It is argued that the criteria of correlation are logically vulnerable, and that the principles of stratigraphy need reformulating if the science is to regain its vitality and productiveness. Two possible lines of advance are indicated. The first, which may be called the paleoecological approach, involves the application of modern knowledge of sedimentation and ecology to stratigraphy and implies greater use of the facies concept. It is suggested second, that greater attention should be paid to the study of restricted groups of organisms as they evolve in time through strata of uniform lithology. Finally the possibility of linking lineage studies with facies-shift is pointed out.