Genesis of the Palaeozoic Belts (redrawn from Fig. 3 in Choubert (1935). Prehercynian Orogeneses: I.- Upper Cambrian and Lower Ordovician. II.- Upper Ordovician, Laurentian Continent (Taconic Belt). Middle and upper Ordovician, Baltic Continent. III − Upper Gothlandian (Caledonian Belt). Post-Downton, Laurentian Continent. Ante and post-Downton, Baltic Continent. IV.- Upper Devonian (Acadian Belt). Hercynian Orogeneses: V.- Upper Dinantian (Sudete Phase). VI. − Upper Westphalian (Main Hercynian Phase). VII. − Stephano-Permian (Appalachian Phase). VIII. − Sketch to refer to the main map. Grey lines: boundaries of the Precambrian continental masses (Situation at the beginning of the advance). Black regular lines: boundaries of the Precambrian continental masses (New situation, at the end of each advance). Thin regular lines: boundaries of the Precambrian continental masses that are not possible to specify today. Pale blue hatching: emerging geanticlines, or Precambrian sialic thresholds. Black: already formed geanticlines. Pale green: previously formed belts. (Sketches IV-V-VI-VII). Brown: Precambrian continental masses. Dashed: geographical outlines. (VIII.) It is obviously impossible to specify the amplitude of the displacements of the continental masses. We simply attempted to represent them by indicating the new position of continental masses with respect to their previous situation. Thus, the new position of a continental mass becomes the previous position in the following sketch. L: Laurentia; B: Baltica; G: Gondwana; CB: Caledonian Belt; AB: Acadian Belt