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T H E GEOLOGY OF HALL HEATH, LACKFORD H. B. MOTTRAM Hall Heath lies on the southern edge of the Suffolk Breckland where arable farming predominates. Tucked in behind Victorian deciduous woodlands is a shallow, former gravel working which is currently used as a landfill site. Centered at National Grid Reference T L 799 692, the site reaches down to the Chalk. According to the British Geological Survey (B.G.S.) this is the Upper Chalk close to its junction with the underlying Middle Chalk. The top surface of the Chalk here occurs at between +28 and +32m O.D. It is fairly flat with occasional hummocks and hollows. Some Solution pipes are known and these are infilled with either a chocolate-brown clay with black flecks or a reddishbrown, cobbly gravel. Where the infilling consists of both materials the clay tends to line the base and sides, with the cobbly gravel Alling the centre and top of the pipes. An admixture of the two materials is uncommon. The gravel is composed of flint material. Flints of cobble and boulder size are not worn and are often unbroken - characteristics which indicate minimal transportation and thus local derivation from the Chalk. It is likely that these clay and flint deposits were derived from weathering of the Chalk and soils which formed upon the Chalk, during warm and moist climates in the Tertiary to Lower Pleistocene, (Thorez, et al, 1971; Matthews, 1977).
Previous accounts of the sand and gravel At Hall Heath the Chalk is generally overlain with sand and gravel which has traditionally been interpreted as a glacial outwash deposit. Following its remapping work in the region, the B.G.S. has reaffirmed its support for this inteipretation (Hawkins, 1981; Clayton, 1983; Bristow, 1990). More recently, an interesting alternative interpretation was put forward at a quickly rearranged field meeting of the Joint Association for Quaternary Research. Examination of the composition and sedimentary structures of the sand and gravel at Hall Heath suggested that this deposit was attributable to the Ingham Sand and Gravel (Bridgland & Lewis, 1991; Hunt, et al, 1991). It was therefore reinterpreted as having been laid down by the large. pre-glacial 'Ingham' river of Lower Pleistocene age which flowed approximately eastwards hereabouts.
New evidence Later excavation in the pit at Hall Heath has revealed better exposures than previous researchers had the opportunity to see. A summary description of these is given below. The details are part of a county wide R.I.G.S. survey but must not be taken to infer any such status on the site. The 16 to 32mm fraction of the sand and gravel deposit has an average composition of 75% flinty, 23% quartzose and 2% other pebble types. The flinty component is essentially composed of angular flint while the quartzose component is mainly made up of Lower Palaeozoic quartzite. Jurassic fossils and pebbles of chalk are absent, although trace quantities of chalk pebbles are known in boreholes adjacent to the site (Hawkins, 1981). The sand fraction is devoid of chalk grains. In part, the sand and gravel passes into laminated muds and also tili (boulder clay), and these have been shown to directly overlie the
Trans. Suffolk Nat. Soc. 30 (1994)