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
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