Previous studies of age determination and correlation of the Poronai shale in the Ishikari Coal field, Hokkaido were based almost entirely on megafossils., The presence of numerous foraminiferal species has been reported by the writer, but the general foraminiferal sequence has not yet been disscussed., In this paper, the writer divides the whole sequence into 4 zonules., The lowest Ammobaculites zonule crops out in the Hobetsu area, but the uppermost Plectofrondicularia zonule is distributed from the Ikushunbetsu to the Nokanan area., This suggests that the transgression of the sea which deposited the Poronai progressed from south to north., The Foraminifera from the Wakkanabe formation in the Akabira area consists of characteristic species of the Ammobaculites zonule., It shows that the sea which deposited the Wakkanabe can not be separated from the earlier Poronai sea, and the writer names the whole sea as Paleo-Ishikari Sea., The age of the foraminiferal sequence of the sea is considered to be from Upper Eocene to Lower Oligocene, and is correlated with those of the Cowlitz, Keasey, and Lincoln in Washington., U., S., A.,

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