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 Strangford Drumlins and Islands provide a waterside landscape of drumlins and loughs, islands and inlets that occupies the southern and western shores of Strangford Lough. The drumlins form a dense pattern and many of the hills are unusually high. Inland, drumlin farmland with a robust network of stone walls predominates. The hollows between the drumlins contain marshy pasture or loughs, which often have well wooded margins. Towards the shores of Strangford Lough the pattern is reversed, with water dominating and the drowned drumlins rising out of the water as small round islands. Orford (in Whalley et al. 1985) has described the coastal lowlands around Strangford Lough as a mixture of glaciomarine shelf sediments with a superimposed two-unit drumlin cover, lying on a low undulating basement of Silurian greywacke and mudstones. Strangford Lough is tidal with a distinctive straight east coast and a highly irregular west coast morphology. The lough contains numerous drowned drumlin islands that have been removed completely from the eastern shore to leave remnant shoals or 'pladdies'. On the western shore the drumlin islands are largely retained and linked by limited shoreline deposition. The difference between the lough shores is because of prevailing southwesterly waves that vigorously attack the eastern shore, whilst leaving the western shore largely untouched. There are extensive intertidal mud and sand flats in the north of the lough that act as sinks for most of the sediment derived from the erosion of the east coast. Sites such as those at Rough Island (LCA 101) and Ringneill Quay have been important in documenting post-glacial sea level flutuations. In particular, McCabe and Knight (in Knight 2002) have observed that at the head of Strangford Lough there are well defined late- and post-glacial wave-cut terraces at around 20m O.D..
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 |
| Upper Palaeozoic - Carboniferous, about 350 million years old |
| Lower Palaeozoic - Silurian Hawick Group, about 420 million years old |
| Lower Palaeozoic - Ordovician (predominant) - Gala Sandstone, about 490 million years old |
Predominantly Lower Palaeozoic greywackes (sandstones) and shales with numerous minor igneous intrusions. Northeastern tip covers the Carboniferous Castle Espie succession. Over 95% of the LCA comprises Lower Palaeozoic (predominantly Ordovician Gala Group) greywacke sandstones and shales, the remainder being Carboniferous and Tertiary intrusives. 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 volcanic ash-beds (or bentonites) occur.
The northern end of LCA94 encroaches onto Carboniferous rocks. These comprise the fossiliferous limestones and thin shales of the Castle Espie Group. This is a unique location for rocks of this age and lithology, the only equivalent in the north of Ireland being the Blackwater Limestone Formation in the south of Northern Ireland. ESCR Site 250.
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, in the north and south of 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 post-glacial inundation of the coastal drumlins along the western shore of Strangford Lough is particularly well illustrated in the south of the LCA along the Quoile estuary. This was filled with estuarine clays that accumulated to a height some 3m above present-day mean sea level. The record of sea level change is demonstrated by the depositional sequence at Woodgrange ASSI in LCA 91.
Key Elements ASSI034 STRANGFORD LOUGH PART 3
Extensive mudflats, saltmarsh and other types of shoreline habitat, including The Dorn (NNR), a unique and exceptionally important site for intertidal flora and fauna.
Other sites/units identified in the Earth Science Conservation Review250 Castle Espie
Carboniferous limestones of Castle Espie Group. Only occurrence in north Down. Highly fossiliferous. Not exposed.
AONBsMuch of the eastern margin of this LCA lies within the Strangford Lough AONB (1972). This designation is indicative of the scenic quality of the landscape.
OthersRingneill Quay
A coastal sequence on the western shore of Strangford Lough, south of Comber, comprising a sequence of estuarine silt, shelly sands and a storm shingle beach, interdigitated with occupation evidence including a hearth and middens. These have been used to show that the maximum post-glacial marine transgression began after 5.200 years B.P. and continued after 3 500 years B.P.. For further information see Davies, G.L. and Stephens, N. (1978).