About 730 million years ago an ancient continent began to split apart as the Iapetus Ocean was born. Layer upon layer of sands, silts and iron and aluminium rich muds were deposited in marine basins within the continent. ?When the Iapetus Ocean closed between 480 and 390 million years ago to form Euramerica the continents on either side collided and were forced upwards to build an enormous mountain chain which would have been similar in size to the Himalayas. The remains of this Caledonian mountain chain can be traced from North America through Greenland, Ireland, Scotland and Scandinavia and form the spine of Shetland today. The sands, silts and muds were metamorphosed to form the metamorphic rocks of the Dalradian Supergroup which make up much of Shetland’s Central Mainland and the western part of Unst as well as most of the Central Highlands of Scotland. Shetland’s Dalradian rocks - psammites, schists, quartzites and limestones - were originally laid down horizontally but were tilted up almost vertically ?Between 450 and 350 million years ago rocks melting in the roots of the mountain chain generated a magma that forced its way up into the colder crust to solidify below the surface into granitic bodies called plutons. These plutons were later exposed on the surface of the Earth through tectonic uplift and the erosion of the overlying rocks. Much of Northmavine was formed in this way, including Shetland’s highest point Ronas Hill.