Stratigraphy is concerned mainly with the genesis and interpretation of stratified rocks, which include some of wide extent and of great scientific as well as economic interest that are largely of chemical rather than of detrital origin. Chemical agencies have been recognized to some extent in genetic studies of these rocks, but little work has been done approaching in maturity the type of study now given to the genesis of igneous rocks and of ores, in which physical chemistry plays so important a part.A plea is presented to geologists with training in physical chemistry to interest themselves in stratigraphic problems that involve the use of this science. Examples cited are the phosphate beds and bedded cherts of the Phosphoria formation in Idaho and adjacent States and the potash-bearing Salado halite of the Permian basin in New Mexico and Texas. The interplay of ions in the solutions from which these formations were derived must have been controlled by such conditions as temperature, pressure, degree of concentration, and the like. Possibly laboratory study would enable us to reproduce these conditions and results and thus better interpret the geologic history of the times when these formations were built.