The Spanish region of Galicia is situated in the extreme north-western part of the country due North of Portugal and West of Asturias. It is bordered by the Atlantic Ocean to the West and by the Bay of Biscay to the North (see fig. 1). The area under investigation concerns the western provinces of La Coruña and Pontevedra mainly. Apart from early reconnaissance work by Schulz (1858), Barrois (1892), Sampelayo (1922), Lotze (1945), Carlé (1945), Navarro and del Valle (1959) the area is at present being investigated and mapped on a scale of 1:50.000 by López de Azcona, Parga Pondal and their associates for the Instituto Geológico y Minero de España. So far nine sheets and explanatory memoirs have been published between 1948 and 1956. Parga Pondal has also published a geological sketch map on a scale of 1:400.000 and an explanatory note of the province of La Coruña in 1956, and since 1931 he has contributed substantially to the knowledge of Galician geology in a series of papers concerning petrological, mineralogical, tectonic and sedimentological aspects of it. Between 1955 and 1959 de Sitter and Zwart conducted geological research by the Department of Structural and Applied Geology of the University of Leyden in the area between Lage and Malpica. Summaries of their results appeared in 1955 and 1957, while one of their associates, Insinger, published a short account of his work in the vicinity of Mugía in 1961.