The present memoir is the final report of a geological mapping project which has been executed by staff and students of the Department of Structural Geology of the Geological Institute of Leiden University. The project was initiated by professor Dr. L.U. de Sitter, to whom this memoir is dedicated. In the first instance this project was intended as a field training program for undergraduate and M. Sc. students, but at the same time many important contributions to the geological knowledge of this mountain chain were obtained by these students, by Ph. D. students and by staff members.