Examination of cable-tool cuttings from water wells has resulted in the establishment of four zones in the "Plattin" and two zones in the "Joachim" as previously described. The zoning is based upon lithology and insoluble residues. A cross section through 14 selected wells extending approximately 300 miles, from Kirksville in northeast Missouri to Cape Girardeau in southeast Missouri, indicates the position and thickness of the zones where present.

At Cape Girardeau the "Plattin" is 600 feet thick and the "Joachim" is 250 feet thick. In the type areas approximately 75 miles northwest, the "Plattin" thickness is 200 feet and the "Joachim" is 175 feet. In northeast Missouri in the vicinity of Kirksville both formations are overlapped by the "Decorah," where the latter rests on the St. Peter. The cross section indicates that older beds are overlapped from southeast to northwest and suggests an unconformity at the base of the "Decorah."

Some of the subsurface zones have been located at the outcrop at widely separated localities and can be used in surface mapping. Re-definition of the "Plattin-Joachim" boundary is desirable. The name Rock Levee, derived from a place of that name approximately 3 miles southwest of Cape Girardeau and near the intersection of U. S. Highway 61 and Missouri Highway 74 is proposed for the rocks lying between the re-defined Plattin and Joachim. The term "Decorah" as used in Missouri requires more specific definition.