The use of a cultural overlay in defining Landscape Character Areas (LCAs) means that they frequently subdivide natural physiographic units. It is common therefore for significant geomorphological features to run across more than one LCA. It is also possible in turn, to group physiographic units into a smaller number of natural regions. These regions invariably reflect underlying geological, topographic and, often, visual continuities between their component physiographic units, and have generally formed the basis for defining landscape areas such as AONBs. It is essential therefore, that in considering the 'Geodiversity' of an individual LCA, regard should be given to adjacent LCAs and to the larger regions within which they sit. In the original Land Utilisation Survey of Northern Ireland, Symons (1962) identified twelve such natural regions.
This LCA lies within the region described as the Plateau and Valley Lands of Fermanagh. This is a series of sharply defined plateau blocks separated by steep-sided, glacially deepened, lake strewn valleys. The morphology of the Carboniferous uplands is largely controlled by the presence of a series of gritstone caprocks. Beneath these, well-jointed limestones have allowed the development of extensive subterranean drainage systems as well as a variety of surface karst phenomena for which the region is internationally renown.
The south-west corner of Fermanagh includes the only true mountain in the area (Cuilcagh at 665m) and has some of the most dramatic countryside in the district. Underlying Carboniferous strata dip to the south and west and the Upper Limestone forms a magnificent escarpment, riddled with potholes and caves. There are also dry valleys, limestone pavements and gorges, with prominent rounded hills known as 'reef knolls' rising above the land surface. Impermeable flagstones and shales form the long broken slopes of the Cuilcagh Mountain. There is a rich variety of vegetation, with montane grassland and blanket bog on the grits and fine species-rich dry grassland on the limestone. Poorly drained hollows on the limestone reflect the presence of till (boulder clay). Hazel scrub grows in irregular patches on steeper limestone slopes but there is a more luxuriant woodland cover at sink-holes. Key elements in the landscape include: karst landforms of limestone cliffs, pavements, gorges and caves, with peat moorland on gritstone summits. There is also a history of slope instability associated with the upper slopes of Guilcagh Mountain, typified by bogbursts associated with prolonged and/or intense rainfall.
Pre-Quaternary (Solid) GeologyThe stratigraphy of this area is made up of the mapped formations in the table, the youngest of which usually overlie the oldest.
Stratigraphic Table (youngest rocks at the top of the table)| Tertiary - dolerite dyke, about 60 million years old |
| Carboniferous Formations - about 350 million years old |
| Bencroy Shale, Lackagh Sandstone & Gowlaun Shale |
| Dergvone & Carraun |
| Glenade Sandstone & Bellavalley |
| Meenymore (includes Quarry Sandstone Member at base) |
| Dartry Limestone (inc Knockmore Limestone Member near base) |
| Glencar Limestone |
| Benbulben Shale |
This LCA is comprised of Carboniferous fossiliferous sedimentary rocks north of Cuilcagh Mountain (ASSI 069) with the exception of the Tertiary dolerite dyke. The Benbulben - Glencar - Knockmore (Dartry) succession can be observed along the Tullyhona river valley (ESCR Site 187); the Glencar - Knockmore contact can be seen along the Cladagh River (ESCR 188). The Carboniferous formations occur as arcuate east-west and northwest-southeast striking, discontinuous outcrops. Dartry Limestone includes the unique Cloghan Hill Limestone Member (ESCR Site 192). Similarly, the Cloghany Limestone Member is also seen in the this LCA (This LCA at ESCR Site 194. The Dartry comprises the northwestern and eastern third of LCA9. All the above strata were deformed during the end-Carboniferous phase of Variscan tectonic activity.
