C. W. Tomlinson and the writer began a cooperative study of the Stanley-Jackfork-Johns Valley-Atoka stratigraphic sequence in the Ouachita province of southeastern Oklahoma in June, 1953. Although the work is still in progress, it is advanced enough to permit some conclusions.

Several members of the Stanley-Jackfork succession, which Harlton differentiated and named in Wildhorse Mountain and Prairie Mountain in the western Ouachitas, persist as far east as the Arkansas-Oklahoma line. Their recognition on the outcrop and on air photographs has made possible the differentiation of a large area of Atoka, and perhaps younger rocks, in a belt in the Kiamichi Range which has been mapped as Jackfork on the recent Oklahoma geologic map. Two unfaulted stratigraphic sections, showing the upper Stanley, a complete Jackfork sequence, and several thousand feet of overlying Atoka, have been discovered in the Kiamichi Range and have been described in detail. The Jackfork sandstone totals only 5,600 feet in the Kiamichi Range, which is considerably less than thicknesses or inarily assigned to it. Work in the western Ouachitas has revealed that the lower part of the type Prairie Mountain formation, including the Prairie Hollow maroon shale, is equivalent to the upper part of the underlying Wildhorse Mountain formation at the type locality, and recognition of this duplication also reduces considerably the thickness assigned to the Jackfork in the western Ouachitas.

Several new occurrences of boulder-bearing Johns Valley shale are noted. In each outcrop the Johns Valley lies above a fossiliferous sandstone formerly included in the Jackfork, but correlated by Harlton with the Union Valley sandstone of the Arbuckle facies, and below another fossiliferous sandstone which was mapped as basal Atoka by Hendricks but which was correlated with the Barnett Hill by Harlton (Harlton regards the Barnett Hill as a split from the upper part of the Wapanucka or older reports). The boulder beds occupy persistent stratigraphic horizons within the Johns Valley and, whereas they contain numerous boulders foreign to the Ouachita province, they are indigeneous

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to the containing beds. Many of the rock fragments show evidence of profound chemical weathering prior to transportation and deposition, and they could hardly have been part of a friction carpet along a thrust sheet. The tentative conclusion is reached that the so-called Mississippi Caney boulders of the Johns Valley shale in Johns Valley are not erratics but are sideritic concretions which are in place in the lower part of the Johns Valley. A similar conclusion is reached concerning the "Caney boulders" at the bend in the Hairpin Curve on Oklahoma Highway No. 2 south of Wilburton. The logical conclusion is that the Jackfork sandstone must be Mississippian or older. This correlation of the lower part of the Johns Valley with the Mississippi Caney is based on the presence of the cephal pods Cravenoceras choctawensis and Actinoceras (Rayonnoceras) vaughianum, and the presence of abundant representatives of the pelecypod Caneyella, and on similar lithologic features.

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