According to the geological history of the coast at Botany Bay, the earth's crust there has risen in the past, so that the lowest points in the Georges River are around Liverpool, where much of the river's burden of silt was therefore dropped, until, over millions of years, the river could cut its way through the Woronora Plateau to the sea. While this left lower reaches with sandy beds, more suited to building materials, there were also higher concentrations of acid sulphate soils in the riverbed as a result of bacterial and chemical interactions around past and present riverine vegetation. The riverbed materials below Liverpool, therefore, seemed more suited to building, but carried substantial risks to environmental health, to be discovered later. Haworth, Baker and Flood, 'Predicted and Observed Holocene Sea-