Quaternary (Drift) GeologyNorthern Ireland has experienced repeated glaciations during the Pleistocene period that produced vast amounts of debris to form the glacigenic deposits that cover >90% of the landscape. Their present morphology was shaped principally during the last glacial cycle (the Midlandian), with subsequent modification throughout the post-glacial Holocene period. The Late Midlandian, the last main phases of ice sheet flow, occurred between 23 and 13ka B.P. from dispersion centres in the Lough Neagh Basin, the Omagh Basin and Lower Lough Erne/Donegal. The clearest imprint of these ice flows are flow transverse rogen moraines and flow parallel drumlin swarms which developed across thick covers of till, mostly below 150m O.D. during a period that referred to as the Drumlin Readvance. At the very end of the Midlandian, Scottish ice moved southwards and overrode parts of the north coast. Evidence for deglaciation of the landscape is found in features formed between the glacial maximum to the onset of the present warm stage from 17 and 13ka B.P. - a period of gradual climatic improvement. Most commonly these are of glaciofluvial and glaciolacustrine origin and include: eskers, outwash mounds and spreads, proglacial lacustrine deposits, kame terraces, kettle holes and meltwater channels. During the Holocene, marine, fluvial, aeolian and mass movement processes, combined with human activities and climate and sea-level fluctuations, have modified the appearance of the landscape. The landforms and associated deposits derived from all of these processes are essentially fossil. Once damaged or destroyed they cannot be replaced since the processes or process combinations that created them no longer exist. They therefore represent a finite scientific and economic resource and are a notable determinant of landscape character.
The drift map of Cuilcagh shows that drift free bedrock outcrops, many of which are blanketed by peat, dominate the Mountain itself. Glacial striae and streamlined rock ridges show, however that it has been overridden by ice moving westwards, and within the uplands there are areas, often marked by depressions that are masked by a thin cover of Late Midlandian till. The lowland areas to the north and east of the mountain carry a more complete till cover and are characterised by an extensive suite of drumlins. The orientation of these suggests that ice flow was from the Lough Erne lowlands to the northeast, although it was deflected around the Cuilcagh massif to produce drumlins parallel to the mountain front. To the north of the LCA, on the border with LCA8, Legg et al. (1998) have mapped a series of moraine ridges that indicate glaciofluvial deposition as the ice wasted and Cuilcagh emerged as an ice free area.
Within Northern Ireland drumlins take a variety of forms; some are rounded in plan, although the majority are elongated in the direction of ice flow. Some have sharp crests, whereas others are more whaleback in profile. Although most drumlins are composed of glacial till or tills, a small number are 'drumlinoid features' are rock-cored and some are composed of sand and gravel. Where drumlins are rock cored there may have been significant frost shattering prior to their shaping by ice flow. It is possible therefore to see tails of shattered debris within till leading away from the feature in the direction of flow (Davies and Stephens 1978). It is generally accepted that the drumlins of Northern Ireland were formed by deposition beneath fast flowing ice. In the majority of cases this has resulted in a thick layer of Upper (younger) Till overlying a core of Lower (older) Till. This pattern has been observed across Northern Ireland, apart from a limited area in the north of County Down. The precise temporal relationship between the two tills has not been definitively resolved, but Davies and Stephens (1978) refer to an organic layer between the tills in County Fermanagh that has been dated at 30 500 ± 1170/1030 years B.P. and shelly material between the tills on the Ards Peninsula dated at 24 050 ± 650 years B.P. However, these deposits only indicate that the Lower Till is older than the dates obtained.
It can be argued that an equally important component of any 'drumlin landscape' are the similarly numerous inter-drumlin hollows. The majority of these hollows would have held open water from local runoff at the end of the Pleistocene. Whilst some continue to exist as isolated small loughs, many have now been infilled by sediment washing off the surrounding drumlins. This has created typically flat-bottomed, marshy areas between the drumlins that are subject to seasonal inundation. Much of the infilling probably occurred early in the Holocene, as the landscape adjusted to increasingly temperate conditions. However, erosion may also have been accelerated in historical times, when rural population densities were considerably higher and much of the lowland landscape of Northern Ireland was more intensively cultivated. Whatever the stimulus for erosion and deposition, the sediments within these hollows typically contain an important record of local environmental change.
Key Elements ASSI1069 CUILCAGH MOUNTAIN
Geologically the area holds complete representation of the Carboniferous Leitrim Group, including richly fossiliferous sequences, while physiographical interest centres around active processes notably slope weathering and peat pseudo-karst features.
