ABSTRACT
Some geomorphologists, mainly the ‘big names’ in the field, have turned their attention to the long-term change of landscapes. Starting with William Morris Davis’s ‘geographical cycle’ (p. 6), several theories to explain the prolonged decay of regional landscapes have been promulgated. Common to all these theories is the assumption that, however the land surface may appear at the outset, it will gradually be reduced to a low-lying plain that cuts across geological structures and rock types. These planation surfaces or erosion surfaces are variously styled peneplains, panplains, and etchplains. Cliff Ollier (1991, 78) suggested that the term palaeoplain is
preferable since it has no genetic undertones and simply means ‘old plain’. It is worth bearing in mind when discussing the classic theories of landscape evolution that palaeoplain formation takes hundreds of millions of years to accomplish, so that during the Proterozoic aeon enough time elapsed for but a few erosion surfaces to form. In south-eastern Australia, the palaeoplain first described by Edwin Sherbon Hills is still preserved along much of the Great Divide and is probably of Mesozoic age. In South America, where uplift has been faster, there are three or more erosion surfaces. Old erosion surfaces are commonly preserved in the geological record as unconformities.
