The revision of the classification of the Pennsylvanian System of Missouri is necessary because of recent changes to the stratigraphic column in neighboring states, in particular Kansas. Geologists with the Missouri Geological Survey are attempting to avoid , as much as possible, the discontinuity of stratigraphic boundaries, informally known as "state-line faults" at the border of geologic maps between adjacent states. The majority of the changes in the classification of stratigraphic units in Kansas are acceptable to Missouri geologists. Unfortunately,the efforts to standardize and to stabilize the classification is complicated by facies changes, variation in thickness or the pinching –out of some units when traced between states. Examples are the black phosphatic shales that are used to establish stratigraphic boundaries in Kansas whereas in Missouri they are not the most useful stratigraphic markers because they are absent in some areas and are almost everywhere covered by slump or vegetation. In comparison, the thick overlying limestone beds are continuous and traceable in outcrop and easily identified in the subsurface. The primary goal of Missouri geologists is to formulate a practical classification system that can be applied with a minimum of confusion by the numerous geologists and geotechnicians engaged in geologic activities in Missouri that require the interpretation of geologic data between states.