Karst ComplexesThe dominant geomorphological features of this LCA are associated with the development of extensive surface and subsurface karst systems. In total, Western Fermanagh contains approximately 52 km2 of karst landscape developed predominantly in limestones of Viséan (Lower Carboniferous) age. There are hundreds of cave entrances and 30+ km of explored cave passage. The bulk of these features are contained in two main belts of exposed upland limestone, the Marlbank - Cuilcagh Mountain Region and the Belmore, Ballintempo and Tullybrack Uplands. Almost the entire former region occurs in this LCA. The Karst Geomorphology of the Marlbank - Cuilcagh Mountain Region is strongly influenced by the extensive clastic deposits on Cuilcagh that form an impermeable cap causing rainfall to form discrete streams and rivers, which generally sink on reaching the Dartry Limestone. The Dartry is underlain by the argillaceous limestones and shales of the Glencar Limestone, and resurgences and springs are mostly located along the Dartry - Glencar contact. The caves and karst of the Marlbank - Cuilcagh Mountain are developed in three main areas: East Cuilcagh, the eastern Marlbank, where three major cave systems are developed within a sequence of massive carbonate mudbanks, and the Western Marlbank. Detailed descriptions can be found in Fogg and Kelly (1995).
EAST CUILCAGH
The East Cuilcagh Karst is a north - south oriented belt of upland limestone extending from Greenan Townland at it's southern margin, through Gortalughany and Beihy townlands and Aghitirourke Townland east of the Owenbrean River. The karst hydrology of the area is complex and poorly understood. Highlights include deep potholes developed along major joints and faults in horizontally bedded cherty limestones. There are unique glaciokarst features in the area (Legacurragh Gap, The Pound and Greenan Arch) and the Legacurragh Doline Field is one of the best developed and preserved fields in Northern Ireland.
TULLYHONA, BROOKFIELD AND TRIEN (eastern Marlbank)
The Tullyhona Karst is located at the eastern end of the Marlbank area. Topography is dominated by carbonate mudbank "knoll" topography. Highlights include the excellent example of a vadose dendritic river cave at Tullyhona Rising Cave completely formed within one carbonate mudbank "stack". Features present include well developed speleothems, perched active sumps, fracture and bedding passage control, partial dolomitization along faults, roof collapse along shale bands and abandoned stream passages. The cave and surface karst are, at present, in a very good state of preservation.
PROD'S POT - CASCADES RISING AREA (eastern Marlbank)
This area lies between the Tullyhona and Marble Arch areas. It contains one major cave system and a large number of minor associated sites. The Prod's Pot - Cascades Rising Cave System is a superb example of a fracture controlled dendritic river cave system. The entrance series of Cascades Rising Cave is the only known major cave development within the interbedded shales and limestones of the Glencar Limestone Formation. Features present include well-developed speleothems, perched phreas, fracture and bedding passage control, partial dolomitization along faults, roof collapse along shale bands and abandoned stream passages. The cave and surface karst are, at present, in a very good state of preservation.
MARBLE ARCH (eastern Marlbank)
Marble Arch is the largest karst resurgence in Northern Ireland and one of the largest in Britain and Ireland. The caves and surface karst associated with the Marble Arch System represent the best karst development in Northern Ireland and compare well with classic British karst areas such as the Yorkshire Dales. A wide range of surface and underground features are present and many of the features and processes of temperate karst development can be demonstrated here. Polyphase development of the system and concepts of karst stream capture and rejuvenation are especially evident. The cave contains considerable amounts of clastic and chemical deposits which have major potential for further scientific research.
WESTERN MARLBANK (100% 0f Northen Ireland component in this LCA)
The western Marlbank covers the area between the presumed western edge of the Marble Arch System catchment and the border with the Republic of Ireland. It contains numerous well developed and preserved doline fields and partially vegetated limestone pavements, especially in the Crossmurrin-Killykeeghan and Gortaree-Cullentragh-Cloghan Hill areas, that are some of the best developed and preserved in Northern Ireland. There is presumed to be an extensive cave system developed within the area, although only a small portion of this system has been explored.
Other sites/units identified in the Earth Science Conservation Review187 Tullyhona
Carboniferous. Exposure of top beds of Benbulben Shale Formation and their conformable contact with overlying Glencar Limestone Formation, and of abrupt contact between this and Knockmore Member of Dartry Limestone Formation.
188 Cladagh River
Carboniferous. Easily accessible exposure of contact between Glencar Limestone Formation and succeeding Knockmore Limestone Member of Dartry Limestone Formation.
192 Cloghan Hill
Carboniferous. Dartry Limestone Formation. Exposure of unique lithologies of Cloghan Hill Limestone Member which succeeds Knockmore Limestone Member.
194 Cloghany
Carboniferous. Exposure of lithologies of Cloghany Limestone Member of Dartry Limestone Formation. Abundant fossils of foraminifera and algae.