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Earth Science Conservation Review
| Magho Cliffs | Fermanagh |
| Site number: | 186 | File Number: | H05 |
| ESCC: | EO | ||
| Locality Type: | Cliff | Status: | local interest |
| Grid Reference: | H0056,H087579 End(s) of linear site, Not Entered | ||
| Google maps: | 54.45297,-7.99998 | ||
| County: | Fermanagh | Council area: | Fermanagh & Omagh District Council |
| Period: | Carboniferous | ||
| Stages: | Asbian, Visean | ||
| Lithostrat: | Benbulben Shale Formation, Dartry Limestone Formation, Glencar Limestone Formation | ||
| Site Description | |
|---|---|
| Highlights: | |
The limestones and shales exposed in the Magho Cliffs form part of an extensive outcrop of Lower Carboniferous rocks in NW Ireland. The continuous nature of the exposure in the cliffs for about 9km is quite exceptional and allows the relationships between the various lithological formations to be seen in great detail. | |
| Introduction: | |
The Magho Cliffs are one of the most scenically attractive landmarks in the Fermanagh Lakeland and form a splendid backdrop to the southern shoreline of the western part of Lower Lough Erne. The upper part of the cliff line is a vertical rock face formed of Carboniferous limestones of the Glencar and Dartry formations. Below this face is a zone of steeply sloping ground in which the bedrock is totally obscurred by rock scree, falling from the cliffs above, and by mass movement downslope of the glacial till and bedrock either as soil creep, till flow or rotational landslip. At the eastern end of this unstable zone, the coast road cuts through these deposits and in situ exposures only occur at the lake margin. These consist of rocks belonging to the Benbulben Shale Formation which are the oldest Carboniferous strata, of the Tyrone Group, that are exposed at Magho. The limestone cliffs at Magho represent the most northerly occurrence of strata belonging to the Glencar and Dartry formations in Northern Ireland. Location: The Magho Cliffs occur on the south shore of Lower Lough Erne and form an impressive rock escarpment at the northern edge of the Fermanagh Highlands in Lough Navar Forest. They extend from Pollaphuca (H087579) in the east to Ardgart (H0056) some 9km to the west. The highest point on the cliff line occurs at Magho, about 1.5km west of Pollaphuca, and is almost 330m (1100ft) above sea level. In this area the zone of unstable ground below the rock cliffs is at least 600m wide and extends down to the lough shore. Westwards however this zone thins rapidly and finally disappears, together with the limestone cliffs, at Ardgart. From the Magho viewpoint at H061576, on a clear day, the mountains of Donegal are clearly visible and views NE to Bessy Bell, and east to Brougher Mountain in Cos. Tyrone and Fermanagh respectively, emphasise the relatively low-lying landscapes of much of the Kesh-Omagh Carboniferous outcrop and the Upper Palaeozoic rocks of the Fintona Block. Bibliographic Review: The outcrop of sedimentary rocks belonging to the Benbulben Shale, Glencar Limestone and Dartry Limestone formations of the Tyrone Group extends throughout much of Co. Fermanagh and covers a vast area of Co. Sligo in the Republic of Ireland. In Northern Ireland the rocks have been described by Brunton and Mason (1979) and by the Geological Survey of Northern Ireland (GSNI) who published 1:50,000 geological maps of the Derrygonnelly/Marble Arch area in 1991 and a memoir describing, in detail, the geology of this area, including most of the Magho Cliffs. The geology of the northern part of the cliffs is included in the geological map of the Kesh area (1:50,000 Sheet 32, GSNI, 1994). General Geology: At the Magho Cliffs the thickness of the Benbulben Shale, Glencar Limestone and Dartry Limestone formations is estimated at 150m, 170m and c. 80-100m respectively. The strata are inclined southwards at between 5-10 deg. and are intruded by narrow basic dykes of Palaeocene (Tertiary) age. Based on the presence of foraminifera and of coral/brachiopod faunas these strata are of Lower Carboniferous (late Vis‚an) age and are assigned to the Asbian. | |
| Description: | |
