Gravels of the River Thames as a guide to Pleistocene catchment changes

Variability of composition and of pebble shape in river gravels are discussed. Catchment changes, progressive down-valley changes and less systematic cross-valley effects are recognized as sources of variability. Intercomponent ratios and pebble shape are analysed in the Pleistocene gravels of the Thames and its tributaries between High Wycombe and Hertford in England, and evidence of catchment change is identified. Glaciation on one or more occasions in the upper catchment of the Thames in the pre-Anglian Pleistocene is suggested to explain the high frequencies (>50 per cent) of far-travelled material in pre-Anglian gravels. The pattern of drainage development in the Vale of St. Albans at the time of the Anglian glaciation is also discussed