A specific solution to prediction of thickness of the Middle Kittanning-Lower Freeport interval from the thickness of enclosed channel sandstone by use of a linear regression model is presented. Application as a predicting equation has increased data of complete stratigraphic sections twofold. Thickness is controlled by thickness of enclosed channel sandstones along the fluviolacustrine and brackish-marine facies. That is, the thicker the sandstones, the thicker the section. Further, the section thickens toward the brackish-marine boundary and thins toward the fluviolacustrine boundary. The data indicate that the linear regression relationship between the two facies does not vary significantly so that a common regression formula was used. This device should be useful in other similar stratigraphic conditions.