South Wales Coal Measures Group
The South Wales Coal Measures Group is a lithostratigraphical term referring to the coal-bearing succession of rock strata which occur in South Wales within the Westphalian Stage of the Carboniferous Period. The Group name is also applied to rocks of similar age across southern England from the Bristol Coalfield east to the concealed Oxfordshire, Berkshire and Kent Coalfields.
Source: Wikipedia — South Wales Coal Measures Group (CC BY-SA 4.0)