The rocks developed in the Teshio Oil Field of Hokkaido are, in the main, the so-called “Upper” and “Uppermost” Tertiary Series. According to K. WATANABE of our Survey, the “Upper Series” is divided into three beds, namely, enumerated from the lower, Wakkanai Hard Shale, Koitoiye Sandstone, and Yftchi Sandstcrne. They yield molluscan fossils, those collected by him being preserved in our Survey, and which the writer describes in this paper.
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