BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 23, pp. 709-712, PL. 41 DECEMBER 4, 1912 



MINGLING OF PLEISTOCENE FORMATIONS ' 



BY B. SHIMEK 



{Presented before the Society December 29, 1911) 



CONTENTS 



Page 



Introduction 709 



Previous work ., 709 



Recent observations 710 



Illustrations of mingling 710 



The Des Moines section 710 



Location 710 



The loesses 710 



The Wisconsin drift 710 



Mingled loess and drift 710 



The Sioux Falls section 71 1 



Location 711 



The Kansan drift 712 



The silt 712 



Conclusion 712 



Intkoduction 



Among the difficulties which beset the student of Pleistocene deposits 

 in the field, none cause greater perplexity than the real or apparent 

 intermingling of strata or masses belonging to different portions of tliis 

 period. It thus sometimes appears as if masses of different drifts are 

 transposed or interglacial formations are out of place. 



Peevious Work 



Such intermingling has already been noted, particularly in connection 

 with the Aftonian, at Afton Junction, and Thayer, Iowa, by Calvin,- 

 and in western Iowa by Calvin^ and the writer.* 



1 Manuscript received by the Secretary of the Society December 29, 1911. 



2 Proceedings of the Davenport Academy of Sciences, vol. x, 1905, pp. 18-30. 



3 Bull. Geo!. Soc. America, vol. 20, 1909, pp. 137-139. 



* Ibid., vol. 20. 1909, pp. 406-7 ; vol. 21, 1910, p. 133 ; Iowa Geological Survey, vol. 

 sx, 1910, pp. 351-2, 355 and 371. 



(709) 



