The structure of the southern slope of the Cantabrian Mountains: explanation of a geological map with sections scale (1 : 100.000)

Since 1952 the Geological Department of the Leiden University has carried out the geological mapping of the southern slopes of the Cantabrian Mountains in the provinces of Palencia and León in northern Spain, slowly progressing from east to west. Our interest has been centred almost exclusively on the Palaeozoic rocks. Untill recently very little was known or published about this part of the Cantabrian Mountains. Quiring, 1939, had given some provisional maps, the 1 : 400.000 Spanish maps gave only the broadest of outlines and the survey by Comte dating from before the war was not published until 1959, when our mapping had already covered the same territory. The stratigraphic sequence of the Paleozoic extends from the earliest Cambrian, resting on some Pre-Cambrian (de Sitter, 1961b), up to the highest Carboniferous. The Lower Palaeozoic, Cambrian to Silurian, crops out only in the western portion of the map and has a rather uniform development, described adequately by Comte, 1959, and further details of the Cambrian by Lotze and Sdzuy, 1961. Devonian outcrops occur scattered over the whole map area, and are of particular interest to stratigraphers because of their rich fauna (Comte, 1959, Kullman, 1960). The Devonian is less uniform than the older formations and shows variations indicating its development in well defined separate areas. Comte (1959) gave an excellent description of the rocks of the Bernesga-Esla zone. The development of the Carboniferous sequence is very variable due to several distinct folding periods of varying intensity (de Sitter, 1961a) and its stratigraphical development is still doubtful in many areas.