This compilation of stratigraphic and structural data accompanying the (re)issue of the 1:50000 sheets completes the project initiated by Prof. L.U. de Sitter in 1950. The total area mapped comprises about 400 km² in a strip more than 150 km from east to west. This part of the Hercynian tectogene is characterized by a very consistent sequence of Palaeozoic shelf sediments only interrupted by syn- to late-orogenetic flysch-molasse development. Neither of these sequences lend themselves to a simple geosynclinal model. Only the suprastructures of the orogene are exposed here; essentially decollement thrusting and folding. Fold and thrust vergences vary through 180° giving the centripetal pattern of the well-known Knee of Asturias. Very minor amounts of igneous rock have been mapped although activity in some form has been registered throughout most of the systems represented. The degree of metamorphism is so slight to have been negligible for the mapping.