318 
The American Geologist. 
May, 1896 
field seasons similar exposures along the streams of Mahaska, 
Keokuk and Washington counties have been studied and thus 
an independent general section, which may be called the cen- 
tral Iowa section, has been constructed. At the present these 
two sections have not been connected by detailed stratigraphic 
work though the continuity of the major divisions has been 
traced. 
FORMATION. 
BEDS. 
EXPOSURES. 
Saint Louis. 
Pella. 
Yerdi. 
Springvale. 
Marion coiuit.v. 
Washington county. 
Keokuk county. 
Augusta. 
Keokuk and Washing- 
ton counties. 
Kinderliool<. 
Wassonville 
limestone. 
Eniilish River grits. 
Maple Mill sliale. 
Washington county. 
Saint Louis Formation. 
Pella beds. — These beds are typically developed in Marion 
county, but also occur in all three of the other counties men- 
tioned. They represent the quiet settled conditions of open 
sea deposition and mark the period when the shore line had 
probably reached its maximum northern position. The beds 
consist largely of thin shelly limestone with the interstices 
filled with a calcareous marly deposit crowded with fossils. 
The limestones are also fossiliferous but the major portion of 
the forms occur in these marly layers. At the Klein quarry 
near Pella a portion of the beds is well exposed and the fol- 
lowing section may be seen : 
Feet. 
8. Drift 12 
7. Clay marls with brachiopods 2 
Clay marl "coral layer" 2 
Cla3' with brachiopods 4 
Clay shale. "Spirifer layer" 1 
Limestone 2 
Clay shale, "Rhynchonella layer" 1 
Limestone 5 
The limestones at times become more heavily bedded and 
occasionally occur in considerable thickness. Along the Des 
Moines river in Marion and Mahaska counties they attain a 
maximum thickness of probably seventy-five feet. 
