By Dr Lloyd Boardman
There are actually four coalfields that make up the North Staffordshire
Coalfield as such. In the extreme north of the county, between Leek
and Buxton, lies the small Goldsitch Moss Coalfield. This is only a few
square miles in extent and here, only the lowermost 400 feet (120m) of coal
measures, i.e. rock strata containing coal seams, are present. About 8 miles
(13km) to the south lies the larger Cheadle Coalfield, covering an area of some
20 square miles (53 sq km) in which all of the lower half of the coal measures
sequence is represented. To the west of Cheadle lies the Shaffalong Coalfield,
another very small coalfield, in which, like Goldsitch Moss, only the very lowest
part of the coal measures are to be found. A little further west, centred on the
City of Stoke-on-Trent, is the main Pottery Coalfield. This, with its area of
over 100 square miles, is by far the most important in north Staffordshire.
This coalfield has been the scene of the most industrial activity and from an
economic standpoint the terms ‘North Staffordshire Coalfield’ and ‘Pottery or
Potteries Coalfield’ are really synonymous.
The coalfields of Britain are not scattered indiscriminately over the countryside.
Their presence in a particular area is controlled by two main factors. Firstly,
conditions must have existed in the distant past that were suitable for the accumulation
of great thicknesses of peat. Secondly, this peat must have been preserved by burial.
Subsequently it has been converted into bituminous coal. The start of this process took
place during a part of the earth’s geological history a staggering 300 million years or
so ago. In the world of geology to be dealing with rocks of such vast ages and such
long periods of time as millions of years is not unusual, in fact it is commonplace.
Many people will be familiar with the processes that form coal from vegetable matter,
but the important thing from the point of view of making the coalfields attractive
economically is that the processes of coal formation and preservation didn’t just happen
once, but many times over a large period of time, measured in millions of years, creating
a series of coal seams within a sandwich of shales and sandstones, just like the layers
of jam in a multi-layered sponge cake. The period of time during which the vegetable matter
was accumulating needed to be long enough to produce thick peat layers and hence, when turned
into coal, produced thick coal seams. Also, during the subsequent many millions of years of
geological history, earth movements must not have exposed the coal seams and their containing
rock strata at the earth’s surface to any agents of destruction. The atmosphere would have
oxidised the coal and then it could be eroded away, say, by rivers, and lost forever. Nor must
they have been forced down too deeply into the earth’s crust by subsequent earth movements
leaving them beyond a workable depth.
Throughout most of the period of the earth’s geological history, which is known as the
Carboniferous Period, (which lasted from about 360 to 285 million years ago), during
which the coal measures of north Staffordshire were formed, north and central England lay
in equatorial latitudes and underwent prolonged subsidence or sagging of the earth’s crust,
forming a vast basin of deposition which is known as the ‘Central Province’. The amount
of subsidence increased towards the centre of the basin and probably reached it’s maximum
somewhere in the general area of Manchester, where it amounted to several thousands of feet
in total. The position of the Potteries or North Staffordshire Coalfield, fairly close to
the centre of the basin, is reflected directly in the nature of its Carboniferous rocks.
As a result the coal seams and their containing measures are very thick and form a complete,
unbroken, sequence of rocks from the very earliest coal seam to the last coal seam to be
formed in this area. This is in marked contrast to other coalfields in the Midlands that
lie close to the edge of the basin (e.g. the Coalbrookdale Coalfield), where the coal
measures sequence is thin and far from complete.
The oldest rocks of Carboniferous age in or near to the North Staffordshire Coalfield
are the limestones of the Astbury area near Congleton. These are overlain by some
2,000 ft (600m) of shales and sandstones of what used to be called the Millstone Grit
Series, which takes its name from the coarse sandstones that occur at the top of the
succession which have in the past been quarried for millstones. These coarse sandstones
can be readily observed at the surface at Mow Cop where scours in some of the rock faces
identify places where large rounded blocks have been hewn for millstones. Finally, the
last group of rocks laid down in the Carboniferous era was the Coal Measures. These total
some 8,000ft (2,400m) in thickness. They include, resting on top of the productive coal
measures, the thick barren ‘red beds’ at the top of the sequence that includes the famous
‘Etruria Marl’, prized as a raw material in the manufacture of bricks and tiles, in particular
the Staffordshire engineering blue brick that has helped to build many a railway bridge.
