In the neighbourhood of the city of Hukuoka, northern Kyusyu, there are alternations of green (metamorphic) rocks and crystalline schists., In contrasts to the occurrence of the similar rocks in the outer zone of the Japanese Archipelago, where, developed in distinct facies, the green rock series (the Mikabu Series) are commonly considered to be geologically younger than the crystalline schist series (the Sambagawa Series), both kinds of rocks here, occurring intimately associated, may reasonably be supposed to be of the same age (probably Palaeozoic) differing only in degree of metamorphism.,