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Geology
The Mournes developed by the slow sinking of a circular block of shale some 10 km in diameter, deep into the earth's crust. As it did so, granite magma welled up around the sides of the descending block and filled the roof cavity left in its place. This Cauldron Subsidence, as it is called, produced the high eastern Mournes. The lower western Mournes were formed through the collapse of a second thinner block of shale. As the granite filled the cavities it solidified in five main stages, each recognisably different. In the zone of contact with the surrounding shale the cooling granite metamorphosed the shale into a harder rock, more able to withstand later erosion. Their formation complete, the granites were hidden under an overlying mantle of the original shale, which subsequent erosion has slowly removed leaving the younger, more resistant granites intact as a ring of mountains. Landscape
As the ice sheets retreated, vast quantities of sand and stone deposited by the melting ice were left covering the coastal plain to a depth of several feet; shallow near the base of the hills and thicker near the coast, where great accumulations of glacial till were heaped in hummocky ridges called moraines. Along the northern and western fringe of the mountains drumlins were formed when large mounds of deposited drift were moulded and streamlined as the ice passed over them. Many granite boulders carried from the mountains by the ice still litter low lying areas, and many, such as Clough Mor Stone at Rostrevor, were left on the summits of hills. Soil and Natural Vegetation.
The Mourne upland is composed of hard, acidic granite, which produces a poor soil base. High rainfall leaches out nutrients faster than they can be replaced by weathering of the rock particles, making the soil become progressively more acid and less fertile. Peat bogs formed in the flatter parts of the hills where the soil is constantly waterlogged and its surface acid. The surrounding countryside was covered with glacial drift, enabling the development of a diversity of soils, reflecting the composition of the base material. They range from deep acid sands on the coastal plain to shallower, more fertile on the northern foothills of the mountains. Before the early Celtic farmers cleared the land for agriculture and their grazing animals prevented tree regeneration, broad-leaved woodland covered the Mourne lowland and hillsides. Today's Mourne countryside is a mosaic of fragmented habitats surviving in a landscape dominated by human land use. The general pattern is from farmed lowland with thin corridors of native trees remaining in hedgerows and along riverbanks, through marginal land across which scattered trees and gorse scrub give way to sheep-grazed heather hillsides. At higher levels dwarf-shrub heaths and grasslands occur, with a zone of stony moss heaths on the highest ground. Other special habitats, such as screes, cliffs, bogs, lakes and streams are found at various elevations throughout the landscape. Upland Habitats
With the final retreat of the ice trees colonized the area. It was a productive environment for Mesolithic hunters, some of whose remains have recently been discovered. Around 5000 years ago, farming communities settled in the area, attracted by the light fertile soils. They left behind megalithic tombs, the most prominent of which are the cairns on Slieve Donard.
Resources In the 1890s the Water Commissioners, to service a growing population in Belfast and County Down purchased 9,000 acres of the high Mournes, areas around Slieve Binnian and Ben Crom were chosen. At the time of the surveys done by the Water Commissioners this area had an annual rainfall of 70 inches and was free from industry and pollution. They then decided to enclose the main catchment area of the Mourne Mountains with a wall. The wall, which stretches 22 miles over 11 peaks, took 18 years to build. It was started in 1904 and, with a break in the war years, was completed in 1922. Work started in March and ended in mid-October each year. The task of building the wall (in some places it is eight feet high), on very steep slopes, using heavy and awkward granite slabs, must have been very onerous and called for great strength and endurance on the part of the workers. Their descendants described them as "Men with powerful shoulders and hands like shovels". Many of the men who built the wall were later involved in the construction of the Silent Valley and other reservoirs. These men and many more locals from the Mourne area, 2000 in all spent the next 10 years building a dam across the Kilkeel river. The project began in 1923 and was completed in 1933, they encountered many obstacles and the main problems that slowed dow the work was the volumes of silt, gravel and boulders that had to be removed by hand. There is a third resource provided by the mountains, recreation and tourism. By the middle of the nineteenth century Newcastle, at the foot of Slieve Donard, was already a favourite Watering Place and the coming of the railway in 1869 opened up the resort to day trippers from Belfast, Portadown, Ballynahinch, Downpatrick and other places. Tours of the Mournes, including Coach connections through the mountains between Newcastle and Warrenpoint stations, which also had the effect of opening up Newcastle to visitors from Dublin and other points south, were well established by the end of the century. Over the past twenty years there has been a growing recognition of the vulnerability of the environment and of the need to maintain and preserve it for the benefit of future generations, as well as making it available for the enjoyment of the present generation. The region has been designated an Area of Outstanding Natural Beauty and an Environmental Protection Area. Part of it is managed by the National Trust and the Mourne Heritage Trust has been established to maintain its paths and walls. These require constant maintenance, not only to repair the ravages of the weather, but the impact of human beings. The many walkers who enjoy the mountains inevitably affect the fragile ground cover and the effects of water and wind exacerbate the damage. The Trust has launched an ambitious programme to repair the wall and the paths. The mountains were of course made famous by Percy French (1854 -1920) in his popular song The Mountains of Mourne.
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