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
Bell-Irving River and the headwaters of the Unuk River, which flows southwest to the sea near Ketchikan, Alaska, and the Bear River, which flows south to the head of Portland Canal at the community of Stewart, British Columbia. From its source the Bell-Irving River flows generally south through mostly mountainous terrain. It is joined by Craven Creek, then Rochester Creek. The Yukon Telegraph Trail follows Rochester Creek and part of the Bell-Irving River. The Yukon Telegraph line, also called the Dominion Telegraph, grew out of part of the earlier, failed Russian–American Telegraph, and connected Ashcroft, BC, to Dawson City, Yukon. The telegraph