Pre-Quaternary and long-term landscape evolution

Abstract

The main outline of South-West England’s landscape owes its origin to a combination of geological and tectonic controls and geomorpho-logical processes in pre-Quaternary time. Together with other areas of southern Britain which escaped the major erosive and deposi-tional effects of Pleistocene ice sheets, South-West England became a focus for numerous studies concerned with establishing the nature, distribution, ages and origins of various perceived erosion surfaces and related drainage networks (e.g. Balchin, 1937, 1946, 1952, 1964; Trueman, 1938; Wooldridge and Linton, 1939; Wooldridge, 1950; Bradshaw, 1961; Weiler, 1959, 1960, 1961). These morphological studies mark an important stage in the development of geo-morphological thought and technique. However, over much of South-West England there are relatively few on-land pre-Pleistocene deposits, and the great majority of relict features in the landscape are erosional and therefore almost impossible to date precisely. Overwhelmingly, the morphological evidence has proved profoundly unsatisfying, and until recently has lacked any serious confirmation from deposits (Kidson, 1977). However, two sites in particular provide significant evidence for establishing the nature and timing of major pre-Quaternary land-shaping events and processes in the South-West, and are the subject of this chapter. St Agnes Beacon provides unique evidence for establishing the relative age(s) of erosion surfaces in the region (Walsh et al., 1987; Jowsey et al., 1992), while Beer Quarry shows a spectacular example of the controversial clay-with-flints, and has a major bearing on the pattern and nature of Palaeogene weathering processes. A brief synopsis of the early work on erosion surfaces and drainage networks, and a more detailed account of pre-Quaternary weathering residues, sediments and landform development are given here, both as an introduction to the subject and to the selected GCR sites. The long-term evolution of the characteristic granite terrains of the South-West merits separate consideration in Chapter 4.