The effect of a layer on surface wave propagation on a half-space can be separated into terms arising from elastic and from inertial restraining forces. In a number of situations of practical importance, it turns out that the inertial terms are dominant. The period equations governing the dispersion for this pure mass loading are obtained in suitable form and numerical solutions for Rayleigh waves for both solid and fluid loading are obtained. It is shown that by presenting the results in terms of appropriate variables, extremely simple, approximately linear, dispersion characteristics are found. A single computation suffices for substrate materials having the same Poisson ratio. The validity of this approximation is explored for modified Rayleigh waves for both solid and liquid layers, and for Love waves. © 1971, Acoustical Society of America. All rights reserved.