Jukes-Browne & Hill (1903, 1904) - Ammonites varians Zone
Biostratigraphical correlation: Inferred to approximately equate with the M. mantelli, M. dixoni and C. inerme zones of current usage. In areas where the Totternhoe Stone is developed, Jukes-Browne & Hill (1903) recorded that the top of the A. varians Zone was coincident with the base of that unit.
Lithostratigraphical correlation: Equates with the West Melbury Marly Chalk Formation of southern England.
Age: Early Cenomanian.