The Sheeffrys as seen from Corvockrback. All pics: John O'Callaghan
A tale of two hills, endangered names and fascinating rocks
Many of us have heard of Louisburgh’s beautiful Lost Valley. However, there’s another one to discover too. Louisburgh’s other ‘lost valley’ is the geologically significant Bunowen River Valley – from its source to the sea in Louisburgh, in Bunowen townland.
The Bunowen (Bún-Abhainn, the bottom – or mouth – of the river), is about 15km long from beginning to end. It rises in the tiny Sheeffry mountain corrie lake, Lough Brawn – Bran’s Lake, named in honour of Fionn MacCool’s favourite hound. This lake lies in the townland of Laghta Oughter – Leachta Úchtar, translated as ‘memorial cairn upper’ or ‘low, flat-topped hill, upper’.
Sometimes it is better not to translate townland names. I think Laghta, which is an anglicised version of the word ‘leachta’, is one that is best left alone. The word ‘leacht’ means flagstone, burial mound or large rocky slab, and whenever I hear it, I immediately think of large slabs of rock. For example, Slieve Carr in the Nephinbeg mountain range is topped with an enormous cairn, called Laghtdaghybaun, translated as the ‘burial mound of Fair Davy’.
Save the names
The principal townlands through which the Bunowen River flows, Laghta Oughter and Laghta Eighter (‘Lower Laghta’) are named, I contend, not after any particular ‘memorial cairns’ or ‘burial mounds’ but for the ‘twin low, flat-topped hills’ that dominate the Laghta valley. ‘Logainmneacha Mhaigh Eo 2 – Barúntacht Mhuraisce’, by Fiachra Mac Gabhann, quotes Rev Patrick S Dinneen’s ‘Foclóir Gaedhilge agus Béarla: Irish-English dictionary’ (1904) giving ‘a low, flat-topped hill’ as another meaning of ‘leachta’.
These hills are of great interest to me, as their respective logainmneacha, or place names, may be in danger of being lost forever.
Their appearance is described as ‘mammillated’, or covered with rounded mounds or lumps. If you venture up the valley from Louisburgh, the hill on your left is named Knockakishaun (possibly ‘wicker-basket hill’). It was previously known as Knockaskeheen (‘little thornbush hill’). The one on the right, to the southwest, is named Laghta Eighter Hill. At least that’s what it’s called on the latest 1:25,000 Adventure Series OSI map. It was previously called Corvockbrack.
On a calm, clear morning in late August, I climbed Corvockbrack for the first time. The Laghta valley was cloudless. A bank of low, white clouds lay stationary over Clew Bay. We did not linger long on the summit as some sunbathing flies began to take too close an interest in us. Our descent route led us out along the Owennasallagh (‘Willow’) River with its series of tempting cascades and pools that we reluctantly eschewed, opting instead for a swim in Lecanvey on our way home. The whole trip was made all the more interesting by the area’s remarkable geology.
Special speckled rock
On the geological map of South Mayo, the most eye-catching orange-coloured area is labelled ‘Corvock Granite’. This extends roughly from the northwest at Tully Bridge to southwest at Creggaunbaun and eastwards over the two hills, with a dolerite dyke thrown in for good measure immediately west of Knockakishaun.
Corvockbrack derives from the Irish ‘cloch-chormaic breac’ and means a ‘(type of) speckled granite’, a very apt description. It is a specific form of granite, different to ‘cloch eibhir’, the more general Irish term for this rock type. The map legend describes Corvock Granite as ‘Biotite granodiorite to syenogranite’, whatever this means! I assume it is a blend of diorite and granite or, as the ‘breac’ would indicate, it’s a ‘speckled’ mixture. The following extract from the 1876 ‘Memoirs of the Geological Survey of Ireland’ may help to clarify these explanations:
“The two rounded hills of Corvockbrack (1287 feet), and Knockaskeheen (of about the same altitude), standing out in bold relief in the comparatively low ground south of Croagh Patrick, indicate at some distance their geological composition, as they assume that peculiar mammillated appearance so common in granitic hills, while they are also almost entirely free from any covering of drift deposits, or heather.
“These two hills are separated from one another by a north-west valley, or gorge, lying along the line of a fault; […] the Louisburgh River pass[es] through, and the eastern side is bounded by massive vertical walls of granite. These walls follow the joints which are everywhere perceptible […].
“The general appearance of the granite when fractured, presents a greyish colour, is, generally speaking, coarse in texture and friable, consisting of two felspars – orthoclase and oligoclase, black or green mica, quartz, and invariably a few crystals or iron pyrites. This granite is irruptive, and of later date than the Upper Silurian period, as it is to be found penetrating the fossiliferous Upper Silurian beds at Creggaunbaun.
“On top of Knockaskeheen which lies to the north-east of Corvockbrack, the granite has caught up with it a mass of claret-coloured schists, highly contorted and penetrated by granite veins, while both schists and granites are cut up by a large dyke of minutely crystalline basalt, which traversing the rocks […] passes through almost every description of rock in the district, which undoubtedly proclaims it to be the newest of the whole area under description.”
As the Laghta townlands are home to the youngest rock formations in Mayo, we should treasure this valley and appreciate their ‘low, flat-topped hills’ with renewed awe and respect.
Dr John O’Callaghan is a mountain walk leader who has organised and led expeditions both at home and abroad. He has served on the board of Mountaineering Ireland and is currently on the Irish Uplands Forum board. In 2012, he wrote the winning article that secured Westport’s accolade as the Irish Times’ ‘Best Place to Live in Ireland’.