"In a Tertiary ring complex at Carlingford, Eire, a large mass of eucrite is cut by porphyritic cone-sheets. A major granophyre intrusion later than the cone-sheets alters the clinopyroxene of the sheets to hornblende whilst the clinopyroxene of the adjacent eucrite remains unaltered. By elimination of several possibilities it is shown that the different behaviour of the two pyroxenes reflects their thermal stabilities. It is argued that the two pyroxenes represent a pyroxene trend of crystallization and that thermal metamorphism attacked them in the reverse order of their magmatic crystallization. Importance is attached to extensive replacement of Ca" by Fe" in the cone-sheet pyroxene as a factor of instability."

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