Coalification patterns of Pennsylvanian coal basins in the eastern United States reflect (1) depth of burial during later Pennsylvanian and Permian times, when the main coalification took place; and (2) regional thermal disturbances from Permian to recent times. In most of the eastern United States, rank was determined during the main phase of coalification in Pennsylvanian and Permian times and thus reflects former greatest depths of burial. The general decrease in rank toward the Canadian Shield corresponds well to the general northward thinning of the mantle of sediments over the basement. In the coalification map of a reference seam, basins (for example, Illinois Basin) show up as northward extensions of high-rank areas, and positive structures (for example, Cincinnati Arch, Ozark Uplift) appear as southward protrusions of low-rank areas. The sedimentary column over the reference seam, or its stratigraphic equivalents, was thicker within the basins than over the positive structures. If data on rank are plotted on maps for coal seams lying at or near the surface regardless of their stratigraphic age, the close relation to the large structural units is much less pronounced, and the geologic interpretation of such coalification maps is more difficult. Superimposed upon this broad-scale and rather simple coalification pattern that reflects burial depth are several areas of anomalously high rank that are interpreted as being the result of unusually high heat flow sometime after the main coalification had terminated, probably in connection with deep-seated plutonic activity. These comprise the Rhode Island Meta-anthracite region, the Pennsylvania Anthracite region extending westward into the area of low- and medium-volatile bituminous coals of Pennsylvania and northern West Virginia, the eastern portion of the Arkoma Basin in Arkansas, and possibly also the southern portion of the Illinois Basin and the area of high-rank bituminous coals in southern West Virginia. In the last two regions, the high rank may be explainable solely by greater former depths of burial. The coalification patterns of all these areas are considered anomalous compared to the patterns of adjacent areas and of other coal basins. Supporting evidence for this interpretation of the coalification pattern is furnished by the presence in the same areas of other manifestations of large-scale regional heating and deep-seated plutonic activity.