Biotite phenocryst composition shows that two K-bentonites in the Little Oak limestone (Ordovician) at Old Ragland Quarry, Alabama, are the same structurally repeated tephra layerv. 36No. 285-95
Haynes, John T., Melson, William G., and Goggin, Keith E. 1996. "Biotite phenocryst composition shows that two K-bentonites in the Little Oak limestone (Ordovician) at Old Ragland Quarry, Alabama, are the same structurally repeated tephra layer." Southeastern Geology, 36, (2) 85–95.