ThePennant Measures is the traditional name for a sequence ofsedimentary rocks of theSouth Wales Coalfield. They were also referred to as the UpperCoal Measures and assigned to theWestphalian 'C' and Westphalian 'D' stages of theCarboniferous Period. The Pennant Measures were divided into the Lower Pennant Measures and the Upper Pennant Measures, differing from the underlying Middle and Lower Coal Measures in being principally of sandstoneunits – known collectively as thePennant Sandstone – with mudstone being the subsidiary rock type. Numerouscoal seams occur within the Pennant Measures though they are less common than in the underlying Coal Measures.[1]
However recent reclassification of the sequence has resulted in the definition by theBritish Geological Survey of thePennant Sandstone Formation as a sub-unit of the newly establishedWarwickshire Group. The formation is recognised to be of Bolsovian to 'Westphalian D' age. It overlies the uppermost strata of the newly definedSouth Wales Coal Measures Group and underlies the rocks of the succeedingGrovesend Formation. The Pennant Sandstone Formation is now formally subdivided (in ascending order) into the Llynfi, Rhondda, Brithdir, Hughes and Swansea members, each of which units formerly had 'bed' status.[2][3]
Being relatively resistant to erosion, the Pennant Sandstones form the plateau surface of the Coalfield into which the coalfield valleys have been deeply incised by water and ice. They reach their greatest height (though not their highest stratigraphic level) at the flat summit ofCraig y Llyn where they are represented by the Hughes Member.[4]
The sandstone were quarried both in South Wales and the Bristol area for use in paving and roofing is also known asPennant Stone.[5]
Pennant Stone: Hard, fine grained, blue/grey coloured sandstone. Quarried in South Wales and the Bristol area and commonly used, throughout the country, as a stone roofing material (stone slate).