Field meeting: landscape evolution in the eastern South Downs, with particular reference to sarsens and Quaternary deposits, Saturday 17 October, 1998 J. Stewart Ullyott, Colin A. Whiteman and David J. Nash ULLYOTI , J. S, WHITEMAN, C. W. & NASH, D. J. 2000. Landscape evolution in the eastern South Downs, with particular reference to sarsens and Quaternary deposits, Saturday 17 October, 1998. Proceedings of the Geologists' Association, 111, 91-96. The development of chalkland landscapes has long been a subject of debate in the UK. This excursion provided an opportunity to review some of these ideas in the context of the eastern South Downs. The morning was devoted principally to discussion of established theories, in particular the nature of Sussex sarsens and their origins: in the afternoon attention switched to Quaternary landscapes and the sensitive question of geological conservation. School of the Environm ent, University of Brighton, Cockcroft Building, Lewes Road, Brighton BN2 4GJ (e-mail:j.s.ullyolI@brighton.ac.uk) 1. LANDSCAPE EVOLUTION IN THE SOUTH DOWNS A party of 28 members and friends assembled in the grounds of Stanmer Park before proceeding to the first site at Ditchling Beacon, the highest point in the area. Inspired by views extending over the Weald and the English Channel, Stewart Ullyott introduced the two differing approaches to landscape evolution in southern England. The first, based on identification of erosion surfaces, had been proposed by Wooldridge & Linton (1938, 1955) and supported by Sparks (I 949). Wooldridge & Linton identified two surfaces on the chalklands: a higher Mid- Tertiary subaerial peneplain, which included Ditchling Beacon, and a lower marine cut surface attributed to the Pliocene. Sparks (1949) claimed to have identified up to eight other erosion surfaces in this area. As tectonic activity was considered by these authors to be confined to a 'storm' in the early Miocene, they assumed stability since that time and thus thought it possible to identify region-wide surfaces on the basis of altitude alone. Later investigations failed to verify these ideas, as Hodgson, Catt & Weir (1967) discovered that Clay-with- flints in the Worthing area had formed more or less in situ by the weathering and cryoturbation of a thin Palaeogene cover. Partly as a result of this work, and a growing appreciation of the pulsed nature of Alpine tectonics, new models of landscape evolution had been advanced suggesting that the dominant palaeosurface in the southern English chalklands was polycyclic and of Palaeogene age (Jones, 1980, 1981; Small, 1980). Jones (1999) has recently elaborated these ideas arguing that the major driving force in landscape development has been movement related to inversion of faults and thrusts in the Palaeozoic floor. The combination of major and minor inversion axes effectively subdivides the chalklands into a Proceedings of the Geologists ' Association. 111 ,91 - 96. number of tectonic/structural units, each of which may have a distinct history of uplift, warping and erosion. As a result, Jones (1999) has suggested that the search 'for uniform ity of chalkland evolution must finally be abandoned' . As well as Clay-with-flints, Palaeogene debris, both in dissolution pipes and scattered in the soil (Mantell, 1822; White, 1924, 1926; Young & Lake, 1988), has been reported and this supports the concept of a widespread sub-Palaeogene surface on the South Downs (Hodgson et al., 1967; Jones, 1981, 1999). Such evidence can be found from the edges of the Palaeogene outliers, in the south, to the escarpment crest. 2. SARSENS Rock Pond, Standean [TQ 3158 1206] Having survived the bracing conditions on Ditchling Beacon the party continued to the next site, Rock Pond, Standean, which offered an opportunity for 'hands-on' experience of Sussex sarsens and to hear some results of the ongoing work of Stewart Ullyott and David Nash into the characteristics and origins of silcretes in the UK and southern Africa. Standean is one of the few accessible localities where sarsens can be seen near to their natural position in the landscape (Fig. 1.). An archaeological context has been suggested for this site by Martin (1910) but Toms (1926) determined that the stones were dug up and cleared from nearby fields more recently. It was emphasized that the term 'sarsen' is best reserved for silcrete boulders and should not be taken to include ferruginous or calcareous materials. Sarsens were viewed both on the surface around Rock Pond and directly in 'natural position' in Clay-with-flints in a pit excavated especially for the field visit (Figs 2, 3). 0016-7878/00 $15·00 © 2000 Geologists' Association