342 S. CALVIN AFTONIAN MAMMALIAN FAUNA 





streams which had their origin in the rapid melting of the pre-Kansan 

 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 reason- 

 able explanation of vigorous, swollen streams such as might carry and 

 deposit loads of gravel, and no efficient cause of such floods at any time 

 between the beginning and the close of the Aftonian interval was so read- 

 ily conceivable. Work on the gravel pits at Afton Junction and Thayer 

 was stopped some years before the deposits came under the observation of 

 geologists. If fossil bones were found during the progress of the excava- 

 tion, there was no record of the fact. In view of the conclusion as to the 

 conditions under which the gravels were laid down, contemporary faunas 

 were regarded as impossible and no inquiries were made. Bones and teeth 

 of post-Tertiary mammals have been found in the surficial deposits of 

 Iowa, but they have usually been referred in a broad way to the Pleisto- 

 cene. The many known Aftonian peat beds have so far yielded no mam- 

 malian remains, and very few mammals which could be referred definitely 

 to any given stage of the Pleistocene have been heretofore discovered in 

 the area between the two great rivers. 4 



Relation of the Gravels, in Time, to the Aftonian Interval 



Within the past few months, in Harrison, Monona, and other western 

 counties of Iowa, Shimek has found stratified sands and gravels of great 

 thickness and extent lying between the pre-Kansan and the Kansan drift. 5 

 The stratigraphic position is clear and well established; the gravels are 

 Aftonian in age, but they contain evidence that they were not deposited 

 until some time after the old pre-Kansan ice-sheet had completely disap- 

 peared. In the light of this evidence, it may be necessary to revise the 

 opinion concerning the precise date of deposition of the Thayer and Afton 

 Junction beds, expressed in the Proceedings of the Davenport Academy 

 of Sciences. The new evidence comes in the form of a fairly rich mam- 

 malian fauna that must have been contemporary with the deposition of 

 the gravels, but which certainly did not live in the wet, chill, verdureless 

 region that coexisted with the melting of the pre-Kansan ice. As noted 



3 Samuel Calvin : The Aftonian gravels and their relation to the drift sheets in the 

 region about Afton Junction and Thayer. Proceedings of the Davenport Academy of 

 Sciences, vol. x, 1905, pp. 18-30, plates i-vii. 



4 In the third edition of The Great Ice Age, by James Geikie, 1895, p. 759, Professor 

 Chamberlin refers to Equus complicates, Lepus sylvaticus, and Mephitis mephitica as 

 occurring in interglacial deposits in Iowa, but the horizon is not definitely stated. Mure 

 definite is Leverett's reference to the occurrence of Lepus and Mephitis at the Yarmouth 

 horizon, between the Kansan and the Illinoian drift sheets, near Yarmouth, Iowa. See 

 Proceedings of the Iowa Academy of Sciences, vol. v, 1898, p. 82. 



5 B. Shimek : Aftonian sands and gravel in western Iowa. Science, new series, vol. 

 xxviii, December 25, 1908, p. 923. 



