A xenolithic minor intrusion of Caledonian age at Slievenagriddle, County Down, Ireland, shows the existence of feldspathic replacement rims and rheomorphic veins associated with the xenoliths, and derived from them by metasomatic action of the magma. Chemical and spectrographic analyses of the main rock of the intrusion, and of a rheomorphic vein, establish an order of geochemical migration for the metals of the alkali series.

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