174 
IOWA ACADEMY OP SCIENCES. 
gypseous cements takes place principally through a combina- 
tion with water rather than in the manner of ordinary hydrau- 
lic cement, where the hardening is brought about by re -crystal- 
lization of the calcium, alumnia and silica present. 
The Mississippian series includes all the rocks lying between 
the base of the coal measures and the top of the Devonian. 
They have been principally studied in southeastern Iowa and 
adjacent portions of neighboring states. More recently the 
study of the exposures of that portion of central Iowa which 
includes Marion, Mahaska, Keokuk and Washington counties 
has allowed the construction of a central Iowa section. 
As shown in this region the rocks include the following 
divisions ; 
Augusta. 
1 Wasson ville limestone. 
Kinderhook-< English river gritstone. 
( Maple mill shale. 
These beds are separated on lithologic and stratigraphic 
grounds. Faunal studies have not yet been carried to any 
degree of completion, but seem so far to confirm the divisions. 
The divisions of this section are readily correlated with those 
of the southeast. The minor divisions of the Augusta found in 
the latter region are not traceable farther north. 
The Maple mill shale contains certain fossils with Devonian 
affinities and may be ultimately placed in that series. 
"^Abstract of a paper published in full in American Geologist, vol. xv, under the 
title Central Iowa Section of the Mississippian Series. 
MISSISSIPPIAN ROCKS OF CENTRAL lOWA^. 
BY H. POSTER BAIN. 
