While a graduate student at Yale University, the writer was asked by Professor Schuchert for an explanation of the repeated vertical land movements apparently involved in the changing shorelines of ancient seas as depicted upon his paleogeographic maps, then in preparation. The principle of diastrophism seemed to be overworked when called on to ex‐ plain marked recessions and advances of shorelines during a single geologic period. The quest for a solution of this problem continued during succeeding years without result, until a study was made of the stratigraphy of the southern plains of Canada for the Canadian Geological Survey. Here the thick series of alternating continental and marine sediments of Upper Cretaceous age, with their varying facies from sand in the west to shale in the east, provided data for comparative studies of rate of deposition of coarse and fine detritals, and for a quantitative comparison of deposition of . . .