The limestones of the Pamelia, Lowville, Chaumont, and Rockland Formations have been examined over 130 mi in the Ottawa Valley, and the lithostratigraphy and conodont biostratigraphy of the Chaumont have been studied in detail. East of Ottawa, the latter is composed of uniform, thick-bedded calcarenites (fossiliferous pelmicrites). These underlie similar Rockland limestones and overlie thin-bedded calcilutites (micrites and pelmicrites) of the Lowville and Pamelia. To the west of Ottawa, the Chaumont lithology is variable and includes "Lowville-type" calcilutites and reflects four minor regressive phases within the overall transgression. The lower Rockland above is characterized by cross-stratified calcirudites (biosparrudites and intrasparrudites) that form a wedge-shaped facies thickening westwards from Ottawa.Data on stratigraphic relations, sedimentary features, petrography, and paleontology are combined to interpret paleoenvironments, which are shown to be directly analogous to those on most modern carbonate banks. The four formations are regarded as contemporaneous lateral facies representing lagoonal muds, stable muddy sands, and local mobile shoal banks. Hence, results strongly favor stratigraphic interpretations postulating diachronous facies as opposed to chronostratigraphic rock units. Moreover, conodont biostratigraphic evidence shows diachronism in the Chaumont Formation in the Ottawa Valley. This is regarded as the first sufficiently detailed paleontological evidence capable of settling the stratigraphie controversy.