The analysis deals with the formulation of a boundary value problem where the complex immitivity has a principal axis tilted to the interface between the regions. An example is a half-space model of the earth where the fine layering or striations are not parallel to the air interface. The objective is to obtain expressions for effective surface impedance when the source is an obliquely incident plane wave from the upper (air) region. The case treated in detail is when the magnetic field direction is parallel to the strike of the structure which is a purely 2D problem. The more difficult case is when the incidence is arbitrary which leads to coupled wave equations for the E and H fields parallel to the srike of the structure. We also deal with the simplification achieved when the conductivity of the structure is sufficiently high. The general layered case is also treated where the analogy with the layered isotropic media problem is exploited.