The Geology of the Area

Extract

Mr B W Conway of the Institute of Geological Sciences has kindly made the following comments on the geology of the site:

“The causewayed enclosure is sited on the eroded terminal surface of the gravel train of the Upper Floor Plain Terrace at the junction of the Coinè and Thames river valleys (see OS 6 inch geological maps Buckinghamshire 56 SE, 58 NE and Middlesex 19 NE and SE (and Fig 2)). The late Professor Zeuner traced the profile of this terrace and claimed that it grades into the Late Monasirian sea level (7.5 metres) of the latter part of the last interglacial. The Coinè valley Flood Plain joins that of the Thames at Wraysbury and projects into the Thames as a distinct, slightly raised, delta. This delta was formed by the piling up of aggradation by the Coinè beyond the capacity of the Thames to remove it. The presence of this delta was the cause of the breaking up of the Coinè into a series of distributory channels: mainly those of the River Coinè, the Coinè Brook and Wyrardisbury River. These in turn eroded the Cclne delta and the Flood Plain gravel train. Erosion by the several distributory channels left slightly elevated gravel ridges between their valleys and clays, peats, and silts accumulated in these valleys. The eroded remnants of the delta and the Flood Plain Terrace appear as low “islands” of gravel between marshy stream valleys. The Staines causewayed enclosure is sited on the southern tip of the largest of these islands, which is approximately 4km long, has an average width of about 0.4km, and an area of approximately 182.lha.”