112 
IOWA ACADEMY OF SCIENCES. 
NOTES AND EXPLANATION OF MAP. 
THE EXPOSURES ARE REPRESENTED BY HEAVY LINES. 
Exposures A B and C. These were cut out of the same ridge in street- 
grading. The shell-bearing stratum shows well on the east, north and 
west sides of C. It is about twelve or fifteen feet thick. Above it there 
is a layer of clay about fifty feet thick and almost entirely devoid of 
fossils. 
