Mynydd y Grug is a

hill A hill is a landform that extends above the surrounding terrain. It often has a distinct Summit (topography), summit. Terminology The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally con ...

lying just west of the village of

Cwmfelinfach Cwmfelinfach is a small village located in the Sirhowy valley of south-east Wales. It is part of the district of Caerphilly within the historic boundaries of Monmouthshire. It is located north of Wattsville, about 5 miles north of the nearest ...

and about 4 km to the northeast of

Caerphilly Caerphilly (, ; cy, Caerffili, ) is a town and community in Wales. It is situated at the southern end of the Rhymney Valley. It is north of Cardiff and northwest of Newport. It is the largest town in Caerphilly County Borough, and lies wit ...

in Caerphilly county borough in South

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

. Its summit was formerly at a height of around 358 m, but since the top has been covered by a large spoil heap and landscaped its height has now increased to 375 m, though some authorities take other values for the summit height. A number of ancient cairns are found along its edge overlooking the

Sirhowy Valley The Sirhowy Valley ( ) is an industrialised valley in the eastern part of the Valleys region of Wales. It is named from the Sirhowy River () which runs through it. Its upper reaches are occupied by the town of Tredegar within the unitary area of ...

, the slopes up from which are largely wooded.

Geology

Mynydd y Grug is formed from

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

s of the

Pennant Sandstone Formation Pennant may refer to: Flag or banner * Pennon (or pennant), a narrow, tapering flag ** Commissioning pennant, the traditional sign of a warship, flown from its masthead while the ship is in commission ** Broad pennant, flown from the masthead o ...

assigned to the

Warwickshire Group The Warwickshire Group is a lithostratigraphic unit of rock strata defined within the British Carboniferous system. Within the Pennine Basin it overlies (i.e. postdates) the Coal Measures Group and is deemed to be of late Westphalian and St ...

and laid down during the latest part of the

Carboniferous 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 ''Carbonifero ...

Period. The hill lies in the southeastern part 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, espec ...

and

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 such as the 'Dirty' and the 'Cefn Glas' have been worked around its flanks.

Access

The hill is crossed by a number of public footpaths, one of which is a restricted byway linking two cul-de-sac minor roads approaching from

Machen Machen (from Welsh language, Welsh ' "place (of)" + ', a personal name) is a large village three miles east of Caerphilly, south Wales. It is situated in the Caerphilly (county borough), Caerphilly borough within the Historic counties of Wales, ...

to the east and Blackwood to the north. This route is followed by the

Rhymney Valley Ridgeway Walk The Rhymney Valley Ridgeway Walk is a waymarked long distance footpath in the UK forming a circular walk in the Rhymney Valley area of South Wales.open access Open access (OA) is a set of principles and a range of practices through which research outputs are distributed online, free of access charges or other barriers. With open access strictly defined (according to the 2001 definition), or libre op ...

and available for walkers to wander freely.Ordnance Survey Explorer map 166 ''Rhondda & Merthyr Tydfil/Merthyr Tudful''

References

{{reflist

External links

images of Mynydd y Grug and area on Geograph website
Mountains and hills of Caerphilly County Borough