This is an area of granodiorite, granite and syenite overlain by an extensive sequence of ash-flow tuffs. Some facies of the granites and syenites contain abundant riebeckite which Mercer et al. (1985) consider to be metasomatic, but K.L. Currie (personal communication, 1985) feels is not. Similarly, the tuffs in some areas contain riebeckite which Mercer et al. (1985) describe as forming oikocrysts which overgrow fiamme and other textures.