Did you know that Cardiff has the biggest underground cave system of any city in the UK? I thought not. Uncharacteristically, the authorities do nothing to publicise what could be a unique amenity, attraction and selling point; in fact they go to great trouble to conceal what lies beneath. Why so shy? Well, partly because the labyrinth of uncharted tunnels, hidden chasms, bottomless pits, subterranean lakes and collapsed roofs is extremely dangerous – but mainly because to publicise the caves would draw attention to one of the city’s most shameful and extraordinary secrets: a hollow mountain.
The 210m (690ft) high Lesser Garth in Morganstown is a geological paradise where man has scratched, burrowed, dug and quarried since prehistory. The dolomitic limestones of the ridge of hills either side of the Taff Gorge were in demand as soon as hominids sussed out how to bash them with a flint, containing as they do iron ore, lead and silver as well as the predominate limestone. The excavations of Neolithic cave dwellers, Iron Age Celts, 1st century Romans, 5th century Welsh metal workers, 16th century iron industry pioneers and the Pentyrch Ironworks operation of the 18th & 19th centuries have intermingled and interweaved to form an amazing, multi-level warren stretching for miles through the soft and porous band of Carboniferous Limestone hills that mark the southern edge of the coalfield and Cardiff’s northern limits. Subsequent quarrying for building materials, continuing to this day, has not only wrecked much of the Lesser Garth’s complex cave system but also gradually and inexorably eaten away the mountain’s innards so that today the steep wooded slopes act as an entirely cosmetic bracelet hiding a vast astonishing void within (see below).
The Lesser Garth Quarry is the last fully working quarry in Cardiff, but the area’s rich and varied mineral resources and Wales’ long centuries as an extractive economy ripe for exploitation mean there are plenty more. These quarries are the easiest points to access the extant cave systems deep below (it goes without saying that such caving is definitely not for beginners). Most of the quarries are disused and have evolved into a series of curious biospheres in various stages of being re-colonised by nature. All are well worth visiting, especially in winter when there are no security guards or jobsworths patrolling and vegetation die-back permits better views of the rocks. Here then, for urban explorers, is the (unofficial) guide to the quarries of Cardiff:
At the very top of Rhiwbina Hill, Blaengwynlais Quarry is famed among geologists for its goethite iron ores which outcrop in rusty orange and brown pyrite crystals in a rich variety of shapes from needles to concentric blobs. Classified as ‘dormant’ rather than abandoned, this Quarry is supposedly out-of-bounds, but nobody was around to stop me entering the voracious maw of this petrifying place. Beware of old air shafts in the woods and meadows to the north.
Castell Coch Quarry
The sheer, red cliff on the east side of the Taff Gorge is the Castell Coch Quarry, also sometimes called the Taffs Well Quarry, laid bare by the construction of the A470 in 1971. Here, where the Taff carves through the last daunting obstacles on its journey from the Brecon Beacons to the alluvial flood plain and the sea, the rocks were quarried for their haematite iron for 300 years until the 19th century. The iron seeps its rusty tint into the rock, and when a low sun bathes the cliff on a winter afternoon it becomes a wall of fire in every shade of red. Access is via a path by the roundabout at the foot of the cliff, much frequented by crampon-clanking rock-climbers scaling the vertiginous face. The path eastward into Fforest Fawr leads to a dramatic offshoot, Castell Quarry, a menacing grotto hidden by a dense canopy of trees.
Cefn Garw Quarry
Another geologists’ shrine, on the southern side of Heol-y-Fforest above Castell Coch. After 19th century quarrying into the massive beds of dolomite exposed the transition anticline between the Carboniferous Limestone and the Devonian period Old Red Sandstone on the north face of the Quarry, this fantastic display of faults, folds and thrust planes entered the geology textbooks. Not worked since 1987, the huge, boulder-strewn, shelved cavity is in an early phase of plant colonisation, notwithstanding the concrete batching plant at the entrance.
A formidable complex, best approached from near the Heol Pant-y-Gored bridges over the parallel cuttings of the disused Barry Railway and the Taff Vale Railway’s Waterhall Branch at Creigiau. First quarried for its dolomite ironstone, used in the building of Roath Basin and Roath Dock, later for its limestone, used in the steel-making process on the East Moors, the Quarry was a source of road stone in its last decades and only closed in 2001 after 130 years getting ever wider and deeper. A summer day in Creigiau Quarry is a special Cardiff treat. One time, sitting on a hot rock eating a sandwich, I had the strange sensation of being watched. Half turning, I came eyeball to eyeball with a basking viper, assessing the air with its flickering tongue. You could have heard my shriek in Capel Llanilltern…
Halfway down Rhiwbina Hill close to the footpath along Cwm Nofydd is this sensational mini-universe quite invisible from both the road and the path. The Quarry was last worked in 1930, so plant life has had 80 years to regenerate and – Wow! I don’t want to make too much noise about it just in case anybody reads this stuff, acts on my advice and disturbs this paradise for badgers, foxes, adders, moths, bats, goldfinches, greenfinches, orchids and mighty beeches.
