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 Antrim Plateau and Glens. This upland area is dominated by a series of structural plateaux that dip gently in towards the Lough Neagh Basin. Detailed topography is largely controlled by a succession of Tertiary basalt lava flows that define successive, large-scale steps within the landscape. The plateaux are separated from each other and their frequently dramatic margins are fretted by often fault-guided, steep-sided glens. Recession of the plateaux margins has exposed underlying Mesozoic strata and, in some areas, the Palaeozoic basement. The plateaux margins are typically characterised slope failures that range from large rotational landslides to individual blockfalls.
The Central Ballymena Glens are a pair of scenic valleys that lead from the open fertile farmland around Ballymena up into the isolated Garron Plateau. They radiate north eastwards from Ballymena, along a trend dictated in the south by the Carnlough fault, and lead to the spectacular coastal Antrim glens (a designated Area of Outstanding Natural Beauty) to the east. Gently undulating ridges give the landform interest, and a strong landscape structure is provided by a well maintained stone wall and hedgerow network throughout the glens. There are mounds and knolls on the glen floor. The incised glen narrows towards the uplands where rocky burns and deciduous woodland become more pronounced features. The glens fall partially within the Antrim Coast and Glens AONB. The glens are extremely sensitive to change due to their distinctive character, scenic quality and views from surrounding ridges and major tourist routes. Visual amenity is enhanced by distinctive landforms such as Skerry Rock or Craignamaddy and the undulating land form within the glens serves to shelter and accommodate limited development. The steep slopes of Slemish Mountain ASI occupy a small area in the southeast of the LCA. Slemish is the largest of the Antrim volcanic plugs, and shows evidence of multiple intrusions and the existence of a lava lake in the old volcanic crater.
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 - Upper Basalt Formation & intrusive dykes, a volcanic plug and sills, around 55 million years old |
| Tertiary - Interbasaltic Formation, about 55 million years old |
| Tertiary - Lower Basalt Formation, about 55 million years old |
| Cretaceous - Ulster White Limestone, around 100 million years old |
The geology comprises a mix of Tertiary igneous formations in bedded, faulted and unconformable contact. Tertiary Lower Basalt Formation makes up 60% of the LCA with the remainder being the other formations in varying proportions. A small part of the LCA encroaches on Cretaceous rocks.
The Lower Basalt Formation occurs in an extensive outcrop of the plateau of the LCA. They are extensively quarried for construction materials, especially roadstone.
The two Tertiary-aged basalt formations comprise a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles). Throughout LCA117 these two formations are separated by red, palaeoweathered beds and ashfalls of the Interbasaltic Formation, which in this area is dominated by bauxites and laterites with minor ash falls. The Interbasaltic Formation is coincident with the edge of the LCA boundary in many areas.
Numerous minor faults of varying orientations occur throughout the area. In the southeastern part of LCA117 the NE-SW trending Carnlough Fault juxtaposes upper and lower basalt formation.
NW-SE trending dykes dominate the area of the Lower Basalt Formation outcrop. A dolerite intrusion that was probably the site of a volcano occurs in the east of the LCA east of Soarns Hill.
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 a complex mix of glacial, deglacial and post-glacial sediments. Late Midlandian till predominantly underlies the area, associated with the large ice mass that was centred on the Lough Neagh Basin and moved northeastwards across the region. In the floors of the glens this till is marked by drumlin development. 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. 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. Whatever the stimulus for erosion and deposition, the sediments within these hollows typically contain an important record of local environmental change.
Across the LCA there are also significant areas of drift free bedrock that run down as ridges from the uplands of the Antrim Plateau. Within the intervening glens there are limited areas of deglacial deposits. Davies and Stephens (1978) consider that the final stages of ice-wasting in the east of Northern Ireland probably involved wide scale stagnation, downwasting and withdrawal inland towards the Lough Neagh lowlands (p.176). This would have left upland areas such as the Antrim Plateau ice free and surrounded by encircling ice. It is under these conditions that sand and gravel accumulated at the ice margin as it retreated. Finally, ribbons of alluvial deposits mark the floodplains of the present-day rivers.
Key Elements ASSI/ASISLEMISH ASI (ca 10% in this LCA, shared with LCA 124)
Slemish is the largest of the Antrim volcanic plugs, shows evidence of repeated use a s a feeder vent and preserves the structures indicative of a lava lake in the old volcanic crater. The site is also important for the occurrence of an unusual columnar crystallisation of both olivine and plagioclase, and of corroded xenocrysts bearing spinel.
AONBThe east and northeastern parts of this LCA lies within the Antrim Coast and Glens AONB (1988).