BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 20, PP. 133-152, PLS. 1-5 MARCH 18, 1909 



PRESENT PHASE OF THE PLEISTOCENE PROBLEM IN 



IOWA 1 



PRESIDENTIAL ADDRESS BY SAMUEL CALVIN 



(Read before the Society December 29, 1908) 



CONTENTS 



Page 



Introduction 1 33 



Pleistocene problem of twenty years ago and of today 134 



First and second glacial epochs and first interglacial interval 135 



General characteristics 135 



Pre-Kansan or sub-Aftonian drift 136 



Kansan drift 130 



Aftonian interval 136 



Physical relation of the Kansan to the older deposits 139 



Relative age of Kansan and pre-Kansan 140 



Illinoian drift and the Yarmouth or second interglacial interval 141 



Third interglacial interval, the Sangamon 143 



Iowan drift 143 



Extent of the Iowan 143 



Relative age of the Iowan 144 



Undulating surface of the Iowan 140 



Individual characteristics 140 



Drainage courses in the Iowan 147 



Age of Iowan compared with Kansan 147 



Fourth interglacial interval, the Peorian 148 



Wisconsin drift 140 



Characteristics of the Wisconsin compared with those of the Iowan. . 140 



The Wisconsin compared with the Kansan 151 



Conclusion 1 52 



Introduction 



More than once your speaker has had occasion to say that Iowa was 

 exceptionally fortunate in its location with reference to the movements 

 and marginal limits of the successive ice invasions of the Glacial epoch, 

 and that the state therefore offers unusual facilities for the study of the 



1 Manuscript received by the Secretary of the Society January 11, 1009. 



X — Bull. Geol. Soc. Am., Vol. 20, 1908 (133) 



