The writer has studied the sedimentation of the Harutori formation which is distributed in the area between Shiranuka and Konbumori in the Kushiro plain, eastern Hokkaido, and laid stress especially on the lateral change of cyclothems referring to its relation with development of coal seams.
In conclusion, it is suggested that some mutual relationships exist between the rock facies and the development of coal seams, and that volcanic activities have causal relationships with the formation of some cyclothems.