Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A mountain range is a chain of mountains bordered by highlands or separated from other mountains by passes or valleys. Individual mountains within the same mountain range do not necessarily have the same geology, though they often do; they may be a mix of different orogeny, for example volcanoes, uplifted mountains or fold mountains and may, therefore, be of different rock. The Himalaya Range contains the highest mountains on the Earth''s surface, the highest of which is Mount Everest. The world''s longest mountain range is Ocean Ridge, which runs on the seafloor of five oceans around the world; it has a length of 65,000 kilometres (40,400 mi), and the total length of the system is 80,000 kilometres (49,700 mi). The Andes is the world''s longest mountain range on the surface of a continent; it is 7,000 kilometres (4,300 mi) in length. The Arctic Cordillera is the world''s northernmost mountain system and contains the highest point in eastern North America.