The description and classification of Carboniferous rocks in northeastern Kentucky, as in other areas on the cratonic interior of North America, are based primarily on the “layer-cake” model developed by William Smith early in the 19th century. Application of this model in mapping Carboniferous strata in northeastern Kentucky has encountered increasing difficulties until new roadcuts produced by Interstate Highway 64 have provided necessary data for creating a more viable model. This new model, based on precisely determined characteristics of the rocks and analogies to Holocene depositional environments, shows (1) that Mississippian Newman limestones reflect deposits consisting of offshore carbonate islands surrounded by red and green clays (Pennington), (2) that orthoquartzites of the Lee Formation (Pennsylvanian) represent quartzose barrier islands, tidal delta, and channel deposits, and (3) that strata of the coal-bearing Breathitt Formation can be related to back barrier and deltaic environments. Lateral relations of these rock units to each other indicate that the entire sequence—Newman through Breathitt—represents a depositional continuum with different sedimentary environments intertonguing laterally with one another. Vertical relations indicate that the present superposition is the result of prograding sedimentary environments. These results suggest that previously used stratigraphic classifications of Carboniferous strata should be considerably modified and that the use of the Lee-Pennington or Newman contact as the Mississippian-Pennsylvanian systemic boundary should be discontinued.