I. INTRODUCTIONThrough the study of the Ordovician stratigraphy and palaeontology of N China made by A. W. Grabau, Y. C. Sun and F. F. Mathieu, major stratigraphic subdivisions were established. In 1922, Grabau made an extensive study of the Ordovician fossils of N China, chiefly cephalopods from the Machiakou limestone. In 1935, Sun published a monograph On the