Between the two older drift sheets of Iowa, known respectively as the pre-Kansan and the Kansan, there are many evidences of a long interval of mild climate. Such an interval is indicated by intercalated weathered zones, soil bands, peat beds, buried forests, and aqueous deposits of sand and gravel. Chamberlin pointed out the interglacial position of the extensive gravel beds at Afton Junction and Thayer and gave the name Aftonian2 to the interval which they in part represent. The writer, discussing the age of these gravels in the Proceedings of the Davenport Academy of Sciences, was led to conclude that they are the work of streams which had their origin in the rapid melting of the pre-ICansan ice, and that they belong in reality to the closing phase of the pre-Kansan glaciation.3 In rapidly disappearing glaciers there was offered a reasonable explanation of . . .