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Slieve Gullion Ring - Cloghinny 'pillow lavas'Armagh
Summary Full report
Site Type: Crag, Crags
Site Status: PASSI
District: Newry & Mourne District Council
Grid Reference: J024180
Rock Age: Tertiary (Palaeogene)
Rock Name: Slieve Gullion Complex
Rock Type: Dolerite, Granophyre
Other interest: net veins, Intrusion

Summary of site:

About 500 m north of Cloghinny is an occurrence of rocks originally described as pillow lavas. As the name implies, pillow lavas are pillow-shaped masses and they are formed when lava erupts into water, normally a volcanic sea bed. The lava surface chills as it is extruded, then inflates with more lava while the skin is still plastic and finally detaches as a pillow shaped blob. These rounded masses tend to accumulate in piles around the erupting fissure. Reynolds observed the sac-like forms at Cloghinny and interpreted them as pillow lavas but later work by Bailey and McCallien was able to demonstrate that they are bulges of dolerite on the mobile interface between the dolerite and granophyre while both were molten. The outcrop is in layer 2 of the 13 layers in the sequence.

Since they were originally described and re-assessed weathering has blunted their form and vegetation is starting to mask them. This initially contentious outcrop is ideal for demonstration and should be cleared. To place the layered sequence in context the account of the Slieve Gullion Ring Overview, site 1118, should be read.

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