, where the coastal areas, where most of the rain falls, is drained to the sea, and the inward flowing drainage of the rest of the continent, that receives very little rain, conspires in such a way that vast tracts of central Australia depend for their water on the intermittent floods that are channeled from the monsoonal areas of northern Australia along normally dry channels.
During this time period Australia had After being recycled many times over much of the history of the Earth, with no new rock added by volcanism, the soils of arid Australia have been weathered and leached more than any others making them the most nutrient-deficient soils in the world.
And most of Australia spent many millions of years covered by seas.
In many places these seas were eventually cut off from the ocean and evaporation formed huge deposits which were later buried.
So added to this impoverished state of the soils there are vast areas where there are salt deposits beneath the surface which means when land is cleared for agriculture the removal of deep-rooted trees and shrubs mean the water table rises.
There are 3 major structural components, the stable Western Shield, the gently warped Central Basin, and the ancient orogony of the Eastern Uplands, which have been rejuvenated by differential uplift in Tertiary and later times.
The result is the vast plains and plateaux of the Australian landscape.
Lack of volcanic or seismic activity leading to mountain building over much of the continent for many millions of years means that what mountain ranges there were have been worn down by erosion to mere stubs of their former glory.
The soil over much of Australia, especially the dry central parts, have not been renewed by volcanic activity for a very long time and are impoverished compared to soils from most other parts of the world.
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In the later Tertiary the Basin began to subside, resulting in the internal (endogenetic) drainage system that drains much of inland Australia.