Prior to the Anglian glaciation, a "proto-Mole-Wey" river was flowing northwards from the Weald and North Downs, through the "Finchley depression" and Palmers Green, to join the proto-Thames somewhere around Hoddesdon, at what is today an altitude of around 60 metres.
Prior to the Anglian ice age, a pre-Mole-Wey river flowed northward from the Weald and North Downs through the Finchley depression and Palmers Green, eventually merging with a pre-Thames river near Hoddesdon, now situated at about 60 meters above sea level.