Thorncliffe seam

The coal seams worked in the South Yorkshire Coalfield lie mainly in the middle coal measures. These are a series of mudstones, shales, sandstones, and coal seams laid down during the Carboniferous period about 350 million years ago. The total depth of the strata is about 1.2 kilometres.

The list of coal seams that follows starts at the shallowest seam and proceeds downwards with the outcrops occurring progressively further west until the deepest coal seam, the Silkstone Seam which outcropped at the western edge of the coalfield.

The seam thickness and depths are not given as they vary across the coalfield.

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