Part of this rock formation can be seen from the Potteries ‘D’ Road, the A500, on the
slopes of Bradwell Wood, where a number of red, marly, shallow brick pits scar the landscape.
The productive part of the Coal Measures, i.e. that part that contains the workable coal
seams, is a little over 3,500ft (1070m) thick. In all, some 25 or so principal workable
seams of coal are present in these productive coal measures in the north Staffs area.
All the seams added together would come to a total thickness of coal of around 100ft or
30m of coal, a veritable thickness of coal indeed, particularly bearing in mind that
the Potteries Coalfield is over 100 square miles in extent, stretching from Biddulph
in the north, to Madeley in the south-west and Moddershall in the south-east.
As you can imagine, one hundred feet of coal over such a large area amounts
to many hundreds of millions of tonnes of coal. The wealth of the coalfield
was clearly demonstrated by the first Harecastle canal tunnel constructed
under the supervision of the eminent engineer, James Brindley, which proved
6 workable ironstone seams and 26 coal seams. The south end of the tunnel
is located near Tunstall in rocks occurring near the base of the Etruria Marl
‘red beds’ and the north end is at the Ten Feet Coal level. (see the list of
the coal seams in their sequence order below).
For practical purposes the productive Coal Measures can be divided into four
main parts. The topmost of these has been called the ‘Blackband Group’ on
account of the occurrence of at least four workable seams of blackband
ironstone that were very important economically during the earlier part of
the Industrial Revolution. These ironstones occur in some 300ft (90m) of
mainly shales with thin sandstones. All of these ironstones lie immediately
above a coal seam and they share their names with the coals. They contain up
to 40% of iron and also have up to 10% of organic matter in them, which renders
some of them self-calcining. Some of the ironstone also have thin oil shales
developed close by in the sequence which were worked historically to support
a local oil industry.
The next group of measures immediately below forms the topmost economic series
of coal seams and these are the measures starting at the topmost workable coal
seam of the coalfield, the Peacock Seam, extending down to the Rowhurst Seam, a
total thickness of strata of about 1,100ft (335m). This sequence of coal measures
contains 6 important coal seams, including the well-known Great Row in addition
to those already mentioned. This group of rocks also contains the so called ‘Lean
Ironstones’, which as the name suggests, are less attractive commercially than the
blackband ironstones above, but nevertheless also played an important part in the
early development of the iron industry in the area. There are some 7 or 8 named
seams of lean ironstone, the majority occurring in the measures between the Cannel
Row Coal Seam and the Winghay Coal Seam. These are very different from the
blackbands in both their nature and occurrence, being concretionary clay ironstones.
This group also contains a number of historically important pottery clays and some
of the coals have long flame burning characteristics, much sought after by the Potter
in the 18th & 19th Centuries. Below this top coal group there occurs a group of
strata with little in the way of coals of any real economic significance, a thickness
of strata of some 700ft (210m). Immediately below this is the lower group of
important coals extending downwards from the Moss Seam at the top to the Bullhurst
Seam at the bottom, a thickness of some 1,900ft (580m). This group includes the
well-known house coal, the Holly Lane Seam, and the thick coals, the Ten Feet ,
Cockshead and the already mentioned Bullhurst Coal Seam. Some of these have
important coking properties and have provided useful fuels for the local steel
Below this last mentioned seam lie a number of thin seams including the Brights,
Diamond, Silver and Crabtree, none of which have been particularly important in the
overall development of the coalfield historically, making up the fourth and lowest
part of the so called productive coal measures.
