Central Iowa Section of the Miss. Series. — Bain. 317 
are made imperative, and future revisional work in this 
direction is reduced to a minimum. With the exception, 
perhaps, of a few limited districts in the south central por- 
tion of the state, every county in Missouri will have a number 
of accurately determined points from which detailed mapping 
may proceed, and all elevations may refer directly to mean 
tide level. 
CENTRAL IOWA SECTION OF THE MISSISSIPPIAN 
SERIES.* 
By H. Foster Bain, Des Moines, la. 
Throughout the broad Mississippi valley there is a series of 
beds, in the main calcareous and largely made up of heavy 
bedded limestones, which lie between the Coal Measures and 
the Devonian. These rocks have been extensively known and 
studied under the names "Subcarboniferous" and "Lower 
Carboniferous" and to them H. S. Williams has applied the 
name Mississippian series, a modification of a term first pro- 
posed by Alexander Winchell. They are typically developed 
in southeastern Iowa and the adjoining regions and have 
been most studied along the Mississippi river. They form, 
however, in the main a definite, easily recognized strati- 
graphic unit throughout the Mississippi valle3^ This term 
has been recently extended to cover a similar calcareous series 
occupying an infra-basal position relative to the Coal Meas- 
ures of the Appalachian provincef and has thus lost its orig- 
inal geographic significance. 
The upper delimitation of the series is throughout Iowa a 
matter of small difl^culty as it is separated from the succeed- 
ing beds of the Coal Measures by a marked unconformity of 
erosion. The lower limit is not, however, so easily recognized 
and around the question of its delimitation considerable con- 
troversy has in times past arisen. Up to the present time the 
chief studies on the series as developed in Iowa have been 
carried on along tlie Mississippi river, and from the exposures 
there a general section has been constructed which may be 
called the southeastern Iowa section. During the two past 
*Published by permission of the State Getilogist of Iowa. 
fCampb.'ll, M.: IJiil. U. S. (ieol. Surv., No. 111. p. '.M. IS!):]. 
