On the basis of benthic foraminiferal zones and ages derived from planktonic foraminiferal evidence, Paleogene formations of Hokkaido are correlated as follows : The Shimokine and Tappu Formations of the Rumoi region with the lower and middle parts of the Poronai Formation of the Ishikari region : The Shitakara Formation of the Kushiro region with the lower or middle part of the Poronai Formation : The lower part of the Charo Formation of the Kushiro region with the upper part of the Poronai Formation : The upper part of the Charo and Nuibetsu Formations of the Kushiro region with the Momijiyama Formation of the Ishikari region : The Utsunai Formation of the Tempoku region with the upper part of the Poronai and Momijiyama Formations : The Magaribuchi Formation of the Tempoku region with the Momijiyama Formation. The Poronai and Momijiyama Formations are considered to have been deposited for the most part in depths ranging from outer neritic to middle bathyal zones on a southeastward deepening, westside slope of the Paleo-Poronai Sea inundated the central part of Hokkaido. The Paleo-Poronai Sea transgressed northward and reached the northernmost region of Japan during a Late Eocene to Early Oligocene time. In the eastern Hokkaido, transgression of the Paleogene sea is interpreted to have occurred during a Late Eocene, submerging the area to inner to middle neritic depths. After a short retreat of the sea, another transgression occurred between Late Eocene and Early Oligocene with the sedimentary basin deepening to upper bathyal environments. A rapid flourishment of calcareous foraminifera which has taken place near the vicinity of the Eocene/Oligocene boundary in the studied area may be related to the rapid deepening of CCD around that time. The systematic description of Paleogene foraminifera excluding new taxa is also given
