X-radiographic prints were made at the Geological Survey of Japan. The author is indebted to Dr. Hajime Katayama and Dr. Yoshiki Saito at the Geological Survey of Japan for their kind instructions and assistance. The author also thanks Dr. Lena Rubensdotter in the Department of Physical Geography, Stockholm University, for her helpful review and Dr. Gary Acton and Lona Dearmont of ODP for their help improving the English and format of the initial version of this manuscript. This research is supported by a grant from the Nissan Science Foundation in 1997.