Earth Science Conservation Review

Slieve Gullion Ring - Glendesha ForestArmagh
Flow-banded Porphyritic Felsite near its outer margin with the vent agglomerate.
Summary Full report
Site Type: Scarp face
Site Status: ASSI
Council area: Newry, Mourne & Down District Council
Grid Reference: H995171
Bing maps: 54.09389,-6.47922
Google maps: 54.09389,-6.47922
Rocks
Rock Age: Tertiary (Palaeogene)
Rock Name: Porphyritic Felsite, Slieve Gullion Complex
Rock Type: Agglomerate, Felsite, Granodiorite
Interest
Other interest: ring-dyke, volcanic vent, Contact, Intrusion
Summary of site:
The context of this site is explained in the overview of the Slieve Gullion Ring complex, site 1118.
The forest now obscures the porphyritic felsite that forms the steep western flank of Slievebrack but it is still possible to see the southerly inclined flow structures that track the contact with the vent agglomerate at its base. The extreme explosive violence preceding the emplacement of the felsite is recorded by the agglomerate that consists mostly of the Newry granodiorite ripped from the wall of the ring during the cataclysmic degassing. The debris-filled vent was then invaded by the molten felsite.
This site, recording the early events in the formation of the ring dyke, is one of a suite of important sites which, taken together, show the evolution of the Slieve Gullion Ring complex. Sites of this kind should be regularly monitored to ensure that outcrops are clearly visible. Minimal felling and clearing should restore this exposure.

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