The Oldham Coalfield is the most easterly part of the south Lancashire Coalfield. Its coal seams were laid down in the Carboniferous period and 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 middle of the 20th century.[1]
The Coal Measures lie above a bed of Millstone Grit and are interspersed with sandstones, mudstones, shales, and fireclays and outcrop in the Oldham district. The Gannister Beds or Lower Coal Measures occupy the high ground of the West Pennine Hills above Oldham where the most productive seam is the Mountain mine.[nb 1] The Lower Coal measures were worked north-east of a line from High Crompton to Greenacres and the Middle Coal Measures to the south-west.[2] The deepest seam in the Middle Coal Measures is the Royley mine which is eqivalent to the Arley mine of the Manchester Coalfield.[3] The coal seams dipped in the direction of central Manchester and were broken by numerous faults including the Oldham Edge, Chamber, Oak and Great Faults.[4]
The early collieries were adits, accessing the coal from outcrops on the side of a hill, employing about a dozen workers. Shallow pits sunk from the surface with wooden headstocks were recorded in the late 1600s. These collieries had two shafts to aid ventilation.[5] The Chamber Colliery Company's pits were sunk around 1750 by James Lees and the company was formed in 1877. James Watt installed a Newcomen type steam pumping engine at the company's Fairbottom Colliery in the latter part of the 18th century. It was an atmospheric engine working at the low pressure of 1.5 lb. to the square inch, and was known as Fairbottom bobs.[6]
From the middle of the 19th century the output of the coalfield was sold locally to the cotton mills and factories and for domestic use.[7]