Basement

Basement rocks occur over almost the entire length of Victoria and Barwick Valleys. They are best exposed at the eastern end of the valley because the Ferrar Dolerites and overlying Beacon sediments obscure them toward the west.

The oldest rocks are the metamorphics of the Ross System, early Palaeozoic or Pre-Cambrian in age. These include graphitic marbles, schists, granulites and gneissic rocks, all with a constant trend of 280°.

At Lake Vida a salmon-pink or grey-coloured granite of the Admiralty Intrusives crosses the valley in a north-south direction, cutting the metamorphic rocks discordantly. Occasional pebbles of this granite are found in the basal Beacon sediments and it might be the major source rock of the sandstone.

Further eastward, the schists and gneisses are cut by a porphyritic granite which is well developed in the Purgatory Peak and Miller Glacier areas. Its ago and relationship to the 'Vida' granite art not certain, but laboratory study of specimens will help to determine this.

The basement rocks, of both Rosa system and Admiralty Intrusives, have been intruded by a wide variety of acid and basic dikes ranging in composition from aplites to pyroxenites. It is hoped that further study of these will give a relative ago for the members of the Admiralty Intrusives.