The origin and development of brown earths on clay-with-flints and coombe deposits

Summary Field investigation of the origin and development of three brown-earth (sol Zessiwk) profiles has been supplemented by mechanical and mineralogical analyses and micromorphological studies. Two profiles, representative of the Batcombe and Winchester series, were on Clay-with-flints and the third, of the Charity series, on a Coombe deposit. Particle-size distribution and petrographic data strongly suggest that all three soils are derived in part from loess. The Charity is interpreted as an autoch- thonous profile formed in a Head deposit composed of chalky and flinty detritus mixed with loess by soliflwion, whereas the Batcombe and Winchester are two- stage profiles, formed in composite (non-uniform) parent materials resulting from the superficial incorporation of loess with the truncated or redeposited remains of previously weathered horizons with rotlehm and/or braunlehm fabrics. These Clay-with-flint substrata contain materials derived from Chalk and Eocene beds in varying proportions, weathered in Tertiary or interglacial periods and rearranged by periglacial agencies. Clay-with-flints sensu stricto, as represented in the Win- chester subsoil, has distinctive physical, mineralogical, and micromorphological characteristics, and appears to have originated by sub-surface solution of the Chalk and illuvial accumulation of clay derived for the most part from overlying deposits. The land surfaces concerned have probably been subjected to at least one alternation of periglacial and temperate conditions after the addition of loess. Hence the extent to which either profile reflects the influence of the contemporary environment is not readily assessed, but evidence is adduced that the upper horizons of each profile bear the impress of similar pedogenic processes, including eluviation of clay-size material and acidic weathering leading to the accumulation of vermiculite, modified in the Winchester by the effects of erosion and soil creep.