In southern South Australia, the meridional Torrens Hinge Zone, at approximately longitude 138º, separates the cratonic Stuart Shelf with its undeformed, relatively thin sedimentary cover in the west, from the folded Adelaide Geosyncline to the east. The thick late Proterozoic and Cambrian sequences of the Adelaide Geosyncline are preserved in a complex, sinuous and branching system of fold belts, imposed during the Cambro-Ordovician Delamerian Orogeny (Thomson, 1969), and outcropping as the present Flinders and Mount Lofty Ranges. It is the stratotype for the Adelaidean period (late Proterozoic), and probably contains the thickest and most complete record of Adelaidean sedimentation in Australia. At their northern extension, the Torrens Hinge Zone and adjacent fold belt curve to the north-west, and the Adelaidean sediments emplaced here were formerly probably partly continuous with those of the Officer and Amadeus Basins of central Australia. Between the central Flinders Ranges and the Muloorina Ridge of interpreted shallow basement (Thomson, 1970), a fold belt extends from the Mount Painter basement inlier in the east through the north Flinders Ranges to the Peake and Denison Ranges in the north-west. In the south, the fold belt swings westerly through Kangaroo Island, to the west of which it is truncated by the present continental margin. The Adelaide Geosyncline was compared by Sprigg (1949, 1952) with typical miogeosynclines developed on continental shelves, but Scheibner (1973) identified it as an aulacogen. However, the Adelaide Geosyncline actually embraces a number of contrasting tectonic environments: of these, the gently folded central Flinders Ranges zone is essentially symmetrical and intracratonic between the Stuart Shelf to the west and the Curnamona Cratonic Nucleus (Thomson and others 1976) to the east. It thus resembles aulacogens, although it does not die out within the craton as do type examples of aulacogens. In contrast, the sigmoidal Kangaroo Island - Mt Lofty - Olary arc displays a polarity of sedimentary facies, tectonic structures and metamorphism, from a craton with marginal sediments in the north-west to a mobile belt with basinal sediments to the south-east; as such, it could represent an ancient continental shelf.