The first occurrence of berthierine-bearing flint clays, one Ordovician and one Pennsylvanian in age, is discussed. These flint clays are characterized by a berthierine-kaolinite-boehmite assemblage. The Pennsylvanian flint clay from northeastern Kentucky is more typical in that it occurs in association with coal measures. Meanwhile, the Ordovician occurrence from northwestern Illinois is the oldest flint clay, forming before the evolution of terrestrial vascular plants.
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Ordovician and Pennsylvanian berthierine-bearing flint clays