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 Lough Macnean valley is in the southwest of Fermanagh. Upper and Lower Lough Macnean, were formed as glaciers excavated deep basins in varied Carboniferous rocks, creating impressive steep valley sides and rocky scarps, notably at Hanging Rock. To the east the valley opens out into the flat Arney Valley and to the northwest it connects with the Garrison lowlands. Limestone outcrops along the slopes of Belmore Mountain form a craggy escarpment, divided from the rest of the uplands by an attractive wooded valley, with waterfalls marking the harder rock strata. To the south of Lower Lough Macnean is the limestone escarpment of Marlbank. Lower Lough Macnean is confined by a steep limestone escarpment and has an outstanding landscape setting. It has a more developed agricultural shoreline, with open wet meadows contrasting with occasional thick woodlands. Limestone soils produce good quality grassland and the southern shores and lower slopes are farmed intensively. Key elements include the karst topography of the southern slopes of Belmore that consists of a gently undulating limestone bench with numerous rock exposures bounded to the north by cliffs and limestone knolls and to the south by moderate to steep slopes covered with glacial drift. There is also significant dry valley lying parallel to the slope in the Moneyouragan townland. There are numerous small sinks within the limestone outcrop, related to streams that originate on the sandstone cap of Belmore Mountain. Associated with the sinks are many small risings.
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 |
Glenade Sandstone |
Meenymore (includes Quarry Sandstone Member at base) |
Dartry Limestone (inc Knockmore Limestone Member near base) |
Glencar Limestone |
Benbulben Shale |
Mullaghmore Sandstone |
Budoran Shale |
This LCA is comprised of fossiliferous Carboniferous sedimentary rocks with the exception of the Tertiary Garrison Sill. Broadly, LCA5 comprises two structural areas of Carboniferous rocks: a southeastern succession of Bundoran to Glenade disposed as a southern east-west anticline and a northern, north-south trending syncline and a northern Meenymore-Glenade faulted succession.
Abundant coral fossils can be observed in the Rahallan Stream section (Bundoran Shale) (ESCR Site 186). The Meenymore - Glenade Sandstone contact is seen in the Lurgan River (ESCR Site 196).
All the above strata were deformed during the end-Carboniferous phase of Variscan tectonic activity. A major east-west trending fault transects the area.
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 LCA shows it to primarily comprise a till covered lowland lying between the two lough Macneans to the south and west and the uplands of Belmore to the northeast and Ballintempo to the north. It was the disposition of these upland areas that controlled ice flow in the Late Midlandian, and a combination of drumlin orientation and glacial striae indicate that ice entered from the east between Belmore and Cuilcagh mountains and then swung northwestwards. Across significant areas of the lowland, the ice eroded the bedrock to create a mix of depressions, such as those occupied by the two loughs, and ice scoured ridges. Where the ice did leave a legacy of till deposits, these are characterised by a dispersed pattern of drumlins, which include a number of islands in Lough Macnean Upper. 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.
The drift geology map also highlights the alluvial deposits associated with the floodplain of the Arney River, east of Lough Macnean Lower.
Key Elements Karst FeaturesBELMORE
Although recorded in the DoE review of karst geomorphology, it is acknowledged that there is little in the area of karst geomorphological importance except for the Holywell Rising, a large karst spring.
Other sites/units identified in the Earth Science Conservation Review186 Rahallan
Carboniferous. Exposure of typical lithologies of Benbulben Shale Formation. Fossiliferous with especially good solitary corals.
196 Lurgan River
Carboniferous. Exposure of Meenymore Formation and its contact with succeeding Glenade Sandstone Formation.