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 LCA itself is defined as the exposed uplands of west Fermanagh lying between 150 and 300 metres, that have been carved out of a broken and undulating sandstone plateau. Different layers of grits, shales and limestones form escarpments, lough basins, rock ridges and the distinctive rock pinnacles of Big Dog and Little Dog. Limestone forms steep escarpments to the north, east and south, cut by deep glens, but to the west the land slopes gently. Conditions have favoured the formation of extensive blanket bog, which now covers much of the area. Much of this is planted with forestry in regular blocks of uniform age that have obscured many pre- existing variations in natural vegetation, topography and cultural features. Unplanted areas are crucial in the appreciation of the landscape and in open areas, the terrain is broken by rocky outcrops and loughs, creating a varied landscape with swathes of trees interrupted with heather clad knolls, patches of native trees and loughs fringed by marsh and fen. Key elements in the landscape include: the broken plateau with rock outcrops and small loughs and valleys.
An important geomorphological component of this LCA are a number of surface and subsurface karst systems. In total, Western Fermanagh contains approximately 52 square kilometres 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. This LCA contains most of the Garrison karst complex, approximately 33% of the Reyfad - Carrickbeg complex and a very small element of the Knockmore - Pollaraftra complex. The latter two are part of the Belmore, Ballintempo and Tullybrack Uplands karst area that lies for the most part in LCA 6.
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 - Garrison Sill - about 60 million years old |
Carboniferous Formations - about 350 million years old |
Carraun & Dergvone Shale |
Glenade Sandstone & Bellavalley |
Meenymore |
Quarry Sandstone Member |
Dartry Limestone (including the Knockmore Limestone Member) |
Glencar Limestone |
This LCA is comprised of Carboniferous fossiliferous sedimentary rocks with the exception of the Tertiary Garrison Sill. The Glencar and Darty formations can be seen in the Cliffs of Magho (ESCR Site 189). The Meenymore Formation crops in the Silees River (Glenasheevar: ESCR Site 290) and the Glenade Sandstone & Bellavalley.
Sandstones (interbedded with thin shales with conglomeratic sandstones near the base of the succession) are areally extensive, comprising 0ver 50% of the LCA4. The syncline in the northwest of the area is bounded by Dartry Limestone and the Garrison Sill. The Carraun & Dergvone Shale includes a limestone bed (the Doagh Member) that occurs in the Carraun Shale - it is seen at Doagh Glebe (ESCR Site 198).
All the above strata were deformed during the end-Carboniferous phase of Variscan tectonic activity.
Major faults and folds have their strike NE-SW, along pre-existing, Caledonian trends.
Tertiary dykes also cross the area - the Blackslee Dyke (ESCR Site 84) is one example.
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 more than 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 geology map for this area shows a clear dichotomy between the drift free, peat blanketed uplands of Lough Navar and Ballintempo in the north and south of the LCA, and the till covered lowland in the centre. This Late Midlandian till is characterised by numerous drumlins, which together with glacial striae on the uplands, indicate that the last major ice flow across the region came from the southeast. The exception to this are drumlins north of Doagh, which suggest that ice may also have moved westwards into the area from the Lough Erne lowlands. 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', some 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.
Key Elements ASSIs111 LARGALINNY (ca 75%, shared with LCA 6)
The geological interest of the site is centred on the silicified fossil fauna from the Glencar Limestone Formations at Carrick Lough,which are of international importance.The scarp and dip slope topography displayed by the Glenade Sandstones are of physiological interest and provide the underlying growing conditions for the diversity of plants and habitats throughout the site
201 WEST FERMANAGH SCARPLANDS (ca33%, shared with LCA 6)
West Fermanagh Scarplands has a diverse range of geological and physiographical features. These support a range of habitats and associated vegetation communities of unparalleled significance in Northern Ireland. The rocks of the area are some 335 million years old and date from the Carboniferous, a time when Ireland lay near the equator. The Limestone formations at Knockmore Hill are particularly significant. The Knockmore area supports a range of surface karst topography including some of the finest limestone pavement in Northern Ireland. Three major cave systems also occur within the site, with over 14km of surveyed passage in total.
191 The Cliffs of Magho (ca 50%, shared with LCA 2)
The Cliffs of Magho consists of a large, north-facing limestone escarpment overlooking Lower Lough Erne. The area includes the dip slopes and a series of smaller sandstone scarps and ridges behind the main cliffs. The continuous nature of the exposure is exceptional and allows the relationships between the strata to be seen in great detail. The limestones and shales exposed are of Lower carboniferous age and the cliffs are the most northerly occurrence of the Glencar and Daltry formations.
Other Karst FeaturesThe 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 latter region occurs in this LCA. Its Karst Geomorphology is strongly influenced by the Meenymore Formation and the Glenade Sandstone that form an impermeable cap to the Tullybrack and Belmore Mountain uplands. These formations overlie the Dartry Limestone exposed on the eastern flank of Tullybrack, in the Boho valley and on the southern and eastern flanks of Belmore. The Dartry Limestone is underlain by the Glencar Limestone, and the Dartry - Glencar contact is exposed close to the floors of the major valleys. The major underground karst features are developed on the eastern flank of Tullybrack Mountain and in the Boho valley. They comprise four major cave systems: Pollaraftra Cave, Noon's Hole - Arch Cave, the Reyfad System, and Boho Caves. Associated with this underground drainage are many classic surface karst features. Detailed descriptions can be found in Fogg and Kelly (1995).
REYFAD-CARRICKBEG (ca 33%, the remainder in LCA 6)
The quality of geomorphological and geological features in the Reyfad-Pollnacrom-Polltullybrack cave system make it arguably the most important underground karst site in Northern Ireland. In a regional context, it contains the most extensive system of passages, has the greatest volume of passage and attains the greatest depth of passage from sink to the lowest explored point in the system. The clastic sediments are the most extensive underground glacial/post-glacial deposits in Ireland. Speleothem deposits are extensive and varied and a wide range of passage cross-sections and smaller features of erosional morphology are present. There is great potential for further research and exploration including investigation of the hydrology of the catchment. Well developed surface karst features include limestone pavements, dry valleys, solution and collapse dolines, relict caves and potholes.
LOUGH FORMAL
Lough Formal is a small mountain lake situated at 240m amsl on a faulted outlier of the Knockmore Limestone Member in the Big Dog Forest. On the northern shore of the lake the Knockmore Limestone is exposed and a substantial notch has developed at water level. Two small hills, Formal More and Formal Beg, are also developed in the Knockmore Limestone and have small areas of exposed bed rock with some karren features. The Lough Formal site is of significant geomorphological and geological interest and quality in a Northern Irish context.
KNOCKMORE - POLLARAFTRA (see LCA 6)
The Pollaraftra system is the one major cave system in the area and the best example of a fault controlled cave in Northern Ireland.
Other sites/units identified in the Earth Science Conservation Review84 Blackslee Dyke
Tertiary.
198 Doagh Glebe
Carboniferous. Outcrop of stratotype section of Doagh Limestone Member of Carraun Shale Formation. It is confined to Doagh Outlier.
290 Mullynaskeagh
Palaeontological. Access to exposure of Sheena Shale Member with rich and diverse marine fossils, especially goniatites.
289 Silees River - Glenasheevar
Palaeontological. Small isolated exposure of Meenymore Formation. Well preserved, articulated fish fossils.