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.
This open and windswept landscape of the Larne Basalt Moorland lies across the Ballymena and Larne district boundary. It includes the upland summits of Slemish, Douglas Top, Agnew's Hill, as well as Black Hill and Robin Youngs Hill which overlook the rocky coastline to the north east of Larne. The exposed rounded summits reach a height of between 300 and 400m and the simplicity of the landform draws the eye to their smooth summits. The hills form prominent landmarks in views from the lowlands and valleys surrounding Ballymena and Larne, particularly the Glenwhirry Valley. Especially prominent is the volcanic plug known as Slemish. This is a large dome of lava that, at a height of 437m, is the highest point in the region and forms a distinctive landmark. The dramatic rounded cliff of Sallagh Braes to the north west of Larne is the product of a massive landslip and is a notable landscape feature and viewpoint. The landscape around Slemish is well maintained; it falls within the Antrim Coast and Glens AONB and is designated as an ASI and an Earth Science Conservation Review Site. The prominent ridge of the Sallagh Braes landslip is designated as an ASI.
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 | Intrusive dykes, sills and volcanic plugs, around 55 million years old |
| Tertiary | Upper Basalt Formation, about 55 million years old |
| Tertiary | Interbasaltic Formation, about 55 million years old |
| Tertiary | Lower Basalt Formation, about 55 million years old |
| Cretaceous | Hibernian Greensand & Ulster White Limestone, around 100 million years old |
| Jurassic | Waterloo Mudstone Formation, about 200 million years old |
This LCA contains igneous and sedimentary rocks of Jurassic to Tertiary age and includes the igneous eruptive and intrusive centre of Slemish Mountain in the west.
In general, Tertiary basalts rest unconformably and in faulted contact with Cretaceous greensands and limestones or dark grey, fossil-bearing Jurassic mudstones.
The igneous complex (dominated by a dolerite plug) at Slemish on the western edge of LCA124 contains the record of Tertiary volcanic activity in the area: (together with Craigcluggan/Skeagh, ESCR 82), Slemish forms ESCR Site 81. Another intrusion, Scawt Hill, produced contact metamorphic minerals and is now ASSI 83.
Normal faults of differing orientations cross the area, juxtaposing all the above formations. The most significant of these is the north - south Ballytober Fault in the east of the LCA.
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 varied topography of this LCA reflects an upland landscape of drift free bedrock, blanketed in part by a cover of peat. Only on the western boundary of the LCA are there very small areas of Late Midlandian till that were associated with the large ice mass that was centred on the Lough Neagh Basin and which moved approximately northeastwards across the region. 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 uplands such as the Antrim Plateau as ice free areas surrounded by
Key Elements ASSI/ASI083 SCAWT HILL ASSI
International type locality for a series of minerals developed by pyrometamorphic and metosomatic interaction of an intrusive dolerite plug with Ulster White Limestone and basalt. Development of crag, scree and landslip features including the major landslide complex of Sallagh Braes.
SLEMISH MOUNTAIN ASI (ca 90% shared with LCA 117)
Slemish is the largest of the Antrim volcanic plugs, shows evidence of repeated use as 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.
Scawt and Sallagh Braes ASSI
The Scawt Hill component of this ASI has been re-designated as an ASSI, see above. The corrie-like backwall and bowl at Sallagh Braes is approximately 2km in diameter and thus comprises the largest rotational feature to be found along the Antrim coast. It is suggested that if ice streamed parallel to the coast and undercut the plateau edge after removing superficial deposits, unstable and unsupported slopes would have been exposed once the ice receded. The combination of these unstable slopes and underlying clay-rich Liassic beds would have encouraged slope failure, especially in the immediate post-glacial period when the land was 'relaxing' as ice loading decreased and abundant water was available to act as an aid to slippage. During this post-glacial period of readjustment many major failures occurred along the East Antrim coast, as demonstrated at Sallagh Braes where jointed basalt and chalk slumped and moved downslope towards the coast. Only the back wall of the landslide occurs in this LCA, the large bowl of the failure lies in LCA 127 to the east.
Karst FeaturesCarncastle
A karst complex in the northeast of the LCA within the the Ulster White Limestone. It comprises a series of dolines, sinks, a dry valley and a rising. To the east are a series of archaeological features including earthworks.
Other sites/units identified in the Earth Science Conservation Review82 Craigcluggan/Skeagh
Tertiary.
AONBAlmost all of this LCA lies within the Antrim Coast and Glens AONB (1988). This designation is indicative of the scenic quality of the landscape.