BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 10, pp. 107-120 March 7, 1899 



lOWAN DRIFT 



BY SAMUEL CALVIN 



{Presented before the Society December 30, 1898) 

 CONTENTS 



• Page 



Introduction , 107 



Previous work on the lowan 108 



Origin of the name 108 



Area occupied by the lowan drift-sheet 109 



Characteristics of the lowan drift 110 



Topography 110 



Clay constituent of the till Ill 



Color and composition Ill 



Condition as to weathering and leaching Ill 



lowan boulders Ill 



Composition, size, and weathering Ill 



Superficial position 112 



Thickness of the lowan drift 112 



Eelation of the lowan to the " Forest bed " of northeastern Iowa 113 



Comparisons with other formations 114 



lowan compared with the Kansan 114 



lowan compared with the Illinoian 116 



lowan compared with the Wisconsin 116 



The lowan margin , 117 



Its sinuosities and digitations 117 



Loess ridges along the margin 117 



Relation to margin of Kansan along edge of driftless area 118 



Relation to distribution of loess 118 



Paha and Loess-Kansan islands near lowan margin 119 



Introduction 



The sheet of drift in northeastern Iowa, which, in the recent Hterature 

 relating to Pleistocene geology, is known as the lowan, has certain indi- 

 vidual characteristics that differentiate it sharply from the other drift- 

 sheets of the Mississippi valley. Before McGee's classic work on the 



XVI— HuT.T,. Geol. Soc. Am., Vol. 10, 1898 (107) 



