398 IOWA ACADEMY OF SCIENCE Vol. XXVI, 1919 



4. The elevations of the sand and gravel deposits and the Ne- 

 braskan gumbotils are approximately the same. 



5. View 3 best explains and accounts for all of the conditions as 

 seen in the field. 



The writer is of the opinion that the lower drift is Nebraskan, 

 that the sand and gravel deposits are Nebraskan outwash materials, 

 that these outwash sands and gravels were oxidized and leached 

 contemporaneously with the formation of the Nebraskan gumbotil 

 and that the upper till is the Kansan. 



Ever since the history of the origin of the gumbotil has been 

 worked out by Professor Kay,* the value of interbedded sand and 

 gravel deposits between drifts has lost its significance as a criterion 

 of interglacial times. It is only when such deposits are oxidized and 

 leached and lie between fresh drifts that any positive value can be 

 attached to them as recording an interglacial interval. 



Department of Geology, 

 State University of Iowa. 



•Kay, G. F., Gumbotil, A New Term In Pleistocene Geology: Science, 

 New Series, Vol. XLIV, Nov. 3, 1916. 



Kay, G. F., Pleistocene Deposits Between Manilla In Crawford county 

 and Coon Rapids in Carroll county, Iowa: Iowa Geol. Survey, Vol. XXVI, 

 pp. 217, 218, Ann. Rep't. for 1915. 



