THE COLLIERY GUARDIAN

AND JOURNAL OF THE COAL AND IRON TRADES.
______________________________________________________________________________

Vol. CV.

FRIDAY, MARCH 28, 1913.

No. 2726.

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THE GEOLOGY AND PALAEONTOLOGY OF THE
WARWICKSHIRE COALFIELD*

By Robert Douglass Vernon, B.A., B.Sc., F.GS.

Warwickshire, the nearest of the Midland coalfields
to London, with an annual output of coal exceeding
3,500,000 tons, is of considerable economic importance.
The potential value of this coalfield is also very great,
because within recent years the coal-producing area has
been nearly doubled, and it is still rapidly extending.
During the preparation of the reports by the Royal
Commission on Coal Supplies, both in 1871 and in 1905,
great difficulty was experienced by the Commissioners
in estimating the coal resources of Warwickshire,
because the geology of the coalfield—especially with
regard to the relationship of the so-called permian to
the coal measures—was not fully understood. Again, as
recently as 1908, Dr. Walcot Gibson expressed the
opinion that “ it would appear advisable, before making
more ambitious attempts at development in the triassic
areas, to first determine the exact geological position and
character of the so-called permian.” It may be added
that the current geological memoir and maps of the
Warwickshire coalfield were published ’more than
50 years ago; and further, until quite recently, there
were no records of fossils from the carboniferous rocks
of the county. Thus, from the points of view of strati-
graphy, of palaeontology, and of economics, there was a
clear need for research work on this coalfield.

Carboniferous—

Upper coal measures or
' Red barren coal
measures .........

Middle coal measures
or productive coal
measures ..........

Cambrian—

Stockingford shales....

Hartshill quartzite....

Pre-Cambrian—

Caldecote rocks.......

"Keele beds.—Red sandstones
and marls with three beds of
Spirorbis limestone.

Haunch wood sandstones.—Grey
J sandstones, marls, and shales
*1 with Spirorbis limestones.

Nuneaton clays.—Red marls
and clays containing Espley
rocks, local breccias, and a
bed of Spirorbis limestone.

( Grey shales, sandstones and
\ under-clays with numerous
j seams of coal and beds of
C ironstone.

Shales (with intrusive diorite).
| Quartzite (with intrusive
( diorite).

(Sheets of breccia, tuffs, and
t grits of volcanic origin.

It is one of the chief objects of this paper to deter-
mine the true age of the so-called permian rocks of
Warwickshire, and to discover their stratigraphical
relationship to the underlying carboniferous rocks and
to the overlying deposits of triassic age. Further, I
attempt on geological evidence to subdivide the carbo-
niferous rocks into groups, and from a study of the
fossil flora to determine the age of the subdivisions.

The so-called permian formation of Warwickshire
was established by Sir Andrew Ramsay, to include the
lower portion of the new red sandstone of previous

In 1909, on my election to a scholarship awarded by
the Royal Commissioners for the Exhibition of 1851
“ for research work bearing upon industry,” I was
enabled to begin this investigation, which has been
prosecuted in the field and at the Sedgwick Museum,
Cambridge, during the past three years.

Stratigraphy.

The Warwickshire coalfield forms a roughly
triangular tract in the north-eastern part of the county;
the towns of Coventry, Nuneaton, and Tam worth being
situated at the angles. The surface area of rocks of
carboniferous age, including the additions necessitated
by the present work, is about 60 square miles. The
general structure of the coalfield is that of a shallow
basin of carboniferous rocks resting discordantly upon
an irregular floor or basement of Cambrian age ; on all
sides it is faulted against, or covered unconformably by,
the succeeding permian and triassic rocks.

The dominant structural features are the two parallel
anticlines ranging north-west and south-east, which
have ridged up the floor of the coalfield both on the east
and on the west of the district. Not only has subsequent
denudation removed the cover of trias and permian, but,
along the crests of these anticlines, even the carbo-
niferous rocks have been stripped off, thus laying bare
the Cambrian and Archaean rocks which form the
pre-carboniferous floor.

The following table embodies a synopsis of the various
formations and groups of rocks, according to the new
classification which it is proposed to establish on the
evidence detailed in a later portion of this paper:—
Table of Formations.

Pleistocene and recent—

»—	p«-W' {P"t

4.™- • 1	V Boulder clays, sands, and

'w c ..............( gravels, with erratic blocks.

Trias—

r Red marls with thin sand-

v	) stones.

euPer ..............1 Soft red and white flags and
(. marls.

Bunter .............. Sandstones and conglomerates.
Permian—

/ Red sandstones, marls and

■p .	) breccias.

Permian..............< Corley conglomerates at the
t base.

* Abstract of a paper read before the Geological Society
of London and published in the Quarterly Journal of the
society.

f The drift deposits are of no great thickness, except near
Kenilworth and also south of Exhall, where clay, sand, and
gravel occur up to 70 ft. in thickness.

observers. In the light of recent research this evidence
appears to be anything but convincing. There can be
little doubt as to the similarity between the Warwick-
shire permian and the permian of South Staffordshire;
but it may be contended that at least the lower portion
of these South Staffordshire rocks is now considered by
Mr. T. 0. Cantrill and Dr. W. Gibson to be of
carboniferous age, and to be the equivalent of the Keele
beds of North Staffordshire. The supposed outlier of
permian is merely an ordinary coal-measure sandstone
(the boundary between the permian and the carbo-
niferous). As delineated on the Geological Survey
maps, this boundary is an arbitrary one, which coincides
neither with any physiographic feature nor with any
break in the stratigraphical succession of the beds.
From a study of these rocks in the field, I propose to
show that the first important break in the stratigraphical
succession occurs at the Corley conglomerates, and that
the underlying 1,000 ft. of rocks of so-called permian
age are conformable to the coal measures, with which
they must therefore be grouped. In confirmation of
this view, I have been able to obtain fossil plants of
Upper coal-measure age from these supposed permian
rocks.

