It consists in the main of an Archean block or " coign,"which still occupies nearly the whole of the western half of the continent, outcrops in north-eastern Queensland, forms the foundation of southern New South Wales and eastern Victoria, and is exposed in western Victoria, in Tasmania, and in the western flank of the Southern Alps of New Zealand.
The chief outcrops occur around Biggarsberg and along the upper slopes of the Drakensberg.
The outcrops of these rocks succeed each other in order of age in roughly concentric belts, with the Archaean mass of the island of Anglesey as a centre, but the arrangement in detail is much disturbed and often very irregular.
The well-water was supposed to have percolated underground, through the Blythesdale Braystone, which outcrops in patches on the eastern edge of the Rolling Downs formation.
With the Beaufort series this occupies over twothirds of the western portion of the province and has wide outcrops in Zululand and in the Vryheid districts.