In discussing this classification, it was pointed out3 that
“When the most significant facts of Pleistocene history are analyzed critically in relation to what might be considered as a logical classification it is evident that from the time of the advance of the first ice sheet, the Nebraskan, to the retreat of the last ice sheet, the Wisconsin, there were recurrences of similar geological events with accompanying similar geological results. In other words, there were within the limits of the Pleistocene period a succession of cycles, the most significant evidences of which are recorded in the deposits which were made during each cycle and in the changes which the deposits underwent before the coming of the succeeding cycle. Reasons were given for the interpretation that . . .