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 Uplands and Drift Covered Lowlands of Down and Armagh. The generally subdued relief associated with the underlying basement complex of highly folded Palaeozoic strata provides the unity of this region. Relative relief is provided in the north by the Silurian hills that overlook the lower Lagan Valley, The Newtownhamilton Plateau in south Armagh, the Caledonian igneous complex of Slieve Croob and the structural depression that underlies and defines Strangford Lough. Below ca 350m, there is an almost complete mantle of drumlins forming an internationally acknowledged type example of a 'drumlin swarm'.
The Ballyroney Basin occupies a lowland waterlogged area of land enclosed by the Slieve Croob Summits to the northeast, the Mourne Mountains to the south-east and the Iveagh Slopes to the west. The area is underlain by a solid geology of intrusive igneous rocks, resulting in a flat and waterlogged landscape of extensive moss and loughs, which is interrupted by distinct drumlins. The moss supports rushes and sedges, heather, gorse and scrubby woodland consisting of regenerating birch and willow. Lackan Bog, to the east of Ballyroney, has been assigned ASSI status and represents one of the largest single blocks of lowland peatland left in County Down. Drumlins are farmed and pastures are enclosed by hedgerows with occasional hedgerow trees. The River Bann passes through the basin but its course has little visual impact on the landscape as it winds its way inconspicuously between drumlins and under stone bridges.
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 - various late intrusives, about 50 million years old |
| Tertiary - early intrusives (Mourne Granites), about 55 million years old |
| Tertiary - various early intrusives |
| Caledonian - Newry Granodiorite, about 420 million years old |
| Lower Palaeozoic - Gala Group & Hawick Group, between 450 and 420 million years old |
This LCA comprises the northern slopes of the Mourne Mountains with Rathfriland in the southwest and has 95% Tertiary G1 Mourne Granite. Lower Palaeozoic greywackes sandstones and shales occur in two small areas to the north and southwest.
Newry Granodiorite occurs near Rathfriland (ESCR Site 417). Contact metamorphosed Silurian country rock, lamprophyre dykes and granodiorite sheets occur at Shannaghan Hill (ESCR Site 415). The Tertiary Mourne Granites were emplaced in successive injections at two centres: LCA76 covers the western centre the early granite G1 is seen.
A cone-sheet extends in an arc through the southern edge of LCA76. This was a late intrusion, forming as the granite solidified, cooled and the overlying ground collapsed and cracked in a crater-like manner, allowing late molten rock to inject in a thin sheet.
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 >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 it to be underlain almost entirely by Late Midlandian till originating from ice that flowed southeastwards across the area from a centre in the Lough Neagh Basin. Evidence of this flow pattern is demonstrated by the numerous drumlins that compose much odf the landscape. Although they also indicate in the south of the LCA that the ice was diverted to the west and east around the Mournes Massif. 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.
It can be argued that an equally important component of any 'drumlin landscape' are the similarly numerous inter-drumlin hollows. The majority of these hollows would have held open water from local runoff at the end of the Pleistocene. Whilst some continue to exist as isolated small loughs, many have now been infilled by sediment washing off the surrounding drumlins. This has created typically flat-bottomed, marshy areas between the drumlins that are subject to seasonal inundation. Much of the infilling probably occurred early in the Holocene, as the landscape adjusted to increasingly temperate conditions. However, erosion may also have been accelerated in historical times, when rural population densities were considerably higher and much of the lowland landscape of Northern Ireland was more intensively cultivated. Whatever the stimulus for erosion and deposition, the sediments within these hollows typically contain an important record of local environmental change.
The drift geology map for the area also indicates the considerable extent of alluvial deposits associated with the Bann and its tributaries.
Key Elements Sites/units identified in the Earth Science Conservation Review417 Rathfriland
Caledonide-Igneous. Newry Igneous Complex. Exposures of unfoliated granodiorite forming central part of NE pluton.
415 Shannaghan Hill
Caledonide-Igneous. Newry Igneous Complex. Access to contact metamorphosed Silurian country rock, lamprophyre dykes and granodiorite sheets of NE pluton intrusion.
AONBThe eastern and southeastern margin of the LCA incorporates limited areas of the Mourne AONB (1986). This designation is indicative of the scenic quality of these areas.