Ferrer Dolerites:

Sills and dikes of the Ferrar Dolerite formation intrude the basement complex and the Beacon Sandstone. Two principal sills occur in Brown Hills - one intruding the basement and another at, or near the basement/Beacon contact. The two sills are in contact but the lower sill is chilled against the upper indicating separate Dolerite intrusions. In the Darwin Mountains dolerite is extensively intruded as irregular sills dikes and lenses (which were too irregular in most cases to serve as marker horizons.) Rafts of Beacon occur irregularly distributed within the dolerite mass both at Bastion Hill and in the Darwin Mountains.