County Donegal in Ulster has one of the most complex geologies in Ireland. Much of the county is underlain by Precambrian gneiss, schist and quartzite, laid down during the Grenvillian Orogeny 700 million years ago. The Border Region's highest point, Errigal, at 751 m (2,464 ft), is composed of Precambrian quartzite. Ireland's oldest rocks, laid down 1.78 billion years ago, are found on the island of Inishtrahull. Inishtrahull is Ireland's most northerly island, located approximately 10 km north of Malin Head, mainland Ireland's most northerly point. Lough Swilly in Donegal is one of Ireland's three fjords. Owing to its scenic and rugged landscape, Donegal was named National Geographic's Coolest place on the Planet in 2017.