The surface morphology of materials is amenable to study by transmission electron microscopy of replicas. In this mode of analysis, the electron transmission image results essentially by replica mass-thickness contrast. Consequently the image interpretations are based solely on the features, and the structure of the replica is itself ignored. It should be apparent that where image contrast of crystalline materials results by diffraction contrast, the ability of specific features of a solid to be distinguishable in such an image will depend primarily on the characteristic phase shift imparted to the transmitted electrons. The resulting screen intensity is therefore a periodic variation in brightness creating fringe patterns corresponding to the tapering contour of holes or etch pits, or an edge. The diffraction contrast effects, including extinction contours and thickness fringes at tetrahedral etch pits, are observed in a thin Si foil having surface orientation.