Geography of Kent and Dungeness have been formed by accumulation of alluvium. Kent's principal river, the River Medway, rises near Edenbridge and flows some 25 miles (40 km) eastwards to a point near Maidstone, when it turns north. Here it breaks through the North Downs at Rochester before joining the River Thames as its final tributary near Sheerness. The river is tidal as far as Allington lock, but in earlier times cargo-carrying vessels reached as far upstream as Tonbridge. The Medway has captured the head waters of other rivers such as the River Darent. There are other rivers in Kent, most notably the
Maidstone Tunbridge Wells, Ashford and Tenterden. Most services are operated by Arriva and some operated by Nu-Venture. Stagecoach also operates route 10X in the town to Ashford via Lenham, with most buses continuing onto Hythe and Folkestone. There are weekday commuter coach services between Maidstone and London. Former bus operators in Maidstone include Maidstone & District Motor Services (M&D); Maidstone Borough Council Transport, later Boro'line Maidstone; and Bygone Buses. In 2004 the centenary of Maidstone Corporation Transport was marked with several events, featuring a preserved Maidstone trolleybus. When the railways were built in the 1840s, Maidstone was not well served. It