Problems in the field of stratigraphic geology are four-dimensional and, as such, require a three-fold system of nomenclature (time, time-rock, and rock units). Because of the failure of unconformities as time-stratigraphic indices, time-stratigraphic boundaries of Paleozoic and laterage must be defined by time, hence by faunae. The distribution of rocks of the different Paleozoic systems shows that several large anticlinal uplifts extended in pre-Pennsylvanian time. During the subsequent erosion, the crests of each were eroded, exposing large areas of Precambrian rocks to the surface before the Pennsylvanian sediments overlapped the surface of North America. The upper Cambrian column is approximately 1500 feet in the Ozark region. The series contain six formations, two of which comprise a group. In order of decreasing age, they are as follows: Lamotte, Bonneterre, Davis, Derby-Doerun, Potosi, and Eminence formations. Carbonate deposition began in the late Lamotte time and continued throughout the Cambrian. A big unconformity separates the Eminence formation from Ordovician Gasconade rocks. Because of paucity of fossils residue assemblages have been used in correlating carbonate rock units.