Overview
The lower slopes of Sliabh an Iarainn hold nearly 120 documented fossil sites – bands of goniatites, trilobites, bivalves, brachiopods and echinoids pressed into shale that is 300 to 320 million years old. Geologist Patricia Yates catalogued them in 1962, and the collection is one of the reasons the mountain is recognised as a natural heritage site. Rising to 585m on the eastern shore of Lough Allen, it takes its name – ‘iron mountain’ – from the ore worked out of these hills for centuries.
Most people never climb it. The mountain’s story is told at its base, at the free Acres Lake Visitor Centre and the timber boardwalk beside it, and that is where an hour is best spent. The summit is for confident hill-walkers only: a boggy, unmarked pull across heather and gritstone.
A Carboniferous time capsule
Long before the iron, this was seabed. The bedrock is unbroken Carboniferous shale and sandstone, laid down when the area was a shallow marine environment during the Namurian and Westphalian stages. Yates’s survey turned up dense fossil beds across the slopes, and many of her specimens now sit in geological collections in Ireland and the UK.
You can spot fossils in exposed shale outcrops along the lower slopes and near the Lough Allen shore. Collecting is discouraged to keep the sites intact, and summer guided walks tend to point out the most accessible beds.
Iron, forges and railways
The name reflects the economy that ran here for two centuries. Ore was being extracted by the 1600s, and by the 1700s furnaces and forges dotted the landscape – the Cornashamsoge smelting works handling raw ore, the Drumshanbo finery forge turning pig iron into malleable products shipped south down Lough Allen.
It came at a cost. Charcoal-fired smelting cleared the ancient forests that once covered the region, and once the timber ran short and coal grew cheaper the ironworks faded. The last of them at Creevelea closed in the mid-19th century. Later, narrow-gauge railway and the canalised waterways moved ore and coal through the same valleys, a network the visitor centre’s displays reconstruct.
Myth and local legend
The Lebor Gabála Érenn has the Tuatha Dé Danann arriving in Ireland in dark clouds and landing on Sliabh an Iarainn’s summit. Among them was Goibniu, the smith god – a fitting patron for an iron mountain – whose craft echoes in later folklore about Gobán Saor, the master builder said to have worked the mountain’s mines.
Local tradition runs darker. In nearby Kiltubrid, an fear ocrach (‘the hungry man’) is a hunger stone at the mountain’s base; step on it, the story goes, and you are struck with an insatiable hunger until you eat.
Visiting the mountain
The Acres Lake Visitor Centre is the hub, and it is free. Its 12-minute audio-visual show runs through the area’s iron and coal mining, railway, canals, lakes and musical heritage, with big windows framing the lake beyond.
- Boardwalk and Blueway: A 600m floating timber boardwalk crosses the lake edge – accessible on foot or by bike – and forms the start of a 6.5km linear trail along the old canal route to Battlebridge Lock. See the dedicated Acres Lake – Boardwalk and Visitor Centre page for more.
- Looped walks: Three waymarked loops climb into the hills – the Aughacashel Loop (3km, easy), the Tullylackan Loop (10km, moderate) and the Crummy Loop (12km, moderate).
- The summit: The pull from the lake to the trig pillar crosses peat bog, heather and steep gritstone. It is unmarked and best left to walkers happy on rough ground in good weather; the reward is a clear sweep across Lough Allen and the Cuilcagh hills.
Practical information
- Location: Acres Lake, north of Drumshanbo, County Leitrim (N41)
- Opening hours: April–October: Mon–Sat 10am–6pm, Sun 2pm–6pm. Closed November–March.
- Contact: +353 71 9641851
- Facilities: Toilets, a small café for hot drinks and light snacks, and a gift shop with books on local geology, history and music.
- Access: Free car park beside the centre. The boardwalk and exhibition are wheelchair accessible; the summit trail is not.
- Getting there: A short drive north of Drumshanbo via the R207. Public transport is limited – the nearest bus stop is in Drumshanbo, with local taxis for onward travel.
Nearby
The Lough Allen Adventure centre nearby has budget beds, camping and lakeside activities looking straight at the mountain. The Cavan & Leitrim Railway runs heritage trips through the same valleys that carried the ore, and in Drumshanbo the Shed Distillery and market square are a break from the trails. Creevelea Abbey and Glencar Waterfall are both a short drive on.