Several persons have helped in compiling maps and texts, others have provided vital information. Their assistance is gratefully acknowledged. Among the overseas contributors I wish to mention especially Prof. D. J. de Laubenfels (Syracuse, U.S.A.) and Mr. D. E. Symon (Adelaide, Australia). Major contributions from inside the institute were provided by Dr. R. D. Hoogland, Miss Wanda Avé, and Messrs. N. A. P. Franken, M. E. Jansen and M. C. Roos.