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
Borough of Maidstone earliest in the county – that to Rochester and Chatham – was opened in 1728. In modern times, two motorways – the M2 and the M20 – pass to the far north of the borough and just north of the town centre of Maidstone respectively. The earliest line through Kent was built by the South Eastern Railway. It was not, however, built to pass through Maidstone: instead, a station was built at Paddock Wood railway station, then named "Maidstone Road", some six miles away. It was only in the period between 1844 (when that main line was connected by a