One of the most prominent features of an ice-eroded region is the formation of a number of basins scoured out of the bedrock by the ice and rock frozen into it. When the ice has retreated these basins usually fill up with water, thus forming lakes, and Windermere appears to occupy two small basins scoured out of the floor of a valley which extends to the south as far as Cark, where it joins the coastal plain. It is, therefore, difficult to explain why the natural outflow of the lake should be through the Leven valley, a gorge extending from Newby Bridge to Haverthwaite, instead of through this broad valley which must have existed when the lake was formed (see map).