Ash beds of Devonian age in the Appalachian basin have been incorrectly called bentonites. The emphasis placed on the volcanic origin of the beds rather than on their mineralogical and physical characteristics apparently led to the erroneous application of the term “bentonite.” Recent study indicates that the lack of smectite in the Tioga, Belpre, and Center Hill Bentonite Beds, compared with the type bentonite, warrants the deletion of the term “bentonite,” and the substitution of the term “ash.” It is recommended that the ash beds of Devonian age be referred to as the Tioga Ash Bed, the Belpre Ash Bed, and the Center Hill Ash Bed.

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