CHALK RAFTS IN ANGLIAN TILL IN NORTH HERTFORDSHIRE

Recent mapping has confirmed the presence, and for the first time demo nstrated the full extent, of large bodies of displaced chalk associate d with till on the scarp south of Royston. A simple model for the empl acement of these chalk rafts (schollen) within Anglian (Lowestoft) til l against the northward-facing scarp formed of Upper Chalk is proposed . An early compressional ice environment encouraged the entrainment of large rafts of the hard nodular Chalk Rock which were incorporated in to the base of the advancing Anglian ice sheet spreading out from the Wash area. This heavily laden ice stagnated, as it impinged on a secon d scarp feature and was overridden by ice without significant chalk ra fts. Subsequent wasting of the Lowestoft ice sheet created an environm ent within which normal faulting and down-scarp slumping of the rafts occurred.