96 IOWA ACADEMY OF SCIENCES. 



FEET. 



Bowlder clay (sub-Aftonian), a blue-black clay not 

 weathered at top and coming into sharp contact 

 with the ferruginated gravels, containing mainly 

 small pebbles, predominantly of vein quartz, but 

 with a fair proportion of granite. Many, if not 

 most, of the pebbles fresh and hard 40 



Red and blue shales of Missourian 20 



The peculiar physical character of the lower bowlder clay- 

 is striking. It is dense and breaks usually in flakes rather 

 than joint blocks. It is of a strikingly dark color. There are 

 few joint cracks and these show no special signs of weathering. 

 The sharpness of the contact between the gravels and the 

 bowlder clay, with the presence of many hard pebbles in the 

 latter, indicates apparently one of two things, (1) either this 

 lower clay was not exposed to surface action before the gravels 

 were laid down, or (2) it was so vigorously eroded immediately 

 before the deposition of the gravels as to cut away all evidence 

 of former surface exposure. 



Thayer Section — The Thayer section is of interest, since it 

 seems that here the evidence of two drifts was detected. The 

 section as now shown varies a little from point to point in the 

 pit but a representative exposure shows the following beds: 



TEET. INCHES. 



9. Black soil 6 



8. Reddish gravelly clay (ferretto) 1 



7. Yellow bowlder clay becoming gravelly 

 below and containing quartzite, 

 greenstones and granite; flattened 

 and striated pebbles with lime con- 

 cretions 10 to 20 



6. Fine sand 1 6 



5. Drab to blue pebbly clay with sticks 



and bits of undetermined wood 4 



4. Fine sand 3 



3. Drab pebbly clay as above 12 



2. Fine sand 2 



1. Gravel as seen before, striated and 

 cross-bedded; pebbles mainly less 

 than li inch in diameter but with 

 some large bowlders. Material seem- 

 ingly of the usual Kansan facies, 

 much weathered and highly col- 

 ored 15 to 20 



Summarizing the above, we have loess and yellow and blue 

 clay phases of the Kansan with the underlying gravels. The 



