South Norwood lies on the southern slopes of the Norwood Ridge which forms the southern edge of the London Basin. This line of hills runs from north-east to south-west for about three miles (5 km) and rises to approximately above sea level at its highest point. It is formed by a ridge of grey silty deposits known as London Clay, capped in places with the gravel of the Claygate Beds. Because of this gravel working was an important local industry and at one time the road along Beulah Hill was called Gravel Pit Road. South Norwood Hill is the most southerly spur of this ridge and the London Clay extends at its foot to the southern edge of the South Norwood Country Park. Here a brook marks the junction with the sands and gravels of the Blackheath Beds that rise to Shirley, Addington Hills and Croham Hurst. Streams join Chaffinch Brook and the Beck to form the River Pool, which eventually flows into the River Ravensbourne.