On the south and southwest flanks of the Ozark dome the middle Mississippian Osage group, where fully represented, comprises, from bottom to top, the St. Joe, the Reeds Spring (in part the Grand Falls chert), the Burlington, the Keokuk, and the Warsaw formations. Heretofore these formations in this area have been collectively referred to the "Boone formation," but it is clear that the term "Boone" should be suppressed as a synonym of the term "Osage." A green shale which crops out at the base of the group and which several previous writers have called Kinderhook is definitely shown to be Osage. The Reeds Spring formation occurs in Arkansas, and it forms a large part of the Osage as that group is exposed in Oklahoma. Lower Burlington limestone is recorded from Oklahoma and is correlated with strata in Arkansas, and the chert in Oklahoma that has previously been called Keokuk and Warsaw is believed to be largely Burlington in age. Chert in the vicinity of Batesville, Arkansas, which Girty believes to be of Warsaw age, should not be referred to the Osage group. Evidence indicates that the lower Caney shale of the Arbuckle Mountain region is not the clastic equivalent of the Osage group, as some geologists now hold.