Forest of Dean Coalfield
Coordinates: 51°47′21″N 2°32′36″W / 51.7891°N 2.5432°W
The Forest of Dean Coalfield, underlying the Forest of Dean, in west Gloucestershire, is one of the smaller coalfields in the British Isles, although intensive mining during the 19th and 20th centuries has had enormous influence on the landscape, history, culture, and economy of the area.
For hundreds of years, mining in the Forest of Dean Coalfield has been regulated through a system of freemining, in which individuals who qualify are granted leases to mine specified areas, known as gales. The Coal Industry Nationalisation Act 1946 exempted the Forest of Dean because of its unique form of ownership and history, allowing the unique privilege to continue intact.
The last of the big gales closed in 1965 and today only a handful of small collieries are still operating.
The Forest of Dean Coalfield formed during Upper Carboniferous times, when the area was a nearshore-intertidal environment of semi-marine estuaries and swamps. The area today is a raised basin plateau of Paleozoic rocks folded in the Variscan Orogeny. It occurs in a raised asymmetrical syncline with a steeper eastern limb that surfaces in the area of Staple Edge and the Soudley Valley producing the steeply dipping strata. An unusual feature of the Forest of Dean Coalfield is that its edges are almost entirely exposed at the surface.
Mining in the coalfield has always been hampered by the excessive amount of water encountered underground - trapped by the basin-shaped strata. Water drains into the basin by general percolation and, more directly, via surface watercourses. For much of their length, streams in the area run over impervious clay deposits, but, where valleys cut through the rim of the basin, carboniferous limestone and sandstone are exposed, allowing water to penetrate underground via swallow holes, cracks, and fissures. Water also enters the basin through geological faults.
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