The plate-tectonics hypothesis fails to explain (1) the geographic distribution of typical, or true i s land arcs; (2) their form, geometry, and orientation; (3) their variety (which is sufficient to warrant classification); and (4) the great range in ages of the rocks composing the arcs. The plate-tectonics concept also fails to provide a plausible explanation for the marginal seas associated with typical island arcs--those of the western Pacific, the
Caribbean Sea, and the Scotia Sea. We postulate, therefore, that island arcs are
formed by surges in the asthenosphere (lowvelocity zone); tha t flow within the asthenosphere is initiated by differential subsidence within the ocean basins or between
ocean basins and adjacent continents; and that t he direction of flow is guided and,
in part, controll ed or modified by t he forces involved in earth rotation--namely, centrifugal force and differential l ag between the lith_osphere and the asthenosphere. All known facts support this postulate which, unlike plate-tectonics postulates, does not require the creation of innumerable had hoc modifications to fit each arc or arc complex.