The Connemara Schist terrane provides evidence of extensive melting under amphibolite facies conditions, and the inferred reaction sequence suggests that much, though not all, of the melting took place in the presence of an aqueous fluid phase. The general disposition of the migmatites appears to suggest however that fluid was derived from crystallising, deep-derived magmas whose heat gave rise to the migmatisation, rather than from dehydration reactions occurring in pelitic rocks at lower grades below the migmatite isograd.