January 14, 1910] 



SCIENCE 



75 



SPECIAL ARTICLES 



THE PLEISTOCENE OF THE MISSOURI VALLEY 



In the course of his recent field studies for 

 the Iowa Geological Survey in the Missouri 

 Valley in western Iowa and eastern Nebraska, 

 the writer was able to determine the following 

 succession of Pleistocene formations: 



1. The oldest drift sheet known in Iowa, to 

 which the names pre-Kansan, sub-Aftonian, 

 Albertan and Jerseyan have been applied, is 

 exposed to a depth of more than fifteen feet, 

 and may be traced along the foot of the blufEs 

 for several miles on both sides of the Missouri 

 near Omaha and Council Bluffs. 



The terms pre-Kansan and sub-Aftonian 

 have been applied merely to designate the 

 relative position of this drift sheet. The Al- 

 bertan deposit is not now regarded as a drift, 

 and moreover neither the Albertan nor the 

 uncertain Jerseyan can be correlated with the 

 sub-Aftonian of Iowa. This drift has now 

 been found in various parts of Iowa, Missouri 

 and Nebraska, and probably in South Dakota, 

 but nowhere does it reach such development 

 as in the region under discussion. 



Because of the great extent of this forma- 

 tion, and the fact that it can not be correlated 

 with any named horizon, it is proposed that 

 the name Nebraslcan be applied to it. 



The typical exposures above Florence and 

 in South Omaha in Nebraska, and about four 

 miles above Council Bluffs in Iowa, have been 

 noticed by geologists, but the deposit was re- 

 ferred to the Kansan, or was identified as 

 Carboniferous shale. 



The Nebraskan consists of a dark, bluish- 

 black tough joint clay which breaks up into 

 very small blocks upon exposure to the air, and 

 through which are scattered small boulders 

 and pebbles which are also mostly dark in 

 color. 



2. Upon the Nebraskan, but sharply sepa- 

 rated from it, rests a deposit of Aftonian 

 sands and gravels. This is very commonly 

 exposed on both sides of the river and reaches 

 a thickness of more than 30 feet. In its lower 

 part the gravels are often cemented into con- 

 glomerates to a depth of several feet. 



Fine exposures of Nebraskan and Aftonian 



(the latter consisting of gravels, sands and 

 sometimes silt) occur on both sides of the 

 river, but those which appear along the Chi- 

 cago Northwestern Railroad between Council 

 Bluffs and Crescent are especially fine. 



The Aftonian is the water-bearing stratum, 

 and everjrwhere springs and seepy places 

 abound at its base. 



3. At several points in this region Kansan 

 drift rests unconformably upon the Aftonian. 

 It is the tjTpical bluish Kansan with an abun- 

 dance of calcium carbonate in streaks, cloud- 

 ings and concretions. 



4. Perhaps more frequently, in the immedi- 

 ate vicinity of Omaha and Council Bluffs, the 

 Aftonian is followed immediately by a de- 

 posit of joint clay which frequently shows 

 stratification, and often contains sand and 

 pebbles in its lower part. This is the deposit 

 which the writer designated as the Loveland,^ 

 from the type exposure at Loveland, Iowa. 

 Great deposits of Loveland, often exceeding 

 30 feet in thickness, occur on both sides of the 

 river. 



This formation, which probably belongs to 

 the period of the melting of the Kansan ice, 

 is of especial interest because it has usually 

 been referred to loess, from which it differs 

 in its joint clay texture, usually reddish color, 

 absence of fossils, and frequent occurrence of 

 pebbles and coarse sand-grains in its lower 

 part. 



5. Overlying the Loveland, and usually 

 separated from it quite sharply, is a bed of 

 characteristic post-Kansan bluish-gray loess, 

 which is usually fossiliferous. This is dis- 

 played at several points near Florence and in 

 South Omaha. 



6. Upon the post-Kansan loess lies a bed of 

 later yellow loess, which is also often fossilif- 

 erous. 



The total thickness of the two loesses in this 

 vicinity does not reach 35 feet at any point 

 observed on the Nebraska side of the river, 

 and its thickness on the Iowa side is much 

 less than has been reported, since the thick- 

 ness of the Loveland must be deducted. 



' Bulletin of the Geological Society of America, 

 Vol. 20, 1909. 



