408 B. SHIMEK APTONIAN SANDS AND GRAVELS IN IOWA 



1. Extensive deposits of sands and gravels in the western part of Iowa 

 are definitely referred to the Aftonian stage. 



2. A distinct and quite extensive molluscan and mammalian fauna is 

 revealed in these Aftonian beds for the first time. 



3. The climate of the interglacial Aftonian stage was mild. 



4. The Aftonian beds are widely distributed along ancient and modern 

 river courses in Iowa. 



Aftonian and Nebraskan — an Addendum 



Since this paper was written the writer has made additional observa- 

 tions on the Aftonian and sub-Aftonian deposits, especially along the 

 Missouri river in Iowa and Nebraska, and along the Big Sioux river, and 

 in various other localities in Iowa. These observations demonstrate that 

 both deposits are of very wide extent. 



Additional fossiliferous Aftonian beds were found near Omaha, Ne- 

 braska, and in Plymouth and Woodbury counties in Iowa, and much 

 additional material was obtained from the exposures previously studied, 

 especially those at Missouri valley and Turin, Iowa. 



Quite recently the writer discovered extensive beds of Aftonian sands 

 and gravels, the latter frequently massed into ledges of conglomerates, 

 resting on well developed strata of pre-Kansan, or sub-Aftonian drift, in 

 South Omaha and near Florence, Nebraska, and between Council Bluffs 

 and Crescent, Iowa. The tough, impervious, bluish-black till which has 

 been known as the sub-Aftonian or pre-Kansan drift in Iowa, is here so 

 well developed, reaching an exposed thickness of more than 15 feet and 

 extending for several miles along the base of the bluffs on both the Ne- 

 braska and Iowa sides of the Missouri river, and moreover occurs at so 

 many other localities in Iowa, Missouri, and Nebraska, that it can no 

 longer be regarded as merely a remnant, but should rank with other well 

 developed drift sheets. 



The terms pre-Kansan and sub-Aftonian have been used merely to 

 designate the position of this drift sheet ; the name Albertan was origin- 

 ally applied to a deposit which can not be correlated with this drift, and 

 which is not now regarded as glacial ; and the doubtful Jerseyan can not 

 be connected with the sheet here discussed. This leaves it without a 

 name, and in view of this fact, and of the wide distribution of this forma- 

 tion, the name Nebraskan is proposed for it. The type exposures are 

 located in the Missouri bluffs in. South Omaha and above Florence, 

 Nebraska, and 4 miles north of Council Bluffs, Iowa. The name Nebraskan 

 was suggested to the writer by Professor Calvin. 



