Fortification Dike

Located on Fortification Creek, 32 km north of Craig, the Fortification Dike is about 18 km in length and sometimes stands as a wall-like feature. The chilled margin, referred to by Ross (1926b) as 'verite', consists of phenocrysts of olivine, augite and biotite in a glassy groundmass. A coarse grained analcime syenite towards the centre of the dyke consists of the same minerals together with 60% orthoclase and oligoclase, 10% analcime, aegirine-augite, a red-brown amphibole and accessories. Modes and two rock analyses are given by Ross (1926b).