 The city is on the River Stour or Great Stour , flowing from its source at Lenham north @-@ east through Ashford to the English Channel at Sandwich . The river divides south east of the city , one branch flowing though the city , the other around the position of the former walls . The two branches rejoin or are linked several times , but finally recombine around the town of Fordwich , on the edge of the marshland north east of the city . The Stour is navigable on the tidal section to Fordwich , although above this point canoes and other small craft can be used . Punts and rowed river boats are available for hire in Canterbury . The geology of the area consists mainly of brickearth overlying chalk . Tertiary sands overlain by London clay form St. Thomas 's Hill and St. Stephen 's Hill about a mile northwest of the city centre . 
