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
Zumbro River The South Fork Zumbro River, long, rises about east of Hayfield in southern Dodge County and flows generally eastwardly into Olmsted County, where it turns northward at Rochester and flows into southwestern Wabasha County. The South Fork's course through Rochester has been channelized as part of a flood control project. It is dammed in Wabasha County, by the Lake Zumbro Hydroelectric Generating Plant to form Lake Zumbro. The Middle Fork Zumbro River, long, rises in northeastern Steele County, about west of West Concord and flows generally eastwardly through northern Dodge, southwestern Goodhue and northeastern Olmsted counties, past Pine Island and