Compared to the geological architecture of other European countries not exceeding a total area of 100,000km², the geology of Scotland is characterised by an unusual diversity of geological features. Due to its tectono-metamorphic complexity Scotland attracted numerous earth scientists in the eighteenth and nineteenth centuries, whose main aim was the development of theories about, on the one hand, rock formation and, on the other, metamorphic alteration of initial lithologies. Besides being the preferred target of foreign scientists, the country has also produced its own important figures in the history of geological research. In this context, James Hutton – the “father of modern geology”, after whom, for example, ‘Hutton’s Unconformity’ at Siccar Point in Berwickshire is named – has to be mentioned, but also Hugh Miller and Archibald Geikie provided valuable contributions to the enlightenment of various geological problems.
Returning to the geology of Scotland, it is possible to subdivide the country into four main geological and geographical units. The Southern Uplands, which extend south of the Southern Uplands Fault, are mainly composed of sedimentary rocks dating back to the Silurian and the Devonian. The Central Lowlands or Midland Valley, which border the Southern Uplands Fault on the north, represent a rift zone that chiefly comprises Palaeozoic rocks of both sedimentary and volcanic origin. North and west of the Highland Boundary Fault lies the Highlands and Islands, which, due to their geological diversity, can be further subdivided into two sub-units. These are the Grampian Mountains, together with the Cairngorms, which extend between the Highland Boundary Fault to the south and the Great Glen Fault to the North, and are composed of Neoproterozoic metamorphites (Dalradian metasedimentary rocks) that are intruded by Palaeozoic lavas over large areas (see the detailed geological map below). And, finally, there are the Northwest Highlands, which border the Grampians to the northwest and cover the outermost north-western margin of Scotland and which are of both Neoproterozoic (Moine metasedimentary rocks) and Archaean (Lewisian gneiss) origin. They are run through by the Moine Thrust, where the rock formations of the south were, for very long periods of time, thrust over those to the north.