The Leicestershire Coalfield is small, being only 11 miles (18km) along the north-south axis and 3 miles (5km) along the east-west axis. The seams outcrop at the northern end of the field and dip gently to the south east under Triassic strata and the coal measures are cut off on the eastern side of the huge Thrislington reverse fault which brings pre Cambrian rocks to the surface, and the seams incrop to the south and west boundaries of the Coalfield into the overlying Triassic rocks. There is a high density of coal seams however, there being some 55’ 6” (17m) of coal in 12 seams over 3’ 3” (1m) thick in section, but unfortunately due to faulting and the close proximity of the water-bearing strata only small areas of coal have been worked, that is, in comparison to the large tracts in Yorkshire, Nottinghamshire and Derbyshire and even in those areas the ‘surface has only just been scratched’. However the portions of coal worked have left the remaining areas difficult to get at by traditional methods. The depth of cover is 129 yards (118m) to the shallowest shaft and 310 yards (284m) to the deepest at Bagworth shafts, whereas it is 400 yards (366m) deep at Ellistown. The maximum thickness of the Triassic rocks is 120 yards (110m) at Desford. All the seams are poor in quality and used for industry, domestic and power stations.
Bagworth Marine Band
- Upper Lount
- Nether Lount
- Heath End.
Marine Band - Millstone Grit
The seam names generally were the same as for South Derbyshire with a few exceptions
- Upper Main
- Moira Main
- Four Foot
- Seven Feet
- Top Main
- Old Main.
Vertical section of principal seams in the Eastern basin of the 2 coalfields
- Stone Smut
- Swannington or Splent
- Jack Head
- Slate Rider
- Swannington Yard
- Cannel or Rattlejack
- Upper Lount
- Middle Lount
- Nether Lount
- Heath End...
Vertical section of principal seams of Western basin
- Dicky Gobler
- Little Woodfield
This area is mentioned because of the close proximity to several collieries in North Derbyshire and North Nottinghamshire where overlapping of the border by underground workings resulted in some seam names being common and others quite alien.
Here generally the seam names change considerably, however several of them were used in 3 of the counties.
- Two Feet or Summer
- Kents Thick or Mapplewell
- Kents Thin
- Warren House
- Swallow Wood
- Top Haigh Moor
- Low Haigh Moor
- Haigh Moor
- Beaston or Beeston
- Low Fenton
- Silkstone to name a few.
As will be seen throughout the book many other local names are mentioned for certain coal seams.
The new colliery Asfordby in North West Leicestershire sunk in the 1980s to accommodate miners from the closing pits of South Leicestershire and South Derbyshire sank to a combined seam of Deep Soft and Deep Hard not worked before, and was called the Deep Main. The Parkgate seam was accessed also. However the enterprise would fail due to ingress of water into the workings.
There are hundreds of seam names throughout the Coalfields of Britain: Listed in Book 8 viz Scotland, Northumberland and Durham, Lancashire, Staffordshire, Cumbria, North Wales, South Wales, Shropshire, Bristol and Somerset, Forest of Dean and Kent. Many Yorkshire names are used as the Yorkshire Coalfield is continuous with the Derbyshire / Nottinghamshire Coalfield and reference is made to several pits near the border of the counties.
There are many bands of unnamed coal seams only inches (mm) thick that are among the workable ones.
The coal mining industry was developed by siting the mines where the coal was to be found and having extracted the coal either economically or as far as practicable or by ending a lease then moved on to another site where further coal was extracted and so on. As will be seen economic extraction became the norm and later government intervention in the late 20th Century by privatising the electricity industry allowed for cheaper imports of foreign coal thereby causing the closure of many mines that had many more years life.
- UK Seam Names -
The Formation Of Coal
All the coal seams differ in some way by quality and are quantified with a Rank number. This is defined by the fixed carbon limits with weight % dry and mineral and matter. The rank is arrived at by the amount of time, heat and depth with pressure. Most seams are comprised of various bands of coal constituents such as clarain - banded bright streaky coal; durain - dull hard coal; vitrain - brilliant coal having a conchoidal fracture and rich in plant tissue, and fusain again dull but soft and dusty with a woody structure, and has the appearance of fragments of vegetable tissues, such as leaves, bark or wood being charred by fires or dry rot and sometimes called the mother of coal or mineral charcoal.
Tropical forest from which coal was to be formed
Some seams have bands of cannel or candle coal (so called because it burned as bright as a candle flame), also known as splint, sparkle, parrot, jacks or crackerjack. This is usually dull looking and clean to the touch and does not soil the hands but burns easily. (a thin sliver can be lit with a match) and tends to crack or split open fiercely when burnt thus giving rise to its other popular names. It is a less common grade of coal and can also be called boghead or bone coal. Other seams have nodules of ironstone or brass knockers (iron pyrites).
