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 Quoile Valley Lowlands extend north-south down the centre of Down District, encompassing the courses of the Ballynahinch, Annacloy and Blackstaff Rivers. To the west, the land rises to the summits of Slieve Croob and to the east, the numerous islands of the Strangford Drumlins and Islands stretch into the sea lough. The height and density of the drumlins varies; the landform becomes progressively shallower towards the south but the drumlins on the fringes of Strangford Lough are relatively steep and have a pronounced egg-shaped form. Water courses wind around the drumlins and form small inland loughs or bogs in the inter-drumlin hollows. The loughs often have wooded margins and the bogs show varying degrees of vegetational succession, from open heather and rushes to gorse scrub and small trees. The landscape can therefore be summarised as one of pronounced drumlins divided by marshy hollows, loughs, bogs and winding rivers.
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 - various intrusives, around 55 million years old |
| Lower Palaeozoic Silurian (Hawick Group), about 430 million years old |
| Ordovician (predominant) - Moffat Shale and Gala Sandstone, between 490 and 450 million years old |
Predominantly Lower Palaeozoic greywackes and shales with numerous minor igneous intrusions. 99% of the LCA comprises Lower Palaeozoic with the northern 2/3 of Gala Group and the southern third comprising Hawick Group greywacke sandstones and shales, the remainder being Tertiary intrusives.
The greywackes are of sandstone grade and vary from a few centimetres to a few metres in thickness with a large proportion of rock fragments and a fine-grained matrix. The greywackes are commonly quarried as a source of aggregate; they are interbedded with thinner beds of siltstone or mudstone, commonly arranged as fining-up cycles. Minor conglomerates and ash-beds (or bentonites) occur.
The southernmost area of LCA91 comprises Silurian age Hawick Group greywacke (sandstones) and red shales. The greywackes vary from a few centimetres to a few metres in thickness with a large proportion of rock fragments and a fine-grained matrix. They are interbedded with thinner beds of siltstone or mudstone, commonly arranged as fining-up cycles.
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 predominantly underlain by Late Midlandian till associated with the large ice mass that was centred on the Lough Neagh Basin. This ice flowed southeastwards from an ice divide that lay approximately SW-NE along the line of the north Belfast Hills. Evidence for this flow direction is found in the orientation of the numerous drumlins that make up much of the landscape. However, within the LCA there are also significant outcrops of drift free bedrock that were scoured by the overriding ice. McCabe and Knight (in Knight 2002) have suggested that this area, and much of central Co. Down, was the site of an ice stream during the Drumlin Readvance that delivered a high sediment flux to the ice margin at areas such as the Lecale Coast to the southeast. This may go some way to explain the partial drift cover in the region and the widespread occurrence of rock cored drumlins. 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, where Hill (1971) observed drumlins composed only of Lower Till. 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 also highlights the alluvial deposits associated with the Quoile and the streams that drain into Dundrum Bay.
Key Elements ASSIs102 WOODGRANGE
The Irish type locality for the Woodgrange Interstadial, the late-glacial climatic oscillation following deglaciation. Dating of the post-glacial marine transgression has been determined. For more details see:
089 MURLOUGH (the southern fringe of the LCA)
A coastal complex exhibiting a range of gravel ridges, re-curved spit, dune systems, palaeosols and contemporary beach processes dating from between late glacial and modern times. This gives rise to an extensive range of coastal habitats, including scarce vegetation communities and rare plant species.
Other sites/units identified in the Earth Science Conservation Review AONBsThe southern part of this LCA lies within the Lecale Coast AONB (1967), whilst a limited area in the southwest lies in the Mourne AONB (1986). A small area in the east of the LCA lies in the Strangford Lough AONB (1972). These designations are indicative of the scenic quality of the landscape.