The crustal structures of the basins of Shikoku, Parece Vela (West Mariana) and West Philippine are oceanic in character resembling those of the Pacific Ocean basin. And the crustal structures of the ridges of Izu-Mariana Arc, Kyushu-Palau Ridge and Ryukyu Arc are different from those of basins. The Izu-Mariana Arc and the Kyushu-Palau Ridge are different from the Ryukyu Arc in point of lacking a granitic layer.