The discontinuity planes of the Riemann curvature tensorRklmi in the Einsteinian vacuumRkl=0 are isotropic hypersurfaces. These surfaces are to be conceived as being constructed of lightlike geodesics, which form, in the eikonal approximation, gravitational radiation. The discontinuity planes themselves describe the wave fronts of disturbances of the metricgik, propagating with the velocity of light. By successively applying continuity conditions for the derivatives of thegik that follow from Einstein's equations, we obtain the universal expression of gravitational wave fields in space-time “strips” (or representations) of arbitrarily selected Einstein spaces.