In the tideway the principal affluents of the Thames are the Brent at Brentford, the Wandle at Wandsworth, the Ravensbourne at Deptford, the Lea at Blackwall, the Darent just below Erith, and the Ingrebourne at Rainham, besides the Medway.
Navigation is also carried on by the Medway to Tonbridge, on the lower parts of the Darent and Cray, from Dartford and Crayford, and on the Wey up to Guildford and Godalming.
In the west the Darent, flowing north to the Thames below Dartford, pierces the hills north of Sevenoaks, but its waters are collected chiefly from a subsidiary ridge of the Downs running parallel to the main line and south of it, and known as the Ragstone Ridge, from 600 to 800 ft.
The principal orchard districts are the valleys of the Darent and Medway, and the tertiary soils overlying the chalk, between Rochester and Canterbury.
Among the principal modern industries are paper-making, carried on on the banks of the Darent, Medway, Cray and neighbouring streams; engineering, chemical and other works along the Thames; manufactures of bricks, tiles, pottery and cement, especially by the lower Medway and the Swale.
DARTFORD, a market town in the Dartford parliamentary division of Kent, England, on the Darent, 17 m.