In Hokkaido, two asynchronous pairs of Jurassic to earliest Tertiary arc-trench systems are recognized. Tlie trench belt of the older pair occupies a part of the Jurassic to Cretaceous Yezo Geosyncline, where the Kamuikotan metamorphic rock belt may represent a west-dipping subduction zone. The trench belt of the younger pair is represented by the latest Cretaceous to earliest Tertiary Small Kuril Geosyncline (new name). In both geosynclines, the trench sediments are characterized by the following fourfold succession, in ascending order: (1) radiolarian chert or siliceous shale and pillow lavas, (2) flysch, (3) shallow-marine muddy sediment, and (4) molasselike sequences. Farther to the south of the Small Kuril Geosyncline, the modern Kuril Trench has been developed. These consecutive developments of arc-trench systems present a good example of oceanward migration patterns of the systems.