Mississippian rocks in southwestern Missouri were studied in detail. Both lateral and vertical variations were studied and attempts were made to correlate with Mississippian rocks in northern Arkansas and northeastern Oklahoma.

The basal Mississippian Sylamore sandstone is thin, locally developed and poorly exposed in southwestern Missouri. The Chattanooga shale occurs only in the extreme southern part of southwestern Missouri and there are no post-Chattanooga pre-Chouteau rocks. The Chouteau, Northview, and Sedalia formations are present in the northern part of the area studied but thin southward and are not present along the southern border of the state.

It is recommended that the term Compton be dropped as a synonym of Chouteau. The Sedalia formation, as defined by Moore, is recognized as a valid formation, but it is Kinderhookian rather than Osagian in age. The lower two thirds of the Sedalia formation is a facies of the Northview formation. The upper non-cherty part of the Sedalia is much more extensive than the underlying part and overlaps the Northview formation over a wide area.

The St. Joe and Reeds Spring limestones are present only in the southern part of southwestern Missouri and transgressively overlap northward. The St. Joe limestone is not typically developed in the Springfield area where it has been called the Pierson formation. The term Pierson should be dropped as a synonym of St. Joe.

The Burlington limestone is divided into 6 faunal zones and they are correlated with equivalent zones in northeastern Missouri. The Burlington formation thins southwestward from Springfield and disappears from the section between Mt. Vernon, Lawrence County, and the Tri-State mining district.

The Keokuk formation is present only in the western part of the area and is not present in the Springfield area. Keokuk limestone grades insensibly up into limestone of Warsaw age in the Tri-State mining district. None of the shaly facies that characterize the Warsaw in northeastern Missouri are developed in southwestern Missouri.

Evidence is presented to prove that a part of the beds that have been referred to the St. Louis formation in western Dade County should be referred to the Keokuk.