The structural complexity of the North Staffordshire Coalfield with, in part, steeply
dipping seams and considerable faulting has made mining a particularly hazardous and
expensive enterprise. The overall structure of the coalfield is well exhibited at the
surface by the pattern of the outcrops of the individual coal seams, (where the rocks,
coal seams and ironstones come out at the surface), and is seen to consist of a
central plunging syncline, (a broad E-W down-fold in the rocks tilting towards
the south), centred on Stoke-on-Trent, producing a characteristic inverted ‘V’
shape, enclosed between eastern and western anticlines, (up-folds).
Numerous faults, (fractures in the ground around which there has been some vertical
movement), some of great magnitude, cross the coalfield, the principal ones trending
north-north-west and north-east. The Apedale Fault is one of the more conspicuous
of these. At its maximum displacement of 600 to 700 yards down to the east in the
vicinity of Apedale, beds high in the Keele Group, (part of the upper ‘red beds’),
are brought against the Bassey Mine Coal; introducing here a strip of barren Upper
Coal Measures between the richly productive central and western parts of the coalfield.
The western margin of the field is bounded by a belt of greatly disturbed strata made
up of many faults and steeply dipping measures: those on the west or Cheshire side
dipping down at angles approaching and sometimes exceeding 90 degrees, i.e. vertical,
hence the name ‘Rearers’ is applied to the disposition of the coals here. At the Diglake
Pits the Bullhurst Seam was encountered twice in the sinking of one shaft, a result
of passing vertically through an ‘s’ shape fold in the coal measures. West of Audley
the Red Rock Fault trending north-east and down-throwing to the west gradually approaches
the coalfield and forms its ultimate western boundary. The most prominent fault in the
central southern part of the coalfield is the Longton Fault. This has a displacement of
some 250 yards and extends from Longton towards Trentham.
Despite all this complexity, it is a coalfield very rich in resources and an idea
of the richness of its coal sequence can be gained from examining the number of seams,
their thickness and the depth at which they were encountered in, for example, the Deep
Pit at Hanley. Note, however, this does not include the top seams in the sequence, the
Peacock, Spencroft, Great Row and Cannel Row seams, nor the bottom seam, the Bullhurst.
Seams Encountered in the Deep Pit, Hanley.
Key:7/4 = 7ft 4in
List of all the coal and ironstone seams in order
from top to bottom of the sequence in the coalfield.
Common Coal Seam Names and some often used alternatives.
BLACKBAND* (or Half Yards)
HOO CANNEL* (or Fenton Low)
LITTLE ROW (or Yard)
GUBBIN IRONSTONE** (or Cannel Mine)
CANNEL ROW IRONSTONE**
CANNEL ROW (or Little Mine)
PENNYSTONE IRONSTONE** (or Rusty Mine)
DEEP MINE IRONSTONE** (or Sheath Mine)
CHALKY MINE IRONSTONE**
LITTLE MINE IRONSTONE**
BUNGILOW (or Hanbury)
NEW MINE IRONSTONE**
BAY (or Lady)
WINGHAY (or Knowles or Brown Mine)
BIG MINE IRONSTONE**
BROWN MINE IRONSTONE** (or Gold Mine)
ROWHURST (or Ash)
STAFFORD (or ? Tabberners)
TWIST (or Gin Mine)
BIRCHENWOOD (or Granville)
ROUGH SEVEN FEET
HAMS (or Birches or Old Whitfield)
BELLRINGER (or Stoney Eight Feet)
TEN FEET (or Main)
TOP TWO ROW IRONSTONE
BOWLING ALLEY (or Top Two Row)
HOLLY LANE (or Bottom two Row)
HARD MINE (or Sparrow Butts)
NEW MOSS (or Stinkers)
BANBURY(or Seven Foot Nabbs or Froggery)
COCKSHEAD (or Eight feet Banbury or Eight Foot Nabbs))
CRABTREE (or Four Foot)
*coal & ironstone (The ‘Blackbands’)
** ‘Lean Mine Ironstones
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