The essays in this volume have developed from the proceedings of Section 27 of the International Geological Congress, held at Rio de Janeiro in August 2000. At that meeting - with a view to the arrival of the end of the second millennium - a symposium was held on 'Major Contributions to
Geology in the Twentieth Century', organized by Dr Silvia Figueiroa, Professor Hugh Torrens, and myself, in our capacity as Members of the IUGS's International Commission on the History of Geological Sciences (INHIGEO), which was responsible for organizing the symposium.