a small village on the A361, south-west of Frome, situated in a narrow
valley where the Nunney Brook has cut into the Carboniferous Limestone
which here dips to the south at about 20° to 50°. It is renowned
by palaeontologists for the discovery in 1867 of one of the world's
Aerial view of Holwell and Nunney (click to enlarge view).
The Carboniferous Limestone here has been quarried for over 150 years,
creating a complex of active and abandoned quarries on either side
of the A361. These quarries are important geological sites and
have been designated as a Site of Special Scientific Interest.
||The active quarries at Holwell
are operated by Bardon Aggregates, a subsidiary of Aggregate Industries
UK. The quarry comprises four pits clustered around the village,
divided by roads. Three of these pits are connected by two tunnels.
A fifth pit, known as Cloford Quarry, lies about 500 m to the south-west.
A viewing platform has been built overlooking the northernmost pit.
The Carboniferous Limestone here is cut by many vertical fissures
known as 'Neptunian dykes' infilled with younger, Triassic and Jurassic
sediment and lined with large calcite crystals. In one of these fissures
the geologist Charles Moore discovered the teeth of one of the earliest
known mammals, Haramiya in 1867.
Sketch of the Jurassic unconformity exposed on the Holwell–Whatley
road (click to enlarge view).
The fissure fills have also yielded vertebrate fossils of Late Triassic
age as well as fragments of Jurassic reptiles and the dinosaurs Thecodontosaurus and Palaeosaurus.
One of these fissures forms the edge of an old quarry just north
of Holwell, although much of the infilling red and yellow-coloured
sediment has now fallen to the quarry floor.
||The overlying Inferior Oolite
is exposed in a couple of roadside exposures, both of which show
the unconformity with the underlying Carboniferous Limestone. One
of these is in Holwell on the slip road towards Frome, the second
in a shallow road cutting on the road towards Whatley. This shows
a small, fault bounded knoll of Black Rock Limestone overlain by
the golden yellow Inferior Oolite.
In the centre of Nunney are the impressive remains of Nunney Castle,
built at the end of the 14th century by Sir Elias de la Mere. It
was besieged by Cromwell's troops during the Civil War and was dismantled
in 1654. The castle, owned by English Heritage, is constructed from
the Inferior Oolite and the Great Oolite 'Bath Stone', and is open
to the public.
Several boulders of silicified sandstone known as 'sarsen' stones
occur in a wall near the castle. These boulders, of Tertiary age,
are the remnants of an outcrop that was once more extensive and long
since eroded away. North of Nunney are the remains of one of the
six iron works owned by the Fussell