The nature reserve is a 2.5km stretch of dramatic wooded
limestone gorge cut by the River Taf Fechan, between the bridges of
Pontsarn and Cefn Coed to the North of Merthyr Tydfil.
It lies adjacent to the eastern side of the popular Taff Trail.
and the reserve incorporates much of the area notified as Cwm
Taf Fechan Woodlands Site of Special Scientific Interest.
The reserve has high nature conservation value and supports
uncommon flora and fauna.
On the western bank of the river you can see a good population
of broad leaved helleborine, as well as small-leaved lime. In
addition, there are large areas of grazed limestone grassland, some
with bracken, with plentiful violets providing a suitable habitiat
for silver-washed fritillary butterflies.
The Eastern bank sees a number of springs, with Tufa deposits,
and the Gurnos quarry face is well developed, with facies and caves
likely to be home to bats.
The reserve has a wide diversity of habitats, fast and slow
flowing fresh water, open and dense deciduous woodland; calcereous
and acidic grassland; exposed limestone cliff faces and old walls
and tufa springs.
Signs of otters are regularly spotted, and the whole river
stretch supports birds such as dipper and grey wagtail.
Goosander are regular in Winter, and evidence of badgers are
The gorge was created by the young Taf Fechan river cutting into
the northern outcrop of carboniferous limestone, forming the
northern border of the south Wales coalfield.
A particularly impressive section is to the east of the
Trefechan estate. The geology is especially obvious in the Gurnos
South of the quarry, millstone grit is the underlying rock. At
the site of the Heads of the Valleys road bridge there are fallen
blocks of honeycomb sandstone, the marker horizon which occurs at
the S zone / D zone boundary in the carboniferous limestone over a
wide area of the north crop of the coalfield.
The sandstone outcrops at the top of the vertical face south of
the Gurnos quarry cliff. The majority of the site, to the north of
the road bridge, consists of the Cil yr Ychen series of
carboniferous limestone. This is richly fossiliferous, with
brachiopods (typically seminula), productids, corals and gastropods
The Pont Sarn bridge by the Blue Pool (Pont-sarn-hir - the
bridge of the long paved road) is the site of the roman road
crossing, travelling from Y Gaer at Brecon to the coastal fort at
Cardiff. From the bridge it went through Gurnos, towards Penydarren
Park and on to Gelligaer.
There are the remains of an eighteenth century corn mill on the
eastern bank of the northernmost section of the reserve, one of
four grinding mills that were located in the Taf Fechan valley. The
original millstone grit millstone is nearby.
Further down the river are the remains of a fullers mill (a pandy)
on western bank just north of timber bridge. Well-known local
weavers, the Harris family, owned both these mills.
The Gurnos quarry supplied limestone for the furnaces of the
Cyfarthfa Ironworks. Following the closure of the Ironworks, the
quarry was planted with a selection of pine trees, with some still
surviving on top of the cliff.
The tramway runs south from the quarry alongside the Taff, to
beyond the Cefn Coed bridge. It was extended to reach the new
Glamorganshire canal in 1792. It supplied the Cyfarthfa Ironworks
with the all important limestone needed for the ironworking
process, and the stones forming the base of the tramway rails are a
scheduled ancient monument, as is the Cyfarthfa leat which runs
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