The Pennant Measures are a sequence of sedimentary rocks of the South Wales Coalfield

South Wales Coalfield

The South Wales Coalfield is a large region of south Wales that is rich with coal deposits, especially the South Wales Valleys.-The coalfield area:...

. They are also referred to as the Upper Coal Measures

Coal Measures

The Coal Measures is a lithostratigraphical term for the coal-bearing part of the Upper Carboniferous System. It represents the remains of fluvio-deltaic sediment, and consists mainly of clastic rocks interstratified with the beds of coal...

 and are assigned to the Westphalian

Westphalian (stage)

The Westphalian is a stage in the regional stratigraphy of northwest Europe with an age between roughly 313 and 304 Ma . It is a subdivision of the Carboniferous system or period and the regional Silesian series. The Westphalian is named for the region of Westphalia in western Germany where strata...

 'C' and Westphalian 'D' stages of the Carboniferous Period.

Divided into the Lower Pennant Measures and the Upper Pennant Measures, they differ from the underlying Middle and Lower Coal Measures in being principally of sandstone units - known collectively as the Pennant Sandstone - with mudstone being the subsidiary rock type. Numerous coal seams occur within the Pennant Measures though they are less common than in the underlying Coal Measures.

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 at the flat summit of Craig y Llyn

Craig y Llyn

Craig y Llyn is a mountain situated in Rhigos on the west side of the upper Cynon Valley in South Wales; it is the highest point in the traditional county of Glamorgan and the highest in the South Wales Valleys...

.

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