lOO GEORGE F. KAY AND J. NEWTON PEARCE 



The distribution of Nebraskan gumbotil in Iowa. — The Nebras- 

 kan gumbotil has been found in widely separated locahties in Iowa. 

 Among the many counties in which it has been studied are Decatur, 

 Clarke, Warren, Madison, Union, Ringgold, Taylor, Adams, Adair, 

 Cass, Montgomery, Page, Shelby, Crawford, Carroll, Tama, and 

 Johnson counties. The topographic positions of the several out- 

 crops indicate that the Nebraskan gumbotil was formed on an 

 extensive plain with slight rehef just as in the case of the formation 

 of the Kansan gumbotil. The maximum thickness of Nebraskan 

 gumbotil thus far studied is about thirteen feet. The zone of 

 oxidation of the Nebraskan drift is rarely fully exposed; depths 

 of oxidation of more than forty feet have been seen without the 

 base of the zone of oxidation having been revealed. 



Some sections showing the relations of lllinoian gumbotil to under- 

 lying Illinoian drift. — That the relations of the lllinoian gumbotil 

 to the underlying lllinoian till are similar to the relations of Kansan 

 and Nebraskan gumbotils to their respective tills may be shown 

 by presenting two sections from many sections which are known to 

 show similar relationships. 



An exposure at the head of a ravine about one hundred yards 

 north of the edge of the bluff north of Fort Madison, Lee County, 

 gives a section as follows: 



■' Feet Inches 



4. Loess and loesslike clay, grayish-yellow to 

 buff -yellow in color .- 7 



3. Gumbotil (lllinoian), drab to chocolate to 

 dark color, starchlike fracture, few pebbles, 

 leached; grades into No. 2 4 6 



2. Glacial till (lllinoian), oxidized, leached 6 



I. Glacial till (lllinoian), oxidized, unleached 

 to base of gulch 15 



A splendid section to show, not only the lllinoian gumbotil 

 and underlying lllinoian drift, but also the Kansan gumbotil 

 and underlying Kansan drift, is a railroad cut on the Chicago, 

 Milwaukee & St. Paul Railway between Fort Madison and Sawyer, 

 in Lee County. The cut is in section 28, Washington Township, 

 and shows the following materials: 



