Jurassic limestones occurring in a screen between two ring dykes are shown to have undergone two periods of thermal metamorphism; the first charac-terized by a high ratio of CO₂:H₂O and the second by a high ratio of H₂O:CO₂ in the vapour phase. The first metamorphism produced minerals characteristic of Bowen's decarbonation series. Some of these minerals became unstable in the second metamorphism and (OH, F) bearing minerls were produced. A stage of fracture-controlled replacement veins with mineral assemblages which indicate a varying CO₂:H₂O ratio in the vapour and a general falling temperature sequence terminate the metamorphic history. Three new minerals, rustumite (Ca₃Si₂O₇.Caterminate (OH)₂), dellaite (Ca₁₂Si₆O₂₂(OH)₄), and kilchoanite (Ca₃Si₂O₇), of which the last has previously been described, are characteristic of the second episode of meta-morphism.