discovered and where the importance of large scale horizontal rather than vertical movements became apparent. Detailed mapping of the Moine Thrust Belt by the survey continued for another two decades, culminating in the classic survey memoir The Geological Structure of the North-West Highlands of Scotland, published in 1907. Caledonian structure The Moine Thrust Belt was formed during the late stages of the Caledonian Orogeny as part of the collision between Laurentia and Baltica. It is the most westerly Caledonian structure in Scotland apart from the Outer Isles Fault in the Outer Hebrides, which is developed within the Hebridean Terrane. The Moine Thrust Belt defines the boundary between the Hebridean Terrane to its northwest and the Northern Highlands Terrane to its southeast. The thrust carried metamorphic material over 200 km across Scotland entirely masking the geology of the previous terrane. However, small windows, such as the Assynt window and the Glen Achall imbricated thrust system, allow geologists to estimate what the geology of Scotland was like before the Caledonian Orogeny. The relationship between the Moine Thrust Belt and other Scandian age structures in Scandinavia and East Greenland remains unclear, due to uncertainties associated with the Great Glen Fault zone. This major sinistral (left-lateral) strike-slip fault was also active during the late stages of the orogeny, but continued to move during the early Devonian and appears to truncate the southern end of the thrust belt. The total late Caledonian displacement on the Great Glen Fault is poorly constrained, making reconstruction of the southern part of the orogenic belt difficult. Involved rock units The stratigraphic sequence of the footwall of the Moine Thrust is the full sequence characteristic of the Hebridean Terrane. Lewisian complex The Lewisian complex consists of mainly granitic gneisses that are of Archaean and Paleoproterozoic age. They form the basement to both the Torridonian Supergroup and the Moine Supergroup of the Northern Highlands Terrane, in the hanging wall of the Moine Thrust. Torridonian The Torridonian Supergroup is of Neoproterozoic age and consists mainly of sandstone with a maximum preserved thickness of over 8 km. It is divided into three groups, the Stoer, Sleat and Torridon groups. The unconformity at the base of this unit is highly irregular, showing that it was deposited on an eroded land surface. Lower Palaeozoic The Cambrian to lower Ordovician rocks consist of two groups, the Ardvreck Group and the Durness Group. The Ardvreck Group lies