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 North Derry Uplands and Sperrin Mountains. This region has a composite geological structure. In the north, the North Derry Plateau is wholly developed on basalt and defined by a steep, unstable escarpment to the west and a set of structural benches dipping gently to the east. Southwest of this plateau land, and beyond the Glenshane Pass, schists and quartzites form the rounded, whaleback ridges of the High and Low Sperrins. The incised, steep-sided valleys of rivers such as the Glennelly and Owenkillew accentuate the southwestwards, Caledonian structural trend of the Mountains. Late Glacial ice recession from around the mountains and the creation of temporary ice-dammed lakes has left valley floors and slope foot zones mantled in thick, complex glaciofluvial deposits. Northwest of the Sperrins is a dissected block of country underlain by schists that forms the Loughermore-Altahullion hills and the Middle Faughan basin.
The Glenshane Slopes are a relatively small upland area on the eastern fringes of the Sperrins. The area is separated from the main block of the Sperrins by the basalt escarpment summits of Carn Hill and Craigmore, but is formed from the same resistant metamorphic rocks as the Sperrins and pre-dates the basalt escarpment by millions of years. The highest summit of Carntogher (464m) towers over the Glenshane Pass, forming a dramatic gateway to the Sperrins from the east. The landform of the uplands is similar to that of the Sperrins to the west, with knife-like ridges and pointed summits that are more sharply defined than that of the upper basalt plateau. There is no escarpment and the summits are surrounded by steep ridges and scree slopes. The steep, open slopes leading to the summits are carpeted with moorland. Even minor variations in land form are revealed by the carpet of low vegetation. The eastern slopes of the uplands have a more diverse landscape pattern, with a transition to the undulating pastures of the drumlin lowlands near Maghera. The landscape can therefore be summarised as one of broad, rounded ridges with sweeping slopes and rocky outcrops leading to steep, pointed summits, deep, branching gullies and open, fast-flowing moorland streams.
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. The older formations can be upside down (tectonically inverted).
Stratigraphic Table (youngest rocks at the top of the table)Tertiary - Upper Basalt Formation and Lower Basalt Formation - about 55 million years old |
Triassic - Sherwood Sandstone Group - about 240 million years old |
Carboniferous - about 350 million years old |
Iniscairn |
Barony Glen |
Dalradian (Neoproterozoic) - about 550 million years old |
Un-named metabasites |
Glenelly |
Dart - Claudy |
Dungiven |
The Dalradian succession comprises metamorphosed sedimentary and volcanic rocks (green beds) and underlies the southern tip of LCA39.
The Carboniferous is dominated by sandstones, occurs in the east and south of LCA39, is unconformable on Dalradian and overlain by Lower Basalt Formation (Tertiary). Triassic - Sherwood Sandstone Formation comprises red, purple and brown cross-stratified sandstones, siltstones with minor clay beds and partings in very small areas along the western margin of the LCA, adjacent to the Tow Valley Fault.
Tertiary Lower Basalt Formation and Upper Basalt Formation comprises a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles).
The southern strand of the Tow Valley Fault runs north - south along the western edge of LCA39.
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 (McCarron et al. 2002). 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.
This LCA transects the boundary between the Sperrin uplands and the lowland Lough Neagh Basin. The quaternary deposits shown on the Drift Geology reflect this gradient. The west of the LCA primarily comprises ice-scoured bedrock that now lies largely under a cover of peat. The lowland area to the west is covered primarily by Late Midlandian till resulting from the expansion of ice centred on Lough Neagh. The map also indicates isolated areas of glaciofluvial sand and gravel in the west and north of the LCA. These are most probably result from depositon during the deglacial phase at the end of the Midlandian.
Key Elements AONBAlmost all of the LCA lies within the Sperrin AONB (1968). This designation is indicative of the scenic quality of the landscape.