The
Manchester Coalfield is part of the South
Lancashire Coalfield, the coal seams of which were laid down in the
Carboniferous Period. Some easily accessible seams were worked on a small scale from the
Middle Ages, and extensively from the beginning of the
Industrial Revolution in the early 19th century until the last quarter of the 20th century. The
Coal Measures lie above a bed of
Millstone Grit and are interspersed with
sandstones,
mudstones,
shales, and
fireclays. The Lower Coal Measures occupy the high ground of the
West Pennine Moors above Bolton and are not worked in the Manchester Coalfield. The most productive of the coal measures are the lower two thirds of the Middle Coal Measures where coal is mined from seams between the Worsley Four Foot and Arley mines. The deepest and most productive collieries were to the south of the coalfield. The coalfield is affected by the northwest to southeast aligned
Pendleton Fault along the
Irwell Valley and the
Rossendale Anticline. The Coal Measures generally dip towards the south and west. Numerous other smaller faults affect the coalfield. The Upper Coal Measures are not worked in the Manchester Coalfield.