In seeking to explain the events observed close to the Earth's bow shock known as hot, diamagnetic cavities (HDC), or active current sheets (ACS), attention has focused on the microphysics of the interaction of a magnetic field directional discontinuity and a collisionless, supercritical shock. Here we investigate the case of a tangential discontinuity (TD) convecting into a shock at some arbitrary angle. As a first stage we adopt an approach in which test particles represent ions specularly reflected at the shock front. Widely different behavior is possible depending on the sense of ion gyration relative to the TD. Particles can be injected into the plane of the TD so that they travel upstream trapped close to the TD. This implies that ACS events, presumed to be the result of the interaction of the solar wind with a large density reflected component, are detached from the bow shock. For other geometries, ions interact with the TD but stay close to the shock, implying that ACS events are modifications of the shock. The TD can deprive a limited spatial region of a downstream reflected-gyrating ion population (necessary for the quasi-perpendicular supercritical shock to be steady), and so we can anticipate where the shock will not be in equilibrium, and consequently where strong reflection may occur. The detailed behavior of the shock in such a situation must be investigated with self-consistent simulations. ¿ American Geophysical Union 1989