The superlattice of spacing about 90 A in Yu Yen Stone, a variety of serpentine, was studied by electron microscopy (Brindley et al: Acta Cryst. 11 (1958) 99). About 500 electron micrographs showing fringes corresponding to the superlattice were taken, many of which were through-focus series. The intensity profile of fringes varies with the amount of defocus and it also varies from specimen to specimen even at the exact focus. These phenomena are explained qualitatively by theories of image formation. “Extra” terminating half-lines and stepped structures of fringes were studied and it was concluded that the former represent real dislocations in the crystal but the latter are ghosts. The spacing of the superlattice was found not to be constant and this material is not therefore adequate for magnification calibration of electron microscopes (Uyeda et al: J. Phys. Soc. Japan 13 (1958) 461).