A drainage divide, water divide, ridgeline, watershed, water parting or height of land is elevated terrain that separates neighboring drainage basins. On rugged land, the divide lies along topographical ridges, and may be in the form of a single range of hills or mountains, known as a dividing range. On flat terrain, especially where the ground is marshy, the divide may be difficult to discern. A triple divide is a point, often a summit, where three drainage basins meet. A valley floor divide is a low drainage divide that runs across a valley, sometimes created by deposition or stream capture. Major divides separating rivers that drain to different seas or oceans are continental divides. The term height of land is used in Canada and the United States to refer to a drainage divide. It is frequently used in border descriptions, which are set according to the "doctrine of natural boundaries". In glaciated areas it often refers to a low point on a divide where it is possible to portage a canoe from one river system to another. Drainage divides can be divided into three types: Continental divide in which waters on each side flow to different oceans, such as the Continental Divide of the Americas and the Congo-Nile Divide. Major drainage divide in which waters on each side of the divide never meet but flow into the same ocean, such as the divide between the Yellow River basin and the Yangtze. Another, more subtle, example is the Schuylkill-Lehigh divide at Pisgah Mountain in Pennsylvania in which two minor creeks divide to flow and grow east and west respectively joining the Lehigh River and Delaware River or the Susquehanna River and Potomac River, with each tributary complex having separate outlets into the Atlantic. Minor drainage divide in which waters part but eventually rejoin at a river confluence, such as the Mississippi River and the Missouri River drainage divides. A valley-floor divide occurs on the bottom of a valley and arises as a result of subsequent depositions, such as scree, in a valley through which a river originally flowed continuously.