In the case of a vertical cliff, Mr. Fisher has shown that the uneroded surface of rock underneath a talus is in the form of a semi-parabola.1 The object of this note is to show that the form is parabolic, even if the cliff be not initially vertical, assuming, with Mr. Fisher, (1) that the cliff-face is weathered uniformly at all points, and (2) that the disintegrated material is spread evenly over the surface of the talus, so as to maintain it always at the same slope. The proposition may be proved analytically, as in Mr. Fisher's paper, or geometrically as follows.