hill
A hill is a landform that extends above the surrounding terrain. It often has a distinct summit.
Terminology
The distinction between a hill and a mountain is unclear and largely subjective, but a hill is universally considered to be not a ...
lying between the town of
Risca
Risca ( cy, Rhisga) is a town in the Caerphilly County Borough and the Historic counties of Wales, historic boundaries of Monmouthshire (historic), Monmouthshire in south-east Wales. Risca has a railway station, opened on the Ebbw Valley Railway ...
and the village of
Machen
Machen (from Welsh ' "place (of)" + ', a personal name) is a large village three miles east of Caerphilly, south Wales. It is situated in the Caerphilly borough within the historic boundaries of Monmouthshire. It neighbours Bedwas and Trethom ...
in
Caerphilly County Borough
Caerphilly County Borough ( cy, Bwrdeistref Sirol Caerffili) is a county borough in the south-east of Wales. It is governed by Caerphilly County Borough Council.
Its main and largest town is Caerphilly. Other towns in the county borough are B ...
in south
Wales
Wales ( cy, Cymru ) is a country that is part of the United Kingdom. It is bordered by England to the east, the Irish Sea to the north and west, the Celtic Sea to the south west and the Bristol Channel to the south. It had a population in ...
. Its summit is crowned by a
trig point
A triangulation station, also known as a trigonometrical point, and sometimes informally as a trig, is a fixed surveying station, used in geodetic surveying and other surveying projects in its vicinity. The nomenclature varies regionally: they a ...
and a mast.
Geology
The hill lies at the southeastern extremity 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, espe ...
where the varied Carboniferous Period rock strata of the
coalfield
A coalfield is an area of certain uniform characteristics where coal is mined. The criteria for determining the approximate boundary of a coalfield are geographical and cultural, in addition to geological. A coalfield often groups the seams of ...
margin are tilted steeply northwestwards into the coalfield basin. The sequence which outcrops on Mynydd Machen in northeast-southwest aligned bands is this (oldest at base):
Warwickshire Group
:*
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 ...
::*Brithdir Member
::*Rhondda member
::*Deri Member
South Wales Coal Measures Group
:*South Wales Middle Coal Measures Formation
:*South Wales Lower Coal Measures Formation
Marros Group
The Marros Group is the name given to a suite of rocks of Namurian age laid down during the Carboniferous Period in South Wales. These rocks were formerly known as the Millstone Grit Series but are now distinguished from the similar but geograph ...
Pembroke Limestone Group
The Pembroke Limestone Group is a stratigraphic unit of Courceyan to Brigantian age (Early Carboniferous) found in southern Wales and northern Somerset. It forms part of the Carboniferous Limestone Supergroup. These carbonate rocks developed i ...
The summit of the hill is formed from the
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 ...
of the ‘Brithdir Member’ 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 ...
. A large quarry towards the south of the hill works the
dolomitic
Dolomite () is an anhydrous carbonate mineral composed of calcium magnesium carbonate, ideally The term is also used for a sedimentary carbonate rock composed mostly of the mineral dolomite. An alternative name sometimes used for the dolomiti ...
limestone
Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
of the Pembroke Limestone Group.
Access
Numerous public footpaths criss-cross the hill, some being followed by promoted recreational walking routes such as 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.Sirhowy Valley Walk and the Raven Walk. The upper slopes of the hill and most of the woodland which clothes its slopes are mapped as open access under the
Countryside and Rights of Way Act 2000
The Countryside and Rights of Way Act 2000 (c. 37), known informally as the CRoW Act or "Right to Roam" Act is a United Kingdom Act of Parliament affecting England and Wales which came into force on 30 November 2000.
Right to roam
The Act imp ...
and thereby open to access on foot by the public.Ordnance Survey Explorer map 152 ''Newport & Pontypool''