Brenckle, P.; Marshall, F. C.; Waller, S. F.; Wilhelm, M. H. (1982). Calcareous microfossils from the Mississippian Keokuk Limestone and adjacent formations, upper Mississippi River valley: Their meaning for North American and intercontinental correlation. Geologica et Palaeontologica. 15: 47-88.
339781
Brenckle, P.; Marshall, F. C.; Waller, S. F.; Wilhelm, M. H.
1982
Calcareous microfossils from the Mississippian Keokuk Limestone and adjacent formations, upper Mississippi River valley: Their meaning for North American and intercontinental correlation