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, including the Holywood 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 Holywood Hills extend across west North Down Borough, forming an area of undulating upland in the centre of a ring of settlement that includes Belfast, Holywood, Bangor, Newtownards and Dundonald. They rise to 200m, with steep, wooded escarpment slopes. Proximity to a number of settlements makes the area an important recreational resource and its easy accessibility, rural identity and exposed, wild character are important characteristics. The plateau drops steeply to Belfast/Lisburn to the south west, and to the Bangor Coastline to the north.
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 |
| Triassic - Sherwood Sandstone Group, about 240 million years old |
| Lower Palaeozoic - Ordovician (predominant) - Moffat Shale and Gala Sandstone, Gilnahirk Group, between 490 and 450 million years old |
Predominantly Lower Palaeozoic greywacke sandstones and shales with minor igneous intrusions. A southern strip along the Dundonald Gap comprises Triassic Sherwood Sandstones, the remainder being Tertiary intrusives.
A NE - SW striking fault-bounded strip in the east of LCA102 brings the predominantly Moffat Shale Group to surface. The Gilnahirk Group is separated from the Gala - Moffat succession by the NE-SW Orlock Bridge Fault which continues east. 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 volcanic ash-beds (or bentonites) occur. Encroaches into Whitespots ASSI188 (continuation of Conlig Lead Mines).
Triassic sandstones comprise red, purple and brown cross-stratified sandstones, siltstones with minor clay beds and partings. The sandstones are usually soft and poorly-consolidated.
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.
Although there is a considerable area of drift free, ice scoured bedrock in the south of the LCA, the drift geology map for the area shows that most of it is underlain by Midlandian till. Topographically the till comprises an extensive suite of drumlins, some with rock cores that are orientated approximately north to south. The majority of drumlins across Northern Ireland comprise a thick layer of Upper (younger) Till overlying a core of Lower (older) Till. The exception to this rule occurs in North Down, where Hill (1971) observed drumlins composed only of Lower Till. These are thought to have formed in response to ice that flowed southwards from the North Channel. 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.
Key Elements ASSI188 WHITE SPOTS
Whitespots is of geological interest on account of its mineralogy, including a range of commercially mined metallic ores. Minerals were deposited within a fault in the Silurian country rocks by hot, mineral-rich fluids. Minerals including galena, sphalerite, chalcopyrite, baryte, dolomite, calcite and chalcedony are present. This site is the only occurrence in Northern Ireland of the unusual barium zeolite, harmotone.