The Great Dividing Range

n geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin. In the same way the sediments and/or sedimentary rocks on top of the basement can be called a "cover" or "sedimentary cover".

Australia was once  joined to a large mass of continents called GONDWANA.  It was locked in between Antarctica, Africa and South America 

Gondwana extended from a point at or near the south pole to near the equator. Across much of Gondwana, the climate was mild.

Australia has some of the oldest geological features in the world with the oldest known rocks dating from more than 3000 million years ago and rare zircon crystals dating back 4400 million years located in much younger rocks.

The Great Dividing Range

The rocks of the present ranges are mere remnants of a much larger mountain range that formed about 500 Ma, subsequently being eroded down to a near level plain. The present ranges resulted from the remnant rocks being uplifted, together with the rest of the east coast of the continent, about 2-3 Ma, during the Kosciusko Uplift.