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.
The Expansive Crumlin Farmland lies near the eastern shores of Lough Neagh, occupying a relatively flat area underlain by rocks of the Upper Basalt formation. The land slopes gently from the lower slopes of the Belfast Hills (Derrykillultagh) to the fringes of Lough Neagh to the west. Clady Water, Dunmore River and the Crumlin River flow from the hills across the farmland but do not have a strong presence in the landscape. The valleys of the Clady and Crumlin rivers are narrow and steep-sided so the water channels are relatively inconspicuous. Essentially this is a structurally controlled landscape comprising the lower dip slope of the Tertiary basalt plateau.
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 - Lough Neagh Group mudstones & lignites - about 20 million years old |
| Tertiary - various intrusives (mostly dykes), 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 |
The two Tertiary-aged basalt formations comprise a crudely-bedded succession of lava flows, columnar jointed lava flows, ash-falls and red-weathered horizons (or boles). In the north of LCA113 these two formations are separated by red, palaeoweathered beds and ashfalls of the Interbasaltic Formation. The basalts were erupted 55 million years ago as the North Atlantic opened. They are extensively quarried for construction materials, especially roadstone.
The Lower Basalt Formation occurs in the north outcrops of LCA113:ash-falls occur in the northwest of the LCA, southwest of Muckamore. The Upper Basalts dominate the central area of LCA113.
NE-SW oriented faults dominate the outcrops of Tertiary rocks and juxtapose all the above 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 and produced a hummocky terrain of 'mixed drifts' (Symons 1962). The exceptions to the complete blanket of till are isolated drift free areas of bedrock in the north of the LCA and a small area of glaciofluvial sand and gravel in the south. The latter was most probably deposited in the late glacial period at the ice margin, as Lough Neagh ice downwasted to leave the Antrim Plateau encircled by ice. There are also ribbons of alluvium associated with the present-day drainage system running down the dip slope towards Lough Neagh.