1 ILLINOIS STATE GEOLOGICAL SURVEY CIRCULAR 486 



C-horizon contains abundant nodules of CaC0 3 and fossil snail shells; it is 

 massive and lighter colored than the A-horizon. A B-horizon is not recognizable 

 in the profile. The percent of less-than-2 -micron clay through the profile, 

 shown in figure 1 and listed in table 1, shows a progressive upward trend of 



-| 1 1 1 1 I - 



10 20 30 40 50 60 



Percent clay and percent clay minerals 



Fig. 1 - Cottonwood School South Section, NW^NW^SWi sec. 12, T. 18 N. , 



R. 11 W. , Cass County, showing percent of less-than-2-micron clay in 

 Peoria Loess and percent of illite and expandable clay minerals in the 

 clay mineral assemblage. Sample numbers at left are ISGS file numbers, 

 and bed numbers at right refer to numbered beds in the described section 

 in this report. 



