Many fossils in the older rocks have been distorted by pressure, and if only one specimen is available it is often difficult to be sure of its original proportions. Sometimes, however, there is a specimen which not only furnishes sufficient data for the determination of its original form, but can be made to yield a photograph in which the distortion is corrected. In his paper on “Slaty Cleavage” Harker1 showed how, in such cases, the distortion can be determined, and he referred to an earlier paper by Dufet2 in which the same principle is used, though in a different way. So far as I know the method of correcting the distortion photographically has not previously been employed.