242 
IOWA ACADEMY OP SCIENCE 
In southeastern Iowa, Coal Measures strata also frequently 
cap the Mississippian. But this higher formation has been long 
since stripped off in many areas. In this region the Pella is 
preserved mainly in the form of local outliers due to both pre- 
Pennsylvanian and post-Pennsylvanian erosion. Small scat- 
tered exposures occur in Lee, Des Moines, Henry, Washington 
and Keokuk counties, and outcrops appear at intervals along 
the Des Moines river and its tributaries in Van Buren, Wapello, 
Mahaska and Marion counties. It is best known to the writers 
as developed in Van Buren county. 
Lithologic Characters and Stratigraphic Relations. — ^Litho- 
logically the Pella is very variable, and it is impossible to give 
a general description of its character which will hold in all cases. 
For this reason, it seems desirable to present a number of de- 
tailed sections, in order that its variability may be better under- 
stood. These sections will also show the stratigraphic relations; 
and thicknesses of the formation at those points where it has. 
been most carefully studied. 
SECTION I. 
Section along bed and banks of a small creek emptying into 
the Des Moines river in the lower part of the town of Croton, 
Lee county, Iowa. 
FEET. INCHES. 
PENNSYLVANIAN I 
15. Sandstone, yellowish, soft- 
(disconformity) 
PELLA : 
14. Limestone, compact, light gray above but 
dark gray below, containing a bed of cal- 
careous shale 2% feet thick in middle 
portion, about 
13. Sandstone, yellowish, fine-grained, some- 
times soft and shaly in lower portion; 
contact with bed below uneven; bearing 
large fucoid-like markings on surface of 
layers 
(disconformity) 
UPPER ST. LOUIS : 
12. Limestone, gray, granular to compact, 
locally slightly oolitic in part; middle 
portion cross-bedded, a layer in lower por- 
tion bearing conspicious wave marks on 
its upper surface 10-13 
11. Limestone, bluish, dolomitic, thinly bedded, 
somewhat shaly, slightly fossiliferous, 
resting on the undulating surface of the 
bed beneath 2 
9 
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