INTRODUCTION The present paper attempts to demonstrate the principle that problems of sedimentary facies are most logically approached along three interrelated but separate paths: lithology, biology, and tectonics. Synthesis of data from each of these lines of investigation leads to a more complete understanding of the events and paleogeographic conditions responsible for the distribution and character of sedimentary deposits. In support of Moore’s (1948, p. 310; 1949) definition of a facies as an “aspect” of a designated stratigraphic unit, the writers stress map representations of facies, rather than cross-sectional reconstructions, as the basis for interpretation. Further, the writers are impressed by the value of broad interregional facies analysis in establishing the fundamental framework within which more detailed and restricted studies may be oriented. Finally, any facies study is initiated by the selection of a stratigraphic unit or interval for analysis. In interregional studies, and in many more local investigations, the established time-stratigraphic units have not proved uniformly useful, since they lack objectively recognizable boundaries. A tentative solution to this recurring problem is sought in the establishment of operational units which may be recognized and studied over large areas. FACIES DEFINITION According to Moore (1949), “fades are areally segregated parts of differing nature belonging to any genetically related body of sedimentary deposits”. Moore emphasizes the point that facies are “variants or ‘aspects’ of stratigraphic units having mutually exclusive space distribution” and clarifies the relationship between facies and lithotopes. The writers are in general agreement with these views but would modify them