The study of Devonian sediments is taken as a starting point in the analysis of late orogenic movements in the Caledonian-Appalachian mobile belt. It is assumed that this belt drifted apart after the Devonian Period.

The sedimentary sequences of 14 main Devonian outcrop areas, from Spitsbergen on the north to New York State on the south, provide evidence of times of deposition and erosion, in marine or nonmarine environments, and rates of sediment accumulation.

The Old Red landmass grew southeastward in late Silurian and Early Devonian times in Scandinavia and Britain. Later in the Devonian, it grew westward in the Appalachians. These times of growth were coincident with the main Caledonian and Acadian phases of deeper crustal mobility.

The geometry of movement of individual basins within the Old Red landmass is analyzed by use of paleocurrents, facies variation, provenance of sediments, and thickness variations.

A distinction can be made between well-defined, relatively small, intermontane basins, and the commonly much larger, extramontane basins. The extramontane basins characterize both flanks of the landmass, whereas intermontane basins are typical of the central and northern parts. Basin mobility, as indicated by rapid downwarp rates, characterized most of the landmass during Silurian and Early Devonian times. Great mobility was restricted to East Greenland, western Norway, and northeastern Scotland during the Middle Devonian, and to the Appalachians during the Late Devonian.

Basin movement generally reactivated folding along trends already present in the basement. Graben faults were generally postdepositional. Rapid downwarp in one area, indicated by thick basin fills, commonly was followed by rapid subsidence nearby--but not on the site of the earlier basin.