This paper presents the results of an investigation of two of the stratigraphic problems of the upper Mississippi Valley, pointed out by Trowbridge and Atwater1 in 1934. At that time a review of the stratigraphy of the upper Mississippi Valley was given, a number of problems that the authors believed to be as yet unsolved were outlined, and suggested lines of work on the problems were presented. The problem of the relation between the Hinckley sandstone of Minnesota and the Mt. Simon sandstone of Wisconsin was undertaken by the authors, and the results presented orally at the Geological Society of America meeting in Chicago in 1933.2 The problem of the relation of the Red Clastic series of Minnesota with Keweenawan outcrops of the Lake Superior region, as well as the possible Cambrian age of the upper Keweenawan, was found to be so intimately related to this investigation that the . . .