EVIDENCE THAT THE BEDS ARE AFTONIAN 407 



Other exposures showing the folding and tilting of Aftonian gravels by 

 the Kansan are found near Mapleton and Grant Center, in Monona 

 county; Pisgah, in Harrison county; Smithland, in Woodbury county, 

 and Loveland, in Pottawattamie county. All the larger pits already men- 

 tioned also show this in their uppermost portions. 40 



3. The sand and gravel beds are not glacial, but interglacial. That 

 the materials were deposited in streams is shown by the fact that they are 

 water-worn, cross-bedded, with frequent interbedding of sand and gravel, 

 the latter deposited by stronger currents, and that they contain fluviatile 

 shells, with such intermingling of land shells as is common in the same 

 region in modern alluvial deposits. 



That the climate was mild during this interglacial period is shown by 

 the presence of the large numbers of herbivorous mammals, which re- 

 quired a vigorous flora for their maintenance, and of fresh-water and 

 land mollusks, which are identical with species now living in Iowa. The 

 aquatic shells suggest the same biotic conditions as exist in the state 

 today, and the land shells required plant-covered land surfaces on which 

 they could find food and shelter, and these surfaces were not radically 

 different from those which prevail in Iowa tocla}% if we are to judge 

 from the identity of the land shells. 



The abundance of Mn0 2 in the Aftonian beds also suggests the presence 

 of a large amount of organic matter. 



The Aftonian in other Counties 



The Aftonian beds extend also into counties other than Harrison and 

 Monona, in the western part of the state. Thus the gravels at Sioux 

 City, 41 in Woodbury county, between Loveland and Council Bluffs, in 

 Pottawattamie county, at Denison, in Crawford county, and between 

 Glenwood, in Mills count}'-, and the northern part of Fremont county, 

 are certainly Aftonian, as the writer has ascertained by personal examina- 

 tion, and those described by Bain from Plymouth county 42 and by Udden 

 from Mills county 43 are evidently the same. Thus it will be seen that the 

 Aftonian is well represented in the western part of Iowa. 



Conclusions 

 The conclusions may be briefly stated as follows : 



40 A fine illustration of the same kind is also found in the eastern part of the state, 

 in Muscatine, near Hershey avenue, where the Aftonian and sub-Aftonian have been 

 plowed and folded by the Kansan in a most complicated manner. 



41 See H. F. Bain's account in the Report of the Iowa Geological Survey, vol. v, 1896, 

 p. 277. 



43 Reports of the Iowa Geological Survey, vol. viii, 1898, p. 338. 

 * 3 Ibid., vol. xiii, 1903, p. 165. 



XXXVI — Bull. Geol. Soc. Am., Vol. 20, 1908 