The coal measures rest upon an irregular floor of
Cambrian rocks, which is only known where it is
exposed at the surface, or where it has been proved in
deep borings. This floor, together with the overlying
coal measures, has been elevated along three parallel
lines which trend in a north-west to south-east direction.
Portions of two of these old ridges are the anticlines of
Nuneaton and Dosthill; but there is a third ridge in the
neighbourhood of Market Bosworth, which is com-
pletely hidden beneath the trias. The occurrence of a
faulted anticline of Upper coal measures at Arley may
indicate yet another fold in the pre-carboniferous floor.

Resting unconformably on the Cambrian (Stocking-
ford shales) is the basement bed of the coal measures—
a soft, coarse, false-bedded, ferruginous sandstone with
quartz pebbles. This rock, which was first noticed by
Dr. Strahan, is of value in mapping the boundary
between the Cambrian and carboniferous formations
near Merevale, where it makes a conspicuous feature,
and at Dosthill. This conglomerate, as well as the
succeeding strata of shales and fireclays, may be absent
so that the lowest seam of coal comes to rest directly
upon the Cambrian. Where the conglomerate is absent,
or where there is no section, the junction is clearly
indicated by the rising ground, at the points at which
the Cambrian comes to the surface. The base of the

coal measures has also been proved some distance away
from the outcrop in certain of the colliery sinkings near
Bedworth.

Between the basement conglomerate of the coal
measures and the Corley conglomerate at the base of
the permian, there is a vertical thickness of more than
2,500 ft. of coal measures. It is possible, on both litho-
logical and palaeontological evidence, to effect a twofold
grouping of these rocks. The lower subdivision, about
700ft. in thickness, includes all the chief seams of coal;
the Strata have a prevalent grey tint, and possess an
abundant flora and fauna. The upper subdivision, about
2,000 ft. thick, contains only a few thin impersistent
seams of coal; its constituent strata have, on the whole,
a prevalent red tint. This distinction in lithological
character is accompanied by a remarkable absence of
animal life, and by the occurrence of a limited but
characteristic flora, very different from that of the lower
subdivision.

The Productive Coal Measures.—From base to summit
the strata are made up of repeated alternations of sand-
stone, underclay and shale, with beds of ironstone and
coalseams. The rocks fall naturally into a lower
argillaceous series, which contains the workable seams
of coal, and an upper arenaceous series* which contains
only a few thin seams. In lithological character these
rocks show a general similarity to the productive
measures of the other coalfields of the Midlands, but
a few minor differences have been observed. The coals
belong exclusively to the bituminous variety, steam coals
and cannel coals being practically unrepresented.
Locally some of these seams—more particularly the
Thick coal—contain numerous macrospores, which are
found in a flattened state between the planes of bedding
of the dull hard layers of the coal. Macrospores have
also been obtained from the shales overlying the coal.
In the Stockingford clay pit, fossil trees (Sigillaria) are
not uncommon. They are found both erect and recum-
bent, being usually preserved as casts in ironstone, but
sometimes as casts in shale. These casts attain a
diameter of several feet, and are often accompanied by
a thin layer of coal representing the bark. Sometimes
such erect trees, often many feet long, may be observed
to extend almost vertically across the beds of shale
separating two seams of coal. In such cases it may be
inferred that the time taken for the deposition of the
strata separating the coalseams must have been com-
paratively short. Nodules and bands of clay-ironstone
occur at several horizons, interstratified with the shales
and sometimes even with the coals. The smaller sym-
metrical nodules are sometimes fossiliferous; while the
large, irregular, septarian ironstones or “ big balls,”
which frequently attain a diameter of 6 ft., are almost
invariably barren. A peculiar form of oolitic ironstone
or “ sph aero siderite,” composed of smalls pherules of
siderite, frequently occurs in the fireclays and sometimes
in the coal. Underclays and sandstones are of common
occurrence : the former tending to predominate in the
south of the coalfield, and the latter in the north. There is
abundant proof,in the form of local breccias, “ wash-outs,”
and local unconformities, that the deposition of the coal
measures was not continuous, but that, at certain
periods, sedimentation was interrupted by local
elevation and contemporaneous erosion. In the measures
above the Thick coal, local breccias are not infrequent.
These rocks consist of angular fragments of coal, iron-
stone or shale, often several inches long, set in a matrix
of coarse sandstone or of an extremely hard ganister-
like sandstone. Fragments of plants and casts in shale
or ironstone of Trigonocarpus, as also large specimens
of Carbonicola, may sometimes be found in these coal
breccias. Extensive barren areas or “ wash-outs ” affect
some of the seams—especially the Ryder coal at
Kingsbury and Arley and the Thick coal at Exhall
Colliery.

Coalseams — In the following general sections the
more important coalseams in each half of the coalfield

* Including the Four-feet sandstone.