FORMATIONS IN SOUTHEASTERN IOWA. 293 
Be ics GENERAL DESCRIPTION OF THE REGION. 
ate The area included in this investigation 
fy comprises the two counties of Lee and Van 
a 3 Buren. The former lies on the north side 
ale of the Des Moines River at its confluence 
with the Mississippi, while the latter joins 
re Lee on the west and is traversed by the Des 
Moines River diagonally from northwest to 
southeast. This river and most of its trib- 
utaries, as well as those of the Mississippi, 
vf 
27ADuY hy ! 
have penetrated the drift and cut deep 
channels into the underlying rock, thus 
offering favorable opportunities for the 
study of these formations. 
The general relief of the region is that 
of a broad, flat plain gently sloping to the 
southeast, and intersected by a_ parallel 
system of drainage dating from the with- 
drawal of the ice-sheet. Considerable areas 
have, as yet, been but partially invaded by 
the backward erosion of the streams, and 
the divides are still characterized by flat tops 
representing the original plain out of which 
they have been carved. 
STRATIGRAPHY OF THE REGION. 
Structure —In this region, the rock floor 
upon which the drift rests is made up chiefly 
of the Lower Coal Measure deposits and the 
Saint Louis limestone. By the erosion of 
the streams, however, lower formations are 
Fic. 1.—Section line A-B from Keokuk to northwestern corner of Van Buren county.0)(See map.) 
frequently exposed so thatthe area vhas 
BuRLINGTON 
e 3 furnished typical sections of a considerable 
Cal el part of the Lower, Carboniferous series. 
Ons =) 
‘ipigatianenena Extensive preglacial erosion has greatly 
Nene 
isha He f " 
ea reduced the surface area of the Saint Louis 
3 é 
a 8 
