Silurian in age, the Caledonian orogebic belt extends from Wales and on to Scottish Highlands, the Caledonia, the Celtic term from which ir derives its name. The orogenic belt is much more comples in its structural and tectonic history in Norway and Sweden and part of Rumania. It was in Sweden and Norway that the ideas of diapiric granitic emplacement were born as was the strain determination work by Hossack on Bygdin conglomerate. The hypothesis of gravitational spreading of nappe piles also evolved in this belt and this orogen can be considered as the cradle of theoretical development of structural geology. The studies on theoretical and experimental modeling were strongly supported by classic sections of natural structures in their progressive evolution.