 Following the end of the last glaciation 15,000 years ago, the climate appears to have dried out somewhat as a layer of calcrete overlays the clay deposits.The Gulf St Vincent was an alluvial plain drained by an ancient river when Aboriginals first settled on the Hallett Cove clifftops and their tools have been found in the sand that lies above the calcrete.As the glaciers retreated in the Northern Hemisphere, the sea levels rose worldwide.