This leg of our journey takes us across the broken soft strata of the generations of tiny sea shells that lived right here capturing carbon and calcium for millions of years sinking to the bottom of their warm sea before the climate changed and extinguished them to be buried under the mud of some newer lives in very different seas. Where we start this leg the rivers flow back down south to London but by the time we finish we have joined the springs and brooks that flow north, with us, and on past Cambridge to the sea.

 We are walking over the broken edge of the thick dish of chalk that now contains the clay of London. Over millions of years whilst the dinosaurs roamed the land, the microscopic sea life that was here dropped dead day be day like the algae blooms still are in the seas around us today. The chalk was up to 200 metres thick here by the time the asteroid struck and the dinosaurs went making way for us mammals and the sea level dropped and clay started washing down from nearby land and dropping on the sea bed instead, before the whole of southern england was gradually buckled as the drifting continent of Africa pushed up and made the alps

Milestones - Leg 4

Soar over us mile by mile as we head onwards, by selecting each image