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 Central Lowlands. This region owes its large-scale morphology to the early Tertiary subsidence of the Lough Neagh basin into the magma chamber from which the basalts that underlie much of the landscape originated. This has produced a largely centripetal drainage system from the rim of the basin into Lough Neagh that ultimately drains northwards via the Lower Bann. To the south of the Lough Neagh basin, the lowlands extend southwestwards along a Caledonian structural trend into the Monaghan-Clones depression. In the east of the region the lowlands extend northeastwards along the fault-guided Lagan Valley. There are no strong topographical barriers in the region and boundaries between LCAs tend to be subtle. The low gradients of the rivers, especially on the clay lowlands immediately around Lough Neagh, create inherent drainage problems and frequently it is only the slopes of the many drumlins that provide permanently dry sites. The Lough Neagh Basin was a major ice accumulation centre during the Late Midlandian and much of the lowland areas to the north and south of the Lough are dominated by extensive drumlin swarms.
This drumlin landscape forms a wide band within the lowlands to the east of Long Mountain Ridge, traversing the steep River Main valley and extending south to Ballymena. The drumlins are distinctive amongst areas of undulating land alongside the River Main. Steep sided ridges, small hills and numerous troughs and hollows typify the landform in these areas, with the land falling gradually towards the river valley. Pastures on the drumlins respond to the shape and scale of the land form. The Clogh River meanders between the drumlins in an attractive small-scale valley. Place names such as Drumnacross Hill emphasise the part these drumlins play in creating a distinctive landscape character. The west of the LCA also includes most of the Gkarryford esker/outwash complex, where the ridge and mound topography adds interest to the low-lying, frequently bog-dominated, valley of the River Main. The drier, agricultural, glaciofluvial landforms contrast seasonally with adjacent raised bogs and produce a distinctive rural landscape. Abandoned gravel pits exist on the main esker ridge.
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. The older formations can be upside down (tectonically inverted).
Stratigraphic Table (youngest rocks at the top of the table)| Tertiary Antrim Lava Group - 50 - 60 million years old |
| Cretaceous Hibernian Greensand & Ulster White Limestone - about 100 million years old |
| Triassic Mercia Mudstone & Sherwood Sandstone Group - between 240 and 210 million years old |
| Neoproterozoic (Dalradian) OwencamFormation - about 550 million years old |
The geology comprises a mix of Neoproterozoic metamorphic, Mesozoic sedimentary and Tertiary igneous rocks in faulted and unconformable contact. Lower Basalt Formation dominates the outcrop, forming 95% 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 epoch. 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 extensive deposits of late Midlandian till that underlies the numerous, approximately S-N orientated drumlins that dominate much of the landscape. These were formed by ice that moved northwards out of the Lough Neagh Basin. Within Northern Ireland drumlins take a variety of forms; some are rounded in plan, although the majority are elongated in the direction of ice flow. Some have sharp crests, whereas others are more whaleback in profile. 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. Where drumlins are rock cored there may have been significant frost shattering prior to their shaping by ice flow. It is possible therefore to see tails of shattered debris within till leading away from the feature in the direction of flow (Davies and Stephens 1978). 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.
This LCA contains two deglacial complexes that that total 7.5km2 and are important scientifically and for their sand and gravel resources. These were laid down in the valley as Midlandian ice ablated and the ice margin retreated southwards towards the ice centre in Lough Neagh.
The Glarryford Esker/Outwash is an esker ridge and adjacent outwash spreads are located extends along the western side of the River Main at Ballymoney. Landforms record subglacial esker deposition, followed by proglacial outwash deposition, late in the deglacial cycle, within a tunnel valley cut into bedrock. Mounds of stratified sediment are probably the eroded remnants of more extensive gravelly spreads formed over ice or ice-rich sediment during final ice wastage.
Glarryford Esker is an intact, pristine, continuous esker ridge extends along the western side of the River Main in the centre of the LCA. The landform records subglacial deposition, late in the deglacial cycle, within a tunnel valley cut into bedrock. Adjacent glacigenic features show evidence of streamlining which, together drumlins along both sides of the valley, is evidence of a later fast ice flow event.
Key Elements Deglacial ComplexesGLARRYFORD ESKER/OUTWASH (BALLYMONEY)
The esker/outwash association is an important element in the reconstruction of the processes which pertained during the final stages of the Lough Neagh ice mass.
GLARRYFORD ESKER
The undeformed sediments of the Glarryford esker indicate that deposition postdated the streamlining event. The esker is therefore an important element in the reconstruction of the dynamics of the final stages of the Lough Neagh ice mass.