Ancestral Thames

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In central and southern Britain, during the Early and Middle Pleistocene, two rivers drained Britain, the Bytham River and the Thames. For most of Early Pleistocene, the ancestral Thames was the main river with, at its maximum extent, a catchment area that extended into Wales, and across East Anglia, and what is now the North Sea, to join the ancestral Rhine. Initially, the Bytham River was a tributary of the Thames, but progressively, extended its catchment and became the major river of Southern Britain. During the Anglian glaciation, the Bytham river disappeared, and the Thames was diverted to its present route to London.

During the early Ice Age the Thames flowed to the north of London, through north Essex, Suffolk and Norfolk and out across what is now the southern North Sea to become a tributary of the Rhine. At that time, the Thames, and its tributaries, would have been a huge river system draining the Welsh mountains and bringing their characteristic volcanic rocks into the Thames basin. The evidence for this being a substantial thickness of what is called Kesgrave Sands and Gravels which represents the actual bed of the river. These old Thames gravels contain a variety of unusual pebbles from as far away as North Wales, proving that.

These gravels also contain large boulders of puddingstone and sarsens, which are very hard conglomerates and sandstones respectively. They are believed to be derived from pebble and sand seams in the Reading Beds, and which have subsequently become cemented by quartz. They have been put to use by man as ancient way markers at road junctions. The gravels have great commercial value and are worked in numerous gravel pits between Harlow, Chelmsford and Colchester, which was the route of the ancestral Thames at least 600,000 years ago.

During this time the River Medway flowed north across east Essex to join the Thames near Clacton, leaving behind a ribbon of distinctive gravel which can be found between Burnham-on-Crouch and Bradwell-on-Sea. There were also other northward-flowing tributaries of the early Thames. Evidence of these are the patches of gravel that are found on the tops of the hills in south Essex, such as the Langdon Hills, Warley and High Beach in Epping Forest.

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