Summary. Pollen, plant macrofossils and Mollusca suggesting a mid-Ipswichian age are described from a clast of detritus mud found in gravels underlying the floodplain of the River Kennet at Thatcham, Berkshire. The clast of fluvial mud contained rich fossil assemblages giving evidence of deciduous forest habitats and fens, besides conditions within the river. Non-marine Mollusca from a sample of clay-silt from the interglacial site at Sandy Lane, Aveley are described. Thirteen species are added to the published list of Mollusca. Among these additions, Pseudamnicola confusa is important in providing the first evidence from the site of slightly brackish conditions. The fauna as a whole is similar to fluvial faunas of Ipswichian Interglacial age.