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 Lagan Parkland is an amenity parkland landscape set within the historic, designed landscapes of a series of 18th and 19th century estates. It is an integral component of the Lagan Valley landscape and derives much of its character from its location in the floor of this fault-guided depression. The River Lagan itself drains eastwards from Silurian highlands immediately south of the Lagan valley along a topographic low underlain by Triassic sandstones, Cretaceous chalk and greensands. The valley occurs between the southern margin of the Antrim Plateau basalts forming Divis Mt and Cave Hill (476m and 300m O.D.) and the Silurian highlands to the south. The undulating, steep slopes of the narrow river valley in this LCA are well wooded, with a variety of formal designed landscapes, commercial forests and natural habitats. To the south of the river, a neat, rolling agricultural landscape of estate farmlands has belts of mature trees. Winding, linear woodlands follow the local streams and narrow roads that characterise the landscape close to the foot of the Castlereagh Slopes. The key geomorphological feature of the Lagan Parkland is the extensive suite of glaciofluvial deposits that define its topography. These sand and gravel deposits have historically been used as the preferred sites for building and today underlie the most of the urban areas in the valley. No active quarries remain. However, they remain a vital source of evidence for understanding the late-glacial history of this area and of Northern Ireland.
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)
| Triassic - Sherwood Sandstone Group, around 240 million years old |
| Permian - Enler and Belfast Group, between 280 and 250 million years old |
| Lower Palaeozoic (Ordovician) - Gilnahirk Group, around 480 million years old |
The eastern side of the Lagan Valley encroaches upon the Lower Palaeozoic outcrop. These comprise greywacke sandstones and shales. Two mapped units occur: the Ordovician Gilnahirk Group dominate the outcrop, comprising greywackes from a few centimetres to a few metres in thickness with a large proportion of rock fragments and a fine-grained matrix. the younger (latest Ordovician to possibly youngest Silurian) Gala Group occur as a very small area in the far southeast of the LCA
The Permian occurs in the centre of LCA106, and their outcrop is broken by three NW-SE trending faults in the southwest of the area. Red-brown sandstones, conglomerates, siltstones and the (topmost 1-4 metres) Magnesian Limestone Formation, occur.
The Triassic sandstones comprise red, purple and brown cross-stratified sandstones, siltstones with minor clay beds and partings. The sandstones are mostly soft and poorly-consolidated or more rarely well-cemented where they are and have been exploited for building stones in the past. They too are cut by the NW-SE faults mentioned above.
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.
This LCA contains a significant area (9.4km2) of the Lagan Valley Deglacial Complex. This is a discontinuous belt of glaciofluvial and glaciolacustrine deposits occurs for 40km along the axis of the Lagan valley from Belfast WSW to Aghalee, Co. Antrim. The complex consists of four main elements; (1) poorly exposed deltaic sands which underlie most of south Belfast; (2) steep-sided esker remnants at Lisburn; (3) flat-topped cross-valley ridges with associated feeder channels at Drumbeg, Sandymount and Hillhall; (4) a flat glaciofluvial outwash spread at the Maze. Kettle-hole depressions and meltwater channels also occur occasionally. Other significant elements of the complex can be found in LCAs 97 and 107, with minor areas in LCAs 62, 108 and 109.
The drift geology map for the LCA also highlights the extensive alluvial deposits associated with the present-day floodplain of the lagan. Where these late- and post-glacial deposits are absent, it is possible to identify the underlying Late Midlandian till.
Key Elements Deglacial ComplexesLAGAN VALLEY DEGLACIAL COMPLEX,
The Lagan Valley Deglacial Complex is highly important in understanding the complexity of deglacial processes. Streamlined landforms along the margins of the valley and glacially moulded bedforms indicate ice advance and episodes of fast ice flow from the west. Glaciolacustrine deposits indicate that during initial deglaciation the lower valley contained an ice-dammed lake, probably impounded by Scottish ice in outer Belfast Lough. A lobe of Irish ice located in the valley, related to ice pressure from the Lough Neagh Lowlands contained subglacial conduits now recorded by eskers that probably supplied sediment to the Malone deltaic sands that now underlie most of south Belfast. The phased retreat of the ice lobe further westward is recorded by cross-valley ice-contact ridges. During the final deglaciation, drainage was to the west, indicating a reversal in the drainage gradient probably due to isostatic depression of the Lough Neagh Lowlands during the last glacial cycle.
AONBThis LCA lies within the Lagan Valley AONB (1965). This designation is indicative of the scenic quality of the landscape.