Physical Landscape
The two great mountain systems of Europe, north of the Alps, converge westwards to meet and mingle in Ireland. The older (Caledonian) extends from Scandinavia through Scotland to the north and west of Ireland, where it gives rise to the rugged and mountainous landscapes of Counties Donegal, Mayo and Galway. The higher mountains are of quartzite which weathers into bare, cone-shaped peaks such as Errigal (752 m) in Donegal, Croagh Patrick (765m) in Mayo and the Twelve Bens in Galway. Structures of similar age are responsible for the Wicklow and Blackstairs mountains which extend south-westwards from Dublin Bay for a distance of more than 100 km. In these, long-continued denudation of a great anticlinal structure has exposed a granite core which now forms rounded peat-covered uplands, the crests being notched in places by glacial cirques. The mountains are penetrated by deep glacially modified valleys of which the best known is Glendalough in County Wicklow.