The Tertiary Ring Complex of Slieve Gullion (Ireland), with Petrological Notes by Herbert Henry Thomas

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Abstract
I. I ntroduction T he Tertiary plutonic rocks of north-eastern Ireland are confined to two main areas—the Mourne Mountains in Co. Down and the mountainous tract of country extending from the Carlingford peninsula, in Louth, north-westwards to beyond Slieve Gullion, in Co. Armagh. They are intruded into the middle of the well-known belt of Ordovician and Silurian strata which continues north-eastwards across the Irish Sea to form the Southern Uplands of Scotland. Near Carlingford, the Carboniferous Limestone also is cut by the plutonic rocks, while the country rocks immediately around Slieve Gullion consist of the Caledonian (or Lower Old Red Sandstone) granite of Newry (fig. 1). The Tertiary age of the plutonic rocks has been for many years accepted, on account of their petrological similarity to those intruded into the Tertiary basalt lavas in western Scotland. In Ireland, the basalts overlie the Antrim chalk and transgress southwards across the Carboniferous, Silurian, and Ordovician sediments of Armagh and Down. Remnants of the basalts are now known to occur still farther south, within the Slieve Gullion and Carlingford area. These, as is shown below, are earlier than the Slieve Gullion plutonic rocks, and direct evidence of the Tertiary date of the intrusive complexes is thus forthcoming. reservoir was formed by subsidence rather than by melting. Not improbably the western portion of the Newry granite itself occupies the space left by a cauldron subsidence of Lower Old Red Sandstone date. If at some depth in the crust there lay a subsided mass of country rock,

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