THE IOWAN DRIFT PROBLEM 75 



A NOTE REGARDING THE PRESENT STATUS OF THE 

 IOWAN DRIFT PROBLEM. 



GEORGE F. KAY. 



Among the many persons who, by their publications, have, 

 made known to the world the Pleistocene history of Iowa, no 

 one has had a greater part than Doctor Calvin, who spent his 

 life endeavoring to interpret the geological phenomena of the 

 state. For many years, but chiefly from about 1895 until his 

 death in 1911, important papers were written by him in tV 

 reports of the Iowa Geological Survey, of which he was Director, 

 and in other channels of publication. None of these publica- 

 tions are of greater interest than those which describe the char- 

 acteristics, relationships, and age of the lowan drift. It was 

 he who, after he had done detailed work on the Pleistocene of 

 the northeastern and north-central parts of Iowa, became con- 

 vinced that in this part of the state the evidence indicated that 

 the ice had invaded the region not twice only, as had been held 

 by earlier workers in this field, but three times. It was he who 

 gave to the uppermost of these drift sheets the name "lowan," 

 and presented arguments in favor of recognizing the lowan as 

 a distinct epoch in the Pleistocene. 



For a number of years the conclusions of Doctor Calvin were 

 accepted, but a few years before his death in 1911 some Pleisto- 

 cene geologists, particularly Mr. Frank Leverett of the United 

 States Geological Survey, raised the question whether or not 

 there was sufficient evidence to justify the recognition of the 

 lowan as a drift sheet separate from the Kansan. In defense 

 of his interpretations Doctor Calvin prepared a paper entitled 

 '"The lowan Drift," which he read at the Pittsburgh meeting of 

 the Geological Society of America, in December, 1910, and which 

 was published after his death in the Journal of Geology, vol- 

 ume XIX, No. 7, October-November, 1911. 



Since the death of Doctor Calvin, a co-operative study of the 

 lowan problem has been made, especially during the field sea- 

 sons of 1914 and 1915, by Dr. W. C. Alden, Chief of the Pleis- 

 tocene Section of the United States Geological Survey, and Dr. 



