Loughermore Hills Geodiversity Profile

Outline Geomorphology and Landscape Setting

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.

In broad terms, the Loughermore Hills are bounded to the west and south by the Rivers Faughan and Foreglen and to the east, by the River Roe. They overlook Lough Foyle to the north. The Loughermore Hills rise to 396m (Loughermore) with the surrounding hills averaging 280m. They are broad rounded ridges with shallow valleys and gently undulating slopes. Blanket bog stretches across the upper valley of the Burntollet River, with gleyed pastures on the slopes alongside. This is a relatively homogeneous landscape, with a simple, large scale pattern of moorland, bog and the conifer plantations of Loughermore Forest on the upper slopes. Within the valleys, patches of scrubby woodland and marsh form a more finely grained landscape mosaic.

Pre-Quaternary (Solid) Geology

The 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)

This LCA is composed of 99% Dalradian (Neoproterozoic) metamorphosed sedimentary, igneous and volcanic rocks, where structural strike is dominantly east-west to northeast - southwest (NE-SW) with overall northerly dip. An east - west syncline - anticline pair occupies the southern area.

Caledonian tectonics formed the folds seen in the area: a parallel fault to the NE-SW trending Foyle Fault crosses the west of LCA34.

Quaternary (Drift) Geology

Northern 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 that the wider landscape is largely underlain by Late Midlandian drift that Davies and Stephens (1978) attributed to a combination and ice that moved northwards along the Foyle Valley and 'Sperrin/Tyrone ice' that flowed northwestwards from over the Sperin uplands. The high proportion of drift-free bedrock within the LCA indicates the upland character of the landscape. However, the Quaternary features that are of greatest geomorphological and geological significance are located within areas of deglacial sands and gravels. This LCA contains small elements of two such deglacial complexes that are important scientifically and for their sand and gravel resources.

The Faughan/Dungiven Basins Complex in this LCA consists of 1.5km2 of deltaic deposits along the Faughan Valley in the west of the LCA. The Complex itself consists of glaciofluvial deposits that are primarily deltaic in origin and are situated along structural lows in the upper Faughan and upper Roe rivers drainage basins. The area is of high scientific interest due to the presence of extensive glaciolacustrine and glaciofluvial deposits consisting of deltas, moraines, eskers and outwash plains occurring in close field associations. The high relief range allows pleasant views both from the basin bottoms and from the Sperrin valleys. There is a general lack of commercial sand and gravel production in the area except immediately east of Dunnamanagh and another, larger pit at Moyagh. Most of the Complex occurs in LCA 30, smaller areas occur in LCAs 27, 29, 31, 33, and 37.

The Ballykelly Moraine Complex in this LCA consists of a very limited extent (0.2km2) of push ridge in the northeast tip of the area. Most of this Complex occurs in LCA 37, where a fuller description can be found.

Key Elements

ASSI

061 ERVEY WOOD (very small element of ASSI in this LCA)

Woodland with structural diversity and variation ranging from calcifugous to strongly flushed. Physical features include a number of small waterfalls and wet rock faces, as well as a series of high cliffs and a broad river flood plain.

Deglacial Complexes/Sand and Gravel Resources

the Faughan/Dungiven Basins Complex

Deltaic deposits are preserved at seven principal locations and are of special scientific interest, as their widespread extent and relationship to proglacial water levels implies that substantial, deep lakes were impounded along the Faughan and upper Roe valleys as Irish ice masses retreated southwards and Scottish ice advanced southwestwards into the lower Roe valley. The upper Roe (Dungiven) and middle to upper Faughan valley basins have been used for mineral aggregate production in the northwest of the province for approximately twenty years.

Other sites/units identified in the Earth Science Conservation Review

333 Loughermore Mountain

Precambrian. Southern Highland Group. Exposures of coarse-grained psammitic lithologies of Claudy Formation.