[BULL. 243. i 
160 CEMENT MATERIALS AND INDUSTRY. 
DES MOINES FORMATION. 
DISTRIBUTION. 
The Des Moines (lower Coal Measures) contains very little lime 
stone. Its principal importance in the present connection arises from 
the coal and clay which make up so large a portion of the formation 
The clays and shales are extensively used in the brick-making indus 
try. They are available over wide areas, and may prove of servici 
in connection Avith limestones of the formations above and below. 
COMPOSITION. 
The following analyses are typical of these clays: 
Analyses of Coal Measures shales and clays. 
Silica (Si0 2 ) 
Alumina (A1 2 3 ) 
Iron oxide (Fe 2 3 ) 
Lime (CaO) 
Magnesia (MgO) , 
Soda (Na 2 0) 
Potash (K 2 0) 
Sulphur trioxide (S0 3 ) 
Carbon dioxide (C0 2 ) 
Water (H 2 0), combined 
Water (H 2 0), free 
Undetermined and ignitious. 
53.08 
17.71 
8.64 
4.05 
.94 
3.70 
1.25 
64.41 
20.43 
5.88 
.34 
1.71 
1.90 
2.53 
6.77 
3.93 
1.27 
1.33 
53.1 
26. 
4. 
1. Brick clay, Fort Dodge. 
2. Brick clay, Des Moines. C O. Bates, analyst. 
3. Brick clay, Ottumwa. J. B. Weems, analyst. 
AI'I'AXOOSK BEDS. 
Near the middle of the Des Moines formation are strata which ha 
been called the Appanoose beds. These have been mapped and d 
cussed in connection with the report on Appanoose County, and th< 
outcropping edge is shown on the accompanying map (PL V). Th 
include the Mystic or Centerville coal and certain associated shales a 
limestones. The latter are known locally, from their relations to t 
coal, as the "Bottom rock," "Cap rock," " Thirteen-foot limeston 
and " Fifty-foot limestone." The limestone bed is thin, usually froi 
to 6 feet in thickness, but near Rathbun andClarkdale it reaches a thi 
ness of 10 to 15 feet. It is a soft limestone, easily crushed, and beca 
