Geology Site Account

Historical site only. Excavations for the Weeley Heath bypass in 1994.

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Deposits that appear to have been laid down by the River Medway were exposed in 1994 in a cutting excavated for the A133 Weeley Heath bypass. Although marked on the geological map as Wivenhoe/Cooks Green Gravel, the sediments proved to be mainly fine-grained deposits indicating slow moving water. These included organic deposits containing plant fossils and pollen which are currently being studied. Beneath the organic sediments, at the base of the cutting, was a gravel containing soft, local rocks such as claystone nodules and even pieces of London Clay. Such non-durable rocks are extremely rare in cold-climate gravels that make up the major part of all river terraces in Britain and it is therefore clear that these sediments are very different from what would normally be expected.

Studies of samples taken from the gravel above and below the organic deposits revealed that some layers were poor in Medway-derived pebbles and others were strongly dominated by Medway material. The implication of this is that at the time the gravel was laid down the confluence between the River Medway and the River Thames was very close by, so that the poorly mixed deposits of both rivers occur at this site and the variations are due to changes in the flow of each river.

The result of research at this site suggest that the basal gravel at Weeley Heath, and perhaps the fine-grained sediments that overlie it, were laid down in a channel of the River Medway upstream from its confluence with the Thames. The nature of the gravel, and the fact that it contains plant fossils, suggests that it is of interglacial origin.