An Ice Age is made up of a series of both cold periods, known as glacials, and warmer periods, known as interglacials. As the ice eventually receded at the beginning of the next interglacial stage, which geologists refer to as the Hoxnian Stage, the landscape of Essex bore some resemblance to that of the present day. The Stour, Colne, Chelmer, Blackwater and Crouch rivers followed roughly their present courses, but the Medway joined the Thames at Southend and the combined river continued north-east across what is now the coast of east Essex to join the Rhine.
There is nothing to indicate that glaciers ever covered Essex again, but there were several very cold periods. Changes in sea level and climate affected the rivers and coastal flood plains, leading to the creation of gravel terraces. This sequence of terrace deposits contains a wide variety of human artefacts and environmental data rendering it crucial to our understanding of the Palaeolithic in Britain. At Clacton the deposits from the former channel of the River Thames have revealed a wealth of worked flints, animal remains and a spear, the oldest wooden artefact from Britain. The spear dated to about 408,000 BC and was made of yew; other complete spears of a similar date have recently been found at Schonigen, Germany. The animal remains included horse, rhinoceros, fallow and red deer, Bos or bison, giant beaver, straight-tusked elephant, lion, pig and numerous small mammals.
During the Mesolithic period, from about 10,000 years ago, most of lowland Britain was covered by a succession of forest types with breaks in the canopy around rivers and lakes. A number of important Mesolithic sites survive as submerged land-surfaces in the Crouch and Blackwater estuaries and at Stone Point, Walton-on-the-Naze. Analysis of the remains of ancient pollen found on the site indicates that these locations were at the time well wooded dryland slopes bordering freshwater rivers, with oak and lime the dominant trees.