The author wishes to express his gratitude to Professors J. T. liyama, S. Aramaki, I. Kushiro, S. Takenouchi, H. Shimazaki, Y. Nakamura, and Dr. N. Shikazono of the University of Tokyo and Dr. M. Takahashi of Ibaragi University for their advice and many stimulating discussions during the course of this study.

He is grateful to Dr. A. Kato of the National Science Museum for his advice on miner-alogy, Professors T. Fujii and Y. Kajiwara of the University of Tsukuba for their help in using the Kappameter KT-3, Mr. H. Haramura of the University of Tokyo for his guidance in wet chemical analysis of ferric iron, late Professor K. Nagashima and Dr. I. Nakai of the University of Tsukuba for their help in ICP analysis, Mr. S. Nakano of the Geological Survey of Japan and Dr. T. Fukuoka of Gakushuin University for their kind help in INA analysis, Professor H. Sakai of the University of Tokyo, Professor H. Honma and Dr. H. Chiba of Okayama University and Mr. Y. Okamoto of Kyushu University for their help in oxygen isotope analysis, Dr. K. Kawamura of Hokkaido University for his help in computer programming, Professors K. Tsunoda and T. Ishida of Yamanashi University for their help during the field work, and members of the University Museum and Geo-logical Institute of the University of Tokyo for their encouragement. This study was partly supported by a grant-in-aid for Scientific Research (No. 5974015) from the Ministry of Education, Japan and by Funds from the Cooperative Program (No. 84135) provided by the Ocean Research Institute, the University of Tokyo.