It is generally recognized that massive thick-bedded sandstones and relatively weak shales and soluble limestones form characteristic surface features. The uncommon effect of a thin argillaceous sandstone in producing ridges in an area in northern Virginia, in which the writer has recently done detailed field work, is briefly described in this paper. This bed, with an average thickness of 2 feet, where it crops out in a nearly vertical position, commonly forms discontinuous ridges ranging.in height from a few feet to as much as 20 feet. The areas southeast of Winchester (Fig. 9) and northwest of Stephens City (Fig. 10) were chosen as typical localities to illustrate the ridge-making influence of this sandstone on the local topography.