Kent coastline of Kent is continuously changing, due to tectonic uplift and coastal erosion. Until about 960, the Isle of Thanet was an island, separated by the Wantsum channel, formed around a deposit of chalk; over time, the channels silted up with alluvium. Similarly Romney Marsh and Dungeness have been formed by accumulation of alluvium. Kent's principal river, the River Medway, rises near East Grinstead in Sussex and flows eastwards to Maidstone. Here it turns north and breaks through the North Downs at Rochester, then joins the estuary of the River Thames as its final tributary near Sheerness. The Medway is
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