Geology of Kent to uplift, sedimentation, and marine erosion. The Isle of Thanet was till recently (AD 960) an island, formed around a deposit of chalk. 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 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
River Esk, Dumfries and Galloway River Esk, Dumfries and Galloway The River Esk (), also called the Border Esk, is a river in Dumfries and Galloway, Scotland, that flows into the Solway Firth. It also flows for a small way through the English county of Cumbria before entering the Solway. The river rises in the hills to the east of Moffat and its two main tributaries, the Black Esk and the White Esk, merge at the southern end of Castle O'er Forest. It flows south east through Eskdale past Langholm before merging with Liddel Water (which defines the border between Scotland and England. Before passing