Clay mineral analyses of underclays directly below the Upper Elkhorn Coals (eastern Kentucky) and the Lower Kittanning Coal (western Pennsylvania) demonstrate systematic lateral and vertical variations that include changes in the kaolinite-illite ratio, mica loss ratio, weathering ratio, apparent thickness of mica, and distribution of chlorite. Clay mineral analyses of associated, unweathered shales indicate that approximately 30 percent of the regional variation in Lower Kittanning underclay mineralogy is inherited from the parent material. The remaining variation is attributed to in situ pedogenesis.

Petrographic analysis of thin sections from a fluvial sandstone subjacent to the Upper Elkhorn underclay suggests that position...