THE IOWAN DRIFT 583 



able interpretation of what the authors had in mind when describ- 

 ing the physical characteristics of the two drift sheets and mapping 

 their areal distribution. A departure from this usage, which would 

 make the sub-Af tonian till Kansan and would apply the term Iowan 

 to the old, weathered till above the Aftonian, with its blue color, 

 its strikingly conspicuous array of greenstones, and with relations to 

 the loess so entirely different from the relations correctly described 

 in the text as pertaining to the Iowan, would necessitate the making 

 of radical and revolutionary changes in the map and descriptive 

 texts above noted. It surely accords better with what was pub- 

 lished at the time the names were applied to let recent usage remain 

 unchallenged and unchanged. 



EVIDENCE CONCERNING THE IOWAN DRIFT AND ITS GEOLOGICAL 



RELATIONS 



The surprising attitude toward the Iowan drift, expressed 

 in the papers by Leverett, is something difficult to understand. 

 A very little field study in the right places will demonstrate : 



1. The Iowan drift is. 



2. The Iowan drift is young as compared with the Kansan. 



3. The Iowan drift is not a phase of the Kansan. 



4. The Iowan drift has very intimate relations to certain bodies 

 of loess. 



5. The Iowan drift is not related to the Illinoian. 



The Iowan Drift Is 



To discuss the question of whether there is an Iowan drift dis- 

 tinct from the super-Aftonian till that has been called Kansan is 

 like undertaking a task that one knows is absolutely useless and 

 unnecessary. For, while the Iowan is thin, and in places is absent, 

 there is here a very substantial drift sheet overlying the Kansan 

 and possessing distinctive characters of its own. The Iowan is 

 separated from the Kansan by a ferretto zone in some places and 

 by weathered gravels in others, while its characteristic topography 

 and remarkable bowlders proclaim its presence throughout exten- 

 sive areas where no sections are available. Buchanan gravels, 

 distributed by volumes of water from the melting Kansan glaciers, 



