It is shown that a depth change such as a fault line acts as a wave guide to long period waves in a two-layer rotating sea, in a similar way to the Double Kelvin waves of Longuet-Higgins (1968a, b) for a homogeneous sea. For a sea with a step discontinuity in depth, the effect of an extra layer leads to only small changes in the dispersion characteristics. For a continuous monotonic depth change taking place over a width l it is found that as l increases the Double Kelvin wave period increases, and the elevation at the interface decreases relative to the free surface elevation. Finally the effect of a time periodic wind stress suddenly applied is considered for step discontinuity in depth. For a maximum wind stress of 1 dyne the free surface wave amplitudes of the Double Kelvin wave are significantly less than those given by Mysak (1968). The corresponding interface amplitudes are about 10 cm. It is suggested, unlike their one-layer counterparts, that it may be possible to detect the two-layer waves successfully in practice, since they are predicted to have relatively large elevations at the interface.