1. Department of Earth and Planetary Systems Science, Faculty of Science, Hiroshima University, Higashi-Hiroshima 724, Japan
2. Sumikawa Hydrological Institute, 4-14 Hiramatsu-cho, Nishinomiya 662, Japan
3. Faculty of Education, Gifu University, Gifu 501-11, Japan
4. Geological Survey of Japan, Tsukuba 305, Japan