Slieve Gullion, Co. Armagh

Below is some text from the Geological Society’s ‘100 Great Geosites’ webpage (

Geologically, Slieve Gullion and the encircling ‘ring dyke’ hills are considered to be the best example of a volcanic ring dyke system in the UK or Ireland. The complex attracts international research interest and has made contributions of world significance to scientific understanding of volcanicity.

“”The oldest rocks in the area formed in an ancient ocean more than 400 million years ago during the Silurian period. Masses of molten granitic rock or magma, were later intruded into these rocks, which underlie Newry town and much of the Slieve Gullion area. These granites are some 390 million years old and date from a major period of mountain building in Ireland.

In the Tertiary period, commencing some 65 million years ago, the area once again became the centre of volcanic activity. Slieve Gullion is the eroded heart of a volcano active in the area some 60 million years ago. Volcanoes often develop an encircling ring fault or fracture around them and the Ring Dyke which gives the area its name is caused by magma, or molten rock, reaching the surface at several points in the fracture resulting in explosive eruptions of which there is still evidence today; the encircling ring dyke is some 11km in diameter and includes the hills of Crosslieve, Mullaghbane Mountain, Slievenacappel, Anglesey Mountain, Flagstaff and the Sugarloaf or Sturgan Mountain.

More specific trip details to follow here shortly….