Geographic location: The site is located approximately 90 metres above sea level to the east of the River Gade on the north west bank of the Colne valley. The gravels deposited by the Thames form a series of gently sloping river terraces along the earlier course of the river through the Vale of St. Albans. Younger terraces occur at successively lower levels.

Stratigraphy: There is some disagreement about the date of the gravels laid down in the vale of St. Albans which the Colne forms part of. Some date them at around 475,000 years ago, but most appear to support Bridgland who places the nearby Gerrards Cross gravels with Oxygen Isotope 21 or earlier i.e. preceding the Cromerian complex.

The gravel here appears to be the same as that at Chorleywood i.e. contemporaneous with the Winter Hill gravels. The majority of lithics recovered from this site have been from the top perimeter of the sand and gravel layer (layer 3 in photo to left). The hypothesis is that the tools and sculptures were made between cold periods i.e. during the Cromerian, possibly abandoned upon the advancement of the Anglian glaciation.

Geology: From 130m above sea level these terraces where formed from gravel deposits of the proto-Thames dating from a period (Pleistocene) when it flowed north-eastwards toward the primeval Rhine rather than the present course through London. The site is marked A1 in the map (top left).

Around 475,000 years ago the Anglian glaciation heralded the arrival of glaciers from the North Sea reaching as far south-west as Bricket Wood. The path of the proto-Thames was blocked by a mass of ice near Hatfield causing a pool to build up to the west around St.Albans. Finally the water eventually broke through near Staines cutting the present day course of the Thames through central London. The Colne reversed direction becoming a tributary to the modern Thames. In later cold stages of the Quaternary loess (powdered rock) was deposited by wind throughout the area forming thin layers between one and three feet deep forming the top soil renowned for its' agricultural value.

References:

Bridgland D. R., 1994,The Quaternary record of the River Thames.

http://www.hertsgeolsoc.ology.org.uk/IntroToHertsGeology.htm

http://www.bgs.ac.uk/