The Warwickshire Coalfield extends between Warwick

Warwick

Warwick is the county town of Warwickshire, England. The town lies upon the River Avon, south of Coventry and just west of Leamington Spa and Whitnash with which it is conjoined. As of the 2001 United Kingdom census, it had a population of 23,350...

 and Tamworth

Tamworth

Tamworth is a town and local government district in Staffordshire, England, located north-east of Birmingham city centre and north-west of London. The town takes its name from the River Tame, which flows through the town, as does the River Anker...

 in the English Midlands

English Midlands

The Midlands, or the English Midlands, is the traditional name for the area comprising central England that broadly corresponds to the early medieval Kingdom of Mercia. It borders Southern England, Northern England, East Anglia and Wales. Its largest city is Birmingham, and it was an important...

. It is about 40km / 25 miles from north to south and its width is around half that distance. Its western margin is defined by the 'Western Boundary Fault'. In the northeast it abuts against steeply dipping shale

Shale

Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...

s of Cambrian

Cambrian

The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...

 age. The larger part of the outcrop at the surface consists of the Warwickshire Group

Warwickshire Group

The Warwickshire Group is a lithostratigraphic unit of rock strata defined within the British Carboniferous system. Within the Pennine Basin it overlies the Coal Measures Group and is deemed to be of late Westphalian and Stephanian age...

 of largely coal-barren red beds

Red beds

Red beds are sedimentary rocks, which typically consist of sandstone, siltstone, and shale that are predominantly red in color due to the presence of ferric oxides. Frequently, these red-colored sedimentary strata locally contain thin beds of conglomerate, marl, limestone, or some combination of...

. The Daw Mill

Daw Mill

Daw Mill is a coal mine located near the village of Arley in the English county of Warwickshire. The mine is Britain's biggest coal producer, mining a five-metre thick section of the Warwickshire Coalfield in the north of the county...

 mine near Arley

Arley, Warwickshire

Arley is a civil parish in the North Warwickshire district of Warwickshire, England. The parish includes two settlements, New Arley and Old Arley. Old Arley is to the west of the Bourne Brook and the railway line, and New Arley is to the east....

 within the coalfield is now Britain's biggest coal-producer.

The principal coal seams within the productive Lower and Middle Coal Measures

Coal Measures Group

The Coal Measures Group is a lithostratigraphical term coined to refer to the coal-bearing succession of rock strata which occur in Great Britain within the Westphalian Stage of the Carboniferous Period. The Coal Measures Group is preceded by the Millstone Grit Group which is of Namurian age...

include (in stratigraphic order):

Middle Coal Measures

• Half Yard
• Four Feet
• Thin Rider
• Two Yard
• Bare, Ryder, Ell
• Nine Feet, High Main
• Smithy (Low Main)

Lower Coal Measures

• Thin, Seven Feet
• Trencher
• Yard
• Deep Rider, Double
• Upper Bench, bench Thin
• Lower Bench
• Stumpy
• Stanhope

The Two Yard, Thin Rider, Ryder, Ell, Nine Feet and High Main merge as one massive bed of coal known as the 'Thick Coal' in parts of the coalfield.