Table 1

. Description of the soils and stratigraphic units around Horndean

UnitPeriodEpochDescriptionNotes
Made or worked groundQuaternaryHoloceneRemnants of A3(M) construction. Likely to be soft varicoloured slightly silty clay with occasional gravel, chalk, brick, plastic and metalVariable extent and thickness, adjacent to A3(M)
HeadQuaternaryPleistoceneVariable deposits of sandy silty clay, locally gravelly, chalky and flinty in dry valleys. Poorly sorted and poorly stratified deposits formed mostly by solifluction and/or hillwash and soil creep. Composition depends on upslope source and distance from sourceVariable extent and thickness across lower ground and within sinkholes
Head GravelQuaternaryPleistoceneVariable deposit of clayey gravel derived locally from older gravel-rich deposits. Formed mostly by periglacial solifluction or gelifluction but may include hillwash or soil creepPresent on Hazelton Farm
Reading FormationTertiaryPalaeoceneDominantly clay, mottled by pedogenetic processes in a humid environment. Red hues dominate with a more or less equal proportion of blue–grey and brown. The proportion of sand beds varies greatly, and may constitute more than half the formation, dominantly in the basal part. Thickness is 0–12 m locallyPart of Reading Beds under traditional nomenclature. Now regarded as the upper member of the Lambeth Formation
Upnor FormationTertiaryPalaeoceneFine- to medium-grained sand and clayey sand with variable amounts of glauconite grains of fine to medium sand grade and sporadic beds of well-rounded flint gravels. Of variable extent, generally <3 m thickKnown as Basement Beds (of the Reading Beds) under traditional nomenclature. Not differentiated on BGS maps but invariably present beneath Reading Formation
Tarrant Chalk MemberCretaceousCampanianSoft white chalk with relatively widely spaced joints and large flint seams. Surface weathering and residual clay-with-flints common beneath cover depositsPart of Upper Chalk under traditional nomenclature. Now regarded as a member of the Culver Chalk Formation of the White Chalks
  • Sources: British Geological Society Lexicon of Named Rock Units (www.bgs.ac.uk/lexicon/lexicon_intro.html); Rawson et al. (2001); Miles (2003); Hight et al. (2004).