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.
In common with the hills overlooking Larne Lough, the Larne Ridgeland is dominated by long ridges on which are superimposed a more complex relief of low hills and shallow hollows. The Six Mile Water Fault traverses the area, extending from Lough Neagh to Larne; the southwest to northeast alignment of the fault is reflected by that of the long basalt ridges. To the south west of the area, the fault is constricted between the uplands of Spennin Hill and Carninard, forming a distinct valley with a more tightly rolling topography. The massive Mageramorne quarry on the steep slopes overlooking Larne Lough is prominent in views from Island Magee and the Lough shore road. The area to the north west of the A8 to Larne falls within the Antrim Coast and Glens Area of Outstanding Natural Beauty.
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 | Intrusives, about 55 million years old |
| Tertiary | Upper Basalt Formation, about 55 million years old |
| Tertiary | Interbasaltic Formation & andesites, about 55 million years old |
| Tertiary | Lower Basalt Formation, about 55 million years old |
| Cretaceous | Hibernian Greensand & Ulster White Limestone, about 100 million years old |
| Jurassic | Waterloo Mudstone Formation, about 200 million years old |
| Triassic | Mercia Mudstone Group, Penarth Group, between 220 and 205 million years old |
LCA127 contains igneous and sedimentary rocks of Triassic to Tertiary age.
In general, Cretaceous greensands and limestones or Tertiary basalts rest unconformably and in faulted contact with and on a range of older Mesozoic rock units. The LCA covers the waterfalls associated with Tertiary igneous rocks around Glenoe.
Below the Cretaceous - Tertiary escarpment to the east of LCA127, low coastal ground is underlain by soft sedimentary rocks of the Triassic Mercia Mudstone Group. The Mercia Mudstone Group is predominantly red-brown and unfossiliferous in the lower parts of the exposed succession, becoming grey-green, sometimes fossiliferous and sometimes carbonate-cemented toward the top. The group is an aquiclude, soft and contains anhydrite, making it part of the landslip sequence, acting as a horizon of failure. They have been quarried for brick clays here and elsewhere in last 200 years.
Above the Mercia Mudstone Group, the Triassic Penarth Group comprises a succession (from the base) of carbonate-cemented siltstones, limestones, mudstone and black shales. The succession is interpreted as representing the latest Triassic transgression of the sea; this continued into the earliest Jurassic. The cemented beds of the Penarth Group have been used as building stones.
The Waterloo Mudstone Formation spans the Triassic - Jurassic boundary, and comprises dark grey mudstones and shales, alternating with grey limestones.
The Cretaceous succession forms a faulted outcrop strip to the east of LCA127, and in a fault-bounded strip in the south of the LCA. A basal greensand succession comprises is followed by the limestones of the Ulster White Limestone Group.
Tertiary-aged basalts comprise a crudely-bedded succession of lava flows, columnar jointed lava flows, andesitic lavas, ash-falls and red-weathered horizons (or boles) of the Antrim Lava Group. Andesites with magnetite can be seen at Glynn Hill quarry and crags (ESCR Site 75).
Normal faults of differing orientations cross the area, juxtaposing all the above formations. The major Sixmilewater Fault transects the northwestern part of the LCA, juxtaposing various Tertiary and Mesozoic formations.
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 moved approximately northeastwards from an ice divide running along the crestline of the Belfast Hills. The drift cover is, however, not complete and there are significant extents of drift free bedrock. This is particularly the case in the area of steep slopes below the basalt escarpment the west of the LCA. In the east of the LCA, bedrock crops out as a series of NNW-SSE alignments that reflect the control exerted by a series of underlying fault lines running in the same direction. These contrast with the SW-NE alignment of the Six Mile Water fault that conditioned the till covered lowland between the Larne Basalt Moorland (LCA 124) to the north and the Carrickfergus Upland Pastures (LCA 98) to the south.
Key Elements ASISallagh Braes ASI
The Scawt Hill component of this ASI has been re-designated as an ASSI and occurs in LCA 124. However, part of the Sallagh Braes landslide complex can be found in the north of this LCA 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 large bowl of the failure lies in this LCA, the back wall of the landslide occurs in LCA 124 to the west.
Sites/units identified in the Earth Science Conservation Review
75 Glynn Hill
Tertiary. Disused quarry previously contained magmatic rolls, but is now infilled. Silica-rich Glynn Hill andesite lava occurs in crags. These lavas allow comparison with Scottish Tertiary Province on Skye and Mull.
AONBThe northern corner of this LCA lies within the Antrim Coast and Glens AONB (1988). This designation is indicative of the scenic quality of the landscape.