Greenmeadow Wood Quarry
Differing from most of the other quarries in that it was cut into sandstone rather than limestone, this old working closed more than a century ago and the enchanting site, accessible via a path off Greenmeadow Drive, has been swallowed up by the thick mixed woodland. I accept no liability if you encounter the Cŵn Annwn (Hell Hounds), spectral beasts with glaring eyes that haunt the Fforest according to age-old local superstition.
Lesser Garth Quarry
Known over the years as the Dolomite, the Taffs Well Quarry, the Steetley (one-time owners), the Walnut Tree Quarry and, since bought by the giant Mexican cement producer in 1999, the Cemex Quarry, this Mother Of All Quarries has to be seen to be believed. PAY ATTENTION: if you only ever go to one place highlighted in this entire blog, go here. The best approach is from the back of the Tŷ Nant pub car park in Morganstown. After a long, steady climb through the most westerly native beech woods in the British Isles, past the hidden entrance of the Lesser Garth Cave, home of the extremely rare white cave spider Porrhomma Rosenhaueri, beyond the breathtaking portal of the Barry Railway’s 1901 tunnel through the mountain, and up vestiges of tramroads and inclines that sent the ores down to the Pentyrch Ironworks, you reach the rim of a stupendous abyss. With the dimensions of an amphitheatre that could hold the entire population of Wales and the plunging depths of a crater left by an enormous meteorite impact, the disembowelled Lesser Garth defies description. Think Blofeld’s extinct volcano hideout in You Only Live Twice and you’re getting close. Often, on long mid-summer days, I trek to the summit, ignore the ‘Danger! No Entry!’ signs, pick my way past the scintillating debris of centuries of industry, and settle down to feast on the eye-popping panorama from a creaking, rusty, metal viewing platform that precariously hangs over the north edge of the Quarry – my favourite spot in all of Cardiff. Leave me alone.
Outcrops of Jurassic Blue Lias limestone form high ground on both flanks of the River Ely in western Cardiff. Quarrying of this valued building stone still goes on at Leckwith and Wenvoe on the Vale of Glamorgan side of the river, but has long ceased at Pentrebane on the Cardiff side. Engulfed by the Pentrebane housing estate in the 1960s, overgrown shards of the Quarry remain off St Fagans Road and Beechley Drive.
The most difficult of all these quarries to visit is a designated Site of Special Scientific Interest (SSSI), a wild wonderland in the incongruously tame heart of middle-class Penylan. Unless you know someone who lives in one of the houses on the north side of Dorchester Avenue, where the gardens back onto the Quarry, the only way in is over a fairly high wall at the end of Ferry Court (on your own head be it) or by clambering up a steep embankment from the hard shoulder of the A48 Eastern Avenue dual carriageway and squeezing through a gap in a fence (you will probably die in the attempt). Completely overgrown with impenetrable thickets of shrubs and brambles, the Quarry hasn’t been worked since the 19th century when this outcrop of Silurian mudstone, Cardiff’s oldest rocks, was identified as one of the most important fossil sites in Wales, crammed with a rich shelly fauna of brachiopods, corals, graptolites and trilobites. This is a veritable Eldorado of palaeontology, but that SSSI designation looks increasingly feeble as salivating property developers hover with intent.
Worked between 1850 and 1910 for its distinct Triassic sandstone breccia, the warm-hued stone that was one of the building blocks of Victorian Cardiff (most explicitly used for the knobbly slabs of the Gorsedd Circle in front of the National Museum), Radyr Quarry became a household refuse tip in the 1930s, its rock face a dump-and-go rubbish chute for fly-tippers. Today it is part of the absorbing Radyr Woods Nature Area, opened in 1986 and including the Hermit Wood Nature Reserve to the south. Access is from Taff Terrace or via a footpath opposite the 1894 mansion Radyr Chain (named after the chain stretched across the old turnpike road to Llantrisant to stop travellers until the hated tolls were abolished in 1851).
Abandoned in the 1920s, its gritty shales having provided road stone for Cardiff’s Victorian expansion, Rumney Quarry was cut into an exposed vein of ancient Silurian strata teeming with fossils of the bivalves and gastropods that inhabited the warm shallow seas here 430 million years ago. Extremely important to both palaeontology and geology, the Quarry is a designated SSSI doubling as a public park accessible from Tŷ-Mawr Road – a contradictory dual role that has done more damage to the fossil record in a few decades than the shifting of tectonic plates managed across unimaginable aeons of time.
Ton Mawr Quarry
Finally, just west of the Lesser Garth, is another massive bite out of the 350 million year-old Carboniferous Limestone. Disused and tricky to reach via pathways through Garth Wood, Ton Mawr is a designated SSSI where spectacular mineralisation is exposed in the Quarry walls. The display of beautiful, sparkling, geometric Calcite crystals in several stages of growth is policed only by peregrine falcons and buzzards drifting on thermals high overhead, scanning for rabbits and voles in the pioneer undergrowth.
Pictures: Pentyrch & District Local History Society; Leigh James