towards the north. The best exposure
is in the Abbey Farm dingle -which crosses the strike from the
farm to the Towv.



Fuj. 1. Generalised Section alow/ the Abbey Farm Dingle.
(H. H. Thomas.)



1ST.


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