The writers presented orally at the Toronto meeting of the Geological Society and by printed abstract1 some observations and opinions concerning the stratigraphy of the upper Mississippi Valley. It was hoped that the tentative conclusions of 1930 would by 1933 have changed into something like mature judgments, and that by this time a comprehensive and less tentative paper on this subject could be presented. Although considerable additional field, laboratory, and library work during the intervening years has served to confirm some of the judgments and to change others, the study is at this writing still in an early stage. The effort made in the present paper is to assemble the several classifications that have been given and used before, to review the literature, to state the several unsolved problems, to present what evidence is now in hand bearing on their solutions, to offer a tentative new classification, and to . . .