The application of N. L. Bowen's reaction-principle (2', pp.177-198; 3 p.60) tothe study of certain igneous textures and the crystallisation and cooling of magmas hasbeen widely accepted. The plagioclase series ranging from the calcic end-to the sodicis the best example of a continuous reaction series, while the olivine-pyroxene-amphibole-biotite series-the existence of which can be easily convinced by the presence of coronastructure in certain gabbroic rock-is a discontinuous series of frequent occurrence.During his study of the mixed rocks-migmatites-of a portion of an injection-complexin North Sutherland. Scotland (5), the writer has found certain mineral changes whichmay be interpreted in the light of Bowen's reaction-principle. Such changes, as aredifferent from those occurred in the course of the cooling of a magma, were takingplace in a solid rock-system under high temperature, strong stress and the dominantinfluence of certain chemically active. fluids related to a granitic magma.