Enigmatic rocks and sarsen stones of the West Sussex Coastal Plain, southern Britain

Abstract

The coastal plain of West Sussex and south-east Hampshire preserves a succession of Pleistocene raised beaches, periglacial deposits, and estuarine channels. These incorporate numerous ‘erratics’ or ‘exotic’ rocks, here described as enigmatic rocks, and sarsen stones. The enigmatic rocks include large boulders of non-local igneous, metamorphic, and sedimentary rocks, which have attracted interest since the early 19th century. Many suggestions have been made regarding their origins, transport, and date of emplacement. More recently, it has been realised that these rocks may have important implications for understanding the Quaternary history of southern Britain and the palaeogeography of the English Channel region during the Pleistocene. This paper presents a literature review, supported by details of historic and extant boulders, distribution, and dimensions. In agreement with previous authors, it is concluded that the enigmatic rocks were likely transported within ice floes or icebergs, but further studies are required to identify possible sources. Suggestions have included northern Britain, Scotland, Scandinavia, Greenland and Laurentia. There are doubts concerning an adequate build-up of periglacial sea-ice to accept the historic consensus for a source in Brittany, the Cotentin Peninsula, and the Channel Islands. The date of emplacement is suggested to be MIS 13, but multiple phases of emplacement cannot be excluded. In contrast, the sarsen stones are considered to be relic of pre-MIS 7 periglacial erosion of weathered Lambeth Group in a regolith of Clay-with-flints formerly capping the local Chalk outcrop. Many questions remain unanswered, particularly regarding the enigmatic rocks, so aspects for future study are identified.