Picture a treeless landscape, almost bare hillsides covered with chalk rubble, the river 25 metres (80 feet) below you, the sea far to the south in the Channel, a mean annual temperature of well below freezing, and the only sign of life herds of bison and reindeer! The little cliff face by the layby on the concrete road carries evidence of just such a time.

The South Downs in the Last Glaciation had a very cold climate, and only the surface 1.6 metres (five-and-a-half feet) thawed out when the summer temperature rose above freezing point. The alternate freezing and thawing shattered and loosened the surface chalk and this moved downslope like a thick porridge with the onset of meltwater from the snow. The process, which acted on slopes as low as 1 degree, is known as solifluction and the material which sludged downslope is locally called Coombe Rock. This is found in and named after, the hollows or Coombes which are particularly evident along the steep north-facing scarp of the South Downs and give them their characteristic crenulated shape. On the Park Coombe Bottom, which can be seen from the layby on the concrete road, is an isolated example.

At the base of the vertical part of the bank, there are pieces of chalk and flint set in a series of U-shaped involutions which is possibly a section of a honeycomb-like structure. Within this there are fragments of chalk in a fine pasty-looking mud. This is Coombe Rock which has been dated to around 10,000 B.C., and the chalk involutions, younger by about 1000 years, resulted from frost-heaving of the surface during the very last throes of the Ice Age. The dark looking soil above is of Post-Glacial age and the light brown chalky hillwash, although largely derived from soliflucted material and windblown silt, (brickearth or loess), was laid down in its present form in recent times and is probably associated with the formation of the lynchet above.