Mineralogical analyses of the heavy coarse silt fraction, including microprobe identifications of certain clastic minerals, and bulk chemical analyses of 186 sediment samples from DSDP sites 291, 299, 301, 436, 447, 449, 450, 453, 459 and 460 are compared with similar data for Quaternary sediments on a profile across the Pacific from Central America to the Far East. As a result, new details of the history of the Philippine and Japan Seas suggest that the active marginal complex has a variety of "states" (stages). These states differ in terms of (1) the number of associated "echelons" (i.e. parts of the complex), each consisting of a subduction zone, island arc and back-arc basin situated one behind the other, and (2) their orientations. Changes in state are caused by blocking, i.e. hindering, the subduction. Continental as well as oceanic lithosphere is involved in the system. The "island arc" lithosphere, which is more simatic than continental lithosphere and more sialic than oceanic lithosphere, is a final product of the development of the marginal complex irrespective of whether the parent was continental or oceanic lithosphere
