Because high rainfalls are experienced over the entire IIIawarra region soils here are almost invariably acidic (pH 4 - 6), and have been generally leached of the more mobile elements and compounds. Notwithstanding these common characteristics, there is a considerable complexity of soil types and distribution over the region. This complexity can in part be attributed to variations in the types of rocks on which the soils have weathered. For instance, the volcanic rocks break down to clays, but the sandstones undergo little real chemical alteration. Moreover, even on the sandstones, four or five types of soil can normally be found. It is certainly easy to recognise distinctive catenas, in which soils vary systematically with changes in steepness of slope and freedom of drainage. On the sandstones, for example, deep Yellow Earths on well-drained sites generally give way to organically rich soils in swampy locations further downslope. But not all changes in soil type can be explained in terms of simple catenary relationships. The occurrence of Ferricretes (Laterites) on sandstones is a case in point. Indeed, this example shows that the duration of weathering, changes in the intensity of weathering caused by climatic change, and local variations in the mineral composition of the parent material also are factors which must be considered.