Quaternary
The Quaternary period is the shortest division of time in the geological column covering only the last two million years or so of Earth’s history. It can be divided into four major phases of ice-sheet advance, (glacial), and retreat (interglacial). Many smaller cycles of advance and retreat occur within each major phase. The Quaternary can be divided into two stages, the Pleistocene - which covers all deposits between two million and ten thousand years ago, and the Holocene - encompassing deposits from ten thousand years ago to the present day.
Devensian
The most recent ice sheets to occupy the Tees Valley were during the Devensian stage when ice advanced on the area from the Lake District and Scotland in the north. Pressure from Scandinavian ice in the North Sea Basin also affected conditions locally by forcing the Scottish ice stream inland at Saltburn and Staithes.
Some landforms, such as Freeborough Hill, were sculpted as the ice-sheets carved up the original landscape as they advanced. Others, such as Cat Nab at Saltburn, resulted as the ice melted and the material it had picked up en route was dumped. Immense amounts of melt water; unable to escape in any other direction, flowed along the ice margins forming temporary lakes where the landscape allowed. Longer-lived water bodies tended to fill until they eventually overflowed, the escaping streams often cut distinctive channels which were abandoned as flow rates diminished.
The most extensive evidence of former occupation by ice-sheets are the thick deposits of boulder clay that cloak the landscape, softening its contours to heights of between 250 and 300 metres above sea level. This material has also in-filled some of the pre-Devensian features producing buried valleys, most notably at Upgang and Saltwick Bay, near Whitby.