In western Norway thick continental sediments of Devonian age are found in four basins each bounded to the east by major fault zones. Shallowly dipping fault segments previously identified as thrusts have recently been reinterpreted (Hossack 1984) as parts of a single large extensional fault. Detailed fieldwork along this structure shows it to be a classic detachment (here redefined and renamed as the Nordfjord-Sogn Detachment) similar to those described from the Basin and Range province of the western USA (e.g. Davis 1983). Most of the features attributed to a late Devonian 'Svalbardian' Solundian' orogeny are explained as related to irregularities in the detachment surface. Other possible Devonian extensional structures in southern Norway are evaluated.