To a certain extent the Lower and the Higher Steppes merge into one another ; but, roughly speaking, we may regard the dividing line as coterminous with the northern edge of the great Cretaceous plain which rolls up against the southern flank of the central ranges. Approaching from the south it is quite a welcome change, after traversing the dreary country of the Lower Steppes, with its flat-topped hills, to see ahead a range of rugged, dark-red rocks, the southernmost ridges of the more ancient formations which constitute the backbone, as it were, of Central Australia, running for between three and four hundred miles east and west across the country. A reference to the maps and sections will give some idea of the main physiographic features of this remarkable part of Australia.

Broadly speaking there are two great ranges running parallel to one another, separated by a trough which varies in width from at least twenty miles at its western end to rather less than half a mile at its eastern limit in the neighbourhood of Alice Springs (Fig. 50). The southern, which is known as the James Range, does not extend so far east as the northern one, dying down into an intermittent series of small hills to the east of the Todd River.