Most coal is fossil peat and rotting vegetation and dead foliage formed in swamp ecosystems where plant remains decay in shallow water of inland seas which is covered by mud then oxidised, then bio-graded and with extreme pressure becomes a combustible sedimentary rock. Examples of fossils are displayed. All the seams in this region are bituminous coals formed in the Carboniferous period of the Palaeozoic era of geological time and laid down in cyclothems, i.e. generally, seatearth, coal, shale/ mudstone/siltstone, sandstone, seatearth, coal, shale … and so on. Of course there are variations on the theme, and in Derbyshire particularly where the Pennine uplift brought the formed coal seams back to the surface, many were eroded and the area was heavily faulted with the stresses, leaving difficult working areas. However it does show without doubt that inland seas once covered the counties of Derbyshire, Nottinghamshire, Yorkshire and Leicestershire many times, in order that the coal seams and other rocks were able to be formed and that all manner of strata was subjected to extreme pressures over many millions of years. Many sea creature fossils are to be found exposed in the hills also. The coal seams can generally be identified by their position relative to the marine bands as mentioned. The important ones are the Mansfield marine band, above which are classified the Upper coal measures and below that are the Middle coal measures down to the Clay Cross marine band, below which are the Lower coal measures. Deeper still are the Alton marine band and the Pot Clay marine band, the first two identifiable divisions above the Millstone grit, which is classified as the base of the coal measures. Evidence of the now dormant volcanoes in Via Gellia was found in the strata sunk through at Ollerton, the volcanic ash being about 3” (0.08m) thick, assumed to have been deposited by the direction of the prevailing winds at that time and distance that the ash would be held in the air before falling to earth, before compacting and being submerged beneath the seas again then overlain with mud.
The Carboniferous period lasting some 65 million years is underlain by the Devonian, 50 million years, which had a warm to moderate climate giving the old red sandstone, conglomerates, red marls and sandstones and grey flaggy beds, and overlain by the Permian, up to 55 million years which had desert conditions with red breccias, conglomerates and sandstones and red siltstones, dolomitic limestones and evaporates. This was overlain by the Triassic, 45 million years, which gives us equisetites (horse tails) and ferns, cyclads, conifers and ginkgo (maidenhair tree). The Carboniferous climate began to form some 300 million years ago and was equatorial for much of the period in Britain in two main facies (a body of rock with specified characteristics) :-
(a) with deltaic conditions laid down over large flat areas with coastal swamps containing shales, carbonaceous and ferruginous, mudstones, ironstones, siltstones, sandstones, seat-earths, and coal seams, and
(b) marine, calcareous shales and argillaceous, clastic, crinoidal and coral limestones and local turbidites.
The coal measures had very rich flora forests including calamites, sphenophyllum, alethopteris, mariopteris, sphenopteris, rhacopteris, giant club mosses, lycopods, lepidodendron, neuropteris and sigillaria and stigmarian rootlets, pteridosperms (seed bearing plants with fern-like foliage, petioles), rare true ferns and cordaites. These forests grew and died and then subsided and formed a ‘peaty’ structure. The conversion of heterogeneous assemblage of plant debris into a more or less structureless mass for in some cases the original structure disappeared apart from some cells, sporangia and spores, probably produced by the action of bacteria. This decay would also cause changes in the chemical nature of the mass.
It is thought that approximately 5 to 10 times of vegetation material was required to make a coal seam, e.g. a seam 5 feet (1.52m) thick would have required 50 feet (15m) of compressed material. Coal is formed by the bark, roots and leaves and charcoal (where forests have been on fire) and mingled with the remains of other plants and vegetable matter with spores and cases of lycopodiaceous trees in great quantity.
The chemical constituents of coal are similar to wood, however there is more carbon in coal but less oxygen. Branches and stems are often found in the roof of some seams and in the seat earth floor of others. The peat, the beginning of ‘coal’ was converted into brown coal initially and does not show any obvious evidence of woody structure. It more closely resembles a very hard and compact peat and over the many millions of years, the continuing effects of temperature and pressure changed the maturity of the brown coal into sub-bituminous coal and as further chemical and physical changes took place, the coals became harder and more mature and were transformed into bituminous coals or hard coals. Lignite is a variety of coal in which the dominant constituent consists of wood and is a fuel of a fibrous character and is rare in Britain and the greatest extent of any deposits is in Devon, southwest of Exeter and the wood in the seams are thought to be allied to the Sequoias, such as the giant Redwoods. This lignite was known about and worked since 1714.