Sip back as we discover the rugged northwest coastal province of Connacht in Ireland also affectionately known as Yeats Country and explore the Gleniff Horseshoe a hidden gem near to the ancient town of Sligo. Only a 30-minute drive north from the town up the N15 you soon realise that this land has been shaped by forces of nature, glacial activity and a long relationship with the sea. Afterall the word Sligo comes from the Gaelic word Sligeach meaning the shelly place. This is a landscape reigned over by the ever present Benbulben one of Ireland’s most famous and enigmatic mountains. Part of the Dartry Mountains whose flat-topped silhouette and Carboniferous Period limestone cliffs conceal a stunning valley loop drive taking in the sights of the Gleniff Horseshoe and the Diarmuid and Gráinne’s Cave known for providing sanctuary in a Irish mythical love story.
Located on part of Ireland’s Wild Atlantic Way one of the longest defined coastal routes in the world at 2,600Km. The town of Sligo is nestled between the Garrow and Benbulben Mountains. Dating back over 5,000 years Sligo has one of Europe’s oldest and largest Stone Age burial sites at the Carrowmore Megalithic Cemetery. Sligo is a gateway town to some of Ireland’s most breath taking landscapes. You have a choice of how to experience this landscape either by hiking, biking or surfing at Strandhill or immerse yourself in local culture, wholesome food or take in a authentic Irish music night at the pub and enjoy the craic.
This is a place deep rooted in myth so it's hardly surprising that this part of the world was the inspirational backdrop to W. B. Yeats whose grave lies at Drumcliff Churchyard beneath the Benbulben Mountain.
Among County Sligo’s most eminent former residents was William Butler Yeats who is credited as Ireland’s greatest contemporary poet, playwright, and literary figure who was inspired by ordinary life, familiar traditions and Irish myths. He was recognised in 1923 with the Nobel Prize in Literature. Born in Dublin, Yeats spent much of his early life in Sligo and considered this place as his spiritual home. The landscape, myths, and folklore of Sligo deeply influenced his poetry.
The Gleniff Horseshoe is an incised valley shaped by the influence of millions of years of sedimentation, tectonic activity and glacial erosion and whose dramatic limestone cliffs are part of the Dartry Mountains (Irish - Sléibhte Dhartraí) that stretch along Sligo's border with County Leitrim.
As you look at the Gleniff Horseshoe you will see two distinct layers of rock that together are roughly 350 – 500 meters thick. The younger Dartry Limestone Formation rests on top the Glencar Limestone Formation and both provide an insight into the prevailing environmental conditions for this part of Ireland during the early Carboniferous Period when Ireland was just south of the Equator and inundated by a warm sea.
At the end of the Devonian Period the Island of Ireland was not located close to any crustal plate boundaries but it was a time when sea levels from the warm tropical Rheic Ocean rose from the south until it submerged much of Ireland up to and around Sligo. This specifically was during the the Viséan Stage of the early Carboniferous Period.
The Viséan Stage was part of the British and Irish Dinantian Epoch characterised by the extensive deposition of marine limestone across Great Britain and Ireland known as the British Carboniferous Limestone Supergroup.
The succession from the Glencar Limestone Formation to the Dartry Limestone Formation happened between 337 – 330.9 million years ago during the Asbian Substage of the Viséan Stage. These limestone deposits lay in Irelands North–West Carboniferous Basin and reflects changes in sea levels during the Carboniferous marine transgression.
The older Glencar Limestone Formation is a calcareous shale and limestone and was deposited in a shallow marine environment. The fossils within the Glencar Limestone Formation show bioturbation by organisms engineering the sea floor to forage and burrow as well as to colonise such as Siphonodendron rugosa corals.
Other fossils include brachiopods, crinoids and bryozoans, ostracods, sponge spicules, molluscs and the micro-fossils of single celled foraminifera. In terms of fossil hunting the Glencar Limestone Formation it is best to explore the beach areas at low tide at Streedagh Point and Serpent Rock at Ballyconnell - do follow local fossil hunting guidelines.
The Dartry Limestone Formation of cherty limestone with mudstone that dominates the upper sections of the cliffs of the Gleniff Horseshoe were deposited in a moderately deeper water given the darker colour of the rock where oxygen may have been lower. The fossil record is sparse but does include corals, brachiopods and bryozoans. Its interesting to note that the rugosa colonial corals never formed extensive reefs on this regionally extensive carbonate platform.
Towards the end of the Carboniferous Period and during the start of the Variscan Orogeny a major mountain-building event the seas receded and over time the Carboniferous limestones were uplifted to form the Dartry Mountains where they became exposed to the elements.
From between 33,000 - 13,000 years ago the last glacial period known as the Late Devensian glaciation or Midlandian glaciation covered most of Ireland, Scotland, Wales, and northern England. This ice carved out the steep cliff valleys sides of the Gleniff Horseshoe exposing the limestone to weathering and erosion from the process of dissolution from acidic rainwater and the force of meltwaters.
These processes were responsible for the developing numerous karst features including sinkholes, underground drainage networks and caves such as the Diarmuid and Gráinne Cave thought to be the highest cave in Ireland.
Having several large chambers and connected passages it is the Diarmuid and Gráinne Caves that feature in a W.B Yeats play and the Fenian Cycle of early Irish literature focusing on the exploits of the mythical hero Finn or Fionn mac Cumhaill and his warrior band the Fianna. It is believed that Fion and his warriors pursued his betrothed named Gráinne the daughter of High King Cormac mac Airt who had a change of mind and decided instead to runaway with the warrior Diarmuid Ua Duibhne. These caves are believed to have been one of their places of sanctuary to rest during their escape. Still today this geological features remains and enduring symbol to the power of love, fate, and betrayal in Irish mythology.