Summary The development of soil classification as a basis for soil mapping in England and Wales is briefly reviewed, and a system for future use is described. The things classified are soil profiles, and classes are defined by relatively permanent characteristics that can be observed or measured in the field, or inferred within limits from field examination by comparison with analysed samples. Profile classes are defined at four categorical levels by progressive division, and are termed major groups, groups, subgroups, and soil series respectively. Classes in the three higher categories are defined partly by the composition of the soil material and partly by the presence or absence of particular diagnostic horizons, or evidence of recent alluvial origin, within specified depths. Soil series are distinguished by other characteristics, chiefly lithologic, not differentiating in higher categories. Most of the soil groups, regarded as the principal category above the soil series, are closely paralleled in other European systems, in the U.S.D.A. system (7th Approximation with subsequent amendments), or in both. Compared with the system used hitherto, the main innovations are the use of specific soil properties to define classes at all categorical levels, and the separation at group level of classes based primarily on inherited lithologic characteristics. The soil‐profile classification provides a uniform basis for identifying soil map units, considered as classes of delineated soil bodies. When a map unit is identified by the name of a profile class, it is implied that most of the soil in each delineation conforms to that class, and that unconforming inclusions belong to one or more closely related classes or occupy an insignificant proportionate area. Map units identified by land attributes not differentiating in the profile classification are termed phases.

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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 autochthonous profile formed in a Head deposit composed of chalky and flinty detritus mixed with loess by soliflwion, whereas the Batcombe and Winchester are twostage 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 Winchester 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. (1949), the major group of brown earths or brown forest soils comprises well-drained and moderately well-drained acid mull soils, occurring naturally under deciduous forest, and characterized by brown, friable, sub-surface horizons which are leached of carbonates and show little or no differential eluviation of sesquioxides. This group includes braunerde Kubiena, 19 ) or sols bruns acides relatively young land surfaces on silicate rocks or their clastic derivatives, to ether with texturally differentiated profiles conformin ABC profiles typical of grey-brown podzolic soils or parabraunerde (Tavernier and Smith, 1957; Kubiena, 1956a) but those associated with Clay-with-flints and other high-level deposits normally have thick, intensively weathered subsoils, resembling those of red-yellow odzolic soils, within which no well defined B and C horizons can ge identified. In general, on upland surfaces little affected by recent * Present address : AS defined by Robinson

The chalk and associated superficial deposits of the Chiltern Hills give rise under beechwoods to a sequence of soils ranging from rendzina through brown earth (sol lessivd) to podzol, closely paralleled in developmental sequences established elsewhere on uniform calcareous materials. The salient features of the genetic soil types represented are described and their evolution discussed in relation to vegetation and site characteristics. On base-deficient soils, mor formation under beech is conditioned by local climatic factors and management practices as well as by inherent fertility variations and is only associated with advanced podzolization on appreciably sandy materials. On silty plateau soils with imperfect drainage, 'micro-podzols', which may be transitory, are formed. Tansley 194 ) is based to a considerable extent on Watt's (1934) detailed study ( 4 of t e extensive semi-natural woods on the Buckinghamshire and Oxfordshire Chilterns. These woods, traditionally managed by selection and natural regeneration, are associated with a sequence of soils ranging from shallow rendzina on chalk to strongly acid and locally podzolized loams on Clay-with-flints and allied superficial deposits. I n this paper the morphology, composition, and eographic distribution of the soil to vegetation and site characteristics. THE ecological classification of British beechwoods given by Soil-forming Factors Physical features and geologyThe Chiltern Hills constitute a chalk cuesta, modified by sub-aerial and marine planation (Wooldridge and Linton, 1955). From the indented scarp overlooking the Vale of A lesbury, which rises to 750-850 ft. O.D., the dip-slope plateau, score C T by numerous dry valleys, falls gradually south-east towards the London basin. Tributaries of the Thames and Colne rise in the principal valleys, dry continuations of which intersect the scarp by way of broad 'wind-gaps' at Princes Risborough, Wendover, and Tring (see Fig. I).On the plateau surface, the underlying Chalk is everywhere obscured by Clay-with-flints or 'Pebbly Clay and Sand', enclosing lenses of gravel and brick-earth and representing the weathered remains of Chalk and Tertia formations, disturbed and redistributed by solifluxion or iceaction%herlock, 1947). The scar face and the steeper valley sides are by more or less decalcified, flinty solifluxion (Coombe) de osits, passing erosion, the su erficial layers of both plateau and valley drift are rich in types represented are outlined and t K eir evolution discussed in relation virtually drift-free, but the dry-va P ley floors and foot-slopes are covered locally into roughly sorted flint gravel. Where undistur E ed by recent silt (2-sop) an B probably incorporate loessial additions (cf. Perrin, 1956).

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