The Pennant Measures is the traditional name for a sequence of

sedimentary Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles t ...

rocks of the

South Wales Coalfield The South Wales Coalfield ( cy, Maes glo De Cymru) extends across Pembrokeshire, Carmarthenshire, Swansea, Neath Port Talbot, Bridgend, Rhondda Cynon Taf, Merthyr Tydfil, Caerphilly, Blaenau Gwent and Torfaen. It is rich in coal deposits, especi ...

. They were also referred to as the Upper

Coal Measures In lithostratigraphy, the coal measures are the coal-bearing part of the Upper Carboniferous System. In the United Kingdom, the Coal Measures Group consists of the Upper Coal Measures Formation, the Middle Coal Measures Formation and the Lower Coa ...

and assigned to the Westphalian 'C' and Westphalian 'D' stages of the

Carboniferous Period The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferous ...

. 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 sandstone

units Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatrical presentation Music * ''Unit'' (al ...

– known collectively as the Pennant Sandstone – with mudstone being the subsidiary rock type. Numerous

coal seam Coal mining is the process of extracting coal from the ground. Coal is valued for its energy content and since the 1880s has been widely used to generate electricity. Steel and cement industries use coal as a fuel for extraction of iron from ...

s occur within the Pennant Measures though they are less common than in the underlying Coal Measures.British Geological Survey 1:50,000 map sheet 231 'Merthyr Tydfil' & accompanying memoir. However recent reclassification of the sequence has resulted in the definition by the

British Geological Survey The British Geological Survey (BGS) is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS he ...

of the Pennant Sandstone Formation as a sub-unit of the newly established Warwickshire Group. The formation is recognised to be of Bolsovian to 'Westphalian D' age. It overlies the uppermost strata of the newly defined South Wales Coal Measures Group and underlies the rocks of the succeeding Grovesend 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. 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 of

Craig y Llyn Craig y Llyn (Welsh, 'rock/cliff of the lake') is a mountain situated to the south of the village of Rhigos in the Cynon Valley on the south side of the upper Vale of Neath and north of the Rhondda Valleys in South Wales; it is the highest poi ...

where they are represented by the Hughes Member. Side view, St Pauls Church, Clifton

The sandstone where quarried both in South Wales and the Bristol area for use in paving and roofing is also known as Pennant Stone.

References

{{Reflist Sandstone formations Coal in Wales Geology of Wales Carboniferous Wales Carboniferous System of Europe Geologic formations of the United Kingdom Stratigraphy of the United Kingdom