The origin and early history of the upper Thames

Abstract

The earliest gravel unit of the middle Thames is earlier than any yet recognised in the upper Thames basin. Its pebble-content nevertheless suggests deposition at a time when the upper Thames already existed, draining outcrops of Lower Cretaceous rocks and passing southwards through an ancestral Goring Gap. The next oldest middle Thames gravels contain Triassic pebbles from the Midlands. The third oldest unit in the succession is represented in the upper Thames basin itself. Its composition shows that the Thames headwaters now included a stream from North Wales, perhaps also an outwash stream from an Irish Sea glacier; its distribution shows that the river already flowed down an ancestral Evenlode valley. The extension of the drainage area is tentatively ascribed to a combination of glacial diversion and river capture.