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 Western River Basins, although it grades westwards into the Highlands and Lowlands of East Donegal. This region consists essentially of the connected river systems that drain the Carboniferous and Old Red Sandstone plateau of County Tyrone, as well as the foothills of the Sperrin Mountains to the east and Donegal to the west. The region extends from the Omagh Basin in the south, northwards along the lower Foyle valley. The Omagh Basin has particular significance as an ice centre during the Late Midlandian and is now largely covered by a complex mixture of glaciofluvial sands and gravels and drumlins overlying Rogen moraines. When the headwaters of these river systems rise together they have in the past been responsible for serious flooding at the bottleneck of Strabane. Although this has been mitigated by extensive drainage control works in and around the town.
The West Derry Slopes are between the River Foyle and the border with Donegal. They encompass the northern and eastern slopes of Minkey Hill and the southern ridges of Scalp Mountain in Donegal. The area is dominated by the historic city centre of Londonderry/Derry and the built up areas on the western banks of the Foyle, including the port of Culmore. The headwaters and broad valley of the Skeoge River are directly to the west of the city centre and the built up area is concentrated on the relatively low-lying land. The slopes of the Foyle River are relatively steep, with a stronger field pattern and relatively little built development beyond the limits of the city. The rounded summit of Minkey Hill is capped with open moorland. The landscape can therefore be summarised as one of smooth rounded hill tops with undulating lower slopes, steep slopes down to the River Foyle and a broad, shallow vale leading to the west.
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)Carboniferous |
Barony Glen |
Dalradian (Neoproterozoic) |
Londonderry |
Ballykelly - Southern Highland Group (undivided) |
This LCA is dominated by Dalradian (Neoproterozoic) metamorphosed sedimentary and minor igneous rocks.
Key SitesDalradian
Schistose grits and phyllites of the Londonderry Formation crop out at ESCR Site 338, Creevagh Old Quarry.
Two tectonic phases have affected the area: the Caledonian (Ordovician - Silurian) and Variscan (end Carboniferous). Caledonian deformation is very apparent throughout the Dalradian succession. A parallel fault to the NE-SW trending Foyle Fault crosses the east of LCA32.
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.
The drift geology map for this LCA shows a landscape underlain primarily by a mix of Late Midlandian till and drift-free areas of bedrock. The till was deposited by ice that moved northeastwards down the Foyle Valley. As it did so, it left a legacy of streamlined rock ridges on the higher ground to the west of the LCA. Wastage of the ice at the end of the Midlandian resulted in the deposition of glaciofluvial sand and gravel, especially in the broad valley of the Skeoge. These deposits are now partly masked by alluvial sand and silt associated with the present-day river. Similar alluvium can be found along the Foyle floodplain.
Key Elements ASSI051 Lough foyle (5-10% of ASSI)
Contemporary coastal processes especially chenier ridge development. Exposure through the southern (earliest) portion of the Magilligan foreland complex.
Other sites/units identified in the Earth Science Conservation Review338 Creevagh Hill Old Quarry
Precambrian. Good outcrop of Londonderry Formation. Interbedded schistose grits and phyllites, with clear cleavage/strata relationships.