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 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 Craigantlet Escarpment is a prominent ridge of Silurian rocks that forms the escarpment to the Holywood Hills. The escarpment encloses and shelters the urban edge of east Belfast that pushes up against the ridge, extending into the woodlands at Stormont.
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.
Stratigraphic Table (youngest rocks at the top of the table)
| Tertiary - various intrusives, around 55 million years old |
| Triassic - Sherwood Sandstone Group, around 240 million years old |
| Lower Palaeozoic (Ordovician) - Gala Sandstone, Gilnahirk Group, about 480 - 450 million years old |
Lower Palaeozoic greywacke sandstones and shales form about 60% of the outcrop in this LCA. The arcuate eastern edge of LCA104 is formed of Gilnahirk Group which forms the lower slopes of the Craigantlet Hills: exposed in the stream/road cutting of Ballymiscaw (ESCR Site 441) where tectonically deformed turbidites may be observed. The far eastern end of this outcrop includes a fault-bounded outcrop of younger Ordovician Gala Group greywackes.
Triassic sandstones comprise red, purple and brown cross-stratified sandstones, siltstones with minor clay beds and partings. The sandstones are mostly soft and poorly-consolidated or more rarely well-cemented where they are and have been exploited for building stones in the past. They unconformably overly and are also in faulted contact with the Lower Palaeozoic groups.
NW-SE trending dolerite dykes occur throughout the area: mapped locations include the far western end of the LCA north of Stormont. Other dyke orientations do occur (e.g. in the Craigantlet Hills in the south of LCA104.
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 >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 to the south of the LCA. Along the southern margin of the LCA, the drift geology map shows a limited extent glaciofluvial deposits. These are the product of late-glacial deposition by meltwater along the Enler Valley between Belfast and Comber - the so-called 'Dundonald Gap'. Smith et al. (1991) describe these deposits as mounded outwash that consists of laminated sand and gravel with subordinate red clays.
Key ElementsSites/units identified in the Earth Science Conservation Review
441 Ballymiscaw
Exposure of outcrops of tectonised turbidites of Gilnahirk Group. Some sedimentary structures such as interbeds and intercalations are visible.