The outcrop of the Benbulben Shale Formation occurs on the lower slopes of the cliff line, at Magho, extending from the lough shore to an altitude of about 110m (350ft). Exposures however are largely concealed beneath the wide zone of unstable ground and are confined to the coastal fringe and occasional deeply incised, north-flowing streams. Long continuous sections occur in two streams at Pollaphuca and expose the upper beds of the Benbulben Shale and their contact with limestones of the succeeding Glencar Formation. The Benbulben Formation consists of dark grey and black, calcareous and micaceous shales and mudstones with abundant fossils, in particular of solitary corals such as Siphonophyllia benburbensis, fenestellid and pennireteporid bryozoa, scattered crinoid ossicles and prolific brachiopods. Lenticular beds of blue-grey bioclastic limestone are rarely more than 5cm thick and limestones usually comprise less than 10% of the formation thickness. Although the Glencar Limestone Formation forms the middle, vertical rock face of the Magho Cliffs only the top half of the formation is exposed, the lower part being concealed by landslip. The contact with the underlying Benbulben Shale Formation is transitional and the Glencar Formation is represented by equal proportions of limestone and mudstone. The limestones are chert- free, grey, argillaceous biomicrites up to 20cm thick which are interbedded with greyish brown calcareous, micaceous mudstone. Locally the rocks are extremely fossiliferous with brachiopods dominating the fauna. The contact between the Glencar and Dartry formations occurs at about 230m O.D. at Magho corresponding to a pronounced slope and vegetation change, and to a spring line. The Dartry Limestone Formation forms the upper part of the rock face at the Magho Cliffs but only the lower part of the formation is exposed there. The outcrop of the top of the formation lies to the south of the cliff line crest and is usually concealed by peat bog. The limestones are blue-black and dark grey bituminous, fine-grained micrites which often display fine laminations resulting from variations in the mud and silt content. The formation is characterised by the presence of blue-black chert as large lenticular nodules, irregular and bedding parallel layers and as amorphous masses. Thin layers of dark grey to black foetid, splintery shales intervene between the limestones and appear to envelop the chert nodules. Both lithologies contain a restricted fauna of rare brachiopods and bryozoan fragments. Intrusive Igneous Rocks: Vertical dolerite dykes of Palaeocene age intrude the Carboniferous strata at 3 places along the Magho Cliffs. At Magho townland (H07435765) are two closely spaced dykes trending SSE. While the western dyke is 3m wide and relatively fresh the other dyke is deeply weathered and less than 2m wide. A third dyke intrudes the Dartry Limestone Formation in the cliffs at Bolusty Beg, c. 2.5km west of Magho. | |
| Conclusions: | |
The Carboniferous rocks exposed in the Magho Cliffs belong to the Benbulben Shale, Glencar Limestone and Dartry Limestone formations, of the Tyrone Group, and are of Asbian age (Vis‚an). While the limestones form spectacular cliffs, and are frequently inaccessible, exposures of the Benbulben Shale Formation are restricted to deeply incised stream gullies on lower slopes and along the lough shore. Here the limestones are at the northern edge of their outcrop and provide an exceptional opportunity for studying their lithological and faunal variations and the boundary between the formations. | |
| Notes: | |
For information on other sites in Subarea-1 see; Key Site 1174 - Subarea-1; Derrygonnelly-Marble Arch-Cuilcagh. | |
| Keywords | |
|---|---|
| Rocks: | Limestone, Mudstone, Shale |
| Fossil Groups: | Brachiopod, Coral, Crinoid, Polyzoan |
| Fossil List: | Siphonophyllia benburbensis |
| Relations: | Marine sediments |
| Measurements | |||||
|---|---|---|---|---|---|
| Length: | ~9 km | Width: | Height: | 330 m | |
| Depth: | Area: | ||||
| Access | |
|---|---|
| Approach: | The cliffs run from Pollaphuca in the E to Ardees Upper in the W, a distance of approximately 9km. This area lies approximately 20km NW of Enniskillen on the southern side of the A46. |
| References (4) | |||
|---|---|---|---|
| Brunton, C.H.C. & Mason, T.R., 1979. Palaeoenvironments and correlations of the Carboniferous rocks in west Fermanagh, Ireland. Bulletin of the British Museum (Natural History), Geology, vol. 32, pp.91-108. | |||
| Geological Survey N.Ireland, 1991. 1:50,000 Solid Geology of Sheet 44/56 (Derrygonnelly/Marble Arch), Belfast. | |||
| Geological Survey N.Ireland, 1994. 1:50,000 Solid Geology of Sheets 32 & 31 (Kesh), Belfast. | |||
| Legg, I.C., Johnston, T.P., Mitchell, W.I. & Smith, R.A., 1998. Geology of the country around Derrygonnelly and Marble Arch. Memoirs of the Geological Survey Northern Ireland, numb. 44/56 HMSO, Belfast. | |||
| Map(s): | See the 1:50,000 O.S. Sheet 17 (Lower Lough Erne); GSNI (1994) 1:50,000 Sheets 32 and 31 (Kesh); GSNI (1991) 1:50,000 Sheet 44/56 (Derrygonnelly/Marble Arch). | ||
| Record type: | ESCR report | ||
| Entered by: | Doughty, P.J. | ||
| Enlander, I., Dempster, M. & Doughty, P., 2026. Magho Cliffs, County Fermanagh, site details. [In] Earth Science Conservation Review. https://www.habitas.org.uk/escr/site.php?item=186. Accessed on 2026-11-06. |
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