 It is a small river, once past Virginia Water lake about 3–5 m wide and flows over land which is geologically between the Bagshot and London Formations, where sands and gravel overlie chalk with limited clay, described as "loamy soils with naturally high groundwater".Soils are generally around the upper reaches acid heath followed in the lower reaches by alluvium (flood plain deposits).Below Thorpe the Bourne is one of more Thames tributaries and the wider plain of surrounding land is lower lying.