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 character area includes three different types of landscape that together form a single area with its own distinct identity. At its centre is Larne Lough, which stretches between its sea outlet at Larne, and the wide valley that extends southwards to Whitehead. The flat expanse of the lough and its valley is set between long basalt ridges to its west and east. Island Magee, to the east of the Lough, itself comprises a series of ridges which run north-south, culminating at sheer basalt cliffs along the eastern coastline. North of Black Head these cliffs are prone to occasional rock falls as they are undermined by a combination of marine erosion and weathering of the basalt. Between Black Head and the town of Whitehead, the coast is backed by hummocky terrain produced by a series of slumps, mainly in superficial drift deposits. To the west of the coast are farmed valley slopes. The lough and valley are open with a floodplain of rough grassland extending from the lough sides to the base of the ridges which enclose them. Island Magee is defined as an `Area of Scenic Quality'. The eastern coast of the peninsula 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 | Intrusives, around 55 million years old |
| Tertiary | Upper Basalt Formation, around 55 million years old |
| Tertiary | Interbasaltic Formation, around 55 million years old |
| Tertiary | Lower Basalt Formation, around 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 |
This LCA extends over Island Magee, Larne Lough and Ballycarry, it is parallel to the north Antrim coast LCA128 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. Contains the ASSI of Portmuck (ASSI 177); ESWCR Site of Brown's Bay (263), Cloghfin Port (excellent Hibernian Greensand: ESCR Site 264), Whitehead (ESCR Site 283), Kilcoan (ESCR 285) and the ESCR Site of Black Head (449).
Below the Cretaceous - Tertiary escarpments throughout LCA128, low coastal ground around Larne Lough is underlain by soft sedimentary rocks of the Triassic Mercia Mudstone Group and Penarth Group. Above the Penarth Group, the Waterloo Mudstone Formation spans the Triassic - Jurassic boundary
The Cretaceous succession forms a faulted outcrop strip around the coastal areas of LCA128, and in a fault-bounded strip in the south of the LCA and comprises sandstones and white limestones (chalks). These are well-exposed at Portmuck (ASSI 177) at the northern end of Island Magee and at Cloghfin Port, at the southern end.
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.
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 across the LCA, although Davies and Stephens (1978) show it lying approximately on an ice divide that ran along the crestline of the Belfast Hills. Ice to the south of this divide flowed approximately southeastwards across Belfast Lough and much of Co. Down. As well as the till deposits, there are a number of drift free ridges that run NNW-SSE across the LCA and reflect a series of fault lines running in the same direction. The effects of this structural control are best seen in the orientation of Larne Lough and behind Brown's Bay, where a fault guided valley is now partially infilled by alluvium. The drift map also highlights an area of raised marine deposits along the eastern shore at the bottom of Larne Lough.
Key Elements ASSI/ASI177 PORTMUCK ASSI
Portmuck contains the best exposure of the Cretaceous Hibernian Formation in Northern Ireland, the only occurrence of the mineral sodalite in Ireland and the international type locality of Gobbinsite. A range of other minerals and basalt related features are also present. The tombolo between Isle of Muck and the mainland is the only such feature on the open coast of Northern Ireland. A range of features associated with formerly higher sealevels are also present.
ISLAND MAGEE ASI
The ASI extends along the eastern and northern cliffline of Island Magee, with a small outlying area on the west coast of the 'Island' around Barney's Point.
Sites/units identified in the Earth Science Conservation Review263 Brown's Bay
Mesozoic. Illustrates stratigraphic and structural relationships between sediments and igneous rocks. Valuable as a teaching aid, especially for field mapping principles.
264 Cloghfin Port
Mesozoic. Good exposures of range of Mesozoic strata - Mercia Mudstone Group to Glenarm Chalk Member. Richly fossiliferous Belfast Marl Member exposed.
283 White Head
Mesozoic. Type section for Cloghfin Sponge Beds Member, basal member of Ulster White Limestone Formation.
285 Kilcoan
Mesozoic. Type locality for Island Magee Siltstones Member and Kilcoan Sands Member of Hibernian Greensands Formation. Belfast Marl Member also exposed.
69 East Islandmagee Coast
Tertiary.
449 Black Head
Exposures of well preserved pipe amygdales within lava flows of Lower Basalt Formation. Considered the best exposed to date in Northern Ireland.