FIRST SERIES No. 40 JANUARY 1, 1921 



UNIVERSITY OF IOWA 

 STUDIES 



STUDIES IN NATURAL HISTORY 



VOLL'ME IX Number 3 



THE EROSIONAL HISTORY OF THE 

 DRIFTLESS AREA 



by 

 ARTHUR C. TROWnSRIDGE 



PUBLISHED BY THE UNIVERSITY, IOWA CITY 



Issued semi-monthly throughout the year. Entered at the post office at Iowa City, 

 lovra. as second class matter. Acceptance for mailing at special rates of postage 

 provided for in section 1103, Act of October 2, 1917, authorized on July 3, 1918. 



