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 Larne Coast is an undulating lowland to the east of the Larne Basalt Moorland. To the north of Ballygalley, the lowland forms a narrow strip between the steep slopes of the basalt uplands to the west and the coast. To the south, the coastal lowlands broaden to form an attractive, undulating landscape that extends from Carncastle to the town of Larne at the mouth of Larne Lough. The dramatic coast road is confined to a narrow platform (a raised beach), which hugs the coastline with superb seaward views. The steep, stepped basalt cliffs and rocky headlands provide a sequence of 'gateways' along the coast, framing the views and lending an air of anticipation. The coastline is renowned for its landslips and the coastal road shows signs of frequent repair. Inland, the lowlands are backed by the steep slopes of the Larne Basalt Moorland, and the circular cliffs of Sallagh Braes (LCA 124) are a dramatic landmark to the south. This entire northern coastline of the LCA is dominated by an integrated system of landslides and other slope failures operating at a range of scales. In detail it can be seen that small terraces or 'terracettes' cut across many of the low angled slopes. These are generally taken to indicate the downward creep of the superficial glacial till that covers many of the lower slopes and/or the Lias clays that underlie it. When viewed from afar it can be seen that what appears to be the cliff line is only the front of a series of large, rotated landslides that extend up to half a kilometre inland before the true edge of the plateau is reached. Typically, each landslide consists of an arcuate block of basalt above chalk that has both dropped and rotated backwards. This forms a steep cliff behind the block, a backwards-tilted surface that was formerly part of the plateau and a forward edge to the block that was once the cliff edge. The origin of these failures lies in the structurally weak Lias clays that occur beneath the chalk and basalt, combined with the over-steepening of the coast during the last glaciation and the subsequent disappearance of supporting ice. The resulting failures both pushed back the plateau edge and elevated the Lias to form much of the coastline. The coastal margins of these rotated blocks are themselves subject to a range of slope failures, most notably at Minnis North (see Key Elements below).
The shoreline sediments have been described by Orford (in Whalley et al. 1985) as predominantly basalt and chalk boulders with a matrix of sand and clay from debris flows that are moved longshore and offshore. The SW-NE trending Antrim Glens define offset re-entrant bays in which sand and gravel have been deposited as prograding beach ridges. The coast road runs along a series of raised beach platforms that are mainly of late- and post-glacial age and are most prominent at Larne. The coast road is protected along much of its length by a reflective sea wall that denies much fresh sediment to the beach and has resulted in the scouring away of beach sediment down to a boulder lag. North of Cushendall the basalt is replaced by Triassic sediments and the Palaeozoic basement. Good examples of abrasion platforms with associated stacks, arches and caves occur, testify to the scale of post-glacial isostatic uplift in the area. The coastline is described in further detail by Carter (1991), including human impact on the coast related in particular to sand and gravel removal.
This is a landscape of high scenic quality, which is within the Antrim Coast and Glens AONB. The Larne Coast has a number of important sites of earth science interest, including the Waterloo ASSI at Chaine Memorial Park, where the underlying Antrim basalts and chalk are exposed at the shore within a series of fossil-rich strata.
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, 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 (between 220 and 205 million years old), Penarth Group, about 205 million years old |
This LCA extends along the north Antrim coast from Larne to Glenarm, parallel to the coastal escarpment. LCA126 contains igneous and sedimentary rocks of Triassic to Tertiary age. 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 type Triassic - Jurassic stratigraphic succession at Waterloo (Larne) and the type mineralogical locatity of Scawt Hill (ASSI 083).
Below the Cretaceous - Tertiary escarpment to the west of LCA126, 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.
Conformably above the Mercia Mudstone Group, the Triassic Penarth Group comprises a succession (from the base) of carbonate-cemented siltstones, limestones, mudstone and black shales seen on the Waterloo foreshore. The succession is interpreted as representing the latest Triassic transgression of the sea; this continued into the earliest Jurassic. Conformably above the Penarth Group, the Waterloo Mudstone Formation of the Lias Group spans the Triassic - Jurassic boundary. The Waterloo Mudstone Formation comprises dark grey mudstones and shales, alternating with grey limestones. This is the only permanently exposed Triassic - Jurassic boundary succession in N.Ireland and is designated as ASSI 084. The Jurassic succession with fossiliferous Cretaceous greensand blocks and fossils can be seen in the mudflows at Minnis (ESCR Site 294).
The Cretaceous succession forms a faulted outcrop strip to the east of LCA126 and is dominated by greensands at the base with white limestones above. The succession is interpreted as being deposited during a mid to late Cretaceous period of sea-level rise. The limestones are quarried extensively for lime and aggregate.
Tertiary-aged basalts comprise a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles) of the Antrim Lava Group. The Lower Basalt Formation crops out at the base of the escarpment in this area, where its hard, durable nature makes it resistant to erosion. Together with the Ulster White Limestone below, this provides a resistant cap to soft, underlying formations, allowing the formation of the plateau that extends along the western boundary of LCA126 and into adjacent LCAs. The dolerite plug (the core of an ancient volcan0) at Scawt Hill on the western edge of LCA126 has caused alteration of the Ulster White Limestone and associated chert (flint) nodules to produce an array of unusual minerals, including scawtite (ASSI 083).
Normal faults of differing orientations cross the area, juxtaposing all the above formations and that parallel the coast, being NNW - SSE. Many of these structures have been activated in the last 10,000 years during landslip activity.
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 that much of the top of the coastal escarpment is drift free. However, Late Midlandian till underlies the south of the LCA 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 map also highlights the large area of landslip south of Glenarm that is associated with the large scale rotational failures discussed in the geomorphological desription of the LCA. The southern tip of the LCA is marked by an area of raised beach deposits at Larne Harbour and of raised marine sediments beneath the town itself.
Key Elements ASSI/ASI084 WATERLOO
The site offers some of the best exposures in Ireland of Penarth and Lower Lias strata. The site is of considerable importance in the context of Irish geological studies and, as the western most exposures in Europe, in studies of continental palaeogeography.
Scawt and Sallagh Braes ASSI
The Scawt Hill component of this ASI has been re-designated as an ASSI and can be found in LCA 124. However, a small area of the corrie-like backwall and bowl at Sallagh Braes landslide is within this LCA
Other sites/units identified in the Earth Science Conservation Review
294 Minnis
Palaeontological. Lower Lias mudstones exposed by mudflows. Rich and diverse fossils of Lower Jurassic vertebrates and invertebrates. Also diverse fossil fish teeth from Hibernian Greensands.
AONBApart from a small area in the south, all of this LCA lies within the Antrim Coast and Glens AONB (1988).
OthersMinnis North Flowslides
Minnis North is the name given by a succession of geomorphologists to one of the most intensively studied slope failure complexes in the whole of the British Isles. Essentially it is a flowslide system contained within the front slope of a rotated landslide. They are termed flowslides because elements of both flow and slide occur during failure episodes. The lateral extent of the flowslide is very limited and belies the intensity with which it was monitored throughout the 1970s. There are two linked elements to the system, an upper basin or bowl in which debris accumulates from surrounding slopes and the chalk escarpment behind, and a lower section (or toe) of the system that comprises a series of clearly defined channels in which mixtures of glacial till, Lias clays, chalk and basalt debris periodically flow downslope.