The purposes of this investigation were to determine the effect of chemical weathering on the distribution of thorium and uranium in a single weathering profile, and to investigate the distribution of these elements in a single, well-defined, and extensive shale body. Particular objectives were to determine the manner in which thorium and uranium may occur in source rocks and in sediments, particularly shales, and to relate the variations in the distribution of thorium and uranium in a shale to the fundamental geological processes. For these purposes 13 samples were collected from a Pennsylvanian weathering profile and more than 150 samples from the Upper Cretaceous Mancos shale. Most of these samples have been analyzed for thorium, uranium, and potassium by radiometric and chemical methods.