1. Geological Survey, Mail Stop 404, Federal Center, Denver, CO 80225
2. Institute of Geological Sciences, Polish Academy of Sciences, 31-002 Krakow, Senacka 3, Poland
3. Geotechnical Institute, Federal Testing and Research Institute-Arsenal, Faradayg, 3, Post Office Box 8, A-1030 Vienna, Austria
4. Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario, Canada K1A OE8
5. U.S. Geological Survey, Mail Stop 963, Federal Center, Denver, CO 80225